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A complete flat-spectrum radio-loud sample of AGN includes a significant fraction of Seyfert-like AGN including a NLS1. Analysis of their optical spectra suggests that the reddest continuum colours are either associated with AGN in nearby resolved galaxies, or distant quasars showing relatively narrow permitted emission lines., Comment: Poster contribution presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-workshop

The Multibeam survey at the Parkes Radio Telescope has provided a wealth of 21 cm HI data. We have mosaicked ten standard HIPASS cubes to produce a datacube approximately 25 deg x 25 deg in size, centred on NGC1399, the optical centre of the Fornax Cluster. Some properties of the initial approx. 80 galaxies identified in HI are described. In the optical, Ferguson's Fornax Cluster Catalogue (FCC) identified 340 likely member galaxies in the central 40 sq.deg. In the radio we have detected a more uniform sheet of about 80 galaxies at the cluster velocity extending up to 15 deg from the cluster centre. At the cluster distance of about 15 Mpc, this corresponds to an elongated large-scale structure (LSS) more than 7 Mpc in extent. Galaxies were detected to a lower mass limit of 1x10^8M_sun and fewer than 25 of these were within the central 40 sq.deg, suggesting considerable HI depletion of galaxies in the centre of the cluster. Further, these results strongly indicate that HI surveys do not readily identify galaxy clusters., Comment: 8 pages, 5 figures, to appear in "Mapping the Hidden Universe" conference proceedings, LaTeX, uses newpasp.sty (included)

We are using the Multibeam 21cm receiver on the Parkes Telescope combined with the optical Two degree Field spectrograph (2dF) of the Anglo-Australian Telescope to obtain the first complete spectroscopic sample of the Fornax cluster. In the optical the survey is unique in that all objects (both ``stars'' and ``galaxies'') within our magnitude limits (Bj=16.5 to 19.7) are measured, producing the most complete survey of cluster members irrespective of surface brightness. We have detected two new classes of high surface brightness dwarf galaxy in the cluster. With 2dF we have discovered a population of very low luminosity (Mb approx -12) objects which are unresolved from the ground and may be the stripped nuclei of dwarf galaxies; they are unlike any known galaxies. In a survey of the brighter (Bj=16.5 to 18) galaxies with the FLAIR-II spectrograph we have found a number of new high surface brightness dwarf galaxies and show that the fraction of star-forming dwarf galaxies in the cluster is about 30 per cent, about twice that implied by earlier morphological classifications. Our radio observations have greatly improved upon the sensitivity of the standard Multibeam survey by using a new ``basket weave'' scanning pattern. Our initial analysis shows that we are detecting new cluster members with HI masses of order 10-to-the-8 Msun and HI mass-to-light ratios of 1-2 Msun/Lsun., Comment: To appear in "Mapping the Hidden Universe". 8 pages, 5 figures, LaTeX, uses newpasp.sty (included)

The four bright images of the gravitationally lensed quasar Q2237+0305 are being monitored from the ground (eg. OGLE collaboration, Apache Point Observatory) in the hope of observing a high magnification event (HME). Over the past three seasons (1997-1999) the OGLE collaboration has produced microlensing light-curves with unprecedented coverage. These demonstrate smooth, independent (therefore microlensing) variability between the images (Wozniak et al. 2000a,b; OGLE web page). We have retrospectively compared probability functions for high-magnification event parameters with several observed light-curve features. We conclude that the 1999 image C peak was due to the source having passed outside of a cusp rather than to a caustic crossing. In addition, we find that the image C light-curve shows evidence for a caustic crossing between the 1997 and 1998 observing seasons involving the appearance of new critical images. Our models predict that the next image C event is most likely to arrive 500 days following the 1999 peak, but with a large uncertainty (100-2000 days). Finally, given the image A light-curve derivative at the end of the 1999 observing season, our modelling suggests that a caustic crossing will occur between the 1999 and 2000 observing seasons, implying a minimum for the image A light-curve ~1-1.5 magnitudes fainter than the November 1999 level., Comment: 11 pages, 15 figures. Accepted for publication in M.N.R.A.S

