Search

We have used spectra of hot stars from the RAVE Survey in order to investigate the visibility and properties of five diffuse interstellar bands previously reported in the literature. The RAVE spectroscopic survey for Galactic structure and kinematics records CCD spectra covering the 8400-8800 Ang wavelength region at 7500 resolving power. The spectra are obtained with the UK Schmidt at the AAO, equipped with the 6dF multi-fiber positioner. The DIB at 8620.4 Ang is by far the strongest and cleanest of all DIBs occurring within the RAVE wavelength range, with no interference by underlying absorption stellar lines in hot stars. It correlates so tightly with reddening that it turns out to be a reliable tool to measure it, following the relation E(B-V) = 2.72 (+/- 0.03) x E.W.(Ang), valid throughout the general interstellar medium of our Galaxy. The presence of a DIB at 8648 Ang is confirmed. Its intensity appears unrelated to reddening, in agreement with scanty and preliminary reports available in the literature, and its measurability is strongly compromised by severe blending with underlying stellar HeI doublet at 8649 Ang. The two weak DIBS at 8531 and 8572 Ang do not appear real and should actually be blends of underlying stellar lines. The very weak DIB at 8439 Ang cannot be resolved within the profile of the much stronger underlying hydrogen Paschen 18 stellar line., Accepted in press by A&A

We use the first data release from the SINGG H-alpha survey of HI-selected galaxies to study the quantitative behavior of the diffuse, warm ionized medium (WIM) across the range of properties represented by these 109 galaxies. The mean fraction f_WIM of diffuse ionized gas in this sample is 0.59+/- 0.19, slightly higher than found in previous samples. Since lower surface-brightness galaxies tend to have higher f_WIM, we believe that most of this difference is due to selection effects favoring large, optically-bright, nearby galaxies with high star-formation rates. As found in previous studies, there is no appreciable correlation with Hubble type or total star-formation rate. However, we find that starburst galaxies, defined here by an H-alpha surface brightness > 2.5x 10^39 erg s^-1 kpc^-2 within the H-alpha half-light radius, do show much lower fractions of diffuse H-alpha emission. The cause apparently is not dominated by a lower fraction of field OB stars. However, it is qualitatively consistent with an expected escape of ionizing radiation above a threshold star-formation rate, predicted from our model in which the ISM is shredded by pressure-driven supernova feedback. The HI gas fractions in the starburst galaxies are also lower, suggesting that the starbursts are consuming and ionizing all the gas, and thus promoting regions of density-bounded ionization. If true, these effects imply that some amount of Lyman continuum radiation is escaping from most starburst galaxies, and that WIM properties and outflows from mechanical feedback are likely to be pressure-driven. However, in view of previous studies showing that the escape fraction of ionizing radiation is generally low, it is likely that other factors also drive the low fractions of diffuse ionized gas in starbursts., 16 pages plus separate 2-page PostScript table. Accepted to the Astrophysical Journal

We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG), a census of star formation in HI-selected galaxies. The survey consists of H-alpha and R-band imaging of a sample of 468 galaxies selected from the HI Parkes All Sky Survey (HIPASS). The sample spans three decades in HI mass and is free of many of the biases that affect other star forming galaxy samples. We present the criteria for sample selection, list the entire sample, discuss our observational techniques, and describe the data reduction and calibration methods. This paper focuses on 93 SINGG targets whose observations have been fully reduced and analyzed to date. The majority of these show a single Emission Line Galaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs in a single field. All of the targets in this sample are detected in H-alpha indicating that dormant (non-star forming) galaxies with M(HI) > ~3e7 M_sun are very rare. A database of the measured global properties of the ELGs is presented. The ELG sample spans four orders of magnitude in luminosity (H-alpha and R-band), and H-alpha surface brightness, nearly three orders of magnitude in R surface brightness and nearly two orders of magnitude in H-alpha equivalent width (EW). The surface brightness distribution of our sample is broader than that of the Sloan Digital Sky Survey spectroscopic sample, the (EW) distribution is broader than prism-selected samples, and the morphologies found include all common types of star forming galaxies (e.g. irregular, spiral, blue compact dwarf, starbursts, merging and colliding systems, and even residual star formation in S0 and Sa spirals). (abridged), 28 pages, ApJS, in press. Full resolution version with all panels of Fig. 8 available at http://sungg.pha.jhu.edu/publications.html . On line data available at http://sungg.pha.jhu.edu/PubData/ . Author list corrected. Wrong value for f_ap used in eq. 7 now corrected; typos corrected, non-used references replaced, others updated

