Journal articles on the topic 'Radio WISE Selected Galaxies'
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Penney, J. I., A. W. Blain, D. Wylezalek, N. A. Hatch, C. Lonsdale, A. Kimball, R. J. Assef, et al. "The environments of luminous radio-WISE selected infrared galaxies." Monthly Notices of the Royal Astronomical Society 483, no. 1 (November 18, 2018): 514–28. http://dx.doi.org/10.1093/mnras/sty3128.
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Ferris, E. R., A. W. Blain, R. J. Assef, N. A. Hatch, A. Kimball, M. Kim, A. Sajina, et al. "The black hole masses of extremely luminous radio-WISE selected galaxies." Monthly Notices of the Royal Astronomical Society 502, no. 1 (January 11, 2021): 1527–48. http://dx.doi.org/10.1093/mnras/stab048.
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ABSTRACT We present near-IR photometry and spectroscopy of 30 extremely luminous radio and mid-IR-selected galaxies. With bolometric luminosities exceeding ∼1013 $\rm {L_{\odot }}$ and redshifts ranging from z = 0.880 to 2.853, we use Very Large Telescope instruments X-shooter and Infrared Spectrometer and Array Camera to investigate this unique population of galaxies. Broad multicomponent emission lines are detected in 18 galaxies and we measure the near-IR lines $\rm {H\,\rm {\beta }}$, $\rm{[O\,{\small III}]}\, \rm {\lambda }\rm {\lambda }4959,5007$, and $\rm {H\,\rm {\alpha }}$ in 6, 15, and 13 galaxies, respectively, with 10 $\rm {Ly\,\alpha }$ and 5 C iv lines additionally detected in the UVB arm. We use the broad $\rm{[O\,{\small III}]}\, \rm {\lambda }5007$ emission lines as a proxy for the bolometric active galactic nucleus luminosity, and derive lower limits to supermassive black hole masses of 107.9–109.4 M⊙ with expectations of corresponding host masses of 1010.4–1012.0 M⊙. We measure $\rm {\lambda }_{Edd}$ > 1 for eight of these sources at a 2σ significance. Near-IR photometry and SED fitting are used to compare stellar masses directly. We detect both Balmer lines in five galaxies and use these to infer a mean visual extinction of AV = 2.68 mag. Due to non-detections and uncertainties in our ${\rm H}\, \beta$ emission line measurements, we simulate a broad ${\rm H}\, \beta$ line of FWHM = 1480 $\rm {kms^{-1}}$ to estimate extinction for all sources with measured ${\rm H}\, \alpha$ emission. We then use this to infer a mean AV = 3.62 mag, demonstrating the highly obscured nature of these galaxies, with the consequence of increasing our estimates of black hole masses by a 0.5 orders of magnitude in the most extreme and obscured cases.
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Patil, Pallavi, Mark Whittle, Kristina Nyland, Carol Lonsdale, Mark Lacy, Amy E. Kimball, Colin Lonsdale, et al. "Radio Spectra of Luminous, Heavily Obscured WISE-NVSS Selected Quasars." Astrophysical Journal 934, no. 1 (July 1, 2022): 26. http://dx.doi.org/10.3847/1538-4357/ac71b0.
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Abstract We present radio spectra spanning 0.1–10 GHz for the sample of heavily obscured luminous quasars with extremely red mid-infrared-optical colors and compact radio emission. The spectra are constructed from targeted 10 GHz observations and archival radio survey data that together yield 6–11 flux-density measurements for each object. Our primary result is that most (62%) of the sample have peaked or curved radio spectra and many (37%) could be classified as Gigahertz-Peaked Spectrum (GPS) sources. This indicates compact emission regions likely arising from recently triggered radio jets. Assuming synchrotron self-absorption (SSA) generates the peaks, we infer compact source sizes (3–100 pc) with strong magnetic fields (6–100 mG) and young ages (30–104 yr). Conversely, free-free absorption (FFA) could also create peaks due to the high column densities associated with the deeply embedded nature of the sample. However, we find no correlations between the existence or frequency of the peaks and any parameters of the MIR emission. The high-frequency spectral indices are steep (α ≈ −1) and correlate, weakly, with the ratio of MIR photon energy density to magnetic energy density, suggesting that the spectral steepening could arise from inverse Compton scattering off the intense MIR photon field. This study provides a foundation for combining multifrequency and mixed-resolution radio survey data for understanding the impact of young radio jets on the ISM and star-formation rates of their host galaxies. faGithub
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Ward, Charlotte, Suvi Gezari, Peter Nugent, Eric C. Bellm, Richard Dekany, Andrew Drake, Dmitry A. Duev, et al. "Variability-selected Intermediate-mass Black Hole Candidates in Dwarf Galaxies from ZTF and WISE." Astrophysical Journal 936, no. 2 (September 1, 2022): 104. http://dx.doi.org/10.3847/1538-4357/ac8666.
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Abstract While it is difficult to observe the first black hole seeds in the early universe, we can study intermediate-mass black holes (IMBHs) in local dwarf galaxies for clues about their origins. In this paper we present a sample of variability-selected active galactic nuclei (AGN) in dwarf galaxies using optical photometry from the Zwicky Transient Facility (ZTF) and forward-modeled mid-IR photometry of time-resolved Wide-field Infrared Survey Explorer (WISE) co-added images. We found that 44 out of 25,714 dwarf galaxies had optically variable AGN candidates and 148 out of 79,879 dwarf galaxies had mid-IR variable AGN candidates, corresponding to active fractions of 0.17% ± 0.03% and 0.19% ± 0.02%, respectively. We found that spectroscopic approaches to AGN identification would have missed 81% of our ZTF IMBH candidates and 69% of our WISE IMBH candidates. Only nine candidates have been detected previously in radio, X-ray, and variability searches for dwarf galaxy AGN. The ZTF and WISE dwarf galaxy AGN with broad Balmer lines have virial masses of 105 M ⊙ < M BH < 107 M ⊙, but for the rest of the sample, BH masses predicted from host galaxy mass range between 105.2 M ⊙ < M BH < 107.25 M ⊙. We found that only 5 of 152 previously reported variability-selected AGN candidates from the Palomar Transient Factory in common with our parent sample were variable in ZTF. We also determined a nuclear supernova fraction of 0.05% ± 0.01% yr−1 for dwarf galaxies in ZTF. Our ZTF and WISE IMBH candidates show the promise of variability searches for the discovery of otherwise hidden low-mass AGN.
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Mickaelian, A. M., H. V. Abrahamyan, M. V. Gyulzadyan, G. A. Mikayelyan, and G. M. Paronyan. "Multi-wavelength studies of the statistical properties of active galaxies using Big Data." Proceedings of the International Astronomical Union 12, S325 (October 2016): 32–38. http://dx.doi.org/10.1017/s1743921316012916.
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AbstractStatistical studies of active galaxies (both AGN and Starburst) using large multi-wavelength data are presented, including new studies of Markarian galaxies, large sample of IR galaxies, variable radio sources, and large homogeneous sample of X-ray selected AGN. Markarian survey (the First Byurakan Survey) was digitized and the DFBS database was created, as the biggest spectroscopic database by the number of objects involved ( ~ 20 million). This database provides both 2D images and 1D spectra. We have carried out a number of projects aimed at revealing and multi-wavelength studies of active galaxies among optical, X-ray, IR and radio sources. Thousands of X-ray sources were identified from ROSAT, including many AGN (52% among all identified sources). IRAS PSC/FSC sources were studied having accurate positions from WISE and a large extragalactic sample was created for further search for AGNs. The fraction of active galaxies among IR-selected galaxies was estimated as 24%. Variable radio sources at 1.4 GHz were revealed by cross-correlation of NVSS and FIRST catalogues using the method introduced by us for optical variability. Radio-X-ray sources were revealed from NVSS and ROSAT for detection of new active galaxies. Big Data in astronomy is described that provide new possibilities for statistical research of active galaxies and other objects.
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Chhetri, R., A. Kimball, R. D. Ekers, E. K. Mahony, E. M. Sadler, and T. Jarrett. "WISE mid-infrared properties of compact active galactic nuclei selected from the high radio frequency AT20G survey." Monthly Notices of the Royal Astronomical Society 494, no. 1 (February 24, 2020): 923–40. http://dx.doi.org/10.1093/mnras/staa513.
