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Sivarani, T. "Stellar Relics from the Early Galaxy". Journal of Astrophysics and Astronomy 34, nr 1 (marzec 2013): 5–17. http://dx.doi.org/10.1007/s12036-013-9165-9.
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Salvadori, Stefania, Raffaella Schneider i Andrea Ferrara. "Cosmic stellar relics in the Galactic halo". Monthly Notices of the Royal Astronomical Society 381, nr 2 (26.09.2007): 647–62. http://dx.doi.org/10.1111/j.1365-2966.2007.12133.x.
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Paron, S., A. Granada i M. B. Areal. "Studying the interstellar medium to look for relics of triggered star formation among stellar clusters". Monthly Notices of the Royal Astronomical Society 505, nr 4 (10.06.2021): 4813–20. http://dx.doi.org/10.1093/mnras/stab1646.
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ABSTRACT Evidence of triggered star formation at large spatial scales involving stellar clusters is scarce. We investigate a Galactic region (l = 130${_{.}^{\circ}}$0, b = 0${_{.}^{\circ}}$35) populated by several open stellar clusters that according to the last Gaia data release, are located at a distance of about 2.9 kpc. By analysing the interstellar medium (ISM) at infrared, centimeter, and millimeter wavelengths towards this group of clusters we discovered a shell of material of about 2° in size at the same distance. We suggest that the shell, mainly observed at 12 μm and in the H i emission at 21 cm, was generated by the action of massive stars belonging to clusters Berkeley 7 and UBC 414, which lie at its centre. Five clusters (MWSC0152, Czernik 6, Czernik 7, Berkeley 6, NGC 663, and NGC 654) lie at the border of this shell. From the comparison between the dynamical time of the discovered H i shell and the analysis of the ages of stellar populations in these clusters, we conclude that the expansion of the shell could have triggered in the past the formation of stars in some of them. We point out that in order to find physical evidence supporting a genetic connection between stellar clusters, it is necessary not only to study the individual clusters and their stellar populations, but also to investigate their surrounding ISM at a large spatial scale.
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Efremov, Yuri N., Bruce G. Elmegreen i Paul W. Hodge. "Giant Shells and Stellar Arcs as Relics of Gamma-Ray Burst Explosions". Astrophysical Journal 501, nr 2 (10.07.1998): L163—L165. http://dx.doi.org/10.1086/311468.
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Li, Haining, Wako Aoki, Gang Zhao, Takuma Suda, Satoshi Honda, Norbert Christlieb i Tadafumi Matsuno. "LAMOST-Subaru exploration of chemical relics of first stars". Proceedings of the International Astronomical Union 13, S334 (lipiec 2017): 21–24. http://dx.doi.org/10.1017/s1743921317008109.
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AbstractVery metal-poor (VMP) stars preserve chemical signatures of early generations of stars, and are crutial to understand the early nucleosynthesis and first stars. Millions of stellar spectra obtained by LAMOST provide an unprecedented chance to enlarge the currently limited VMP star sample. Since 2014, a joint project on searching for VMP stars has been conducted based on the LAMOST survey and Subaru follow-up observations. So far, the project has obtained chemical abundances for about 250 VMP stars and a number of chemically interesting objects, e.g., three ultra metal-poor stars with [Fe/H] ~ − 4.0, a dozen Li-rich VMP stars distributed in a wide range of evolutionary stages. Statistics of the large homogeneous sample of VMP stars will be of great interest and importance to probe the chemical enrichment in the early Galaxy and low-mass star evolution.
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Lai, David K., Michael Bolte, Jennifer A. Johnson, Sara Lucatello, Alexander Heger i S. E. Woosley. "Detailed Abundances for 28 Metal‐poor Stars: Stellar Relics in the Milky Way". Astrophysical Journal 681, nr 2 (10.07.2008): 1524–56. http://dx.doi.org/10.1086/588811.
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Tortora, C., N. R. Napolitano, M. Radovich, C. Spiniello, L. Hunt, N. Roy, L. Moscardini i in. "Nature versus nurture: relic nature and environment of the most massive passive galaxies at z < 0.5". Astronomy & Astrophysics 638 (czerwiec 2020): L11. http://dx.doi.org/10.1051/0004-6361/202038373.
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Relic galaxies are thought to be the progenitors of high-redshift red nuggets that for some reason missed the channels of size growth and evolved passively and undisturbed since the first star formation burst (at z > 2). These local ultracompact old galaxies are unique laboratories for studying the star formation processes at high redshift and thus the early stage of galaxy formation scenarios. Counterintuitively, theoretical and observational studies indicate that relics are more common in denser environments, where merging events predominate. To verify this scenario, we compared the number counts of a sample of ultracompact massive galaxies (UCMGS) selected within the third data release of the Kilo Degree Survey, that is, systems with sizes Re < 1.5 kpc and stellar masses M⋆ > 8 × 1010 M⊙, with the number counts of galaxies with the same masses but normal sizes in field and cluster environments. Based on their optical and near-infrared colors, these UCMGS are likely to be mainly old, and hence representative of the relic population. We find that both UCMGS and normal-size galaxies are more abundant in clusters and their relative fraction depends only mildly on the global environment, with denser environments penalizing the survival of relics. Hence, UCMGS (and likely relics overall) are not special because of the environment effect on their nurture, but rather they are just a product of the stochasticity of the merging processes regardless of the global environment in which they live.
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Lohmann, F. S., A. Schnorr-Müller, M. Trevisan, R. Riffel, N. Mallmann, Ana L. Chies-Santos i C. Furlanetto. "The Quest for Relics: Massive compact galaxies in the local Universe". Proceedings of the International Astronomical Union 15, S359 (marzec 2020): 441–43. http://dx.doi.org/10.1017/s1743921320002045.
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AbstractObservations at high redshift reveal that a population of massive, quiescent galaxies (called red nuggets) already existed 10 Gyr ago. These objects undergo a significant size evolution over time, likely due to minor mergers. In this work we present an analysis of local massive compact galaxies to assess if their properties are consistent with what is expected for unevolved red nuggets (relic galaxies). Using integral field spectroscopy (IFS) data from the MaNGA survey from the Sloan Digital Sky Survey (SDSS), we characterized the kinematics and properties of stellar populations of massive compact galaxies, and find that these objects exhibit, on average, a higher rotational support than a control sample of average sized early-type galaxies. This is in agreement with a scenario in which these objects have a quiet accretion history, rendering them candidates for relic galaxies.
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van der Marel, Roeland P. "Relics of Nuclear Activity: Do All Galaxies Have Massive Black Holes?" Symposium - International Astronomical Union 186 (1999): 333–40. http://dx.doi.org/10.1017/s0074180900112926.
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The distribution of black hole (BH) masses M• in galaxies is constrained by photometric and kinematic studies of individual galaxies, and by the properties of the quasar population. I review our understanding of these topics, present new results of adiabatic BH growth models for HST photometry of elliptical galaxies with brightness profiles of the ‘core’ type, and discuss the implications of ground-based stellar kinematical data. It is not yet possible to uniquely determine the BH mass distribution, but the available evidence is not inconsistent with a picture in which: (i) a majority of galaxies has BHs; (ii) there is a correlation (with large scatter) between M• and spheroid luminosity Lsph of the form M• ≈ 10−2Lsph (solar B-band units); and (iii) the BHs formed in a quasar phase through mass accretion with efficiency ε ≈ 0.05.
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Schnorr-Müller, A., M. Trevisan, F. S. Lohmann, N. Mallmann, R. Riffel, A. Chies-Santos i C. Furlanetto. "The quest for relics: Massive compact galaxies in the local Universe". Proceedings of the International Astronomical Union 15, S352 (czerwiec 2019): 320–21. http://dx.doi.org/10.1017/s1743921319009505.
