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.
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