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1
Evans, Neal J., Lee G. Mundy, John H. Davis, and Paul Vanden Bout. "Sub-Millimeter Spectral Line Observations in Very Dense Regions." Symposium - International Astronomical Union 115 (1987): 173. http://dx.doi.org/10.1017/s0074180900095322.
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In a search for very high density (n ≳ 107 cm−3) regions, the Millimeter Wave Observatory 5-m telescope was used to observe several submillimeter lines. The regions studied were Orion A, M17, S140, and NGC2024. The lines were CS(J=7-6), H2CO(JK-1K1=515→414), and HCN(J=4-3). These data are combined with data at millimeter wavelengths to derive the volume density and the results are compared to those deduced from millimeter lines alone (Snell et al. 1984). In NGC2024, higher densities (≳ 107 cm−3) are clearly indicated by the sub-mm lines than were derived by Snell et al. In M17, derived densities are also higher, but uncertainties overlap the Snell et al. solutions. The range of densities derived from CS and HCN are consistent. The sub-millimeter lines of these species appear to be good probes of the highest densities present in regions of active star formation.
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Tafoya, D., J. A. Toalá, W. H. T. Vlemmings, M. A. Guerrero, E. De Beck, M. González, S. Kimeswenger, A. A. Zijlstra, Á. Sánchez-Monge, and S. P. Treviño-Morales. "(Sub)millimeter emission lines of molecules in born-again stars." Astronomy & Astrophysics 600 (March 22, 2017): A23. http://dx.doi.org/10.1051/0004-6361/201630074.
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David, F., M. Chatras, C. Dalmay, L. Lapierre, L. Carpentier, and P. Blondy. "Surface-Micromachined Rectangular Micro-Coaxial Lines for Sub-Millimeter-Wave Applications." IEEE Microwave and Wireless Components Letters 26, no. 10 (October 2016): 756–58. http://dx.doi.org/10.1109/lmwc.2016.2604867.
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Lankhaar, Boy, and Wouter Vlemmings. "PORTAL: Three-dimensional polarized (sub)millimeter line radiative transfer." Astronomy & Astrophysics 636 (April 2020): A14. http://dx.doi.org/10.1051/0004-6361/202037509.
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Context. Magnetic fields are important to the dynamics of many astrophysical processes and can typically be studied through polarization observations. Polarimetric interferometry capabilities of modern (sub)millimeter telescope facilities have made it possible to obtain detailed velocity resolved maps of molecular line polarization. To properly analyze these for the information they carry regarding the magnetic field, the development of adaptive three-dimensional polarized line radiative transfer models is necessary. Aims. We aim to develop an easy-to-use program to simulate the polarization maps of molecular and atomic (sub)millimeter lines in magnetized astrophysical regions, such as protostellar disks, circumstellar envelopes, or molecular clouds. Methods. By considering the local anisotropy of the radiation field as the only alignment mechanism, we can model the alignment of molecular or atomic species inside a regular line radiative transfer simulation by only making use of the converged output of this simulation. Calculations of the aligned molecular or atomic states can subsequently be used to ray trace the polarized maps of the three-dimensional simulation. Results. We present a three-dimensional radiative transfer code, POlarized Radiative Transfer Adapted to Lines (PORTAL), that can simulate the emergence of polarization in line emission through a magnetic field of arbitrary morphology. Our model can be used in stand-alone mode, assuming LTE excitation, but it is best used when processing the output of regular three-dimensional (nonpolarized) line radiative transfer modeling codes. We present the spectral polarization map of test cases of a collapsing sphere and protoplanetary disk for multiple three-dimensional magnetic field morphologies.
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Humphreys, E. M. L. "Submillimeter and millimeter masers." Proceedings of the International Astronomical Union 3, S242 (March 2007): 471–80. http://dx.doi.org/10.1017/s1743921307013622.
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AbstractDespite theoretical predictions of the existence of many submillimeter masers, and some pioneering observational discoveries over the past few decades, these lines have remained relatively unstudied due to (i) challenges associated with observing at shorter wavelength; and, (ii) the lack of possibility of high (< 14″ at 345 GHz) angular resolution observations. With the advent of the SMA, the first submillimeter imaging array capable of sub-arcsecond resolution, APEX, and the promise of ALMA, opportunities are opening for performing new science with millimeter/submillmeter masers. In this talk, I will review recent work in the field - including extragalactic H2O millimeter masers, hydrogen recombination masers, submillimeter masers in star-forming regions, and in the envelopes of evolved stars - and discuss prospects for the future.
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Ohno, Yuki, Takahiro Oyama, Akemi Tamanai, Shaoshan Zeng, Yoshimasa Watanabe, Riouhei Nakatani, Takeshi Sakai, and Nami Sakai. "Laboratory Measurement of Millimeter-wave Transitions of 13CH2DOH for Astronomical Use." Astrophysical Journal 932, no. 2 (June 1, 2022): 101. http://dx.doi.org/10.3847/1538-4357/ac6b9e.
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Abstract Methanol (CH3OH) is an abundant interstellar species and is known to be an important precursor of various interstellar complex organic molecules. Among the methanol isotopologues, CH2DOH is one of the most abundant isotopologues and it is often used to study the deuterium fractionation of CH3OH in interstellar medium. However, the emission lines of CH2DOH can sometimes be optically thick, making the derivation of its abundance unreliable. Therefore, observations of its presumably optically thin 13C substituted species, 13CH2DOH, are essential to overcome this issue. In this study, the rotational transitions of 13CH2DOH have been measured in the millimeter-wave region from 216 GHz to 264 GHz with an emission-type millimeter- and submillimeter-wave spectrometer by using a deuterium and 13C enriched sample. The frequency accuracy of measured 13CH2DOH is less than a few kHz, and the relative line intensity error is less than 10% in most of the frequency range by taking advantage of the wide simultaneous frequency-coverage of the emission-type spectrometer. These results offer a good opportunity to detect 13CH2DOH in space, which will allow us to study the deuterium fractionation of CH3OH in various sources through accurate determination of the CH2DOH abundance.
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Meyer, Romain A., Fabian Walter, Claudia Cicone, Pierre Cox, Roberto Decarli, Roberto Neri, Mladen Novak, Antonio Pensabene, Dominik Riechers, and Axel Weiss. "Physical Constraints on the Extended Interstellar Medium of the z = 6.42 Quasar J1148+5251: [C ii]158 μm, [N ii]205 μm, and [O i]146 μm Observations." Astrophysical Journal 927, no. 2 (March 1, 2022): 152. http://dx.doi.org/10.3847/1538-4357/ac4e94.
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Abstract We report new Northern Extended Millimeter Array observations of the [C ii]158 μm, [N ii]205 μm, and [O i]146 μm atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a z = 6.42 quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged [C ii]158 μm and dust continuum emission have similar extensions (up to θ = 2.51 − 0.25 + 0.46 arcsec , corresponding to r = 9.8 − 2.1 + 3.3 kpc , accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest [C ii]158 μm-emitting reservoir known at these epochs. Moreover, if the [C ii]158 μm emission is examined only along its NE–SW axis, a significant excess (>5.8σ) of [C ii]158 μm emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad [C ii]158 μm line wings that were reported in previous studies. We also report the first detection of the [O i]146 μm and (tentatively) [N ii]205 μm emission lines in J1148+5251. Using FSL ratios of the [C ii]158 μm, [N ii]205 μm, [O i]146 μm, and previously measured [C i]369 μm emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (103.5–4.5 G 0), a high gas density (n ≃ 103.5–4.5 cm−3), and an H i column density of 1023 cm−2 reproduce the observed FSL ratios well.
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Baron, Philippe, Donal Murtagh, Patrick Eriksson, Jana Mendrok, Satoshi Ochiai, Kristell Pérot, Hideo Sagawa, and Makoto Suzuki. "Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder." Atmospheric Measurement Techniques 11, no. 7 (July 31, 2018): 4545–66. http://dx.doi.org/10.5194/amt-11-4545-2018.
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Abstract. Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform, with launch planned for around 2022. It is intended to fill the altitude gap between 30 and 70 km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10 and 90 km when current satellite missions will probably come to an end. Line-of-sight winds are retrieved from the Doppler shift of molecular emission lines introduced by the wind field. Observations will be performed with two antennas pointing toward the limb in perpendicular directions in order to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view (FOV) of 5 km. The chosen spectral band, near 655 GHz, contains a dense group of strong O3 lines suitable for exploiting the small amount of wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured, including O3 isotopologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents a simulation study that assesses measurement performance. The line-of-sight winds are retrieved between 30 and 90 km with the best sensitivity between 35 and 70 km, where the precision (1σ) is 5–10 m s−1 for a single scan. Similar performance can be obtained during day and night conditions except in the lower mesosphere, where the photo-dissociation of O3 in daytime reduces the sensitivity by 50 % near 70 km. Profiles of O3, H2O and temperature are retrieved with high precision up to 50 km ( < 1 %, < 2 %, 1 K, respectively). Systematic errors due to uncertainties in spectroscopic parameters, in the radiometer sideband ratio and in the radiance calibration process are investigated. A large wind retrieval bias of 10–30 m s−1 between 30 and 40 km could be induced by the air-broadening parameter uncertainties of O3 lines. This highlights the need for good knowledge of these parameters and for studying methods to mitigate the retrieval bias.