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AbstractIn the local Universe there exists a rare population of compact galaxies resembling the high-redshift quiescent population in mass and size. It has been found that some of these objects have survived largely unchanged since their formation at high-z. They are called relic galaxies. With the goal of finding relic galaxies, we searched the SDSS-MaNGA DR15 release for massive compact galaxies. We find that massive compact galaxies are mostly composed of old, metal-rich and alpha enhanced stellar populations. In terms of kinematics, massive compact galaxies show ordered rotation in their velocity fields and σ* profiles rising towards the center. They are predominantly fast rotators and show increased rotational support when compared to a mass-matched control sample of average-sized early-type galaxies. These properties are consistent with these objects being relic galaxies. However, to confirm their relic status, we need to probe larger radii (⪎3Re) than probed with the current data.
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Da Costa, G. S., R. Soria, S. A. Farrell, D. Bayliss, M. S. Bessell, F. P. A. Vogt, G. Zhou i in. "SMSS J130522.47−293113.0: a high-latitude stellar X-ray source with pc-scale outflow relics?" Monthly Notices of the Royal Astronomical Society 477, nr 1 (16.03.2018): 766–79. http://dx.doi.org/10.1093/mnras/sty680.
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Gao, Hua, Luis C. Ho i Zhao-Yu Li. "The Carnegie-Irvine Galaxy Survey. X. Bulges in Stellar Mass–based Scaling Relations". Astrophysical Journal Supplement Series 262, nr 2 (1.10.2022): 54. http://dx.doi.org/10.3847/1538-4365/ac8dea.
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Abstract We measure optical colors for the bulges of 312 disk galaxies from the Carnegie-Irvine Galaxy Survey and convert their previously available R-band structural parameters to stellar-mass parameters. We also measure their average stellar-mass surface density in the central 1 kpc (Σ1). Comparing the mass-based Kormendy relation with the original one based on flux, we find that the majority of the classifications into classical and pseudo bulges, as well as their overall statistical properties, remain essentially unchanged. While the bulge-type classifications of the Kormendy relation are robust against stellar population effects, the mass-based classification criteria do produce better agreement between bulge structural properties and their stellar populations. Moreover, the mass-based Kormendy relation reveals a population of ultradense bulges akin to high-z compact early-type galaxies, which are otherwise hidden in the original Kormendy relation. These bulges are probably relics of spheroids assembled in the early universe, although for some we cannot rule out some contribution from secular growth. We confirm previous studies that Σ1 correlates well with bulge surface densities.
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Bogdán, Ákos, Orsolya E. Kovács, Christine Jones, William R. Forman, Ralph P. Kraft, Victoria Strait, Dan Coe i Maruša Bradač. "Exploring Gravitationally Lensed z ≳ 6 X-Ray Active Galactic Nuclei Behind the RELICS Clusters". Astrophysical Journal 927, nr 1 (1.03.2022): 34. http://dx.doi.org/10.3847/1538-4357/ac4ae5.
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Abstract Although observations of high-redshift quasars demonstrate that many supermassive black holes (BHs) reached large masses within one billion years after the Big Bang, the origin of the first BHs is still a mystery. A promising way to constrain the origin of the first BHs is to explore the average properties of z ≳ 6 BHs. However, typical BHs remain hidden from X-ray surveys, which is due to their relatively faint nature and the limited sensitivity of X-ray telescopes. Gravitational lensing provides an attractive way to study this unique galaxy population as it magnifies the faint light from these high-redshift galaxies. Here, we study the X-ray emission originating from 155 gravitationally lensed z ≳ 6 galaxies that were detected in the Reionization Lensing Cluster Survey. We utilize Chandra X-ray observations to search for active galactic nuclei (AGNs) in the individual galaxies and in the stacked galaxy samples. We did not identify an individual X-ray source that was undoubtedly associated with a high-redshift galaxy. We stack the signal from all galaxies and do not find a statistically significant detection. We split our sample based on stellar mass, star formation rate, and lensing magnification and stack these subsamples. We obtain a 2.2σ detection for massive galaxies with an X-ray luminosity of (3.7 ± 1.6) × 1042 erg s−1, which corresponds to a (3.0 ± 1.3) × 105 M ⊙ BH accreting at its Eddington rate. Other stacks remain undetected and we place upper limits on the AGN emission. These limits imply that the bulk of BHs at z ≳ 6 either accrete at a few percent of their Eddington rate and/or are 1–2 orders of magnitude less massive than expected based on the stellar mass of their host galaxy.
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Trujillo, Ignacio. "The growth channel of massive galaxies". Proceedings of the International Astronomical Union 10, S311 (lipiec 2014): 130–35. http://dx.doi.org/10.1017/s1743921315003531.
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AbstractThere is growing evidence suggesting that massive galaxies have growth both in mass and size mainly by the accretion of smaller satellites. This evolutionary path qualitative explains many different observations. However, there is still much work to do on trying to quantify whether this merging scenario is enough to explain the significant growth of massive galaxies since z~2. In this contribution, we show that both the number of satellite galaxies around massive galaxies at all redshifts, and the existence of massive relic galaxies in the nearby Universe are in quantitative agreement with this merging picture. Nonetheless, there is still open questions related to the properties of the stellar halos of present-day massive galaxies and the number density of massive relics at all redshifts that remain open.
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Duc, P. –A, J. C. Cuillandre, K. Alatalo, L. Blitz, M. Bois, F. Bournaud, M. Bureau i in. "Probing the mass assembly of massive nearby galaxies with deep imaging". Proceedings of the International Astronomical Union 8, S295 (sierpień 2012): 358–61. http://dx.doi.org/10.1017/s174392131300536x.
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AbstractAccording to a popular scenario supported by numerical models, the mass assembly and growth of massive galaxies, in particular the Early-Type Galaxies (ETGs), is, below a redshift of 1, mainly due to the accretion of multiple gas–poor satellites. In order to get observational evidence of the role played by minor dry mergers, we are obtaining extremely deep optical images of a complete volume limited sample of nearby ETGs. These observations, done with the CFHT as part of the ATLAS3D, NGVS and MATLAS projects, reach a stunning 28.5 – 29 mag.arcsec−2 surface brightness limit in the g' band. They allow us to detect the relics of past collisions such as faint stellar tidal tails as well as the very extended stellar halos which keep the memory of the last episodes of galactic accretion. Images and preliminary results from this on-going survey are presented, in particular a possible correlation between the fine structure index (which parametrizes the amount of tidal perturbation) of the ETGs, their stellar mass, effective radius and gas content.
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Lai, David K., Michael Bolte, Jennifer A. Johnson, Sara Lucatello, Alexander Heger i S. E. Woosley. "ERRATUM: “DETAILED ABUNDANCES FOR 28 METAL-POOR STARS: STELLAR RELICS IN THE MILKY WAY” (2008, ApJ, 681, 1524)". Astrophysical Journal 722, nr 2 (5.10.2010): 1984. http://dx.doi.org/10.1088/0004-637x/722/2/1984.
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Gupta, Aashish, i Wen-Ping Chen. "Interplay between Young Stars and Molecular Clouds in the Ophiuchus Star-forming Complex". Astronomical Journal 163, nr 5 (26.04.2022): 233. http://dx.doi.org/10.3847/1538-3881/ac5cc8.
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Abstract We present spatial and kinematic correlation between the young stellar population and the cloud clumps in the Ophiuchus star-forming region. The stellar sample consists of known young objects at various evolutionary stages, taken from the literature, some of which are diagnosed with Gaia EDR3 parallax and proper-motion measurements. The molecular gas is traced by the 850 μm Submillimetre Common-User Bolometer Array-2 image, reaching ∼2.3 mJy beam−1, the deepest so far for the region, stacked from the James Clerk Maxwell Telescope/Transient program aiming to detect submillimeter outburst events. Our analysis indicates that the more evolved sources, namely the class II and III young stars, are located further away from clouds than class I and flat-spectrum sources that have ample circumstellar matter and are closely associated with natal clouds. Particularly the class II and III population is found to exhibit a structured spatial distribution indicative of passage of shock fronts from the nearby Sco–Cen OB association thereby compressing clouds to trigger star formation, with the latest starbirth episode occurring now in the densest cloud filaments. The young stars at all evolutionary stages share similar kinematics. This suggests that the stellar patterns trace the relics of parental cloud filaments that now have been dispersed.
