The Arecibo Dual-Beam Survey is a "blind" 21 cm search for galaxies covering ~430deg^2^ of sky. We present the data from the detection survey as well as from the follow-up observations to confirm detections and improve positions and flux measurements. We find 265 galaxies, many of which are extremely low surface brightness. Some of these previously uncatalogued galaxies lie within the zone of avoidance, where they are obscured by the gas and dust in our Galaxy. Eighty-one of these sources are not previously catalogued optically, and there are 11 galaxies that have no associated optical counterpart or are only tentatively associated with faint wisps of nebulosity on the Digitized Sky Survey images. We discuss the properties of the survey, and in particular we make direct determinations of the completeness and reliability of the sample. The behavior of the completeness and its dependencies is essential for determining the H I mass function. We leave the discussion of the mass function for a later paper, but do note that we find many low surface brightness galaxies and seven sources with M_HI_<10^8^M_{sun}_.
We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA (ALFALFA) Survey. We report 541 detections over 136deg^2^, within the region of the sky having 22h<RA<03h and 24<DE<26{deg}. This complements a previous catalog in the region 26<DE<28{deg}. We present here the detections falling into three classes: (1) extragalactic sources with signal-to-noise ratio (S/N)>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.
We present the first installment of HI sources extracted from the Arecibo Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in 2005. Sources have been extracted from three-dimensional spectral data cubes exploiting a matched filtering technique and then examined interactively to yield global HI parameters. A total of 730 HI detections are cataloged within the solid angle 11h44<RA(J2000.0)<14h00 and +12{deg}<DE(J2000.0)<+16{deg} and redshift range -1600km/s<cz<18000km/s. In comparison, the HI Parkes All-Sky Survey (HIPASS, Meyer et al. 2004, Cat. VIII/73) detected 40 HI signals in the same region. Optical counterparts are assigned via examination of digital optical imaging databases.
We present the catalog of HI sources extracted from the ongoing Arecibo Legacy Fast ALFA (ALFALFA) extragalactic HI line survey, found within the sky region bounded by 9:36<RA<11:36 and +08<DE<+12. The HI catalog presented here for this 118deg^2^ region is combined with the ones derived from surrounding regions also covered by the ALFALFA survey to examine the large-scale structure in the complex Leo region. Because of the combination of wide sky coverage and superior sensitivity, spatial and spectral resolution, the ALFALFA HI catalog of the Leo region improves significantly on the numbers of low HI mass sources as compared with those found in previous HI surveys.
We present a second catalog of HI sources detected in the Arecibo Legacy Fast ALFA Survey. We report 488 detections over 135deg^2^, within the region of the sky having 22<RA<03 and +26<DE<+28. 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^ solMass 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^M_{sun}_.
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<RA(J2000)<13h52m and +08{deg}<DE(J2000)<+12{deg}, and cz_{sun}_<18000km/s. 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. 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, Cat. VIII/65). 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.
We present the results of an unbiased survey for 6.7GHz methanol masers in the Galactic plane carried out using the 305m Arecibo radio telescope. A total of 18.2deg^2^ was surveyed with uniform sampling at 35.2<=l<=53.7, |b|<=0.41. The large collecting area of Aecibo and the sensitive C-Band High receiver allowed the survey to be complete at the level of 0.27Jy, making this the most sensitive blind survey carried out to date. We detected a total of 86 sources, 48 of which are new detections. Most of the new detections have a peak flux density below 2Jy. Many methanol masers are clustered, reflecting the formation of massive stars in clusters.
We present an analysis of the properties of the 6.7GHz methanol maser sample detected in the Arecibo Methanol Maser Galactic Plane Survey. The distribution of the masers in the Galaxy, and statistics of their multiwavelength counterparts is consistent with the hypothesis of 6.7GHz maser emission being associated with massive young stellar objects. Using the detection statistics of our survey, we estimate the minimum number of methanol masers in the Galaxy to be 1275.
The completeness of the Arecibo 1612 MHz survey of color-selected/IRAS sources (see references) is extended to (25-12){mu}m>-0.7. In addition (1) most IR sources with spectral types normally associated with OH/IR stars and colors outside the coverage of the original survey have been examined; (2) most ambiguous observations during the survey have been reobserved: (3) most single peaked sources have been reexamined, and 17 found with second peaks. We report 39 new 1612MHz detections, of which 34 are original. These are also surveyed in the mainlines. Analysis of the complete flux-limited survey confirms the existence of a longitude sensitivity effect in the detection of sources, which reduces the total number detected by ~4%. This analysis sets an upper limit of 16%, on the proportion of a color-selected sample that may be identified with carbon stars and/or star-formation regions.
We report observations of the formaldehyde (H_2_CO) 6cm (4.8GHz) line toward L1551. The observations were conducted with the Arecibo Telescope (beam FWHP~1') to verify the tentative detection of H_2_CO thermal emission reported by Duncan and collaborators in 1987MNRAS.224..721D. The H_2_CO emission lines were expected to be present with a signal-to-noise ratio of >~10 in our spectra. However, we did not detect H_2_CO emission; i.e., our data rule out their tentative detection. The absence of H_2_CO emission is also confirmed by the fact that the H_2_CO line profiles at the two positions of expected emission are well fitted by a single absorption component (accounting for the hyperfine structure of the line) in one of the positions and by a single absorption line plus a red-wing absorption component in the second position. The Orion BN/KL region remains the only H_2_CO 6cm thermal emitter known. Our observations also demonstrate that the H_2_CO 6cm absorption line traces not only the quiescent molecular cloud but also the kinematics associated with the star formation process in L1551-IRS5.
