859 research outputs found
Star formation rates of distant luminous infrared galaxies derived from Halpha and IR luminosities
We present a study of the star formation rate (SFR) for a sample of 16
distant galaxies detected by ISOCAM at 15um in the CFRS0300+00 and CFRS1400+52
fields. Their high quality and intermediate resolution VLT/FORS spectra have
allowed a proper correction of the Balmer emission lines from the underlying
absorption. Extinction estimates using the Hbeta/Hgamma and the Halpha/Hbeta
Balmer decrement are in excellent agreement, providing a robust measurement of
the instantaneous SFR based on the extinction-corrected Halpha luminosity. Star
formation has also been estimated exploiting the correlations between IR
luminosity and those at MIR and radio wavelengths. Our study shows that the
relationship between the two SFR estimates follow two distinct regimes: (1) for
galaxies with SFRIR below ~ 100Msolar/yr, the SFR deduced from Halpha
measurements is a good approximation of the global SFR and (2) for galaxies
near of ULIRGs regime, corrected Halpha SFR understimated the SFR by a factor
of 1.5 to 2. Our analyses suggest that heavily extincted regions completely
hidden in optical bands (such as those found in Arp 220) contribute to less
than 20% of the global budget of star formation history up to z=1.Comment: (1) GEPI, Obs. Meudon, France ;(2) CEA-Saclay, France ;(3) ESO,
Gemany ;(4) IAC, Spain. To appear in A&
A unique distant submillimeter galaxy with an X-ray-obscured radio-luminous active galactic nucleus
We present a multiwavelength study of an atypical submillimeter galaxy in the
GOODS-North field, with the aim to understand its physical properties of
stellar and dust emission, as well as the central AGN activity. Although it is
shown that the source is likely an extremely dusty galaxy at high redshift, its
exact position of submillimeter emission is unknown. With the new NOEMA
interferometric imaging, we confirm that the source is a unique dusty galaxy.
It has no obvious counterpart in the optical and even NIR images observed with
HST at lambda~<1.4um. Photometric-redshift analyses from both stellar and dust
SED suggest it to likely be at z~>4, though a lower redshift at z~>3.1 cannot
be fully ruled out (at 90% confidence interval). Explaining its unusual
optical-to-NIR properties requires an old stellar population (~0.67 Gyr),
coexisting with a very dusty ongoing starburst component. The latter is
contributing to the FIR emission, with its rest-frame UV and optical light
being largely obscured along our line of sight. If the observed fluxes at the
rest-frame optical/NIR wavelengths were mainly contributed by old stars, a
total stellar mass of ~3.5x10^11Msun would be obtained. An X-ray spectral
analysis suggests that this galaxy harbors a heavily obscured AGN with
N_H=3.3x10^23 cm^-2 and an intrinsic 2-10 keV luminosity of L_X~2.6x10^44
erg/s, which places this object among distant type 2 quasars. The radio
emission of the source is extremely bright, which is an order of magnitude
higher than the star-formation-powered emission, making it one of the most
distant radio-luminous dusty galaxies. The combined characteristics of the
galaxy suggest that the source appears to have been caught in a rare but
critical transition stage in the evolution of submillimeter galaxies, where we
are witnessing the birth of a young AGN and possibly the earliest stage of its
jet formation and feedback.Comment: 13 pages in printer format, 10 figures, 1 table, accepted for
publication in the A&
The Luminosity-Metallicity Relation of distant luminous infrared galaxies
One hundred and five 15mu selected objects in three ISO deep survey fields
(CFRS 3h, UDSR and UDSF) are studied on the basis of the high quality optical
spectra with resolution R>1000 from VLT/FORS2. Ninety two objects (88%) have
secure redshifts, ranging from 0 to 1.16 with a median value of 0.587.
