132 research outputs found
Linking stellar mass and star formation in Spitzer/MIPS 24 micron galaxies
We present deep Ks<21.5 (Vega) identifications, redshifts and stellar masses
for most of the sources composing the bulk of the 24 micron background in the
GOODS/CDFS. Our identified sample consists of 747 Spitzer/MIPS 24 micron
objects, and includes ~94% of all the 24 micron sources in the GOODS-South
field which have fluxes Snu(24)>83 microJy (the 80% completeness limit of the
Spitzer/GTO 24 micron catalog). 36% of our galaxies have spectroscopic
redshifts (mostly at z<1.5) and the remaining ones have photometric redshifts
of very good quality, with a median of |dz|=|zspec-zphot|/(1+zspec)=0.02. We
find that MIPS 24 micron galaxies span the redshift range z~0-4, and that a
substantial fraction (28%) lie at high redshifts z>1.5. We determine the
existence of a bump in the redshift distribution at z~1.9, indicating the
presence of a significant population of galaxies with PAH emission at these
redshifts. Massive (M>10^11 Msun) star-forming galaxies at redshifts 2<z<3 are
characterized by very high star-formation rates (SFR>500 Msun/yr), and some of
them are able to construct a mass of 10^10-10^11 Msun in a single burst
lifetime (~0.01-0.1 Gyr). At lower redshifts z<2, massive star-forming galaxies
are also present, but appear to be building their stars on long timescales,
either quiescently or in multiple modest burst-like episodes. At redshifts
z~1-2, the ability of the burst-like mode to produce entire galaxies in a
single event is limited to some lower (M<7x10^10 Msun) mass systems, and it is
basically negligible at z<1. Our results support a scenario where
star-formation activity is differential with assembled stellar mass and
redshift, and where the relative importance of the burst-like mode proceeds in
a down-sizing way from high to low redshifts. (abridged)Comment: Accepted for publication in the ApJ. 19 pages, 10 figures. Uses
emulateap
Study of a homogeneous QSO sample: relations between the QSO and its host galaxy
We analyse a sample of 69 QSOs which have been randomly selected in a
complete sample of 104 QSOs (R<18, 0.142 < z < 0.198). 60 have been observed
with the NTT/SUSI2 at La Silla, through two filters in the optical band (WB#655
and V#812), and the remaining 9 are taken from archive databases. The filter
V#812 contains the redshifted Hbeta and forbidden [OIII] emission lines, while
WB#655 covers a spectral region devoid of emission lines, thus measuring the
QSO and stellar continua. The contributions of the QSO and the host are
separated thanks to the MCS deconvolution algorithm, allowing a morphological
classification of the host, and the computation of several parameters such as
the host and nucleus absolute V-magnitude, distance between the luminosity
center of the host and the QSO, and colour of the host and nucleus. We define a
new asymmetry coefficient, independent of any galaxy models and well suited for
QSO host studies. The main results from this study are: (i) 25% of the total
number of QSO hosts are spirals, 51% are ellipticals and 60% show signs of
interaction; (ii) Highly asymmetric systems tend to have a higher gas
ionization level (iii) Elliptical hosts contain a substantial amount of ionized
gas, and some show off-nuclear activity. These results agree with hierarchical
models merger driven evolution.Comment: accepted for publication in MNRAS, 19 pages, 22 figures, 8 table
Numerical Investigation of the Interface Tension in the three-dimensional Ising Model
The interface tension in the three-dimensional Ising model in the low
temperature phase is investigated by means of the Monte Carlo method. Together
with other physically relevant quantities it is obtained from a calculation of
time-slice correlation functions in a cylindrical geometry. The results at
three different values of the temperature are compared with the predictions
from a semiclassical approximation in the framework of renormalized
theory in three dimensions, and are in good agreement with them.Comment: 17 pages, MS-TPI-92-13 (replaced due to correction of minor numerical
errors
A peculiar galaxy appears at redshift 11: properties of a moderate redshift interloper
Laporte et al. (2011) reported a very high redshift galaxy candidate: a
lensed J-band dropout (A2667-J1). J1 has a photometric redshift of z=9.6-12,
the probability density function for which permits no low or intermediate z
solution. We here report new spectroscopic observations of this galaxy with
VLT/XShooter, which show clear [OIII]5007AA, Ly-alpha, H-alpha, and H-beta
emission and place the galaxy firmly at z=2.082. The oxygen lines contribute
only ~25% to the H-band flux, and do not significantly affect the dropout
selection of J1. After correcting the broadband fluxes for line emission, we
identify two roughly equally plausible natures for A2667-J1: either it is young
heavily reddened starburst, or a maximally old system with a very pronounced