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ABSTRACT Past studies of compact active galactic nuclei (AGNs), the dominant population at high radio frequencies, selected them using flat spectral index criteria. This biases the sample due to the steepening of AGN spectra at high radio frequencies. We improve upon this by selecting 3610 compact AGNs using their angular size information ($\lesssim$0.15 arcsec scale) from the Australia Telescope 20 GHz (AT20G) high-angular resolution catalogue. We cross-match these against the Wide-field Infrared Survey Explorer AllWISE catalogue and present a catalogue with 3300 (91 per cent) matches, 91 (3 per cent) rejects, and 219 (6 per cent) non-detections that are excellent high-redshift candidates. Of the matched compact AGNs, 92 per cent exhibit QSO mid-infrared colours (W1−W2 > 0.5). Therefore, our sample of high frequency compact sources has a very high rate of identification with mid-infrared QSOs. We find counterparts for 88 per cent of 387 compact steep-spectrum (CSS) sources in the AT20G survey, 82 ± 5 per cent of which exhibit QSO mid-infrared colours and have moderate redshifts (zmedian = 0.82), while those dominated by host galaxy colours in mid-infrared have lower redshifts (zmedian = 0.13). The latter classified into late- and early-type galaxies using their mid-infrared colours shows a majority (68 ± 4 per cent) have colours characteristic of late-type galaxies. Thus, we find that a larger fraction of these CSS sources are embedded in hosts with higher gas densities than average early-type galaxies. We compare mid-infrared colours of our AGNs against those reported for AGNs primarily selected using non-radio techniques. This shows that mid-infrared SED of high frequency selected compact radio AGN is comparatively less red, possibly due to contributions from their hosts.
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Missaglia, V., F. Massaro, A. Capetti, M. Paolillo, R. P. Kraft, R. D. Baldi, and A. Paggi. "WATCAT: a tale of wide-angle tailed radio galaxies." Astronomy & Astrophysics 626 (May 30, 2019): A8. http://dx.doi.org/10.1051/0004-6361/201935058.
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We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the WATCAT, mainly built including a radio morphological classification; WATs were selected by combining observations from the National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan Digital Sky Survey (SDSS). We included in the catalog only radio sources showing two-sided jets with two clear “warmspots” (i.e., jet knots as bright as 20% of the nucleus) lying on the opposite side of the radio core, and having classical extended emission resembling a plume beyond them. The catalog is limited to redshifts z ≤ 0.15, and lists only sources with radio emission extended beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT sources are all luminous (−20.5 ≳ Mr ≳ −23.7), red early-type galaxies with black hole masses in the range 108 ≲ MBH ≲ 109 M⊙. The spectroscopic classification indicates that they are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties with those of FR I and FR II radio galaxies at the same redshifts, we conclude that WATs show multifrequency properties remarkably similar to FR I radio galaxies, having radio power of typical FR IIs.
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Singh, Swapnil, M. L. N. Ashby, Sarita Vig, S. K. Ghosh, T. Jarrett, T. M. Crawford, Matthew A. Malkan, M. Archipley, and J. D. Vieira. "The cold dust content of the nearby galaxies IC 5325, NGC 7496, NGC 7590, and NGC 7599." Monthly Notices of the Royal Astronomical Society 504, no. 3 (April 15, 2021): 4143–59. http://dx.doi.org/10.1093/mnras/stab1048.
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ABSTRACT Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust (VCD) component has also been revealed via millimetre/submillimetre (mm/sub-mm) photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here, we analyse the dust content of a carefully selected sample of four galaxies detected by IRAS, WISE, and South Pole Telescope (SPT), whose spectral energy distributions (SEDs) were modelled to constrain their potential cold dust content. Low-frequency radio observations using the Giant Metrewave Radio Telescope (GMRT) were carried out to segregate cold dust emission from non-thermal emission in mm/sub-mm wavebands. We also carried out AstroSat/Ultraviolet Imaging Telescope (UVIT) observations for some galaxies to constrain their SED at shorter wavelengths so as to enforce energy balance for the SED modelling. We constructed their SEDs across a vast wavelength range (extending from UV to radio frequencies) by assembling global photometry from GALEX FUV + NUV, UVIT, Johnson BRI, 2MASS, WISE, IRAC, IRAS, AKARI, ISO PHOT, Planck HFI, SPT, and GMRT. The SEDs were modelled with cigale to estimate their basic properties, in particular to constrain the masses of their total and VCD components. Although the galaxies’ dust masses are dominated by warmer dust, there are hints of VCD in two of the targets, NGC 7496 and NGC 7590.
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de Menezes, Raniere, Harold A. Peña-Herazo, Ezequiel J. Marchesini, Raffaele D’Abrusco, Nicola Masetti, Rodrigo Nemmen, Francesco Massaro, et al. "Optical characterization of WISE selected blazar candidates." Astronomy & Astrophysics 630 (September 23, 2019): A55. http://dx.doi.org/10.1051/0004-6361/201936195.
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Context. Over the last decade more than five thousand γ-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of γ-ray counterpart candidates and several follow up campaigns in the last decade. Aims. Recently, two new catalogs of blazar candidates were released. These are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars. Methods. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. Results. We found that at least ∼30% of each catalog is made up of confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (≈58%) and normal galaxies in the case of KDEBLLACS (≈38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects.
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Li, Megan G., Karin M. Sandstrom, and Adam K. Leroy. "A Resolved Search for AGN in the Centers of Nearby Galaxies with WISE." Research Notes of the AAS 6, no. 6 (June 7, 2022): 117. http://dx.doi.org/10.3847/2515-5172/ac7569.
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Abstract We investigate the mid-infrared detection of active galactic nucleus (AGN) in nearby galaxies and the effects of contamination by starlight and dust emission from the host galaxy. We used a sample of ∼14,000 nearby galaxies from the z = 0 Multiwavelength Galaxy Synthesis to study the effect of isolating the galaxy center on AGN detection. We identify 39 known AGN and 9 additional previously selected AGN candidates using color selection in WISE Bands 1 and 2. Most AGN identified using the smallest apertures around the nucleus are lost from the WISE color selection at larger aperture radii. This suggests that when low spatial resolution or integrated galaxy measurements are used to identify AGN in the mid-IR, lower luminosity AGN may go undetected due to contamination from the galaxy’s dust emission and starlight.
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Baldi, Ranieri D., Marco Chiaberge, and Alessandro Capetti. "Study of Spectral Energy Distributions of low-luminosity radio galaxies at z ~ 1–3: a high-z view of the host/AGN connection." Proceedings of the International Astronomical Union 9, S304 (October 2013): 298–301. http://dx.doi.org/10.1017/s1743921314004116.
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AbstractLow-luminosity radio galaxies, common in the local Universe, are associated with giant elliptical galaxies and typically with a FR I radio morphology. However, they are rare in flux-limited samples of distant radio-loud (RL) AGN due to a selection bias. Chiaberge et al. (2009) selected the first sizeable sample of FRI candidates at 1<z<3, in the COSMOS field. We study the Spectral Energy Distributions (SEDs) of this low radio power sample from the far-UV to the Mid-IR wavelengths. Our results show that the hosts of these high-z low-luminosity radio sources are old massive galaxies, similar to the local FR Is. However, for half of the sample the UV and MIR excesses indicate the possible significant contribution from star formation and/or nuclear activity, not seen in low-z FR Is. Our sources display a wide variety of properties: from possible quasars at the highest luminosities, to low-luminosity old galaxies.
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Lacy, M., S. Rawlings, M. Wold, A. Bunker, K. M. Blundell, S. A. Eales, and P. B. Lilje. "Radio Source Environments at Redshifts > 0.5." Symposium - International Astronomical Union 175 (1996): 321–22. http://dx.doi.org/10.1017/s0074180900080943.
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The most powerful radio sources in the local Universe are found in giant elliptical galaxies. Looking back to a redshift of 0.5 (≈ half the age of the Universe for ω = 1), we see that these host galaxies are increasingly found in moderately rich clusters. This fact gives us hope that radio sources can be used as tracers of high density environments at high redshift. By exploiting radio source samples selected over a wide range in luminosity (Blundell et al., these proceedings), we will also be able to test whether the luminosities of radio sources are correlated with their environments.
