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As part of our Survey of the Circumgalactic Regions of the ALFALFA Galaxies (CRAG), we report on the analysis of QSO sightlines that pass within ~100 kpc of ALFALFA galaxies that show no discernable evidence of a circumgalactic medium (CGM) as probed by the presence of Lyα absorption. Many of these corresponding galaxies reside in group or cluster environments, in agreement with recent studies that indicate the nearby galaxy environment plays a significant role in determining the physical conditions of the CGM. However, we also identify a sample of isolated ALFALFA galaxies that show no evidence of HI within ~100 kpc - suggesting the physical distribution of the CGM around these galaxies is patchy and non-uniform, even within relatively small volumes around the galaxies. We explore photometric, spectroscopic, and imaging observations from the Sloan Digital Sky Survey in an attempt to characterize the properties these galaxies and the environments in which they reside. This work has been supported by NSF grant AST-1716569.
As part of our Survey of the Circumgalactic Regions of the ALFALFA Galaxies (CRAG), we report on the identification and analysis of strong HI absorption in the circumgalactic medium (CGM) of the ALFALFA galaxies as identified in archival HST/COS G130M QSO spectroscopic observations. We characterize the HI and metal content of these strong absorbers and explore the physical distribution of the CGM for these galaxies. Using photometric, spectroscopic, and imaging observations from the Sloan Digital Sky Survey, we analyze the environments of these galaxies. We also summarize the gas-galaxy connection for this sample of strong HI absorbers and HI-rich galaxies. This work has been supported by NSF grant AST-1716569.
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.
The Arecibo Pisces-Perseus Supercluster Survey (APPSS) will provide strong observational constraints on the mass-infall rate onto the main filament of the Pisces-Perseus Supercluster. The survey data consist of HI emission-line spectra of cluster galaxy candidates, obtained primarily at the Arecibo Observatory (with ALFA as part of the ALFALFA Survey and with the L-Band Wide receiver as part of APPSS observations). Here we present the details of the data reduction process and spectral-analysis techniques used to determine if a galaxy candidate is at a velocity consistent with the Supercluster, as well as the detected HI-flux and rotational velocity of the galaxy, which will be used to estimate the corresponding HI-mass. We discuss the results of a preliminary analysis on a subset of the APPSS sample, corresponding to 98 galaxies located within ~1.5° of DEC = +35.0°, with 65 possible detections. We also highlight several interesting emission-line features and galaxies discovered during the reduction and analysis process and layout the future of the APPSS project. This work has been supported by NSF grants AST-1211005 and AST-1637339.