Publications (42)92.09 Total impact
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Article: An HI Survey of Six Local Group Analogs. II. HI properties of group galaxies
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ABSTRACT: We have conducted an HI 21 cm emission-line survey of six loose groups of galaxies chosen to be analogs to the Local Group. The survey was conducted using the Parkes Multibeam instrument and the Australia Telescope Compact Array (ATCA) over a ~1 Mpc^2 area and covering the full depth of each group, with a M(HI) sensitivity of ~7x10^5 M(sun). Our survey detected 110 sources, 61 of which are associated with the six groups. All of these sources were confirmed with ATCA observations or were previously cataloged by HIPASS. The sources all have optical counterparts and properties consistent with dwarf irregular or late-type spiral galaxies. We present here the HI properties of the groups and their galaxies. We derive an HI mass function for the groups that is consistent with being flatter than the equivalent field HIMF. We also derive a circular velocity distribution function, tracing the luminous dark matter halos in the groups, that is consistent with those of the Local Group and HIPASS galaxies, both of which are shallower than that of clusters or predictions from CDM models of galaxy formation.10/2011; -
Article: Measuring the halo mass function in loose groups
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ABSTRACT: Using data from our Parkes & ATCA HI survey of six groups analogous to the Local Group, we find that the HI mass function and velocity distribution function for loose groups are the same as those for the Local Group. Both mass functions confirm that the "missing satellite" problem exists in other galaxy groups. Comment: 2 pages, to appear in the proceedings of JENAM 2010 symposium "Environment and the Formation of Galaxies: 30 years later", eds. I. Ferreras and A. Pasquali12/2010; -
Article: New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group
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ABSTRACT: We have commenced a 21 cm survey of the entire southern sky (δ < 0°, -1200 km s-1 < v☉ < 12,700 km s-1) that is "blind," i.e., unbiased by previous optical information. In the present paper we report on the results of a pilot project that is based on data from this all-sky survey. The project was carried out on an area of 600 deg2 centered on the nearby Centaurus A (Cen A) group of galaxies at a mean velocity of v☉ ~ 500 km s-1. This was recently the subject of a separate and thorough optical survey. We found 10 new group members to add to 21 galaxies already known in the Cen A group: five of these are previously uncataloged galaxies, while five were previously catalogued but not known to be associated with the group. Most of the new members have H I masses close to our survey limit of 107 M☉ at the assumed group distance of 3.5 Mpc. The new detection with the largest H I mass is ESO 174-G?001 with M = 2.1 × 108 M☉. Prior to our survey this galaxy was an uncertain optical identification because of high Galactic extinction. We found optical counterparts for all the H I detections, most of them intrinsically very faint (MB> -13.0), low surface brightness dwarf galaxies with H I profile line-widths suggestive of dynamics dominated by dark matter. The new group members add approximately 6% to the H I mass of the group and 4% to its light. The H I mass function, derived from all the known group galaxies in the interval 107 M☉ < M < 109 M☉, has a faint-end slope of 1.30 ± 0.15, allowing us to rule out a slope of 1.7 at 95% confidence. Even if the number in the lowest mass bin is increased by 50%, the slope only increases to 1.45 ± 0.15.The Astrophysical Journal 01/2009; 524(2):612. · 6.02 Impact Factor -
Article: HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group
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ABSTRACT: We report the discovery from the H I Parkes All-Sky Survey (HIPASS) of a gas cloud associated with the asymmetric spiral galaxy NGC 2442. This object, designated HIPASS J0731-69, contains ~109 M☉ of H I, or nearly one-third as much atomic gas as NGC 2442 itself. No optical counterpart to any part of HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse and its streamlike kinematics. If the gas in HIPASS J0731-69 was once part of NGC 2442, then it was most likely a fairly recent tidal encounter with a moderately massive companion that tore it loose, although the possibility of ram-pressure stripping cannot be ruled out. This discovery highlights the potential of the HIPASS data for yielding new clues to the nature of some of the best-known galaxies in the local universe.The Astrophysical Journal 12/2008; 555(1):232. · 6.02 Impact Factor -
Article: The 1000 Brightest HIPASS Galaxies: The H I Mass Function and ΩH I
