527 research outputs found
The evolution of the star formation activity per halo mass up to redshift ~1.6 as seen by Herschel
Aims. Star formation in massive galaxies is quenched at some point during hierarchical mass assembly. To understand where and when the quenching processes takes place, we study the evolution of the total star formation rate per unit total halo mass (Σ(SFR)/M) in three different mass scales: low mass halos (field galaxies), groups, and clusters, up to a redshift z ≈ 1.6.
Methods. We use deep far-infrared PACS data at 100 and 160 μm to accurately estimate the total star formation rate of the luminous infrared galaxy population of 9 clusters with mass ~10^(15) M_⊙, and 9 groups/poor clusters with mass ~5 × 10^(13) M_⊙. Estimates of the field Σ(SFR)/M are derived from the literature, by dividing the star formation rate density by the mean comoving matter density of the universe.
Results. The field Σ(SFR)/M increases with redshift up to z ~ 1 and it is constant thereafter. The evolution of the Σ(SFR)/M – z relation in galaxy systems is much faster than in the field. Up to redshift z ~ 0.2, the field has a higher Σ(SFR)/M than galaxy groups and galaxy clusters. At higher redshifts, galaxy groups and the field have similar Σ(SFR)/M, while massive clusters have significantly lower Σ(SFR)/M than both groups and the field. There is a hint of a reversal of the SFR activity vs. environment at z ~ 1.6, where the group Σ(SFR)/M lies above the field Σ(SFR)/M − z relation. We discuss possible interpretations of our results in terms of the processes of downsizing, and star-formation quenching
The RASS-SDSS galaxy cluster survey
Solid observational evidences indicate a strong dependence of the galaxy
formation and evolution on the environment. In order to study in particular the
interaction between the intracluster medium and the evolution of cluster
galaxies, we have created a large database of clusters of galaxies based on the
largest available X-ray and optical surveys: the ROSAT All Sky Survey (RASS),
and the Sloan Digital Sky Survey (SDSS). We analyzed the correlation between
the total optical and the X-ray cluster luminosity. The resulting correlation
of L_X and L_{op} shows a logarithmic slope of 0.6, a value close to the
self-similar correlation. We analysed also the cluster mass to light ratio, by
finding a significant dependence of M/L on the cluster mass with a logarithmic
slope ranging from 0.27 in the i and r bands to 0.22 in the z band.Comment: proceedings of 'Multiwavelength mapping of galaxy evolution'
conference held in Venice (Italy), October 2003, A. Renzini and R. Bender
(Eds.), 2 pages, 1 figur
Bulges and disks in the local Universe. Linking the galaxy structure to star formation activity
We use a sample built on the SDSS DR7 catalogue and the bulge-disc
decomposition of Simard et al. (2011) to study how the bulge and disc
components contribute to the parent galaxy's star formation activity, by
determining its position in the star formation rate (SFR) - stellar mass
(M) plane at 0.020.1. We use the bulge and disc colours as proxy
for their SFRs. We study the mean galaxy bulge-total mass ratio (B/T) as a
function of the residual from the MS () and find that the
B/T- relation exhibits a parabola-like shape with the peak of the
MS corresponding to the lowest B/Ts at any stellar mass. The lower and upper
envelop of the MS are populated by galaxies with similar B/T, velocity
dispersion and concentration () values. Bulges above the MS are
characterised by blue colours or, when red, by a high level of dust
obscuration, thus indicating that in both cases they are actively star forming.
