Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs II. Star formation rates and metallicities at z < 1

Aims. Long gamma-ray bursts (LGRBs) are associated with the deaths of massive stars and might therefore be a potentially powerful tool for tracing cosmic star formation. However, especially at low redshifts (z< 1.5) LGRBs seem to prefer particular types of environment. Our aim is to study the host galaxies of a complete sample of bright LGRBs to investigate the effect of the environment on GRB formation. Methods. We studied host galaxy spectra of the Swift/BAT6 complete sample of 14 z< 1 bright LGRBs. We used the detected nebular emission lines to measure the dust extinction, star formation rate (SFR), and nebular metallicity (Z) of the hosts and supplemented the data set with previously measured stellar masses M_*. The distributions of the obtained properties and their interrelations (e.g. mass-metallicity and SFR-M_* relations) are compared to samples of field star-forming galaxies. Results. We find that LGRB hosts at z< 1 have on average lower SFRs than if they were direct star formation tracers. By directly comparing metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match between the two populations up to 12 +log (O/H)~8.4−8.5, after which the paucity of metal-rich LGRB hosts becomes apparent. The LGRB host galaxies of our complete sample are consistent with the mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find a hint of an increased incidence of starburst galaxies in the Swift/BAT6 z< 1 sample with respect to that of a field star-forming population. Given that the SFRs are low on average, the latter is ascribed to low stellar masses. Nevertheless, the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of LGRB host galaxies, prevents us from investigating more quantitatively whether the starburst incidence is such as expected after taking into account the high-metallicity aversion of LGRB host galaxies.

Consecuencias literarias del 11-S: la representación de la violencia en la novela angloamericana

In my eight years as a professional journalist, I have been a front line observer of the extreme level of violence which occurs everyday in our society. As victims, consumers or perpetrators of violence, this phenomenon is now a part of our existence. As a reporter for the Spanish national newspaper El País I have been witness to the most terrible acts of violence. In Venezuela, with one of the highest rates of criminality in the world, I saw piles of bodies stacked up in mortuaries. In Argentina, I reported on the most brutal crimes including the rape of children by policemen. I believe that my interest in the manifestations and causes of violence was aroused during my time as a journalist. On a personal level, I was deeply affected by the twin poles of attraction/repulsion which the violent images produced in me. The first time I visited New York in 2003, I talked to various people who were selling photos of the victims of the Twin Tower attacks. They had laid out their wares along the wire fence that separated Ground Zero from the main public areas. One particular photograph made an indelible impression on my mind: a ghost like corpse covered in white dust which was streaked with blood. It is an image I will never forget. If I remember well, a complete album of these gruesome images cost about ten dollars. At the same time, I also became interested in islamic terrorism: its complexity and the great impact it has made on Western society. One only has to look at the front page of the press around the world to read about war, terrorism or the constant violation of human rights. The words Al-Qaeda, Daesh, Boko Haram and Islamic State have sadly become parts of our everyday language. The nihilistic philosophy which promisess eternal life in exchange for self-inmolation is a new, highly worrying reality, especially painful when it involves young people who become indoctrinated through the social media. They have become the most loyal supporters of a fanatical and uncompromising version of Islam. The stark reality is that these young recruits to Jihad (holy war) were born in places like London, Paris, Rome or Madrid...