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ABSTRACT: We present a new, accurate measurement of the H I mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest H I peak flux densities in the southern (δ < 0°) hemisphere. This sample spans nearly 4 orders of magnitude in H I mass [log (MH I/M) + 2 log h75 = 6.8–10.6] and is the largest sample of H I–selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies and show that this is a robust method, insensitive to the effects of large-scale structure. The resulting H I mass function can be fitted satisfactorily with a Schechter function with faint-end slope α = -1.30. This slope is found to be dependent on morphological type, with late-type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the H I mass function, including peculiar motions of galaxies, large-scale structure, selection bias, and inclination effects, and we quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: ΩH I = (3.8 ± 0.6) × 10-4 h. Low surface brightness galaxies contribute only ~15% to this value, consistent with previous findings.The Astronomical Journal 12/2007; 125(6):2842. · 4.03 Impact Factor -
Article: The 1000 Brightest HIPASS Galaxies: Newly Cataloged Galaxies
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ABSTRACT: The H I Parkes All-Sky Survey (HIPASS) is a blind 21 cm survey for extragalactic neutral hydrogen, covering the whole southern sky. The HIPASS Bright Galaxy Catalog (BGC) is a subset of HIPASS and contains the 1000 H I–brightest (peak flux density) galaxies. Here we present the 138 HIPASS BGC galaxies that had no redshift measured prior to the Parkes multibeam H I surveys. Of the 138 galaxies, 87 are newly cataloged. Newly cataloged is defined as having no optical (or infrared) counterpart in the NASA/IPAC Extragalactic Database. Using the Digitized Sky Survey, we identify optical counterparts for almost half of the newly cataloged galaxies, which are typically of irregular or Magellanic morphological type. Several H I sources appear to be associated with compact groups or pairs of galaxies rather than an individual galaxy. The majority (57) of the newly cataloged galaxies lie within 10° of the Galactic plane and are missing from optical surveys as a result of confusion with stars or dust extinction. This sample also includes newly cataloged galaxies first discovered by Henning et al. in the H I shallow survey of the zone of avoidance. The other 30 newly cataloged galaxies escaped detection because of their low surface brightness or optical compactness. Only one of these, HIPASS J0546-68, has no obvious optical counterpart, as it is obscured by the Large Magellanic Cloud. We find that the newly cataloged galaxies with |b| > 10° are generally lower in H I mass and narrower in velocity width compared with the total HIPASS BGC. In contrast, newly cataloged galaxies behind the Milky Way are found to be statistically similar to the entire HIPASS BGC. In addition to these galaxies, the HIPASS BGC contains four previously unknown H I clouds.The Astronomical Journal 12/2007; 124(4):1954. · 4.03 Impact Factor -
Article: A Catalog of H I-selected Galaxies from the South Celestial Cap Region of Sky
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ABSTRACT: The first deep catalog of the H I Parkes All Sky Survey (HIPASS) is presented, covering the south celestial cap (SCC) region. The SCC area is ~2400 deg2 and covers δ < -62°. The average rms noise for the survey is 13 mJy beam-1. Five hundred thirty-six galaxies have been cataloged according to their neutral hydrogen content, including 114 galaxies that have no previous cataloged optical counterpart. This is the largest sample of galaxies from a blind H I survey to date. Most galaxies in optically unobscured regions of sky have a visible optical counterpart; however, there is a small population of low-velocity H I clouds without visible optical counterparts whose origins and significance are unclear. The rms accuracy of the HIPASS positions is found to be 19. The H I mass range of galaxies detected is from ~106 to ~1011 M. There are a large number of late-type spiral galaxies in the SCC sample (66%), compared with 30% for optically selected galaxies from the same region in the NASA Extragalactic Database. The average ratio of H I mass to B luminosity of the sample increases according to optical type, from 1.8 M/L for early types to 3.2 M/L for late-type galaxies. The H I–detected galaxies tend to follow the large-scale structure traced by galaxies found in optical surveys. From the number of galaxies detected in this region of sky, we predict the full HIPASS catalog will contain ~5000 galaxies, to a peak flux density limit of ~39 mJy (3 σ), although this may be a conservative estimate as two large voids are present in the region. The H I mass function for this catalog is presented in a subsequent paper.The Astronomical Journal 12/2007; 124(2):690. · 4.03 Impact Factor -
Chapter: HI in Local Group Analogs: What does it Tell Us about Galaxy Formation?
