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We present the second data release of the MeerKAT Absorption Line Survey (MALS), consisting of wideband continuum catalogues of 391 pointings observed at L band. The full wideband catalogue covers 4344 deg2 of sky, reaches a depth of 10 µJy beam−1, and contains 971 980 sources. With its balance between survey depth and sky coverage, MALS DR2 covers five orders of magnitude of flux density, presenting a robust view of the extragalactic radio source population down to 200 µJy. Using this catalogue, we perform a measurement of the cosmic radio dipole, an anisotropy in the number counts of radio sources with respect to the cosmic background, analogous to the dipole found in the cosmic microwave background (CMB). For this measurement, we present the characterisation of completeness and noise properties of the catalogue, and show that a declination-dependent systematic affects the number density of faint sources. In the dipole measurement on the MALS catalogue, we recover reasonable dipole measurements once we model the declination systematic with a linear fit between the size of the major axis of the restoring beam and the amount of sources of each pointing. The final results are consistent with the CMB dipole in terms of direction and amplitude, unlike many recent measurements of the cosmic radio dipole made with other centimetre wavelength catalogues, which generally show a significantly larger amplitude. This result demonstrates the value of dipole measurements with deeper and more sparse radio surveys, as the population of faint sources probed may have had a significant impact on the measured dipole. [ABSTRACT FROM AUTHOR]

We report a new, rare detection of H I 21 cm absorption associated with a quasar (only six quasars are known at 1 < z < 2) toward J2339−5523 at zem = 1.3531, discovered through the MeerKAT Absorption Line Survey (MALS). The absorption profile is broad (∼400 km s−1), and the peak is redshifted by ∼200 km s−1 from zem. Interestingly, optical/far-UV spectra of the quasar from the Magellan-MIKE/HST-COS spectrographs do not show any absorption features associated with the 21 cm absorption, despite the coincident presence of the optical quasar and the radio core inferred from a flat-spectrum component with a flux density of ∼65 mJy at high frequencies (> 5 GHz). The simplest explanation would be that no large H I column (N(H I) > 1017 cm−2) is present toward the radio core and the optical active galactic nucleus. Based on the joint optical and radio analysis of a heterogeneous sample of 16 quasars (zmedian = 0.7) and 19 radio galaxies (zmedian = 0.4) with H I 21 cm absorption detection and matched in 1.4 GHz luminosity (L1.4 GHz), a consistent picture emerges according to which quasars primarily trace the gas in the inner circumnuclear disk and cocoon created by the interaction of the jet with interstellar medium. They (i.e., quasars) exhibit a L1.4 GHz – ΔVnull correlation and a frequent mismatch of the radio and optical spectral lines. The radio galaxies show no such correlation and likely trace the gas from the cocoon and the galaxy-wide interstellar medium outside the photoionization cone. The analysis presented here demonstrates the potential of radio spectroscopic observations to reveal the origin of the absorbing gas associated with active galactic nuclei that may be missed in optical observations. [ABSTRACT FROM AUTHOR]

The BL Lac object PKS 1413+135 was observed by the Large Survey Project MeerKAT Absorption Line Survey (MALS) in the L-band, at 1139 MHz and 1293–1379 MHz, targeting the H I and OH lines in absorption at z = 0.24671. The radio continuum might come from the nucleus of the absorbing galaxy or from a background object at redshift lower than 0.5, as suggested by the absence of gravitational images. The H I absorption line is detected at a high signal-to-noise ratio, with a narrow central component, and with a red wing, confirming previous results. The OH 1720 MHz line is clearly detected in (maser) emission, peaking at a velocity shifted by −10 to −15 km s−1 with respect to the H I peak. The 1612 MHz line is lost due to radio frequency interference. The OH 1667 MHz main line is tentatively detected in absorption, but not the 1665 MHz line. Over 30 years a high variability is observed in optical depths, due to the rapid changes of the line of sight caused by the superluminal motions of the radio knots. The H I line has varied by 20% in depth, while the OH-1720 MHz depth has varied by a factor of ∼3. The position of the central velocity and the widths also varied. The absorbing galaxy is an early-type spiral (maybe S0) seen edge-on, with a prominent dust lane, covering the whole disk. Given the measured mass concentration and the radio continuum size at centimeter wavelengths (100 mas corresponding to 400 pc at z = 0.25), the width of the absorption lines from the nuclear regions are expected up to 250 km s−1. The narrowness of the observed lines (< 15 km s−1) suggests that the absorption comes from an outer gas ring, as frequently observed in S0 galaxies. The millimetric lines are even narrower (< 1 km s−1), which corresponds to the continuum size restricted to the core. The radio core is covered by individual 1 pc molecular clouds, whose column density is a few 1022 cm−2, which is compatible with the gas screen detected in X-rays. [ABSTRACT FROM AUTHOR]

