科研之友
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摘要
We present the Green Bank Telescope absorption survey of cold atomic hydrogen (<= 300 K) in the inner halo of low-redshift galaxies. The survey aims to characterize the cold gas distribution and to address where the condensation-the process where ionized gas accreted by galaxies condenses into cold gas within the disks of galaxies-occurs. Our sample consists of 16 galaxy-quasar pairs with impact parameters of <= 20 kpc. We detected an H I absorber associated with J0958+3222 (NGC 3067) and H I emission from six galaxies. We also found two Ca II absorption systems in the archival SDSS data associated with galaxies J0958+3222 and J1228+3706. Our detection rate of H I absorbers with optical depths of. >= 0.06 is similar to 7%. We also find that the cold H I phase (<= 300 K) is 44(+/- 18)% of the total atomic gas in the sightline probing J0958+3222. We find no correlation between the peak optical depth and impact parameter or stellar and H I radii normalized impact parameters, rho/R-90 and rho/R-H I. We conclude that the process of condensation of inflowing gas into cold (. 300 K) H I occurs at the rho << 20 kpc. However, the warmer phase of neutral gas (T similar to 1000 K) can exist out to much larger distances, as seen in emission maps. Therefore, the process of condensation of warm to cold H I is likely occurring in stages from ionized to warm H I in the inner halo and then to cold H I very close to the galaxy disk.
- 出版日期2016-10-1
