38 research outputs found
Spectroscopic follow up of arclets in AC114 with the VLT
We present the first results on the VLT/FORS-1 spectroscopic survey of
amplified sources and multiple images in the lensing cluster AC114. Background
sources were selected in the cluster core, close to the critical lines, using
photometric redshifts combined with lensing inversion criteria. Spectroscopic
results are given, together with a brief summary of the properties of some of
these high-z galaxies.Comment: 4pages. To appear in the Proceedings of the XXth Moriond Astrophysics
Meeting "Cosmological Physics with Gravitational Lensing", eds. J.-P. Kneib,
Y. Mellier, M. Moniez and J. Tran Thanh Van, Les Arcs, France, March
11th-18th 200
Properties of high-z galaxies as seen through lensing clusters
We discuss the first results obtained on the study of a sample of high-z
galaxies (2 < z < 7), using the gravitational amplification effect in the core
of lensing clusters. Sources are located close to the critical lines in
clusters with well constrained mass distributions, and selected through
photometric redshifts, computed on a large wavelength domain, and lens
inversion techniques.Comment: 5 pages, 3 figures, Conference Proceedings of the "Clustering at High
Redshift" Conference, June 29 to July 2, 1999, Marseille (France
ZEN2: A narrow J-band search for z~9 Lya emitting galaxies directed towards three lensing clusters
We present the results of a continuing survey to detect Lya emitting galaxies
at redshifts z~9: the ZEN ("z equals nine'') survey. We have obtained deep
VLT/ISAAC observations in the narrow J-band filter NB119 directed towards three
massive lensing clusters: Abell clusters 1689, 1835, and 114. The foreground
clusters provide a magnified view of the distant universe and permit a
sensitive test for the presence of very high-redshift galaxies. We search for
z~9 Lya emitting galaxies displaying a significant narrow-band excess relative
to accompanying J-band observations that remain undetected in HST/ACS optical
images of each field. No sources consistent with this criterion are detected
above the unlensed 90% point-source flux limit of the narrow-band image,
F_NB=3.7e-18 ergs/s/cm2. To date, the total coverage of the ZEN survey has
sampled a volume at z~9 of approximately 1700 co-moving Mpc3 to a Lya emission
luminosity of 1e43 erg/s. We conclude by considering the prospects for
detecting z~9 Lya emitting galaxies in light of both observed galaxy properties
at z7.Comment: 7 pages, MNRAS accepte
VIMOS-IFU survey of z~0.2 massive galaxy clusters. I. Observations of the strong lensing cluster Abell 2667
(abridged) We present extensive multi-color imaging and low resolution VIMOS
Integral Field Unit spectroscopic observations of the X-ray luminous cluster
Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is
easily identified as part of a triple image system and other fainter multiple
images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations
cover a field of view of 54'' x 54'' and enable us to determine the redshift of
all galaxies down to V=22.5. Furthermore, redshifts could be identified for
some sources down to V=23.2. In particular we identify 21 cluster members in
the cluster inner region, from which we derive a velocity dispersion of
\sigma=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses
within a 110 kpc radius. Using the multiple images constraints and priors on
the mass distribution of cluster galaxy halos we construct a detailed lensing
mass model leading to a total mass of 2.9 x 10^{13} solar masses within the
Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good
agreement although the dynamical one is much less accurate. Comparing these
measurements with published X-ray analysis, is however less conclusive.
Although the X-ray temperature matches the dynamical and lensing estimates, the
published NFW mass model derived from the X-ray measurement with its small
concentration of c ~3 can not account for the large Einstein radius observed in
this cluster. A larger concentration of ~6 would however match the strong
lensing measurements. These results are likely reflecting the complex structure
of the cluster mass distribution, underlying the importance of panchromatic
studies from small to large scale in order to better understand cluster
physics.Comment: 14 pages, 12 figures. Submitted to A
Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2--1.0) I. Sample description, photometric properties and spectral measurements
We present the spectrophotometric properties of a sample of 141 emission-line
galaxies at redshifts in the range with a peak around
. The analysis is based on medium resolution
(), optical spectra obtained at VLT and Keck. The
targets are mostly {} "Canada-France Redshift Survey" emission-line galaxies,
with the addition of field galaxies randomly selected behind lensing clusters.
We complement this sample with galaxy spectra from the {} "Gemini Deep Deep
Survey" public data release. We have computed absolute magnitudes of the
galaxies and measured the line fluxes and equivalent widths of the main
emission/absorption lines. The last two have been measured after careful
subtraction of the fitted stellar continuum using the \texttt{platefit}
software originally developed for the SDSS and adapted to our data. We present
a careful comparison of this software with the results of manual measurements.
