NED Abstract 
Copyright by American Astronomical Society.
Reproduced by permission

2008AJ....136..713K

The Arecibo Legacy Fast ALFA Survey. VI. Second HI Source Catalog of the
Virgo Cluster Region

Brian R. Kent, Riccardo Giovanelli, Martha P. Haynes, Ann M. Martin, Amelie
Saintonge, Sabrina Stierwalt, Thomas J. Balonek, Noah Brosch, and Rebecca
A. Koopmann

ABSTRACT We present the third installment of HI sources extracted from
the Arecibo Legacy Fast ALFA extragalactic survey. This data set
continues the work of the Virgo ALFALFA catalog. The catalogs and
spectra published here consist of data obtained during the 2005 and 2006
observing sessions of the survey. The catalog consists of 578 HI
detections within the range 11h36m < right ascension (R.A.)(J2000)
<13h52m and +08deg < declination (decl.)(J2000) <+12deg, and czsun < 18,
000 km s^-1^. The catalog entries are matched with optical counterparts
where possible through the examination of digitized optical images. The
catalog detections can be classified into three categories: (a)
detections of high reliability with a signal-to-noise ratio (S/N) > 6.5;
(b) high-velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and
known redshift. 75% of the sources are newly published HI detections. Of
particular note is a complex of HI clouds projected between M87 and M49
that do not coincide with any optical counterparts. Candidate objects
without optical counterparts are few. The median redshift for this
sample is 6500 km s-1and the cz distribution exhibits the local
large-scale structure consisting of Virgo and the background void and
the A1367-Coma supercluster regime at czsun~ 7000 km s^-1^. Position
corrections for telescope pointing errors are applied to the data set by
comparing the ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey (NVSS). The uncorrected positional accuracy averages
27"(21" median) for all sources with S/N > 6.5 and is of order ~21"(16"
median) for signals with S/N > 12. Uncertainties in distances toward the
Virgo cluster can affect the calculated HI mass distribution

Key words: galaxies: distances and redshifts, galaxies: halos, galaxies:
luminosity function, mass function, galaxies: photometry, galaxies: spiral,
radio lines: galaxies