20 research outputs found
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
Temperature gradients in XMM-Newton observed REFLEX-DXL galaxy clusters at z~0.3
We present XMM-Newton results on the temperature profiles of a volume-limited
sample of galaxy clusters at redshifts z~0.3, selected from the REFLEX survey
(REFLEX-DXL sample). In the spectral analysis, where only the energies above 1
keV were considered, we obtained consistent results on the temperature derived
from the EPN, EMOS1 and EMOS2 data. Useful temperature measurements could be
performed out to radii with overdensity 500 (r500) for all nine clusters. We
discovered a diversity in the temperature gradients at the outer cluster radii
with examples of both flat and strongly decreasing profiles. Using the total
mass and the gas mass profiles for the cluster RXCJ0307.0-2840 we demonstrate
that the errors on the mass estimates for the REFLEX-DXL clusters are within
25% up to r500.Comment: Revised version accepted for publication in A&A, 18 page
Extragalactic Results from the Infrared Space Observatory
More than a decade ago the IRAS satellite opened the realm of external
galaxies for studies in the 10 to 100 micron band and discovered emission from
tens of thousands of normal and active galaxies. With the 1995-1998 mission of
the Infrared Space Observatory the next major steps in extragalactic infrared
astronomy became possible: detailed imaging, spectroscopy and
spectro-photometry of many galaxies detected by IRAS, as well as deep surveys
in the mid- and far- IR. The spectroscopic data reveal a wealth of detail about
the nature of the energy source(s) and about the physical conditions in
galaxies. ISO's surveys for the first time explore the infrared emission of
distant, high-redshift galaxies. ISO's main theme in extragalactic astronomy is
the role of star formation in the activity and evolution of galaxies.Comment: 106 pages, including 17 figures. Ann.Rev.Astron.Astrophys. (in
press), a gzip'd pdf file (667kB) is also available at
http://www.mpe.mpg.de/www_ir/preprint/annrev2000.pdf.g
Powerful obscured AGN among X-ray hard, optically-dim serendipitous Chandra sources
We present a small sample of Chandra X-ray sources selected from the fields
of ACIS observations which probe fluxes around the break in the hard band
source counts. The targets of these fields include 9 nearby galaxy clusters, 1
distant cluster and 2 powerful radio galaxy fields. The follow-up of this
serendipitous sample was biased towards X-ray hard and optically-dim sources
mostly not seen on the Digitized Sky Survey; for these, we present X-ray
fluxes, optical and near-infrared photometry leading to 51 photometric
redshifts in all and 18 independently measured spectroscopic redshifts. Few
sources are associated with the target fields themselves. Fifty-six of 58
sources imaged in the K-band are detected at K<~20 with K_median=18, and of
these, 38 have hard X-ray count ratios and 24 of these are significantly hard
with most of the counts emerging about 2 keV. We find that almost all are AGN
hosted in massive early-type host galaxies with a photometric redshift
distribution peaking at z~1. Two type 2 quasars with intrinsic X-ray luminosity
L>~10^{45} erg/s, Fe K_alpha emission lines and absorbing column density
nH>10^{23} cm^{-2} -- and nH>~10^{24} cm^{-2} in one case -- are discussed in
detail; the sample contains at least 12 potential type 2 quasars in all. We
discuss various detection strategies for type 2 quasars and calculate their
inferred space density. This combines and extends a number of results from
subsamples already published by us.Comment: MNRAS accepted; 30 pages, 12 figures, 8 tables; Figures of all
targets and other information available in the electronic journal and
temporarily at http://www-xray.ast.cam.ac.uk/~pg/xrbsources/imsp
Ultraluminous Infrared Galaxies
Ever since their discovery in the 1970's, UltraLuminous InfraRed Galaxies
(ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their
immense luminosities, and frustrated them due to their singularly opaque
nature, almost in equal measure. Over the last decade, however, comprehensive
observations from the X-ray through to the radio have produced a consensus
picture of local ULIRGs, showing that they are mergers between gas rich
galaxies, where the interaction triggers some combination of dust-enshrouded
starburst and AGN activity, with the starburst usually dominating. Very recent
results have thrown ULIRGs even further to the fore. Originally they were
thought of as little more than a local oddity, but the latest IR surveys have
shown that ULIRGs are vastly more numerous at high redshift, and tantalizing
suggestions of physical differences between high and low redshift ULIRGs hint
at differences in their formation modes and local environment. In this review
we look at recent progress on understanding the physics and evolution of local
ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared
background and the global history of star formation, and the role of ULIRGs as
diagnostics of the formation of massive galaxies and large-scale structures.Comment: Review article, published in "Astrophysics Update 2 - topical and
timely reviews on astronomy and astrophysics". Ed. John W. Mason.
Springer/Praxis books. ISBN: 3-540-30312-X. 53 pages, 5 figures. Higher
quality figures available on reques