David F. Malin

The AAO/UKST SuperCOSMOS Hα survey

The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatory completed a narrowband Ha plus [N II] 6548, 6584-A survey of the Southern Galactic Plane and Magellanic Clouds in late 2003. The survey, which was the last UKST wide-field photographic survey and the only one undertaken in a narrow-band, is now an online digital data product of the Wide-Field Astronomy Unit of the Royal Observatory Edinburgh (ROE). The survey utilized a high specification, monolithic Hα interference bandpass filter of exceptional quality. In conjunction with the fine-grained Tech-Pan film as a detector it has produced a survey with a powerful combination of area coverage (4000 square degrees), resolution (∼1 arcsec) and sensitivity (≤5 Rayleighs), reaching a depth for continuum point sources of R ≃ 20.5. The main survey consists of 233 individual fields on a grid of centres separated by 4° at declinations below +2° and covers a swathe approximately 20° wide about the Southern Galactic Plane. The original survey films were scanned by the SuperCOSMOS measuring machine at the Royal Observatory, Edinburgh, to provide the online digital atlas called the SuperCOSMOS Ha Survey (SHS). We present the background of the survey, the key survey characteristics, details and examples of the data product, calibration process, comparison with other surveys and a brief description of its potential for scientific exploitation.

Discovery of a huge low-surface-brightness galaxy - a protodisk galaxy at low redshift

The accidental discovery of an extremely large, extremely H I-rich low-surface-brightness galaxy located at a redshift of z = 0.083 is reported. Its nuclear spectrum exhibits broad, low-level emission lines. Surface photometry at V indicates the presence of a bulge component and a very extended disk, with scale length of about 45 arcsec and with central surface brightness of V(0) of about 25.5 mag/sq arcsec. The total amount of H I is at least 1.0 x 10 to the 11th solar masses. This amount of H I is at least 5 times more H I than any spiral galaxy previously observed. If disk formation is a quiescent process, then it is likely that a disk was caught in the process of formation. The properties of this disk are likely to be similar to the suspected sources that produce the observed damped Ly-alpha absorption profiles that are so conspicuous at z of about 2. 31 references.

New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group

We have commenced a 21 cm survey of the entire southern sky (δ -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.

SN 1978K: An extraordinary supernova in the nearby galaxy NGC 1313

We have identified an extremely luminous radio and X-ray source with an optically variable emission-line object in the outskirts of the nearby barred spiral galaxy NGC 1313. Archival data show that the object (officially designated SN 1978K) had a major optical outburst (M B <−12.3) in mid-1978 and that a radio and X-ray outburst followed this event. The light curve, optical spectra, radio data, and the X-ray data all indicate that the event was a very unusual Type II supernova, with many similar properties to the so-called Type V supernovae SN 1961V in NGC 1058 and SN 1986J in NGC 891

Galaxy destruction and diffuse light in clusters

ABSTRACT Deep images of the Centaurus and Coma clusters reveal two spectacular arcs ofdiffuse light that stretch for over 100 kpc, yet are just a few kpc wide. At a surfacebrightness of m b ∼ 27−28th arcsec −2 , the Centaurus arc is the most striking exampleknown of structure in the diffuse light component of a rich galaxy cluster. We usenumerical simulations to show that the Centaurus feature can be reproduced by thetidal debris of a spiral galaxy that has been tidally disrupted by the gravitational po-tential of NGC 4709. The surface brightness and narrow dimensions of the diffuse lightsuggest that the disk was co-rotating with its orbital path past pericenter. Featuresthis prominent in clusters will be relatively rare, although at fainter surface bright-ness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveysmay be able to trace this feature for several times its presently observed extent andsomewhere along the tidal debris, a fraction of the original stellar component of thedisk will remain bound, but transformed into a faint spheroidal galaxy. It should bepossible to confirm the galactic origin of the Centaurus arc by observing planetarynebulae along its length with redshifts close to that of NGC 4709.Key words: galaxies: evolution – galaxies: clusters – galaxies: interactions – galaxies:formation.