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Lee, Seungwon, Paul von Allmen, Lucas Kamp, Samuel Gulkis, and Björn Davidsson. "Non-LTE radiative transfer for sub-millimeter water lines in Comet 67P/Churyumov-Gerasimenko." Icarus 215, no. 2 (October 2011): 721–31. http://dx.doi.org/10.1016/j.icarus.2011.07.007.
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Tong, Cheuk‐yu Edward, Raymond Blundell, Bruce Bumble, Jeffrey A. Stern, and Henry G. LeDuc. "Quantum limited heterodyne detection in superconducting non‐linear transmission lines at sub‐millimeter wavelengths." Applied Physics Letters 67, no. 9 (August 28, 1995): 1304–6. http://dx.doi.org/10.1063/1.114405.
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Pei-bin, Chen, Liu Jia-min, and Zhao Ying-he. "Progress of the Study on (Sub)millimeter Lines in Galaxies During the Herschel Period." Chinese Astronomy and Astrophysics 46, no. 1 (January 2022): 1–35. http://dx.doi.org/10.1016/j.chinastron.2022.02.001.
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Kim, W. J., J. S. Urquhart, F. Wyrowski, K. M. Menten, and T. Csengeri. "New detections of (sub)millimeter hydrogen radio recombination lines towards high-mass star-forming clumps." Astronomy & Astrophysics 616 (August 2018): A107. http://dx.doi.org/10.1051/0004-6361/201732330.
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Aims. Previous radio recombination line (RRL) observations of dust clumps identified in the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) have led to the detection of a large number of RRLs in the 3 mm range. Here, we aim to study their excitation with shorter wavelength (sub)millimeter radio recombination line (submm-RRL) observations. Methods. We made observations of submm-RRLs with low principal quantum numbers (n ≤ 30) using the APEX 12 m telescope, toward 104 H II regions associated with massive dust clumps from ATLASGAL. The observations covered the H25α, H28α, and H35β transitions. Toward a small subsample the H26α, H27α, H29α, and H30α lines were observed to avoid contamination by molecular lines at adjacent frequencies. Results. We have detected submm-RRLs (signal-to-noise (S∕N)≥ 3 σ) from compact H II regions embedded within 93 clumps. The submm-RRLs are approximately a factor of two brighter than the mm-RRLs and consistent with optically thin emission in local thermodynamic equilibrium (LTE). The average ratio (0.31) of the measured H35β/H28α fluxes is close to the LTE value of 0.28. No indication of RRL maser emission has been found. The Lyman photon flux, bolometric, and submm-RRL luminosities toward the submm-RRL detected sources present significant correlations. The trends of dust temperature and the ratio of bolometric luminosity to clump mass, Lbol ∕Mclump, indicate that the H II regions are related to the most massive and luminous clumps. By estimating the production rate of ionizing photons, Q, from the submm-RRL flux, we find that the Q(H28α) measurements provide estimates of the Lyman continuum photon flux consistent with those determined from 5 GHz radio continuum emission. Six RRL sources show line profiles that are a combination of a narrow and a broad Gaussian feature. The broad features are likely associated with high-velocity ionized flows. Conclusions. We have detected submm-RRLs toward 93 ATLASGAL clumps. Six RRL sources have high-velocity RRL components likely driven by high-velocity ionized flows. Their observed properties are consistent with thermal emission that correlates well with the Lyman continuum flux of the H II regions. The sample of H II regions with mm/submm-RRL detections probes, in our Galaxy, luminous clumps (Lbol > 104 L⊙) with high Lbol∕Mclump. We also provide suitable candidates for further studies of the morphology and kinematics of embedded, compact H II regions with the Atacama Large Millimeter/submillimeter Array (ALMA).
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Despringre, V., and D. Fraix-Burnet. "First millimeter Mapping of the jet and nucleus of M87." Symposium - International Astronomical Union 175 (1996): 175–76. http://dx.doi.org/10.1017/s0074180900080438.
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An intriguing question about extragalactic jets is why they are so few being seen at optical wavelengths, or equivalently, why the cutoff frequency of the synchrotron radiation is generally not in the optical, but rather in the infrared or even in the sub- millimeter domain. The answer is undoubtedly related to the efficiency of the acceleration of the relativistic electrons responsible for the synchrotron emission. The presence of a break at low frequency somewhere in the synchrotron spectrum is another feature that constrains the model parameters, but its precise location is unknown for most jets, because of the lack of photometry in the millimeter domain. It was thus necessary to fill the gap between radio and optical wavelengths in the synchrotron spectrum of optical jets. The required observation had to be of high sensitivity and high spatial resolution (of the order of 1″). Another reason for observing at millimeter wavelengths is that molecular lines and thermal emission from cold dust are detectable in this frequency range.
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Hong, Young-Pyo, Kyung-Min Lee, Sung-Yeol Kim, Meehyun Lim, Taekjin Kim, Hyung-Jung Yong, and Dong-Joon Lee. "Micrometer Scale Resolution Limit of a Fiber-Coupled Electro-Optic Probe." Sensors 19, no. 13 (June 28, 2019): 2874. http://dx.doi.org/10.3390/s19132874.
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We present the practical resolution limit of a fine electrical structure based on a fiber-coupled electro-optic probing system. The spatial resolution limit was experimentally evaluated on the sub-millimeter to micrometer scale of planar electrical transmission lines. The electrical lines were fabricated to have various potential differences depending on the dimensions and geometry. The electric field between the lines was measured through an electro-optic probe, which was miniaturized up to the optical bare fiber scale so as to investigate the spatial limit of electrical signals with minimal invasiveness. The experimental results show that the technical resolution limitation of a fiber-coupled probe can reasonably approach a fraction of the mode field diameter (~10 μm) of the fiber in use.
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Faisst, A., M. Béthermin, P. Capak, P. Cassata, O. Le Fèvre, D. Schaerer, J. Silverman, and L. Yan. "Panchromatic study of the first galaxies with large ALMA programs." Proceedings of the International Astronomical Union 15, S341 (November 2019): 12–16. http://dx.doi.org/10.1017/s1743921319001881.
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AbstractThanks to deep optical to near-IR imaging and spectroscopy, significant progress is made in characterizing the rest-frame UV to optical properties of galaxies in the early universe (z > 4. Surveys with Hubble, Spitzer, and ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and photometric redshifts, measurements of the spatial structure, stellar masses, and optical emission lines for large samples of galaxies. Recently, the Atacama Large (Sub) Millimeter Array (ALMA) has become a major player in pushing studies of high redshift galaxies to far-infrared wavelengths, hence making panchromatic surveys over many orders of frequencies possible. While past studies focused mostly on bright sub-millimeter galaxies, the sensitivity of ALMA now enables surveys like ALPINE, which focuses on measuring the gas and dust properties of a large sample of normal main-sequence galaxies at z > 4. Combining observations across different wavelengths into a single, panchromatic picture of galaxy formation and evolution is currently and in the future an important focus of the astronomical community.
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Ilyushin, V. V., H. S. P. Müller, J. K. Jørgensen, S. Bauerecker, C. Maul, Y. Bakhmat, E. A. Alekseev, et al. "Rotational and rovibrational spectroscopy of CD3OH with an account of CD3OH toward IRAS 16293−2422." Astronomy & Astrophysics 658 (February 2022): A127. http://dx.doi.org/10.1051/0004-6361/202142326.
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Solar-type protostars have been shown to harbor highly deuterated complex organics, as evidenced, for instance, by the high relative abundances of doubly and triply deuterated isotopologs. While this degree of deuteration may provide important clues in studying the formation of these species, spectroscopic information on multiply deuterated isotopologs is often insufficient. In particular, searches for triply deuterated methanol, CD3OH, are hampered to a large extent by the lack of intensity information from a spectroscopic model. The aim of the present study is to develop a spectroscopic model of CD3OH in low-lying torsional states that is sufficiently accurate to facilitate further searches for CD3OH in space. We performed a new measurement campaign for CD3OH involving three spectroscopic laboratories that covers the 34 GHz−1.1 THz and the 20−900 cm−1 ranges. The analysis was performed using the torsion-rotation Hamiltonian model based on the rho-axis method. We determined a model that describes the ground and first excited torsional states of CD3OH, up to quantum numbers J ≤ 55 and Ka ≤ 23, and we derived a line list for radio-astronomical observations. The resulting line list is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. This line list was used to search for CD3OH in data from the Protostellar Interferometric Line Survey of IRAS 16293−2422 using the Atacama Large Millimeter/submillimeter Array. Specifically, CD3OH is securely detected in the data, with a large number of clearly separated and well-reproduced lines. We not only detected lines belonging to the ground torsional state, but also several belonging to the first excited torsional state. The derived column density of CD3OH and abundance relative to the non-deuterated isotopolog confirm the significant enhancement of this multiply deuterated variant. This finding is in line with other observations of multiply deuterated complex organic molecules and may serve as an important constraint on their formation models.
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Taniguchi, Kotomi, Kei E. I. Tanaka, Yichen Zhang, Rubén Fedriani, Jonathan C. Tan, Shigehisa Takakuwa, Fumitaka Nakamura, Masao Saito, Liton Majumdar, and Eric Herbst. "Vibrationally Excited Lines of HC3N Associated with the Molecular Disk around the G24.78+0.08 A1 Hypercompact H ii Region." Astrophysical Journal 931, no. 2 (May 27, 2022): 99. http://dx.doi.org/10.3847/1538-4357/ac69d1.