The central regions of the gravitationally lensed quasar Q2237+0305 can be indirectly resolved on nano-arcsecond scales if viewed spectrophotometricly during a microlensing high magnification event (HME). Q2237+0305 is currently being monitored from the ground (eg. OGLE collaboration, Apache Point Observatory), with the goal, among others, of triggering ground and spacecraft based target of opportunity (TOO) observations of an HME. In this work we investigate the rate of change (trigger) in image brightness that signals an imminent HME and importantly, the separation between the trigger and the event peak. In addition, we produce colour dependent model light-curves by combining high-resolution microlensing simulations with a realistic model for a thermal accretion disc source. We make hypothetical target of opportunity spectroscopic observations using our determination of the appropriate trigger as a guide. We find that if the source spectrum varies with source radius, a 3 observation TOO program should be able to observe a microlensing change in the continuum slope following a light-curve trigger with a success rate of >80%., Comment: 17 pages, 16 figures, accepted for publication in M.N.R.A.S

Microlensing in Q2237+0305 between 1985 and 1995 (eg. Irwin et al. 1989; Corrigan et al. 1991; Ostensen et al. 1996) has been interpreted in two different ways; as microlensing by stellar mass objects of a continuum source having dimensions significantly smaller than the microlens Einstein radius (ER) (eg. Wambsganss, Paczynski & Schneider 1990; Rauch & Blandford 1991), and as microlensing by very low mass objects of a source as large as 5 ER (Refsdal & Stabell 1993; Haugan 1996). In this paper we present evidence in favour of a small source. Limits on the source size (in units of ER) are obtained from the combination of limits on the number of microlens Einstein radii crossed by the source during the monitoring period with two separate light-curve features. Firstly, recently published monitoring data (Wozniak et al. 2000; OGLE web page) show large variations (~0.8-1.5 magnitudes) between image brightnesses over a period of 700 days or ~15% of the monitoring period. Secondly, the 1988 peak in the image A light-curve had a duration that is a small fraction (<0.02) of the monitoring period. Such rapid microlensing rises and short microlensing peaks only occur for small sources. We find that the observed large-rapid variation limits the source size to be <0.2 ER (95% confidence). The width of the light-curve peak provides a stronger constraint of <0.02 ER (99% confidence). The Einstein radius (projected into the source plane) of the average microlens mass (m) in Q2237+0305 is ER ~ 10^{17}\sqrt{m} cm. The interpretation that stars are responsible for microlensing in Q2237+0305 therefore results in limits on the continuum source size that are consistent with current accretion disc theory., Comment: 8 pages, 3 figures, accepted for publication in M.N.R.A.S

Spectrophotometric observation of the gravitationally microlensed quasar Q2237+0305 during a High Magnification Event (HME) is potentially a very powerful tool for probing the structure of the quasars accretion disc on scales of less than 10^-8 arc seconds. How often we can expect to observe a HME is dependent on the lens system parameters of galactic transverse velocity, mean microlens mass and the size of the magnified continuum source. We have previously used published microlensed light-curves to obtain expressions for the likely-hood of the values for these parameters (Wyithe, Webster & Turner 1999b,2000; Wyithe, Webster, Turner & Mortlock 2000). Here we use this information to investigate the expected rate of SHMEs. We find the average rate of SHMEs as well as the number that we can expect to observe over periods of a decade and of a single observing season. We find that the average SHME rate summed over all images in Q2237+0305 is 1.5\pm0.6 - 6.3\pm1.3 events per decade. During the period following a caustic crossing we find that the event rate in the corresponding image is enhanced by 50-100%, and therefore that the overall event rate may be higher during these periods. From the distribution of events expected during a 6 month period we find that there is 1 chance in 4-10 of observing a SHME per observing season. The systematic dependence in these values arises from the different assumptions for smooth matter content, orientation of the galactic transverse velocity and the size of photometric error in the monitoring data. The results support continued monitoring of Q2237+0305 with the aim of obtaining detailed spectroscopic and photometric observations of a SHME., Comment: 8 pages, 5 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Society

Following the detection of a gravitational microlensing high magnification event (HME) in Q2237+0305A attempts have been made to place limits on the dimensions of the quasar continuum source. The analyses have studied either the observed event magnitude or the event duration. The latter approach has been hampered by lack of knowledge about the transverse velocity of the lensing galaxy. We obtain both upper and lower statistical limits on the size of the continuum source from the observed HME using determinations of transverse velocity obtained from the published monitoring data. Our calculations take account of the caustic orientation as well as the component of the caustic velocity that results from stellar proper motions. Our determination of source size relies on an estimated duration of 52 days for the HME, and so will be refined when more HMEs are observed. We find that the upper and lower limits on the magnified region of the R-band continuum source are 6 times 10^15 and 2 times 10^13 cm respectively (99% confidence). Through consideration of the joint probability for source size and mean microlens mass we find that the mean mass lies between ~0.01 solar masses and ~1 solar mass (95% confidence)., Comment: 7 pages, 5 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society. Revised version has improved presentation