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Mahatma, V. H., M. J. Hardcastle, W. L. Williams, P. N. Best, J. H. Croston, K. Duncan, B. Mingo, et al. "LoTSS DR1: Double-double radio galaxies in the HETDEX field." Astronomy & Astrophysics 622 (February 2019): A13. http://dx.doi.org/10.1051/0004-6361/201833973.
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Context. Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. Aims. The sensitivity and field of view of LOFAR enables the observation of DDRGs on a population basis rather than single-source observations. Using statistical comparisons with a control sample of RLAGN, we may obtain insights into the nature of DDRGs in the context of their host galaxies, where physical differences in their hosts compared to RLAGN as a population may allow us to infer the conditions that drive restarting jets. Methods. We utilised the LOFAR Two-Metre Sky Survey (LoTSS) DR1, using a visual identification method to compile a sample of morphologically selected candidate DDRGs, showing two pairs of radio lobes. To confirm the restarted nature in each of the candidate sources, we obtained follow-up observations with the Karl. G. Jansky Very Large Array (VLA) at higher resolution to observe the inner lobes or restarted jets, the confirmation of which created a robust sample of 33 DDRGs. We created a comparison sample of 777 RLAGN, matching the luminosity distribution of the DDRG sample, and compared the optical and infrared magnitudes and colours of their host galaxies. Results. We find that there is no statistically significant difference in the brightness of the host galaxies between double-doubles and single-cycle RLAGN. The DDRG and RLAGN samples also have similar distributions in WISE mid-infrared colours, indicating similar ages of stellar populations and dust levels in the hosts of DDRGs. We conclude that DDRGs and “normal” RLAGN are hosted by galaxies of the same type, and that DDRG activity is simply a normal part of the life cycle of RLAGN. Restarted jets, particularly for the class of low-excitation radio galaxies, rather than being a product of a particular event in the life of a host galaxy, must instead be caused by smaller scale changes, such as in the accretion system surrounding the black hole.
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Keel, William C., Jean Tate, O. Ivy Wong, Julie K. Banfield, Chris J. Lintott, Karen L. Masters, Brooke D. Simmons, et al. "Gems of the Galaxy Zoos—A Wide-ranging Hubble Space Telescope Gap-filler Program*." Astronomical Journal 163, no. 4 (March 7, 2022): 150. http://dx.doi.org/10.3847/1538-3881/ac517d.
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Abstract We describe the Gems of the Galaxy Zoos (Zoo Gems) project, a gap-filler project using short windows in the Hubble Space Telescope's schedule. As with previous snapshot programs, targets are taken from a pool based on position; we combine objects selected by volunteers in both the Galaxy Zoo and Radio Galaxy Zoo citizen-science projects. Zoo Gems uses exposures with the Advanced Camera for Surveys to address a broad range of topics in galaxy morphology, interstellar-medium content, host galaxies of active galactic nuclei, and galaxy evolution. Science cases include studying galaxy interactions, backlit dust in galaxies, post-starburst systems, rings and peculiar spiral patterns, outliers from the usual color–morphology relation, Green Pea compact starburst systems, double radio sources with spiral host galaxies, and extended emission-line regions around active galactic nuclei. For many of these science categories, final selection of targets from a larger list used public input via a voting process. Highlights to date include the prevalence of tightly wound spiral structure in blue, apparently early-type galaxies, a nearly complete Einstein ring from a group lens, redder components at lower surface brightness surrounding compact Green Pea starbursts, and high-probability examples of spiral galaxies hosting large double radio sources.
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Irwin, Judith, Ancor Damas-Segovia, Marita Krause, Arpad Miskolczi, Jiangtao Li, Yelena Stein, Jayanne English, et al. "CHANG-ES: XVIII—The CHANG-ES Survey and Selected Results." Galaxies 7, no. 1 (March 26, 2019): 42. http://dx.doi.org/10.3390/galaxies7010042.
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The CHANG-ES (Continuum Halos in Nearby Galaxies) survey of 35 nearby edge-on galaxies is revealing new and sometimes unexpected and startling results in their radio continuum emission. The observations were in wide bandwidths centred at 1.6 and 6.0 GHz. Unique to this survey is full polarization data showing magnetic field structures in unprecedented detail, resolution and sensitivity for such a large sample. A wide range of new results are reported here, some never before seen in any galaxy. We see circular polarization and variability in active galactic nuclei (AGNs), in-disk discrete features, disk-halo structures sometimes only seen in polarization, and broad-scale halos with reversing magnetic fields, among others. This paper summarizes some of the CHANG-ES results seen thus far.
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Bruni, G., M. Brienza, F. Panessa, L. Bassani, D. Dallacasa, T. Venturi, R. D. Baldi, et al. "Hard X-ray selected giant radio galaxies – III. The LOFAR view." Monthly Notices of the Royal Astronomical Society 503, no. 4 (March 17, 2021): 4681–99. http://dx.doi.org/10.1093/mnras/stab623.
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ABSTRACT Giant radio galaxies (GRGs), with extended structures reaching hundreds of kpc, are among the most spectacular examples of ejection of relativistic plasma from supermassive black holes. In this work, third of a series, we present Low-Frequency Array (LOFAR) images at 144 MHz, collected in the framework of the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources extracted from our sample of hard X-ray-selected GRGs (HXGRGs, i.e. from INTEGRAL/Imager on-Board the INTEGRAL Satellite and Swift/Burst Alert Telescope catalogues at >20 keV). Thanks to the resolution and sensitivity of LoTSS, we could probe the complex morphology of these GRGs, unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint off-axis wings, or a misaligned inner jet. In particular, for one source (B2 1144+35B), we could clearly detect a ∼300 kpc wide off-axis emission, in addition to an inner jet whose orientation is not aligned with the lobes axis. For another source (J1153.9+5848), a structure consistent with jet precession was revealed, appearing as an X-shaped morphology with relic lobes having an extension larger than the present ones, and with a different axis orientation. From an environment analysis, we found two sources showing an overdensity of cosmological neighbours, and a correspondent association with a galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs from LoTSS DR1 suggested that, on average, HXGRGs can grow to larger extents. These results highlight the importance of deep low-frequency observations to probe the evolution of radio galaxies, and ultimately estimate the duty cycle of their jets.
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Baldi, R. D., A. Capetti, and F. Massaro. "FR0CAT: a FIRST catalog of FR 0 radio galaxies." Astronomy & Astrophysics 609 (December 22, 2017): A1. http://dx.doi.org/10.1051/0004-6361/201731333.
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With the aim of exploring the properties of the class of FR 0 radio galaxies, we selected a sample of 108 compact radio sources, called FR0CAT, by combining observations from the NVSS, FIRST, and SDSS surveys. We included in the catalog sources with redshift ≤0.05, with a radio size ≲5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their radio luminosities at 1.4 GHz are in the range 1038 ≲ νL1.4 ≲ 1040 erg s-1. The FR0CAT hosts are mostly (86%) luminous (−21 ≳ Mr ≳ −23) red early-type galaxies with black hole masses 108 ≲ MBH ≲ 109M⊙. These properties are similar to those seen for the hosts of FR I radio galaxies, but they are on average a factor ~1.6 less massive. The number density of FR0CAT sources is ~5 times higher than that of FR Is, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR 0s with respect to FR Is. An age-size scenario that considers FR 0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR 0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR 0s might be intrinsically different from those of the FR Is, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR 0s and FR I/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.
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Pascale, Massimo, Brenda L. Frye, Liang Dai, Nicholas Foo, Yujing Qin, Reagen Leimbach, Adam Michael Bauer, et al. "Possible Ongoing Merger Discovered by Photometry and Spectroscopy in the Field of the Galaxy Cluster PLCK G165.7+67.0." Astrophysical Journal 932, no. 2 (June 1, 2022): 85. http://dx.doi.org/10.3847/1538-4357/ac6ce9.
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Abstract We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; z = 0.348). A multiband photometric catalog is generated incorporating new imaging from the Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin2 field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of M 600 kpc = (2.36 ± 0.23) × 1014 M ⊙. In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of ≲100 km s−1, favoring an orientation in the plane of the sky with a transverse velocity of 100–1700 km s−1. At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.