We present the analysis of ∼100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs; L IR ≥ 1011 L ⊙), using FWHM ≲ 0.″1â€"0.″2 resolution 15 and 33 GHz observations with the Karl G. Jansky Very Large Array. We identify a total of 133 compact radio sources with effective radii of 8â€"170 pc, which are classified into four main categoriesâ€"“AGN” (active galactic nuclei), “AGN/SBnuc” (AGN-starburst composite nucleus), “SBnuc” (starburst nucleus), and “SF” (star-forming clumps)â€"based on ancillary data sets and the literature. We find that “AGN” and “AGN/SBnuc” more frequently occur in late-stage mergers and have up to 3 dex higher 33 GHz luminosities and surface densities compared with “SBnuc” and “SF,” which may be attributed to extreme nuclear starburst and/or AGN activity in the former. Star formation rates (SFRs) and surface densities (ÎŁSFR) are measured for “SF” and “SBnuc” using both the total 33 GHz continuum emission (SFR ∼ 0.14â€"13 M ⊙ yrâˆ'1, ÎŁSFR ∼ 13â€"1600 M ⊙ yrâˆ'1 kpcâˆ'2) and the thermal freeâ€"free emission from H ii regions (median SFRth ∼ 0.4 M ⊙ yrâˆ'1, ÎŁ SFR th ∼ 44 M ⊙ yrâˆ'1 kpcâˆ'2). These values are 1â€"2 dex higher than those measured for similar-sized clumps in nearby normal (non-U/LIRGs). The latter also have a much flatter median 15â€"33 GHz spectral index (∼âˆ'0.08) compared with “SBnuc” and “SF” (∼âˆ'0.46), which may reflect higher nonthermal contribution from supernovae and/or interstellar medium densities in local U/LIRGs that directly result from and/or lead to their extreme star-forming activities on 100 pc scales. [ABSTRACT FROM AUTHOR]

We present MeerKAT Absorption Line Survey (MALS) observations of the H  i gas in the Klemola 31 galaxy group (z  = 0.029), located along the line of sight to the radio-loud quasar PKS 2020−370 (z  = 1.048). Four galaxies of the group are detected in H  i emission, and H  i absorption is also detected in front of PKS 2020−370 in Klemola 31A. The emission and absorption are somewhat compensating on the line of sight of the quasar, and the derived column density of the absorption appears underestimated, with respect to the neighbouring emission. A symmetric tilted-ring model of Klemola 31A, assuming the absorbing gas in regular rotation in the plane, yields a rather high spin temperature of 530 K. An alternative interpretation is that the absorbing gas is extra-planar, which will also account for its non-circular motion. The Na  i /Ca  ii ratio also suggests that the absorbing gas is unrelated to cold H  i disc. Two of the galaxies in the Klemola group are interacting with a small companion, and reveal typical tidal tails, and velocity perturbations. Only one of the galaxies, ESO 400−13, reveals a strong H  i deficiency, and a characteristic ram-pressure stripping, with a total asymmetry in the distribution of its gas. Since a small galaxy group as Klemola 31 is not expected to host a dense intra-group gas, this galaxy must be crossing the group at a very high velocity, mostly in the sky plane. [ABSTRACT FROM AUTHOR]

