Observational evidence for a different IMF in the early Galaxy

The unexpected high incidence of carbon-enhanced, s-process enriched unevolved stars amongst extremely metal-poor stars in the halo provides a significant constraint on the Initial Mass Function (IMF) in the early Galaxy. We argue that these objects are evidence for the past existence of a large population of intermediate-mass stars, and conclude that the IMF in the early Galaxy was different from the present, and shifted toward higher masses.Comment: 14 pages, 1 color figure, accepted for publication on Ap

Exhaled Nitric Oxide in Children with Asthma and Short-Term PM(2.5) Exposure in Seattle

The objective of this study was to evaluate associations between short-term (hourly) exposures to particulate matter with aerodynamic diameters < 2.5 μm (PM(2.5)) and the fractional concentration of nitric oxide in exhaled breath (Fe(NO)) in children with asthma participating in an intensive panel study in Seattle, Washington. The exposure data were collected with tapered element oscillation microbalance (TEOM) PM(2.5) monitors operated by the local air agency at three sites in the Seattle area. Fe(NO) is a marker of airway inflammation and is elevated in individuals with asthma. Previously, we reported that offline measurements of Fe(NO) are associated with 24-hr average PM(2.5) in a panel of 19 children with asthma in Seattle. In the present study using the same children, we used a polynomial distributed lag model to assess the association between hourly lags in PM(2.5) exposure and Fe(NO) levels. Our model controlled for age, ambient NO levels, temperature, relative humidity, and modification by use of inhaled corticosteroids. We found that Fe(NO) was associated with hourly averages of PM(2.5) up to 10–12 hr after exposure. The sum of the coefficients for the lag times associated with PM(2.5) in the distributed lag model was 7.0 ppm Fe(NO). The single-lag-model Fe(NO) effect was 6.9 [95% confidence interval (CI), 3.4 to 10.6 ppb] for a 1-hr lag, 6.3 (95% CI, 2.6 to 9.9 ppb ) for a 4-hr lag, and 0.5 (95% CI, −1.1 to 2.1 ppb) for an 8-hr lag. These data provide new information concerning the lag structure between PM(2.5) exposure and a respiratory health outcome in children with asthma

A New Algorithm for Supernova Neutrino Transport and Some Applications

We have developed an implicit, multi-group, time-dependent, spherical neutrino transport code based on the Feautrier variables, the tangent-ray method, and accelerated ${\bf \Lambda}$ iteration. The code achieves high angular resolution, is good to O($v/c$), is equivalent to a Boltzmann solver (without gravitational redshifts), and solves the transport equation at all optical depths with precision. In this paper, we present our formulation of the relevant numerics and microphysics and explore protoneutron star atmospheres for snapshot post-bounce models. Our major focus is on spectra, neutrino-matter heating rates, Eddington factors, angular distributions, and phase-space occupancies. In addition, we investigate the influence on neutrino spectra and heating of final-state electron blocking, stimulated absorption, velocity terms in the transport equation, neutrino-nucleon scattering asymmetry, and weak magnetism and recoil effects. Furthermore, we compare the emergent spectra and heating rates obtained using full transport with those obtained using representative flux-limited transport formulations to gauge their accuracy and viability. Finally, we derive useful formulae for the neutrino source strength due to nucleon-nucleon bremsstrahlung and determine bremsstrahlung's influence on the emergent $\nu_{\mu}$ and $\nu_{\tau}$ neutrino spectra.Comment: 58 pages, single-spaced LaTeX, 23 figures, revised title, also available at http://jupiter.as.arizona.edu/~burrows/papers, accepted for publication in the Ap.

The Origin of the Mass--Metallicity Relation: Insights from 53,000 Star-Forming Galaxies in the SDSS

We utilize Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z~0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques which make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (+/-0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 10^{8.5} - 10^{10.5} M_sun, in good accord with known trends between luminosity and metallicity, but flattens above 10^{10.5} M_sun. We use indirect estimates of the gas mass based on the H-alpha luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anti-correlated with baryonic mass, with low mass dwarf galaxies being 5 times more metal-depleted than L* galaxies at z~0.1. Evidence for metal depletion is not confined to dwarf galaxies, but is found in galaxies with masses as high as 10^{10} M_sun. We interpret this as strong evidence both of the ubiquity of galactic winds and of their effectiveness in removing metals from galaxy potential wells.Comment: ApJ accepted, 15 pages, 9 figures, emulateapj.st

Early-type galaxies in the SDSS. I. The sample

A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. This paper describes how the sample was selected, presents examples of images and seeing corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.Comment: 63 pages, 21 figures. Accepted by AJ (scheduled for April 2003). This paper is part I of a revised version of astro-ph/0110344. The full version of Tables 2 and 3, i.e. the tables listing the photometric and spectroscopic parameters of ~ 9000 galaxies, are available at http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/TABLE

Chemical and Photometric Evolution of Extended Ultraviolet Disks: Optical Spectroscopy of M83 (NGC5236) and NGC4625

We present the results from the analysis of optical spectra of 31 Halpha-selected regions in the extended UV (XUV) disks of M83 (NGC5236) and NGC4625 recently discovered by GALEX. The spectra were obtained using IMACS at Las Campanas Observatory 6.5m Magellan I telescope and COSMIC at the Palomar 200-inch telescope, respectively for M83 and NGC4625. The line ratios measured indicate nebular oxygen abundances (derived from the R23 parameter) of the order of Zsun/5-Zsun/10. For most emission-line regions analyzed the line fluxes and ratios measured are best reproduced by models of photoionization by single stars with masses in the range 20-40 Msun and oxygen abundances comparable to those derived from the R23 parameter. We find indications for a relatively high N/O abundance ratio in the XUV disk of M83. Although the metallicities derived imply that these are not the first stars formed in the XUV disks, such a level of enrichment could be reached in young spiral disks only 1 Gyr after these first stars would have formed. The amount of gas in the XUV disks allow maintaining the current level of star formation for at least a few Gyr.Comment: 52 pages, 8 tables, 7 figures, accepted for publication in Ap

Probing the Intermediate-Age Globular Clusters in NGC 5128 from Ultraviolet Observations

We explore the age distribution of the globular cluster (GC) system of the nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from Galaxy Evolution Explorer (GALEX) observations, with UV - optical colors used as the age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and Milky Way in UV - optical color-color diagram, which indicates that the majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31 and Milky Way. A large fraction of spectroscopically identified intermediate-age GC (IAGC) candidates with ~ 3-8 Gyr are not detected in the FUV passband. Considering the nature of intermediate-age populations being faint in the far-UV (FUV) passband, we suggest that many of the spectroscopically identified IAGCs may be truly intermediate in age. This is in contrast to the case of M31 where a large fraction of spectroscopically suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but rather older GCs with developed blue horizontal branch stars. Our UV photometry strengthens the results previously suggesting the presence of GC and stellar subpopulation with intermediate age in NGC 5128. The existence of IAGCs strongly indicates the occurrence of at least one more major star formation episode after a starburst at high redshift.Comment: 8 pages, 3 figures, accepted for ApJ Lette