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Jurlin, Nika, Raffaella Morganti, Natasha Maddox, and Marisa Brienza. "The Photometric and Spectroscopic Properties of Remnant and Restarted Radio Galaxies in the Lockman Hole Field." Galaxies 9, no. 4 (December 17, 2021): 122. http://dx.doi.org/10.3390/galaxies9040122.
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Radio galaxies are known to undergo phases of activity, where the stage after the jets have switched off is referred to as the remnant phase. This state can be followed by a restarted phase when the activity reignites. Remnant and restarted radio sources are important for testing models of the evolution of radio active galactic nuclei (AGN) and for understanding the impact the recurrent jet activity has on their host galaxies. Although we now have statistical samples of radio sources in various stages of their life cycle, how this intermittent radio activity is reflected in the optical properties in this sample has not yet been addressed, and is overall a much less studied aspect in the literature. In this work, we use the Wide-field Infrared Survey Explorer and the Sloan Digital Sky Survey (SDSS) photometry, and SDSS spectra to study these properties in a sample of the remnant, candidate restarted, and active radio galaxies selected using the LOw Frequency ARray at 150 MHz in the Lockman Hole extragalactic field. Within the range of radio luminosities and stellar masses studied in this work, we find no difference between the properties of the host galaxy and of the optical emission lines for objects in different phases of their radio life cycle. The vast majority of our radio sources (either remnant, candidate restarted, or comparison sample) are associated with radiatively inefficient optical AGN and red galaxies dominated by old stellar populations. Thus, the radio and emission-line AGN activity appears to be independent and regulated by different mechanisms. This suggests that, at least for the radio luminosities of our sample, the life cycle of the radio may depend on intrinsic reasons, such as the stability of the accretion disc, more than variation in the accretion rate and fuelling of the central black hole.
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Vigotti, M., S. G. Djorgovski, L. Gregorini, U. Klein, K. H. Mack, L. Maxfield, H. P. Reuter, and D. Thompson. "The B3-VLA Sample." Symposium - International Astronomical Union 175 (1996): 519–21. http://dx.doi.org/10.1017/s0074180900081705.
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The use of radio sources to identify the most distant object in the Universe has been proved to be a very successful approach in observational cosmology. Studies of high flux, powerful 3CR and 1-Jy galaxies show dramatic evidence for color and luminosity evolution, reaching to look-back times 80% of the Hubble time. In order to disentangle the selection effect, correlation with redshift, and correlation with radio power, it is necessary to obtain well defined, complete samples of radio galaxies at a large range of redshifts, and with a wide baseline of radio power. We need the identifications of complete samples in the flux range of a factor 10 smaller than 3CR sample. The B3VLA sample (Vigotti et al. 1989) is a subset of 1050 sources selected in restricted areas at high galactic latitudes from the B3 survey, which is complete down to S(408 MHz) = 100 mJy. For the B3VLA sample detailed VLA maps were obtained at 1.4 GHz using A, C and D arrays. We are conducting a long-term effort to provide optical ID's and redshifts for well-defined, complete subsamples of the B3VLA survey (Djorgovski et al. 1990, Vigotti et al. 1990, Thompson et al., 1994), a similar effort is being conducted independently by others. We present here the “status of the art” for the B3VLA sample: a new low flux sample of 124 QSS selected at meter wavelenghts, a sample of 194 radio galaxies (77 with measured redshift) and a sample of 732 Empty Fields (EF : no optical counterpart on POSS I plate).
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Nascimento, R. S., A. Rodríguez-Ardila, L. Dahmer-Hahn, M. A. Fonseca-Faria, R. Riffel, M. Marinello, T. Beuchert, and J. R. Callingham. "Optical properties of Peaked Spectrum radio sources." Monthly Notices of the Royal Astronomical Society 511, no. 1 (January 7, 2022): 214–30. http://dx.doi.org/10.1093/mnras/stab3791.
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ABSTRACT In this work, we study the optical properties of compact radio sources selected from the literature in order to determine the impact of the radio-jet in their circumnuclear environment. Our sample includes 58 Compact Steep Spectrum (CSS) and GigaHertz Peaked Spectrum (GPS) and 14 Megahertz-Peaked spectrum (MPS) radio sources located at z ≤ 1. The radio luminosity (LR) of the sample varies between Log LR ∼ 23.2 and 27.7 W Hz−1. We obtained optical spectra for all sources from SDSS-DR12 and performed a stellar population synthesis using the starlight code. We derived stellar masses (M⋆), ages 〈t⋆〉, star formation rates (SFR), metallicities 〈Z⋆〉 and internal reddening AV for all young AGNs of our sample. A visual inspection of the SDSS images was made to assign a morphological class for each source. Our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources. Also, we found that young AGNs can be hosted by elliptical, spiral and interacting galaxies, confirming recent findings. When comparing the optical properties of CSS/GPS and MPS sources, we do not find any significant difference. Finally, the Mid-Infrared WISE colours analysis suggests that the compact radio sources defined as powerful AGNs are, in general, gas-rich systems.
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Gupta, N., G. Shukla, R. Srianand, J. K. Krogager, P. Noterdaeme, A. J. Baker, F. Combes, et al. "MALS SALT-NOT Survey of MIR-selected Powerful Radio-bright AGN at 0 < z < 3.5." Astrophysical Journal 929, no. 1 (April 1, 2022): 108. http://dx.doi.org/10.3847/1538-4357/ac4220.
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Abstract We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median z = 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δi = 0.6 mag) and redder (Δ(g−i) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)–65% of these, at z < 0.5 are galaxies without strong nuclear emission, and 10% at z > 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (z em = 3.132), and the largest radio source (size ∼330 kpc) is M0909-3133 (z em = 0.884). We discuss in detail 110 AGN at 1.9 < z < 3.5. Despite representing the radio loudest quasars (median R = 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower R. We detect four C iv broad-absorption line (BAL) QSOs, all among AGN with least R, and highest black hole masses and Eddington ratios. The BAL detection rate ( 4 − 2 + 3 %) is consistent with that seen in extremely powerful (L 1.4GHz > 1025 W Hz−1) quasars. Using optical light curves, radio polarization, and γ-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H i 21 cm and OH 18 cm lines at z < 2.
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Harrison, C. M., S. J. Molyneux, J. Scholtz, and M. E. Jarvis. "Establishing the impact of powerful AGN on their host galaxies." Proceedings of the International Astronomical Union 15, S359 (March 2020): 203–11. http://dx.doi.org/10.1017/s1743921320001696.
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AbstractEstablishing the role of active galactic nuclei (AGN) during the formation of galaxies remains one of the greatest challenges of galaxy formation theory. Towards addressing this, we summarise our recent work investigating: (1) the physical drivers of ionised outflows and (2) observational signatures of the impact by jets/outflows on star formation and molecular gas content in AGN host galaxies. We confirm a connection between radio emission and extreme ionised gas kinematics in AGN hosts. Emission-line selected AGN are significantly more likely to exhibit ionised outflows (as traced by the [O iii] emission line) if the projected linear extent of the radio emission is confined within the spectroscopic aperture. Follow-up high resolution radio observations and integral field spectroscopy of 10 luminous Type 2 AGN reveal moderate power, young (or frustrated) jets interacting with the interstellar medium. We find that these sources live in highly star forming and gas rich galaxies. Additionally, by combining ALMA-derived dust maps with integral field spectroscopy for eight host galaxies of z ≈ 2 X-ray AGN, we show that Hα emission is an unreliable tracer of star formation. For the five targets with ionised outflows we find no dramatic in-situ shut down of the star formation. Across both of these studies we find that if these AGN do have a negative impact upon their host galaxies, it must be happening on small (unresolved) spatial scales and/or an observable galaxy-wide impact has yet to occur.
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Angelakis, E., S. Kiehlmann, I. Myserlis, D. Blinov, J. Eggen, R. Itoh, N. Marchili, and J. A. Zensus. "Optical polarisation variability of radio-loud narrow-line Seyfert 1 galaxies." Astronomy & Astrophysics 618 (October 2018): A92. http://dx.doi.org/10.1051/0004-6361/201832890.
