366 research outputs found
HTC Scientific Computing in a Distributed Cloud Environment
This paper describes the use of a distributed cloud computing system for
high-throughput computing (HTC) scientific applications. The distributed cloud
computing system is composed of a number of separate
Infrastructure-as-a-Service (IaaS) clouds that are utilized in a unified
infrastructure. The distributed cloud has been in production-quality operation
for two years with approximately 500,000 completed jobs where a typical
workload has 500 simultaneous embarrassingly-parallel jobs that run for
approximately 12 hours. We review the design and implementation of the system
which is based on pre-existing components and a number of custom components. We
discuss the operation of the system, and describe our plans for the expansion
to more sites and increased computing capacity
The Infrared Einstein Ring in the Gravitational Lens MG1131+0456 and the Death of the Dusty Lens Hypothesis
We have obtained and modeled new NICMOS images of the lens system
MG1131+0456, which show that its lens galaxy is an H=18.6 mag, transparent,
early-type galaxy at a redshift of about z_l = 0.85; it has a major axis
effective radius R_e=0.68+/-0.05 arcsec, projected axis ratio b/a=0.77+/-0.02,
and major axis PA=60+/-2 degrees. The lens is the brightest member of a group
of seven galaxies with similar R-I and I-H colors, and the two closest group
members produce sufficient tidal perturbations to explain the ring morphology.
The host galaxy of the MG1131+0456 source is a z_s > 2 ERO (``extremely red
object'') which is lensed into optical and infrared rings of dramatically
different morphologies. These differences imply a strongly wavelength-dependent
source morphology that could be explained by embedding the host in a larger,
dusty disk. At 1.6 micron (H), the ring is spectacularly luminous, with a total
observed flux of H=17.4 mag and a de-magnified flux of 19.3 mag, corresponding
to a 1-2L_* galaxy at the probable source redshift of z_s > 2. Thus, it is
primarily the stellar emission of the radio source host galaxy that produces
the overall colors of two of the reddest radio lenses, MG1131+0456 and
B~1938+666, aided by the suppression of optical AGN emission by dust in the
source galaxy. The dusty lens hypothesis -- that many massive early-type
galaxies with 0.2 < z_l < 1.0 have large, uniform dust opacities -- is ruled
out.Comment: 27 pages, 8 COLOR figures, submitted to ApJ. Black and white version
available at http://cfa-www.harvard.edu/castle
The Case Against Cosmology
It is argued that some of the recent claims for cosmology are grossly
overblown. Cosmology rests on a very small database: it suffers from many
fundamental difficulties as a science (if it is a science at all) whilst
observations of distant phenomena are difficult to make and harder to
interpret. It is suggested that cosmological inferences should be tentatively
made and sceptically received.Comment: 9 pages, no figure
Radio-loud Active Galaxies in the Northern ROSAT All-Sky Survey III: New Spectroscopic Identifications from the RGB BL Lac Survey
We present new spectroscopic identifications for 169 objects in the
RASS-Green Bank (RGB) catalog of radio- and X-ray-emitting AGN. These data
significantly increase the fraction of bright RGB objects with classifications.
Specifically, we report and discuss the classification of 66 radio-loud
quasars, 53 BL Lacs, 33 Broad Line Radio Galaxies, 5 Narrow Line Radio
Galaxies, 1 Seyfert I galaxy and 11 galaxies or galaxies in clusters. Over 78%
of the identifications we present here are new. The observations we report were
undertaken as part of our targeted search program to identify a new, large
unbiased sample of BL Lac Objects and we therefore discuss the BL Lac sample
extensively. Unlike many previous surveys, we impose no selection criteria
based on optical morphology, color or broadband spectral energy distribution.
Our classifications are based solely on a carefully defined set of
self-consistent spectroscopic classification criteria. We show the 53 RGB
presented here exhibit transitional properties between normal galaxies and BL
Lacs discovered previously. We show there is no clear separation in CaII break
strength between RGB BL Lacs and galaxies, with the distribution of break
strengths varying smoothly between 0% and 50%. We also show that the newly
discovered RGB BL Lacs reside in a "zone of avoidance" in the log(S_x/S_r) vs.
log(S_o/S_r) diagram. This has important implications for BL Lac search
strategies since it shows that RASS BL Lac samples will be severely incomplete
if candidates are chosen only from among those objects with the highest S_x/S_r
flux ratios.Comment: 21 pages text, 189 Figures, 4 tables, LaTeX2E, 4.2MB tar file
(compressed); special style file paper.sty provide
The Quasar Pair Q 1634+267 A, B and the Binary QSO vs. Dark Lens Hypotheses
Deep HST/NICMOS H (F160W) band observations of the z=1.96 quasar pair Q
1634+267A,B reveal no signs of a lens galaxy to a 1 sigma threshold of
approximately 22.5 mag. The minimum luminosity for a normal lens galaxy would
be a 6L_* galaxy at z > 0.5, which is 650 times greater than our detection
threshold. Our observation constrains the infrared mass-to-light ratio of any
putative, early-type, lens galaxy to (M/L)_H > 690h_65 (1200h_65) for
Omega_0=0.1 (1.0) and H_0=65h_65 km/s/Mpc. We would expect to detect a galaxy
somewhere in the field because of the very strong Mg II absorption lines at
z=1.1262 in the Q 1634+267 A spectrum, but the HST H-band, I-band (F785LP) and
V-band (F555W) images require that any associated galaxy be very under-luminous
less than 0.1 L^*_H (1.0 L^*_I) if it lies within less than 40 h^{-1} (100
h^{-1}) kpc from Q 1634+267 A,B.
While the large image separation (3.86 arcsec) and the lack of a lens galaxy
strongly favor interpreting Q 1634+267A,B as a binary quasar system, the
spectral similarity remains a puzzle. We estimate that at most 0.06% of
randomly selected quasar pairs would have spectra as similar to each other as
the spectra of Q 1634+267 A and B. Moreover, spectral similarities observed for
the 14 quasar pairs are significantly greater than would be expected for an
equivalent sample of randomly selected field quasars. Depending on how strictly
we define similarity, we estimate that only 0.01--3% of randomly drawn samples
of 14 quasar pairs would have as many similar pairs as the observational
sample.Comment: 24 pages, including 4 figures, LaTex, ApJ accepted, comments from the
editor included, minor editorial change
PMN J1838-3427: A new gravitationally lensed quasar
We report the discovery of a new double-image quasar that was found during a
search for gravitational lenses in the southern sky. Radio source PMN
J1838-3427 is composed of two flat-spectrum components with separation 1", flux
density ratio 14:1 and matching spectral indices, in VLA and VLBA images.
Ground-based BRI images show the optical counterpart (total I=18.6) is also
double with the same separation and position angle as the radio components. An
HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is
higher than the radio value probably due to differential extinction of the
components by the lens galaxy. An optical spectrum of the bright component
contains quasar emission lines at z=2.78 and several absorption features,
including prominent Ly-alpha absorption. The lens galaxy redshift could not be
measured but is estimated to be z=0.36 +/- 0.08. The image configuration is
consistent with the simplest plausible models for the lens potential. The flat
radio spectrum and observed variability of PMN J1838-3427 suggest the time
delay between flux variations of the components is measurable, and could thus
provide an independent measurement of H_0.Comment: 23 pages, incl. 6 figures, to appear in A.J.; replaced with accepted
version; minor changes to text, improved figure
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