HIPASS detection of an intergalactic gas cloud in the NGC 2442 group

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 similar to 10(9) 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.

HIDEEP: an extragalactic blind survey for very low column-density neutral hydrogen

We have earned out an extremely long integration time (9000 s beam - 1 ) 21-cm blind survey of 60 deg 2 in Centaurus using the Parkes multibeam system. We find that the noise continues to fall as √t o b s throughout, enabling us to reach an HI column-density limit of 4.2 x 10 1 8 cm - 2 for galaxies with a velocity width of 200 km s - 1 in the central 32 deg 2 region, making this the deepest survey to date in terms of column density sensitivity. The H i data are complemented by very deep optical observations from digital stacking of multi-exposure UK Schmidt Telescope R-band films, which reach an isophotal level of 26.5 R mag arcsec - 2 (≃27.5 B mag arcsec - 2 ). 173 Hi sources have been found, 96 of which have been uniquely identified with optical counterparts in the overlap area. There is not a single source without an optical counterpart. Although we have not measured the column densities directly, we have inferred them from the optical sizes of their counterparts. All appear to have a column density of N H 1 = 10 2 0 . 6 5 ′ 0 . 3 8 . This is at least an order of magnitude above our sensitivity limit, with a scatter only marginally larger than the errors on N H 1 . This needs explaining. If confirmed it means that H 1 surveys will only find low surface brightness (LSB) galaxies with high M H 1 /L B . Gas-rich LSB galaxies with lower HI mass to light ratios do not exist. The paucity of low column-density galaxies also implies that no significant population will be missed by the all-sky H 1 surveys being carried out at Parkes and Jodrell Bank.

An Extragalactic H I Cloud with No Optical Counterpart

We report the discovery, from the H I Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen, which we believe to be extragalactic. The H I mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10(7) M-circle dot, using an estimated distance of similar to 3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits [mu(B) similar to 27 mag arcsec(-2)]. HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, H I 1225 + 01 (the Virgo H. I cloud) and has a size of at least 15 kpc. The mean velocity dispersion measured with the Australia Telescope Compact Array (ATCA) is only 4 km s(-1) for the main component and, because of the weak or nonexistent star formation, possibly reflects the thermal line width (T < 2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 1019 cm(-2), which is estimated to be a factor of 2 below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognized class of compact high-velocity clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud-Galaxy system at perigalacticon similar to 2 x 10(8) yr ago.

The Introduction of Tech Pan film at the UK Schmidt Telescope

Kodak Technical Pan (Tech Pan) emulsion on a fllm base has been in use at the UK Schmidt Telescope (UKST) since 1992. This material is extremely flne grained and its resolution is well matched to images produced by the UKST under good conditions. Tech Pan yields wide-angle photographs that are about 1 (stellar) magnitude fainter than equivalent IIIa-F plates but have considerably lower grain noise. A wide variety of new projects are under way which take advantage of this remarkable material. In this paper empirical results from experiments with Tech Pan from a number of sources are tied in with UKST experience to present an overview of the properties of the emulsion from an astronomical perspective. We compare Tech Pans properties with those of equivalent IIIa-F emulsion, to which it seems superior in almost every respect. This overview and groundwork are currently missing from the published astronomical literature. The technical background and developments leading to adoption of this material at the UKST are presented.

Radio Continuum Structure of the Orion Nebula

We have imaged the large-scale radio continuum structure in the Orion region with the Very Large Array at 330 MHz. Arcminute-resolution morphology of the extended emission in the H II regions M42 and M43 (NGC 1976 and NGC 1982) and in the NGC 1973-75-77 nebulosity to the north are presented. A low surface brightness thermal radio halo is detected in the H II region M42: comparison with an optical photograph indicates that the radio emission distinguishes optical emission structures from reflection nebulosities. In NGC 1977 we have discovered a compact, steep-spectrum radio source coincident with a bright optical rim.