Gravitational microlensing at cosmological distances is potentially a powerful tool for probing the mass functions of stars and compact objects in other galaxies. In the case of multiply-imaged quasars, microlensing data has been used to determine the average microlens mass. However the measurements have relied on an assumed transverse velocity for the lensing galaxy. Since the measured mass scales with the square of the transverse velocity, published mass limits are quite uncertain. In the case of Q2237+0305 we have properly constrained this uncertainty. The distribution of light curve derivatives allows quantitative treatment of the relative rates of microlensing due to proper motions of microlenses, the orbital stream motion of microlenses and the bulk galactic transverse velocity. By demanding that the microlensing rate due to the motions of microlenses is the minimum that should be observed we determine lower limits for the average mass of stars and compact objects in the bulge of Q2237+0305. If microlenses are assumed to move in an orbital stream the lower limit ranges between 0.005 and 0.023 solar masses where the the systematic dependence is due to the fraction of smooth matter and the size of photometric error assumed for published monitoring data. However, if the microlenses are assumed to move according to an isotropic velocity dispersion then a larger lower limit of 0.019-0.11 solar masses is obtained. A significant contribution of Jupiter mass compact objects to the mass distribution of the galactic bulge of Q2237+0305 is therefore unambiguously ruled out., Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society. New version has improved presentation

Determination of microlensing parameters in the gravitationally lensed quasar Q2237+0305 from the statistics of high magnification events will require monitoring for more than 100 years (Wambsganss, Paczynski & Schneider 1990). However we show that the effective transverse velocity of the lensing galaxy can be determined on a more realistic time-scale through consideration of the distribution of light-curve derivatives. The 10 years of existing monitoring data for Q2237+0305 are analysed. These data display strong evidence for microlensing that is not associated with a high magnification event. An upper limit of v < 500 km/sec is obtained for the galactic transverse velocity which is smaller than previously assumed values. The analysis suggests that the observed microlensing variation may be predominantly due to stellar proper motions. The statistical significance of the results obtained from our method will be increased by the addition of data points from current and future monitoring campaigns. However reduced photometric errors will be more valuable than an increased sampling rate., Comment: 16 pages, including 17 figures. Accepted for publication in M.N.R.A.S

We present a method for computing the probability distribution of microlensed light curve derivatives both in the case of a static lens with a transverse velocity, and in the case of microlensing that is produced through stellar proper motions. The distributions are closely related in form, and can be considered equivalent after appropriate scaling of the input transverse velocity. The comparison of the distributions in this manner provides a consistent way to consider the relative contribution to microlensing (both large and small fluctuations) of the two classes of motion, a problem that is otherwise an extremely expensive computational exercise. We find that the relative contribution of stellar proper motions to the microlensing rate is independent of the mass function assumed for the microlenses, but is a function of optical depth and shear. We find that stellar proper motions produce a higher overall microlensing rate than a transverse velocity of the same magnitude. This effect becomes more pronounced at higher optical depth. With the introduction of shear, the relative rates of microlensing become dependent on the direction of the transverse velocity. This may have important consequences in the case of quadruply lensed quasars such as Q2237+0305, where the alignment of the shear vector with the source trajectory varies between images., Comment: 12 pages, including 9 figures. Submitted to M.N.R.A.S. Revised version includes a short section on the applicability of the method

The method devised by Lewis et al. (1993) for calculating the light curve of a microlensed point source is expanded to two dimensions to enable the calculation of light curves of extended sources. This method is significantly faster than the ray shooting method that has been used in the past. The increased efficiency is used to obtain much higher resolution light curves over increased timescales. We investigate the signatures arising from different source geometries in a realistic microlensing model. We show that a large fraction of high magnification events (HMEs) in image A of Q2237+0305 involve only one caustic, and could therefore yield information on the structure of the quasar continuum through the recognition of a characteristic event shape. In addition, the cataloguing of HMEs into morphological type will, in theory, enable the direction of the transverse motion, as well as the source size to be obtained from long term monitoring., Comment: 10 pages including 4 figures. Accepted for publication in M.N.R.A.S