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Context. Narrow-line Seyfert 1 galaxies (NLSy1s) constitute the active galactic nuclei subclass associated with systematically lower black hole masses. A few radio-loud NLSy1s have been detected in MeV-GeV energy bands by Fermi, and evidence that blazar-like jets are operating also in radio-loud NLSy1s, has been accumulated. Aims. We wish to quantify the temporal behaviour of the optical polarisation, fraction, and angle for a selected sample of radio-loud NLSy1s. We also search for rotations of the polarisation plane similar to those commonly observed in blazars. Methods. We have conducted R-band optical linear polarisation monitoring of a sample of ten radio-loud NLSy1 galaxies; five of them have previously been detected by Fermi. The dataset obtained with our pivoting instrument, the RoboPol polarimeter of the Skinakas observatory, has been complemented with observations from the KANATA, Perkins, and Steward observatories. When evidence for long rotations of the polarisation plane was found (at least three consecutive measurements covering at least 90°), we carried out numerical simulations to assess the probability that they are caused by intrinsically evolving electric vector position angles (EVPAs) instead of observational noise. Results. Even our moderately sampled sources show clear indications of variability in both polarisation fraction and angle. For the four best-sampled objects in our sample we find multiple periods of significant polarisation angle variability. Several of these events qualify as long rotations. In the two best-sampled cases, namely J1505+0326 and J0324+3410, we find indications for three long rotations of the polarisation angle. We show that although noise can induce the observed behaviour, it is much more likely that the apparent rotation is indeed caused by intrinsic evolution of the EVPA. To our knowledge, this is the very first detection of such events in this class of sources. In the largest dataset (J0324+3410), we find that the EVPA concentrates around a direction that is at 49.3° to the 15 GHz radio jet, implying a projected magnetic field at an angle of 40.7° to that axis. Conclusions. We assess the probability that pure measurement uncertainties are the reason behind the observed long rotations of the polarisation plane. We conclude that although this is not improbable, it is much more likely that intrinsic rotations are responsible for the observed phenomenology. We conclude, however, that much better sampled and larger datasets of larger source samples are necessary to constrain the physical mechanism(s) that generate long EVPA rotations in NLSy1s.
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Gürkan, Gülay, M. J. Hardcastle, P. N. Best, L. K. Morabito, I. Prandoni, M. J. Jarvis, K. J. Duncan, et al. "LoTSS/HETDEX: Optical quasars." Astronomy & Astrophysics 622 (February 2019): A11. http://dx.doi.org/10.1051/0004-6361/201833892.
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The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter (R =L144 MHz/Li band). The examination of the radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of ℛ). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of ℛ on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).
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Johnston, S., M. Bailes, N. Bartel, C. Baugh, M. Bietenholz, C. Blake, R. Braun, et al. "Science with the Australian Square Kilometre Array Pathfinder." Publications of the Astronomical Society of Australia 24, no. 4 (2007): 174–88. http://dx.doi.org/10.1071/as07033.
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AbstractThe future of centimetre and metre-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline an ambitious science program for ASKAP, examining key science such as understanding the evolution, formation and population of galaxies including our own, understanding the magnetic Universe, revealing the transient radio sky and searching for gravitational waves.
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Kakkad, D., B. Groves, M. Dopita, A. D. Thomas, R. L. Davies, V. Mainieri, P. Kharb, J. Scharwächter, E. J. Hampton, and I.-T. Ho. "Spatially resolved electron density in the narrow line region of z < 0.02 radio AGNs." Astronomy & Astrophysics 618 (October 2018): A6. http://dx.doi.org/10.1051/0004-6361/201832790.
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Context. Although studying outflows in the host galaxies of active galactic nuclei (AGNs) have moved to the forefront of extragalactic astronomy in recent years, estimating the energy associated with these outflows has been a major challenge. Determining the energy associated with an outflow often involves an assumption of uniform density in the narrow line region (NLR), which spans a wide range in the literature, leading to large systematic uncertainties in energy estimation. Aims. In this paper we present electron density maps for a sample of outflowing and non-outflowing Seyfert galaxies at z < 0.02 drawn from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7) and try to understand the origin and values of the observed density structures to reduce the systematic uncertainties in outflow energy estimation. Methods. We use the ratio of the [S II]λ6716,6731 emission lines to derive spatially resolved electron densities (≲50–2000 cm−3). Using optical Integral Field Unit observations from the Wide Field Spectrograph (WiFeS), we are able to measure densities across the central 2–5 kpc of the selected AGN host galaxies. We compare the density maps with the positions of the H II regions derived from the narrow Hα component, ionization maps from [O III] and spatially resolved BPT diagrams to infer the origin of the observed density structures. We also use the electron density maps to construct density profiles as a function of distance from the central AGN. Results. We find a spatial correlation between the sites of high star formation and high electron density for targets without an active ionized outflow. The non-outflowing targets also show an exponential drop in the electron density as a function of distance from the centre, with a mean exponential index of ∼0.15. The correlation between the star forming sites and electron density ceases for targets with an outflow. The density within the outflowing medium is not uniform and shows both low- and high-density sites, most likely due to the presence of shocks and highly turbulent medium. We compare these results in the context of previous results obtained from fibre and slit spectra.
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Mahony, Elizabeth K., James R. Allison, Elaine M. Sadler, Sara L. Ellison, Sui Ann Mao, Raffaella Morganti, Vanessa A. Moss, et al. "H i absorption at z ∼ 0.7 against the lobe of the powerful radio galaxy PKS 0409−75." Monthly Notices of the Royal Astronomical Society 509, no. 2 (October 25, 2021): 1690–702. http://dx.doi.org/10.1093/mnras/stab3041.
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ABSTRACT We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy sample, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted samples.
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Duncan, Kenneth J. "All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8." Monthly Notices of the Royal Astronomical Society 512, no. 3 (March 8, 2022): 3662–83. http://dx.doi.org/10.1093/mnras/stac608.
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ABSTRACT In this paper, we present photometric redshift (photo-z) estimates for the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, currently the most sensitive optical survey covering the majority of the extragalactic sky. Our photo-z methodology is based on a machine-learning approach, using sparse Gaussian processes augmented with Gaussian mixture models (GMMs) that allow regions of parameter space to be identified and trained separately in a purely data-driven way. The same GMMs are also used to calculate cost-sensitive learning weights that mitigate biases in the spectroscopic training sample. By design, this approach aims to produce reliable and unbiased predictions for all parts of the parameter space present in wide area surveys. Compared to previous literature estimates using the same underlying photometry, our photo-zs are significantly less biased and more accurate at z > 1, with negligible loss in precision or reliability for resolved galaxies at z < 1. Our photo-z estimates offer accurate predictions for rare high-value populations within the parent sample, including optically selected quasars at the highest redshifts (z > 6), as well as X-ray or radio continuum selected populations across a broad range of flux (densities) and redshift. Deriving photo-z estimates for the full Legacy Imaging Surveys Data Release 8, the catalogues provided in this work offer photo-z estimates predicted to be of high quality for ≳9 × 108 galaxies over ${\sim}19\, 400\, \text{deg}^{2}$ and spanning 0 < z ≲ 7, offering one of the most extensive samples of redshift estimates ever produced.
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Urrutia, T., L. Wisotzki, J. Kerutt, K. B. Schmidt, E. C. Herenz, J. Klar, R. Saust, et al. "The MUSE-Wide Survey: survey description and first data release." Astronomy & Astrophysics 624 (April 2019): A141. http://dx.doi.org/10.1051/0004-6361/201834656.
