Highlights - Volume 468-1 (June II 2007)

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HIGHLIGHTS: this week in A&A

Volume 468-1 (June II 2007)


Star formation-density relation at z~1

The reversal of the star formation-density relation in the distant universe”, by D. Elbaz et al. A&A 468, p. 33

An unprecedented sample of galaxies at z~1 in the GOODS field is used in a very careful study of the star formation rate (SFR) as a function of local density with the help of the 24 microns images from Spitzer. They find that the SFR increases with density, contrary to what is observed at z=0, where SFR is quenched in galaxy clusters. This was predicted by several models and numerical simulations but is the first time it is shown so clearly. This shows how the environment, as well as large-scale structure formation, affects the formation of stars, maybe even more than galaxy-galaxy interactions.


Properties of massive stars in the Galactic center

Stellar and wind properties of massive stars in the central parsec of the Galaxy”, by F. Martins et al. A&A 468, p. 233

This study uses both the highest possible resolution IR data for the massive stars, a comprehensive analysis of both the mass loss and spectral characteristics for the atmospheres and winds, and stellar evolutionary models to specify the population in the innermost clusters of the Galactic center. Application of the combined continua to the ionization of the gas also allows the authors to reassess the abundances of heavy elements in the interstellar medium, solving several problems related to the abundances and properties of the gas that have remained unresolved for nearly a decade. This complex region provides a view of the process of massive star formation in a nearly active nucleus in the vicinity of a massive black hole, with unprecedented detail. This is far higher than available in distant starburst systems. The results will be essential for understanding the feedback process of star formation in such dense, star-packed environments and discovering how the Galactic center feeds the central engine.


In section 1. Letters

“Ferromagnetic inclusions in silicate thin films: insights into the magnetic properties of cosmic grains”, by Z. Djouadi et al. A&A 468, p. L9

This paper reports measurements of the magnetic properties of a laboratory approximation of the "GEMS" found in interplanetary dust particles. The relatively high remanent magnetisation that has been found suggests that iron inclusions may play a role in the alignment of interstellar grains.  
In section 4. Extragalactic astronomy

“Rapid-response mode VLT/UVES spectroscopy of GRB 060418: conclusive evidence for UV pumping from the time evolution of FeII and NiII excited- and metastable-level populations”, by P.M. Vreeswijk et al. A&A 468, p. 83

This paper reports high-resolution (~ 7 km/s) VLT/UVES spectroscopy of the bright Swift gamma ray burst on 2006 April 18 within 10 minutes of trigger that extends for nearly two hours after that. For the first time, neutral and slightly ionized interstellar metallic lines arising from metastable excited states have been identified at the redshift of the host galaxy, pumped by ultraviolet photons produced during the GRB afterglow. The lines were observed to decay on a timescale of hours. The interstellar medium very near the GRB is likely to be highly ionized, no neutral species were observed at the same velocity as the ions, and the authors derive a distance of about 1 kpc from the source. The authors discuss how this constrains the nature of the GRB progenitor.  


© Astronomy & Astrophysics 2007