G. Lyle Hoffman

THE ARECIBO LEGACY FAST ALFA SURVEY. I. SCIENCE GOALS, SURVEY DESIGN, AND STRATEGY

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map ~7000 deg2 of the high Galactic latitude sky visible from Arecibo, providing a H I line spectral database covering the redshift range between -1600 and 18,000 km s-1 with ~5 km s-1 resolution. Exploiting Arecibos large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the H I mass function in the local universe and will provide a census of H I in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide-area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local Supercluster and nearby superclusters, allow measurement of the H I diameter function, and enable a first wide-area blind search for local H I tidal features, H I absorbers at z < 0.06, and OH megamasers in the redshift range 0.16 < z < 0.25. Although completion of the survey will require some 5 years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique that samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large-scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic H I line sources out to z ~ 0.06, including several hundred with H I masses M < 107.5 M⊙.

The Arecibo Legacy Fast ALFA Survey: the α.40 H I source catalog, its characteristics and their impact on the derivation of the H I mass function

We present a current catalog of 21 cm H I line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800 deg^2 of sky: the α.40 catalog. Covering 40% of the final survey area, the α.40 catalog contains 15,855 sources in the regions 07^h30^m < R.A. < 16^h30^m, +04° < decl. <+16°, and +24° < decl. <+28° and 22^h < R.A. < 03^h, +14° < decl. <+16°, and +24° < decl. < + 32°. Of those, 15,041 are certainly extragalactic, yielding a source density of 5.3 galaxies per deg^2, a factor of 29 improvement over the catalog extracted from the H I Parkes All-Sky Survey. In addition to the source centroid positions, H I line flux densities, recessional velocities, and line widths, the catalog includes the coordinates of the most probable optical counterpart of each H I line detection, and a separate compilation provides a cross-match 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 H I 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 of the α.40 catalog. The impact of survey selection, distance errors, current volume coverage, and local large-scale structure on the derivation of the H I mass function is assessed. While α.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the H I mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.

THE ARECIBO LEGACY FAST ALFA SURVEY. II. RESULTS OF PRECURSOR OBSERVATIONS

In preparation for the full Arecibo Legacy Fast ALFA (ALFALFA) extragalactic H I survey, precursor observations were carried out in 2004 August–September with the seven-beam Arecibo L-band Feed Array (ALFA) receiver system and the Wideband Arecibo Pulsar Processor spectral processors. While these observations were geared mainly at testing and debugging survey strategy, hardware, and software, approximately 48 hr of telescope time yielded science-quality data. The efficiency of system usage (allowing for minor malfunctions and the impact of radio-frequency interference) during that time was 75%. From those observations, an initial list of 730 tentative detections of varying degrees of reliability was extracted. Ninety-eight high signal-to-noise ratio candidates were deemed to be bona fide H I line detections. To test our ability to discriminate cosmic signals from radio-frequency interference and noise, 165 candidates ranging in reliability likelihood were reobserved with the single-beam L-band wide system at Arecibo in 2005 January–February. Of those, 41% were confirmed as real. We present the results of both the ALFA and the single-beam observations for the sample of 166 confirmed H I sources, as well as our assessment of their optical counterparts. Of the 166 sources, 62 coincided with previously known H I sources, while optical redshifts were available for an additional 18 galaxies; thus, 52% of the redshifts reported here were previously unknown. Of the 166 H I detections, 115 are identified with previously cataloged galaxies of either known or unknown redshift, leaving 51 objects identified for the first time. Because of the higher sensitivity of the Arecibo system, fewer than 10% of the 166 H I sources would have been detected by a HIPASS-like survey of the same region. Three of the objects have H I masses less than 107 M⊙. The full ALFALFA survey, which commenced in 2005 February, should detect more than 100 times as many objects of similarly low H I mass over the next 5 years.

H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area

New single-beam Arecibo H I observations of 298 late-type galaxies in the Virgo Cluster drawn mostly from the new catalog of Binggeli, Sandage, and Tammann (1985) are presented. Two hundred seventeen of these constitute a magnitude-limited complete sample of such galaxies, types Sdm through Im and BCD. Sixty-one percent of this complete sample was detected, greatly enhancing the store of redshifts and H I masses for such galaxies in the Virgo Cluster. For detected galaxies, heliocentric velocities, 50 percent profile widths, and single-beam fluxes are presented. For those that escaped detection, upper limits are computed to the flux appropriate to the redshift range (-600 to +3000 km/s). 27 references.