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Gupta, Aashish, i Wen-Ping Chen. "Interplay between Young Stars and Molecular Clouds in the Ophiuchus Star-forming Complex". Astronomical Journal 163, nr 5 (26.04.2022): 233. http://dx.doi.org/10.3847/1538-3881/ac5cc8.
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Abstract We present spatial and kinematic correlation between the young stellar population and the cloud clumps in the Ophiuchus star-forming region. The stellar sample consists of known young objects at various evolutionary stages, taken from the literature, some of which are diagnosed with Gaia EDR3 parallax and proper-motion measurements. The molecular gas is traced by the 850 μm Submillimetre Common-User Bolometer Array-2 image, reaching ∼2.3 mJy beam−1, the deepest so far for the region, stacked from the James Clerk Maxwell Telescope/Transient program aiming to detect submillimeter outburst events. Our analysis indicates that the more evolved sources, namely the class II and III young stars, are located further away from clouds than class I and flat-spectrum sources that have ample circumstellar matter and are closely associated with natal clouds. Particularly the class II and III population is found to exhibit a structured spatial distribution indicative of passage of shock fronts from the nearby Sco–Cen OB association thereby compressing clouds to trigger star formation, with the latest starbirth episode occurring now in the densest cloud filaments. The young stars at all evolutionary stages share similar kinematics. This suggests that the stellar patterns trace the relics of parental cloud filaments that now have been dispersed.
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Gupta, Aashish, i Wen-Ping Chen. "Interplay between Young Stars and Molecular Clouds in the Ophiuchus Star-forming Complex". Astronomical Journal 163, nr 5 (26.04.2022): 233. http://dx.doi.org/10.3847/1538-3881/ac5cc8.
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Abstract We present spatial and kinematic correlation between the young stellar population and the cloud clumps in the Ophiuchus star-forming region. The stellar sample consists of known young objects at various evolutionary stages, taken from the literature, some of which are diagnosed with Gaia EDR3 parallax and proper-motion measurements. The molecular gas is traced by the 850 μm Submillimetre Common-User Bolometer Array-2 image, reaching ∼2.3 mJy beam−1, the deepest so far for the region, stacked from the James Clerk Maxwell Telescope/Transient program aiming to detect submillimeter outburst events. Our analysis indicates that the more evolved sources, namely the class II and III young stars, are located further away from clouds than class I and flat-spectrum sources that have ample circumstellar matter and are closely associated with natal clouds. Particularly the class II and III population is found to exhibit a structured spatial distribution indicative of passage of shock fronts from the nearby Sco–Cen OB association thereby compressing clouds to trigger star formation, with the latest starbirth episode occurring now in the densest cloud filaments. The young stars at all evolutionary stages share similar kinematics. This suggests that the stellar patterns trace the relics of parental cloud filaments that now have been dispersed.
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Petrovic, Jelena. "The evolution of massive binary systems". Serbian Astronomical Journal, nr 201 (2020): 1–13. http://dx.doi.org/10.2298/saj2001001p.
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The evolution of massive stars in close binary systems is significantly different from single star evolution due to a series of interactions between the two stellar components. Such massive close binary systems are linked to various astrophysical phenomena, for example Wolf-Rayet stars, supernova type Ib and Ic, X-ray binaries and gamma-ray bursts. Also, the emission of gravitational waves, recently observed by the LIGO-Virgo detectors, is associated with mergers in binary systems containing compact objects, relics of massive stars - black holes and neutron stars. Evolutionary calculations of massive close binary systems were performed by various authors, but many aspects are not yet fully understood. In this paper, the main concepts of massive close binary evolution are reviewed, together with the most important parameters that can influence the final outcome of the binary system evolution, such as rotation, magnetic fields, stellar wind mass loss and mass accretion efficiency during interactions. An extensive literature overview of massive close binary models in the light of exciting observations connected with those systems is presented.
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Mainali, Ramesh, Daniel P. Stark, Mengtao Tang, Jacopo Chevallard, Stéphane Charlot, Keren Sharon, Dan Coe i in. "RELICS: spectroscopy of gravitationally lensed z ≃ 2 reionization-era analogues and implications for C iii] detections at z > 6". Monthly Notices of the Royal Astronomical Society 494, nr 1 (20.03.2020): 719–35. http://dx.doi.org/10.1093/mnras/staa751.
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ABSTRACT Recent observations have revealed the presence of strong C iii] emission (EW$_{\rm {C\,{\small III}]}}\gt 20$ Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting C iii] emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J125-band flux excesses indicative of intense [O iii] + H β emission (EW$_{\rm {[O\,{\small III}]+H\,\beta }}$ = 500–2000 Å), similar to what has been observed at z > 6. We detect C iii] emission in three of the four sources, with the C iii] EW reaching values seen in the reionization era (EW$_{\rm {C\,{\small III}]}}\simeq 17\!-\!22$ Å) in the two sources with the strongest optical line emission (EW$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$ Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C iii] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C iii] and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C iii] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C iii] to measure redshifts of objects with IRAC excesses indicating EW$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$ Å, providing a method of spectroscopic confirmation independent of Ly α.
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Amarante, João A. S., Victor P. Debattista, Leandro Beraldo E Silva, Chervin F. P. Laporte i Nathan Deg. "Gastro Library. I. The Simulated Chemodynamical Properties of Several Gaia–Sausage–Enceladus-like Stellar Halos". Astrophysical Journal 937, nr 1 (1.09.2022): 12. http://dx.doi.org/10.3847/1538-4357/ac8b0d.
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Abstract The Milky Way (MW) stellar halo contains relics of ancient mergers that tell the story of our galaxy’s formation. Some of them are identified due to their similarity in energy, actions, and chemistry, referred to as the “chemodynamical space,” and are often attributed to distinct merger events. It is also known that our galaxy went through a significant merger event that shaped the local stellar halo during its first billion years. Previous studies using N-body only and cosmological hydrodynamical simulations have shown that such a single massive merger can produce several “signatures” in the chemodynamical space, which can potentially be misinterpreted as distinct merger events. Motivated by these, in this work we use a subset of the GASTRO library, which consists of several smoothed particle hydrodynamics+N-body models of a single accretion event in a MW-like galaxy. Here, we study models with orbital properties similar to the main merger event of our galaxy and explore the implications to known stellar halo substructures. We find that (i) supernova feedback efficiency influences the satellite’s structure and orbital evolution, resulting in distinct chemodynamical features for models with the same initial conditions; (ii) very retrograde high-energy stars are the most metal-poor of the accreted dwarf galaxy and could be misinterpreted as a distinct merger; (iii) the most bound stars are more metal-rich in our models, the opposite of what is observed in the MW, suggesting a secondary massive merger; and, finally, (iv) our models can reconcile other known apparently distinct substructures to a unique progenitor.
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Greco, Claudia, Gisella Clementini, E. V. Held, E. Poretti, M. Catelan, L. Federici, M. Maio i in. "Looking for building blocks of the Galactic halo: variable stars in the Fornax, Bootes I, Canes Venatici II dwarfs and in NGC 2419". Proceedings of the International Astronomical Union 5, S266 (sierpień 2009): 411. http://dx.doi.org/10.1017/s1743921309991530.