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Abstract We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of the hypercompact H ii region G24.78+0.08 A1 (G24 HC H ii) and report the detection of vibrationally excited lines of HC3N (v 7 = 2, J = 24 − 23). The spatial distribution and kinematics of a vibrationally excited line of HC3N (v 7 = 2, J = 24 − 23, l = 2e) are found to be similar to the CH3CN vibrationally excited line (v 8 = 1), which indicates that the HC3N emission is tracing the disk around the G24 HC H ii region previously identified by the CH3CN lines. We derive the 13CH3CN/HC13CCN abundance ratios around G24 and compare them to the CH3CN/HC3N abundance ratios in disks around Herbig Ae and T Tauri stars. The 13CH3CN/HC13CCN ratios around G24 (∼3.0–3.5) are higher than the CH3CN/HC3N ratios in the other disks (∼0.03–0.11) by more than 1 order of magnitude. The higher CH3CN/HC3N ratios around G24 suggest that the thermal desorption of CH3CN in the hot dense gas and efficient destruction of HC3N in the region irradiated by the strong UV radiation are occurring. Our results indicate that the vibrationally excited HC3N lines can be used as a disk tracer of massive protostars at the HC H ii region stage, and the combination of these nitrile species will provide information of not only chemistry but also physical conditions of the disk structures.
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Fedele, D., and C. Favre. "Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths." Astronomy & Astrophysics 638 (June 2020): A110. http://dx.doi.org/10.1051/0004-6361/202037927.
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Over million years of evolution, gas dust and ice in protoplanetary disks can be chemically reprocessed. There is evidence that the gas-phase carbon and oxygen abundances are subsolar in disks belonging to nearby star forming regions. These findings have a major impact on the composition of the primary atmosphere of giant planets (but it may also be valid for super-Earths and sub-Neptunes) as they accrete their gaseous envelopes from the surrounding material in the disk. In this study, we performed a thermochemical modeling analysis with the aim of testing how reliable and robust are the estimates of elemental abundance ratios based on (sub)millimeter observations of molecular lines. We created a grid of disk models for the following different elemental abundance ratios: C/O, N/O, and S/O, and we computed the line flux of a set of carbon-nitrogen and sulphur-bearing species, namely CN, HCN, NO, C2H, c–C3H2, H2CO, HC3N, CH3CN, CS, SO, H2S, and H2CS, which have been detected with present (sub)millimeter facilities such as ALMA and NOEMA. We find that the line fluxes, once normalized to the flux of the 13CO J = 2−1 line, are sensitive to the elemental abundance ratios. On the other hand, the stellar and disk physical parameters have only a minor effect on the line flux ratios. Our results demonstrate that a simultaneous analysis of multiple molecular transitions is a valid approach to constrain the elemental abundance ratio in protoplanetary disks.
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Chen, Cheng-Lung, and Shao-Kang Hung. "Visual Servo Control System of a Piezoelectric2-Degree-of-Freedom Nano-Stepping Motor." Micromachines 10, no. 12 (November 25, 2019): 811. http://dx.doi.org/10.3390/mi10120811.
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A nano-stepping motor can translate or rotate when its piezoelectric element pair is electrically driven in-phase or anti-phase. It offers millimeter-level stroke, sub-micron-level stepping size, and sub-nanometer-level scanning resolution. This article proposes a visual servo system to control the nano-stepping motor, since its stepping size is not consistent due to changing contact friction, using a custom built microscopic instrument and image recognition software. Three kinds of trajectories—straight lines, circles, and pentagrams—are performed successfully. The smallest straightness and roundness ever tested are 0.291 µm and 2.380 µm. Experimental results show that the proposed controller can effectively compensate for the error and precisely navigate the rotor along a desired trajectory.
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Spilker, Justin. "Galactic outflows at high spatial resolution via gravitational lensing." Proceedings of the International Astronomical Union 15, S352 (June 2019): 187–93. http://dx.doi.org/10.1017/s1743921319009232.
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AbstractThe completion of the Atacama Large Millimeter/submillimeter Array (ALMA) has led to the ability to make observations with unprecedented resolution at sub-millimeter wavelengths, allowing novel probes of the ISM and kinematics of high-redshift galaxies. Because they are magnified by foreground galaxies or clusters, gravitationally lensed galaxies allow the highest possible spatial resolution to be obtained, and/or a sharp reduction in the observing time required to detect faint objects or spectral lines. These benefits have made lensed galaxies useful benchmark systems for ALMA, enabling a wide variety of science cases. Here I focus in particular on spatially-resolved observations of massive galactic outflows in the very distant z > 4 universe, summarizing plausible tracers of the cold molecular phase of these outflows. The prospects of joint JWST and ALMA observations will be revolutionary, including the chance to take a full census of galactic outflows in multiple gas phases at matched spatial resolution.
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Brogan, C. L., T. R. Hunter, A. P. M. Towner, B. A. McGuire, G. C. MacLeod, M. A. Gurwell, C. J. Cyganowski, et al. "Sub-arcsecond (Sub)millimeter Imaging of the Massive Protocluster G358.93−0.03: Discovery of 14 New Methanol Maser Lines Associated with a Hot Core." Astrophysical Journal 881, no. 2 (August 20, 2019): L39. http://dx.doi.org/10.3847/2041-8213/ab2f8a.
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Falstad, N., F. Hallqvist, S. Aalto, S. König, S. Muller, R. Aladro, F. Combes, et al. "Hidden or missing outflows in highly obscured galaxy nuclei?" Astronomy & Astrophysics 623 (February 27, 2019): A29. http://dx.doi.org/10.1051/0004-6361/201834586.
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Context. Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission from vibrationally excited HCN (HCN-vib), which is thought to trace warm and highly enshrouded galaxy nuclei. It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. Aims. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (ultra)luminous infrared galaxies ((U)LIRGs). Methods. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 μm OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. Results. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission have fast and collimated outflows that can be seen in spectral lines at longer wavelengths, including in millimeter emission lines of CO and HCN (in its vibrational ground state) and in radio absorption lines of OH. Conclusions. We conclude that the galaxy nuclei with the highest LHCN − vib/LIR do not drive wide-angle outflows that are detectable using the median velocities of far-infrared OH absorption lines. This is possibly because of an orientation effect in which sources oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed.
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Lowenthal, J. D., K. Harrington, D. Berman, M. Yun, R. Cybulski, G. W. Wilson, I. Aretxaga, et al. "Gravitationally Lensed CO and Dust at High Redshift: New LMT/GTM Images and Spectra of Sub-Millimeter Galaxies." Proceedings of the International Astronomical Union 11, S321 (March 2016): 363. http://dx.doi.org/10.1017/s1743921316011145.
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AbstractWe have assembled a new sample of some of the most FIR-luminous galaxies in the Universe and have imaged them in 1.1 mm dust emission and measured their redshifts 1 < z < 4 via CO emission lines using the 32-m Large Millimeter Telescope / Gran Telescopio Milimétrico (LMT/GTM). Our sample of 31 submm galaxies (SMGs), culled from the Planck and Herschel all-sky surveys, includes 14 of the 21 most luminous galaxies known, with LFIR > 1014L⊙ and SFR > 104M⊙/yr. These extreme inferred luminosities – and multiple / extended 1.1 mm images – imply that most or all are strongly gravitationally lensed, with typical magnification μ ~ 10 × . The gravitational lensing provides two significant benefits: (1) it boosts the S/N, and (2) it allows investigation of star formation and gas processes on sub-kpc scales.
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Nazarikov, Gleb, Simon Rommel, Weiming Yao, and Idelfonso Tafur Monroy. "Optical Injection Locking for Generation of Tunable Low-Noise Millimeter Wave and THz Signals." Applied Sciences 11, no. 21 (October 30, 2021): 10185. http://dx.doi.org/10.3390/app112110185.
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This article presents the experimental demonstration of synchronization of two integrated semiconductor distributed Bragg reflector lasers, fabricated with a generic multiproject wafer platform, by means of injection locking. Substantial linewidth reduction and frequency stabilization of the lasers were shown during locking of the lasers to an optical frequency comb. Phase noise was measured for different injected powers and different laser cavities. For a generation of millimeter-wave signals up to 80 GHz, two lasers were simultaneously locked to the comb. Fine-tuning was performed by tuning the repetition rate of the comb and coarse-tuning was carried out by switching to another comb line. A suppression ratio of 37 dB was achieved for unwanted comb lines. The achieved signal purity, phase noise, and suppression of unwanted components demonstrate the viability of injection locking for the generation of high-quality signals at sub-THz and THz frequencies and with substantial tunability.
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Saito, Toshiki, Shuro Takano, Nanase Harada, Taku Nakajima, Eva Schinnerer, Daizhong Liu, Akio Taniguchi, et al. "AGN-driven Cold Gas Outflow of NGC 1068 Characterized by Dissociation-sensitive Molecules." Astrophysical Journal 935, no. 2 (August 1, 2022): 155. http://dx.doi.org/10.3847/1538-4357/ac80ff.
