563 research outputs found
The Ha luminosity function and star formation rate up to z~1
We describe ISAAC/ESO-VLT observations of the Ha(6563) Balmer line of 33
field galaxies from the Canada-France Redshift Survey (CFRS) with redshifts
selected between 0.5 and 1.1. We detect Ha in emission in 30 galaxies and
compare the properties of this sample with the low-redshift sample of CFRS
galaxies at z~0.2 (Tresse & Maddox 1998). We find that the Ha luminosity,
L(Ha), is tightly correlated to M(B(AB)) in the same way for both the low- and
high-redshift samples. L(Ha) is also correlated to L([OII]3727), and again the
relation appears to be similar at low and high redshifts. The ratio
L([OII])/L(Ha) decreases for brighter galaxies by as much as a factor 2 on
average. Derived from the Ha luminosity function, the comoving Ha luminosity
density increases by a factor 12 from =0.2 to =1.3. Our results confirm a
strong rise of the star formation rate (SFR) at z<1.3, proportional to
(1+z)^{4.1+/-0.3} (with H_0=50 km/s/Mpc, q_0=0.5). We find an average SFR(2800
Ang)/SFR(Ha) ratio of 3.2 using the Kennicutt (1998) SFR transformations. This
corresponds to the dust correction that is required to make the near UV data
consistent with the reddening-corrected Ha data within the self-contained,
I-selected CFRS sample.Comment: 16 pages, 16 figures and 3 tables included, figures and text updated,
same results as in the 1st version, accepted in MNRA
The Star Formation Rate Density and Dust Attenuation Evolution over 12 Gyr with the VVDS Surveys
[Abridged] We investigate the global galaxy evolution over 12 Gyr
(0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS
Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a
single homogeneous spectroscopic redshift sample, totalizing about 11000
galaxies. We estimate the rest-frame FUV luminosity function (LF) and
luminosity density (LD), extract the dust attenuation of the FUV radiation
using SED fitting, and derive the dust-corrected SFRD. We find a constant and
flat faint-end slope alpha in the FUV LF at z1.7, we set alpha
steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire
range 02 it is on average brighter than in the literature,
while phi* is smaller. Our total LD shows a peak at z=2, present also when
considering all sources of uncertainty. The SFRD history peaks as well at z=2.
It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases
by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by
a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag.
As times goes by, the total SFRD is dominated by fainter and fainter galaxies.
The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is
compelling for models of galaxy formation. The mean dust attenuation A_FUV of
the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2,
reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag
during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after
the SFRD peak, implying a contribution from the intermediate-mass stars to the
dust production at z<2.Comment: 23 pages, 15 figures, accepted for publication in A&
The VIMOS VLT Deep Survey - Evolution of the luminosity functions by galaxy type up to z=1.5 from first epoch data
From the first epoch observations of the VVDS up to z=1.5 we have derived
luminosity functions (LF) of different spectral type galaxies. The VVDS data,
covering ~70% of the life of the Universe, allow for the first time to study
from the same sample and with good statistical accuracy the evolution of the
LFs by galaxy type in several rest frame bands from a purely magnitude selected
sample. The magnitude limit of the VVDS allows the determination of the faint
end slope of the LF with unprecedented accuracy. Galaxies have been classified
in four spectral classes, using their colours and redshift, and LFs have been
derived in the U, B, V, R and I rest frame bands from z=0.05 to z=1.5. We find
a significant steepening of the LF going from early to late types. The M*
parameter is significantly fainter for late type galaxies and this difference
increases in the redder bands. Within each of the galaxy spectral types we find
a brightening of M* with increasing redshift, ranging from =< 0.5 mag for early
type galaxies to ~1 mag for the latest type galaxies, while the slope of the LF
of each spectral type is consistent with being constant with redshift. The LF
of early type galaxies is consistent with passive evolution up to z~1.1, while
the number of bright early type galaxies has decreased by ~40% from z~0.3 to
z~1.1. We also find a strong evolution in the normalization of the LF of latest
type galaxies, with an increase of more than a factor 2 from z~0.3 to z~1.3:
the density of bright late type galaxies in the same redshift range increases
of a factor ~6.6. These results indicate a strong type-dependent evolution and
identifies the latest spectral types as responsible for most of the evolution
of the UV-optical luminosity function out to z=1.5.Comment: 18 pages with encapsulated figures, revised version after referee's
comments, accepted for publication in A&
Evaporation of the gluon condensate: a model for pure gauge SU(3)_c phase transition
We interpret lattice data for the equation of state of pure gauge
