197 research outputs found
Critical Charges on Strange Quark Nuggets and Other Extended Objects
We investigate the behavior of the critical charge for spontaneous pair
production, , defined as the charge at which the total energy of a
-shell electron is , as a function of the radius of the charge
distribution. Our approach is to solve the Dirac equation for a potential
consisting of a spherically symmetrical charge distribution of radius
and a Coulomb tail. For a spherical shell distribution of the type usually
associated with color-flavor locked strange quark nuggets, we confirm the
relation for sufficiently large obtained by Madsen,
who used an approach based on the Thomas-Fermi model. We also present results
for a uniformly charged sphere and again find that for large enough
. Also discussed is the behavior of when simple {\it ad hoc}
modifications are made to the potential for .Comment: 7 pages, 6 figure
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
Plasma Energy Loss into Kaluza-Klein Modes
Recently, Barger {\em et al.} computed energy losses into Kaluza Klein modes
from astrophysical plasmas in the approximation of zero density for the
plasmas. We extend their work by considering the effects of finite density for
two plasmon processes. Our results show that, for fixed temperature, the energy
loss rate per cm is constant up to some critical density and then falls
exponentially. This is true for transverse and longitudinal plasmons in both
the direct and crossed channels over a wide range of temperature and density. A
difficulty in deriving the appropriate covariant interaction energy at finite
density and temperature is addressed. We find that, for the cases considered by
Barger {\em et al.}, the zero density approximation and the neglect of other
plasmon processes is justified to better than an order of magnitude.Comment: 17 pages, LaTeX2e, 4 figures, 11 table
Charges on Strange Quark Nuggets in Space
Since Witten's seminal 1984 paper on the subject, searches for evidence of
strange quark nuggets (SQNs) have proven unsuccessful. In the absence of
experimental evidence ruling out SQNs, the validity of theories introducing
mechanisms that increase their stability should continue to be tested. To
stimulate electromagnetic SQN searches, particularly space searches, we
estimate the net charge that would develop on an SQN in space exposed to
various radiation baths (and showers) capable of liberating their less strongly
bound electrons, taking into account recombination with ambient electrons. We
consider, in particular, the cosmic background radiation, radiation from the
sun, and diffuse galactic and extragalactic -ray backgrounds. A
possible dramatic signal of SQNs in explosive astrophysical events is noted.Comment: CitationS added, new subsection added, more discussion, same
numerical result
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
Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features
Spectra have been obtained with the low-resolution modules of the Infrared
Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources
having f(24 micron) > 0.75 mJy. Sources were chosen from a survey of
8.2 deg within the NOAO Deep Wide-Field Survey region in Bootes (NDWFS)
using the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope.
Most sources are optically very faint (I > 24mag). Redshifts have previously
been determined for 34 sources, based primarily on the presence of a deep 9.7
micron silicate absorption feature, with a median z of 2.2. Spectra are
presented for the remaining 24 sources for which we were previously unable to
determine a confident redshift because the IRS spectra show no strong features.
Optical photometry from the NDWFS and infrared photometry with MIPS and the
Infrared Array Camera on the Spitzer Space Telescope (IRAC) are given, with K
photometry from the Keck I telescope for some objects. The sources without
strong spectral features have overall spectral energy distributions (SEDs) and
distributions among optical and infrared fluxes which are similar to those for
the sources with strong absorption features. Nine of the 24 sources are found
to have feasible redshift determinations based on fits of a weak silicate
absorption feature. Results confirm that the "1 mJy" population of 24 micron
Spitzer sources which are optically faint is dominated by dusty sources with
spectroscopic indicators of an obscured AGN rather than a starburst. There
remain 14 of the 58 sources observed in Bootes for which no redshift could be
estimated, and 5 of these sources are invisible at all optical wavelengths.Comment: Accepted by Ap
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
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