HI Parkes All Sky Survey Research Articles

HIPASS study of southern ultradiffuse galaxies and low surface brightness galaxies

ABSTRACT We present results from an H i counterpart search using the HI Parkes All Sky Survey (HIPASS) for a sample of low surface brightness galaxies (LSBGs) and ultradiffuse galaxies (UDGs) identified from the Dark Energy Survey (DES). We aimed to establish the redshifts of the DES LSBGs to determine the UDG fraction and understand their properties. Out of 409 galaxies investigated, none were unambiguously detected in H i. Our study was significantly hampered by the high spectral rms of HIPASS and thus in this paper we do not make any strong conclusive claims but discuss the main trends and possible scenarios our results reflect. The overwhelming number of non-detections suggest that (a) Either all the LSBGs in the groups, blue or red, have undergone environment aided pre-processing and are H i deficient or the majority of them are distant galaxies, beyond the HIPASS detection threshold. (b) The sample investigated is most likely dominated by galaxies with H i masses typical of dwarf galaxies. Had there been Milky Way (MW) size (Re) galaxies in our sample, with proportionate H i content, they would have been detected, even with the limitations imposed by the HIPASS spectral quality. This leads us to infer that if some of the LSBGs have MW-size optical diameters, their H i content is possibly in the dwarf range. More sensitive observations using the SKA precursors in future may resolve these questions.

Environmental processing of galaxies in H i-rich groups

ABSTRACT We present and explore the resolved atomic hydrogen (H i) content of 13 H i-rich and late-type dominated groups denoted ‘Choirs’. We quantify the H i content of the Choir galaxies with respect to the median of the H i-mass fraction ($f_{\rm{{H {\small I}}}}$) of their grandparent H i Parkes All Sky Survey (HIPASS) sample. We find that the H i-mass fraction of the Choir galaxies is dispersed around the HIPASS median in the range $-1.4\le \Delta f_{\rm{{H {\small I}}}}\textrm{[dex]}\le$ 0.7, from H i-excess to H i-deficient galaxy regime. The H i-excess/H i-deficient galaxies contain more/less than 2.5 times their expected H i content with respect to the HIPASS median. We show and discuss that the environmental processing in Choirs occurs via tidal stripping and galaxy mergers. Our analysis suggests that tidal stripping contributes to the loss of the H i, while galaxy mergers contribute to the enhancement of the H i. Exploring the mid-infrared properties of Choir galaxies, we find possible environmental processing in only nine Choir galaxies, which indicates that environmental processing is more perceptible in the H i content than the mid-infrared properties. Moreover, we find that environmental processing occurs in Choir groups regardless of their global environment, whether they are in isolation or in proximity to the denser structures, such as cosmic web filaments. We explore possible scenarios of the Choirs evolution, taking into account their H i content, velocity dispersion, crossing time, and their global environment. We conclude that the most likely evolution for the majority of Choir groups is that they will become more compact as their members undergo multiple H i-rich mergers.

H i deficiencies and asymmetries in HIPASS galaxies

ABSTRACT We present an analysis of the sky distribution of neutral hydrogen (H i) deficiency and spectral asymmetry for galaxies detected by the H i Parkes All-Sky Survey (HIPASS) as a function of projected environment density. Previous studies of galaxy H i deficiency using HIPASS were sensitive to galaxies that are extremely H i rich or poor. We use an updated binning statistic for measuring the global sky distribution of H i deficiency that is sensitive to the average deficiencies. Our analysis confirms the result from previous studies that galaxies residing in denser environments, such as Virgo, are on average more H i deficient than galaxies at lower densities. However, many other individual groups and clusters are not found to be on average significantly H i poor, in contradiction to previous work. In terms of H i spectral asymmetries, we do not recover any significant trend of increasing asymmetry with environment density as found for other galaxy samples. We also investigate the correlation between H i asymmetry and deficiency, but find no variation in the mean asymmetry of galaxies that are H i rich, normal, or poor. This indicates that there is either no dependence of asymmetry on H i deficiency, or a galaxy’s H i deficiency only has a small influence on the measured H i asymmetry that we are unable to observe using only integrated spectra.