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We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the CANDELS/GOODS-S and CANDELS/COSMOS regions. The final survey will cover 100 × 1 arcmin2 MUSE fields. Each MUSE-Wide pointing has a depth of one hour and hence targets more extreme and more luminous objects over ten times the area of the MUSE-Deep fields. The legacy value of MUSE-Wide lies in providing “spectroscopy of everything” without photometric pre-selection. We describe the data reduction, post-processing and PSF characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released with this publication. Using a 3D matched filtering approach we detect 1602 emission line sources, including 479 Lyman-α (Lyα) emitting galaxies with redshifts 2.9 ≲ z ≲ 6.3. We cross-matched the emission line sources to existing photometric catalogs, finding almost complete agreement in redshifts (photometric and spectroscopic) and stellar masses for our low redshift (z < 1.5) emitters. At high redshift, we only find ∼55% matches to photometric catalogs. We encounter a higher outlier rate and a systematic offset of Δz ≃ 0.2 when comparing our MUSE redshifts with photometric redshifts from the literature. Cross-matching the emission line sources with X-ray catalogs from the Chandra Deep Field South, we find 127 matches, mostly in agreement with the literature redshifts, including ten objects with no prior spectroscopic identification. Stacking X-ray images centered on our Lyα emitters yields no signal; the Lyα population is not dominated by even low luminosity AGN. Other cross-matches of our emission-line catalog to radio and submillimeter data, yielded far lower numbers of matches, most of which already were covered by the X-ray catalog. A total of 9205 photometrically selected objects from the CANDELS survey lie in the MUSE-Wide footprint, of which we provide optimally extracted 1D spectra. We are able to determine the spectroscopic redshift of 98% of 772 photometrically selected galaxies brighter than 24th F775W magnitude. All the data in the first data release - datacubes, catalogs, extracted spectra, maps - are available on the MUSE-Wide data release webpage.
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Schmidt, Philip, Marita Krause, Volker Heesen, Aritra Basu, Rainer Beck, Theresa Wiegert, Judith A. Irwin, et al. "CHANG-ES." Astronomy & Astrophysics 632 (November 26, 2019): A12. http://dx.doi.org/10.1051/0004-6361/201834995.
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Context. Cosmic-ray electrons (CREs) originating from the star-forming discs of spiral galaxies frequently form extended radio haloes that are best observable in edge-on galaxies, where their properties can be directly investigated as a function of vertical height above the disc. Aims. For the present study, we selected two nearby edge-on galaxies from the Continuum Halos in Nearby Galaxies – an EVLA Survey (CHANG-ES), NGC 891 and 4565, which differ largely in their detectable halo extent and their star-formation rates (SFRs). Our aim is to figure out how such differences are related to the (advective and/or diffusive) CRE transport in the disc and in the halo. Methods. We use wide-band 1.5 and 6 GHz Very Large Array (VLA) observations obtained in the B, C, and D configurations, and combine the 6 GHz images with Effelsberg observations to correct for missing short spacings. After subtraction of the thermal emission, we investigate the spatially resolved synchrotron spectral index distribution in terms of CRE spectral ageing. We further compute total magnetic field strengths assuming equipartition between the cosmic-ray (CR) energy density and the magnetic field, and measure synchrotron scale heights at both frequencies. Based on the fitted vertical profiles of the synchrotron intensity and on the spectral index profile between 1.5 and 6 GHz, we create purely advective and purely diffusive CRE transport models by numerically solving the 1D diffusion–loss equation. In particular, we investigate for the first time the radial dependence of synchrotron and magnetic field scale heights, advection speeds, and diffusion coefficients, whereas previous studies of these two galaxies only determined global values of these quantities. Results. We find that the overall spectral index distribution of NGC 891 is mostly consistent with continuous CRE injection. In NGC 4565, many of the local synchrotron spectra (even in the disc) feature a break between 1.5 and 6 GHz and are thus more in line with discrete-epoch CRE injection (Jaffe–Perola (JP) or Kardashev–Pacholczyk (KP) models). This implies that CRE injection time-scales are lower than the synchrotron cooling time-scales. The synchrotron scale height of NGC 891 increases with radius, indicating that synchrotron losses are significant. NGC 891 is probably dominated by advective CRE transport at a velocity of ≳150 km s−1. In contrast, NGC 4565 is diffusion-dominated up to z = 1 kpc or higher, with a diffusion coefficient of ≥2 × 1028 cm2 s−1.
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Desira, Christopher, Yiping Shu, Matthew W. Auger, Richard G. McMahon, Cameron A. Lemon, Timo Anguita, and Favio Neira. "Discovery of two bright high-redshift gravitationally lensed quasars revealed by Gaia." Monthly Notices of the Royal Astronomical Society 509, no. 1 (October 14, 2021): 738–47. http://dx.doi.org/10.1093/mnras/stab2960.
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ABSTRACT We present the discovery and preliminary characterisation of two high-redshift gravitationally lensed quasar systems in Gaia Data Release 2 (DR2). Candidates with multiple close-separation Gaia detections and quasar-like colours in WISE, Pan-STARRS, and DES are selected for follow-up spectroscopy with the New Technology Telescope. We confirm DES J215028.71−465251.3 as a $z$ = 4.130 ± 0.006 asymmetric, doubly imaged lensed quasar system and model the lensing mass distribution as a singular isothermal sphere. The system has an Einstein radius of 1.202 ± 0.005 arcsec and a predicted time delay of ∼122.0 d between the quasar images, assuming a lensing galaxy redshift of $z$ = 0.5, making this a priority system for future optical monitoring. We confirm PS J042913.17+142840.9 as a $z$ = 3.866 ± 0.003 four-image quasar system in a cusp configuration, lensed by two foreground galaxies. The system is well modelled using a singular isothermal ellipsoid for the primary lens and a singular isothermal sphere for the secondary lens with Einstein radii 0.704 ± 0.006 and 0.241 ± 0.030 arcsec, respectively. A maximum predicted time delay of 9.6 d is calculated, assuming lensing galaxy redshifts of $z$ = 1.0. Furthermore, PS J042913.17+142840.9 exhibits a large flux ratio anomaly, up to a factor of 2.66 ± 0.37 in i band, that varies across optical and near-infrared wavelengths. We discuss LSST and its implications for future high-redshift lens searches and outline an extension to the search using supervised machine learning techniques.
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Pişmiş, P., M. Manteiga, A. Mampaso, E. Recillas-Cruz, and G. Cruz-Gonzàlez. "The Nuclear Region of the Sbc Spiral Galaxy NGC 5055: A Mildly Active Nucleus." Symposium - International Astronomical Union 159 (1994): 454. http://dx.doi.org/10.1017/s0074180900176351.
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NGC 5055 is one of a list of nearby large spiral galaxies we have selected for a morphological and kinematic study of their bulges. CCD images are obtained at various spectral bands and in the Hα line using the 2.1 m reflector at San Pedro Martir observatory in México, while long-slit spectra at four different PA's are secured with the IDS spectrograph of the Isaac Newton Telescope of the observatory Roque de los Muchachos at La Palma, Spain. Some of the galaxies on our list for which observations are already performed are, aside from NGC 5055, NGC 3351, 4314, 5383 and 5915. These galaxies are not known to have active nuclei. However, we believe that activity may be a common phenomenon spanning a wide range of energetics, from the most active quasars and radio-galaxies (with jets) down to the mildest cases like our Galaxy or M31. The latter may be designated as MAGN (mildly active galactic nuclei). These ideas are treated in a review by Pişmiş (1987, Rev. Mex. Astron. Astrof. 14). The MAGN are usually nearby, and hence offer the possibility to study them in sufficient detail. It is reasonable to expect that the physical phenomenon underlying activity in galactic nuclei is one and the same, and it is essentially the global parameters such as energy at the nucleus that give rise to the different classes of AGN. Thus by studying the nearby mildly active galaxies one can construct a physically acceptable model supported by observation; such model, based on firmer grounds, can then be applied to all AGN.NGC 5055 (Sbc) with an adopted distance of 8.2 Mpc has a very bright bulge with a tenuous multiple arm structure around it, extending to 8 arcmin. Our velocity field and morphology of NGC 5055 lead to the following conclusions.1. The galaxy presents a north-south asymmetry; the southern approaching side has its isophotes closer together than at the farther side. We adopt PA 101° for the line of nodes. Our long-slit spectra cover the position angles: 58°, 101°, 112° and 155°.2. The rotation curve shows a linear region around the nucleus. At PA 101°, the line of nodes, the amplitude is 270 km s−1 between points ±5 arcsec on either side of the nucleus.3. There is high concentration of mass at the nuclear region (the bulge of the galaxy). An estimate of the mass for the region where the rotation curve is linear ±5 arcsec, is 1.5 × 108 M⊙. Burbidge et al. (1960) give a total mass of 7.6 × 1010 M⊙. The bulge density is thus found to be 500 times the average density of this galaxy.Analysis of the general velocity field based on four long-slit spectra shows an asymmetry between the East and West sides, ±5 arcsec around the nucleus of NGC 5055, suggestive of the existence of non-circular motion. Indeed evidence is found of an outflow on the west side of the Galaxy within a cone emanating from the center towards the NW with a projected radial velocity of around 80 km s−1. Thus this galaxy shows activity at its center and is a candidate for the MAGN group.
