811 research outputs found
NICMOS Snapshot Survey of Damped Lyman Alpha Quasars
We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap
Synthesis Study: Facilities (Enterprise Development, Sponsorship/Privatization)
The Indiana Department of Transportation maintains 17 rest area locations with 28 separate rest area facilities located on interstates for driver safety and convenience. Although the rest areas provide many benefits to the traveling public, the rest areas do not earn direct profits. Moreover, the Indiana Department of Transportation is increasingly challenged by inadequate funding from taxes generated on the interstates. Constrained by Title 23, that prohibits the commercialization and the privatization of the rest areas, the state of Indiana has a high interest in sustainable sources of revenue at the rest areas that would be able to promote the states and facilities tourism and commerce. The benefits that can be recognized by taking up this project are (i) higher revenues for the INDOT (ii) cost savings wherever possible (iii) environmental benefits (iv) better services and safety measures for overnight travelers (v) partnerships with local businesses
NGC 2992 in an X-ray high state observed by XMM: Response of the Relativistic Fe K Line to the Continuum
We present the analysis of an XMM observation of the Seyfert galaxy NGC 2992.
The source was found in its highest level of X-ray activity yet detected, a
factor higher in 2--10 keV flux than the historical minimum. NGC
2992 is known to exhibit X-ray flaring activity on timescales of days to weeks,
and the XMM data provide at least factor of better spectral resolution
in the Fe K band than any previously measured flaring X-ray state. We find that
there is a broad feature in the \sim 5-7 keV band which could be interpreted as
a relativistic Fe K emission line. Its flux appears to have increased
in tandem with the 2--10 keV continuum when compared to a previous Suzaku
observation when the continuum was a factor of lower than that during
the XMM observation. The XMM data are consistent with the general picture that
increased X-ray activity and corresponding changes in the Fe K line
emission occur in the innermost regions of the putative accretion disk. This
behavior contrasts with the behavior of other AGN in which the Fe K
line does not respond to variability in the X-ray.Comment: 30 pages, 6 figures, Accepted to Ap
The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System
We describe the layout and unique features of the focal plane system for
MIRI. We begin with the detector array and its readout integrated circuit
(combining the amplifier unit cells and the multiplexer), the electronics, and
the steps by which the data collection is controlled and the output signals are
digitized and delivered to the JWST spacecraft electronics system. We then
discuss the operation of this MIRI data system, including detector readout
patterns, operation of subarrays, and data formats. Finally, we summarize the
performance of the system, including remaining anomalies that need to be
corrected in the data pipeline
Cost-Effectiveness of Constructing Minimal Shelter to Store INDOT Equipment (Weather Protection)
Currently vehicles used by INDOT are more likely to be subject to maintenance and repair than to replacement. The extent of wear and tear on the vehicles is likely to be impacted by the lack of covered storage in all districts. There are many different levels of covered storage—from tent-like structures to completely covered garages to temperature-controlled environments—each of which has different associated costs. But the associated reduction in equipment wear, speed of startup of equipment, and perhaps better mileage may all reflect savings to INDOT. This project evaluates INDOT’s expected return on investment to create covered areas for equipment (vehicles, other assets), while also assessing the cost difference between vehicles left in covered versus uncovered areas.
This project can be used to benchmark certain lot sizes of equipment in order to decide whether or not implementing an indoor storage facility is efficient given the harsh conditions that the equipment may be facing during certain periods of the year. The information can be used to see the impact of weathering on snowplow trucks, the maintenance costs that can be reduced, and the payback period of building a shelter facility
The Spitzer Archival Far-InfraRed Extragalactic Survey
We present the Spitzer Archival Far-InfraRed Extragalactic Survey (SAFIRES).
