2,459 research outputs found
Absorption spectra of Q 0000-263 and Q 1442+101
Studying the Lyman-alpha forest allows us to trace the cosmological distribution of matter through time, and may reveal insights into important questions such as the onset of galaxy formation. An equation for determining the number of Lyman-alpha absorption lines per redshift per rest equivalent in the Lyman-alpha forest is given. For a nonevolving population of clouds gamma = 1 for q(sub 0) = 0, and gamma = 0.5 for q(sub 0) = 0.5. A detailed study of the Lyman-alpha forests of Q 1442+101 at z(sub em) = 3.54 and Q 0000-263 at z(sub em) = 4.11
Calibrating the Star Formation Rate at z=1 from Optical Data
We present a star-formation rate calibration based on optical data that is
consistent with average observed rates in both the red and blue galaxy
populations at z~1. The motivation for this study is to calculate SFRs for
DEEP2 Redshift Survey galaxies in the 0.7<z<1.4 redshift range, but our results
are generally applicable to similar optically-selected galaxy samples without
requiring UV or IR data. Using SFRs fit from UV/optical SEDs in the AEGIS
survey, we explore the behavior of restframe B-band magnitude, observed [OII]
luminosity, and restframe (U-B) color with SED-fit SFR for both red sequence
and blue cloud galaxies. We find that a SFR calibration can be calculated for
all z~1 DEEP2 galaxies using a simultaneous fit in M_B and restframe colors
with residual errors that are within the SFR measurement error. The resulting
SFR calibration produces fit residual errors of 0.3 dex RMS scatter for the
full color-independent sample with minimal correlated residual error in L[OII]
or stellar mass. We then compare the calibrated z~1 SFRs to two diagnostics
that use L[OII] as a tracer in local galaxies and correct for dust extinction
at intermediate redshifts through either galaxy B-band luminosity or stellar
mass. We find that a L[OII] - M_B SFR calibration commonly used in the
literature agrees well with our calculated SFRs after correcting for the
average B-band luminosity evolution in L* galaxies. However, we find better
agreement with a local L[OII]-based SFR calibration that includes stellar mass
to correct for reddening effects, indicating that stellar mass is a better
tracer of dust extinction for all galaxy types and less affected by systematic
evolution than galaxy luminosity from z=1 to the current epoch.Comment: 16 pages, 15 figures, emulateapj format, to be submitted to Ap
Crossover from Conserving to Lossy Transport in Circular Random Matrix Ensembles
In a quantum dot with three leads the transmission matrix t_{12} between two
of these leads is a truncation of a unitary scattering matrix S, which we treat
as random. As the number of channels in the third lead is increased, the
constraints from the symmetry of S become less stringent and t_{12} becomes
closer to a matrix of complex Gaussian random numbers with no constraints. We
consider the distribution of the singular values of t_{12}, which is related to
a number of physical quantities. Changing the number of channels in the third
lead corresponds to increasing the amount of loss in the system (and is
distinct from prior uses of a third lead to model dephasing)
A New Star-Formation Rate Calibration from Polycyclic Aromatic Hydrocarbon Emission Features and Application to High Redshift Galaxies
We calibrate the integrated luminosity from the polycyclic aromatic
hydrocarbon (PAH) features at 6.2\micron, 7.7\micron\ and 11.3\micron\ in
galaxies as a measure of the star-formation rate (SFR). These features are
strong (containing as much as 5-10\% of the total infrared luminosity) and
suffer minimal extinction. Our calibration uses \spitzer\ Infrared Spectrograph
(IRS) measurements of 105 galaxies at , infrared (IR) luminosities
of 10^9 - 10^{12} \lsol, combined with other well-calibrated SFR indicators.
The PAH luminosity correlates linearly with the SFR as measured by the
extinction-corrected \ha\ luminosity over the range of luminosities in our
calibration sample. The scatter is 0.14 dex comparable to that between SFRs
derived from the \paa\ and extinction-corrected \ha\ emission lines, implying
the PAH features may be as accurate a SFR indicator as hydrogen recombination
lines. The PAH SFR relation depends on gas-phase metallicity, for which we
supply an empirical correction for galaxies with 0.2 < \mathrm{Z} \lsim
0.7~\zsol. We present a case study in advance of the \textit{James Webb Space
Telescope} (\jwst), which will be capable of measuring SFRs from PAHs in
distant galaxies at the peak of the SFR density in the universe () with
SFRs as low as ~10~\sfrunits. We use \spitzer/IRS observations of the PAH
features and \paa\ emission plus \ha\ measurements in lensed star-forming
galaxies at to demonstrate the ability of the PAHs to derive
accurate SFRs. We also demonstrate that because the PAH features dominate the
mid-IR fluxes, broad-band mid-IR photometric measurements from \jwst\ will
trace both the SFR and provide a way to exclude galaxies dominated by an AGN.Comment: Accepted for publication in Ap
The information needs of older people who choose supportive care over dialysis: A case study approach
Background: Supportive care is increasingly being viewed as an appropriate alternative option to dialysis or transplantation for older people with advanced chronic kidney disease (ACKD). The purpose of this study was to explore the information needs of older people with ACKD who choose supportive care as their treatment. Methods: A case study approach using semi-structured interviews and medical case note review methods was used to explore the information needs of six older people receiving supportive care. Results: The majority of the information the participants had recalled receiving placed a greater emphasis on dialysis over supportive care. Although they did not want dialysis, they were not clear on what supportive care meant or whether they had a supportive care plan. Participants perceived they had never been given specific information about supportive care. Medical case note review revealed infrequent and non-systematic documentation in medical case notes. Conclusions: In the absence of a formal nephrology supportive care program, information may be provided in an unplanned, non-systematic approach to older people and their families who choose supportive care
Total Infrared Luminosity Estimation of Resolved and Unresolved Galaxies
The total infrared (TIR) luminosity from galaxies can be used to examine both
star formation and dust physics. We provide here new relations to estimate the
TIR luminosity from various Spitzer bands, in particular from the 8 micron and
24 micron bands. To do so, we use 45" subregions within a subsample of nearby
face-on spiral galaxies from the Spitzer Infrared Nearby Galaxies Survey
(SINGS) that have known oxygen abundances as well as integrated galaxy data
from the SINGS, the Local Volume Legacy Survey (LVL) and Engelbracht et al.
(2008) samples. Taking into account the oxygen abundances of the subregions,
the star formation rate intensity, and the relative emission of the polycyclic
aromatic hydrocarbons at 8 micron, the warm dust at 24 micron and the cold dust
at 70 micron and 160 micron we derive new relations to estimate the TIR
luminosity from just one or two of the Spitzer bands. We also show that the
metallicity and the star formation intensity must be taken into account when
estimating the TIR luminosity from two wave bands, especially when data
longward of 24 micron are not available.Comment: 11 pages, 10 figures, accepted for publication in Ap
Forming Early-type Galaxies in Groups Prior to Cluster Assembly
We study a unique proto-cluster of galaxies, the supergroup SG1120-1202. We
quantify the degree to which morphological transformation of cluster galaxies
occurs prior to cluster assembly in order to explain the observed early-type
fractions in galaxy clusters at z=0. SG1120-1202 at z~0.37 is comprised of four
gravitationally bound groups that are expected to coalesce into a single
cluster by z=0. Using HST ACS observations, we compare the morphological
fractions of the supergroup galaxies to those found in a range of environments.
We find that the morphological fractions of early-type galaxies (~60 %) and the
ratio of S0 to elliptical galaxies (0.5) in SG1120-1202 are very similar to
clusters at comparable redshift, consistent with pre-processing in the group
environment playing the dominant role in establishing the observed early-type
fraction in galaxy clusters.Comment: 5 pages, 2 figures, 2 tables. Accepted for publication in ApJ Letter
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