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Register a new userA blind HI Mass Function from the Arecibo Ultra-Deep Survey (AUDS)
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The Arecibo Ultra Deep Survey (AUDS) combines the unique sensitivity of the telescope with the wide field of the Arecibo L-band Feed Array (ALFA) to directly detect 21cm HI emission from galaxies at distances beyond the local Universe bounded by the lower frequency limit of ALFA (z=0.16). AUDS has collected 700 hours of integration time in two fields with a combined area of 1.35 square degrees. In this paper we present data from 60% of the total survey, corresponding to a sensitivity level of 80 micro-Jy. We discuss the data reduction, the search for galaxies, parametrisation, optical identification and completeness. We detect 102 galaxies in the mass range of log M_HI/M_sun-2log h=5.6-10.3. We compute the HI mass function (HIMF) at the highest redshifts so far measured. A fit of a Schechter function results in alpha=-1.37+-0.03, Phi=(7.72+-1.4)*10^3 h^3/Mpc^3 and log M_HI/M_sun=9.75+-0.041+2log h. Using the measured HIMF, we find a cosmic HI density of Omega_HI=(2.33+-0.07)*10^-4/h for the sample z=0.065. We discuss further uncertainties arising from cosmic variance. Because of its depth, AUDS is the first survey that can determine parameters for the HI mass function in independent redshift bins from a single homogeneous data set. The results indicate little evolution of the co-moving mass function and Omega_HI within this redshift range. We calculate a weighted average for Omega_HI in the range $0<z<0.2$, combining the results from AUDS as well as results from other 21cm surveys and stacking, finding a best combined estimate of Omega_HI=(2.63+-0.10)*10-4/h.
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The Arecibo Ultra Deep Survey (AUDS) is a blind HI survey aimed at detecting galaxies beyond the local Universe in the 21-cm emission line of neutral hydrogen (HI). The Arecibo $L$-band Feed Array (ALFA) was used to image an area of 1.35~deg$^2$ to a redshift depth of 0.16, using a total on-source integration time of over 700 hours. The long integration time and small observation area makes it one of the most sensitive HI surveys, with a noise level of $sim 75$~$mu$Jy per 21.4~kHz (equivalent to 4.5~km~s$^{-1}$ at redshift $z=0$). We detect 247 galaxies in the survey, more than doubling the number already detected in AUDS60. The mass range of detected galaxies is $log(M_{rm HI}~[h_{70}^{-2}{rm M}_odot]) = 6.32 - 10.76$. A modified maximum likelihood method is employed to construct an HI mass function (HIMF). The best fitting Schechter parameters are: low-mass slope $alpha = -1.37 pm 0.05$, characteristic mass $log(M^*~[h_{70}^{-2}{rm M}_odot]) = 10.15 pm 0.09$, and density $Phi_* = (2.41 pm 0.57) times 10^{-3} h_{70}^3$~Mpc$^{-3}$~dex$^{-1}$. The sample was divided into low and high redshift bins to investigate the evolution of the HIMF. No change in low-mass slope $alpha$ was measured, but an increased characteristic mass $M^*$, was noted in the higher-redshift sample. Using Sloan Digital Sky Survey (SDSS) data to define relative galaxy number density, the dependence of the HIMF with environment was also investigated in the two AUDS regions. We find no significant variation in $alpha$ or $M^*$. In the surveyed region, we measured a cosmic HI density $Omega_{rm HI} = (3.55 pm 0.30) times 10^{-4} h_{70}^{-1}$. There appears to be no evolutionary trend in $Omega_{rm HI}$ above $2sigma$ significance between redshifts of 0 and 0.16.
We present the results of a deep survey of the nearby Sculptor group and the associated Sculptor filament taken with the Parkes 64-m radio telescope in the 21-cm emission line of neutral hydrogen. We detect 31 HI sources in the Sculptor group/filament, eight of which are new HI detections. We derive a slope of the HI mass function along the Sculptor filament of $alpha = -1.10^{+0.20}_{-0.11}$, which is significantly flatter than the global mass function and consistent with the flat slopes previously found in other low-density group environments. Some physical process, such as star formation, photoionisation or ram-pressure stripping, must therefore be responsible for removing neutral gas predominantly from low-mass galaxies. All of our HI detections have a confirmed or tentative optical counterpart and are likely associated with luminous rather than dark galaxies. Despite a column density sensitivity of about $4 times 10^{17}~mathrm{cm}^{-2}$, we do not find any traces of extragalactic gas or tidal streams, suggesting that the Sculptor filament is, at the current time, a relatively quiescent environment that has not seen any recent major interactions or mergers.
We present the first interferometric blind HI survey of the Fornax galaxy cluster, which covers an area of 15 deg$^2$ out to the cluster $R_{vir}$. The survey has a resolution of 67x95 and 6.6 km$s^{-1}$ with a 3$sigma$ sensitivity of N(HI)~2x10$^{19}$ cm$^{-2}$ and MHI 2x10$^7$ M$_odot$. We detect 16 galaxies out of 200 spectroscopically confirmed Fornax cluster members. The detections cover ~3 orders of magnitude in HI mass, from 8x10$^6$ to 1.5x10$^{10}$ M$_odot$. They avoid the central, virialised region of the cluster both on the sky and in projected phase-space, showing that they are recent arrivals and that, in Fornax, HI is lost within a crossing time, ~2 Gyr. Half of these galaxies exhibit a disturbed HI morphology, including several cases of asymmetries, tails, offsets between HI and optical centres, and a case of a truncated HI disc suggesting that they have been interacting within or on their way to Fornax. Our HI detections are HI-poorer and form stars at a lower rate than non-cluster galaxies in the same $M_star$ range. Low mass galaxies are more strongly affected throughout their infall towards the cluster. The MHI/$M_star$ ratio of Fornax galaxies is comparable to that in the Virgo cluster. At fixed $M_star$, our HI detections follow the non-cluster relation between MHI and the star formation rate, and we argue that this implies that so far they have lost their HI on a timescale $gtrsim$1-2 Gyr. Deeper inside the cluster HI removal is likely to proceed faster, as confirmed by a population of HI-undetected but H$_2$-detected star-forming galaxies. Based on ALMA data, we find a large scatter in H$_2$-to-HI mass ratio, with several galaxies showing an unusually high ratio that is probably caused by faster HI removal. We identify an HI-rich subgroup of possible interacting galaxies dominated by NGC 1365, where pre-processing is likey to have taken place.
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 catalogs 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.
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.
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