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ABSTRACT: We present the results of our HI survey of six loose groups of galaxies analogous to the Local Group. The survey was conducted using the Parkes telescope and the Australia Telescope Compact Array to produce a census of all the gas-rich galaxies and potential analogs to the high-velocity clouds (HVCs) within these groups down to MHI ≤ 107M⊙as a test of models of galaxy formation. We present the HI mass function and halo mass function for these analogous groups and compare them with the Local Group and other environments. We also demonstrate that our non-detection of HVC analogs in these groups implies that they must have low HI masses and be clustered tightly around galaxies, including around our own Milky Way, and are not distributed throughout the Local Group.07/2007: pages 33-38; -
Article: An HI survey of six Local Group analogs: I. Survey description and the search for high-velocity clouds
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ABSTRACT: We have conducted an HI 21 cm emission-line survey using the Parkes 20cm multibeam instrument and the Australia Telescope Compact Array (ATCA) of six loose groups of galaxies chosen to be analogs to the Local Group. The goal of this survey is to make a census of the HI-rich galaxies and high-velocity clouds (HVCs) within these groups and compare these populations with those in the Local Group. The Parkes observations covered the entire volume of each group with a rms M(HI) sensitivity of 4-10x10^5 M(sun) per 3.3 km/s channel. All potential sources detected in the Parkes data were confirmed with ATCA observations at ~2' resolution and the same M(sun) sensitivity. All the confirmed sources have associated stellar counterparts; no starless HI clouds--HVC analogs--were found in the six groups. In this paper, we present a description of the survey parameters, its sensitivity and completeness. Using the population of compact HVCs (CHVCs) around the Milky Way as a template coupled with the detailed knowledge of our survey parameters, we infer that our non-detection of CHVC analogs implies that, if similar populations exist in the six groups studied, the CHVCs must be clustered within 90 kpc of group galaxies, with average M(HI) < 4x10^5 M(sun) at the 95% confidence level. The corollary is that the same must apply to Milky Way CHVCs. This is consistent with our previous results from a smaller sample of groups, and in accordance with recent observational and theoretical constraints from other authors. These results confirm that there is very little neutral matter around galaxies, and that any substantial reservoir of baryons must be in other phases.03/2007; -
Chapter: STUDYING GALAXY FORMATION IN LOOSE GALAXY GROUPS
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ABSTRACT: We present the results of our Hi survey of six loose groups of galaxies analogous to the Local Group. The survey was conducted using the Parkes telescope and the Australia Telescope Compact Array to produce a census of all the gas-rich galaxies and analogs to the high-velocity clouds (HVCs) within these groups down to MHI< 107 as a test of models of galaxy formation. We present the Hi mass function and halo mass function of the loose groups and show that they are consistent with those of the Local Group. We discuss the possible role of HVCs in solving the “missing satellite” problem and discuss the implications of our observations for models of galaxy formation.12/2006: pages 319-322; -
Article: The Northern HIPASS catalogue – data presentation, completeness and reliability measures
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ABSTRACT: The Northern HIPASS catalogue (NHICAT) is the northern extension of the HIPASS catalogue, HICAT. This extension adds the sky area between the declination (Dec.) range of +2° < δ < +25°30′ to HICAT's Dec. range of −90° < δ < +2°. HIPASS is a blind H i survey using the Parkes Radio Telescope covering 71 per cent of the sky (including this northern extension) and a heliocentric velocity range of −1280 to 12 700 km s−1. The entire Virgo Cluster region has been observed in the Northern HIPASS. The galaxy catalogue, NHICAT, contains 1002 sources with vhel > 300 km s−1. Sources with −300 < vhel < 300 km s−1 were excluded to avoid contamination by Galactic emission. In total, the entire HIPASS survey has found 5317 galaxies identified purely by their HI content. The full galaxy catalogue is publicly available at http://hipass.aus-vo.org.Monthly Notices of the Royal Astronomical Society 09/2006; 371(4):1855 - 1864. · 4.90 Impact Factor -
Article: Studying Galaxy Formation in Loose Galaxy Groups
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ABSTRACT: We present the results of our HI survey of six loose groups of galaxies analogous to the Local Group. The survey was conducted using the Parkes telescope and the Australia Telescope Compact Array to produce a census of all the gas-rich galaxies and analogs to the high-velocity clouds (HVCs) within these groups down to M(HI) < 10^7 M(sun) as a test of models of galaxy formation. We present the HI mass function and halo mass function of the loose groups and show that they are consistent with those of the Local Group. We discuss the possible role of HVCs in solving the ``missing satellite'' problem and discuss the implications of our observations for models of galaxy formation.10/2005; -
