25 research outputs found
Probing the gravitational potential of a nearby lensing cluster Abell 2104
The cluster Abell 2104 is one of the lowest redshift clusters (z=0.153) known
to have a gravitational lensing arc. We present detailed analysis of the
cluster properties such as the gravitational potential using the X-ray data
from ROSAT (HRI) and ASCA, as well as optical imaging and spectroscopic data
from the CFHT. The cluster is highly luminous in the X-ray with a bolometric
luminosity of Lx ~3x10^{45} ergs/s and a high gas temperature of ~10.4 keV. The
X-ray emission extending out to at least a radius of 1.46 Mpc, displays
significant substructure. The total mass deduced from the X-ray data under the
assumption of hydrostatic equilibrium and isothermal gas, is found to be
M_tot(r<1.46Mpc) ~(8.0 +/- 0.8)x10^{14} solar mass. The gas fraction within a
radius of 1.46 Mpc is ~5-10%. The cluster galaxy velocity distribution has a
dispersion of 1200 +/- 200 km/s with no obvious evidence for substructure. The
total mass within 1.46 Mpc, deduced from Jean's equation using the observed
galaxy number density distribution and velocity dispersion, is found to be
\~6.8x10^{14} solar mass to ~2.6x10^{15} solar mass marginally consistent with
the X-ray deduced total mass.Comment: 13 pages, 10 postscript figures, use aa.sty, to appear in Astronomy
and Astrophysic
Magellan Spectroscopy of the Galaxy Cluster RX J1347.5-1145: Redshift Estimates for the Gravitationally Lensed Arcs
We present imaging and spectroscopic observations of the gravitationally
lensed arcs in the field of RX J1347.5-1145, the most X-ray luminous galaxy
cluster known. Based on the detection of the [OII] 3727 emission line, we
confirm that the redshift of one of the arcs is z = 0.806. Its color and [OII]
line strength are consistent with those of distant, actively star forming
galaxies. In a second arc, we tentatively identify a pair of absorption lines
superposed on a red continuum; the lines are consistent with Ca II H & K at z =
0.785. We detected a faint blue continuum in two additional arcs, but no
spectral line features could be measured. We establish lower limits to their
redshifts based on the absence of [OII] emission, which we argue should be
present and detectable in these objects. Redshifts are also given for a number
of galaxies in the field of the cluster.Comment: To appear in The Astrophysical Journal (September 2002). 6 page
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
Faint Submillimeter Counts from Deep 850 Micron Observations of the Lensing Clusters A370, A851, and A2390
We present deep 850 micron maps of three massive lensing clusters, A370,
A851, and A2390, with well-constrained mass models. Our cluster exposure times
are more than 2 to 5 times longer than any other published cluster field
observations. We catalog the sources and determine the submillimeter number
counts. The counts are best determined in the 0.3 to 2 mJy range where the
areas are large enough to provide a significant sample. At 0.3 mJy the
cumulative counts are 3.3 (1.3,6.3) 10^4 per square degree, where the upper and
lower bounds in the brackets are the 90% confidence range. The surface density
at these faint count limits enters the realm of significant overlap with other
galaxy populations.The corresponding percentage of the extragalactic background
light (EBL) residing in this flux range is about 45-65%, depending on the EBL
measurement used. Given that 20-30% of the EBL is resolved at flux densities
between 2 and 10 mJy, most of the submillimeter EBL is arising in sources above
0.3 mJy. We also performed a noise analysis to obtain an independent estimate
of the counts. The upper bounds on the counts determined from the noise
analysis closely match the upper limits obtained from the direct counts. The
differential counts from this and other surveys can reasonably be described by
the parameterization n(S)=3 10^4/(0.7 + S^3) per square degree per mJy with S
in mJy, which also integrates to match the EBL
Resolving the Stellar Populations in a z=4 Lensed Galaxy
We present deep near-infrared Keck/NIRC imaging of a recently-discovered
z=4.04 galaxy (Frye & Broadhurst 1998). This is lensed by the rich foreground
cluster Abell~2390 (z~0.23) into highly-magnified arcs 3-5arcsec in length. Our
H- and K'-band NIRC imaging allows us to map the Balmer+4000Ang break
amplitude. In combination with high-quality archival HST/WFPC2 data, we can
spatially resolve stellar populations along the arcs. The WFPC2 images clearly
reveal several bright knots, which correspond to sites of active star
