29 research outputs found
Infrared Surface Brightness Analysis of Galaxies in Compact Groups
Images of 7 Compact groups of galaxies (CG) were obtained using the 2.1m
telescope in San Pedro Martir (B.C. Mexico) equipped with the NIR camera
CAMILA. The NIR images trace the mass of the galaxies, through the oldest and
more evolved stellar populations. The goal of this project is to search for
evidence of morphological perturbations correlated with the level of activity
(AGN or star formation) of the galaxies. We find that the level of perturbation
is well correlated with activity observed in optical spectrocopy (Coziol et al.
2004). Evidence for perturbations decreases from more active groups to less
active groups, confirming the classification. Our analysis suggests that
galaxies in more active groups are undergoing important transformations due to
interaction and merging and that the whole groups is on a merger path. Galaxies
in less active CG have gone through similar processes in the recent past and
are either in a final merging phase or in equilibrium due to a more massive
halo of dark matter.Comment: 2 pages, 1 figure, Proc. ESO Workshop "Groups of galaxies in the
nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia,
eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verla
Comparative Study of Asymmetry Origin of Galaxies in Different Environments. II. Near-Infrared observations
In this second paper of two analyses, we present near-infrared (NIR)
morphological and asymmetry studies performed in sample of 92 galaxies found in
different density environments: galaxies in Compact Groups (HCGs), Isolated
Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs). Both studies have
proved useful for identifying the effect of interactions on galaxies. In the
NIR, the properties of the galaxies in HCGs, KPGs, and KIGs are more similar
than they are in the optical. This is because the NIR band traces the older
stellar populations, which formed earlier and are more relaxed than the younger
populations. However, we found asymmetries related to interactions in both KPG
and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher
than what we found in the optical. In the KPGs the interactions look like very
recent events, while in the HCGs galaxies are more morphologically evolved and
show properties suggesting they suffered more frequent interactions. The key
difference seems to be the absence of star formation in the HCGs; while
interactions produce intense star formation in the KPGs, we do not see this
effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol &
Plauchu-Frayn 2007); the interaction between galaxies in compact groups, (CGs),
is happening without the presence of gas. If the gas was spent in stellar
formation (to build the bulge of the numerous early-type galaxies), then the
HCGs possibly started interacting sometime before the KPGs. On the other hand,
the dry interaction condition in CGs suggests that the galaxies are on merging
orbits, and consequently such system cannot be that much older either.
[abridge]Comment: 36 pages, 16 figures. Accepted for publication in AJ: corrected typos
and reference
Comparative Study of Asymmetry Origin of Galaxies in Different Environments. I. Optical observations
This paper presents the first of two analyses about the influence of
environment on the formation and evolution of galaxies observed in the nearby
universe. For our study, we used three different samples representing different
density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of
Galaxies (KPGs), and Isolated Galaxies (KIGs), which were taken as reference.
Using both characteristic isophotal parameters and evidence of asymmetries in
the optical and the near-infrared, we are able to establish differences in the
characteristics of galaxies with different morphologies in different
environments, allowing us to better understand their different formation
histories. In this first paper, we present the isophotal and asymmetry analyses
of a sample of 214 galaxies in different environments observed in the optical
(V and I images). For each galaxy, we have determined different characteristic
isophotal parameters and (V-I) color profiles, as a function of semi-major
axis, and performed a full asymmetry analysis in residual images using the V
filter. Evidence of asymmetry in the optical is almost missing in the KIG
sample and significantly more common in the KPG than in the HCG samples. Our
isophotal analysis suggests that the stellar populations in the HCG galaxies
are older and more dynamically relaxed than in the KPG. The HCG galaxies seem
to be at a more advanced stage of interaction than the KPGs. One possible
explanation is that these structures formed at different epochs: compact groups
of galaxies would have formed before close pairs of galaxies, which only began
interacting recently. However, similarities in the formation process of
galaxies with same morphology suggest CGs and close pairs of galaxies share
similar conditions; they are new structures forming relatively late in
low-density environments.Comment: 48 pages, 21 figures. Accepted for publication in AJ : corrected
typos and references
Evidence for tidal interaction and merger as the origin of galaxy morphology evolution in compact groups
We present the results of a morphological study based on NIR images of 25
galaxies, with different levels of nuclear activity, in 8 Compact Groups of
Galaxies (CGs). We perform independently two different analysis: a isophotal
study and a study of morphological asymmetries. The results yielded by the two
analysis are highly consistent. For the first time, it is possible to show that
deviations from pure ellipses are produced by inhomogeneous stellar mass
distributions related to galaxy interactions and mergers. We find evidence of
mass asymmetries in 74% of the galaxies in our sample. In 59% of these cases,
the asymmetries come in pairs, and are consistent with tidal effects produced
by the proximity of companion galaxies. The symmetric galaxies are generally
small in size or mass, inactive, and have an early-type morphology. In 20% of
the galaxies we find evidence for cannibalism. In 36% of the early-type
galaxies the color gradient is positive (blue nucleus) or flat. Summing up
these results, as much as 52% of the galaxies in our sample could show evidence
of an on going or past mergers. Our observations suggest that galaxies in CGs
merge more frequently under ``dry'' conditions. The high frequency of
interacting and merging galaxies observed in our study is consistent with the
bias of our sample towards CGs of type B, which represents the most active
phase in the evolution of the groups. In these groups we also find a strong
correlation between asymmetries and nuclear activity in early-type galaxies.
This correlation allows us to identify tidal interactions and mergers as the
cause of galaxy morphology transformation in CGs.[abridge]Comment: 64 pages, 35 figures. Accepted for publication in Ap