The ALFALFA "Almost Darks" Campaign: Pilot VLA HI Observations of Five High Mass-to-Light Ratio Systems

We present VLA HI spectral line imaging of 5 sources discovered by ALFALFA. These targets are drawn from a larger sample of systems that were not uniquely identified with optical counterparts during ALFALFA processing, and as such have unusually high HI mass to light ratios. These candidate "Almost Dark" objects fall into 4 categories: 1) objects with nearby HI neighbors that are likely of tidal origin; 2) objects that appear to be part of a system of multiple HI sources, but which may not be tidal in origin; 3) objects isolated from nearby ALFALFA HI detections, but located near a gas-poor early-type galaxy; 4) apparently isolated sources, with no object of coincident redshift within ~400 kpc. Roughly 75% of the 200 objects without identified counterparts in the $\alpha$.40 database (Haynes et al. 2011) fall into category 1. This pilot sample contains the first five sources observed as part of a larger effort to characterize HI sources with no readily identifiable optical counterpart at single dish resolution. These objects span a range of HI mass [7.41 < log(M$_{\rm HI}$) < 9.51] and HI mass to B-band luminosity ratios (3 < M$_{\rm HI}$/L$_{\rm B}$ < 9). We compare the HI total intensity and velocity fields to SDSS optical imaging and to archival GALEX UV imaging. Four of the sources with uncertain or no optical counterpart in the ALFALFA data are identified with low surface brightness optical counterparts in SDSS imaging when compared with VLA HI intensity maps, and appear to be galaxies with clear signs of ordered rotation. One source (AGC 208602) is likely tidal in nature. We find no "dark galaxies" in this limited sample. The present observations reveal complex sources with suppressed star formation, highlighting both the observational difficulties and the necessity of synthesis follow-up observations to understand these extreme objects. (abridged)Comment: Astronomical Journal, in pres

The Arecibo Legacy Fast ALFA Survey: The alpha.40 HI Source Catalog, its Characteristics and their Impact on the Derivation of the HI Mass Function

We present a current catalog of 21 cm HI line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800 square degrees of sky: the alpha.40 catalog. Covering 40% of the final survey area, the alpha.40 catalog contains 15855 sources in the regions 07h30m < R.A. < 16h30m, +04 deg < Dec. < +16 deg and +24 deg < Dec. < +28 deg and 22h < R.A. < 03h, +14 deg < Dec. < +16 deg and +24 deg < Dec. < +32 deg. Of those, 15041 are certainly extragalactic, yielding a source density of 5.3 galaxies per square degree, a factor of 29 improvement over the catalog extracted from the HI Parkes All Sky Survey. In addition to the source centroid positions, HI line flux densities, recessional velocities and line widths, the catalog includes the coordinates of the most probable optical counterpart of each HI line detection, and a separate compilation provides a crossmatch to identifications given in the photometric and spectroscopic catalogs associated with the Sloan Digital Sky Survey Data Release 7. Fewer than 2% of the extragalactic HI line sources cannot be identified with a feasible optical counterpart; some of those may be rare OH megamasers at 0.16 < z < 0.25. A detailed analysis is presented of the completeness, width dependent sensitivity function and bias inherent in the current alpha.40 catalog. The impact of survey selection, distance errors, current volume coverage and local large scale structure on the derivation of the HI mass function is assessed. While alpha.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the HI mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.Comment: 62 pages, 28 figures. See http://egg.astro.cornell.edu/alfalfa/data for ASCII and CSV datafiles corresponding to Tables 1, 2 and 3. A higher resolution PDF version can be found at http://egg.astro.cornell.edu/alfalfa/pubs.php. To appear in Nov 2011 Astron.