To investigate the growth history of galaxies, we measure the rest-frame radio, ultraviolet (UV), and optical sizes of 98 radio-selected, star-forming galaxies (SFGs) distributed over 0.3 ≲ z ≲ 3 with a median stellar mass of. We compare the size of galaxy stellar disks, traced by rest-frame optical emission, relative to the overall extent of star formation activity that is traced by radio continuum emission. Galaxies in our sample are identified in three Hubble Frontier Fields: MACS J0416.1−2403, MACS J0717.5+3745, and MACS J1149.5+2223. Radio continuum sizes are derived from 3 and 6 GHz radio images (≲0.″6 resolution, ≈0.9 μJy beam−1 noise level) from the Karl G. Jansky Very Large Array. Rest-frame UV and optical sizes are derived using observations from the Hubble Space Telescope and the Advanced Camera for Surveys and Wide Field Camera 3 instruments. We find no clear dependence between the 3 GHz radio size and stellar mass of SFGs, which contrasts with the positive correlation between the UV/optical size and stellar mass of galaxies. Focusing on SFGs with , we find that the radio/UV/optical emission tends to be more compact in galaxies with high star formation rates (≳100 M⊙ yr−1), suggesting that a central, compact starburst (and/or an active galactic nucleus) resides in the most luminous galaxies of our sample. We also find that the physical radio/UV/optical size of radio-selected SFGs with log(M⋆/M⊙) > 10 increases by a factor of 1.5–2 from z ≈ 3 to z ≈ 0.3, yet the radio emission remains two to three times more compact than that from the UV/optical. These findings indicate that these massive, radio-selected SFGs at 0.3 ≲ z ≲ 3 tend to harbor centrally enhanced star formation activity relative to their outer disks. [ABSTRACT FROM AUTHOR]

The Frontier Fields project is an observational campaign targeting six galaxy clusters, with the intention of using the magnification provided by gravitational lensing to study galaxies that are extremely faint or distant. We used the Karl G. Jansky Very Large Array (VLA) at 3 and 6 GHz to observe three Frontier Fields: MACS J0416.1−2403 (z = 0.396), MACS J0717.5+3745 (z = 0.545), and MACS J1149.5+2223 (z = 0.543). The images reach noise levels of ∼1 μJy beam−1 with subarcsecond resolution (∼2.5 kpc at z = 3), providing a high-resolution view of high-z star-forming galaxies that is unbiased by dust obscuration. We generate dual-frequency continuum images at two different resolutions per band, per cluster, and derive catalogs totaling 1966 compact radio sources. Components within the areas of Hubble Space Telescope and Subaru observations are cross-matched, providing host galaxy identifications for 1296 of them. We detect 13 moderately lensed (2.1 < μ < 6.5) sources, one of which has a demagnified peak brightness of 0.9 μJy beam−1, making it a candidate for the faintest radio source ever detected. There are 66 radio sources exhibiting complex morphologies, and 58 of these have host galaxy identifications. We reveal that MACS J1149.5+2223 is not a cluster with a double relic, as the western candidate relic is resolved as a double-lobed radio galaxy associated with a foreground elliptical at z = 0.24. The VLA Frontier Fields project is a public legacy survey. The image and catalog products from this work are freely available. [ABSTRACT FROM AUTHOR]

We have performed a spectral decomposition to search for dual active galactic nuclei (DAGNs) in the Sloan Digital Sky Survey (SDSS) quasars with z < 0.25. Potential DAGN candidates are searched by referencing velocity offsets and spectral shapes of double-peaked [O iii ] lines of known DAGNs. Out of 1271 SDSS quasars, we have identified 77 DAGN candidates. Optical and mid-infrared (MIR) diagnostic diagrams are used to investigate the ionizing source in the DAGN candidates. The optical diagnostic analysis suggests 93% of them are powered by AGNs, and MIR diagnostic analysis suggests 97% are powered by AGNs. About one-third of the SDSS images of the DAGN candidates show signs of tidal interaction, but we are unable to identify double nuclei in most of them due to the low spatial resolution of the archival imaging data available for most of the sample. The radio-loud fraction of the DAGN candidates (∼10%) is similar to that of typical AGNs. [ABSTRACT FROM AUTHOR]