4000AA break, upon which a minor secondary burst of star formation is
superimposed. Fits show that to make a 3 sigma detection of this object in the
B-band (V-band), imaging of depth AB=30.2 (29.5) would be required - despite
the relatively bright NIR magnitude, we would need optical data of equivalent
depth to the Hubble Ultra Deep Field to rule out the mid-z solution on purely
photometric grounds. Assuming that this stellar population can be scaled to the
NIR magnitudes of recent HST/WFC3 IR-selected galaxies, we conclude that
infeasibly deep optical data AB~32 would be required for the same level of
security. There is a population of galaxies at z~2 with continuum colours alone
that mimic those of our z=7-12 candidates.Comment: Accepted by Monthly Notices. 5 pages, 2 figure
The role of the LIRG and ULIRG phases in the evolution of Ks-selected galaxies
We investigate the role of the luminous infrared galaxy (LIRG) and
ultra-luminous infrared galaxy (ULIRG) phases in the evolution of Ks-selected
galaxies and, in particular, Extremely Red Galaxies (ERGs). With this aim, we
compare the properties of a sample of 2905 Ks<21.5 (Vega mag) galaxies in the
GOODS/CDFS with the sub-sample of those 696 sources which are detected at 24
microns. We find that LIRGs constitute 30% of the galaxies with stellar mass
M>1x10^{11} Msun assembled at redshift z=0.5. A minimum of 65% of the galaxies
with M>2.5x10^{11} Msun at z~2-3 are ULIRGs at those redshifts. 60% of the
ULIRGs in our sample have the characteristic colours of ERGs. Conversely, 40%
of the ERGs with stellar mass M>1.3x10^{11} Msun at 1.5<z<2.0 and a minimum of
52% of those with the same mass cut at 2.0<z<3.0 are ULIRGs. The average
optical/near-IR properties of the massive ERGs at similar redshifts that are
identified with ULIRGs and that are not have basically no difference,
suggesting that both populations contain the same kind of objects in different
phases of their lives.
LIRGs and ULIRGs have an important role in galaxy evolution and mass
assembly, and, although they are only able to trace a fraction of the massive
(M>1x10^{11} Msun) galaxies present in the Universe at a given time, this
fraction becomes very significant (>50%) at redshifts z>~2.Comment: Accepted for publication in A&A. 9 pages, 6 figure
On the evolution of clustering of 24um-selected galaxies
This paper investigates the clustering properties of a complete sample of
1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping
region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the
two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z
sample) as it is in these regions were we expect the mid-IR population to be
dominated by intense dust-enshrouded activity such as star formation and black
hole accretion. Investigations of the angular correlation function produce a
correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the
low-z one. Comparisons with physical models reveal that the high-z sources are
exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable
to those which locally host groups-to-clusters of galaxies, and are very common
within such (rare) structures. Conversely, lower-z galaxies are found to reside
in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems.
While recent studies have determined a strong evolution of the 24um luminosity
function between z~2 and z~0, they cannot provide information on the physical
nature of such an evolution. Our clustering results instead indicate that this
is due to the presence of different populations of objects inhabiting different
structures, as active systems at z<~1.5 are found to be exclusively associated
with low-mass galaxies, while very massive sources appear to have concluded
their active phase before this epoch. Finally, we note that the small-scale
clustering data seem to require steep profiles for the distribution of galaxies
within their halos. This is suggestive of close encounters and/or mergers which
could strongly favour both AGN and star-formation activity.Comment: 13 pages, 8 figures, to appear in MNRA
Deep imaging of Q2112+059: A bright host galaxy but no DLA absorber
In a ongoing programme aimed at studying galaxy counterparts of Damped
Ly-alpha Absorbers (DLAs) we have obtained high resolution deep I-band imaging
data of the field around the z_em = 0.457 BAL QSO Q2112+059. In the literature
this QSO is listed to have a candidate DLA at z_abs = 0.2039 along the line of
sight. After subtraction of the QSO Point Spread Function (PSF) we detect a
galaxy centred on the position of Q2112+059. To help answer whether this galaxy
is the DLA or the QSO host galaxy we retrieved a GHRS spectrum of Q2112+059
from the HST-archive. This spectrum shows that there is no Ly-alpha absorption
line at z_abs = 0.2039. This fact in combination with the perfect alignment on
the sky of the galaxy and Q2112+059 lead us to the conclusion that the galaxy
must be the host galaxy of Q2112+059.