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Abstract Recent developments in (sub)millimeter facilities have drastically changed the amount of information obtained from extragalactic spectral scans. In this paper, we present a feature extraction technique using principal component analysis (PCA) applied to arcsecond-resolution (1.″0–2.″0 = 72–144 pc) spectral scan data sets for the nearby type-2 Seyfert galaxy NGC 1068, using Band 3 of the Atacama Large Millimeter/submillimeter Array. We apply PCA to 16 well-detected molecular line intensity maps convolved to a common 150 pc resolution. In addition, we include the [S iii]/[S ii] line ratio and [C i] 3 P 1–3 P 0 maps in the literature, both of whose distributions show a remarkable resemblance to that of a kiloparsec-scale biconical outflow from the central active galactic nucleus. We identify two prominent features: (1) central concentration at the circumnuclear disk (CND) and (2) two peaks across the center that coincide with the biconical outflow peaks. The concentrated molecular lines in the CND are mostly high-dipole molecules (e.g., H13CN, HC3N, and HCN). Line emissions from molecules known to be enhanced in an irradiated interstellar medium, CN, C2H, and HNC, show similar concentrations and extended components along the bicone, suggesting that molecule dissociation is a dominant chemical effect of the cold molecular outflow of this galaxy. Although further investigation should be made, this scenario is consistent with the faintness or absence of emission lines from CO isotopologues, CH3OH, and N2H+ in the outflow, which are easily destroyed by dissociating photons and electrons.
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Ortiz-León, Gisela N., Karl M. Menten, Andreas Brunthaler, Timea Csengeri, James S. Urquhart, Friedrich Wyrowski, Yan Gong, et al. "A global view on star formation: the GLOSTAR Galactic plane survey." Astronomy & Astrophysics 651 (July 2021): A87. http://dx.doi.org/10.1051/0004-6361/202140817.
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The Cygnus X complex is covered by the Global View of Star Formation in the Milky Way (GLOSTAR) survey, an unbiased radio-wavelength Galactic plane survey, in 4–8 GHz continuum radiation and several spectral lines. The GLOSTAR survey observed the 6.7 GHz transition of methanol (CH3OH), an exclusive tracer of high-mass young stellar objects. Using the Very Large Array in both the B and D configurations, we observed an area in Cygnus X of 7° × 3° in size and simultaneously covered the methanol line and the continuum, allowing cross-registration. We detected thirteen sources with Class II methanol maser emission and one source with methanol absorption. Two methanol maser sources are newly detected; in addition, we found four new velocity components associated with known masers. Five masers are concentrated in the DR21 ridge and W75N. We determined the characteristics of the detected masers and investigated the association with infrared, (sub)millimeter, and radio continuum emission. All maser sources are associated with (sub)millimeter dust continuum emission, which is consistent with the picture of masers tracing regions in an active stage of star formation. On the other hand, only five masers (38 ± 17%) have radio continuum counterparts seen with GLOSTAR within ~1″, testifying to their youth. Comparing the distributions of the bolometric luminosity and the luminosity-to-mass ratio of cores that host 6.7 GHz methanol masers with those of the full core population, we identified lower limits LBol ~ 200 L⊙ and LBol/Mcore ~ 1 L⊙M⊙−1 for a dust source to host maser emission.
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Melli, Alessio, Mattia Melosso, Kevin G. Lengsfeld, Luca Bizzocchi, Víctor M. Rivilla, Luca Dore, Vincenzo Barone, Jens-Uwe Grabow, and Cristina Puzzarini. "Spectroscopic Characterization of 3-Aminoisoxazole, a Prebiotic Precursor of Ribonucleotides." Molecules 27, no. 10 (May 20, 2022): 3278. http://dx.doi.org/10.3390/molecules27103278.
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The processes and reactions that led to the formation of the first biomolecules on Earth play a key role in the highly debated theme of the origin of life. Whether the first chemical building blocks were generated on Earth (endogenous synthesis) or brought from space (exogenous delivery) is still unanswered. The detection of complex organic molecules in the interstellar medium provides valuable support to the latter hypothesis. To gather more insight, here we provide the astronomers with accurate rotational frequencies to guide the interstellar search of 3-aminoisoxazole, which has been recently envisaged as a key reactive species in the scenario of the so-called RNA-world hypothesis. Relying on an accurate computational characterization, we were able to register and analyze the rotational spectrum of 3-aminoisoxazole in the 6–24 GHz and 80–320 GHz frequency ranges for the first time, exploiting a Fourier-transform microwave spectrometer and a frequency-modulated millimeter/sub-millimeter spectrometer, respectively. Due to the inversion motion of the −NH2 group, two states arise, and both of them were characterized, with more than 1300 lines being assigned. Although the fit statistics were affected by an evident Coriolis interaction, we were able to produce accurate line catalogs for astronomical observations of 3-aminoisoxazole.
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Jafarzadeh, S., S. Wedemeyer, M. Szydlarski, B. De Pontieu, R. Rezaei, and M. Carlsson. "The solar chromosphere at millimetre and ultraviolet wavelengths." Astronomy & Astrophysics 622 (February 2019): A150. http://dx.doi.org/10.1051/0004-6361/201834205.
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Solar observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide us with direct measurements of the brightness temperature in the solar chromosphere. We study the temperature distributions obtained with ALMA Band 6 (in four sub-bands at 1.21, 1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of, a sunspot, comprising quasi-quiet and active regions with different amounts of underlying magnetic fields. We compare these temperatures with those obtained at near- and far-ultraviolet (UV) wavelengths (and with the line-core intensities of the optically-thin far-UV spectra), co-observed with the Interface Region Imaging Spectrograph (IRIS) explorer. These include the emission peaks and cores of the Mg II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the mid-to-high chromosphere and the low transition region. Splitting the ALMA sub-bands resulted in an slight increase of spatial resolution in individual temperature maps, thus, resolving smaller-scale structures compared to those produced with the standard averaging routines. We find that the radiation temperatures have different, though somewhat overlapping, distributions in different wavelengths and in the various magnetic regions. Comparison of the ALMA temperatures with those of the UV diagnostics should, however, be interpreted with great caution, the former is formed under the local thermodynamic equilibrium (LTE) conditions, the latter under non-LTE. The mean radiation temperature of the ALMA Band 6 is similar to that extracted from the IRIS C II line in all areas with exception of the sunspot and pores where the C II poses higher radiation temperatures. In all magnetic regions, the Mg II lines associate with the lowest mean radiation temperatures in our sample. These will provide constraints for future numerical models.
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Gratier, Pierre, Jérôme Pety, Emeric Bron, Antoine Roueff, Jan H. Orkisz, Maryvonne Gerin, Victor de Souza Magalhaes, et al. "Quantitative inference of the H2 column densities from 3 mm molecular emission: case study towards Orion B." Astronomy & Astrophysics 645 (December 23, 2020): A27. http://dx.doi.org/10.1051/0004-6361/202037871.
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Context. Based on the finding that molecular hydrogen is unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-infrared, which requires space telescopes, or on star counting, which is limited in angular resolution by the stellar density. The (sub)millimeter observations of numerous trace molecules can be effective using ground-based telescopes, but the relationship between the emission of one molecular line and the H2 column density is non-linear and sensitive to excitation conditions, optical depths, and abundance variations due to the underlying physico- chemistry. Aims. We aim to use multi-molecule line emission to infer the H2 molecular column density from radio observations. Methods. We propose a data-driven approach to determine the H2 gas column densities from radio molecular line observations. We use supervised machine-learning methods (random forest) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of the H2 column density, using a limited set of molecular lines between 72 and 116 GHz as input, and the Herschel-based dust-derived column densities as “ground truth” output. Results. For conditions similar to those of the Orion B molecular cloud, we obtained predictions of the H2 column density within a typical factor of 1.2 from the Herschel-based column density estimates. A global analysis of the contributions of the different lines to the predictions show that the most important lines are 13CO(1–0), 12CO(1–0), C18O(1–0), and HCO+(1–0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended that the N2H+(1–0) and CH3OH(20–10) lines be added for the prediction of the H2 column density in dense core conditions. Conclusions. This article opens a promising avenue for advancing direct inferencing of important physical parameters from the molecular line emission in the millimeter domain. The next step will be to attempt to infer several parameters simultaneously (e.g., the column density and far-UV illumination field) to further test the method.
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Beuther, H., A. Ahmadi, J. C. Mottram, H. Linz, L. T. Maud, Th Henning, R. Kuiper, A. J. Walsh, K. G. Johnston, and S. N. Longmore. "High-mass star formation at sub-50 au scales." Astronomy & Astrophysics 621 (January 2019): A122. http://dx.doi.org/10.1051/0004-6361/201834064.
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Context. The hierarchical process of star formation has so far mostly been studied on scales from thousands of au to parsecs, but the smaller sub-1000 au scales of high-mass star formation are still largely unexplored in the submillimeter regime. Aims. We aim to resolve the dust and gas emission at the highest spatial resolution to study the physical properties of the densest structures during high-mass star formation. Methods. We observed the high-mass hot core region G351.77-0.54 with the Atacama Large Millimeter Array with baselines extending out to more than 16 km. This allowed us to dissect the region at sub-50 au spatial scales. Results. At a spatial resolution of 18/40 au (depending on the distance), we identify twelve sub-structures within the inner few thousand au of the region. The brightness temperatures are high, reaching values greater 1000 K, signposting high optical depth toward the peak positions. Core separations vary between sub-100 au to several 100 and 1000 au. The core separations and approximate masses are largely consistent with thermal Jeans fragmentation of a dense gas core. Due to the high continuum optical depth, most spectral lines are seen in absorption. However, a few exceptional emission lines are found that most likely stem from transitions with excitation conditions above 1000 K. Toward the main continuum source, these emission lines exhibit a velocity gradient across scales of 100–200 au aligned with the molecular outflow and perpendicular to the previously inferred disk orientation. While we cannot exclude that these observational features stem from an inner hot accretion disk, the alignment with the outflow rather suggests that it stems from the inner jet and outflow region. The highest-velocity features are found toward the peak position, and no Hubble-like velocity structure can be identified. Therefore, these data are consistent with steady-state turbulent entrainment of the hot molecular gas via Kelvin–Helmholtz instabilities at the interface between the jet and the outflow. Conclusions. Resolving this high-mass star-forming region at sub-50 au scales indicates that the hierarchical fragmentation process in the framework of thermal Jeans fragmentation can continue down to the smallest accessible spatial scales. Velocity gradients on these small scales have to be treated cautiously and do not necessarily stem from disks, but may be better explained with outflow emission. Studying these small scales is very powerful, but covering all spatial scales and deriving a global picture from large to small scales are the next steps to investigate.