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AbstractΛ cold-dark-matter hierarchical models of galaxy formation suggest that the halo of the Milky Way (MW) has been assembled, at least in part, through accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. Investigation of the stellar populations of the MW's globular clusters (GCs) and dSph companions can thus provide excellent tests to infer the dominant Galaxy-formation scenario, whether merger/accretion or cloud collapse. Pulsating variable stars offer a very powerful tool in this context, since variables of different types allow tracing the different stellar generations in a galaxy and to reconstruct the galaxy's star-formation history and assembly back to the first epochs of galaxy formation. In particular, the RR Lyrae stars, belonging to the old population (t > 10 Gyr), witnessed the epoch of halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to build up the Galactic halo. In the MW, most GCs with an RR Lyrae population sharply divide into two distinct groups (Oosterhoff types I and II) based on the mean periods and relative proportion of fundamental-mode (RRab) and first-overtone (RRc) RR Lyrae stars. On the other hand, the Galactic-halo field RR Lyrae stars show a dominance of Oosterhoff I properties. Here, we investigate the Oosterhoff properties of a number of different stellar systems, starting from relatively undisturbed dwarf galaxies (the Fornax dSph and its globular clusters), through distorted and tidally disrupting ones (the Bootes and Canes Venatici II dSphs), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the crucial question of whether the RR Lyrae pulsation properties in these systems conform to the Oosterhoff dichotomy characterizing the MW variables. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling the present-day dSph companions of the MW. We have reduced and combined long time series from different telescopes, both ground- and space-based. Variable stars have been detected with image-subtraction techniques using the package isis2.1. Periods, amplitudes and Oosterhoff type for all variable stars, as well as color–magnitude diagrams of the stellar populations are discussed for each stellar cluster analyzed.
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Krajnović, Davor, Ugur Ural, Harald Kuntschner, Paul Goudfrooij, Michael Wolfe, Michele Cappellari, Roger Davies i in. "Formation channels of slowly rotating early-type galaxies". Astronomy & Astrophysics 635 (marzec 2020): A129. http://dx.doi.org/10.1051/0004-6361/201937040.
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We study the evidence for a diversity of formation processes in early-type galaxies by presenting the first complete volume-limited sample of slow rotators with both integral-field kinematics from the ATLAS3D Project and high spatial resolution photometry from the Hubble Space Telescope. Analysing the nuclear surface brightness profiles of 12 newly imaged slow rotators, we classify their light profiles as core-less, and place an upper limit to the core size of about 10 pc. Considering the full magnitude and volume-limited ATLAS3D sample, we correlate the presence or lack of cores with stellar kinematics, including the proxy for the stellar angular momentum (λRe) and the velocity dispersion within one half-light radius (σe), stellar mass, stellar age, α-element abundance, and age and metallicity gradients. More than half of the slow rotators have core-less light profiles, and they are all less massive than 1011 M⊙. Core-less slow rotators show evidence for counter-rotating flattened structures, have steeper metallicity gradients, and a larger dispersion of gradient values (Δ[Z/H]¯ = −0.42 ± 0.18) than core slow rotators (Δ[Z/H]¯ = −0.23 ± 0.07). Our results suggest that core and core-less slow rotators have different assembly processes, where the former, as previously discussed, are the relics of massive dissipation-less merging in the presence of central supermassive black holes. Formation processes of core-less slow rotators are consistent with accretion of counter-rotating gas or gas-rich mergers of special orbital configurations, which lower the final net angular momentum of stars, but support star formation. We also highlight core fast rotators as galaxies that share properties of core slow rotators (i.e. cores, ages, σe, and population gradients) and core-less slow rotators (i.e. kinematics, λRe, mass, and larger spread in population gradients). Formation processes similar to those for core-less slow rotators can be invoked to explain the assembly of core fast rotators, with the distinction that these processes form or preserve cores.
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Bezanson, Rachel. "Spatially resolving the relics: The inferring the physics driving the quenching of massive galaxies from kinematics at z ∼ 1 and beyond". Proceedings of the International Astronomical Union 15, S352 (czerwiec 2019): 267. http://dx.doi.org/10.1017/s1743921320001222.
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AbstractToday's massive elliptical galaxies are primarily red-and-dead, dispersion supported ellipticals. The physical process(es) driving the shutdown or ‘quenching’ of star formation in these galaxies remains one of the least understood aspects of galaxy formation and evolution. Although today's spiral and elliptical galaxies exhibit a clear bimodality in their structures, kinematics, and stellar populations, it may be that the quenching and structural transformation do no occur simultaneously. In this talk I will present evidence that early quiescent galaxies, observed much closer to their quenching epoch at z ∼ 1, retain significant rotational support (∼ twice as much as local ellipticals). This suggests that the mechanisms responsible for shutting down star formation do not also have to destroy ordered motion in massive galaxies; the increased dispersion support could occur subsequently via hierarchical growth and minor merging. I will discuss this evidence in conjunction with recent ALMA studies of the dramatic range in molecular gas reservoirs of recently quenched high redshift galaxies to constrain quenching models. Finally, I will discuss prospects for extending spatially resolved spectroscopic studies of galaxies immediately following quenching with JWST and eventually 30-m class telescopes.
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Smith, Linda J., Antonella Nota, Anna Pasquali, Claus Leitherer, Mark Clampin i Paul A. Crowther. "Ring Nebulae Abundances: Probes of the Evolutionary History of Luminous Blue Variable Stars". International Astronomical Union Colloquium 169 (1999): 400–404. http://dx.doi.org/10.1017/s0252921100072298.
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The ring nebulae that surround most Luminous Blue Variable (LBV) stars are believed to be the relics of one or more giant eruptions (cf. Nota, these proc.). The nebulae thus represent the stellar surface layers at the time of the eruption(s) and by analysing their chemical composition and dynamics, it is possible to infer the past evolutionary state of the star.Observations with the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) were obtained for the nebulae around the two LMC LBVs R127 and R143, and the Ofpe/WN9 star S119 for the purpose of obtaining abundances. The spectra cover the wavelength range 3235–6818 Å and aslit of dimensions 1″.7 × 0″.2 was placed on the brightest portion of each nebula. Full details of these observations are given in Smith et al. (1998).
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Spalding, Christopher, i Joshua N. Winn. "Tidal Erasure of Stellar Obliquities Constrains the Timing of Hot Jupiter Formation". Astrophysical Journal 927, nr 1 (1.03.2022): 22. http://dx.doi.org/10.3847/1538-4357/ac4993.
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Abstract Stars with hot Jupiters sometimes have high obliquities, which are possible relics of hot Jupiter formation. Based on the characteristics of systems with and without high obliquities, it is suspected that obliquities are tidally damped when the star has a thick convective envelope, as is the case for main-sequence stars cooler than ∼6100 K, and the orbit is within ∼8 stellar radii. A promising theory for tidal obliquity damping is the dissipation of inertial waves within the star’s convective envelope. Here, we consider the implications of this theory for the timing of hot Jupiter formation. Specifically, hot stars that currently lack a convective envelope possess one during their pre-main sequence. We find that hot Jupiters orbiting within a critical distance of ∼0.02 au from a misaligned main-sequence star lacking a thick convective envelope must have acquired their tight orbits after a few tens of millions of years in order to have retained their obliquities throughout the pre-main sequence. There are four known systems for which this argument applies–XO-3b, Corot-3b, WASP-14b, and WASP-121b–subject to uncertainties surrounding inertial wave dissipation. Moreover, we conclude that a recently identified overabundance of near-polar hot Jupiters is unlikely sculpted by tides, instead reflecting their primordial configuration. Finally, hot Jupiters arriving around cool stars after a few hundreds of millions of years likely find the host star rotating too slowly for efficient obliquity damping. We predict that the critical effective temperature separating aligned and misaligned stars should vary with metallicity, from 6300 to 6000 K as [Fe/H] varies from −0.3 to +0.3.
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Sharina, M. E., L. N. Makarova i D. I. Makarov. "Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66". Proceedings of the International Astronomical Union 14, S344 (sierpień 2018): 420–21. http://dx.doi.org/10.1017/s1743921318005550.
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AbstractWe compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.
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Buitrago, F., I. Ferreras, L. S. Kelvin, I. K. Baldry, L. Davies, J. Angthopo, S. Khochfar i in. "Galaxy and Mass Assembly (GAMA): Accurate number densities and environments of massive ultra-compact galaxies at 0.02 < z < 0.3". Astronomy & Astrophysics 619 (listopad 2018): A137. http://dx.doi.org/10.1051/0004-6361/201833785.
