6 research outputs found
On the X-ray emission of the low-mass galaxy groups
It is shown that the low-mass groups obey the law
deduced for galaxy clusters. The impression of the more shallow slope of the
correlation for groups is created not by enhanced X-ray
emission, but by underestimation of the radial velocity dispersion of some
groups.Comment: 4 pages, 2 figures, accepted in ApJ
On the Xray Luminosity - velocity dispersion relation of groups of galaxies
We analyse the Lx-sigma relation for the new Mulchaey et al. group Atlas. We
find that once we take into account the possible statistical bias introduced by
the cutoff in luminosity, we recover a relation which is consistent with that
of clusters, ie., Lx ~ sigma^4. The larger scatter of this relation for groups
of galaxies could be attributed to an orientation effect, due to which the
radial velocity dispersion of groups oriented close to orthogonal to the line
of sight, would be underestimated. This effect could also contribute in the
direction of flattening the slope of the group Lx-sigma relation.Comment: 6 pages, Astronomy & Astrophysics, in pres
Merging Galaxies in the SDSS EDR
We present a new catalog of merging galaxies obtained through an automated
systematic search routine. The 1479 new pairs of merging galaxies were found in
approximately 462 sq deg of the Sloan Digital Sky Survey Early Data Release
(SDSS EDR; Stoughton et al. 2002) photometric data, and the pair catalog is
complete for galaxies in the magnitude range 16.0 <= g* <= 20.
The selection algorithm, implementing a variation on the original
Karachentsev (1972) criteria, proved to be very efficient and fast. Merging
galaxies were selected such that the inter-galaxy separations were less than
the sum of the component galaxies' radii.
We discuss the characteristics of the sample in terms of completeness, pair
separation, and the Holmberg effect. We also present an online atlas of images
for the SDSS EDR pairs obtained using the corrected frames from the SDSS EDR
database. The atlas images also include the relevant data for each pair member.
This catalog will be useful for conducting studies of the general
characteristics of merging galaxies, their environments, and their component
galaxies. The redshifts for a subset of the interacting and merging galaxies
and the distribution of angular sizes for these systems indicate the SDSS
provides a much deeper sample than almost any other wide-area catalog to date.Comment: 58 pages, which includes 15 figures and 6 tables. Figures 2, 8, 9,
10, 11, 13, and 14 are provided as JPEG files. For online atlas, see
http://home.fnal.gov/~sallam/MergePair/ . Accepted for publication in A
Properties of Hickson Compact Groups and of the Loose Groups within which they are Embedded
We use the Sloan Digital Sky Survey (SDSS) redshift catalogue to look for
galaxies with accordant redshifts in the nearby environment (up to ~2 Mpc) of
15 Hickson Compact Groups (HCG) and 7 more HCG+environment from the literature.
We find that: (a) HCG's tend to be aligned with the overall galaxy distribution
in their ~1 Mpc environment, (b) the well-established orientation effect by
which the group velocity dispersion correlates with group axial ratio, is
present also in the HCG+environment systems, (c) the radial velocity dispersion
of the HCG+environment systems and of ordinary poor groups only weakly depends
on the group richness, (d) the mean absolute K-band magnitude of E/S0 galaxies
in HCGs is similar to that in ordinary poor groups, and is brighter than that
of isolated E/S0's, indicating that they were formed by the merging of two
galaxies of similar luminosity, (e) the fraction of E/S0 galaxies in these HCGs
depends only weakly on the group richness and velocity dispersion, (f) the
fraction of AGNs is similar in the HCGs and their close environment, while that
of starbursts is significantly higher in the HCGs, (g) the fraction of AGNs and
starbursts is anti-correlated with the velocity dispersion of the
HCG+environment systems. Furthermore, the observed fractions of early-type and
active galaxies as well as their correlations with the group velocity
dispersion suggests a picture by which nuclear activity and galaxy
transformation by merging is instigated by effective gravitational interactions
in the low-velocity dispersion groups, which then dynamically evolve via
virialization processes to higher velocity dispersion groups, which thus have a
higher fraction of early-type galaxies.Comment: accepted for publication in A