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Drozdovskaya, Maria N., Laurent H. Coudert, Laurent Margulès, Audrey Coutens, Jes K. Jørgensen, and Sébastien Manigand. "Successive deuteration in low-mass star-forming regions: The case of D2-methanol (CHD2OH) in IRAS 16293-2422." Astronomy & Astrophysics 659 (March 2022): A69. http://dx.doi.org/10.1051/0004-6361/202142863.
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Context. Di-deuterated molecules are observed in the earliest stages of star formation at abundances of a few percent relative to their nondeuterated isotopologs, which is unexpected considering the scarcity of deuterium in the interstellar medium. With sensitive observations leading to the detection of a steadily increasing number of di-deuterated species, it is becoming possible to explore successive deuteration chains. Aims. The accurate quantification of the column density of di-deuterated methanol is a key piece of the puzzle that is missing in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS 16293-2422. A spectroscopic dataset for astrophysical purposes was built for CHD2OH and made publicly available to facilitate the accurate characterization of this species in astrochemical surveys. Methods. The newly computed line list and partition function were used to search for CHD2OH toward IRAS 16293-2422 A and B in data from the Atacama Large Millimeter/submillimeter Array (ALMA) Protostellar Interferometric Line Survey (PILS). Only nonblended, optically thin lines of CHD2OH were used for the synthetic spectral fitting. Results. The constructed spectroscopic database contains line frequencies and strengths for 7417 transitions in the 0–500 GHz frequency range. ALMA-PILS observations in the 329–363 GHz range were used to identify 105 unique, nonblended, optically thin line frequencies of CHD2OH for synthetic spectral fitting. The derived excitation temperatures and column densities yield high D/H ratios of CHD2OH in IRAS 16293-2422 A and B of 7.5 ± 1.1% and 7.7 ± 1.2%, respectively. Conclusions. Deuteration in IRAS 16293-2422 is not higher than in other low-mass star-forming regions (L483, SVS13-A, NGC 1333-IRAS2A, -IRAS4A, and -IRAS4B). Di-deuterated molecules consistently have higher D/H ratios than their mono-deuterated counterparts in all low-mass protostars, which may be a natural consequence of H–D substitution reactions as seen in laboratory experiments. The Solar System’s natal cloud, as traced by comet 67P/Churyumov–Gerasimenko, may have had a lower initial abundance of D, been warmer than the cloud of IRAS 16293-2422, or been partially reprocessed. In combination with accurate spectroscopy, a careful spectral analysis, and the consideration of the underlying assumptions, successive deuteration is a robust window on the physicochemical provenance of star-forming systems.
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Pety, Jérôme, Maryvonne Gerin, Emeric Bron, Pierre Gratier, Jan H. Orkisz, Pierre Palud, Antoine Roueff, et al. "Revealing which Combinations of Molecular Lines are Sensitive to the Gas Physical Parameters of Molecular Clouds." EPJ Web of Conferences 265 (2022): 00048. http://dx.doi.org/10.1051/epjconf/202226500048.
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Atoms and molecules have long been thought to be versatile tracers of the cold neutral gas in the universe, from high-redshift galaxies to star forming regions and proto-planetary disks, because their internal degrees of freedom bear the signature of the physical conditions where these species reside. However, the promise that molecular emission has a strong diagnostic power of the underlying physical and chemical state is still hampered by the difficulty to combine sophisticated chemical codes with gas dynamics. It is therefore important 1) to acquire self-consistent data sets that can be used as templates for this theoretical work, and 2) to reveal the diagnostic capabilities of molecular lines accurately. The advent of sensitive wideband spectrometers in the (sub)- millimeter domain (e.g., IRAM-30m/EMIR, NOEMA, …) during the 2010s has allowed us to image a significant fraction of a Giant Molecular Cloud with enough sensitivity to detect tens of molecular lines in the 70 – 116 GHz frequency range. Machine learning techniques applied to these data start to deliver the next generation of molecular line diagnostics of mass, density, temperature, and radiation field.
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Kan, Xue Fen, Zhi Xin Zou, Cheng Yin, Hui Ping Xu, Xian Ping Wang, Qing Bang Han, and Zhuang Qi Cao. "Continuous Goos-Hänchen Shift of Vortex Beam via Symmetric Metal-Cladding Waveguide." Materials 15, no. 12 (June 16, 2022): 4267. http://dx.doi.org/10.3390/ma15124267.
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Goos-Hänchen shift provides a way to manipulate the transverse shift of an optical beam with sub-wavelength accuracy. Among various enhancement schemes, millimeter-scale shift at near-infrared range has been realized by a simple symmetrical metal-cladding waveguide structure owing to its unique ultrahigh-order modes. However, the interpretation of the shift depends crucially on its definition. This paper shows that the shift of a Gaussian beam is discrete if we follow the light peak based on the stationary phase approach, where the M-lines are fixed to specific directions and the beam profile is separated near resonance. On the contrary, continuous shift can be obtained if the waveguide is illuminated by a vortex beam, and the physical cause can be attributed to the position-dependent phase-match condition of the ultrahigh-order modes due to the spatial phase distribution.
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Teng, Yu-Hsuan, Karin M. Sandstrom, Jiayi Sun, Adam K. Leroy, L. Clifton Johnson, Alberto D. Bolatto, J. M. Diederik Kruijssen, et al. "Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351." Astrophysical Journal 925, no. 1 (January 1, 2022): 72. http://dx.doi.org/10.3847/1538-4357/ac382f.
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Abstract The CO-to-H2 conversion factor (α CO) is critical to studying molecular gas and star formation in galaxies. The value of α CO has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on ~kiloparsec scales revealed low values of α CO in the centers of some barred spiral galaxies, including NGC 3351. We present new Atacama Large Millimeter/submillimeter Array Band 3, 6, and 7 observations of 12CO, 13CO, and C18O lines on 100 pc scales in the inner ∼2 kpc of NGC 3351. Using multiline radiative transfer modeling and a Bayesian likelihood analysis, we infer the H2 density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of 2–3 × 103 cm−3 in the central ∼1 kpc and a high temperature of 30–60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H2 abundance of 3 × 10−4, our analysis yields α CO ∼ 0.5–2.0 M ⊙ (K km s−1 pc2)−1 with a decreasing trend with galactocentric radius in the central ∼1 kpc. The inflows show a substantially lower α CO ≲ 0.1 M ⊙ (K km s−1 pc2)−1, likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted α CO of ∼1.5 M ⊙ (K km s−1 pc2)−1, which is similar to previous dust-modeling-based results at kiloparsec scales. This suggests that low α CO on kiloparsec scales in the centers of some barred galaxies may be due to the contribution of low-optical-depth CO emission in bar-driven inflows.
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Remijan, A., C. Xue, L. Margulès, A. Belloche, R. A. Motiyenko, J. Carder, C. Codella, et al. "Expanding the submillimeter wave spectroscopy and astronomical search for thioacetamide (CH3CSNH2) in the ISM." Astronomy & Astrophysics 658 (February 2022): A85. http://dx.doi.org/10.1051/0004-6361/202142504.
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Context. One of the biggest unsolved mysteries of modern astrochemistry is understanding chemical formation pathways in the interstellar medium (ISM) and circumstellar environments. The detections (or even nondetections) of molecules composed of low-abundance atomic species (such as S, P, Si, and Mg) may help to constrain chemical pathways. Thioacetamide (CH3CSNH2) is the sulfur analog to acetemide (CH3CONH2) and it is a viable candidate to search for in astronomical environments – specifically toward regions where other S-bearing molecules have been found and, if possible, that also contain a detection of CH3CONH2. If detected, it would not only continue to expand the view of molecular complexity in astronomical environments, but also help to better elucidate the possible formation pathways of these types of species in these environments. Aims. Our aim is to expand the frequency range of the measured rotational spectrum of CH3CSNH2 beyond 150 GHz and then to use those measurements to extend the search for this species in the ISM. The new laboratory measurements and expanded search cover more parameter space for determining under what conditions CH3CSNH2 may be detected, leading to possible constraints on the formation of large S-bearing molecules found in the ISM. Methods. The rotational spectrum of CH3CSNH2 was investigated up to 650 GHz. Using the newly refined spectrum of CH3CSNH2, as well as additional spectroscopic data on the chemically related species CH3CONH2, a variety of astronomical sources were searched including data from the following large surveys: Prebiotic Interstellar Molecule Survey conducted with the Green Bank Telescope; Exploring molecular complexity with ALMA conducted with the Atacama Large Millimeter/submillimeter Array; and Astrochemical Surveys at IRAM conducted with the Institut de Radioastronomie Millimétrique 30 m Telescope. Results. A total of 1428 transitions from the vt = 0 state with maximum values J = 47 and Ka = 20 in the range up to 330 GHz, and J = 95 and Ka = 20 in the range from 400–660 GHz were assigned. We also assigned 321 transitions from the vt = 1 state with the maximum values J = 35 and Ka = 9 up to 330 GHz. We achieved a final fit with a root-mean-square deviation of 43.4 kHz that contains 2035 measured lines from our study and the literature for vt = 0 and vt = 1 states of A and E symmetries. The final fit is based on the rho-axis-method Hamiltonian model that includes 40 parameters. An astronomical search for CH3CSNH2 was conducted based on all the new spectroscopic data. No transitions of CH3CSNH2 were detected toward any of the sources contained in our survey. Using the appropriate telescope and physical parameters for each astronomical source, upper limits to the column densities were found for CH3CSNH2 toward each source.
