3,072 research outputs found
Galaxies in group and field environments: a comparison of optical-NIR luminosities and colors
We compare properties of galaxies in loose groups with those in field
environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy
systems. We consider as group galaxies, objects belonging to systems with at
least five members identified by means of the "friends of friends method", and,
as field galaxies, all galaxies with no companions. We analyze both a
magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies,
respectively, B<14 mag, and 2000<cz<6000 km/s) and a volume-limited sample (M_B
<-19.01 mag, 2000<cz<4000 km/s 369 group and 548 field galaxies). For all these
galaxies, blue corrected magnitudes and morphological types are available. The
cross-correlation of NOG with the 2MASS second release allow us to assign K
magnitudes and obtain B-K colors for about half of the galaxies in our samples.
We analyze luminosity and color segregation-effects in relation with the
morphological segregation. For both B and K bands, we find that group galaxies
are, on average, more luminous than field galaxies and this effect is not
entirely a consequence of the morphological segregation. After taking into
account the morphological segregation, the luminosity difference between group
and field galaxies is about 10%. When considering only very early-type galaxies
(T<-2) the difference is larger than 30%. We also find that group galaxies are
redder than field galaxies, Delta(B-K) about 0.4 mag. However, after taking
into account the morphological segregation, we find a smaller B-K difference,
poorly significant (only at the c.l. of about 80%).Comment: 11 pages, 10 eps figures, A&A in pres
The Mass Function of Nearby Galaxy Clusters
We present the distribution of virial masses for nearby galaxy clusters, as
obtained from a data-set of 75 clusters, each having at least 20 galaxy members
with measured redshifts within 1 Abell radius. After having accounted for
problems of incompleteness of the data-set, we fitted a power-law to the
cluster mass distribution.Comment: 10 pages (2 figures not included, available upon request), LATEX,
Ref.SISSA 54/93/
The nature of the giant diffuse non-thermal source in the A3411-A3412 complex
VLA deep radio images at 1.4 GHz in total intensity and polarization reveal a
diffuse non-thermal source in the interacting clusters A3411 - A3412. Moreover
a small-size low power radio halo at the center of the merging cluster A3411 is
found. We present here new optical and X-ray data and discuss the nature and
properties of the diffuse non-thermal source. We suggest that the giant diffuse
radio source is related to the presence of a large scale filamentary structure
and to multiple mergers in the A3411-A3412 complex.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Structures in Galaxy Clusters
The analysis of the presence of substructures in 16 well-sampled clusters of
galaxies suggests a stimulating hypothesis: Clusters could be classified as
unimodal or bimodal, on the basis of to the sub-clump distribution in the {\em
3-D} space of positions and velocities. The dynamic study of these clusters
shows that their fundamental characteristics, in particular the virial masses,
are not severely biased by the presence of subclustering if the system
considered is bound.Comment: (16 pages in LATEX, 4 tables in LATEX are at the end of the file, the
figures not included are available upon request), REF SISSA 158/93/
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