We present here an alternative method for calculating magnifications in gravitational lensing calculations -- the Ray Bundle method. We provide a detailed comparison between the distribution of magnifications obtained compared with analytic results and conventional ray-shooting methods. The Ray Bundle method provides high accuracy in the weak lensing limit, and is computationally much faster than (non-hierarchical) ray shooting methods to a comparable accuracy. The Ray Bundle method is a powerful and efficient technique with which to study gravitational lensing within realistic cosmological models, particularly in the weak lensing limit., Comment: 9 pages Latex, 8 figures, submitted to MNRAS

We investigate the X-ray properties of the Parkes sample of flat-spectrum radio sources using data from the ROSAT All-Sky Survey and archival pointed PSPC observations. In total, 163 of the 323 sources are detected. For the remaining 160 sources 2 sigma upper limits to the X-ray flux are derived. We present power-law photon indices for 115 sources, which were either determined with a hardness ratio technique or from direct fits to pointed PSPC data. For quasars, the soft X-ray photon index is correlated with redshift and with radio spectral index. Webster et al. (1995) discovered many sources with unusually red optical continua among the quasars of this sample and interpreted this result in terms of extinction by dust. Although the X-ray spectra in general do not show excess absorption, we find that low-redshift optically red quasars have significantly lower soft X-ray luminosities on average than objects with blue optical continua. The difference disappears for higher redshifts, as is expected for intrinsic absorption by cold gas associated with the dust. Alternative explanations are briefly discussed. We conclude, however, that dust does play an important role in some of the radio-loud quasars with red optical continua., Comment: 21 pages, 13 figures, to appear in MNRAS

Interactions between galaxies are common and are an important factor in determining their physical properties such as position along the Hubble sequence and star-formation rate. There are many possible galaxy interaction mechanisms, including merging, ram-pressure stripping, gas compression, gravitational interaction and cluster tides. The relative importance of these mechanisms is often not clear, as their strength depends on poorly known parameters such as the density, extent and nature of the massive dark halos that surround galaxies. A nearby example of a galaxy interaction where the mechanism is controversial is that between our own Galaxy and two of its neighbours -- the Large and Small Magellanic Clouds. Here we present the first results of a new HI survey which provides a spectacular view of this interaction. In addition to the previously known Magellanic Stream, which trails 100 degrees behind the Clouds, the new data reveal a counter-stream which lies in the opposite direction and leads the motion of the Clouds. This result supports the gravitational model in which leading and trailing streams are tidally torn from the body of the Magellanic Clouds., Comment: 17 pages with 5 figures in gif format, scheduled for publication in the August 20th, 1998 issue of Nature

We present a new sample of Parkes half-Jansky flat-spectrum radio sources having made a particular effort to find any previously unidentified sources. The sample contains 323 sources selected according to a flux limit of 0.5 Jy at 2.7 GHz, a spectral index measured between 2.7 and 5.0 GHz of alpha > -0.5 (where S(v) is proportional to v to the power of alpha), Galactic latitude abs(b) > 20 deg and -45 deg < Declination (B1950) < +10 deg. The sample was selected from a region 3.90 steradians in area. We have obtained accurate radio positions for all the unresolved sources in this sample and combined these with accurate optical positions from digitised photographic sky survey data to check all the optical identifications. We report new identifications based on \R- and \Kn-band imaging and new spectroscopic measurements of many of the sources. We present a catalogue of the 323 sources of which 321 now have identified optical counterparts and 277 have measured spectral redshifts., Comment: 23 pages, 10 figures, accepted for publication in MNRAS, 3 appendices available at http://www.aao.gov.au/local/www/mjd/papers/

There is controversy about the measurement of statistical associations between bright quasars and faint, presumably foreground galaxies. We look at the distribution of galaxies around an unbiased sample of 63 bright, moderate redshift quasars using a new statistic based on the separation of the quasar and its nearest neighbour galaxy. We find a significant excess of close neighbours at separations less than about 10 arcsec which we attribute to the magnification by gravitational lensing of quasars which would otherwise be too faint to be included in our sample. About one quarter to one third of the quasars are so affected although the allowed error in this fraction is large., Comment: uuencoded Postscript file (including figures and tables), SUSSEX-AST 94/8-4