by an evaporation model. At low temperatures gluons are frozen inside the gluon
condensate, whose dynamics is described in terms of a dilaton lagrangian. Above
the critical temperature quasi-free gluons evaporate from the condensate: a
first order transition is obtained by minimizing the thermodynamical potential
of the system. Within the model it is possible to reproduce lattice QCD results
at finite temperature for thermodynamical quantities such as pressure and
energy. The gluonic longitudinal mass can also be evaluated; it vanishes below
the critical temperature, where it shows a discontinuity. At very large
temperatures we recover the perturbative scenario and gluons are the only
asymptotic degrees of freedom.Comment: 21 pages, 8 figures. Expanded version including a discussion of the
asymptotic degrees of freedom and of the gluon mas
Tracing the Filamentary Structure of the Galaxy Distribution at z~0.8
We study filamentary structure in the galaxy distribution at z ~ 0.8 using
data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey
and its evolution to z ~ 0.1 using data from the Sloan Digital Sky Survey
(SDSS). We trace individual filaments for both surveys using the Smoothed
Hessian Major Axis Filament Finder, an algorithm which employs the Hessian
matrix of the galaxy density field to trace the filamentary structures in the
distribution of galaxies. We extract 33 subsamples from the SDSS data with a
geometry similar to that of DEEP2. We find that the filament length
distribution has not significantly changed since z ~ 0.8, as predicted in a
previous study using a \LamdaCDM cosmological N-body simulation. However, the
filament width distribution, which is sensitive to the non-linear growth of
structure, broadens and shifts to smaller widths for smoothing length scales of
5-10 Mpc/h from z ~ 0.8 to z ~ 0.1, in accord with N-body simulations.Comment: 10 pages, 8 figures, accepted for the publication in MNRA
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model. II. The colour-density relation up to z=1.5
[Abridged] We perform on galaxy mock catalogues the same colour-density
analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep
survey, and compare the results from mocks with observed data. We use mocks
with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-
analytic model by De Lucia & Blaizot (2007) applied to the Millennium
Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS
observational strategy (OMOCKS). We computed the B-band Luminosity Function LF
and the colour-density relation (CDR) in the mocks. We find that the LF in
mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of
the model LF is steeper than the VVDS one. Computing the LF for early and late
type galaxies, we show that mocks have an excess of faint early-type and of
bright late-type galaxies with respect to data. We find that the CDR in OMOCKS
is in excellent agreement with the one in CMOCKS. At z~0.7, the CDR in mocks
agrees with the VVDS one (red galaxies reside mainly in high densities). Yet,
the strength of the CDR in mocks does not vary within 0.2<z<1.5, while the
observed relation flattens with increasing z and possibly inverts at z=1.3. We
argue that the lack of evolution in the CDR in mocks is not due only to
inaccurate prescriptions for satellite galaxies, but that also the treatment of
central galaxies has to be revised. The reversal of the CDR can be explained by
wet mergers between young galaxies, producing a starburst event. This should be
seen on group scales. A residual of this is found in observations at z=1.5 on
larger scales, but not in the mocks, suggesting that the treatment of physical
processes affecting satellites and central galaxies in models should be
revised.Comment: 15 pages, 12 figures, accepted for publication in A&
The dust obscuration bias in Damped Lyman alpha systems
We present a new study of the effects of quasar obscuration on the statistics
of Damped Ly alpha (DLA) systems. We show that the extinction of any Galactic
or extragalactic HI region increases with the column density of zinc with a
turning point above which background sources are suddenly obscured. We derive a
relation between the extinction of a DLA system and its HI column density, N,
metallicity, Z, fraction of iron in dust, f_Fe(Z), and redshift, z. From this
relation we estimate the fraction of DLA systems missed as a consequence of
their own extinction in magnitude-limited surveys. We derive a method for
recovering the true frequency distributions of N and Z in DLAs, f_N and f_Z,
using the biased distributions measured in the redshift range where the
observations have sufficient statistics (1.8 </= z </= 3). By applying our
method we find that the well-known empirical thresholds of DLA column
densities, N(ZnII) </~ 10^13.1 cm^-2 and N(HI) </~ 10^22 cm^-2 can be
successfully explained in terms of the obscuration effect without tuning of the
local dust parameters. The obscuration has a modest effect on the distribution
of quasar apparent magnitudes, but plays an important role in shaping the
statistical distributions of DLAs. The exact estimate of the bias is still
limited by the paucity of the data (~40 zinc measurements at 1.8 </~ z </~ 3).
