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Identifier 000418775
Title Galaxy morphology in different environments
Alternative Title Μορφολογία γαλαξιών σε διαφορετικά περιβάλλοντα
Author Ψυχογυιός, Αλέξανδρος
Thesis advisor Χαρμανδάρης, Βασίλειος
Reviewer Παπαδάκης, Ιωσήφ
Ζέζας, Ανδρέας
Diaz-Santos, T.
Ηλιόπουλος, Ελευθέριος
Τάσσης, Κωνσταντίνος
Ξυλούρης, Μ
Abstract The present thesis is examining a few open topics of galaxy evolution due to their environment, based on the analysis of galaxy morphology using imagery in optical and near-IR wavelengths. Our study was focused on two distinct samples, and it is thus divided in two parts. The first part deals with the morphological classification of 89 luminous infrared galaxies (LIRGs), systems with total infrared emission brighter than 1011 L , of the Great Observatories All-sky LIRG Survey (GOALS) sample, that have been imaged with the Hubble Space Telescope. GOALS is a complete subset of the IRAS Revised Bright Galaxy Sample (RBGS) and consists of 202 systems in the local Universe (z < 0.09). The activity in LIRGs is largely interaction triggered, with the progenitors observed to be gasrich disk galaxies involved in primarily minor interactions (at the low luminosity end) or major merger events (at luminosities over 1012 L: ULIRGs). These interactions drive inflows of gas which give rise to both intense nuclear star formation (with star formation rates, SFR ∼ 10 - 200 M/yr) and Active Galactic Nuclei (AGN) activity. As such, LIRGs are ideal for studying star formation in extreme environments and the interplay between star formation and AGN. At the high LIR end, LIRGs represent the brief (∼several 108 years) but energetic transformation of normal disk galaxies into elliptical and S0 galaxies. Improving our understanding on of these systems will be critical for similar studies of starbursts in cosmologically distant LIRGs which comprise the bulk of the IR energy density at z > 0.5. We used automatically calculated non-parametric coefficients (Gini and M20; the second order of light surface density) to quantify their morphology in the optical (B- and I-band) as well as in the infrared (H-band and 5.8μm). We explored the morphology of (U)LIRGs as a function of stellar mass (M*), infrared luminosity (LIR), star formation rate (SFR) and dust temperature (Tdust). We find that M20 is a better morphological tracer than Gini, as it allows us to distinguish systems that were formed by double systems from isolated and post-merger LIRGs. Our multi-wavelength analysis allows us to identify a region in the Gini-M20 parameter space where ongoing mergers reside, regardless of the band used. This particular region is best defined in the H-band, with minimal contamination from LIRGs in other stages. Exploring the distribution of our galaxies on the specific SFR (sSFR)-M20 plane, we also find a spatial decoupling between obscured and unobscured star formation. The sSFR is positively correlated with M20 when measured in the mid-infrared (star-bursting galaxies display more compact emission) while it is anti-correlated with the B-band- measured M20. This has important implications for high redshift surveys of dusty sources, where sizes of galaxies are routinely measured in the rest-frame ultraviolet. In the second part of the thesis, we focus on the analysis of optical and near NIR observations of over 1000 galaxies in 9 clusters, selected from WIde-field Nearby Galaxy- cluster Survey (WINGS), a wide field multi-wavelength imaging and spectroscopic survey of 77 nearby galaxy clusters. We calculated the structural parameters (magnitudes, effective radius (Re), Sersic index (n), axis ratio and position angle) using the state of the art software GALAPAGOSII to examine how galaxy structure varies as a function of wavelength and environment, by comparing with similar field galaxies. We simultaneously fit single-Sersic functions on three optical (u, B and V) and two near-infrared (J and K) bands thus creating a wavelength- dependent model of each galaxy. We find that the light profiles of cluster galaxies do not substantially change (nearly constant Sersic index) with wavelength while Re decreases across all bands for all morphological types. The environment (as measured by the projected local density and distance from the clusters center) does not substantially affect the values of structural parameters (n and Re) for galaxies that are located in regions smaller than 0.64✕R200 (close to the cluster center). Our results clearly show that brighter cluster galaxies are more concentrated and compact (display high n values and smaller Re values). Moreover, the light profile (N) and size (R) parameters of bright cluster and non-cluster galaxies are distinctly different as a function of wavelength.
Language English
Subject Galaxies
Galaxy clusters
Galaxy evolution
Δομή γαλαξιών
Εξέλιξη γαλαξιών
Issue date 2018-10-08
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
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