The Halo Mass Function of Late-type Galaxies from H i Kinematics

Abstract We present an empirical method to measure the halo mass function (HMF) of galaxies. We determine the relation between the H i line width from single-dish observations and the dark matter halo mass (M 200) inferred from rotation-curve fits in the Spitzer Photometry and Accurate Rotation Curves (SPARC) database, then we apply this relation to galaxies from the H i Parkes All Sky Survey (HIPASS) to derive the HMF. This empirical HMF is well fit by a Schechter function, and matches that expected in the Λ Cold Dark Matter (ΛCDM) model over the range 1010.5 < M 200 < 1012 M ⊙. More massive halos must be poor in neutral gas to maintain consistency with the power law predicted by ΛCDM. We detect no discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is just greater than the mass scale where the Local Group missing satellite problem sets in. The integrated mass density associated with the dark matter halos of H i-detected galaxies sums to Ωm,gal ≈ 0.03 over the probed mass range.

The Local Volume H i Survey (LVHIS)

The `Local Volume HI Survey' (LVHIS) comprises deep HI spectral line and 20-cm radio continuum observations of 82 nearby, gas-rich galaxies, supplemented by multi-wavelength images. Our sample consists of all galaxies with Local Group velocities v_LG < 550 km/s or distances D < 10 Mpc that are detected in the HI Parkes All Sky Survey (HIPASS). Using full synthesis observations in at least three configurations of the Australia Telescope Compact Array (ATCA), we obtain detailed HI maps for a complete sample of gas-rich galaxies with Dec < -30 deg. Here we present a comprehensive LVHIS Galaxy Atlas, including the overall gas distribution, mean velocity field, velocity dispersion, and position-velocity diagrams, together with a homogeneous set of measured and derived galaxy properties. Our primary goal is to investigate the HI morphologies, kinematics, and environment at high resolution and sensitivity. LVHIS galaxies represent a wide range of morphologies and sizes; our measured HI masses range from ~10^7 to 10^10 Msun, based on independent distance estimates. The LVHIS Galaxy Atlas (including FITS files) is available on-line.

The H ix galaxy survey – II. H i kinematics of H i eXtreme galaxies

By analysing a sample of galaxies selected from the HI Parkes All Sky Survey (HIPASS) to contain more than 2.5 times their expected HI content based on their optical properties, we investigate what drives these HI eXtreme (HIX) galaxies to be so HI-rich. We model the HI kinematics with the Tilted Ring Fitting Code TiRiFiC and compare the observed HIX galaxies to a control sample of galaxies from HIPASS as well as simulated galaxies built with the semi-analytic model Dark Sage. We find that (1) HI discs in HIX galaxies are more likely to be warped and more likely to host HI arms and tails than in the control galaxies, (2) the average HI and average stellar column density of HIX galaxies is comparable to the control sample, (3) HIX galaxies have higher HI and baryonic specific angular momenta than control galaxies, (4) most HIX galaxies live in higher-spin haloes than most control galaxies. These results suggest that HIX galaxies are HI-rich because they can support more HI against gravitational instability due to their high specific angular momentum. The majority of the HIX galaxies inherits their high specific angular momentum from their halo. The HI content of HIX galaxies might be further increased by gas-rich minor mergers. This paper is based on data obtained with the Australia Telescope Compact Array (ATCA) through the large program C 2705.

HI properties and star formation history of a fly-by pair of blue compact dwarf galaxies