We present neutral hydrogen (H  i) and ionized hydrogen (H α) observations of 10 galaxies out to a redshift of 0.1. The H  i observations are from the first epoch (178 h) of the COSMOS H  i Large Extragalactic Survey (CHILES). Our sample is H  i biased and consists of 10 late-type galaxies with H  i masses that range from 1.8 × 107 M⊙ to 1.1 × 1010 M⊙. We find that although the majority of galaxies show irregularities in the morphology and kinematics, they generally follow the scaling relations found in larger samples. We find that the H  i and H α velocities reach the flat part of the rotation curve. We identify the large-scale structure in the nearby CHILES volume using DisPerSE with the spectroscopic catalogue from SDSS. We explore the gaseous properties of the galaxies as a function of location in the cosmic web. We also compare the angular momentum vector (spin) of the galaxies to the orientation of the nearest cosmic web filament. Our results show that galaxy spins tend to be aligned with cosmic web filaments and show a hint of a transition mass associated with the spin angle alignment. [ABSTRACT FROM AUTHOR]

Absorption lines in front of distant quasars are quite rare in the millimeter domain. They can, however, bring very useful and complementary information to emission lines. We report here the detection with NOEMA of CO(1–0) and CN(1–0) lines in absorption, and the confirmation of CO emission in the quasar/galaxy pair Q0248+430/G0248+430. The system G0248+430 corresponds to two merging galaxies (a Seyfert and a LINER) at z = 0.0519 with a tidal tail just on the line of sight to the background quasar Q0248+430 at z = 1.313. Optical (CaII, NaI), H I 21 cm, and OH-1667 MHz absorption lines associated with the tidal tail of the foreground system have previously been detected toward the quasar, while four CO lines at different rotation J levels have been detected in emission from the foreground galaxies. New H I 21 cm line observations with the upgraded GMRT array are also presented. We discuss the molecular content of the merging galaxies, and the physical conditions in the absorbing interstellar medium of the tidal tail. [ABSTRACT FROM AUTHOR]

Study of the composition from diverse sources of the Universe helps to us to understand their evolution. Molecular spectroscopy provides detailed information of the observed objects. We present a small study of the starburst NGC 253 with ALMA at 1mm. We detect the prebiotic molecules NH2CHO, and CNCHO. We obtain the integrated intensity maps and abundances of HNCO, CH3OH, H3O+ and CH3C2H. We propose the use of Artificial Intelligence for big data to find prebiotic molecules in galaxies. [ABSTRACT FROM AUTHOR]

Context. Quantifying the fraction of active galactic nuclei (AGN) in the faint radio population and understanding their relation with star-forming activity are fundamental to studies of galaxy evolution. Very long baseline interferometry (VLBI) observations are able to identify AGN above relatively low redshifts (z > 0.1) since they provide milli-arcsecond resolution. Aims. We have created an AGN catalogue from 2865 known radio sources observed in the Cosmic Evolution Survey (COSMOS) field, which has exceptional multi-wavelength coverage. With this catalogue we intend to study the faint radio sky with statistically relevant numbers and to analyse the AGN – host galaxy co-evolution, making use of the large amount of ancillary data available in the field. Methods. Wide-field VLBI observations were made of all known radio sources in the COSMOS field at 1.4 GHz to measure the AGN fraction, in particular in the faint radio population. We describe in detail the observations, data calibration, source detection and flux density measurements, parts of which we have developed for this survey. The combination of number of sources, sensitivity, and area covered with this project are unprecedented. Results. We have detected 468 radio sources, expected to be AGN, with the Very Long Baseline Array (VLBA). This is, to date, the largest sample assembled of VLBI detected sources in the sub-mJy regime. The input sample was taken from previous observations with the Very Large Array (VLA). We present the catalogue with additional optical, infrared and X-ray information. Conclusions. We find a detection fraction of 20 ± 1%, considering only those sources from the input catalogue which were in principle detectable with the VLBA (2361). As a function of the VLA flux density, the detection fraction is higher for higher flux densities, since at high flux densities a source could be detected even if the VLBI core accounts for a small percentage of the total flux density. As a function of redshift, we see no evolution of the detection fraction over the redshift range 0.5 < z < 3. In addition, we find that faint radio sources typically have a greater fraction of their radio luminosity in a compact core – ∼70% of the sub-mJy sources detected with the VLBA have more than half of their total radio luminosity in a VLBI-scale component, whereas this is true for only ∼30% of the sources that are brighter than 10 mJy. This suggests that fainter radio sources differ intrinsically from brighter ones. Across our entire sample, we find the predominant morphological classification of the host galaxies of the VLBA detected sources to be early type (57%), although this varies with redshift and at z > 1.5 we find that spiral galaxies become the most prevalent (48%). The number of detections is high enough to study the faint radio population with statistically significant numbers. We demonstrate that wide-field VLBI observations, together with new calibration methods such as multi-source self-calibration and mosaicing, result in information which is difficult or impossible to obtain otherwise. [ABSTRACT FROM AUTHOR]