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Context. Massive ultra-compact galaxies (MUGs) are common at z = 2−3, but very rare in the nearby Universe. Simulations predict that the few surviving MUGs should reside in galaxy clusters, whose large relative velocities prevent them from merging, thus maintaining their original properties (namely stellar populations, masses, sizes and dynamical state). Aims. Our goal is to obtain a complete census of the MUG population at 0.02 < z < 0.3, determining the number density, population properties and environment. Methods. We have taken advantage of the high-completeness, large-area spectroscopic GAMA survey, complementing it with deeper imaging from the KiDS and VIKING surveys. We find a set of 22 bona-fide MUGs, defined as having high stellar mass (> 8 × 1010 M⊙) and compact size (Re < 2 kpc). An additional set of seven lower-mass objects (6 × 1010 < M⋆/M⊙ < 8 × 1010) are also potential candidates according to typical mass uncertainties. Results. The comoving number density of MUGs at low redshift (z < 0.3) is constrained at (1.0 ± 0.4)×10−6 Mpc−3, consistent with galaxy evolution models. However, we find a mixed distribution of old and young galaxies, with a quarter of the sample representing (old) relics. MUGs have a predominantly early or swollen disk morphology (Sérsic index 1 < n < 2.5) with high stellar surface densities (⟨Σe⟩∼1010 M⊙ Kpc−2). Interestingly, a large fraction feature close companions – at least in projection – suggesting that many (but not all) reside in the central regions of groups. Halo masses show these galaxies inhabit average-mass groups. Conclusions. As MUGs are found to be almost equally distributed among environments of different masses, their relative fraction is higher in more massive overdensities, matching the expectations that some of these galaxies fell in these regions at early times. However, there must be another channel leading some of these galaxies to an abnormally low merger history because our sample shows a number of objects that do not inhabit particularly dense environments.
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Walsh, Jeremy R., George H. Jacoby, Harald Kuntschner, Reynier F. Peletier, Marina Rejkuba, Nicholas A. Walton i Kristin A. Woodley. "NGC 5128 - a nearby laboratory for planetary nebulae in a giant early-type galaxy". Proceedings of the International Astronomical Union 7, S283 (lipiec 2011): 279–82. http://dx.doi.org/10.1017/s174392131201109x.
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AbstractNGC 5128 at 3.8 Mpc is the nearest large elliptical galaxy and is ideally suited to a detailed study of its planetary nebula population. Two spectroscopic programmes are summarised. More than 1200 PNe candidates are known from imaging campaigns in NGC 5128 and accurate radial velocities of 1070 have been measured with the VLT FLAMES/Giraffe spectrometer. From these data a variety of studies of the galaxy kinematics are enabled, such as search for PN sub-groups, representing the relics of accretion of small galaxies. Emission line spectra were observed with VLT FORS and the light element abundances determined for 40 PNe through photoionization modelling. A spread in O abundance of about 0.9 dex is found but no obvious radial gradient out to 19 kpc. Comparison of the O abundance from these PN with the metallicity for the stellar population in the neighbourhood of the PN will probe the star formation and enrichment history of the galaxy. Full results from this analysis will be presented in a forthcoming paper.
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Eliche-Moral, M. C., C. Rodríguez-Pérez, A. Borlaff, M. Querejeta i T. Tapia. "Formation of S0 galaxies through mergers". Astronomy & Astrophysics 617 (wrzesień 2018): A113. http://dx.doi.org/10.1051/0004-6361/201832911.
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Context. Major mergers are popularly considered too destructive to produce the relaxed regular structures and the morphological inner components (ICs) usually observed in lenticular (S0) galaxies.Aims. We aim to test if major mergers can produce remnants with realistic S0 morphologies.Methods. We have selected a sample of relaxed discy remnants resulting from the dissipative merger simulations of the GalMer database and derived their properties mimicking the typical conditions of current observational data. We have compared their global morphologies, visual components, and merger relics in mock photometric images with their real counterparts.Results. Only Ȉ1–2 Gyr after the full merger, we find that: 1) many remnants (67 major and 29 minor events) present relaxed structures and typical S0 or E/S0 morphologies, for a wide variety of orbits and even in gas-poor cases. 2) Contrary to popular expectations, most of them do not exhibit any morphological traces of their past merger origin under typical observing conditions and at distances as nearby as 30 Mpc. 3) The merger relics are more persistent in minor mergers than in major ones for similar relaxing time periods. 4) No major-merger S0-like remnant develops a significant bar. 5) Nearly 58% of the major-merger S0 remnants host visually detectable ICs, such as embedded inner discs, rings, pseudo-rings, inner spirals, nuclear bars, and compact sources, very frequent in real S0s too. 6) All remnants contain a lens or oval, identically ubiquitous in local S0s. 7) These lenses and ovals do not come from bar dilution in major-merger cases, but are associated with stellar halos or embedded inner discs instead (thick or thin).Conclusions. The relaxed morphologies, lenses, ovals, and other ICs of real S0s do not necessarily come from internal secular evolution, gas infall, or environmental mechanisms, as traditionally assumed, but they can result from major mergers as well.
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Cisternas, Mauricio, i Knud Jahnke. "The downplayed role of secular processes in the co-evolution of galaxies and black holes". Proceedings of the International Astronomical Union 10, H16 (sierpień 2012): 344. http://dx.doi.org/10.1017/s1743921314011168.
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AbstractAccording to the current co-evolution picture, most present-day galaxies experienced at least one phase of vigorous black hole (BH) activity in the past, during which a tight link between galaxy and BH gets established. While during the last two decades we have witnessed tremendous progress in the field, additional robust observational constraints are required on how galaxy and BH related at earlier times, and which mechanisms are responsible for triggering these BH growth phases. In our recent studies, we analyzed a large sample of active galactic nuclei (AGN) out to z ~ 1 from the COSMOS survey (Scoville et al. 2007), allowing us to study in detail growing BHs together with their host galaxies. In Cisternas et al. (2011b) we found that, for a sample of 32 active galaxies at z ~ 0.7, BH mass scales with total galaxy stellar mass in the same way as it does locally, at z = 0, with galactic bulge mass. I will argue that for these galaxies to obey the local relation only a disk-to-bulge stellar mass redistribution is needed, likely driven by passive secular evolution. I will also present the results from Cisternas et al. (2011a), aiming to understand the relevance of major mergers as AGN activity triggering mechanisms. By looking for merging signatures on the morphologies of 140 AGN (some examples shown in Figure 1), and comparing them with a sample of over 1200 matched inactive galaxies, we found that the merger fraction between samples is statistically the same, at roughly 15%. Together with the fact that the majority of the AGN host galaxies are disk-dominated, unlikely relics of a recent major merger, these results are the strongest evidence to date that secular evolution rather than major merging has dominated BH fueling at least since z ~ 1.
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Reefe, Michael, Shobita Satyapal, Remington O. Sexton, Nathan J. Secrest, William Matzko, Emma Schwartzman, Kristina Nyland i in. "Nuclear Activity in the Low-metallicity Dwarf Galaxy SDSS J0944-0038 : A Glimpse into the Primordial Universe". Astrophysical Journal Letters 946, nr 2 (30.03.2023): L38. http://dx.doi.org/10.3847/2041-8213/acb4e4.
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Abstract Local low-metallicity dwarf galaxies are relics of the early universe and are thought to hold clues into the origins of supermassive black holes. While recent studies are uncovering a growing population of active galactic nuclei (AGNs) in dwarf galaxies, the vast majority reside in galaxies with solar or supersolar metallicities and stellar masses comparable to that of the LMC. Using Multi-Unit Spectroscopic Explorer (MUSE) and Very Large Telescope observations, we report the detection of [Fe x] λ6374 coronal line emission and a broad Hα line in the nucleus of SDSS J094401.87−003832.1, a nearby (z = 0.0049) metal-poor dwarf galaxy almost 500 times less massive than the LMC. Unlike the emission from the lower-ionization nebular lines, the [Fe x] λ6374 emission is compact and centered on the brightest nuclear source, with a spatial extent of ≈100 pc, similar to that seen in well-known AGNs. The [Fe x] luminosity is ≈1037 erg s−1, within the range seen in previously identified AGNs in the dwarf-galaxy population. The [Fe x] emission has persisted over the roughly 19 yr time period between the SDSS and MUSE observations, ruling out supernovae as the origin for the emission. The FWHM of the broad component of the Hα line is 446 ± 17 km s−1 and its luminosity is ≈1.5 × 1038 erg s−1, corresponding to a black hole mass of ≈ 3150 M ⊙, in line with its stellar mass if virial mass relations and black hole–galaxy scaling relations apply in this mass regime. These observations, together with previously reported multiwavelength observations, can most plausibly be explained by the presence of an accreting intermediate-mass black hole in a primordial galaxy analog.