A fly-by interaction has been suggested to be one of the major explanations for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct evidence for this scenario has been found to date. In the HI Parkes all-sky survey (HIPASS), ESO 435-IG 020 and ESO 435- G 016, a BCD pair were found in a common, extended gas envelope of atomic hydrogen, providing an ideal case to test the hypothesis that the starburst in BCDs can be indeed triggered by a fly-by interaction. Using high-resolution data from the Australia Telescope Compact Array (ATCA), we investigated HI properties and the spectral energy distribution (SED) of the BCD pair to study their interaction and star formation histories. The high-resolution HI data of both BCDs reveal a number of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of the HIPASS flux is not accounted for in the ATCA observations with no HI gas bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS and the ATCA data, 10% of the missing flux appears to be located between the two BCDs. While the SED-based age of the most dominant young stellar population is old enough to have originated from the interaction with any neighbors (including the other of the two BCDs), the most recent star formation activity traced by strong H$\alpha$ emission in ESO 435-IG 020 and the shear motion of gas in ESO 435- G 016, suggest a more recent or current tidal interaction. Based on these and the residual emission between the HIPASS and the ATCA data, we propose an interaction between the two BCDs as the origin of their recently enhanced star formation activity. The shear motion on the gas disk, potentially with re-accretion of the stripped gas, could be responsible for the active star formation in this BCD pair.

H i emission and absorption in nearby, gas-rich galaxies – II. Sample completion and detection of intervening absorption in NGC 5156

We present the results of a survey for intervening 21cm HI absorption in a sample of 10 nearby, gas-rich galaxies selected from the HI Parkes All-Sky Survey (HIPASS). This follows the six HIPASS galaxies searched in previous work and completes our full sample. In this paper we searched for absorption along 17 sightlines with impact parameters between 6 and 46 kpc, making one new detection. We also obtained simultaneous HI emission-line data, allowing us to directly relate the absorption-line detection rate to the HI distribution. From this we find the majority of the non-detections in the current sample are because sightline does not intersect the HI disc of the galaxy at sufficiently high column density, but that source structure is also an important factor. The detected absorption-line arises in the galaxy NGC 5156 ($z = 0.01$) at an impact parameter of 19 kpc. The line is deep and narrow with an integrated optical depth of 0.82 km s$^{-1}$. High resolution Australia Telescope Compact Array (ATCA) images at 5 and 8 GHz reveal that the background source is resolved into two components with a separation of 2.6 arcsec (500 pc at the redshift of the galaxy), with the absorption likely occurring against a single component. We estimate that the ratio of the spin temperature and covering factor, $T_{\mathrm{S}}/f$, is approximately 950 K in the outer disc of NGC 5156, but further observations using VLBI would allow us to accurately measure the covering factor and spin temperature of the gas.

H i-deficient galaxies in intermediate-density environments

Observations show that spiral galaxies in galaxy clusters tend to have on average less neutral hydrogen (HI) than galaxies of the same type and size in the field. There is accumulating evidence that such HI-deficient galaxies are also relatively frequent in galaxy groups. An important question is, which mechanisms are responsible for the gas deficiency in galaxy groups. To gain a better understanding of how environment affects the gas content of galaxies, we identified a sample of six HI-deficient galaxies from the HI Parkes All Sky Survey (HIPASS) using HI-optical scaling relations. One of the galaxies is located in the outskirts of the Fornax cluster, four are in loose galaxy groups and one is in a galaxy triplet. We present new high resolution HI observations with the Australia Telescope Compact Array (ATCA) of these galaxies. We discuss the possible cause of HI-deficiency in these galaxies based on HI observations and various multi-wavelength data. We find that the galaxies have truncated HI disks, lopsided gas distribution and some show asymmetries in their stellar disks. We conclude that both ram pressure stripping and tidal interactions are important gas removal mechanisms in low density environments.

Kathryn's Wheel: a spectacular galaxy collision discovered in the Galactic neighbourhood