The arecibo legacy fast ALFA survey: The ALFALFA extragalactic HI source catalog

We present the catalog of ∼31,500 extragalactic H i line sources detected by the completed Arecibo Legacy Fast ALFA (ALFALFA) survey out to z 6.5) detections and ones of lower quality that coincide in both position and recessional velocity with galaxies of known redshift. We review the observing technique, data reduction pipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital H i line spectra associated with the cataloged sources. In addition to the extragalactic H i line detections, we report nine confirmed OH megamasers (OHMs) and 10 OHM candidates at 0.16 < z < 0.22 whose OH line signals are redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-horn array on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.© 2018. The American Astronomical Society. All rights reserved.The authors acknowledge the work of the entire ALFALFA collaboration who have contributed to the many aspects of the survey over the years. The ALFALFA team at Cornell has been supported by NSF grants AST-0607007, AST-1107390, and AST-1714828 and grants from the Brinson Foundation. Participation of the Undergraduate ALFALFA Team has been made possible by NSF grants AST-0724918, AST-0725267, AST-0725380, AST-0902211, AST-0903394, AST-1211005, AST-1637339, AST-1637271, AST-1637299, AST-1637262, and AST-1637276. EAKA is supported by the WISE research program, which is financed by the Netherlands Organisation for Scientific Research (NWO). BRK acknowledges the National Radio Astronomy Observatory (NRAO). The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. MGJ acknowledges support from grant AYA2015-65973-C3-1-R (MINECO/FEDER, UE). We thank Dmitry Makarov for comments and suggestions on cross-identifications. This work is based on observations made with the Arecibo Observatory. The Arecibo Observatory has been operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968) and in alliance with Ana G. Mendez-Universidad Metropolitana and the Universities Space Research Association. We thank the staff of the Arecibo Observatory, especially Phil Perillat, Ganesh Rajagopalan, Arun Venkataraman, Hector Hernandez, and the telescope operations group for their outstanding support of the ALFALFA survey program. We acknowledge the use of NASA's SkyView facility (http://skyview.gsfc.nasa.gov), located at NASA Goddard Space Flight Center, and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. The Second Palomar Observatory Sky Survey (POSS-II) was made by the California Institute of Technology with funds from the National Science Foundation, the National Geographic Society, the Sloan Foundation, the Samuel Oschin Foundation, and the Eastman Kodak Corporation. This research used data from the Sloan Digital Sky Survey. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England

The Alfalfa “Almost Darks” Campaign: Pilot VLA HI Observations of Five High Mass-To-Light Ratio Systems

We present new Very Large Array (VLA) H i spectral line imaging of five sources discovered by the ALFALFA extragalactic survey. These targets are drawn from a larger sample of systems that were not uniquely identified with optical counterparts during ALFALFA processing, and as such have unusually high H i mass to light ratios. The candidate “Almost Dark” objects fall into four broad categories: (1) objects with nearby H i neighbors that are likely of tidal origin; (2) objects that appear to be part of a system of multiple H i sources, but which may not be tidal in origin; (3) objects isolated from nearby ALFALFA H i detections, but located near a gas-poor early type galaxy; (4) apparently isolated sources, with no object of coincident redshift within ˜400 kpc. Roughly 75% of the 200 objects without identified counterparts in the α.40 database (Haynes et al. 2011) fall into category 1 (likely tidal), and were not considered for synthesis follow-up observations. The pilot sample presented here (AGC193953, AGC208602, AGC208399, AGC226178, and AGC233638) contains the first five sources observed as part of a larger effort to characterize H i sources with no readily identifiable optical counterpart at single dish resolution (3.‧5). These objects span a range of H i mass [7.41 <log(MHi ) <9.51] and H i mass to B-band luminosity ratios (3 <MHi /LB <9). We compare the H i total intensity and velocity fields to optical imaging drawn from the Sloan Digital Sky Survey and to ultraviolet imaging drawn from archival GALEX observations. Four of the sources with uncertain or no optical counterpart in the ALFALFA data are identified with low surface brightness optical counterparts in Sloan Digital Sky Survey imaging when compared with VLA H i intensity maps, and appear to be galaxies with clear signs of ordered rotation in the H i velocity fields. Three of these are detected in far-ultraviolet GALEX images, a likely indication of star formation within the last few hundred Myrs. One source (AGC208602) is likely tidal in nature, associated with the NGC 3370 group. Consistent with previous efforts, we find no “dark galaxies” in this limited sample. However, the present observations do reveal complex sources with suppressed star formation, highlighting both the observational difficulties and the necessity of synthesis follow-up observations to understand these extreme objects

The Arecibo Legacy Fast ALFA Survey:The ALFALFA Extragalactic HI Source Catalog

We present the catalog of ~31500 extragalactic HI line sources detected by the completed ALFALFA survey out to z < 0.06 including both high signal-to-noise ratio (> 6.5) detections and ones of lower quality which coincide in both position and recessional velocity with galaxies of known redshift. We review the observing technique, data reduction pipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital HI line spectra associated with the catalogued sources. In addition to the extragalactic HI line detections, we report nine confirmed OH megamasers and ten OH megamaser candidates at 0.16 < z < 0.22 whose OH line signals are redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-horn array on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.Comment: 24 pages 8 figures See http://egg.astro.cornell.edu/alfalfa/data for ASCII and CSV datafiles corresponding to Table 2. To appear in Astrophys.J.Supp

ALFALFA extragalactic HI source catalog

VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The Arecibo Legacy Fast ALFA survey: The ALFALFA extragalactic HI source catalog.' (bibcode: 2018ApJ...861...49H