Browsing by Author "Chilingarian, Igor V."

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    Dynamical versus stellar masses of ultracompact dwarf galaxies in the Fornax cluster☆
    (2011) Chilingarian, Igor V.; Mieske, Steffen; Hilker, Michael; Infante, Leopoldo
    The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic stellar systems, is still a puzzle for present galaxy formation models. We present the comprehensive analysis of high-resolution multi-object spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT with Fibre Large Array Multi Element Spectrograph (FLAMES). It comprises previously published data for 19 objects which we re-analysed, including 13 with available Hubble Space Telescope (HST) photometric data. Using Virtual Observatory technologies we found archival HST images for two more UCDs and then determined their structural properties. For all objects we derived internal velocity dispersions, stellar population parameters and stellar mass-to-light ratios (M/L)(*) by fitting individual simple stellar population (SSP) synthetic spectra convolved with a Gaussian against the observed spectra using the NBursts full spectral fitting technique. For 14 objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of them and no more than 40 per cent DM mass fraction in the remaining two, in contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs even have too high values of (M/L)(*) estimated using the Kroupa stellar initial mass function (IMF) resulting in negative formally computed DM mass fractions. The objects with too high (M/L)(*) ratios compared to the dynamical ones have relatively short dynamical relaxation time-scales, close to the Hubble time or below. We therefore suggest that their lower dynamical ratios (M/L)(dyn) are caused by low-mass star depletion due to dynamical evolution. Overall, the observed UCD characteristics suggest at least two formation channels: tidal threshing of nucleated dwarf galaxies for massive UCDs (similar or equal to 108 M-circle dot), and a classical scenario of red globular cluster formation for lower-mass UCDs (less than or similar to 107 M-circle dot).
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    The Next Generation Virgo Cluster Survey. XVII. A Search for Planetary Nebulae in Virgo Cluster Globular Clusters
    (2019) Sun, Weijia; Peng, Eric W.; Ko, Youkyung; Cote, Patrick; Ferrarese, Laura; Lee, Myung Gyoon; Liu, Chengze; Longobardi, Alessia; Chilingarian, Igor V.; Spengler, Chelsea; Zabludoff, Ann I.; Zhang, Hong-Xin; Cuillandre, Jean-Charles; Gwyn, Stephen D. J.
    The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study lowmass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O III] 5007 angstrom emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN (M-5007 = -4.1 mag) associated with an M87 GC. We used the [O III] detection limit for each GC to estimate the luminosity-specific frequency of PNe, a, and measured a in the Virgo cluster GCs to be alpha similar to 3.9(-0.7)(+5.2) x 10(-8) PN/(circle dot). The value of a in the Virgo GCs is among the lowest reported in any environment, due in part to the large sample size, and it is 5-6 times lower than that for the Galactic GCs. We suggest that a decreases toward brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but nonzero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in the Virgo GCs is governed by an internal process (mass, density, binary fraction) or if it is largely regulated by the external environment.
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    The volume density of giant low surface brightness galaxies
    (2023) Saburova, Anna S.; Chilingarian, Igor V.; Kulier, Andrea; Galaz, Gaspar; Grishin, Kirill A.; Kasparova, Anastasia V.; Toptun, Victoria; Katkov, Ivan Yu
    Rare giant low surface brightness galaxies (gLSBGs) act as a stress test for the current galaxy formation paradigm. To answer the question 'How rare are they?', we estimate their volume density in the local Universe. A visual inspection of 120 deg(2) covered by deep Subaru Hyper Suprime-Cam data was performed independently by four team members. We detected 42 giant disky systems (30 of them isolated) at z <= 0.1 with either g-band 27.7 mag arcsec(-2) isophotal radius or four disc scale lengths 4h >= 50 kpc, 37 of which (including 25 isolated) had low central surface brightness (mu(0,g) >= 22.7 mag arcsec(-2)). This corresponds to volume densities of 4.70 x 10(-5) Mpc(-3) for all galaxies with giant extended discs and 4.04 x 10(-5) Mpc(-3) for gLSBGs, which converts to similar to 12700 such galaxies in the entire sky out to z < 0.1. These estimates agree well with the result of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological hydrodynamical simulation. Giant disky galaxies represent the large-sized end of the volume density distribution of normal-sized spirals, suggesting the non-exceptional nature of giant discs. We observe a high active galactic nucleus fraction among the newly found gLSBGs.