We report the discovery of the closest collisional ring galaxy to the Milky Way. Such rare systems occur due to "bulls-eye" encounters between two reasonably matched galaxies. The recessional velocity of about 840 km/s is low enough that it was detected in the AAO/UKST Survey for Galactic H$\alpha$ emission. The distance is only 10.0 Mpc and the main galaxy shows a full ring of star forming knots, 6.1 kpc in diameter surrounding a quiescent disk. The smaller assumed "bullet" galaxy also shows vigorous star formation. The spectacular nature of the object had been overlooked because of its location in the Galactic plane and proximity to a bright star and even though it is the 60$^{\rm th}$ brightest galaxy in the HI Parkes All Sky Survey (HIPASS) HI survey. The overall system has a physical size of $\sim$15 kpc, a total mass of $M_\ast = 6.6\times 10^9$ M$_\odot$ (stars + HI), a metallicity of [O/H]$\sim-0.4$, and a star formation rate of 0.2-0.5 M$_\odot$\,yr$^{-1}$, making it a Magellanic-type system. Collisional ring galaxies therefore extend to much lower galaxy masses than commonly assumed. We derive a space density for such systems of $7 \times 10^{-5}\,\rm Mpc^{-3}$, an order of magnitude higher than previously estimated. This suggests Kathryn's Wheel is the nearest such system. We present discovery images, CTIO 4-m telescope narrow-band follow-up images and spectroscopy for selected emission components. Given its proximity and modest extinction along the line of sight, this spectacular system provides an ideal target for future high spatial resolution studies of such systems and for direct detection of its stellar populations.

The SAMI Galaxy Survey: the discovery of a luminous, low-metallicity H ii complex in the dwarf galaxy GAMA J141103.98−003242.3

We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of ~100 Mpc and contains an unresolved region of H II emission that contributes ~70 per cent of the galaxy's H_alpha luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star-formation rate of 0.147\pm0.041 M_solar yr^-1 and a metallicity of 12+log(O/H) = 8.01\pm0.05 that is lower than the rest of the galaxy by ~0.2 dex. Data from the H I Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star-formation activity of this H II complex, where the kinematics of the ionised gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution.

Source finding, parametrization, and classification for the extragalactic Effelsberg-Bonn H i Survey

Context. Source extraction for large-scale HI surveys currently involves large amounts of manual labor. For data volumes expected from future HI surveys with upcoming facilities, this approach is not feasible any longer. Aims. We describe the implementation of a fully automated source finding, parametrization, and classification pipeline for the Effelsberg-Bonn HI Survey (EBHIS). With future radio astronomical facilities in mind, we want to explore the feasibility of a completely automated approach to source extraction for large-scale HI surveys. Methods. Source finding is implemented using wavelet denoising methods, which previous studies show to be a powerful tool, especially in the presence of data defects. For parametrization, we automate baseline fitting, mask optimization, and other tasks based on well-established algorithms, currently used interactively. For the classification of candidates, we implement an artificial neural network which is trained on a candidate set comprised of false positives from real data and simulated sources. Using simulated data, we perform a thorough analysis of the algorithms implemented. Results. We compare the results from our simulations to the parametrization accuracy of the HI Parkes All-Sky Survey (HIPASS) survey. Even though HIPASS is more sensitive than EBHIS in its current state, the parametrization accuracy and classification reliability match or surpass the manual approach used for HIPASS data.

New H i scaling relations to probe the H i content of galaxies via global H i-deficiency maps

We present new multi-wavelength scaling relations between the neutral hydrogen content (HI) and the stellar properties of nearby galaxies selected from the HI Parkes All-Sky Survey (HIPASS). We use these new scaling relations to investigate the environmental dependency of the HI content of galaxies. We find that galaxies in high density environments tend to have on average less HI than galaxies with the same stellar mass in the low density environment. Our new HI scaling relations allow us to identify individual galaxies, as well as group/cluster environments, that have an `anomalous' HI content. We map the global distribution of HI-deficient and HI-excess galaxies on the sky and compare it to the large scale structure of galaxies. We find galaxy clusters to be HI-deficient, and we identify that the regions surrounding clusters tend to be HI-excess. Finally, we demonstrate the potential of using HI scaling relations to predict future HI surveys based on an optical redshift survey. We apply our scaling relations to 16709 galaxies in the 6dF Galaxy Survey (6dFGS) that lie in the HIPASS volume and compare our predictions to the measurements. We find that scaling relations are good method to estimate the outcome of HI surveys.