This program produces refined mosaics and source lists for all far-infrared
extragalactic data taken during the more than six years of the cryogenic
operation of the Spitzer Space Telescope. The SAFIRES products consist of
far-infrared data in two wavelength bands (70 um and 160 um) across
approximately 180 square degrees of sky, with source lists containing
far-infrared fluxes for almost 40,000 extragalactic point sources. Thus,
SAFIRES provides a large, robust archival far-infrared data set suitable for
many scientific goals.Comment: 7 pages, 6 figures, published in ApJ
Ultradeep Spectroscopy with the Spitzer IRS
Mid-IR spectroscopy has detected the signatures of star-formation (PAH emission) in high redshift (z > 1) ultra- and hyper-luminous infrared galaxies. However, the study of the dominant population of IR-luminous galaxies (10^(11) - 10^(12) Lsun at 1 < z < 3), requires observation of sources a at the 0.1 mJy level. We present the deepest spectra taken to date in the Long-Low module of the the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. We targeted two faint (~0.15 mJy) sources in the Southern GOODS field at z = 1.09 and z = 2.69 as likely star-forming galaxies. Spectra of the lower redshift target were taken in 8-21 micron range (short-low first order and long-low second order), while the higher redshift target was observed from 21-37 microns (longlow first order). Observing times were 3 and 9 hours on-source for SL-1 and LL-2, respectively, and 12 hours for LL-1. We also present the spectra of two serendipitous sources. We detect strong PAH emission in four targets. We compare the spectra to those of local galaxies observed by the IRS. The z = 1.09 source appears to be a typical, star-formation dominated LIRG, while the z = 2.69 source is a composite source with strong star formation and a prominent AGN. The AGN component dominates the IRAC colors of this source, obscuring the 1.6 μm “bump.” Such sources would be excluded from IRAC surveys for starbursts which might then underestimate the star formation density
Enhanced activity of massive black holes by stellar capture assisted by a self-gravitating accretion disc
We study the probability of close encounters between stars from a nuclear
cluster and a massive black hole. The gravitational field of the system is
dominated by the black hole in its sphere of influence. It is further modified
by the cluster mean field (a spherical term) and a gaseous disc/torus (an
axially symmetric term) causing a secular evolution of stellar orbits via Kozai
oscillations. Intermittent phases of large eccentricity increase the chance
that stars become damaged inside the tidal radius of the central hole. Such
events can produce debris and lead to recurring episodes of enhanced accretion
activity. We introduce an effective loss cone and associate it with tidal
disruptions during the high-eccentricity phases of the Kozai cycle. By
numerical integration of the trajectories forming the boundary of the loss cone
we determine its shape and volume. We also include the effect of relativistic
advance of pericentre. The potential of the disc has the efffect of enlarging
the loss cone and, therefore, the predicted number of tidally disrupted stars
should grow by factor of ~10^2. On the other hand, the effect of the cluster
mean potential together with the relativistic pericentre advance act against
the eccentricity oscillations. In the end we expect the tidal disruption events
to be approximately ten times more frequent in comparison with the model in
which the three effects -- the cluster mean field, the relativistic pericentre
advance, and the Kozai mechanism -- are all ignored. The competition of
different influences suppresses the predicted star disruption rate as the black
hole mass increases. Hence, the process under consideration is more important
for intermediate-mass black holes, M_bh~10^4M_s.Comment: 10 pages, 5 figures; Astronomy & Astrophysics accepte
The Effect of Starburst Metallicity on Bright X-Ray Binary Formation Pathways
We investigate the characteristics of young ( 1e36
erg/s) High-Mass X-ray Binaries (HMXBs) and find the population to be strongly
metallicity-dependent. We separate the model populations among two distinct
formation pathways: (1) systems undergoing active Roche Lobe Overflow (RLO),
and (2) wind accretion systems with donors in the (super)giant (SG) stage,
which we find to dominate the HMXB population. We find metallicity to primarily
affect the number of systems which move through each formation pathway, rather
than the observable parameters of systems which move through each individual
pathway. We discuss the most important model parameters affecting the HMXB
population at both low and high metallicities. Using these results, we show
that (1) the population of ultra-luminous X-Ray sources can be consistently
described by very bright HMXBs which undergo stable Roche Lobe overflow with
mild super-Eddington accretion and (2) the HMXB population of the bright
starburst galaxy NGC~1569 is likely dominated by one extremely metal-poor
starburst cluster.Comment: 12 pages, 10 figures, Accepted by Ap
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