397 research outputs found
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
The X-ray luminosity function of galaxies in the Coma cluster
The XMM-Newton survey of the Coma cluster of galaxies covers an area of 1.86
square degrees with a mosaic of 16 pointings and has a total useful integration
time of 400 ksec. Detected X-ray sources with extent less than 10" were
correlated with cataloged galaxies in the Coma cluster region. The redshift
information, which is abundant in this region of the sky, allowed us to
separate cluster members from background and foreground galaxies. For the
background sources, we recover a typical LogN-LogS in the flux range 1.e-15 -
1.e-13 ergs/s/cm^2 in the 0.5-2.0 keV band. The X-ray emission from the cluster
galaxies exhibits X-ray colors typical of thermal emission. The luminosities of
Coma galaxies lie in the 1.e39-1.e41 ergs/s interval in the 0.5-2.0 keV band.
The luminosity function of Coma galaxies reveals that their X-ray activity is
suppressed with respect to the field by a factor of 5.6, indicating a lower
level of X-ray emission for a given stellar mass.Comment: 16 pages, 2004 A&A in pres
Optical spectroscopy and the UV luminosity function of galaxies in the Abell 1367, Coma and Virgo clusters
Optical spectroscopy of 93 galaxies, 60 projected in the direction of Abell
1367, 21 onto the Coma cluster and 12 on Virgo, is reported. The targets were
selected either because they were detected in previous H\alpha, UV or r'
surveys. The present observations bring to 100% the redshift completeness of
H\alpha selected galaxies in the Coma region and to 75% in Abell 1367. All
observed galaxies except one show H\alpha emission and belong to the clusters.
This confirms previous determinations of the H\alpha luminosity function of the
two clusters that were based on the assumption that all H\alpha detected
galaxies were cluster members. Using the newly obtained data we re-determine
the UV luminosity function of Coma and we compute for the first time the UV
luminosity function of A1367. Their faint end slopes remain uncertain (-2.00 <
\alpha < -1.35) due to insufficient knowledge of the background counts. If 90%
of the UV selected galaxies without redshift will be found in the background
(as our survey indicates), the slope of UV luminosity function will be \alpha ~
-1.35, in agreement with the UV luminosity function of the field (Sullivan et
al. 2000) and with the H luminosity functions of the two clusters
(Iglesias-Paramo et al. 2002). We discover a point like H\alpha source in the
Virgo cluster, associated with the giant galaxy VCC873, possibly an
extragalactic HII region similar to the one recently observed in Virgo by
Gerhard et al. (2002).Comment: 8 pages, 6 figures, 2 tables. Accepted for publication on A&
Fossil group origins V. The dependence of the luminosity function on the magnitude gap
In nature we observe galaxy aggregations that span a wide range of magnitude
gaps between the two first-ranked galaxies of a system (). There
are systems with gaps close to zero (e.g., the Coma cluster), and at the other
extreme of the distribution, the largest gaps are found among the so-called
fossil systems. Fossil and non-fossil systems could have different galaxy
populations that should be reflected in their luminosity functions. In this
work we study, for the first time, the dependence of the luminosity function
parameters on using data obtained by the fossil group origins
(FOGO) project. We constructed a hybrid luminosity function for 102 groups and
clusters at . We stacked all the individual luminosity functions,
dividing them into bins of , and studied their best-fit
Schechter parameters. We additionally computed a relative luminosity function,
expressed as a function of the central galaxy luminosity, which boosts our
capacity to detect differences, especially at the bright end. We find trends as
a function of at both the bright and faint ends of the
luminosity function. In particular, at the bright end, the larger the magnitude
gap, the fainter the characteristic magnitude . We also find
differences at the faint end. In this region, the larger the gap, the flatter
the faint-end slope . The differences found at the bright end support a
dissipationless, dynamical friction-driven merging model for the growth of the
central galaxy in group- and cluster-sized halos. The differences in the faint
end cannot be explained by this mechanism. Other processes, such as enhanced
tidal disruption due to early infall and/or prevalence of eccentric orbits, may
play a role. However, a larger sample of systems with is
needed to establish the differences at the faint end.Comment: 11 pages, 10 figures, accepted for publication in A&
The UV luminosity function of nearby clusters of galaxies
We present the UV composite luminosity function for galaxies in the Virgo,
Coma and Abell 1367 clusters. The luminosity function (LF) is well fitted by a
Schechter function with M*(UV} - 5*log h(75) = -20.75 +/- 0.40 and alpha =
-1.50 +/- 0.10 and does not differ significantly from the local UV luminosity
function of the field. This result is in agreement with recent studies carried
out in the Halpha and B-bands which find no difference between the LFs of star
forming galaxies in clusters and in the field. This indicates that, whatever
mechanisms are responsible for quenching the star formation in clusters, they
influence similarly the giant and the dwarf populations, leaving the shape of
the LF unchanged and only modifying its normalization.Comment: 5 pages, 4 figures, 2 tables.Accepted for publication on A&A. Data
avaliable at http://goldmine.mib.infn.it/papers/LF_UV.htm
Star Forming Objects in the Tidal Tails of Compact Groups
A search for star forming objects belonging to tidal tails has been carried
out in a sample of deep Halpha images of 16 compact groups of galaxies. A total
of 36 objects with Halpha luminosity larger than 10^38 erg s-1 have been
detected in five groups. The fraction of the total Halpha luminosity of their
respective parent galaxies shown by the tidal objects is always below 5% except
for the tidal features of HCG95, whose Halpha luminosity amounts to 65% of the
total luminosity. Out of this 36 objects, 9 star forming tidal dwarf galaxy
candidates have been finally identified on the basis of their projected
distances to the nuclei of the parent galaxies and their total Halpha
luminosities. Overall, the observed properties of the candidates resemble those
previously reported for the so-called tidal dwarf galaxies.Comment: 5 gif figures. Accepted for publication in Astrophysical Journa
Fossil Groups Origins III. The relation between optical and X-ray luminosities
This study is part of the FOssil Groups Origin (FOGO) project which aims at
carrying out a systematic and multiwavelength study of a large sample of fossil
systems. Here we focus on the relation between the optical luminosity (Lopt)
and X-ray luminosity (Lx). Out of a sample of 28 candidate fossil systems, we
consider a sample of 12 systems whose fossil classification has been confirmed
by a companion study. They are compared with the complementary sample of 16
systems whose fossil nature is not confirmed and with a subsample of 102 galaxy
systems from the RASS-SDSS galaxy cluster survey. Fossil and normal systems
span the same redshift range 0<z<0.5 and have the same Lx distribution. For
each fossil system, the Lx in the 0.1-2.4 keV band is computed using data from
the ROSAT All Sky Survey. For each fossil and normal system we homogeneously
compute Lopt in the r-band within the characteristic cluster radius, using data
from the SDSS DR7. We sample the Lx-Lopt relation over two orders of magnitude
in Lx. Our analysis shows that fossil systems are not statistically
distinguishable from the normal systems both through the 2D KS test and the fit
of the Lx-Lopt relation. The optical luminosity of the galaxy system does
strongly correlate with the X-ray luminosity of the hot gas component,
independently of whether the system is fossil or not. We conclude that our
results are consistent with the classical "merging scenario" of the brightest
galaxy formed via merger/cannibalism of other group galaxies, with conservation
of the optical light. We find no evidence for a peculiar state of the hot
intracluster medium.Comment: A&A, 12 pages, 4 figures, 3 tables, typos corr. and paper re-numbe
- âŠ