A search for H i absorption in nearby radio galaxies using HIPASS

Using archival data from the HI Parkes All Sky Survey (HIPASS) we have searched for 21 cm line absorption in 204 nearby radio and star-forming galaxies with continuum flux densities greater than $S_{1.4} \approx 250$ mJy within the redshift range $0 < cz < 12000$ km s$^{-1}$. By applying a detection method based on Bayesian model comparison, we successfully detect and model absorption against the radio-loud nuclei of four galaxies, of which the Seyfert 2 galaxy 2MASX J130804201-2422581 was previously unknown. All four detections were achieved against compact radio sources, which include three active galactic nuclei (AGNs) and a nuclear starburst, exhibiting high dust and molecular gas content. Our results are consistent with the detection rate achieved by the recent ALFALFA (Arecibo Legacy Fast Arecibo L-band Feed Array) HI absorption pilot survey by Darling et al. and we predict that the full ALFALFA survey should yield more than three to four times as many detections as we have achieved here. Furthermore, we predict that future all-sky surveys on the Square Kilometre Array precursor telescopes will be able to detect such strong absorption systems associated with type 2 AGNs at much higher redshifts, providing potential targets for detection of H$_{2}$O megamaser emission at cosmological redshifts.

A New 1.4 GHz Radio Continuum Map of the Sky South of Declination +25°

AbstractArchival data from the HI Parkes All-Sky Survey (HIPASS) and the HI Zone of Avoidance (HIZOA) survey have been carefully reprocessed into a new 1.4 GHz continuum map of the sky south of δ = +25°. The wide sky coverage, high sensitivity of 40 mK (limited by confusion), resolution of 14.4 arcmin (compared to 51 arcmin for the Haslam et al. 408 MHz and 35 arcmin for the Reich et al. 1.4 GHz surveys), and low level of artefacts make this map ideal for numerous studies, including: merging into interferometer maps to complete large-scale structures; decomposition of thermal and non-thermal emission components from Galactic and extragalactic sources; and comparison of emission regions with other frequencies. The new map is available for download.

Detection of H i in distant galaxies using spectral stacking

Using the Parkes radio telescope, we study the 21cm neutral hydrogen (HI) properties of a sample of galaxies with redshifts z<0.13 extracted from the optical 2dF Galaxy Redshift Survey (2dFGRS). Galaxies at 0.04<z<0.13 are studied using new Parkes observations of a 42deg^2 field near the South Galactic Pole (SGP). A spectral stacking analysis of the 3,277 2dFGRS objects within this field results in a convincing 12sigma detection. For the low-redshift sample at 0<z<0.04, we use the 15,093 2dFGRS galaxies observed by the HI Parkes All-Sky Survey (HIPASS) and find a 31sigma stacked detection. We measure average HI masses of (6.93 +/- 0.17)*10^9 h^{-2} Msun and (1.48 +/- 0.03)*10^9 h^{-2} Msun for the SGP and HIPASS samples, respectively. Accounting for source confusion and sample bias, we find a cosmic HI mass density of Omega_HI=(3.19_{-0.59} ^{+0.43})*10^{-4} h^{-1} for the SGP sample and (2.82_{-0.59}^{+0.30})*10^{-4} h^{-1} for the HIPASS sample. This suggests no (12 +/- 23%) evolution in the cosmic HI density over the last ~1h^{-1} Gyr. Due to the very large effective volumes, cosmic variance in our determination of Omega_HI is considerably lower than previous estimates. Our stacking analysis reproduces and quantifies the expected trends in the HI mass and mass-to-light ratio of galaxies with redshift, luminosity and colour.

CONFRONTING COLD DARK MATTER PREDICTIONS WITH OBSERVED GALAXY ROTATIONS

The rich statistics of galaxy rotations as captured by the velocity function (VF) provides invaluable constraints on galactic baryon physics and the nature of dark matter (DM). However, the comparison of observed galaxy rotations against cosmological models is prone to subtle caveats that can easily lead to misinterpretations. Our analysis reveals full statistical consistency between ~5000 galaxy rotations, observed in line-of-sight projection, and predictions based on the standard cosmological model (LCDM) at the mass-resolution of the Millennium simulation (HI line-based circular velocities above ~50 km/s). Explicitly, the HI linewidths in the HI Parkes All Sky Survey (HIPASS) are found consistent with those in S3-SAX, a post-processed semi-analytic model for the Millennium simulation. Previously found anomalies in the VF can be plausibly attributed to (1) the mass-limit of the Millennium simulation, (2) confused sources in HIPASS, (3) inaccurate inclination measurements for optically faint sources, and (4) the non-detectability of gas-poor early-type galaxies. These issues can be bypassed by comparing observations and models using linewidth source counts rather than VFs. We investigate if and how well such source counts can constrain the temperature of DM.