We present the results from our survey of H I 21-cm absorption, using Giant Metrewave Radio Telescope, Very Large Array and Westerbork Radio Synthesis Telescope, in a sample of 55 z < 0.4 galaxies towards radio sources with impact parameters (b) in the range ~0-35 kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy pairs, probed by 45 sightlines, we have found seven H I 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity (∫τdv ≤ 0.3 km s-1) from the literature, we find a weak anti-correlation (rank correlation coefficient = -0.20 at 2.42σ level) between ∫τdv and b, consistent with previous literature results. The covering factor of H I 21-cm absorbers (C21) is estimated to be 0.24-0.08+0.12 at b ≤ 15 kpc and 0.06-0.04+0.09 at b = 15-35 kpc. ∫τdv and C21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective H I radius. There is also tentative indication that most of the H I 21-cm absorbers could be co-planar with the extended H I discs. No significant dependence of ∫τdv and C21 on galaxy luminosity, stellar mass, colour and star formation rate is found, though the H I 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ~4) of H I 21-cmabsorption in z<1 damped Lyman-α systems compared to the quasar-galaxy pairs indicates towards small covering factor and patchy distribution of cold gas clouds around low-z galaxies. [ABSTRACT FROM AUTHOR]

We have used the Arecibo L-band Feed Array (ALFA) to map three regions, each of 5 deg2, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523. In the vicinity of these galaxies we have detected two dwarf companions: one near UGC 2082, previously discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey, and one near NGC 1156, discovered by this project and reported in an earlier paper. This is significantly fewer than the 15.4+1.7 -1.5 that would be expected from the field HI mass function from ALFALFA or the 8.9±1.2 expected if the HI mass function from the Local Group applied in these regions. The number of dwarf companions detected is, however, consistent with a flat or declining HI mass function as seen by a previous, shallower, HI search for companions to isolated galaxies. We attribute this difference in HI mass functions to the different environments in which they are measured. This agrees with the general observation that lower ratios of dwarf to giant galaxies are found in lower density environments. [ABSTRACT FROM AUTHOR]

We present HI 21 cm emission observations of the z ~0.006 32 subdamped Lyman-a absorber (sub-DLA) towards PG 1216+069 made using the Arecibo Telescope and theVery Large Array (VLA). The Arecibo HI 21cm spectrum corresponds to an HI mass of ~3.2 × 107 M⊙, two orders of magnitude smaller than that of a typical spiral galaxy. This is surprising since in the local Universe the cross-section for absorption at high HI column densities is expected to be dominated by spirals. The HI 21cm emission detected in the VLA spectral cube has a low signal-to-noise ratio, and represents only half the total flux seen at Arecibo. Emission from three other sources is detected in the VLA observations, with only one of these sources having an optical counterpart. This group of HI sources appears to be part of complex 'W', believed to lie in the background of the Virgo cluster. While several HI cloud complexes have been found in and around the Virgo cluster, it is unclear whether the ram pressure and galaxy harassment processes that are believed to be responsible for the creation of such clouds in a cluster environment are relevant at the location of this cloud complex. The extremely low metallicity of the gas,~1/40 solar, also makes it unlikely that the sub-DLA consists of material that has been stripped from a galaxy. Thus, while our results have significantly improved our understanding of the host of this sub-DLA, the origin of the gas cloud remains a mystery. [ABSTRACT FROM AUTHOR]