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Zhou, Jian-Wen, Tie Liu, Jin-Zeng Li, Hong-Li Liu, Ke Wang, Feng-Wei Xu, Kee-Tae Kim, et al. "ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions–VI. On the formation of the ‘L’ type filament in G286.21+0.17." Monthly Notices of the Royal Astronomical Society 508, no. 3 (October 2, 2021): 4639–55. http://dx.doi.org/10.1093/mnras/stab2801.
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ABSTRACT Filaments play an important role in star formation, but the formation process of filaments themselves is still unclear. The high-mass star-forming clump G286.21+0.17 (G286 for short) that contains an ‘L’ type filament was thought to undergo global collapse. Our high-resolution ALMA band 3 observations resolve the gas kinematics of G286 and reveal two sub-clumps with very different velocities inside it. We find that the ‘blue profile’ (an indicator of gas infall) of HCO+ lines in single dish observations of G286 is actually caused by gas emission from the two sub-clumps rather than gas infall. We advise great caution in interpreting gas kinematics (e.g. infall) from line profiles towards distant massive clumps in single dish observations. Energetic outflows are identified in G286 but the outflows are not strong enough to drive expansion of the two sub-clumps. The two parts of the ‘L’ type filament (‘NW–SE’ and ‘NE–SW’ filaments) show prominent velocity gradients perpendicular to their major axes, indicating that they are likely formed due to large-scale compression flows. We argue that the large-scale compression flows could be induced by the expansion of nearby giant H ii regions. The ‘NW–SE’ and ‘NE–SW’ filaments seem to be in collision, and a large amount of gas has been accumulated in the junction region where the most massive core G286c1 forms.
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Bie, Shuhang, and Shi Pu. "Array Design of 300 GHz Dual-Band Microstrip Antenna Based on Dual-Surfaced Multiple Split-Ring Resonators." Sensors 21, no. 14 (July 19, 2021): 4912. http://dx.doi.org/10.3390/s21144912.
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To meet the increasing need of high-data-rate and broadband wireless communication systems, the devices and its circuits R&D under Millimeter, Sub-Millimeter, or even Terahertz (THz) frequency bands are attracting more and more attention from not only academic, but also industrial areas. Most of the former research on the THz waveband (0.1–10 THz) antenna design is mainly focused on realizing high directional gain, such as horn antennas, even though the coverage area is very limited when comparing with the current Wi-Fi system. One solution for the horizontally omnidirectional communication antenna is using the structure of multiple split-ring resonators (MSRRs). Aiming at this point, a novel 300 GHz microstrip antenna array based on the dual-surfaced multiple split-ring resonators (DSMSRRs) is proposed in this paper. By employing the two parallel microstrip transmission lines, different MSRRs are fed and connected on two surfaces of the PCB with a centrally symmetric way about them. The feeding port of the whole antenna is in between the centers of the two microstrip lines. Thus, this kind of structure is a so-called DSMSRR. Based on the different size of the MSRRs, different or multiple working wavebands can be achieved on the whole antenna. Firstly, in this paper, the quasi-static model is used to analyze the factors affecting the resonance frequency of MSRRs. Simulation and measured results demonstrate that the resonant frequency of the proposed array antenna is 300 GHz, which meets the design requirements of the expected frequency point and exhibits good radiation characteristics. Then, a dual-band antenna is designed on the above methods, and it is proved by simulation that the working frequency bands of the proposed dual-band antenna with reflection coefficient below −10 dB are 274.1–295.6 GHz and 306.3–313.4 GHz.
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Stanley, F., J. B. Jolly, S. König, and K. K. Knudsen. "A spectral stacking analysis to search for faint outflow signatures in z ∼ 6 quasars." Astronomy & Astrophysics 631 (October 23, 2019): A78. http://dx.doi.org/10.1051/0004-6361/201834530.
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Aims. Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms that potentially affect the evolution of the host galaxy. However, systematic millimetre (mm) observations of outflows are only now becoming possible with the advent of sensitive mm telescopes. In this study we used spectral stacking methods to search for a faint high-velocity outflow signal in a sample of [C II] detected, z ∼ 6 quasars. Methods. We searched for broad emission line signatures from high-velocity outflows for a sample of 26 z ∼ 6 quasars observed with the Atacama Large Millimeter Array (ALMA), with a detection of the [C II] line. The observed emission lines of the sources are dominated by the host galaxy, and outflow emission is not detected for the individual sources. We used a spectral line stacking analysis developed for interferometric data to search for outflow emission. We stacked both extracted spectra and the full spectral cubes. We also investigated the possibility that only a sub-set of our sample contributes to the stacked outflow emission. Results. We find only a tentative detection of a broad emission line component in the stacked spectra. When taking a region of about 2″ around the central position of the stacked cubes, the stacked line shows an excess emission due to a broad component of 1.1–1.5σ, but the significance drops to 0.4–0.7σ when stacking the extracted spectra from a smaller region. The broad component can be characterised by a line width of full width at half-maximum FWHM > 700 km s−1. Furthermore, we find a sub-sample of 12 sources, the stack of which maximises the broad component emission. The stack of this sub-sample shows an excess emission due to a broad component of 1.2–2.5σ. The stacked line of these sources has a broad component of FWHM > 775 km s−1. Conclusions. We find evidence suggesting the presence of outflows in a sub-sample of 12 out of 26 sources, which demonstrates the importance of spectral stacking techniques in tracing faint signal in galaxy samples. However, deeper ALMA observations are necessary to confirm the presence of a broad component in the individual spectra.
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Paulish, Andrey G., Anatoly V. Gusachenko, Alexander O. Morozov, Vladimir A. Golyashov, Kirill V. Dorozhkin, and Valentin I. Suslyaev. "Sensitivity of the tetraaminodiphenyl based pyroelectric sensor from visible to sub-THz range." Sensor Review 40, no. 3 (June 15, 2020): 291–96. http://dx.doi.org/10.1108/sr-03-2020-0047.
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Purpose The purpose of this paper is to study the spectral sensitivity characteristics of new pyroelectric sensor based on tetraaminodiphenyl film within the wavelength range of 0.4-10 µm and 300-3,000 µm. Design/methodology/approach Mylar film with the thickness of about 70 µm was used as the input window. The MDR-41 monochromator-based spectrometric complex and the quasi-optical spectrometer with the set of backward-wave oscillators were used for measurements of the pyrodetector spectral characteristics within the 0.4-10 µm and 300-3,000 µm ranges, respectively. Findings Mylar was found to have absorption lines within the range of 0.4-10 µm, which must be taken into account when broadband detectors developing. The noise equivalent power in the visible and infrared ranges was less than 6 × 10–10 W/Hz1/2, which is about five times lower than for analogue ones. In the sub-THz range, the pyrodetector sensitivity is 2-8 times higher than the Golay cell. The sensitivity of such pyrodetector weakly depends on the wavelength in the total measured range. Practical implications The pyroelectric sensor has good prospects for use in super wide spectral range, from ultraviolet to millimeter radiation, in spectrometers for scientific research, in industry for the operational control of THz radiation sources, as well as in security THz-systems. Originality/value The spectral sensitivity characteristics of the pyroelectric photosensor based on TADPh in the visible, infrared and terahertz ranges were measured. The prospects for the use of such sensors were determined.
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Alcalá, J. M., C. F. Manara, K. France, C. P. Schneider, N. Arulanantham, A. Miotello, H. M. Günther, and A. Brown. "HST spectra reveal accretion in MY Lupi." Astronomy & Astrophysics 629 (September 2019): A108. http://dx.doi.org/10.1051/0004-6361/201935657.
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The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs). We revisit the case of MY Lup, an object where VLT/X-shooter data suggested a negligible mass accretion rate, and show it to be accreting on a level similar to other Class II YSOs in Lupus based on Hubble Space Telescope (HST) observations. In our HST-Cosmic Origins Spectrograph (HST-COS) and -Space Telescope Imaging Spectrograph (HST-STIS) spectra, we find many emission lines, as well as substantial far-ultraviolet (FUV) continuum excess emission, which can be ascribed to active accretion. The total luminosity of the C IV λ1549 Å doublet is 4.1 × 10−4 L⊙. Using scalings between accretion luminosity, Lacc, and C IV luminosity from the literature, we derive Lacc ~2 × 10−1 L⊙, which is more than an order of magnitude higher than the upper limit estimated from the X-shooter observations. We discuss possible reasons for the X-shooter-HST discrepancy, the most plausible being that the low contrast between the continuum excess emission and the photospheric+chromospheric emission at optical wavelengths in MY Lup hampered detection of excess emission. The luminosity of the FUV continuum and C IV lines, strong H2 fluorescence, and a “1600 A Bump” place MY Lup in the class of accreting objects with gas-rich discs. So far, MY Lup is the only peculiar case in which a significant difference between the HST and X-shooter Ṁacc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited Lacc estimate is Ṁacc ~ 1(−0.5+1.5) × 10−8 M⊙ yr−1. This value is consistent with the typical value derived for accreting YSOs of similar mass in Lupus and points to less clearing of the inner disc than indicated by near- and mid-infrared observations. This is confirmed by Atacama Large Millimeter Array (ALMA) data, which show that the gaps and rings seen in the sub-millimetre are relatively shallow.
