The Arecibo Legacy Fast ALFA Survey: V. HI Source Catalog of the Anti-Virgo Region at dec=27 degrees

TL;DR

This paper presents a catalog of 488 HI sources from the ALFA survey in a specific sky region, including extragalactic objects and high velocity clouds, with detailed analysis of their properties and distribution.

Contribution

The paper provides a new, detailed catalog of HI sources in the Anti-Virgo region, including high velocity clouds and optical counterparts, expanding the understanding of local galaxy distribution.

Findings

49 high velocity clouds identified, mostly compact and isolated

No HI detections within the Pisces-Perseus void, indicating lack of gas-rich galaxies there

Optically-dark, gas-rich galaxies are rare in the void, challenging certain void formation theories

Abstract

We present a second catalog of HI sources detected in the Arecibo Legacy Fast ALFA Survey. We report 488 detections over 135 square degrees, within the region of the sky having 22h<RA<03h and +26deg<Dec<+28deg. We present here the detections that have either (a) S/N>6.5, where the reliability of the catalog is better than 95% or (b) 5.0<S/N<6.5 and a previously measured redshift that corroborates our detection. Of the 488 objects presented here, 49 are High Velocity Clouds or clumps thereof with negative heliocentric recession velocities. These clouds are mostly very compact and isolated, while some of them are associated with large features such as Wright's Cloud or the northern extension of the Magellanic Stream. The remaining 439 candidate detections are identified as extragalactic objects and have all been matched with optical counterparts. Five of the six galaxies detected with M(HI)<10^7.5 solar masses are satellites of either the NGC672/IC1727 nearby galaxy pair or their neighboring dwarf irregular galaxy NGC784. The data of this catalog release include a slice through the Pisces-Perseus foreground void, a large nearby underdensity of galaxies. We report no detections within the void, where our catalog is complete for systems with HI masses of 10^8 solar masses. Gas-rich, optically-dark galaxies do not seem to constitute an important void population, and therefore do not suffice at producing a viable solution to the void phenomenon.