When on the MS or below it, bulges are mostly red and dead. At stellar masses
above M, bulges on the MS or in the green valley tend to
be significantly redder than their counterparts in the quiescence region,
despite similar levels of dust obscuration. The disc color anti-correlates at
any mass with the distance from the MS, getting redder when approaching the MS
lower envelope and the quiescence region. We conclude that the position of a
galaxy in the LogSFR-LogM plane depends on the star formation
activity of its components: above the MS both bulge and disk are actively star
forming. The nuclear activity is the first to be suppressed, moving the
galaxies on the MS. Once the disk stops forming stars as well, the galaxy moves
below the MS and eventually to the quiescence region. This is confirmed by a
large fraction () of passive galaxies with a secure two component
morphology.Comment: Version modified after referee comment
RASS-SDSS Galaxy Cluster Survey. VII. On the Cluster Mass to Light ratio and the Halo Occupation Distribution
We explore the mass-to-light ratio in galaxy clusters and its relation to the
cluster mass. We study the relations among the optical luminosity (),
the cluster mass () and the number of cluster galaxies within
() in a sample of 217 galaxy clusters with confirmed 3D
overdensity. We correct for projection effects, by determining the galaxy
surface number density profile in our cluster sample. This is best fitted by a
cored King profile in low and intermediate mass systems. The core radius
decreases with cluster mass, and, for the highest mass clusters, the profile is
better represented by a generalized King profile or a cuspy Navarro, Frenk &
White profile. We find a very tight proportionality between and
, which, in turn, links the cluster mass-to-light ratio to the Halo
Occupation Distribution vs. . After correcting for
projection effects, the slope of the and
relations is found to be , close, but still significantly less
than unity. We show that the non-linearity of these relations cannot be
explained by variations of the galaxy luminosity distributions and of the
galaxy M/L with the cluster mass. We suggest that the nonlinear relation
between number of galaxies and cluster mass reflects an underlying nonlinear
relation between number of subhaloes and halo mass.Comment: 15 pages, 15 figures, accepted for publication in A&
Two-Face(s): ionized and neutral gas winds in the local Universe
We present a comprehensive study of the Na I 5890, 5895 (Na I D)
resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample
to look for neutral gas outflows in the local galaxies. Individual galaxy
spectra are stacked in bins of M and SFR to investigate the dependence
of galactic wind occurrence and velocity as a function of the galaxy position
in the SFR- plane. In massive galaxies at the high SFR tail we find
evidence of a significant blue-shifted Na I D absorption, which we interpret as
evidence of neutral outflowing gas. The occurrence of the blue-shifted
absorption is observed at the same significance for purely SF galaxies, AGN and
composite systems at fixed SFR. In all classes of objects the blue-shift is the
largest and the Na I D equivalent width the smallest for face-on galaxies while
the absorption feature is at the systemic velocity for edge-on systems. This
indicates that the neutral outflow is mostly perpendicular or biconical with
respect to the galactic disk. We also compare the kinematics of the neutral gas
with the ionized gas phase as traced by the [OIII]5007, H,
[NII] and [NII] emission lines. Differently for the
neutral gas phase, all the emission lines show evidence of perturbed kinematics
only in galaxies with a significant level of nuclear activity and, they are
independent from the disk inclination. In conclusion, we find that, in the
local Universe, galactic winds show two faces which are related to two
different ejection mechanisms, namely the neutral outflowing gas phase related
to the SF activity along the galaxy disk and the ionized phase related to the
AGN feedback. In both the neutral and ionized gas phases, the observed wind
velocities suggest that the outflowing gas remains bound to the galaxy with no
definitive effect on the gas reservoir.Comment: Accepted to A&A, 13 pages, 9 figure
RASS-SDSS Galaxy Cluster Survey. VI. The dependence of the cluster SFR on the cluster global properties
Using a subsample of 79 nearby clusters from the RASS-SDSS galaxy cluster
catalogue of Popesso et al. (2005a), we perform a regression analysis between
the cluster integrated star formation rate (Sigma_SFR) the cluster total
stellar mass (M_star), the fractions of star forming (f_SF) and blue (f_b)
galaxies and other cluster global properties, namely its richness (N_gal, i.e.
the total number of cluster members within the cluster virial radius), velocity
dispersion (sigma_v), virial mass (M_200), and X-ray luminosity (L_X). All
cluster global quantities are corrected for projection effects before the
analysis. Galaxy SFRs and stellar masses are taken from the catalog of
Brinchmann et al. (2004), which is based on SDSS spectra. We only consider
galaxies with M_r <= -20.25 in our analysis, and exclude AGNs. We find that
both Sigma_SFR and M_star are correlated with all the cluster global
quantities. A partial correlation analysis show that all the correlations are
induced by the fundamental one between Sigma_SFR and N_gal, hence there is no
evidence that the cluster properties affect the mean SFR or M_star per galaxy.
