Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734507j&link_type=abstract
American Astronomical Society, AAS Meeting #217, #345.07; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We report on a search for very weak Mg II absorbers in the highest S/N high resolution spectra obtained with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Although the structures selected by weak Mg II absorbers remain unidentified, they select optically thin gas with metallicities 0.5-2 dex higher than the metallicity of DLA absorbers, and are thought to have a variety of origins, from high velocity gas in external galaxies, to interstellar gas clouds expelled from dwarf galaxies and superwinds, and intergalactic star clusters. With a typical 5 sigma detection limit of 0.002Å, an order of magnitude smaller than that of the deepest previous surveys for weak Mg II absorption, we are able to analyze a population of weak Mg II absorbers with small equivalent widths. We consider whether the population of weak Mg II absorbers increases rapidly in this small equivalent width regime, continuing a trend in the increase of the equivalent width distribution of weak (Wr > 0.02 Å) absorbers at z 1, which have a dN/dz two times higher than that of Lyman Limit Systems. Such very weak absorbers may be detected via a mix of both narrow (b 3 km/s) single low ionization components and broader (b 6-10 km/s) components. Some of the broader components are likely related to CIV absorbers, while many of the narrow components, detected at the resolution limit of the spectrum, may be associated with unresolved cold clouds whose temperature range extends into the molecular regime. With the broad wavelength coverage of the UVES spectra, we also consider the evolution of these absorbers, from z=0.3-2.4 (at ages 2.8 Gyr-10.3 Gyr).
Charlton Jane
Jones Therese
Narayanan Anand
Rodriguez Hidalgo Paola
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