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Register a new userA deep Parkes HI survey of the Sculptor group and filament: HI mass function and environment
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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.
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A blind HI survey of the extragalactic sky behind the southern Milky Way has been conducted with the multibeam receiver on the 64-m Parkes radio telescope. The survey covers the Galactic longitude range 212 < l < 36 and Galactic latitudes |b| < 5, and yields 883 galaxies to a recessional velocity of 12,000 km/s. The survey covers the sky within the HIPASS area to greater sensitivity, finding lower HI-mass galaxies at all distances, and probing more completely the large-scale structures at and beyond the distance of the Great Attractor. Fifty-one percent of the HI detections have an optical/NIR counterpart in the literature. A further 27% have new counterparts found in existing, or newly obtained, optical/NIR images. The counterpart rate drops in regions of high foreground stellar crowding and extinction, and for low-HI mass objects. Only 8% of all counterparts have a previous optical redshift measurement. A notable new galaxy is HIZOA J1353-58, a possible companion to the Circinus galaxy. Merging this catalog with the similarly-conducted northern extension (Donley et al. 2005), large-scale structures are delineated, including those within the Puppis and Great Attractor regions, and the Local Void. Several newly-identified structures are revealed here for the first time. Three new galaxy concentrations (NW1, NW2 and NW3) are key in confirming the diagonal crossing of the Great Attractor Wall between the Norma cluster and the CIZA J1324.7-5736 cluster. Further contributors to the general mass overdensity in that area are two new clusters (CW1 and CW2) in the nearer Centaurus Wall, one of which forms part of the striking 180 deg (100/h Mpc) long filament that dominates the southern sky at velocities of ~3000 km/s, and the suggestion of a further Wall at the Great Attractor distance at slightly higher longitudes.
We exploit a large, complete optical diameter and HI flux limited sample of spiral galaxies with types later than S0a to derive a robust measurement of the HI mass function (HIMF) for masses log(M_HI/M_Sun) > 7.4 which takes into account the effects of local large scale structure. The global HIMF derived for this optically-selected sample is well fit by a Schechter function with alpha = -1.24, log(M* / M_Sun)=9.99, phi* = 3.2 (10^{-3}) Mpc^{-3}. These values match those derived from blind HI surveys to within the estimated uncertainties, yet our estimated HIMF is clearly lower than most other estimates at the lowest masses. We also investigate the variation in the derived HIMF among spiral subclasses, finding a clear distinction between the Schechter parameters found for types Sa-Sc and those Scd and later, in the sense that the HIMF of the latest types is rising at the low mass end, whereas that of the main spiral classes is flat or even declining. We also explore the possible environmental dependence of the HIMF by computing it separately in regimes of differing cosmic density. The HIMFs of higher density regions are found to have flatter low-mass ends and lower values of M* than those of lower density regions, although the statistical significance of the difference is low. We find that the environmental dependence cannot be accounted for by morphological segregation, and must be a consequence of differences among galaxies of the same morphological type but found in different environments. If this dependence is caused by the well known deficiency of galaxies in clusters, then it would suggest that galaxies of small linear optical diameter are characterized by higher HI deficiency, an expectation consistent with gas removal mechanisms such as ram pressure stripping.
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.
We present results of a blind 21cm HI-line imaging survey of a galaxy overdensity located behind the Milky Way at $ell,b$ $approx$ 160 deg, 0.5 deg. The overdensity corresponds to a Zone-of-Avoidance crossing of the Perseus-Pisces Supercluster filament. Although it is known that this filament contains an X-ray galaxy cluster (3C129) hosting two strong radio galaxies, little is known about galaxies associated with this potentially rich cluster because of the high Galactic dust extinction. We mapped a sky area of $sim$9.6 sq.deg using the Westerbork Synthesis Radio Telescope in a hexagonal mosaic of 35 pointings observed for 12 hours each, in the radial velocity range $cz = 2400 - 16600$ km/s. The survey has a sensitivity of 0.36 mJy/beam rms at a velocity resolution of 16.5 km/s. We detected 211 galaxies, 62% of which have a near-infrared counterpart in the UKIDSS Galactic Plane Survey. We present a catalogue of the HI properties and an HI atlas containing total intensity maps, position-velocity diagrams, global HI profiles and UKIDSS counterpart images. For the resolved galaxies we also present HI velocity fields and radial HI surface density profiles. A brief analysis of the structures outlined by these galaxies finds that 87 of them lie at the distance of the Perseus-Pisces Supercluster ($cz sim 4000 - 8000$ km/s) and seem to form part of the 3C129 cluster. Further 72 detections trace an overdensity at a velocity of $cz approx$ 10000 km/s and seem to coincide with a structure predicted from mass density reconstructions in the first 2MASS Redshift Survey.
We analyse the eastern region of a $5^circtimes5^circ$ deep HI survey of the M81 group containing the dwarf galaxy IC 2574 and the HI complex HIJASS J1021+68, located between the dwarf and the M81 system. The data show that IC 2574 has an extended HI envelope that connects to HIJASS J1021+68 in the form of a collection of small clouds, but no evident connection has been found between IC 2574 and the central members of the M81 group. We argue, based on the morphology of the clouds forming HIJASS J1021+68 and its velocity distribution, that the complex is not a dark galaxy as previously suggested, but is instead a complex of clouds either stripped from, or falling onto the primordial HI envelope of IC 2574. We also use the deep HI observations to map the extended HI envelope around IC 2574 and, using a 3D tilted-ring model, we derive the rotation curve of the galaxy to a larger extent than has been done before. Combining the obtained rotation curve to higher resolution curves from the literature, we constrain the galaxys dark matter halo parameters.
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