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Méndez-Hernández, H., E. Ibar, K. K. Knudsen, P. Cassata, M. Aravena, M. J. Michałowski, Zhi-Yu Zhang, et al. "VALES VI: ISM enrichment in star-forming galaxies up to z ∼ 0.2 using 12CO(1–0), 13CO(1–0), and C18O(1–0) line luminosity ratios." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 7, 2020): 2771–85. http://dx.doi.org/10.1093/mnras/staa1964.
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ABSTRACT We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations towards 27 low-redshift (0.02 < z < 0.2) star-forming galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey. We perform stacking analyses of the 12CO(1–0), 13CO(1–0), and C18O(1–0) emission lines to explore the L′ [12CO(1–0)]/L′ [13CO(1–0)] [hereafter L′ (12CO)/L′ (13CO)] and L′ [13CO(1–0)]/L′ [C18O(1–0)] [hereafter L′ (13CO)/L′ (C18O)] line luminosity ratio dependence as a function of different global galaxy parameters related to the star formation activity. The sample has far-IR luminosities of $10^{10.1\!-\!11.9}\,$ L⊙ and stellar masses of 109.8–10.9 M⊙ corresponding to typical star-forming and starburst galaxies at these redshifts. On average, we find an L′ (12CO)/L′ (13CO) line luminosity ratio value of 16.1 ± 2.5. Galaxies with pieces of evidence of possible merging activity tend to show higher L′ (12CO)/L′ (13CO) ratios by a factor of 2, while variations of this order are also found in galaxy samples with higher star formation rates (SFRs) or star formation efficiencies (SFEs). We also find an average L′ (13CO)/L′ (C18O) line luminosity ratio of 2.5 ± 0.6, which is in good agreement with those previously reported for starburst galaxies. We find that galaxy samples with high LIR, SFR, and SFE show low L′ (13CO)/L′ (C18O) line luminosity ratios with high L′ (12CO)/L′ (13CO) line luminosity ratios, suggesting that these trends are produced by selective enrichment of massive stars in young starbursts.
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Gratier, Pierre, Emeric Bron, Maryvonne Gerin, Jérôme Pety, Viviana V. Guzman, Jan Orkisz, Sébastien Bardeau, et al. "Dissecting the molecular structure of the Orion B cloud: insight from principal component analysis." Astronomy & Astrophysics 599 (March 2017): A100. http://dx.doi.org/10.1051/0004-6361/201629847.
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Context. The combination of wideband receivers and spectrometers currently available in (sub-)millimeter observatories deliver wide-field hyperspectral imaging of the interstellar medium. Tens of spectral lines can be observed over degree wide fields in about 50 h. This wealth of data calls for restating the physical questions about the interstellar medium in statistical terms. Aims. We aim to gain information on the physical structure of the interstellar medium from a statistical analysis of many lines from different species over a large field of view, without requiring detailed radiative transfer or astrochemical modeling. Methods. We coupled a non-linear rescaling of the data with one of the simplest multivariate analysis methods, namely the principal component analysis, to decompose the observed signal into components that we interpret first qualitatively and then quantitatively based on our deep knowledge of the observed region and of the astrochemistry at play. Results. We identify three principal components, linear compositions of line brightness temperatures, that are correlated at various levels with the column density, the volume density and the UV radiation field. Conclusions. When sampling a sufficiently diverse mixture of physical parameters, it is possible to decompose the molecular emission in order to gain physical insight on the observed interstellar medium. This opens a new avenue for future studies of the interstellar medium.
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Tetarenko, A. J., E. W. Rosolowsky, J. C. A. Miller-Jones, and G. R. Sivakoff. "Jet–ISM interactions near the microquasars GRS 1758−258 and 1E 1740.7−2942." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 27, 2020): 3504–24. http://dx.doi.org/10.1093/mnras/staa2175.
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ABSTRACT We present Atacama Large Millimeter/Sub-millimeter Array observations of the candidate jet–ISM interaction zones near the black hole X-ray binaries GRS 1758−258 and 1E 1740.7−2942. Using these data, we map the molecular line emission in the regions, detecting emission from the HCN [J = 1−0], HCO+ [J = 1−0], SiO [J = 2−1], CS [J = 2−1], 13CO [J = 1−0], C18O [J = 1−0], HNCO [J = 40,4−30,3], HNCO [J = 50,5−40,4], and CH3OH [J = 21,1−11,0] molecular transitions. Through examining the morphological, spectral, and kinematic properties of this emission, we identify molecular structures that may trace jet-driven cavities in the gas surrounding these systems. Our results from the GRS 1758−258 region in particular, are consistent with recent work, which postulated the presence of a jet-blown cocoon structure in deep radio continuum maps of the region. Using these newly discovered molecular structures as calorimeters, we estimate the time averaged jet power from these systems, finding $(1.1{\!-\!}5.7)\times 10^{36}{\rm erg\, s}^{-1}$ over 0.12−0.31 Myr for GRS 1758−258 and $(0.7{\!-\!}3.5)\times 10^{37}{\rm erg\, s}^{-1}$ over 0.10−0.26 Myr for 1E 1740.7−2942. Additionally, the spectral line characteristics of the detected emission place these molecular structures in the central molecular zone of our Galaxy, thereby constraining the distances to the black hole X-ray binaries to be 8.0 ± 1.0 kpc. Overall, our analysis solidifies the diagnostic capacity of molecular lines, and highlights how astro-chemistry can both identify jet–ISM interaction zones and probe jet feedback from Galactic X-ray binaries.
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Notsu, Shota, Hideko Nomura, Catherine Walsh, Mitsuhiko Honda, Tomoya Hirota, Eiji Akiyama, and T. J. Millar. "Possibility to locate the position of the H2O snowline in protoplanetary disks through spectroscopic observations." Proceedings of the International Astronomical Union 13, S332 (March 2017): 113–20. http://dx.doi.org/10.1017/s1743921317007797.
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AbstractObservationally measuring the location of the H2O snowline is crucial for understanding the planetesimal and planet formation processes, and the origin of water on Earth. The velocity profiles of emission lines from protoplanetary disks are usually affected by Doppler shift due to Keplerian rotation and thermal broadening. Therefore, the velocity profiles are sensitive to the radial distribution of the line-emitting regions. In our work (Notsu et al. 2016, 2017), we found candidate water lines to locate the position of the H2O snowline through future high-dispersion spectroscopic observations. First, we calculated the chemical composition of the disks around a T Tauri star and a Herbig Ae star using chemical kinetics. We confirmed that the abundance of H2O gas is high not only in the hot midplane region inside the H2O snowline but also in the hot surface layer and the photodesorption region of the outer disk. The position of the H2O snowline in the Herbig Ae disk exists at a larger radius from the central star than that in the T Tauri disk. Second, we calculated the H2O line profiles and identified that H2O emission lines with small Einstein A coefficients (∼10−6 − 10−3 s−1) and relatively high upper state energies (∼ 1000K) are dominated by emission from the hot midplane region inside the H2O snowline, and therefore their profiles potentially contain information which can be used to locate the position of the H2O snowline. The wavelengths of the H2O lines which are the best candidates to locate the position of the H2O snowline range from mid-infrared to sub-millimeter, and the total line fluxes tend to increase with decreasing wavelengths. We investigated the possibility of future observations using the ALMA and mid-infrared high-dispersion spectrographs (e.g., SPICA/SMI-HRS). Since the fluxes of those identified lines from a Herbig Ae disk are stronger than those of a T Tauri disk, the possibility of a successful detection is expected to increase for a Herbig Ae disk.
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Seta, Masumichi, Naomasa Nakai, Shun Ishii, Makoto Nagai, Yusuke Miyamoto, Takashi Ichikawa, Naruhisa Takato, and Hideaki Motoyama. "Dome Fuji in Antarctica as a Site for Infrared and Terahertz Astronomy." Proceedings of the International Astronomical Union 8, S288 (August 2012): 251–55. http://dx.doi.org/10.1017/s1743921312016961.
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AbstractDome Fuji on the Antarctic high plateau may be a good site for terahertz astronomy because of its high altitude of 3,810 m and low average temperature of −54°C. We have demonstrated that the opacity at 220 GHz from Dome Fuji in summer is very good and stable; τ = 0.045 ± 0.007. We have developed a transportable 30 cm telescope to map the Milky Way in the CO (J=4–3) and the [CI] (3P1–3P0) lines at Dome Fuji from 2014. It has a 9′ beam. Physical conditions such as density and temperature of molecular clouds could be derived from a direct comparison of CO (J=4–3) and [CI] (3P1–3P0) with CO (J=1–0) taken by the Columbia–CfA survey. We are also developing a 1.2 m sub-millimeter telescope. It will be equipped with a dual superconducting device (SIS) receiver for 500/800 GHz. The 1.2 m telescope produces a 2.2′ beam at 492 GHz and could map a molecular cloud entirely. It could also observe nearby galaxies in the CO (J=4–3), CO (J=7–6), [CI] (3P1–3P0), [CI] (3P2–3P1) and in continuum emission between 460–810 GHz.
