%0 Generic %1 bekhti2012absorptionselected %A Bekhti, N. Ben %A Winkel, B. %A Richter, P. %A Kerp, J. %A Klein, U. %A Murphy, M. T. %D 2012 %K CaII NaI halo milkyway %T An absorption-selected survey of neutral gas in the Milky Way halo %U http://arxiv.org/abs/1203.5603 %X We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Multi-wavelength studies were performed combining optical absorption line data of CaII and NaI with follow-up HI 21-cm emission line observations along 408 sight lines towards low- and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. HI data were extracted from the Effelsberg-Bonn HI survey and the Galactic All-Sky survey. For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope. CaII (NaI) halo absorbers at intermediate and high radial velocities are present in 40-55% (20-35%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65% of the cases, absorption is associated with HI 21-cm emission. The CaII (NaI) column density distribution function follows a power-law with a slope of -2.2 (-1.4). Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common HI high- and intermediate-velocity clouds seen in 21-cm observations. We find that CaII/NaI column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman-alpha systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.

@misc{bekhti2012absorptionselected, abstract = {We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Multi-wavelength studies were performed combining optical absorption line data of CaII and NaI with follow-up HI 21-cm emission line observations along 408 sight lines towards low- and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. HI data were extracted from the Effelsberg-Bonn HI survey and the Galactic All-Sky survey. For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope. CaII (NaI) halo absorbers at intermediate and high radial velocities are present in 40-55% (20-35%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65% of the cases, absorption is associated with HI 21-cm emission. The CaII (NaI) column density distribution function follows a power-law with a slope of -2.2 (-1.4). Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common HI high- and intermediate-velocity clouds seen in 21-cm observations. We find that CaII/NaI column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman-alpha systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.}, added-at = {2012-03-27T19:24:16.000+0200}, author = {Bekhti, N. Ben and Winkel, B. and Richter, P. and Kerp, J. and Klein, U. and Murphy, M. T.}, biburl = {https://www.bibsonomy.org/bibtex/204adcb43c4b07019b01cd37ddde91bdb/miki}, description = {[1203.5603] An absorption-selected survey of neutral gas in the Milky Way halo}, interhash = {ba1b53e4f9ccc45a2fead88e63045772}, intrahash = {04adcb43c4b07019b01cd37ddde91bdb}, keywords = {CaII NaI halo milkyway}, note = {cite arxiv:1203.5603Comment: 17 pages, 20 figures, accepted by A&A}, timestamp = {2012-03-27T19:24:16.000+0200}, title = {An absorption-selected survey of neutral gas in the Milky Way halo}, url = {http://arxiv.org/abs/1203.5603}, year = 2012 }