Using long-slit optical spectra obtained with the 2-m telescope at IUCAA Girawali Observatory, we show that the radio source J094221.98+062335.2 (z = 0.123) is associated with a galaxy pair undergoing a major merger. Its companion is a normal star-forming galaxy infalling with a velocity of 185 km s-1at a projected separation of 4.8 kpc. Using the Westerbork Synthesis Radio Telescope (WSRT) and Giant Metrewave Radio Telescope (GMRT), we detect a strong HI 21-cm absorption at the systemic redshift of the radio galaxy with N(HI)~9 × 1021 cm-2 for an assumed spin temperature of 100 K. Such a strong HI 21-cm absorption is rare and has been seen only in a few compact radio sources associated with similar merging galaxy pairs. Milliarcsecond resolution Very Long Baseline Array (VLBA) observations resolve the radio source into a compact symmetric object with the hotspot separation of 89 pc. The 21-cm absorption is detected in the VLBA spectra towards both the radio lobes albeit with a strong optical depth gradient. We show that the strong 21-cm absorption is consistent with it being arising from a clumpy circumnuclear disc/torus. We also detect two weaker absorption lines redshifted with respect to the radio source in the WSRT/GMRT spectrum. They probably represent cold (i.e. T ≤ 104 K) HI gas falling into the radio source. The presence of high concentration of HI gas in the circumnuclear regions and signature of infalling cold gas allows us to conjecture that the young radio source may have been triggered by the gas infall due to the ongoing merger. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of a H2-bearing metal-rich sub-damped Lyman α system at zabs = 0.10115 towards the radio-loud quasar J0441-4313, at a projected separation of ~7.6 kpc from a star-forming galaxy. The H2, CI and Na I absorption are much stronger in the redder of the two components seen in the Hubble Space Telescope/Cosmic Origins Spectrograph spectrum. The best single-component fit to the strong H2 component gives log N(H2) = 16.61 ± 0.05. However, possible hidden saturation in the medium-resolution spectrum can allow for log N(H2) to be as high as 18.9. The rotational excitation temperature of H2 in this component is 133-22+33K. Photoionization models suggest 30-80 per cent of the total N(HI) is associated with the strong H2 component that has a density ≤100 cm-3 and is subject to a radiation field that is ≤0.5 times the Galactic mean field. The Very Long Baseline Array 1.4 GHz continuum image of the radio source contains only 27 per cent of the arcsecond scale emission. Using a previously published spectrum, no 21-cm absorption is found to be associated with the strong H2 component. This suggests that either the N(H I) associated with this component is ≤50 per cent of the total N(H I) or the gas covering factor is ≤0.27. This is consistent with the results of the photoionization model that uses ultraviolet radiation due to stars in the associated galaxy. The 21-cm absorption previously reported from the weaker H2 component suggests a spin temperature of ≤90 K, at odds with the weakness of H2, CI and Na I absorption in this component. From the inferred physical and chemical conditions, we suggest that the gas may be tracing a recent metal-rich outflow from the host galaxy. [ABSTRACT FROM AUTHOR]

BSTRACT In this paper we describe results from the Arecibo Galaxy Environments Survey (AGES). The survey reaches column densities of ∼3 × 1018 cm−2 and masses of ∼107 M⊙, over individual regions of order 10 deg2 in size, out to a maximum velocity of 18 000 km s−1. Each surveyed region is centred on a nearby galaxy, group or cluster, in this instance the NGC 7448 group. Galaxy interactions in the NGC 7448 group reveal themselves through the identification of tidal tails and bridges. We find ∼2.5 times more atomic gas in the intergalactic medium than in the group galaxies. We identify five new dwarf galaxies, two of which appear to be members of the NGC 7448 group. This is too small, by roughly an order of magnitude, a number of dwarf galaxies to reconcile observation with theoretical predictions of galaxy formation models. If they had observed this region of the sky in previous wide-area blind H i surveys, HIPASS and ALFALFA, they would have detected only 5 and 43 per cent, respectively, of the galaxies we have detected, missing a large fraction of the atomic gas in this volume. We combine the data from this paper with that from our other AGES papers (370 galaxies) to derive an H i mass function with the following Schechter function parameters: α=−1.52(±0.05), M*= 5.1(±0.3) × 109 h−272 M⊙, ϕ= 8.6(±1.1) × 10−3 h372 Mpc−3 dex−1. Integrating the mass function leads to a cosmic mass density of atomic hydrogen of ΩH I= 5.3 (± 0.8) × 10−4 h−172. Our mass function is steeper than that found by both HIPASS and ALFALFA (α= 1.37 and 1.33, respectively), while our cosmic mass density is consistent with ALFALFA, but 1.7 times larger than found by HIPASS. [ABSTRACT FROM AUTHOR]