The host galaxy of Q2112+059 is bright (M_I^obs = -23.6), and has a radial
profile well fitted by a {\it modified Hubble + de Vaucouleurs} profile with
R_c = 0.5 kpc and R_e = 3.6 kpc. Our results are well in line with the
conclusion of earlier work done at lower redshifts, that bright low redshift
QSOs preferentially reside in luminous, elliptical galaxies. The host of
Q2112+059 is however, despite it's brightness, very compact when compared to
early type galaxies at lower redshifts.Comment: 6 pages, 5 figures. Accepted for publication in A&
Discovery of bright z ~ 7 galaxies in the UltraVISTA survey
We have exploited the new, deep, near-infrared UltraVISTA imaging of the
COSMOS field, in tandem with deep optical and mid-infrared imaging, to conduct
a new search for luminous galaxies at redshifts z ~ 7. The unique
multi-wavelength dataset provided by VISTA, CFHT, Subaru, HST and Spitzer over
a common area of 1 deg^2 has allowed us to select galaxy candidates at z > 6.5
by searching first for Y+J-detected (< 25 AB mag) objects which are undetected
in the CFHT+HST optical data. This sample was then refined using a photometric
redshift fitting code, enabling the rejection of lower-redshift galaxy
contaminants and cool galactic M,L,T dwarf stars.The final result of this
process is a small sample of (at most) ten credible galaxy candidates at z >
6.5 which we present in this paper. The first four of these appear to be robust
galaxies at z > 6.5, and fitting to their stacked SED yields z = 6.98+-0.05
with a stellar mass M* = 5x10^9 Msun, and rest-frame UV spectral slope beta =
-2.0+-0.2. The next three are also good candidates for z > 6.5 galaxies, but
the possibility that they are low-redshift galaxies or dwarf stars cannot be
excluded. Our final subset of three additional candidates is afflicted not only
by potential dwarf-star contamination, but also contains objects likely to lie
at redshifts just below z = 6.5. We show that the three even-brighter z > 7
galaxy candidates reported in the COSMOS field by Capak et al. (2011) in fact
all lie at z ~ 1.5-3.5. Consequently the new z ~ 7 galaxies reported here are
the first credible z ~ 7 Lyman-break galaxies discovered in the COSMOS field
and, as the most UV-luminous discovered to date at these redshifts, are prime
targets for deep follow-up spectroscopy. We explore their physical properties,
and briefly consider the implications of their inferred number density for the
form of the galaxy luminosity function at z = 7.Comment: Updated to accepted version, MNRAS. 18 pages, 9 figures, 3 table
Quasar induced galaxy formation: a new paradigm ?
We discuss observational evidence that quasars play a key role in the
formation of galaxies starting from the detailed study of the quasar
HE0450-2958 and extending the discussion to a series of converging evidence
that radio jets may trigger galaxy formation. The direct detection with VISIR
at the ESO-VLT of the 7 kpc distant companion galaxy of HE0450-2958 allows us
to spatially separate the sites of quasar and star formation activity in this
composite system made of two ultra-luminous infrared galaxies (ULIRGs). No host
galaxy has yet been detected for this quasar, but the companion galaxy stellar
mass would bring HE0450-2958 in the local M(BH)-M(stellar bulge) relation if it
were to merge with the QSO. This is bound to happen because of their close
distance (7 kpc) and small relative velocity (~60-200 km/s). We conclude that
we may be witnessing the building of the M(BH)-M(stellar bulge) relation, or at
least of a major event in that process. The star formation rate (~340 Msun/yr),
age (40-200 Myr) and stellar mass ([5-6]x10^10 Msun) are consistent with
jet-induced formation of the companion galaxy. We suggest that HE0450-2958 may
be fueled in fresh material by cold gas accretion from intergalactic filaments.
We map the projected galaxy density surrounding the QSO as a potential tracer
of intergalactic filaments and discuss a putative detection. Comparison to
other systems suggests that inside-out formation of quasar host galaxies and
jet-induced galaxy formation may be a common process. Two tests are proposed
for this new paradigm: (1) the detection of offset molecular gas or dust
emission with respect to the position of distant QSOs, (2) the delayed
formation of host galaxies as a result of QSO activity, hence the two step
building of the M(BH)/M(stellar bulge) ratio.Comment: 15 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics (with minor corrections
A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey
The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the
southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a
limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the
observations, the survey has a much lower resolution in declination than in
right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS
shows that the positional accuracy is less constrained in declination than in
right ascension, but there is no significant systematic error. We present a
source list containing 73570 sources.
We correlate this WISH catalogue with the NVSS to construct a sample of faint
Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies
with large optical telescopes in the southern hemisphere. This sample is aimed
at increasing the number of known high redshift radio galaxies to allow
detailed follow-up studies of these massive galaxies and their environments in
the early Universe.Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in
Astronomy & Astrophysics. The full WISH catalog with 73570 sources is
available from http://www.strw.leidenuniv.nl/wenss
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