arXiv subjects

I. Chilingarian

Publications and source records attributed to I. Chilingarian.

13 recordsLinked to original sources

arXiv2024

Optical spectroscopy of host-galaxies of intermediate mass black holes: evolution of central black holes

Intermediate-mass black holes (IMBHs) with masses below ($2 \times 10^5 M_{\odot}$) are pivotal in understanding the origin and growth mechanisms of supermassive black holes (SMBHs) in galactic nuclei. This study focuses on the search and detailed analysis of central lightweight black holes in various galaxies. An expanded sample of IMBH candidates was selected from the RCSED optical spectral catalog, followed by refined spectral observations using large telescopes, including the Magellan, SALT, Keck and CMO telescopes. Analyzing over 70 spectra, we obtained accurate virial masses, stellar population parameters, and kinematics. One significant finding includes the detection of a binary black hole system with masses ($1.7 \times 10^5 M_{\odot})$ and $(1.4 \times 10^6 M_{\odot}$). Our results indicate that IMBHs and their low-mass SMBH counterparts do not necessarily co-evolve with their host galaxies, suggesting super-Eddington accretion as a dominant growth mechanism. This research enhances the precision of virial mass estimates and offers new insights into the $M_{BH} - \sigma_{bulge}$ relation, potentially impacting future high-redshift SMBH observations using next-generation facilities.

astro-ph.GA↗

arXiv2019

Increasing the Discovery Space in Astrophysics - A Collation of Six Submitted White Papers

We write in response to the call from the 2020 Decadal Survey to submit white papers illustrating the most pressing scientific questions in astrophysics for the coming decade. We propose exploration as the central question for the Decadal Committee's discussions.The history of astronomy shows that paradigm changing discoveries are not driven by well formulated scientific questions, based on the knowledge of the time. They were instead the result of the increase in discovery space fostered by new telescopes and instruments. An additional tool for increasing the discovery space is provided by the analysis and mining of the increasingly larger amount of archival data available to astronomers. Revolutionary observing facilities, and the state of the art astronomy archives needed to support these facilities, will open up the universe to new discovery. Here we focus on exploration for compact objects and multi messenger science. This white paper includes science examples of the power of the discovery approach, encompassing all the areas of astrophysics covered by the 2020 Decadal Survey.

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arXiv2019

Astro2020 Science White Paper: The Next Decade of Astroinformatics and Astrostatistics

Over the past century, major advances in astronomy and astrophysics have been largely driven by improvements in instrumentation and data collection. With the amassing of high quality data from new telescopes, and especially with the advent of deep and large astronomical surveys, it is becoming clear that future advances will also rely heavily on how those data are analyzed and interpreted. New methodologies derived from advances in statistics, computer science, and machine learning are beginning to be employed in sophisticated investigations that are not only bringing forth new discoveries, but are placing them on a solid footing. Progress in wide-field sky surveys, interferometric imaging, precision cosmology, exoplanet detection and characterization, and many subfields of stellar, Galactic and extragalactic astronomy, has resulted in complex data analysis challenges that must be solved to perform scientific inference. Research in astrostatistics and astroinformatics will be necessary to develop the state-of-the-art methodology needed in astronomy. Overcoming these challenges requires dedicated, interdisciplinary research. We recommend: (1) increasing funding for interdisciplinary projects in astrostatistics and astroinformatics; (2) dedicating space and time at conferences for interdisciplinary research and promotion; (3) developing sustainable funding for long-term astrostatisics appointments; and (4) funding infrastructure development for data archives and archive support, state-of-the-art algorithms, and efficient computing.

astro-ph.IM↗

arXiv2018

The Temperature and Ionization of Unshocked Ejecta in Cas A

The supernova remnant Cassiopeia A (Cas A) is one of the few remnants in which it is possible to observe unshocked ejecta. A deep 1.64 micron image of Cas A shows a patch of diffuse emission from unshocked ejecta, as well as brighter emission from Fast-Moving Knots and Quasi-Stationary Flocculi. Emission at 1.64 micron is usually interpreted as [Fe II] emission, and spectra of the bright knots confirm this by showing the expected emission in other [Fe II] lines. We performed NIR spectroscopy on the diffuse emission region and found that the unshocked ejecta emission does not show those lines, but rather the [Si I] 1.607 micron line. This means that the 1.64 micron line from the unshocked ejecta may be the [Si I] 1.645 line from the same upper level, rather than [Fe II]. We find that the [Si I] line is formed by recombination, and we use the [Si I] to [Si II] ratio to infer a temperature about 100 K, close to the value assumed for analysis of low frequency radio absorption and that inferred from emission by cool dust. Our results constrain estimates of Cas A's total mass of unshocked ejecta that are extremely sensitive to temperature assumptions, but they do not resolve the ambiguity due to clumping.