A derivation of the free-free emission on the Galactic plane between ℓ= 20° and 44°

We present the derivation of the free-free emission on the Galactic plane between l=20 and 44 degrees and |b| < 4 degrees, using Radio Recombination Line (RRL) data from the HI Parkes All-Sky Survey (HIPASS). Following an upgrade on the RRL data reduction technique, which improves significantly the quality of the final RRL spectra, we have extended the analysis to three times the area covered in Alves et al. (2010). The final RRL map has an angular resolution of 14.8 arcmin and a velocity resolution of 20 km/s. A map of the electron temperature (Te) of the ionised gas is derived for the area under study using the line and continuum data from the present survey. The mean Te on the Galactic plane is 6000 K. The first direct measure of the free-free emission is obtained based on the derived Te map. Subtraction of this thermal component from the total continuum leaves the first direct measure of the synchrotron emission at 1.4 GHz. A narrow component of width 2 degrees is identified in the latitude distribution of the synchrotron emission. We present a list of HII regions and SNRs extracted from the present free-free and synchrotron maps, where we confirm the synchrotron nature of three objects: G41.12-0.21, G41.15+0.39 and G35.59-0.44. We also identify a bright (42 Jy) new double radio galaxy, J1841-0152, previously unrecognised owing to the high optical extinction in the region. The latitude distribution for the RRL-derived free-free emission shows that the WMAP Maximum Entropy Method (MEM) is too high by ~ 50 per cent, in agreement with other recent results. The extension of this study to the inner Galaxy region l=-50 to 50 degrees will allow a better overall comparison of the RRL result with WMAP.

The Local Volume H i Survey: galaxy kinematics1★

We present a detailed analysis of the neutral hydrogen kinematics of 12 nearby dwarf irregular galaxies observed as part of the Local Volume HI Survey (LVHIS) conducted at the Australia Telescope Compact Array. For each galaxy we measure the disk parameters (inclination, position angle) and the HI rotation curve. Six galaxies in our sample (AM0605-341, Argo Dwarf, ESO059-G001, ESO137-G018, ESO174-G?001, ESO308-G022) have their atomic hydrogen distribution studied for the first time. AM0605-341 was found to have an extension of redshifted HI which we propose is due to a tidal interaction with NGC2188. There is evidence that ESO215-G?009 has extraplanar HI gas. We also compare the global galaxy properties, in particular the integrated HI flux density and velocity widths of the observed HI spectra with the results from the low angular resolution HI Parkes All Sky Survey (HIPASS). We discuss under what circumstances the 21cm emission line profile can accurately predict the galaxy's rotation velocity, an observational parameter crucial to study the classical and baryonic Tully-Fisher relations.

THE H I CONTENT OF LOCAL LATE-TYPE GALAXIES

We present a solid relationship between the neutral hydrogen (HI) disk mass and the stellar disk mass of late-type galaxies in the local universe. This relationship is derived by comparing the stellar disk mass function from the Sloan Digital Sky Survey and the HI mass function from the HI Parkes All Sky Survey (HIPASS). We find that the HI mass in late-type galaxies tightly correlates with the stellar mass over three orders of magnitude in stellar disk mass. We cross-check our result with that obtained from a sample of HIPASS objects for which the stellar mass has been obtained by inner kinematics. In addition, we derive the HI versus halo mass relationship and the dependence of all the baryonic components in spirals on the host halo mass. These relationships bear the imprint of the processes ruling galaxy formation, and highlight the inefficiency of galaxies both in forming stars and in retaining their pristine HI gas.