formation. However, there are considerable portions of the arcs are
significantly redder, consistent with being observed >100Myr after star
formation has ceased. Keck/LRIS long-slit spectroscopy along the arcs reveals
that the Ly-alpha emission is spatially offset by ~1arcsec from the rest-UV
continuum regions. We show that this line emission is most probably powered by
star formation in neighboring HII regions, and that the z=4 system is unlikely
to be an AGN.Comment: Accepted for publication in the Astrophysical Journal. Uses
emulateapj.sty and graphics.sty (included). 34 pages - has 5 tables and 21
encapsulated postscript figures, 4 in colour mail (B&W versions also
provided
Substructure lensing in galaxy clusters as a constraint on low-mass sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell 2390
Certain covariant theories of the modified Newtonian dynamics paradigm seem
to require an additional hot dark matter (HDM) component - in the form of
either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs)
with a mass around 11eV - to be relieved of problems ranging from cosmological
scales down to intermediate ones relevant for galaxy clusters. Here we suggest
using gravitational lensing by galaxy clusters to test such a marriage of
neutrino HDM and modified gravity, adopting the framework of
tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter
(CDM), such HDM is subject to strong phase-space constraints, which allows one
to check cluster lens models inferred within the modified framework for
consistency. Since the considered HDM particles cannot collapse into
arbitrarily dense clumps and only form structures well above the galactic
scale, systems which indicate the need for dark substructure are of particular
interest. As a first example, we study the cluster lens Abell 2390 and its
impressive straight arc with the help of numerical simulations. Based on our
results, we outline a general and systematic approach to model cluster lenses
in TeVeS which significantly reduces the calculation complexity. We further
consider a simple bimodal lens configuration, capable of producing the straight
arc, to demonstrate our approach. We find that such a model is marginally
consistent with the hypothesis of 11eV SNs. Future work including more detailed
and realistic lens models may further constrain the necessary SN distribution
and help to conclusively assess this point. Cluster lenses could therefore
provide an interesting discriminator between CDM and such modified gravity
scenarios supplemented by SNs or other choices of HDM.Comment: 22 pages, 14 figures, 2 tables; minor changes to match accepted
versio
Mid-Infrared Spectroscopy of Lensed Galaxies at 1<z<3: The Nature of Sources Near the MIPS Confusion Limit
We present Spitzer/IRS mid-infrared spectra for 15 gravitationally lensed, 24
micron--selected galaxies, and combine the results with 4 additional very faint
galaxies with IRS spectra in the literature. The median intrinsic 24 micron
flux density of the sample is 130 microJy, enabling a systematic survey of the
spectral properties of the very faint 24 micron sources that dominate the
number counts of Spitzer cosmological surveys. Six of the 19 galaxy spectra
(32%) show the strong mid-IR continuua expected of AGN; X-ray detections
confirm the presence of AGN in three of these cases, and reveal AGNs in two
other galaxies. These results suggest that nuclear accretion may contribute
more flux to faint 24 micron--selected samples than previously assumed. Almost
all the spectra show some aromatic (PAH) emission features; the measured
aromatic flux ratios do not show evolution from z=0. In particular, the high
S/N mid-IR spectrum of SMM J163554.2+661225 agrees remarkably well with
low--redshift, lower--luminosity templates. We compare the rest-frame 8 micron
and total infrared luminosities of star--forming galaxies, and find that the
behavior of this ratio with total IR luminosity has evolved modestly from z=2
to z=0. Since the high aromatic--to--continuum flux ratios in these galaxies
rule out a dominant contribution by AGN, this finding implies systematic
evolution in the structure and/or metallicity of infrared sources with
redshift. It also has implications for the estimates of star forming rates
inferred from 24 micron measurements, in the sense that at z ~2, a given
observed frame 24 micron luminosity corresponds to a lower bolometric
luminosity than would be inferred from low-redshift templates of similar
luminosity at the corresponding rest wavelength.Comment: Accepted to the Astrophysical Journal. Full-res version at
ftp://ftp.ociw.edu/pub/jrigby/jrigby-irs.pd