Article: The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy
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ABSTRACT: The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm emission line survey covering the whole southern sky from declination -90 to +25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from the region south of declination +2, is presented in Meyer et al. (2004a, Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width, and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure.06/2004; -
Article: The HIPASS Catalogue - I. Data Presentation
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ABSTRACT: The HI Parkes All-Sky Survey (HIPASS) Catalogue forms the largest uniform catalogue of HI sources compiled to date, with 4,315 sources identified purely by their HI content. The catalogue data comprise the southern region declination <+2 deg of HIPASS, the first blind HI survey to cover the entire southern sky. RMS noise for this survey is 13 mJy/beam and the velocity range is -1,280 to 12,700 km/s. Data search, verification and parametrization methods are discussed along with a description of measured quantities. Full catalogue data are made available to the astronomical community including positions, velocities, velocity widths, integrated fluxes and peak flux densities. Also available are on-sky moment maps, position-velocity moment maps and spectra of catalogue sources. A number of local large-scale features are observed in the space distribution of sources including the Super-Galactic plane and the Local Void. Notably, large-scale structure is seen at low Galactic latitudes, a region normally obscured at optical wavelengths. Comment: Accepted for publication in MNRAS. 17 pages, 14 figures. HIPASS catalogue data and paper with higher resolution figures can be downloaded from http://hipass.aus-vo.org06/2004; -
Article: The neutral hydrogen environments of the nearby galaxies WLM, NGC 1313 and Sextans A
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ABSTRACT: We have mapped the neutral gas content of the surroundings of three galaxies on the outskirts of the Local Group – Wolf–Lundmark–Melotte (WLM), NGC 1313 and Sextans A – at high velocity resolution and brightness sensitivity. We present high-quality H i spectra and parameters for the target galaxies, and find no unknown companion H i clouds nearer than ∼100 kpc to the targets, despite reaching a sensitivity of ∼106 M⊙ for narrow-linewidth objects.Monthly Notices of the Royal Astronomical Society 05/2004; 351(1):333 - 338. · 4.90 Impact Factor -
Article: The HI Content of Compact Groups of Galaxies
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ABSTRACT: The HI content of Hickson Compact Groups in the southern hemisphere is measured using data from the HI Parkes All Sky Survey (HIPASS), and dedicated observations using the narrowband filter on the Multibeam instrument on the Parkes telescope. The expected HI mass of these groups was estimated using the luminosity, diameter and morphological types of the member galaxies, calibrated from published data. Taking careful account of non-detection limits, the results show that the compact group population that has been detected by these observations has an HI content similar to that of galaxies in the reference field sample. The upper limits for the undetected groups lie within the normal range; improvement of these limits will require a large increase in sensitivity. Comment: 27 pages, 5 figures. Accepted for publication in PASA05/2004; -
Article: The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI
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ABSTRACT: We present a new accurate measurement of the HI mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest HI peak flux densities in the southern hemisphere (Koribalski et al. 2003). This sample spans nearly four orders of magnitude in HI mass (from log M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies, and show that this is a robust method, insensitive to the effects of large scale structure. The resulting HI mass function can be fitted satisfactorily with a Schechter function with faint-end slope alpha=-1.30. This slope is found to be dependent on morphological type, with later type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the HI mass function, including peculiar motions of galaxies, large scale structure, selection bias, and inclination effects, and quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies contribute only 15% to this value, consistent with previous findings.02/2003; -
Article: The Large Scale Distribution of Neutral Hydrogen in the Fornax Region