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Sapienza, V., M. Miceli, G. Peres, F. Bocchino, S. Orlando, E. Greco, J. A. Combi, F. García i M. Sasaki. "X-ray emitting structures in the Vela SNR: ejecta anisotropies and progenitor stellar wind residuals". Astronomy & Astrophysics 649 (maj 2021): A56. http://dx.doi.org/10.1051/0004-6361/202140412.
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Context. The Vela supernova remnant (SNR) shows several ejecta fragments (or shrapnel) protruding beyond the forward shock, which are most likely relics of anisotropies that developed during the supernova (SN) explosion. Recent studies have revealed high Si abundance in two shrapnel (shrapnel A and G), located in opposite directions with respect to the SNR center. This suggests the possible existence of a Si-rich jet-counterjet structure, similar to that observed in the SNR Cassiopea A. Aims. We analyzed an XMM-Newton observation of a bright clump, behind shrapnel G, which lies along the direction connecting shrapnel A and G. The aim is to study the physical and chemical properties of this clump to ascertain whether it is part of this putative jet-like structure. Methods. We produced background-corrected and adaptively-smoothed count-rate images and median photon energy maps, and performed a spatially resolved spectral analysis. Results. We identified two structures with different physical properties. The first one is remarkably elongated along the direction connecting shrapnel A and G. Its X-ray spectrum is much softer than that of the other two shrapnel, to the point of hindering the determination of the Si abundance; however, its physical and chemical properties are consistent with those of shrapnel A and shrapnel G. The second structure, running along the southeast-northwest direction, has a higher temperature and appears similar to a thin filament. By analyzing the ROSAT data, we have found that this filament is part of a very large and coherent structure that we identified in the western rim of the shell. Conclusions. We obtained a thorough description of the collimated, jet-like tail of shrapnel G in Vela SNR. In addition we discovered a coherent and very extended feature roughly perpendicular to the jet-like structure that we interpret as a signature of an earlier interaction of the remnant with the stellar wind of its progenitor star. The peculiar Ne/O ratio we found in the wind residual may be suggestive of a Wolf-Rayet progenitor for Vela SNR, though further analysis is required to address this point.
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Bonatto, Charles, Ana L. Chies-Santos, Paula R. T. Coelho, Jesús Varela, Søren S. Larsen, A. Javier Cenarro, Izaskun San Roman i in. "J-PLUS: A wide-field multi-band study of the M 15 globular cluster". Astronomy & Astrophysics 622 (luty 2019): A179. http://dx.doi.org/10.1051/0004-6361/201732441.
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Context. As a consequence of internal and external dynamical processes, Galactic globular clusters (GCs) have properties that vary radially. Wide-field observations covering the entire projected area of GCs out to their tidal radii (rtidal) can therefore give crucial information on these important relics of the Milky Way formation era. Aims. The Javalambre Photometric Local Universe Survey (J-PLUS) provides wide field-of-view (2 deg2) images in 12 narrow, intermediate and broad-band filters optimized for stellar photometry. Here we have applied J-PLUS data for the first time for the study of Galactic GCs using science verification data obtained for the very metal-poor ([Fe/H] ≈−2.3) GC M 15 located at ~10 kpc from the Sun. Previous studies based on spectroscopy found evidence of multiple stellar populations (MPs) through their different abundances of C, N, O, and Na. Our J-PLUS data provide low-resolution spectral energy distributions covering the near-UV to the near-IR, allowing us to instead search for MPs based on pseudo-spectral fitting diagnostics. Methods. We have built and discussed the stellar radial density profile (RDP) and surface brightness profiles (SBPs) reaching up to rtidal. Since J-PLUS FoV is larger than M 15’s rtidal, the field contamination can be properly taken into account. We also demonstrated the power of J-PLUS unique filter system by showing colour-magnitude diagrams (CMDs) using different filter combinations and for different cluster regions. Results. J-PLUS photometric quality and depth are good enough to reach the upper end of M 15’s main-sequence. CMDs based on the colours (u − z) and (J0378 − J0861) are found to be particularly useful to search for splits in the sequences formed by the upper red giant branch (RGB) and asymptotic giant branch (AGB) stars. We interpret these split sequences as evidence for the presence of MPs. Furthermore, we show that the (u − z) × (J0378 − g) colour–colour diagram allows us to distinguish clearly between field and M 15 stars, which is important to minimize the sample contamination. Conclusions. The J-PLUS filter combinations (u − z) and (J0378 − J0861), which are sensitive to metal abundances, are able to distinguish different sequences in the upper RGB and AGB regions of the CMD of M 15, showing the feasibility of identifying MPs without the need of spectroscopy. This demonstrates that the J-PLUS survey will have sufficient spatial coverage and spectral resolution to perform a large statistical study of GCs through multi-band photometry in the coming years.
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Haan, Sebastian, Jason Surace, Lee Armus i Aaron Evans. "Probing the Build-Up of Stellar Mass in the Center of IR Luminous Major Mergers with HST". Proceedings of the International Astronomical Union 8, S295 (sierpień 2012): 311. http://dx.doi.org/10.1017/s1743921313005139.
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AbstractInteractions and mergers are important drivers of galaxy evolution, transform spiral galaxies into massive ellipticals, and fuel both powerful starbursts and massive nuclear black holes. In particular one galaxy population, namely Luminous Infrared Galaxies (LIRGs), are believed to be responsible for most of the star formation that happened in the history of the universe (see e.g. Le Floch et al. 2005, Caputi et al. 2007, Magnelli et al. 2009), and hence represent a critical phase in the evolution of galaxies where most of the galaxies mass is building up. During a merger process, violent relaxation acts on stars present in gas-rich progenitor disks, while the centers are structured by the relics of dissipational, compact starbursts, imprinting a central “extra light” component or “cusp” into the surface brightness profiles of merger remnants. Our HST NICMOS/WFC3 imaging program of the 88 most luminous LIRGs in the Great Observatories Allsky LIRG Survey (GOALS, see Armus et al. 2009) shows that the central luminosity surface density in nearby LIRGs increases significantly along the merger sequence, indicating that the gas inflow fuels a central starburst and subsequently builds a compact stellar cusp (Haan et al. 2011). A large fraction of all galaxies in our sample possess double or multiple nuclei (~63%). Half of these double nuclei are not visible in the HST B-band images due to dust obscuration, which implies strong limitations on the ability to detect the true nuclear structures of luminous infrared galaxies at high-redshift (z >2) and may explain some of the apparent discrepancy of the LIRG population and merger ratio between local and high-redshift galaxies. We find that ULIRGs (log[LIR/L⊙] > 12.0) have significantly smaller nuclear separations than LIRGs (log[LIR/L⊙] = 11.4 — 12.0) with a median value of 1.2 kpc and 6.7 kpc, respectively. In our sample, merger (regardless of whether LIRG or ULIRG) seem to be prevalent at two time scales (based on the projected nuclear separation and mass ratio of the nuclei): First, at a remaining merger time scale of 0.3<[t-tmerg]<1.3 Gyr (53% of mergers in our sample), and second, at [t-tmerg]~ 0 (26%), likely representing the first passage of interacting galaxies and the final nuclear coalescence, respectively, with a post-merger time (starburst phase after the nuclei merged) of roughly 300 Myrs.
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CLEMENTINI, GISELLA, i RAFFAELE GRATTON. "The oldest stars and the age of the Universe". European Review 10, nr 2 (maj 2002): 237–48. http://dx.doi.org/10.1017/s1062798702000170.