astro-ph.GA↗

arXiv2017

iPTF15eqv: Multi-wavelength Exposé of a Peculiar Calcium-rich Transient

The progenitor systems of the class of "Ca-rich transients" is a key open issue in time domain astrophysics. These intriguing objects exhibit unusually strong calcium line emissions months after explosion, fall within an intermediate luminosity range, are often found at large projected distances from their host galaxies, and may play a vital role in enriching galaxies and the intergalactic medium. Here we present multi-wavelength observations of iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that bridge those observed in Ca-rich transients and Type Ib/c supernovae. iPTF15eqv has among the highest [Ca II]/[O I] emission line ratios observed to date, yet is more luminous and decays more slowly than other Ca-rich transients. Optical and near-infrared photometry and spectroscopy reveal signatures consistent with the supernova explosion of a < 10 solar mass star that was stripped of its H-rich envelope via binary interaction. Distinct chemical abundances and ejecta kinematics suggest that the core collapse occurred through electron capture processes. Deep limits on possible radio emission made with the Jansky Very Large Array imply a clean environment ($n <$ 0.1 cm$^{-3}$) within a radius of $\sim 10^{17}$ cm. Chandra X-ray Observatory observations rule out alternative scenarios involving tidal disruption of a white dwarf by a black hole, for masses > 100 solar masses). Our results challenge the notion that spectroscopically classified Ca-rich transients only originate from white dwarf progenitor systems, complicate the view that they are all associated with large ejection velocities, and indicate that their chemical abundances may vary widely between events.

astro-ph.HE↗

arXiv2016

Young Galaxy Candidates in the Hubble Frontier Fields - III. MACSJ0717.5+3745

In this paper we present the results of our search for and study of $z \gtrsim 6$ galaxy candidates behind the third Frontier Fields (FF) cluster, MACSJ0717.5+3745, and its parallel field, combining data from Hubble and Spitzer. We select 39 candidates using the Lyman Break technique, for which the clear non-detection in optical make the extreme mid-$z$ interlopers hypothesis unlikely. We also take benefit from $z \gtrsim 6$ samples selected using previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the constraints on the properties of very high-redshift objects. We compute the redshift and the physical properties, such emission lines properties, star formation rate, reddening, and stellar mass for all Frontier Fields objects from their spectral energy distribution using templates including nebular emission lines. We study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass, and between the size and the UV luminosity of our candidates. The analysis of the evolution of the UV Luminosity Function with redshift seems more compatible with an evolution of density. Moreover, no robust $z\ge$8.5 object is selected behind the cluster field, and few $z$$\sim$9 candidates have been selected in the two previous datasets from this legacy survey, suggesting a strong evolution in the number density of galaxies between $z$$\sim$8 and 9. Thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with L$>$0.03L$^{\star}$, and confirm the strong decrease observed between $z$$\sim$8 and 9.

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arXiv2013

The portrait of Malin 2: a case study of a giant low surface brightness galaxy

The low surface brightness disc galaxy Malin2 challenges the standard theory of galaxy evolution by its enormous total mass ~2 10^12 Ms which must have been formed without recent major merger events. The aim of our work is to create a coherent picture of this exotic object by using the new optical multicolor photometric and spectroscopic observations at Apache Point Observatory as well as archival datasets from Gemini and wide-field surveys. We performed the Malin2 mass modelling, estimated the contribution of the host dark halo and found that it had acquired its low central density and the huge isothermal sphere core radius before the disc subsystem was formed. Our spectroscopic data analysis reveals complex kinematics of stars and gas in the very inner region. We measured the oxygen abundance in several clumps and concluded that the gas metallicity decreases from the solar value in the centre to a half of that at 20-30 kpc. We found a small satellite and measured its mass (1/500 of the host galaxy) and gas metallicity. One of the unique properties of Malin2 turned to be the apparent imbalance of ISM: the molecular gas is in excess with respect to the atomic gas for given values of the gas equilibrium turbulent pressure. We explain this imbalance by the presence of a significant portion of the dark gas not observable in CO and the Hi 21 cm lines. We also show that the depletion time of the observed molecular gas traced by CO is nearly the same as in normal galaxies. Our modelling of the UV-to-optical spectral energy distribution favours the exponentially declined SFH over a single-burst scenario. We argue that the massive and rarefied dark halo which had formed before the disc component well describes all the observed properties of Malin2 and there is no need to assume additional catastrophic scenarios proposed previously to explain the origin of giant LSB galaxies. [Abbreviated]

astro-ph.CO↗

arXiv2013

The new technique for the determination of the stellar initial mass function of unresolved stellar populations