The Arecibo Legacy Fast Alfa Survey. V. The H I Source Catalog of the Anti-Virgo Region at δ = +27°

We present a second catalog of H I sources detected in the Arecibo Legacy Fast ALFA Survey. We report 488 detections over 135 deg2, within the region of the sky having 22 h 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 Wrights 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 ☉ 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 masses of 108 M ☉. Gas-rich, optically-dark galaxies do not seem to constitute an important void population, and therefore do not suffice for producing a viable solution to the void phenomenon.

ΛCDM SATELLITES AND H i COMPANIONS—THE ARECIBO ALFA SURVEY OF NGC 2903

We have conducted a deep, complete H I survey, using Arecibo/Arecibo L-band Feed Array (ALFA), of a field centered on the nearby, isolated galaxy, NGC 2903, which is similar to the Milky Way in its properties. The field size was 150 kpc × 260 kpc and the final velocity range spanned from 100 to 1133 km s–1. The ALFA beams have been mapped as a function of azimuth and cleaned from each azimuth-specific cube prior to forming final cubes. The final H I data are sensitive down to an H I mass of 2 × 105 M ☉ and column density of 2 × 1017 cm–2 at the 3 σ 2 δ V level, where σ is the rms noise level and δ V is the velocity resolution. NGC 2903 is found to have an H I envelope that is larger than previously known, extending to at least three times the optical diameter of the galaxy. Our search for companions yields one new discovery with an H I mass of 2.6 × 106 M ☉. The companion is 64 kpc from NGC 2903 in projection, is likely associated with a small optical galaxy of similar total stellar mass, and is dark matter dominated, with a total mass >108 M ☉. In the region surveyed, there are now two known companions: our new discovery and a previously known system that is likely a dwarf spheroidal, lacking H I content. If H I constitutes 1% of the total mass in all possible companions, then we should have detected 230 companions, according to Λ cold dark matter (ΛCDM) predictions. Consequently, if this number of dark-matter clumps are indeed present, then they contain less than 1% H I content, possibly existing as very faint dwarf spheroidals or as starless, gasless dark-matter clumps.

THE ARECIBO LEGACY FAST ALFA SURVEY. VIII. H I SOURCE CATALOG OF THE ANTI-VIRGO REGION AT δ = +25°

We present a fourth catalog of H I sources from the Arecibo Legacy Fast ALFA (ALFALFA) Survey. We report 541 detections over 136 deg{sup 2}, within the region of the sky having 22{sup h} 6.5, where the reliability of the catalog is better than 95%; (2) extragalactic sources 5.0 < S/N < 6.5 and a previously measured optical redshift that corroborates our detection; or (3) High Velocity Clouds (HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of the 541 objects presented here, 90 are associated with HVCs, while the remaining 451 are identified as extragalactic objects. Optical counterparts have been matched with all but one of the extragalactic objects.

Blue compact dwarf galaxies in the Virgo Cluster - H I and IRAS data and upper limits on proto-dwarf galaxies

Correlations between various properties of blue compact dwarf (BCD) galaxies in the Virgo Cluster were studied. It was found that, at constant mass, BCD galaxies are comparable to non-BCD irregulars in both blue luminosity and H I flux. About one-third of the BCDs were detected by IRAS at 60 or 100 microns, mostly at intensities just above the threshold sensitivity. 97 refs.

Comparative properties of Virgo Cluster dwarf irregulars and spirals

The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals. 88 references.

Neutral hydrogen detection survey of dwarf galaxies. II. Faint Virgo dwarfs and a field sample

Neutral hydrogen spectra are presented for 53 faint dwarf galaxies in Virgo, completing the Arecibo survey of all late-type dwarfs in the Virgo Cluster Catalog, and for 42 dwarf galaxies from the field sample of Binggeli et al. (1989). For detected galaxies, heliocentric velocities, profile widths, and single-beam fluxes are tabulated. The field sample has been used to investigate the field luminosity function and the clustering of dwarf galaxies vis-a-vis bright galaxies. 31 refs.