The pipeline has also been tested on lower resolution spectra, typical of the
{} "VIMOS/VLT Deep Survey" (), by resampling our medium
resolution spectra. We show that we can successfully deblend the most important
strong emission lines. These data are primarily used to perform a spectral
classification of the galaxies in order to distinguish star-forming galaxies
from AGNs. Among the initial sample of 141 emission-line galaxies, we find 7
Seyfert 2 (narrow-line AGN), 115 star-forming galaxies and 16 {} "candidate"
star-forming galaxies. Scientific analysis of these data, in terms of chemical
abundances, stellar populations, etc, will be presented in subsequent papers of
this serie.Comment: 24 pages. Accepted for publication in A&A; reference added; bug
corrected: flux scaled by (1+z
Physical properties of two low-luminosity z ~ 1.9 galaxies behind the lensing cluster AC 114
We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed
z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large
magnification factors, we have been successful in detecting rest-frame optical
emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in
previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha
luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times
higher than those inferred from the UV continuum flux at 1500 ang without dust
extinction correction. The behavior of S2 and A2 in terms of O/H and N/O
abundance ratios are very different, and they are also different from typical
LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O
ratio, similar to those derived in the most metal-poor nearby HII galaxies. In
contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O
abundance ratio, similar to those derived in the most metal-rich starburst
nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5
and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational
amplification, the line profiles of S2 are spatially resolved, leading to a
velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x
10^10 Msun within the inner 1 kpc radius. Combining these new data with the
sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit
different physical properties in terms of SFRs, abundance and mass-to-light
ratios, and reddening. High-redshift galaxies of different luminosities could
thus have quite different star formation histories (abridged version).Comment: 11 pages, 8 figures. Accepted for publication in A&
Constraining the population of 6 < z < 10 star-forming galaxies with deep near-IR images of lensing clusters
(abridged) We present the first results of our deep survey of lensing
clusters aimed at constraining the abundance of star-forming galaxies at
z~6-10. Deep near-IR photometry of two lensing clusters (A1835 and AC114) was
obtained with ISAAC/VLT. These images, combined with existing data in the
optical bands, including HST images, were used to select very high redshift
candidates at z>~6 among the optical-dropouts. We have identified 18(8) first
and second-category optical dropouts in A1835 (AC114), detected in more than
one filter up to H(Vega)~23.8 (AB~25.2,uncorrected for lensing). Among them,
8(5) exhibit homogeneous SEDs compatible with star-forming galaxies at z>~6,
and 5(1) are more likely intermediate-redshift EROs based on luminosity
considerations. We have also identified a number of fainter sources in these
fields fulfilling our photometric selection and located around the critical
lines. We use all these data to make a first attempt at constraining the
density of star-forming galaxies present at 6<z<10 using lensing clusters.
Taken at face value, it appears that the number of candidates found seems to be
higher than the one achieved in blank fields with similar photometric depth in
the near-IR. The luminosity function derived for z>6 candidates appears
compatible with that of LBGs at z~3. The turnover observed by Bouwens et al.
(2005) towards the bright end relative to the z~3 LF is not observed in this
sample. Also the upper limit for the UV SFR density at z~6-10 is compatible
with the usual values derived at z~5-6, but higher than the estimates obtained
in the NICMOS Ultra Deep Field (UDF). Increasing the number of blank and
lensing fields with ultra-deep near-IR photometry is essential to get more
accurate constraints on the abundance of z>6 galaxies.Comment: 35 pages, 19 figures; Accepted for publication in A&A; Corrected
missing separation line between First/Second candidates in Table C.2 and
added corrections from language editor. Full version with high resolution
figures available at http://astro.caltech.edu/~johan/publi.htm
EROs found behind lensing clusters. II. Stellar populations and dust properties of optical dropout EROs and comparison with related objects
We determine the nature, redshift, stellar populations and dust properties of
optically faint or non-detected extremely red objects (ERO) found from our
survey of the lensing clusters A1835 and AC114. We perform SED fitting and use
deep optical, HST, VLT, Spitzer data, and for some objects and sub-mm data. For
most of the lensed EROs we find photometric redshifts showing a strong
degeneracy between "low-z" (z~1-3) and high-z (z~6-7). Although formally best
fits are often found at high-z, their resulting bright absolute magnitudes, the
number density of these objects, and in some cases Spitzer photometry or longer
wavelength observations, suggest strongly that all of these objects are at
"low-z". The majority of these objects are best fitted with young (<~ 0.5-0.7
Gyr) and dusty starbursts. Indications for strong extinction, with A_V~2.4-4,
are found in some objects. For dusty objects star formation rates (SFR) have
been estimated from the bolometric luminosity determined after fitting of
semi-empirical starburst, ERO, and ULIRG templates. Typically we find
SFR~(1-18) Msun/yr. Again, SMMJ14009+0252 stands out as a LIRG with SFR 1000
Msun/yr. Concerning the comparison objects, we argue that the massive
post-starburst z~6.5 galaxy candidate HUDF-J2 showing observed properties very
similar to our EROs, is more likely a dusty starburst at z~2.3-2.6. This
interpretation also naturally explains the observed 24 micron emission. Both
empirically and from our SED fits we find that the IRAC selectec EROs from Yan
et al (2004) show very similar properties to our lensed EROs. Reasonable fits
are found for most of them with relatively young and dusty stellar populations.Comment: 18 pages, 17 figures, accepted for publication in Astronomy and
Astrophysic
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author