119 research outputs found
A ring galaxy at z=1 lensed by the cluster Abell 370
We present a study of a very peculiar object found in the field of the
cluster-lens Abell 370. This object displays, in HST imaging, a spectacular
morphology comparable to nearby ring-galaxies. From spectroscopic observations
at the CFHT, we measured a redshift of based on the identification of
[O ii] 3727 \AA and [Ne v] 3426 \AA emission lines. These emission lines are
typical of starburst galaxies hosting a central active nucleus and are in good
agreement with the assumption that this object is a ring-galaxy. This object is
also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR)
flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally
distorted by the cluster-lens, and most particularly by a nearby cluster
elliptical galaxy. Using the cluster mass model, we can compute its intrinsic
shape. Requiring that the outer ring follows an ellipse we put constraints on
the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5
0.2. The absolute luminosities of the source are then $L_B = 1.3 \
10^{12} L_{B \odot}\nu_\nu \simeq 4. 10^{10}_\odot$ in the
mid-IR.Comment: 5 pages, 5 figures, uses aa.cls, accepted to A&A Letters. Minor
changes, Figure 1 revisited and typos adde
A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654. II. A high-speed collision?
The mass distribution of the rich cluster of galaxies Cl0024+1654 has
frequently been used to constrain the nature of dark matter yet a model
consistent with all the observational data has been difficult to construct. In
this paper we analyse the three-dimensional structure of this cluster using new
spectroscopic information on ~300 galaxies within a projected radius of 3
Mpc/h. These data reveal an unusual foreground component of galaxies separated
from the main cluster by 3000 km/s. We use numerical simulations to show that a
high speed collision along the line of sight between Cl0024+1654 and a second
cluster of slightly smaller mass can reproduce the observed peculiar redshift
distribution. The collision dramatically alters the internal mass distribution
of the bound remnants, creating constant density cores from initially cuspy
dark matter profiles and scattering galaxies to large projected radii. Our
results can reconcile the inferred mass profile from gravitational lensing with
predictions from hierarchical structure formation models, while at the same
time resolving the mass discrepancy that results from a comparison between
lensing, velocity dispersion and X-ray studies.Comment: 11 pages, 9 Postscript figures, 1 Jpeg; replaced with clearer, more
concise and accepted version, 13 Feb. 200
An ISOCAM survey through gravitationally lensing galaxy clusters
ISOCAM was used to perform a deep survey through three gravitationally
lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the
clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3
microns, showing a total of 145 mid-IR sources and the associated source
counts. The 15 micron counts reach the faintest level yet recorded. All sources
have counterparts in the optical or near-IR. Models of the clusters were used
to correct for the effects of lensing, which increases the sensitivity of the
survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have
redshift between 0.23 & 2.8, with a median of 0.9. The field sources were
counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14
microJy at 7 microns. The counts, corrected for completeness, contamination by
cluster sources and lensing, confirm and extend findings of an excess by a
factor of ten in the 15 micron population with respect to source models with no
evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7
microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2
nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources.
At 15 microns we include the counts from other ISOCAM surveys to integrate from
30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to
resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%,
respectively, of the upper limit to the IBL, derived from photon-photon pair
production of the TeV gamma rays from BL-Lac sources on the IBL photons.
However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428
suggest that the 15 micron background reported implies substantial absorption
of TeV photons from that source.Comment: 35 pages, 17 figures, to appear in Astronomy and Astrophysics, full
paper with high-resolution figures available at
http://www.iso.vilspa.esa.es/science/pub/2003
A Systematic Search for High Surface Brightness Giant Arcs in a Sloan Digital Sky Survey Cluster Sample
We present the results of a search for gravitationally-lensed giant arcs
conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of
the images and an automated search were performed and no arcs were found. This
result is used to set an upper limit on the arc probability per cluster. We
present selection functions for our survey, in the form of arc detection
efficiency curves plotted as functions of arc parameters, both for the visual
inspection and the automated search. The selection function is such that we are
sensitive only to long, high surface brightness arcs with g-band surface
brightness mu_g 10. Our upper limits on
the arc probability are compatible with previous arc searches. Lastly, we
report on a serendipitous discovery of a giant arc in the SDSS data, known
inside the SDSS Collaboration as Hall's arc.Comment: 34 pages,8 Fig. Accepted ApJ:Jan-200
Detecting high redshift evolved galaxies as the hosts of optically faint hard X-ray sources
We combine deep Subaru near-infrared images of the massive lensing clusters
A2390 and A370 with Keck optical data to map the spectral energy distributions
(SEDs) of Chandra X-ray sources lying behind the clusters. The three sources
behind A2390 are found to have extremely red colors with SEDs consistent with
evolved galaxies at redshifts z>1.4. One source has extremely anomalous colors,
which we interpret as evidence for a type Sa SED at a redshift around 2.5. The
photometric redshift of another source has been confirmed at z=1.467 from
near-infrared spectroscopy using the CISCO spectrograph on Subaru. Mapping of
optically faint hard X-ray sources may prove to be an extremely efficient way
to locate luminous evolved galaxies at high redshifts.Comment: 5 pages, ApJ Letters, in pres
Properties of mm galaxies: Constraints from K-band blank fields
We have used the IRAM Plateau de Bure mm interferometer to locate with
subarcsecond accuracy the dust emission of three of the brightest 1.2mm sources
in the NTT Deep Field (NDF) selected from our 1.2mm MAMBO survey at the IRAM
30m telescope. We combine these results with deep B to K imaging and VLA
interferometry. Strikingly, none of the three accurately located mm galaxies
MMJ120546-0741.5, MMJ120539-0745.4, and MMJ120517-0743.1 has a K-band
counterpart down to the faint limit of K>21.9. This implies that these three
galaxies are either extremely obscured and/or are at very high redshifts
(z>~4). We combine our results with literature data for 11 more (sub)mm
galaxies that are identified with similar reliability. In terms of their K-band
properties, the sample divides into three roughly equal groups: (i) undetected
to K~22, (ii) detected in the near-infrared but not the optical and (iii)
detected in the optical with the possibility of optical follow-up spectroscopy.
