The Cosmic Evolution of Gamma-Ray Burst Host Galaxies

Due to their extreme luminosities, gamma-ray bursts (GRBs) can be detected in hostile regions of galaxies, nearby and at very high redshift, making them important cosmological probes. The investigation of galaxies hosting long-duration GRBs (whose progenitor is a massive star) demonstrated their connection to star formation. Still, the link to the total galaxy population is controversial, mainly because of the small-number statistics: ~ 1,100 are the GRBs detected so far, ~ 280 those with measured redshift, and ~ 70 the hosts studied in detail. These are typically low-redshift (z < 1.5), low luminosity, metal poor, and star-forming galaxes. On the other hand, at 1.5< z <4, massive, metal rich and dusty, interacting galaxies are not uncommon. The most distant population (z > 4) is poorly explored, but the deep limits reached point towards very small and star-forming objects, similar to the low-z population. This `back to the future' behavior is a natural consequence of the connection of long GRBs to star formation in young regions of the universe.Comment: Invited talk at the Fall 2012 Gamma-Ray Burst Symposium (Marbella, Oct 2012), revised version after referee's report, to appear in the European Astronomical Society Publications Serie

The Dust Depletion and Extinction of the GRB 020813 Afterglow

The Keck optical spectrum of the GRB 020813 afterglow is the best ever obtained for GRBs. Its large spectral range and very high S/N ratio allowed for the first time the detection of a vast variety of absorption lines, associated with the circumburst medium or interstellar medium of the host. The remarkable similarity of the relative abundances of 8 elements with the dust depletion pattern seen in the Galactic ISM suggests the presence of dust. The derived visual dust extinction A_V=0.40+/-0.06 contradicts the featureless UV spectrum of the afterglow, very well described by a unreddened power law. The forthcoming Swift era will open exciting opportunities to explain similar phenomena in other GRB afterglows.Comment: To be published in "Il Nuovo Cimento", Proceedings of the 4th Rome Workshop on Gamma-Ray Bursts in the Afterglow Era, eds. L. Piro, L. Amati, S. Covino, B. Gendr

Swift publication statistics: a comparison with other major observatories

Swift is a satellite equipped with gamma-ray, X-ray, and optical-UV instruments aimed at discovering, localizing and collecting data from gamma-ray bursts (GRBs). Launched at the end of 2004, this small-size mission finds about a hundred GRBs per year, totaling more than 700 events as of 2012. In addition to GRBs, Swift observes other energetic events, such as AGNs, novae, and supernovae. Here we look at its success using bibliometric tools; that is the number of papers using Swift data and their impact (i.e., number of citations to those papers). We derived these for the publication years 2005 to 2011, and compared them with the same numbers for other major observatories. Swift provided data for 1101 papers in the interval 2005-2011, with 24 in the first year, to 287 in the last year. In 2011, Swift had more than double the number of publications as Subaru, it overcame Gemini by a large fraction, and reached Keck. It is getting closer to the ~400 publications of the successful high-energy missions XMM-Newton and Chandra, but is still far from the most productive telescopes VLT (over 500) and HST (almost 800). The overall average number of citations per paper, as of November 2012, is 28.3, which is comparable to the others, but lower than Keck (41.8). The science topics covered by Swift publications have changed from the first year, when over 80% of the papers were about GRBs, while in 2011 it was less than 30%.Comment: PASP accepted, minor changes after referee's repor

The metal absorption systems of the Hubble Deep Field South QSO

The Hubble Deep Field South (HDFS) has been recently selected and the observations are planned for October 1998. We present a high resolution (FWHM $\simeq 14$ \kms) spectrum of the quasar J2233--606 ($z_{em}\simeq2.22$) which is located 5.1 arcmin East of the HDFS. The spectrum obtained with the New Technology Telescope redward of the Lyman--$\alpha$ emission line covers the spectral range 4386--8270 \AA. This range corresponds to redshift intervals for CIV and MgII intervening systems of $z=1.83-2.25$ and $z=0.57-1.95$ respectively. The data reveal the presence of two complex intervening CIV systems at redshift $z=1.869$ and $z=1.943$ and two complex associated ($z_{abs} \approx z_{em}$) systems. Other two CIV systems at $z=1.7865$ and $z=2.077$, suggested by the presence of strong Lyman--$\alpha$ lines in low resolution ground based and Hubble Space Telescope (HST) STIS observations (Sealey et al. 1998) have been identified. The system at $z=1.943$ is also responsible for the Lyman limit absorption seen in the HST/STIS spectrum. The main goal of the present work is to provide astronomers interested in the Hubble Deep Field South program with information related to absorbing structures at high redshift, which are distributed along the nearby QSO line of sight. For this purpose, the reduced spectrum, obtained from three hours of integration time, has been released to the astronomical community.Comment: revisited version accepted for publication by Astronomical Journal; minor changes; typographical errors corrected; results and discussion unchange