We present the new technique for the determination of the low-mass slope of the stellar mass function from the pixel-space fitting of integrated light spectra. This technique is the extension of the NBursts full spectral fitting technique. It can be used to constrain the stellar initial mass function (IMF) of compact stellar systems having high relaxation timescales (Hubble time or more). We used Monte-Carlo simulations with mock spectra to test the technique and conclude that: (1) age, metallicity, and IMF can be very precisely determined in the first "unrestricted" variant of the code for high signal-to-noise datasets (S/N=100, R=7000 give the uncertainty of alpha of about 0.1); (2) adding the M/L information significantly improves the precision and reduces the degeneracies, however systematic errors in M/L will translate into offsets in the IMF slope.

astro-ph.IM↗

arXiv2011

A complex stellar line-of-sight velocity distribution in the lenticular galaxy NGC 524

We present the detailed study of the stellar and gaseous kinematics of the luminous early-type galaxy NGC 524 derived from the long-slit spectroscopic observations obtained with the Russian 6-m telescope and the IFU data from the SAURON survey. The stellar line-of-sight velocity distribution (LOSVD) of NGC 524 exhibits strong asymmetry. We performed the comprehensive analysis of the LOSVD using two complementary approaches implemented on top of the nbursts full spectral fitting technique, (a) a nonparametric LOSVD recovery and (b) a parametric recovery of two Gaussian kinematical components having different stellar populations. We discuss the origin of the complex stellar LOSVD of NGC 524.

astro-ph.CO↗

arXiv2009

Internal Kinematics and Stellar Populations of the Poststarburst+AGN Galaxy SDSS J230743.41+152558.4

We present the first 3D spectroscopic observations of a nearby HI detected poststarburst, or E+A, galaxy, SDSS J230743.41+152558.4, obtained with the VIMOS IFU spectrograph at ESO VLT. Using the NBursts full spectral fitting technique, we derive maps of stellar kinematics, age, and metallicity out to 2-3 half-light radii. Our analysis reveals a large-scale rapidly rotating disc (v_circ = 300km/s) with a positive age gradient (0.6 to 1.5 Gyr), and a very metal-rich central region ([Fe/H]=+0.25 dex). If a merger or interaction is responsible for triggering the starburst, the presence of this undisturbed disc suggests a minor merger with a gas-rich satellite as the most plausible option, rather than a disruptive major merger. We find spectroscopic evidence for the presence of a LINER or AGN. This is an important clue to the feedback mechanism that truncated the starburst. The presently observed quiescent phase may well be a temporary episode in the galaxy's life. SDSS J230743.41+152558.4 is gas-rich and may restart forming stars, again becoming blue before finally settling at the red sequence.

astro-ph.GA↗

arXiv2007

Chemodynamical evolution of interacting galaxies: the GalMer view

We have undertaken a large set of simulations of galaxy interactions and mergers (GalMer Project) in order to study the physical processes related to galaxy encounters. All morphological types along the Hubble sequence are considered in the initial conditions of the two colliding galaxies, with varying bulge-to-disk ratios and gas mass fractions. Different types of orbits are simulated, direct and retrograde, according to the initial relative energy and impact parameter. The self gravity of stars, gas and dark matter is taken into account through a tree-code algorithm, the gas hydrodynamics through SPH. Star formation is included adopting a density-dependent Schmidt law. This wide library of galaxy interactions and mergers, containing, at present, about 900 simulations of major encounters, represents an unique tool to investigate statistically the chemodynamical evolution of interacting systems. In the following, we present and discuss some results obtained exploring the dataset, together with some future perspectives.

astro-ph↗

arXiv2006

Validation of stellar population and kinematical analysis of galaxies

3D spectroscopy produces hundreds of spectra from which maps of the characteristics of stellar populations (age-metallicity) and internal kinematics of galaxies can be derived. We carried on simulations to assess the reliability of inversion methods and to define the requirements for future observations. We quantify the biases and show that to minimize the errors on the kinematics, age and metallicity (in a given observing time) the size of the spatial elements and the spectral dispersion should be chosen to obtain an instrumental velocity dispersion comparable to the physical dispersion.

astro-ph↗

arXiv2004

Virtual instrumentation to study galaxies

The MIGALE project (http://www.sai.msu.su/migale) provides databases and data analysis tools to study the evolution of galaxies from z=1 to z=0. It develops and maintain a general database, HyperLeda, to give a homogenized parameterization for 3 million objects, and several archives or specialized databases. It also develops tools to analyse on-the-fly data extracted from the database or obtained through the Virtual Observatory (Virtual Instruments). The package made for this project, Pleinpot, is distributed as open source.

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