We find a trend in this sample between near-infrared to submm and submm to
radio spectral indices, which in comparison to spectral energy distributions
(SEDs) of low redshift infrared luminous galaxies suggests that the most
plausible primary factor causing the extreme near-infrared faintness of our
objects is their high redshift. We show that the near-infrared to radio SEDs of
the sample are inconsistent with SEDs that resemble local far-infrared cool
galaxies with moderate luminosities, which were proposed in some models of the
submm sky. We briefly discuss the implications of the results for our
understanding of galaxy formation.Comment: aastex, 5 figures. Accepted by Ap
Gravitational Lensing by Dark Matter Caustics
Dark matter caustics have specific density profiles and, therefore, precisely
calculable gravitational lensing properties. We present a formalism which
simplifies the relevant calculations, and apply it to four specific cases. In
the first three, the line of sight is tangent to a smooth caustic surface. The
curvature of the surface at the tangent point is positive, negative or zero. In
the fourth case the line of sight passes near a cusp. For each we derive the
map between the image and source planes. In some cases, a point source has
multiple images and experiences infinite magnification when the images merge.
Unfortunately, for the dark matter caustics expected in realistic galactic halo
models, the angular resolution required to resolve the multiple images is not
presently achievable. A more promising approach aims to observe the distortions
caused by dark matter caustics in the images of extended sources such as radio
jets.Comment: 36 pages, 11 figure
Caustics of Compensated Spherical Lens Models
We consider compensated spherical lens models and the caustic surfaces they
create in the past light cone. Examination of cusp and crossover angles
associated with particular source and lens redshifts gives explicit lensing
models that confirm previous claims that area distances can differ by
substantial factors from angular diameter distances even when averaged over
large angular scales. `Shrinking' in apparent sizes occurs, typically by a
factor of 3 for a single spherical lens, on the scale of the cusp caused by the
lens; summing over many lenses will still leave a residual effect.Comment: 21 pages, 5 ps figures, eps
The faint counterparts of MAMBO mm sources near the NTT Deep Field
We discuss identifications for 18 sources from our MAMBO 1.2mm survey of the
region surrounding the NTT Deep Field. We have obtained accurate positions from
Very Large Array 1.4GHz interferometry and in a few cases IRAM mm
interferometry, and have also made deep BVRIzJK imaging at ESO. We find
thirteen 1.2mm sources associated with optical/near-infrared objects in the
magnitude range K=19.0 to 22.5, while five are blank fields at K>22. The median
redshift of the radio-identified mm sources is ~2.6 from the radio/mm
estimator, and the median optical/near-infrared photometric redshifts for the
objects with counterparts ~2.1. This suggests that those radio-identified mm
sources without optical/near-infrared counterparts tend to lie at higher
redshifts than those with optical/near-infrared counterparts. Compared to
published identifications of objects from 850micron surveys of similar depth,
the median K and I magnitudes of our counterparts are roughly two magnitudes
fainter and the dispersion of I-K colors is less. Real differences in the
median redshifts, residual mis-identifications with bright objects, cosmic
variance, and small number statistics are likely to contribute to this
significant difference, which also affects redshift measurement strategies. We
discuss basic properties of the near-infrared/(sub)mm/radio spectral energy
distributions of our galaxies and of interferometrically identified submm
sources from the literature. From a comparison with submm objects with
CO-confirmed spectroscopic redshifts we argue that roughly two thirds of the
(sub)mm galaxies are at z>~2.5. This fraction is probably larger when including
sources without radio counterparts. (abridged)Comment: 45 pages, 9 figures. Accepted by ApJ. The resolution of figures 2 and
3 has been degraded. A higher quality pdf version of this paper is available
at http://www.mpe.mpg.de/~dannerb
- …