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ABSTRACT: Using HIPASS data, we have searched for HI in a ~25x25 sq.deg. region centred on the Fornax cluster. Within a velocity search range of 300 - 3700 km/s and a lower flux limit of ~40 mJy, 110 galaxies with HI emission were detected, one of which is previously uncatalogued. None of the detections has early-type morphology. Previously unknown velocities for 14 galaxies have been determined, with a further 4 velocity measurements being significantly dissimilar to published values. Identification of an optical counterpart is relatively unambiguous for more than ~90% of our HI galaxies. The galaxies appear to be embedded in a sheet at the cluster velocity which extends for more than 30 deg across the search area. At the nominal cluster distance of ~20 Mpc, this corresponds to an elongated structure more than 10 Mpc in extent. A velocity gradient across the structure is detected, with radial velocities increasing by \~500 km/s from SE to NW. The clustering of galaxies evident in optical surveys is only weakly suggested in the spatial distribution of our HI detections. Our results suggest a considerable deficit of HI-rich galaxies in the centre of the cluster. However, relative to the field, there is a 3(+/-1)-fold excess of HI-rich galaxies in the outer parts of the cluster where galaxies may be infalling towards the cluster for the first time. Comment: 16 pages, 14 figures, 110 HI spectra. To be published in MNRAS10/2002; -
Article: The Magellanic Stream, High-Velocity Clouds and the Sculptor Group
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ABSTRACT: The Magellanic Stream is a 100\deg x 10\deg filament of gas which lies within the Galactic halo and contains ~ 2 x 10^8 \Msun of neutral hydrogen. We present data from the HI Parkes All Sky Survey (HIPASS) in the first complete survey of the entire Magellanic Stream and its surroundings. We also present a summary of the reprocessing techniques used to recover large-scale structure in the Stream. The Stream properties revealed include: bifurcation along the main Stream filament; dense, isolated clouds which follow the entire length of the Stream; head-tail structures; and a complex filamentary web at the head where gas is being freshly stripped away from the Small Magellanic Cloud and the Bridge. Debris which appears to be of Magellanic origin extends out to 20\deg from the main Stream filaments. The large number of elongated Stream clouds suggests the presence of shearing motions within the Stream, arising from tidal forces or interaction with the tenuous Galactic halo. Clouds along the sightline to the less distant half of the Sculptor Group, show anomalous properties. We argue that these clouds represent halo material, and are not distant Sculptor Group clouds. This result has significant implications for the hypothesis that there might exist distant, massive HVCs within the Local Group. (abridged)10/2002; -
Article: The 1000 Brightest HIPASS Galaxies: Newly Cataloged Galaxies
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ABSTRACT: The HI Parkes All-Sky Survey (HIPASS) is a blind 21-cm survey for extragalactic neutral hydrogen, covering the whole southern sky. The HIPASS Bright Galaxy Catalog (BGC; Koribalski et al. 2002) is a subset of HIPASS and contains the 1000 HI-brightest (peak flux density) galaxies. Here we present the 138 HIPASS BGC galaxies, which had no redshift measured prior to the Parkes multibeam HI surveys. Of the 138 galaxies, 87 are newly cataloged. Newly cataloged is defined as no optical (or infrared) counterpart in the NASA/IPAC Extragalactic Database. Using the Digitized Sky Survey we identify optical counterparts for almost half of the newly cataloged galaxies, which are typically of irregular or magellanic morphological type. Several HI sources appear to be associated with compact groups or pairs of galaxies rather than an individual galaxy. The majority (57) of the newly cataloged galaxies lie within ten degrees of the Galactic Plane and are missing from optical surveys due to confusion with stars or dust extinction. This sample also includes newly cataloged galaxies first discovered in the HI shallow survey of the Zone-of-Avoidance (Henning et al. 2000). The other 30 newly cataloged galaxies escaped detection due to their low surface brightness or optical compactness. Only one of these, HIPASS J0546-68, has no obvious optical counterpart as it is obscured by the Large Magellanic Cloud. We find that the newly cataloged galaxies with |b| > 10 are generally lower in HI mass and narrower in velocity width compared with the total HIPASS BGC. In contrast, newly cataloged galaxies behind the Milky Way are found to be statistically similar to the entire HIPASS BGC. In addition to these galaxies, the HIPASS BGC contains four previously unknown HI clouds. Comment: 39 pages including 14 figures, to appear in the Oct 2002 issue of AJ06/2002;
Top co-authors
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Institutions
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2010
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West Virginia University
Morgantown, WV, USA
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2002–2008
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Swinburne University of Technology
- Centre for Astrophysics and Supercomputing
Melbourne, Victoria, Australia -
University of Colorado at Boulder
- Center for Astrophysics and Space Astronomy
Boulder, CO, USA
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1997–2007
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University of Melbourne
- School of Physics
Melbourne, Victoria, Australia
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