The relations between Sigma_SFR and M_star, on one side, and both N_gal and
M_200, on the other side, are linear, i.e. we see no evidence that different
clusters have different SFR or different M_star per galaxy and per unit mass.
The fraction f_SF does not depend on any cluster property considered, while f_b
does depend on L_X. We note that a significant fraction of star-forming cluster
galaxies are red (~25% of the whole cluster galaxy population). We conclude
that the global cluster properties are unable to affect the SF properties of
cluster galaxies, but the presence of the X-ray luminous intra-cluster medium
can affect their colors, perhaps through the ram-pressure stripping mechanism.Comment: 14 pages, 12 figures, accepted for publication on A&A; corrected
coefficient in Tab.
Luminosity Functions of XMM-LSS C1 Galaxy Clusters
CFHTLS optical photometry has been used to study the galaxy luminosity
functions of 14 X-ray selected clusters from the XMM-LSS survey. These are
mostly groups and poor clusters, with masses (M_{500}) in the range 0.6 to
19x10 ^{13} M_solar and redshifts 0.05-0.61. Hence these are some of the
highest redshift X-ray selected groups to have been studied. Lower and upper
colour cuts were used to determine cluster members. We derive individual
luminosity functions (LFs) for all clusters as well as redshift-stacked and
temperature-stacked LFs in three filters, g', r' and z', down to M=-14.5. All
LFs were fitted by Schechter functions which constrained the faint-end slope,
alpha, but did not always fit well to the bright end. Derived values of alpha
ranged from -1.03 to as steep as -2.1. We find no evidence for upturns at faint
magnitudes. Evolution in alpha was apparent in all bands: it becomes shallower
with increasing redshift; for example, in the z' band it flattened from -1.75
at low redshift to -1.22 in the redshift range z=0.43-0.61. Eight of our
systems lie at z~0.3, and we combine these to generate a galaxy LF in three
colours for X-ray selected groups and poor clusters at redshift 0.3. We find
that at z~0.3 alpha is steeper (-1.67) in the green (g') band than it is
(-1.30) in the red (z') band. This colour trend disappears at low redshift,
which we attribute to reddening of faint blue galaxies from z~0.3 to z~0. We
also calculated the total optical luminosity and found it to correlate strongly
with X-ray luminosity (L_X proportional to L_OPT^(2.1)), and also with ICM
temperature (L_OPT proportional to T^(1.62)), consistent with expectations for
self-similar clusters with constant mass-to-light ratio. We did not find any
convincing correlation of Schechter parameters with mean cluster temperature.Comment: 23 pages, 17 figure
Implications of the remarkable homogeneity of galaxy groups and clusters
We measure the diversity of galaxy groups and clusters with mass M>1E13/h
Msun, in terms of the star formation history of their galaxy populations, for
the purpose of constraining the mass scale at which environmentally-important
processes play a role in galaxy evolution. We consider three different group
catalogues, selected in different ways, with photometry and spectroscopy from
the Sloan Digital Sky Survey. For each system we measure the fraction of
passively-evolving galaxies within R200 and brighter than either Mr=-18 (and
with z<0.05) or Mr=-20 (and z<0.1). We use the (u-g) and (r-i) galaxy colours
to distinguish between star-forming and passively-evolving galaxies. By
considering the binomial distribution expected from the observed number of
members in each cluster, we are able to either recover the intrinsic scatter in
this fraction, or put robust 95% confidence upper-limits on its value. The
intrinsic standard deviation in the fraction of passive galaxies is consistent
with a small value of <0.1 in most mass bins for all three samples. There is no
strong trend with mass; even groups with M=1E13/h Msun are consistent with such
a small, intrinsic distribution. We compare these results with theoretical
models of the accretion history to show that, if environment plays a role in
transforming galaxies, such effects must occur first at mass scales far below
that of rich clusters, at most M=1E13 Msun.Comment: 5 pages, MNRAS Letters, in pres
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