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Zanichelli, A., M. Vigotti, R. Scaramella, G. Grueff, and G. Vettolani. "Radio-optically selected clusters of galaxies." Astronomy & Astrophysics 379, no. 1 (November 2001): 21–34. http://dx.doi.org/10.1051/0004-6361:20011236.
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Zanichelli, A., R. Scaramella, G. Vettolani, M. Vigotti, S. Bardelli, and G. Zamorani. "Radio-optically selected clusters of galaxies." Astronomy & Astrophysics 379, no. 1 (November 2001): 35–45. http://dx.doi.org/10.1051/0004-6361:20011237.
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Mohd Ali, Nur Hidayah, Zamri Zainal Abidin, and Chorng-Yuan Hwang. "Star Formation Rates for Elliptical Galaxies Derived from the Wise 12- and 22-µm Emission." Sains Malaysiana 51, no. 9 (September 30, 2022): 3059–68. http://dx.doi.org/10.17576/jsm-2022-5109-25.
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We investigated the star formation rates (SFRs) of selected elliptical galaxies using the infrared data from the Wide-field Infrared Survey Explorer (WISE). The elliptical galaxies were selected from the Sloan Digital Sky Survey (SDSS) MPA-JHU catalog and morphology classified by Galaxy Zoo catalog. We used the 3.4-µm emission (W1) of WISE to represent the stellar mass of the galaxies and the 12- and 22-µm emission (W3 and W4) of WISE to represent the star formation activity of the galaxies. The W3- and W4-based star formation rates are usually overestimated due to the star emission in low star-forming galaxies. Stellar continuum emission could contribute to MIR fluxes of elliptical galaxies with an average overestimation of ~ 13.95 and ~ 0.77% from the observed fluxes of WISE W3 and W4-bands, which determined by using the estimated WISE W3 and W4 flux correction factors. Better SFRs can be obtained by subtracting the stellar contribution of the sources. Our result highlights the possibility of the existence of unknown mechanisms triggering the continuous star formation activities in elliptical galaxies.
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Kosmaczewski, E., Ł. Stawarz, and A. Wójtowicz. "Infrared Diagnostics of the ISM in the Circumnuclear Environments of the Youngest Radio Galaxies." Proceedings of the International Astronomical Union 14, S342 (May 2018): 268–69. http://dx.doi.org/10.1017/s174392131800738x.
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AbstractHere we present a systematic analysis of the mid-infrared properties of young radio galaxies, based on lower-resolution data provided by WISE and IRAS satellites. We restrict our analysis to sources in the earliest phase of radio galaxy evolution, with corresponding ages of the radio structures ≤ 3,000 yrs. In our sample of 29 objects, we find a variety of WISE colors, which suggests that the mid-infrared continua of studied sources are not exclusively contributed to by the circumnuclear dust. A comparison of the total mid-infrared and absorption-corrected X-ray luminosities for our sample reveals a clear correlation between the two bands. This favors the scenario in which the observed X-ray emission of young radio galaxies — at least the high-luminosity ones — originates predominantly in accretion disk corona.
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Chandola, Yogesh, D. J. Saikia, and Di Li. "H i absorption towards radio active galactic nuclei of different accretion modes." Monthly Notices of the Royal Astronomical Society 494, no. 4 (April 21, 2020): 5161–77. http://dx.doi.org/10.1093/mnras/staa1029.
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ABSTRACT We present results of H i absorption experiment done using the Giant Metrewave Radio Telescope (GMRT) towards 27 low- and intermediate-luminosity ($P_{\rm 1.4 GHz}\, \sim 10^{23}$-1026 W Hz−1) radio active galactic nuclei (AGNs), classified as either low excitation radio galaxies (LERGs) or high excitation radio galaxies (HERGs) and with WISE colour W2[4.6 μm]−W3[12 μm]> 2. We report H i absorption detection towards seven radio AGNs, six of which are new. Combined with other sources from literature classified as LERGs or HERGs, we confirm our earlier result that compact radio AGNs with WISE colour W2−W3 > 2 have higher detection rates compared to those with W2−W3 < 2. We find that H i absorption detection rate is higher for HERGs (37.0$^{+15.8}_{-11.5}$ per cent) compared to LERGs (22.0$^{+3.9}_{-3.4}$ per cent), mainly due to a larger fraction of HERGs being gas and dust rich with a younger stellar population compared to LERGs. However, for similar compact radio structures and host galaxies with WISE colours W2−W3 > 2, we don’t find any significant difference in detection rates of two types of AGNs implying detection of H i gas may not necessarily mean high excitation mode AGN. We further analysed the kinematics towards these sources. We find that while LERGs show a wide range in the shift of centroid velocities ($\sim \, -$479 to +356 km s−1) relative to the optical systemic velocity, most of the HERGs have centroid velocity shift less than 200 km s−1, possibly due to differences in jet-interstellar medium interaction.
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Beck, Sara C., Orly Kovo, and Jean L. Turner. "Wolf-Rayet galaxies at many radio wavelengths and Hα: radio super-star-clusters." Symposium - International Astronomical Union 193 (1999): 587. http://dx.doi.org/10.1017/s007418090020630x.
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We have observed nine Wolf-Rayet galaxies at 20,6, 3.6 and 2 cm from the VLA and at Hα from the Wise Observatory, and have mapped the radio spectral index in each galaxy on sub-arcsec scales. We find that more than half the WR sample has distinct regions where the radio spectrum rises between 6 and 2 cm. We believe that this is the radio signature of the youngest super-star-clusters which are otherwise invisible, and which require NLyc ≳ 1052, or equivalent to 750 stars of the 07 subtype. We call these sources radio super-star-clusters.
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Harvey, Max, Cameron B. Rulten, and Paula M. Chadwick. "A search for γ-ray emission from a sample of local Universe low-frequency selected radio galaxies." Monthly Notices of the Royal Astronomical Society 496, no. 1 (June 9, 2020): 903–12. http://dx.doi.org/10.1093/mnras/staa1593.
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ABSTRACT Radio galaxies are uncommon γ-ray emitters, and only low-redshift radio galaxies are detected with the Fermi Large Area Telescope (Fermi-LAT). However, they offer potential insights into the emission mechanisms of active galaxies, particularly as the alignment of their jets with respect to the Earth means that, unlike blazars, their emission is not necessarily jet dominated. We use the Fermi-LAT data to perform an unbiased survey of 78 radio galaxies from the Bologna complete sample in order to search for new γ-ray-emitting radio galaxies. We observe statistically significant γ-ray emission from four of the six known Fermi-LAT-detected radio galaxies included in this sample, and find some evidence for γ-ray emission spatially coincident with four previously undetected radio galaxies. As a large parameter space is searched, we calculate a probability distribution to compute the look-elsewhere effect. We find that these four spatially coincident sub-threshold γ-ray excesses are most likely a chance association, and are unlikely to be emission from the radio galaxies. Upper limits on flux are calculated for the radio galaxies from which no γ-ray emission is observed.
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Dey, Arjun, Wil van Breugel, and Joseph C. Shields. "Radio Loud Far-Infrared Galaxies." International Astronomical Union Colloquium 124 (1990): 309–14. http://dx.doi.org/10.1017/s0252921100005273.
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AbstractWe present the first results of a multiwavelength study of IRAS galaxies with excess radio emission. The sample was selected by cross-correlating the IRAS Faint Source Survey (for |b| ≥ 50°) and the Point Source Catalogue (for 10° < |b| < 50°) with the Texas radio survey. Recent optical (imaging and spectroscopic) and radio (VLA) observations are discussed. These observations will be used to investigate possible connections between radio galaxy activity, star formation and galaxy interactions.
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Bonzini, M., V. Mainieri, P. Padovani, K. I. Kellermann, N. Miller, P. Rosati, P. Tozzi, and S. Vattakunnel. "Host galaxy properties of radio selected AGN." Proceedings of the International Astronomical Union 9, S304 (October 2013): 343–44. http://dx.doi.org/10.1017/s1743921314004244.