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The Big Bang created primordial material from which the first stars formed. These stars exploded as supernovae and polluted the material from which subsequent generations of stars were made. Astronomers have had difficulty in finding stars made of the pure Big Bang material, but they have found stars with very little polluting material. The age of these cosmological relics of the first eras sets a lower limit for the age of the Universe we live in. European astronomers and their colleagues worldwide have joined in the effort to discover and date these, the oldest stars, and cast a glance into the obscure phases between the very first seconds of the existence of the Universe and the epoch at which galaxies and clusters of stars matured. Many independent techniques have been devised to date the oldest stars and stellar systems in the Universe. Some of them are briefly reviewed. The age of the oldest stars is now converging on a value in the range from 12 to 15 thousand million years. However, a large uncertainty still exists and a value as a large as 17 to18 thousand million years cannot be totally ruled out. Such a large value would be difficult to reconcile with the age of the Universe based on cosmological data. Significant improvements in the uncertainties of this situation are expected from the 8–1 m telescopes and space missions of the next decade.
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Weisz, Daniel R., Alessandro Savino i Andrew E. Dolphin. "On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II". Astrophysical Journal 948, nr 1 (1.05.2023): 50. http://dx.doi.org/10.3847/1538-4357/acc328.
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Abstract Using color–magnitude diagrams from deep archival Hubble Space Telescope imaging, we self-consistently measure the star formation history of Eridanus II (Eri II), the lowest-mass galaxy (M ⋆(z = 0) ∼ 105 M ⊙) known to host a globular cluster (GC), and the age, mass, and metallicity of its GC. The GC (∼13.2 ± 0.4 Gyr, 〈[Fe/H]〉 = −2.75 ± 0.2 dex) and field (mean age ∼13.5 ± 0.3 Gyr, 〈[Fe/H]〉 = −2.6 ± 0.15 dex) have similar ages and metallicities. Both are reionization-era relics that formed before the peak of cosmic star and GC formation (z ∼ 2–4). The ancient star formation properties of Eri II are not extreme and appear similar to z = 0 dwarf galaxies. We find that the GC was ≲4 times more massive at birth than today and was ∼10% of the galaxy's stellar mass at birth. At formation, we estimate that the progenitor of Eri II and its GC had M UV ∼ −7 to −12, making it one of the most common type of galaxy in the early universe, though it is fainter than direct detection limits, absent gravitational lensing. Archaeological studies of GCs in nearby low-mass galaxies may be the only way to constrain GC formation in such low-mass systems. We discuss the strengths and limitations in comparing archaeological and high-redshift studies of cluster formation, including challenges stemming from the Hubble Tension, which introduces uncertainties into the mapping between age and redshift.
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Yang, Xiaolong, i Jun Yang. "Intermediate-Mass Black Holes: The Essential Population to Explore the Unified Model for Accretion and Ejection Processes". Galaxies 11, nr 2 (6.04.2023): 53. http://dx.doi.org/10.3390/galaxies11020053.
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We study radio and X-ray emissions from intermediate-mass black holes (IMBHs) and explore the unified model for accretion and ejection processes. The radio band survey of IMBH (candidate) hosted galaxies indicates that only a small fraction (∼0.6%) of them are radio-band active. In addition, very long baseline interferometry observations reveal parsec-scale radio emission of IMBHs, further resulting in a lower fraction of actively ejecting objects (radio emission is produced by IMBHs other than hosts), which is consistent with a long quiescent state in the evolution cycle of IMBHs. Most (75%, i.e., 3 out of 4 samples according to a recent mini-survey) of the radio-emitting IMBHs are associated with radio relics and there is also evidence of dual radio blobs from episodic ejecting phases. Taking the radio emission and the corresponding core X-ray emission of IMBH, we confirm a universal fundamental plane relation (FMP) of black hole activity. Furthermore, state transitions can be inferred by comparing a few cases in XRBs and IMBHs in FMP, i.e., both radio luminosity and emission regions evolve along these state transitions. These signatures and evidence suggest an analogy among all kinds of accretion systems which span from stellar mass to supermassive black holes, hinting at unified accretion and ejection physics. To validate the unified model, we explore the correlation between the scale of outflows (corresponding to ejection powers) and the masses of central engines; it shows that the largest scale of outflows LS^out follows a power-law correlation with the masses of accretors Mcore, i.e., logLS^out=(0.73±0.01)logMcore−(3.34±0.10). In conclusion, this work provides evidence to support the claim that the ejection (and accretion) process behaves as scale-invariant and their power is regulated by the masses of accretors.
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Christlieb, N., M. S. Bessell, T. C. Beers, B. Gustafsson, A. Korn, P. S. Barklem, T. Karlsson, M. Mizuno–Wiedner i S. Rossi. "A stellar relic from the early Milky Way". Nature 419, nr 6910 (31.10.2002): 904–6. http://dx.doi.org/10.1038/nature01142.
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Alamo-Martínez, Karla A., Ana L. Chies-Santos, Michael A. Beasley, Rodrigo Flores-Freitas, Cristina Furlanetto, Marina Trevisan, Allan Schnorr-Müller, Ryan Leaman i Charles J. Bonatto. "Globular cluster systems of relic galaxies". Monthly Notices of the Royal Astronomical Society 503, nr 2 (25.02.2021): 2406–22. http://dx.doi.org/10.1093/mnras/stab538.
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ABSTRACT We analyse the globular cluster (GC) systems of a sample of 15 massive, compact early-type galaxies (ETGs), 13 of which have already been identified as good relic galaxy candidates on the basis of their compact morphologies, old stellar populations and stellar kinematics. These relic galaxy candidates are likely the nearby counterparts of high-redshift red nugget galaxies. Using F814W (≈I) and F160W (≈H) data from the WFC3 camara onboard the Hubble Space Telescope, we determine the total number, luminosity function, specific frequency, colour, and spatial distribution of the GC systems (GCSs). We find lower specific frequencies (SN < 2.5 with a median of SN = 1) than ETGs of comparable mass. This is consistent with a scenario of rapid, early dissipative formation, with relatively low levels of accretion of low-mass, high-SN satellites. The GC half-number radii are compact, but follow the relations found in normal ETGs. We identify an anticorrelation between the specific angular momentum (λR) of the host galaxy and the (I − H) colour distribution width of their GCSs. Assuming that λR provides a measure of the degree of dissipation in massive ETGs, we suggest that the (I − H) colour distribution width can be used as a proxy for the degree of complexity of the accretion histories in these systems.
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Jerabkova, Tereza, Henri M. J. Boffin, Giacomo Beccari i Richard I. Anderson. "A stellar relic filament in the Orion star-forming region". Monthly Notices of the Royal Astronomical Society 489, nr 3 (20.09.2019): 4418–28. http://dx.doi.org/10.1093/mnras/stz2315.
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ABSTRACT We report the discovery of the oldest stellar substructure in the Orion star-forming region (OSFR), the Orion relic filament. The relic filament is physically associated with the OSFR, as demonstrated by Gaia DR2 photometry and astrometry, as well as by targeted radial velocity follow-up observations of a bright subsample of proper motion-selected candidate members. Gaia DR2 parallaxes place the Orion relic filament in the more distant part of the OSFR, ∼430 pc from the Sun. Given its age, velocity dispersion, spatial extent, and shape, it is not possible for the Orion relic filament to have formed as a single stellar cluster, even taking into account residual gas expulsion. The relic filament is also too young to be a tidal stream, because Galactic tides act on much longer time-scales, of the order of 100 Myr. It therefore appears likely that the structure formed from a molecular cloud filament similar to Orion A in the OSFR and retained its morphology despite decoupling from its natal gas. Hence, the Orion relic filament bears witness to the short-lived evolutionary phase between gas removal and dispersion owing to shears and tides, and provides crucial new insights into how stars are formed in molecular clouds.
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Ashida, Yosuke, i Ken’ichiro Nakazato. "Exploring the Fate of Stellar Core Collapse with Supernova Relic Neutrinos". Astrophysical Journal 937, nr 1 (1.09.2022): 30. http://dx.doi.org/10.3847/1538-4357/ac8a46.
