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We report results from a study of the HI content and stellar properties of nearby galaxies detected by the Arecibo Legacy Fast ALFA blind 21-cm line survey and the Sloan Digital Sky Survey in two declination strips covering a total area of 9 hr X 16 deg. Our analysis seeks to assemble a control sample of galaxies suitable for providing absolute measures of the HI content of gaseous objects. From a database of ~15,000 HI detections, we have assembled three samples of gas-rich galaxies expected to show little or no evidence of interaction with their surroundings that could provide adequate HI standards. The most reliable results are obtained with a sample of 5647 sources found in low density environments, as defined by a nearest neighbor approach. The other two samples contain several hundred relatively isolated galaxies each, as determined from standard isolation algorithms. We find that isolated objects are not particularly gas-rich compared to their low-density-environment counterparts, while they suffer from selection bias and span a smaller dynamic range. All this makes them less suitable for defining a reference for HI content. We have explored the optical morphology of gaseous galaxies in quiet environments finding that, within the volume surveyed, the vast majority of them display unequivocal late-type galaxy features. In contrast, bona fide gas-rich early-type systems account only for a negligible fraction of the 21-cm detections. We argue that HI emission provides the most reliable way to determine the morphological population to which a galaxy belongs. We have also observed that the color distribution of flux-limited samples of optically-selected field HI emitters does not vary significantly with increasing distance, while that of non-detections becomes notably redder. This result suggests that the colors and HI masses of gas-rich galaxies cannot be very closely related.
This is the second paper of two reporting results from a study of the HI content and stellar properties of nearby galaxies detected by the Arecibo Legacy Fast ALFA blind 21-cm line survey and the Sloan Digital Sky Survey in a 2160 deg^2 region covere
We use a stacking technique to measure the average HI content of a volume-limited sample of 1871 AGN host galaxies from a parent sample of galaxies selected from the SDSS and GALEX imaging surveys with stellar masses greater than 10^10 M_sun and reds
We present the analysis of the HI content of a sample of early-type galaxies (ETGs) in low-density environments (LDEs) using the data set provided by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We compare their properties to the sample in the Virg
We combine information from the clustering of HI galaxies in the 100% data release of the Arecibo Legacy Fast ALFA survey (ALFALFA), and from the HI content of optically-selected galaxy groups found in the Sloan Digital Sky Survey (SDSS) to constrain
Galaxies detected in the 21-cm line of neutral hydrogen (HI) from the on-going Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic HI survey have been cross-correlated with Sloan Digital Sky Survey Data Release 7 (Abazajian et al. 2009) in order t