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We report the initial findings of our Survey of the Circumgalactic Regions of the ALFALFA Galaxies (CRAG). We combine the blindly detected 21-cm HI sources of the ALFALFA catalog with archival HST/COS G130M QSO spectroscopic observations taken from the HST Spectroscopic Legacy Archive to quantify and characterize the circumgalactic medium (CGM) around these local, HI-rich galaxies. We find the covering factor of HI, as probed by Lyα, to be near unity within 50 kpc of all ALFALFA galaxies, regardless of HI mass, MHI. However, we have identified a significant correlation between the extent of the HI-bearing CGM beyond 50 kpc and MHI of the ALFALFA galaxies. We find the galaxies with log(MHI/M☉) > 9.5 give rise to Lyα covering factors > 0.5 out to 300 kpc, indicating the CGM of the most HI-rich galaxies of the ALFALFA sample fills a significant volume. At the same time we find the galaxies with log(MHI/M☉) < 9.5 give rise to substantively lower Lyα covering factors beyond 50 kpc. Most notably, the log(MHI/M☉) < 7.5 galaxies give rise to a Lyα covering factor < 0.3 beyond 50 kpc and negligible covering factors beyond 150 kpc. This work has been supported by NSF grant AST-1716569.
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Where do the Disks of Nearby, Massive Spiral Galaxies End?
The structure and properties of the circumgalactic medium (CGM) between R ~30–100 kpc around nearby, massive spiral galaxies remain largely unknown. One hypothesis is that large quantities of gas are held in rotationally-supported disks of neutral hydrogen (HI) that extend out to ~100 kpc. While observations of individual galaxies have detected HI out to distances of 80 kpc, a larger sample is necessary to determine the frequency and characteristics of extended HI disks. Using the Green Bank Telescope (GBT) we conducted a comprehensive survey mapping HI along the major and minor axes of 20 mass-selected galaxies to distances of 100 kpc and a limiting column density of 2 x 1018 cm-2. We have determined the total extended HI mass and its distribution within each galaxy by fitting our data to HI distribution models. We have found rotationally-supported disks in ~50% of the sample that extend to distances between 40 and 100 kpc.
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- Award ID(s):
- 2007013
- PAR ID:
- 10656233
- Publisher / Repository:
- Bulletin of the American Astronomical Society
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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