Exploring the host environments of long-duration gamma-ray bursts

We have conducted the first dedicated spectroscopic survey of long-duration gamma-ray burst (LGRB) host galaxies at z < 1, and use these observations along with data from the literature to determine a wide range of ISM properties and a statistically robust mass-metallicity relation. LGRBs have been proposed as possible tracers of star formation at high redshift; however, such an association is dependent on a thorough understanding of the relationship between LGRB progenitors and their host environments. In particular, the metallicity of LGRB host galaxies has become a matter of hot debate in recent years. We conclude that LGRBs do exhibit a general trend toward lower-metallicity host galaxies, but also detect several high-metallicity hosts in our sample. We have also compared the energetic and environmental properties of the LGRBs in our sample, and find no statistically significant correlation between host metallicity and isotropic or beaming-corrected gamma-ray energy release. This is at odds with previous theoretical and observational predictions of an inverse correlation between gamma-ray energy release and host metallicity, and demonstrates that the complex role of metallicity in LGRB progenitor formation still remains unclear.Comment: 4 pages, 2 figures; to appear in AIP proceedings of "Gamma Ray Bursts 2010

The Host Galaxies of Long-Duration Gamma-Ray Bursts

Long-duration gamma-ray bursts (LGRBs) are the signatures of extraordinarily high-energy events occurring in our universe. Since their discovery, we have determined that these events are produced during the core-collapse deaths of rare young massive stars. The host galaxies of LGRBs are an excellent means of probing the environments and populations that produce their unusual progenitors. In addition, these same young stellar progenitors makes LGRBs and their host galaxies valuable potentially powerful tracers of star formation and metallicity at high redshifts. However, properly utilizing LGRBs as probes of the early universe requires a thorough understanding of their formation and the host environments that they sample. This review looks back at some of the recent work on LGRB host galaxies that has advanced our understanding of these events and their cosmological applications, and considers the many new questions that we are poised to pursue in the coming years.Comment: 33 pages, 4 figures, 1 table; invited review for PASP, in pres

Red Supergiants in the Local Group

Galaxies in the Local Group span a factor of 15 in metallicity, ranging from the super-solar M31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the lowest-metallicity (0.1xZsun) Local Group galaxy currently forming stars. Studies of massive star populations across this broad range of environments have revealed important metallicity-dependent evolutionary trends, allowing us to test the accuracy of stellar evolutionary tracks at these metallicities for the first time. The RSG population is particularly valuable as a key mass-losing phase of moderately massive stars and a source of core-collapse supernova progenitors. By reviewing recent work on the RSG populations in the Local Group, we are able to quantify limits on these stars' effective temperatures and masses and probe the relationship between RSG mass loss behaviors and host environments. Extragalactic surveys of RSGs have also revealed several unusual RSGs that display signs of unusual spectral variability and dust production, traits that may potentially also correlate with the stars' host environments. I will present some of the latest work that has progressed our understanding of RSGs in the Local Group, and consider the many new questions posed by our ever-evolving picture of these stars.Comment: 9 pages, 1 figure; to appear in proceedings of the Betelgeuse 2012 Worksho

Liquid-Vapor Transition and Critical Behavior of The Ultrasoft Restricted Primitive Model of Polyelectrolytes : a Monte Carlo Study

We present a Monte-Carlo study of the liquid-vapor transition and the critical behavior of a model of polyelectrolytes with soft gaussian charge distributions introduced recently by Coslovich, Hansen, and Kahl [J. Chem. Phys. \textbf{134}, 244514 (2011)]. A finite size study involving four different volumes in the grand canonical ensemble yields a precise determination of the critical temperature, chemical potential, and density of the model. Attempts to determine the nature of the criticality and to obtain reliable values for the critical exponents are not conclusive.Comment: 14 pages, 4 figure

Metallicity in the GRB 100316D/SN 2010bh Host Complex

The recent long-duration GRB 100316D, associated with supernova SN 2010bh and detected by Swift, is one of the nearest GRB-SNe ever observed (z = 0.059). This provides us with a unique opportunity to study the explosion environment on ~kpc scale in relation to the host galaxy complex. Here we present spatially-resolved spectrophotometry of the host galaxy, focusing on both the explosion site and the brightest star-forming regions. Using these data, we extract the spatial profiles of the relevant emission features (Halpha, Hbeta, [OIII] 5007A, and [NII] 6584A), and use these profiles to examine variations in metallicity and star formation rate as a function of position in the host galaxy. We conclude that GRB 100316D/SN2010bh occurred in a low-metallicity host galaxy, and that the GRB-SN explosion site corresponds to the region with the lowest metallicity and highest star formation rate sampled by our observations.Comment: 7 pages, 3 figures, accepted for publication in The Astrophysical Journa