Considerable care is taken in estimating the extinction property of individual
galaxy, which can seriously affect diagnostic diagrams and estimates of star
formation rates and of metal abundances. Two independent methods have been
adopted to estimate extinction, e.g. Balmer line ratio (A_V(Balmer)) and energy
balance between IR and Hbeta luminosities (A_V(IR)). For most of the z>0.4
luminous IR galaxies (LIRGs), the two extinction coefficients are consistent
well, with median values of A_V(IR) = 2.36. These distant LIRGs show many
properties strikingly in common with those of local (IRAS) LIRGs studied by
Veilleux et al. (1995). Our sample can provide a good representation of LIRGs
in the distant Universe. Most (>77%) ISO 15mu selected sample galaxies are
dominated by star formation. Oxygen abundances (12+log(O/H), derived from R23
and O32) in ISM in the distant LIRGs range from 8.36 to 8.93 with a median
value of 8.67. Distant LIRGs present a metal content less than half of that of
the local bright disks (i.e. L*). The Pegase2 models predict that total masses
(gas + stars) of the distant LIRGs are from 10^{11} Msun to <=10^{12} Msun. A
significant fraction of distant large disks are indeed LIRGs. Such massive
disks could have formed ~50% of their metals and stellar masses since z~1.Comment: 20 pages, 9 PS figures, Accepted for publication in A&
From fields to a super-cluster: the role of the environment at z=0.84 with HiZELS
At z=0, clusters are primarily populated by red, elliptical and massive
galaxies, while blue, spiral and lower-mass galaxies are common in low-density
environments. Understanding how and when these differences were established is
of absolute importance for our understanding of galaxy formation and evolution,
but results at high-z remain contradictory. By taking advantage of the widest
and deepest H-alpha narrow-band survey at z=0.84 over the COSMOS and UKIDSS UDS
fields, probing a wide range of densities (from poor fields to rich groups and
clusters, including a confirmed super-cluster with a striking filamentary
structure), we show that the fraction of star-forming galaxies falls
continuously from ~40% in fields to approaching 0% in rich groups/clusters. We
also find that the median SFR increases with environmental density, at least up
to group densities - but only for low and medium mass galaxies, and thus such
enhancement is mass-dependent at z~1. The environment also plays a role in
setting the faint-end slope (alpha) of the H-alpha luminosity function. Our
findings provide a sharper view on galaxy formation and evolution and reconcile
previously contradictory results at z~1: stellar mass is the primary predictor
of star formation activity, but the environment also plays a major role.Comment: 5 pages, 4 figures, to appear in the proceedings of JENAM 2010 S2:
`Environment and the Formation of Galaxies: 30 years later', ASSP, Springe
Multiwavelength Observations of one Galaxy in Marano Field
We report the multiwavelength observations of one intermediate redshift
(z=0.3884) galaxy in the Marano Field. These data include ISOCAM middle
infrared, VLT/FORS2 spectroscopic and photometric data, associated with the
ATCA 1.4 GHz radio and ROSAT PSPC X-ray observations from literature. The
Spectral Energy Distribution obtained by VLT spectroscopy exhibits its
early-type galaxy property, while, in the same time, it has obvious [OIII]5007
emission line. The diagnostic diagram from the optical emission line ratios
shows its Seyfert galaxy property. Its infrared-radio relation follows the
correlation of sources detected at 15 \mu and radio. It has a high X-ray
luminosity of 1.26*10^{43} ergs/s, which is much higher than the general
elliptical galaxies s with the similar B band luminosity, and is about 2 orders
of magnitude higher than the derived value from the star forming tracer, the
FIR luminosity. This means that the X-ray sources of this galaxy are not
stellar components, but the AGN is the dominant component.Comment: 6 pages, 1 PS figure and 4 tables. Publication in ChJAA, Suppl., the
Special Issue for The Fifth Microquasar Workshop 2004:
http://chjaa.bao.ac.cn/, 2005, Vol.5, 335-34
The Contribution of Population III to the Enrichment and Preheating of the Intracluster Medium
Intracluster medium (ICM) abundances are higher than expected assuming
enrichment by supernovae with progenitors belonging to the simple stellar
population (SSP) observed in cluster galaxies, if stars formed with a standard
initial mass function (IMF). Moreover, new results on ICM oxygen abundances
imply that nucleosynthesis occurred with nonstandard yields. The hypothesis
that hypernovae (HN) in general, and HN associated with Population III (Pop
III) stars in particular, may significantly contribute to ICM enrichment is
presented and evaluated. The observed abundance anomalies can be explained by a
hypernovae-producing subpopulation of the SSP, but only if it accounts for half
of all supernova explosions and if Type Ia supernova rates are very low. Also,
the implied energy release may be excessive. However, an independent Pop III
contribution -- in the form of metal-free, very massive stars that evolve into
hypernovae -- can also account for all the observed abundances, while avoiding
these drawbacks and accommodating a normal IMF in subsequent stellar
generations. The required number of Pop III stars provides sufficient energy
injection (at high redshift) to explain the ICM ``entropy floor''. Pop III
hypernova pre-enrich the intergalactic medium, and can produce a significant
fraction of the metals observed in the Lyman-alpha forest. Several testable
predictions for ICM and IGM observations are made.Comment: 15 pages Latex including 1 encapsulated postscript file; ApJ, in
pres
Photo-z Performance for Precision Cosmology II : Empirical Verification
The success of future large scale weak lensing surveys will critically depend
on the accurate estimation of photometric redshifts of very large samples of
galaxies. This in turn depends on both the quality of the photometric data and
the photo-z estimators. In a previous study, (Bordoloi et al. 2010) we focussed
primarily on the impact of photometric quality on photo-z estimates and on the
development of novel techniques to construct the N(z) of tomographic bins at
the high level of precision required for precision cosmology, as well as the
correction of issues such as imprecise corrections for Galactic reddening. We
used the same set of templates to generate the simulated photometry as were
then used in the photo-z code, thereby removing any effects of "template
error". In this work we now include the effects of "template error" by
generating simulated photometric data set from actual COSMOS photometry. We use
the trick of simulating redder photometry of galaxies at higher redshifts by
using a bluer set of passbands on low z galaxies with known redshifts. We find
that "template error" is a rather small factor in photo-z performance, at the
photometric precision and filter complement expected for all-sky surveys. With
only a small sub-set of training galaxies with spectroscopic redshifts, it is
in principle possible to construct tomographic redshift bins whose mean
redshift is known, from photo-z alone, to the required accuracy of 0.002(1+z).Comment: 7 pages, 5 figures, accepted for publication in MNRA
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