We find that the fraction of DLAs missed as a consequence of obscuration is
\~30% to 50%, consistent with the results of surveys of radio-selected quasars.
By modelling the metallicity distribution with a Schechter function we find
that the mean metallicity can be ~5 to 6 times higher than the value commonly
reported for DLAs at z~2.3.Comment: Astronomy and Astrophysics, in press, 20 pages, 10 figures; abridged
abstract; improved figs. 3 and 5; most of mathematical formulation moved to
the Appendix; minor change
The evolution of quiescent galaxies at high redshift (z > 1.4)
We have studied the evolution of high redshift quiescent galaxies over an
effective area of ~1.7 deg^2 in the COSMOS field. Galaxies have been divided
according to their star-formation activity and the evolution of the different
populations has been investigated in detail. We have studied an IRAC (mag_3.6 <
22.0) selected sample of ~18000 galaxies at z > 1.4 with multi-wavelength
coverage. We have derived accurate photometric redshifts (sigma=0.06) and other
important physical parameters through a SED-fitting procedure. We have divided
our sample into actively star-forming, intermediate and quiescent galaxies
depending on their specific star formation rate. We have computed the galaxy
stellar mass function of the total sample and the different populations at
z=1.4-3.0. We have studied the properties of high redshift quiescent galaxies
finding that they are old (1-4 Gyr), massive (log(M/M_sun)~10.65), weakly star
forming stellar populations with low dust extinction (E(B-V) < 0.15) and small
e-folding time scales (tau ~ 0.1-0.3 Gyr). We observe a significant evolution
of the quiescent stellar mass function from 2.5 < z < 3.0 to 1.4 < z < 1.6,
increasing by ~ 1 dex in this redshift interval. We find that z ~ 1.5 is an
epoch of transition of the GSMF. The fraction of star-forming galaxies
decreases from 60% to 20% from z ~ 2.5-3.0 to z ~ 1.4-1.6 for log(M/M_sun) >
11, while the quiescent population increases from 10% to 50% at the same
redshift and mass intervals. We compare the fraction of quiescent galaxies
derived with that predicted by theoretical models and find that the Kitzbichler
& White (2007) model is the one that better reproduces the data. Finally, we
calculate the stellar mass density of the star-forming and quiescent
populations finding that there is already a significant number of quiescent
galaxies at z > 2.5 (rho~6.0 MsunMpc^-3).Comment: 17 pages, 20 figures, 5 tables. Accepted for publication in MNRA
The dwarf galaxy population in Abell 2218
We present results from a deep photometric study of the rich galaxy cluster
Abell 2218 (z=0.18) based on archival HST WFPC2 F606W images. These have been
used to derive the luminosity function to extremely faint limits
(M_{F606W}=-13.2 mag, mu_{0}=24.7 mag arcsec^{-2}) over a wide field of view
(1.3 h^{-2} Mpc^2). We find the faint-end slope of the luminosity function to
vary with environment within the cluster, going from alpha=-1.23\pm0.13 within
the projected central core of the cluster (100 < r < 300 h^{-1} kpc) to
alpha=-1.49\pm 0.06 outside this radius (300 < r < 750 h^{-1} kpc). We infer
that the core is 'dwarf depleted', and further quantify this by studying the
ratio of 'dwarf' to 'giant' galaxies and its dependency as a function of
cluster-centric radius and local galaxy density. We find that this ratio varies
strongly with both quantities, and that the dwarf galaxy population in A2218
has a more extended distribution than the giant galaxy population.Comment: Accepted for publication in MNRAS; 11 pages, 12 figure
A frozen super-Earth orbiting a star at the bottom of the Main Sequence
We observed the microlensing event MOA-2007-BLG-192 at high angular
resolution in JHKs with the NACO adaptive optics system on the VLT while the
object was still amplified by a factor 1.23 and then at baseline 18 months
later. We analyzed and calibrated the NACO photometry in the standard 2MASS
system in order to accurately constrain the source and the lens star fluxes. We
detect light from the host star of MOA-2007-BLG-192Lb, which significantly
reduces the uncertainties in its char- acteristics as compared to earlier
analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late
type M-dwarf (0.084 [+0.015] [-0.012] M\odot) at a distance of 660 [+100] [-70]
pc orbited by a 3.2 [+5.2] [-1.8] M\oplus super-Earth at 0.66 [+0.51] [-0.22]
AU. We then discuss the properties of this cold planetary system.Comment: published version A&A 540, A78 (2012) A&A, 10 pages, 7 Figure
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