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Abstract Core collapse of massive stars leads to different fates for various physical factors, which gives different spectra of the emitted neutrinos. We focus on the supernova relic neutrinos (SRNs) as a probe to investigate the stellar collapse fate. We present the SRN fluxes and event rate spectra at a detector for three resultant states after stellar core collapse, the typical mass neutron star, the higher mass neutron star, or the failed supernova forming a black hole, based on different nuclear equations of state. Then possible SRN fluxes are formed as mixtures of the three components. We also show the expected sensitivities at the next-generation water-based Cherenkov detectors, SK-Gd and Hyper-Kamiokande, as constraining the mixture fractions. This study provides a practical example of extracting astrophysical constraints through SRN measurement.
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Flores-Freitas, Rodrigo, Ana L. Chies-Santos, Cristina Furlanetto, María Emilia De Rossi, Leonardo Ferreira, Lucas J. Zenocratti i Karla A. Alamo-Martínez. "Relic galaxy analogues in TNG50 simulation: the formation pathways of surviving red nuggets in a cosmological simulation". Monthly Notices of the Royal Astronomical Society 512, nr 1 (4.02.2022): 245–64. http://dx.doi.org/10.1093/mnras/stac187.
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ABSTRACT Relic galaxies are massive compact quiescent galaxies that formed at high-redshift and remained almost unchanged since then. In this work, we search for analogues to relic galaxies in the TNG50 cosmological simulations to understand relic formation and test the ability of TNG50 to reproduce such rare objects. Using stellar mass, age, radius, quiescence, and stellar assembly criteria, we find five subhaloes in TNG50 that could be potential relic analogues. We compare their properties with other constraints imposed by a sample of 13 observed relic galaxies. We find one analogue in TNG50 that simultaneously satisfies most of the available observational constraints, such as metallicity and morphology. It also shows similarities to the confirmed relic NGC 1277, regarding environment and dark matter fraction. By taking into account a degree of relicness, a second relic analogue may also be considered. However, the central parts of the brightness and density profiles of the analogues are less steep than that of real relic galaxies, possibly due to limited numerical resolution. We identify two formation pathways of relic analogues in TNG50 depending on their environment: they either have their remaining gas stripped during the infall into a cluster at z ≲ 1.2 or consume it before z > 1.5. They are then deprived of significant star formation, leaving their stellar populations almost unaltered during the last 9 Gyr. We also find that the analogue progenitors at z ∼ 4 inhabit more massive haloes than progenitors of quiescent galaxies with similar stellar mass at z ∼ 0.
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Däppen, Werner. "Stellar Seismology". International Astronomical Union Colloquium 121 (1990): 357–70. http://dx.doi.org/10.1017/s0252921100068068.
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AbstractStellar acoustic oscillation frequencies will likely be accurately observed in the near future, in analogy to the well-known solar five-minute oscillation frequencies. Of course, we will never expect the wealth of solar data, which is a result of spatial resolution. We will therefore not be able to solve the inverse problem, that is to probe physical quantities as functions of depth, and the low number of anticipated observed frequencies will make an unambiguous mode identification difficult. Despite this restriction to the forward problem, however, observed stellar oscillation frequencies will become valuable constraints for the determination of stellar parameters. One should not forget that the present knowledge of stellar ages and compositions relies on the calibration of theoretical models (matching effective temperature and luminosity). Additional observational constraints will improve these calibrations, even if the theoretical models themselves are not questioned. We hope, however, that the observation of stellar oscillation frequencies will also lead to improvements in the physics of stellar models, in analogy to the solar case. Again, of course, stellar seismologists will be less ambitious than helioseismologists, since there are more open parameters in stellar models. However, stellar observations will allow tests of models with different age and composition.
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Baraffe, I., M. Viallet i R. Walder. "Towards a New Generation of Multi-Dimensional Stellar Models: Can Our Models Meet the Challenges?" Proceedings of the International Astronomical Union 7, S285 (wrzesień 2011): 138. http://dx.doi.org/10.1017/s1743921312000464.
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SummaryThe talk described the first steps of development of a new multi-dimensional time-implicit code devoted to the study of hydrodynamical processes in stellar interiors. The main motivation stemmed from the fact that our physical understanding of stellar interiors and evolution still largely relies on one-dimensional calculations. The description of complex physical processes like time-dependent turbulent convection, rotation or MHD processes mostly relies on simplified, phenomenological approaches, with a predictive power hampered by the use of several free parameters. These approaches have now reached their limits in the understanding of stellar structure and evolution. The development of multi-dimensional hydrodynamical simulations becomes crucial to progress in the field of stellar physics and to meet the enormous observational efforts aimed at producing data of unprecedented quality (COROT, Kepler GAIA). The code we are developing solves the hydrodynamical equations in spherical geometry and is based on the finite volume method. The talk presented a global simulation of turbulent convective motions in a cold giant envelope, covering 80% in radius of the stellar structure. Our first developments show that the use of an implicit scheme applied to a stellar evolution context is perfectly thinkable.
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Mathews, G. J., L. Boccioli, J. Hidaka i T. Kajino. "Review of uncertainties in the cosmic supernova relic neutrino background". Modern Physics Letters A 35, nr 25 (15.07.2020): 2030011. http://dx.doi.org/10.1142/s0217732320300116.
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We review the computation of and associated uncertainties in the current understanding of the relic neutrino background due to core-collapse supernovae, black hole formation and neutron star merger events. We consider the current status of uncertainties due to the nuclear equation of state (EoS), the progenitor masses, the source supernova neutrino spectrum, the cosmological star formation rate, the stellar initial mass function, neutrino oscillations, and neutrino self-interactions. We summarize the current viability of future neutrino detectors to distinguish the nuclear EoS and the temperature of supernova neutrinos via the detected relic supernova neutrino spectrum.
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Weiss, Nigel O. "Solar and Stellar Dynamos". Proceedings of the International Astronomical Union 6, S271 (czerwiec 2010): 247–60. http://dx.doi.org/10.1017/s1743921311017674.
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AbstractRecords of the solar magnetic field extend back for millennia, and its surface properties have been observed for centuries, while helioseismology has recently revealed the Sun's internal rotation and the presence of a tachocline. Dynamo theory has developed to explain these observations, first with idealized models based on mean-field electrodynamics and, more recently, by direct numerical simulation, notably with the ASH code at Boulder. These results, which suggest that cyclic activity relies on the presence of the tachocline, and that its modulation is chaotic (rather than stochastic), will be critically reviewed. Similar theoretical approaches have been followed in order to explain the magnetic properties of other main-sequence stars, whose fields can be mapped by Zeeman-Doppler imaging. Of particular interest is the behaviour of fully convective, low-mass stars, which lack any tachocline but are nevertheless extremely active.
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Sato, Koichi, Koichi Yokoyama, Kiyotaka Tanikawa i Yukio Goto. "The Observations of the Earth Rotation and the Stellar System". Symposium - International Astronomical Union 109 (1986): 133–41. http://dx.doi.org/10.1017/s0074180900076488.
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The fundamental reference of the Earth rotation observation by the method of optical astrometry, such as VZT, PZT, astrolabe, transit instrument and so on, relies upon the stellar system. Hence the stellar positions and proper motions, and the celestial reference coordinate system are essential to preserve the system of the Earth orientation parameters determined by the optical astrometry.
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Ortolani, S., E. V. Held, D. Nardiello, S. O. Souza, B. Barbuy, A. Pérez-Villegas, S. Cassisi, E. Bica, Y. Momany i I. Saviane. "Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)". Astronomy & Astrophysics 627 (lipiec 2019): A145. http://dx.doi.org/10.1051/0004-6361/201935726.
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Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d⊙ = 8.75 ± 0.12 kpc and a reddening of E(B−V) = 0.81+0.02−0.02. The best-fitting BaSTI isochrones correspond to an age of 12.70+0.72−0.69 Gyr and a metallicity of [Fe/H] = −1.11+0.03−0.03. Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves.