4,299 research outputs found
A Search for Nitrogen Enriched Quasars in the Sloan Digital Sky Survey Early Data Release
A search for nitrogen-rich quasars in the Sloan Digital Sky Survey Early Data
Release (SDSS EDR) catalog has yielded 16 candidates, including five with very
prominent emission, but no cases with nitrogen emission as strong as in
Q0353-383. The quasar Q0353-383 has long been known to have extremely strong
nitrogen intercombination lines at lambda 1486 and lambda 1750 Angstroms,
implying an anomalously high nitrogen abundance of about 15 times solar. It is
still the only one of its kind known. A preliminary search through the EDR
using the observed property of the weak C IV emission seen in Q0353-383
resulted in a sample of 23 objects with unusual emission or absorption-line
properties, including one very luminous redshift 2.5 star-forming galaxy. We
present descriptions, preliminary emission-line measurements, and spectra for
all the objects discussed here.Comment: 20 pages, 5 figures, submitted to AJ; final refereed versio
Evidence for (and Against) Progenitor Bias in the Size Growth of Compact Red Galaxies
Most massive passive galaxies are compact at high redshifts, but similarly
compact massive galaxies are rare in the local universe. The most common
interpretation of this phenomenon is that massive galaxies have grown in size
by a factor of about five since redshift z=2. An alternative explanation is
that recently quenched massive galaxies are larger (a "progenitor bias"). In
this paper we explore the importance of progenitor bias by looking for
systematic differences in the stellar populations of compact early-type
galaxies in the DEEP2 survey as a function of size. Our analysis is based on
applying the statistical technique of bootstrap resampling to constrain
differences in the median ages of our samples and to begin to characterize the
distribution of stellar populations in our co-added spectra. The light-weighted
ages of compact early-type galaxies at redshifts 0.5 < z < 1.4 are compared to
those of a control sample of larger galaxies at similar redshifts. We find that
massive compact early-type galaxies selected on the basis of red color and high
bulge-to-total ratio are younger than similarly selected larger galaxies,
suggesting that size growth in these objects is not driven mainly by progenitor
bias, and that individual galaxies grow as their stellar populations age.
However, compact early-type galaxies selected on the basis of image smoothness
and high bulge-to-total ratio are older than a control sample of larger
galaxies. Progenitor bias will play a significant role in defining the apparent
size changes of early-type galaxies if they are selected on the basis of the
smoothness of their light distributions.Comment: 39 pages, 10 figures. Astrophysical Journal (in press
Quantitative Morphology of Galaxies in the Hubble Deep Field
We measure quantitative structural parameters of galaxies in the Hubble Deep
Field (HDF) on the drizzled F814W images. Our structural parameters are based
on a two-component surface brightness made up of a S\'ersic profile and an
exponential profile. We compare our results to the visual classification of van
den Bergh et al. (1996) and the classification of Abraham et al. (1996a).
Our morphological analysis of the galaxies in the HDF indicates that the
spheroidal galaxies, defined here as galaxies with a dominant bulge profile,
make up for only a small fraction, namely 8% of the galaxy population down to
m = 26.0. We show that the larger fraction of early-type systems
in the van den Bergh sample is primarily due to the difference in
classification of 40% of small round galaxies with half-light radii <
0\arcsecpoint 31. Although these objects are visually classified as elliptical
galaxies, we find that they are disk-dominated with bulge fractions < 0.5.
Given the existing large dataset of HDF galaxies with measured spectroscopic
redshifts, we are able to determine that the majority of distant galaxies
() from this sample are disk-dominated. Our analysis reveals a subset of
HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at
http://astro.berkeley.edu/~marleau/. Accepted for Publication in The
Astrophysical Journa
The Galaxy Populations of X-Ray Detected, Poor Groups
(Abridged) We determine the quantitative morphology and star formation
properties of galaxies in six nearby X-ray detected, poor groups using
multi-object spectroscopy and wide-field R imaging. We measure structural
parameters for each galaxy by fitting a PSF-convolved, two component model to
their surface brightness profiles. To compare directly the samples, we fade,
smooth, and rebin each galaxy image so that we effectively observe each galaxy
at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We
compare results for the groups to a sample of field galaxies. We find that: 1)
Galaxies spanning a wide range in morphological type and luminosity are
well-fit by a de Vaucouleurs bulge with exponential disk profile. 2)
Morphologically classifying these nearby group galaxies by their bulge fraction
(B/T) is fairly robust on average, even when their redshift has increased by up
to a factor of four and the effective resolution of the images is degraded by
up to a factor of five. 3) The fraction of bulge-dominated systems in these
groups is higher than in the field (~50% vs. ~20%). 4) The fraction of
bulge-dominated systems in groups decreases with increasing radius, similar to
the morphology-radius (~density) relation observed in galaxy clusters. 5)
Current star formation in group galaxies is correlated with significant
morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group
galaxies that are most disk-dominated (B/T<0.2) are less star forming and
asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12
figures); Figs 1 & 2 also available at
http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g
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Magnetic Resonance Imaging Pilot Study of Intravenous Glyburide in Traumatic Brain Injury.
Pre-clinical studies of traumatic brain injury (TBI) show that glyburide reduces edema and hemorrhagic progression of contusions. We conducted a small Phase II, three-institution, randomized placebo-controlled trial of subjects with TBI to assess the safety and efficacy of intravenous (IV) glyburide. Twenty-eight subjects were randomized and underwent a 72-h infusion of IV glyburide or placebo, beginning within 10 h of trauma. Of the 28 subjects, 25 had Glasgow Coma Scale (GCS) scores of 6-10, and 14 had contusions. There were no differences in adverse events (AEs) or severe adverse events (ASEs) between groups. The magnetic resonance imaging (MRI) percent change at 72-168 h from screening/baseline was compared between the glyburide and placebo groups. Analysis of contusions (7 per group) showed that lesion volumes (hemorrhage plus edema) increased 1036% with placebo versus 136% with glyburide (p = 0.15), and that hemorrhage volumes increased 11.6% with placebo but decreased 29.6% with glyburide (p = 0.62). Three diffusion MRI measures of edema were quantified: mean diffusivity (MD), free water (FW), and tissue MD (MDt), corresponding to overall, extracellular, and intracellular water, respectively. The percent change with time for each measure was compared in lesions (n = 14) versus uninjured white matter (n = 24) in subjects receiving placebo (n = 20) or glyburide (n = 18). For placebo, the percent change in lesions for all three measures was significantly different compared with uninjured white matter (analysis of variance [ANOVA], p < 0.02), consistent with worsening of edema in untreated contusions. In contrast, for glyburide, the percent change in lesions for all three measures was not significantly different compared with uninjured white matter. Further study of IV glyburide in contusion TBI is warranted
A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey
We compare the structural properties of two classes of galaxies at
intermediate redshift: those in dynamically close galaxy pairs, and those which
are isolated. Both samples are selected from the CNOC2 Redshift Survey, and
have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images
were acquired as part of a snapshot survey, and were used to measure bulge
fraction and asymmetry for these galaxies. We find that paired and isolated
galaxies have identical distributions of bulge fractions. Conversely, we find
that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)
than isolated galaxies. Assuming that half of these pairs are unlikely to be
close enough to merge, we estimate that 40% +/- 11% of merging galaxies are
asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is
even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-
8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that
strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors
close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In
addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We
conclude that close to half of the galaxy pairs in our sample are in the
process of merging, and that most of these mergers are accompanied by triggered
star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages,
including 15 figures. For full resolution version, please see
http://www.trentu.ca/physics/dpatton/hstpairs
Evaluating LANDSAT-4 MSS and TM data
Interband line pixel misregistrations were determined for the four MSS bands of the Mistassini, Ontario scene and multitemporal registration of LANDSAT-4 products were tested for two different geocoded scenes. Line and pixel misregistrations are tabulated as determined by the manual ground control points and the digital band to band correlation techniques. A method was developed for determining the spectral information content of TM images for forestry applications
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