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Mizuno, Norikazu. "The properties of molecular clouds across the Magellanic System." Proceedings of the International Astronomical Union 4, S256 (July 2008): 203–14. http://dx.doi.org/10.1017/s1743921308028469.
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AbstractMost stars form in Giant Molecular Clouds (GMCs) and regulate the evolution of galaxies in various respects. The formed stars affect the surrounding materials strongly via their UV photons, stellar winds, and supernova explosions, which lead to trigger the formation of next-generations of stars in the GMCs. It is therefore crucial to reveal the distribution and properties of GMCs in a galaxy. The Magellanic System is a unique target to make such detailed comprehensive study of GMCs. This is because it is nearby and the LMC is nearly face-on, making it feasible to unambiguously identify associated young objects within GMCs. Recent millimeter and sub-millimeter observations in the Magellanic System have started to reveal the distribution and properties of the individual GMCs in detail and their relation to star formation activities. From the NANTEN CO surveys, three types of GMCs can be classified in terms of star formation activities; Type I is starless, Type II is with H ii regions only, and Type III is associated with active star formation indicated by huge H ii regions and young star clusters. The further observations to obtain detailed structure of the GMCs by Mopra and SEST and to search for the dense cores by ASTE and NANTEN2 in higher tansition lines of CO have been carried out with an angular resolution of about 5 to 10 pc. These observations revealed that the differences of the physical properties represent an evolutionary sequence of GMCs in terms of density increase leading to star formation. Type I and II GMCs are at the early phase of star formation where density does not yet become high enough to show active star formation, and Type III GMCs represent the later phase where the average density is increased and the GMCs are forming massive stars.
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Shivaei, Irene, Gergö Popping, George Rieke, Naveen Reddy, Alexandra Pope, Robert Kennicutt, Bahram Mobasher, et al. "Infrared Spectral Energy Distributions and Dust Masses of Sub-solar Metallicity Galaxies at z ∼ 2.3." Astrophysical Journal 928, no. 1 (March 1, 2022): 68. http://dx.doi.org/10.3847/1538-4357/ac54a9.
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Abstract We present results from Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm continuum observations of a sample of 27 star-forming galaxies at z = 2.1–2.5 from the MOSFIRE Deep Evolution Field survey with metallicity and star formation rate measurements from optical emission lines. Using stacks of Spitzer, Herschel, and ALMA photometry (rest frame ∼8–400 μm), we examine the infrared (IR) spectral energy distributions (SED) of z ∼ 2.3 subsolar-metallicity (∼0.5 Z ⊙) luminous infrared galaxies (LIRGs). We find that the data agree well with an average template of higher-luminosity local low-metallicity dwarf galaxies (reduced χ 2 = 1.8). When compared with the commonly used templates for solar-metallicity local galaxies or high-redshift LIRGs and ultraluminous IR galaxies, even in the most favorable case (with reduced χ 2 = 2.8), the templates are rejected at >98% confidence. The broader and hotter IR SED of both the local dwarfs and high-redshift subsolar-metallicity galaxies may result from different grain properties or a harder/more intense ionizing radiation field that increases the dust temperature. The obscured star formation rate (SFR) indicated by the far-IR emission of the subsolar-metallicity galaxies is only ∼60% of the total SFR, considerably lower than that of the local LIRGs with ∼96%–97% obscured fractions. Due to the evolving IR SED shape, the local LIRG templates fit to mid-IR data overestimate the Rayleigh–Jeans tail measurements by a factor of 2–20. These templates underestimate IR luminosities if fit to the observed ALMA fluxes by >0.4 dex. At a given stellar mass or metallicity, dust masses at z ∼ 2.3 are an order of magnitude higher than z ∼ 0. Given the predicted molecular gas fractions, the observed z ∼ 2.3 dust-to-stellar mass ratios suggest lower dust-to-molecular gas masses than in local galaxies with similar metallicities.
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Lankhaar, Boy, Wouter Vlemmings, and Per Bjerkeli. "Tracing the large-scale magnetic field morphology in protoplanetary disks using molecular line polarization." Astronomy & Astrophysics 657 (January 2022): A106. http://dx.doi.org/10.1051/0004-6361/202141285.
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Context. Magnetic fields are fundamental to the accretion dynamics of protoplanetary disks and they likely affect planet formation. Typical methods to study the magnetic field morphology observe the polarization of dust or spectral lines. However, it has recently become clear that dust-polarization in ALMA’s (Atacama Large (sub)Millimeter Array) spectral regime does not always faithfully trace the magnetic field structure of protoplanetary disks, which leaves spectral line polarization as a promising method for mapping the magnetic field morphologies of such sources. Aims. We aim to model the emergent polarization of different molecular lines in the ALMA wavelength regime that are excited in protoplanetary disks. We explore a variety of disk models and molecules to identify those properties that are conducive to the emergence of polarization in spectral lines and may therefore be viably used for magnetic field measurements in protoplanetary disks. Methods. We used POlarized Radiative Transfer Adapted to Lines in conjunction with the Line Emission Modeling Engine. Together, they allowed us to treat the polarized line radiative transfer of complex three-dimensional physical and magnetic field structures. Results. We present simulations of the emergence of spectral line polarization of different molecules and molecular transitions in the ALMA wavelength regime. We find that molecules that thermalize at high densities, such as HCN, are also the most susceptible to polarization. We find that such molecules are expected to be significantly polarized in protoplanetary disks, while molecules that thermalize at low densities, such as CO, are only significantly polarized in the outer disk regions. We present the simulated polarization maps at a range of inclinations and magnetic field morphologies, and we comment on the observational feasibility of ALMA linear polarization observations of protoplanetary disks. Conclusions. We conclude that those molecules with strong dipole moments and relatively low collision rates are most useful for magnetic field observations through line polarization measurements in high density regions such as protoplanetary disks.
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Olsen, Karen Pardos, Blakesley Burkhart, Mordecai-Mark Mac Low, Robin G. Treß, Thomas R. Greve, David Vizgan, Jay Motka, et al. "sígame v3: Gas Fragmentation in Postprocessing of Cosmological Simulations for More Accurate Infrared Line Emission Modeling." Astrophysical Journal 922, no. 1 (November 1, 2021): 88. http://dx.doi.org/10.3847/1538-4357/ac20d4.
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Abstract We present an update to the framework called Simulator of Galaxy Millimeter/submillimeter Emission (sígame). sígame derives line emission in the far-infrared (FIR) for galaxies in particle-based cosmological hydrodynamics simulations by applying radiative transfer and physics recipes via a postprocessing step after completion of the simulation. In this version, a new technique is developed to model higher gas densities by parameterizing the probability distribution function (PDF) of the gas density in higher-resolution simulations run with the pseudo-Lagrangian, Voronoi mesh code arepo. The parameterized PDFs are used as a look-up table, and reach higher densities than in previous work. sígame v3 is tested on redshift z = 0 galaxies drawn from the simba cosmological simulation for eight FIR emission lines tracing vastly different phases of the interstellar medium. This version of sígame includes dust radiative transfer with Skirt and high-resolution photoionization models with Cloudy, the latter sampled according to the density PDF of the arepo simulations to augment the densities in the cosmological simulation. The quartile distributions of the predicted line luminosities overlap with the observed range for nearby galaxies of similar star formation rate (SFR) for all but two emission lines: [O i]63 and CO(3–2), which are overestimated by median factors of 1.3 and 1.0 dex, respectively, compared to the observed line–SFR relation of mixed-type galaxies. We attribute the remaining disagreement with observations to the lack of precise attenuation of the interstellar light on sub-grid scales (≲200 pc) and differences in sample selection.
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Motiyenko, R. A., I. A. Armieieva, L. Margulès, E. A. Alekseev, and J. C. Guillemin. "Rotational spectroscopy of malononitrile and its corresponding monoisocyanide isomer, isocyanoacetonitrile." Astronomy & Astrophysics 623 (March 2019): A162. http://dx.doi.org/10.1051/0004-6361/201834587.
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Context. Nitriles constitute almost 20% of the molecules observed in the interstellar medium, whereas only one dinitrile and one isocyanonitrile compound have been detected up to now. The lack of detections of such compounds may be partially explained by the lack of accurate spectroscopic data on their rotational spectra.Aims. Two small seven-atom dinitriles, malononitrile NCCH2CN and isocyanoacetonitrile NCCH2NC, were chosen as target species for this study. For malononitrile the goal of the study is to systematize all the previous measurements, and to extend the measurements to the sub-millimeter wavelength range. The spectrum of isocyanoacetonitrile has not been studied before.Methods. The rotational spectra of the two molecules were measured in the frequency range 150–660 GHz using the Lille fast-scan spectrometer. The spectroscopic study was supported by high-level theoretical calculations on the structure of these molecules and their harmonic force field.Results. Accurate frequency predictions for malononitrile and isocyanoacetonitrile were calculated on the basis of the analysis of their rotational spectra. The influence of the spin statistics on the intensities of the lines of malononitrile was taken into account. The provided line lists and sets of molecular parameters meet the needs of astrophysical searches for the two molecules.