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AbstractWith the goal of investigating the link between black hole (BH) and star formation (SF) activity, we study a deep sample of radio selected star forming galaxies (SFGs) and active galactic nuclei (AGNs). Using a multi-wavelength approach we characterize their host galaxies properties (stellar masses, optical colors, and morphology). Moreover, comparing the star formation rate derived from the radio and far-infrared luminosity, we found evidences that the main contribution to the radio emission in the radio-quiet AGNs is star-formation activity in their host galaxy.
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Rhodin, N. H. P., J.-K. Krogager, L. Christensen, F. Valentino, K. E. Heintz, P. Møller, T. Zafar, and J. P. U. Fynbo. "Absorption-selected galaxies trace the low-mass, late-type, star-forming population at z ∼ 2–3." Monthly Notices of the Royal Astronomical Society 506, no. 1 (June 12, 2021): 546–61. http://dx.doi.org/10.1093/mnras/stab1691.
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ABSTRACT We report on the stellar content, half-light radii and star formation rates of a sample of 10 known high-redshift (z ≳ 2) galaxies selected on strong neutral hydrogen (H i) absorption ($\log ({\rm N_{H\, \rm {I}}\: /\: cm}^{-2})\,\gt\, 19$) towards background quasars. We use observations from the Hubble Space Telescope Wide Field Camera 3 in three broad-band filters to study the spectral energy distribution (SED) of the galaxies. Using careful quasar point spread function subtraction, we study their galactic environments, and perform the first systematic morphological characterization of such absorption-selected galaxies at high redshifts. Our analysis reveals complex, irregular hosts with multiple star-forming clumps. At a spatial sampling of 0.067 arcsec per pixel (corresponding to 0.55 kpc at the median redshift of our sample), 40 per cent of our sample requires multiple Sérsic components for an accurate modelling of the observed light distributions. Placed on the mass–size relation and the ‘main sequence’ of star-forming galaxies, we find that absorption-selected galaxies at high redshift extend known relations determined from deep luminosity-selected surveys to an order of magnitude lower stellar mass, with objects primarily composed of star-forming, late-type galaxies. We measure half-light radii in the range r1/2 ∼ 0.4 to 2.6 kpc based on the reddest band (F160W) to trace the oldest stellar populations, and stellar masses in the range log (M⋆/M⊙) ∼ 8 to 10 derived from fits to the broad-band SED. Spectroscopic and SED-based star formation rates are broadly consistent, and lie in the range $\log (\mathrm{SFR}/{\rm M}_{\odot }\, {\rm yr}^{-1}) \sim 0.0$ to 1.7.
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Barrows, R. Scott, Julia M. Comerford, Daniel Stern, and Roberto J. Assef. "A Catalog of Host Galaxies for WISE-selected AGN: Connecting Host Properties with Nuclear Activity and Identifying Contaminants." Astrophysical Journal 922, no. 2 (November 29, 2021): 179. http://dx.doi.org/10.3847/1538-4357/ac1352.
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Abstract We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts z ∼ 3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts z = 0.2–0.3, with relatively blue W1–W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs relative to those of normal star-forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with the Eddington ratio. This result is consistent with a version of the receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.
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Jones, Suzy F., Andrew W. Blain, Daniel Stern, Roberto J. Assef, Carrie R. Bridge, Peter Eisenhardt, Sara Petty, et al. "Submillimetre observations of WISE-selected high-redshift, luminous, dusty galaxies." Monthly Notices of the Royal Astronomical Society 443, no. 1 (July 9, 2014): 146–57. http://dx.doi.org/10.1093/mnras/stu1157.
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Allington-Smith, Jeremy R., Richard Ellis, Esther L. Zirbel, and Augustus, Jr Oemler. "The evolution of galaxies in radio-selected groups." Astrophysical Journal 404 (February 1993): 521. http://dx.doi.org/10.1086/172305.
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de Mello Rabaça, Dulia F., and Zulema Abraham. "Radio Emission in Peculiar Galaxies." International Astronomical Union Colloquium 124 (1990): 343–46. http://dx.doi.org/10.1017/s0252921100005327.
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During the last decades a number of surveys of peculiar galaxies have been carried out and accurate positions become available. Since peculiarities are a possible evidence of radio emission (Wright, 1974; Sulentic, 1976; Stocke et al.,1978), we have selected a sample of 24 peculiar galaxies with optical jet-like features or extensions in different optical catalogues, mainly the Catalogue of Southern Peculiar Galaxies and Associations (Arp and Madore, 1987) and the ESO/Uppsala Survey of the ESO(B) Atlas (Lauberts, 1982) for observation at the radiocontinuum frequency of 22 GHz. The sample is listed in the Table.
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Miraghaei, Halime. "A Statistical Analysis on the Morphology and Color of Galaxies Hosting Radio-loud Active Galactic Nuclei." Astronomical Journal 164, no. 6 (November 14, 2022): 246. http://dx.doi.org/10.3847/1538-3881/ac9b13.
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Abstract The properties of galaxies hosting radio-loud active galactic nuclei (AGN) have been investigated in order to find out the relation between morphology and color of galaxies and radio loudness. The concentration index is used to map the morphology of galaxies as early or late type. 4000 Å break strength and star-formation rate are used to quantify the state of galaxies as blue star forming or red quenched. Due to the environmental dependence of these properties, galaxies with the same environment have been considered. The results show that the prevalence of radio-loud AGN in early-type galaxies is independent of environment. This is confirmed by comparing a sample of galaxies hosting radio-loud AGN with a sample of galaxies hosting radio-quiet AGN or with a randomly selected galaxy sample from the total population of galaxies used in this study. In addition, it is shown that galaxies hosting radio-loud AGN are bluer indicating the role of cold gas in triggering AGN activity. Finally, the optically-selected radio-loud AGN show to have higher [O iii] luminosities compared with their radio-quiet counterparts. We argue the relation between radio size and luminosity with the [O iii] luminosity.
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Whittam, I. H., D. A. Green, M. J. Jarvis, and J. M. Riley. "The faint radio source population at 15.7 GHz – IV. The dominance of core emission in faint radio galaxies." Monthly Notices of the Royal Astronomical Society 493, no. 2 (February 12, 2020): 2841–53. http://dx.doi.org/10.1093/mnras/staa306.
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ABSTRACT We present 15-GHz Karl G. Jansky Very Large Array observations of a complete sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C) survey. 67 out of the 95 sources (71 per cent) are unresolved in the new observations and lower frequency radio observations, placing an upper limit on their angular size of ∼2 arcsec. Thus, compact radio galaxies, or radio galaxies with very faint jets, are the dominant population in the 10C survey. This provides support for the suggestion in our previous work that low-luminosity ($L\lt 10^{25} \, \textrm{W~Hz}^{-1}$) radio galaxies are core dominated, although higher resolution observations are required to confirm this directly. The 10C sample of compact, high-frequency selected radio galaxies is a mixture of high-excitation and low-excitation radio galaxies and displays a range of radio spectral shapes, demonstrating that they are a mixed population of objects.
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Willis, Anthony G., and Christopher P. O'dea. "Polarization Observations of Selected Radio Galaxies at 327 Mhz." Symposium - International Astronomical Union 140 (1990): 455–56. http://dx.doi.org/10.1017/s0074180900190850.
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We have measured the distribution of polarized emission from the radio galaxies NGC315, NGC6251, DA240, 3C236 and 3C326 at 327 MHz (92 cm wavelength) with the Westerbork Synthesis Radio Telescope (WSRT). These radio galaxies were all selected for observation because they exhibited degrees of polarization as high as 60 or 70 percent at 610 MHz (49 cm wavelength) and because they all have angular sizes greater than about 20 arcmin. Therefore they are still well-resolved by the WSRT at 92 cm wavelength. All sources in the sample exhibit significant linear polarization at 92 cm wavelength. Some depolarization does occur in NGC315 and 3C326 but parts of 3C236, DA240 and NGC6251 appear not to depolarize to 92 cm. Assuming an ordered, equipartition magnetic field, we find that the density of thermal depolarizing material in these radio galaxies is very low, typically about 1 × 10−5 cm−3 or less. Therefore these radio galaxies may represent distributions of pure magnetic fields and relativistic particles on scales of several hundred kiloparsecs or more.