We have used the Very Long Baseline Array to image 18 quasars with foreground damped Lyman-α systems (DLAs) at 327, 610 or 1420 MHz, to measure the covering factor f of each DLA at or near its redshifted H i 21 cm line frequency. Including six systems from the literature, we find that none of 24 DLAs at has an exceptionally low covering factor, with for the 14 DLAs at for the 10 systems at , and consistent covering factor distributions in the two subsamples. The observed paucity of detections of H i 21 cm absorption in high- z DLAs thus cannot be explained by low covering factors and is instead likely to arise due to a larger fraction of warm H i in these absorbers. [ABSTRACT FROM AUTHOR]

We present 21 cm H i line observations of 5 × 1 deg2 centred on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new H i measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the H i data with Sloan Digital Sky Survey (SDSS) optical imaging, we show that our H i selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly, all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between H i and optically selected samples resides in their large-scale distribution: whereas optical and X-ray observations trace the cluster core very well, in H i there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and H i distribution for samples selected at different wavelength are also discussed. [ABSTRACT FROM AUTHOR]

The Arecibo Galaxy Environment Survey is a blind neutral hydrogen survey using the ALFA multibeam receiver at Arecibo Observatory to reach unprecedented sensitivities in a number of selected fields in the local Universe. When completed the survey will cover 200 square degrees out to a distance of at least 270 Mpc. If a population of gas-rich dark galaxies exists, then this survey is in a prime position to uncover that population.So far 20 square degrees have been covered in the regions of Abell 1367, the Virgo Cluster, the NGC 7332/9 galaxy pair and the isolated galaxy NGC 1156. Over 200 sources have been found, including a number that have no obvious optical counterparts. We discuss here the potential of AGES for uncovering more such objects and the characteristics of the dark sources identified to date. [ABSTRACT FROM PUBLISHER]

The Arecibo Galaxy Environment Survey (AGES) is one of several H i surveys utilizing the new Arecibo L-band Feed Array (ALFA) fitted to the 305-m radio telescope at Arecibo. a The survey is specifically designed to investigate various galactic environments to higher sensitivity, higher velocity resolution and higher spatial resolution than previous fully sampled, 21-cm multibeam surveys. The emphasis is on making detailed observations of nearby objects although the large system bandwidth (100 MHz) will allow us to quantify the H i properties over a large instantaneous velocity range. In this paper, we describe the survey and its goals and present the results from the precursor observations of a -deg2 region containing the nearby (∼10 Mpc) NGC 628 group. We have detected all the group galaxies in the region including the low-mass dwarf, dw0137+1541. The fluxes and velocities for these galaxies compare well with previously published data. There is no intragroup neutral gas detected down to a limiting column density of . In addition to the group galaxies we have detected 22 galaxies beyond the NGC 628 group, nine of which are previously uncatalogued. We present the H i data for these objects and also SuperCOSMOS images for possible optical galaxies that might be associated with the H i signal. We have used analysis to model how many galaxies beyond 1000 km s−1 should be detected and compare this with our results. The predicted number of detectable galaxies varies depending on the H i mass function (HIMF) used in the analysis. Unfortunately the precursor survey area is too small to determine whether this is saying anything fundamental about the HIMF or simply highlighting the effect of low number statistics. This is just one of many questions that will be addressed by the complete AGES survey. [ABSTRACT FROM AUTHOR]

The Arecibo Galaxy Environments Survey (AGES) is a 2000-hour neutral hydrogen (H I) survey using the new Arecibo L-band Feed Array (ALFA) multibeam instrument at Arecibo Observatory. It will cover 200 square degrees of sky, sampling a range of environments from the Local Void through to the Virgo Cluster with higher sensitivity, spatial resolution and velocity resolution than previous neutral hydrogen surveys. [ABSTRACT FROM PUBLISHER]