The HI Parkes All-Sky Survey (HIPASS) Catalogue forms the largest uniform catalogue of HI sources compiled to date, with 4,315 sources identified purely by their HI content. The catalogue data comprise the southern region declination, Comment: Accepted for publication in MNRAS. 17 pages, 14 figures. HIPASS catalogue data and paper with higher resolution figures can be downloaded from http://hipass.aus-vo.org

We report on a search for long duration microlensing events towards the Large Magellanic Cloud. We find none, and therefore put limits on the contribution of high mass objects to the Galactic dark matter. At 95% confidence level we exclude objects in the mass range 0.3 solar masses to 30.0 solar masses from contributing more than 4 times 10^11 solar masses to the Galactic halo. Combined with earlier results, this means that objects with masses under 30 solar masses cannot make up the entire dark matter halo if the halo is of typical size. For a typical dark halo, objects with masses under 10 solar masses contribute less than 40% of the dark matter.

This talk reviews the internal dynamics of some of the different classes of Local Group galaxies. These include the dwarf spheroidal galaxies, the pure disk galaxy M33, the LMC and M31. The talk concludes with some general remarks about bulges and halos.

The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of $\tau_{meas} = 2.9 +1.4/-0.9 \times 10^{-7}$. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: $\tau_{back} = 5.4\times 10^{-8}$, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass $\sim 0.5 \msun$. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved which allows us to estimate the distance to the lenses. If the source star is not a short period binary star, then we show that the lens system is very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC., Comment: 5 pages, 3 postscript figures included; To appear in the Proceedings of the Dark Matter '96 Conference held in Santa Monica, CA, Feb., 1996

In this scientific overview, I discuss some of the important features of barred galaxies, and attempt to identify some of the outstanding problems.

I review the properties of dark matter in galaxies from an observational perspective. Topics include the mass and extent of the dark halos of large spirals like the Milky Way, modelling the dark halo, the maximum disk problem, the hydrostatics of the HI layer in disk galaxies as a probe of the galactic potential, dark matter in elliptical galaxies and dwarf spheroidal galaxies, scaling laws for dark halos, and the fractional contribution of galactic dark matter to the mass content of the universe.

Lenticular galaxies display the prominent disks that are characteristic of late-type galaxies, but contain no gas, dust or star formation like early-type systems. So are they more closely related to spiral or ellipticals?. One important clue to their origin is recorded in the kinematics. If they are simply quenched spiral galaxies then their stellar motions should be identical to those in spirals, whereas if their origins are closer to an elliptical, produced through merging, then this history should be reflected in more random stellar motions ([1]). We performed a maximum likelihood analysis in order to recover rotation velocity and random motions in the spheroidal and disk component of the galaxy NGC 1023. Its kinematics are consistent with the one of a stripped spiral, somehow complicated by an ongoing minor merger.

The metal weak halo stars are a slowly rotating population. If we assume that their rotation is in the same sense as that of the disk, then their solar motion gives a lower limit to the galactic circular velocity. For a sample of nearby non-kinematically selected metal weak stars, this limit is about 175 ± 12 km s−1. However, about 25 percent of the metal weak stars belong not to the halo but to a rapidly rotating “thick disk” population. Excluding these stars from the halo sample gives a more useful lower limit of 220 ± 10 km s−1 on the galactic circular velocity.

We have derived surface photometry for a sample of five polar ring (PR) galaxies in the optical (B and R bands) and in the near-IR (K band). Our preliminary results show that the morphology of these objects is heavily perturbed by dart, which sometimes completely hides the real distribution of the older stellar population. The analysis of the colour profiles and of the integrated colours of the host galaxy and polar ring in these systems indicates that (1) the ring and the central galaxy appear to have different stellar populations, which supports the accretion /merging scenario for these objects, and (2) although the host galaxies have an early-type morphology, their integrated colours are close to those of spirals, with a strong blueward colour gradient from the centre outward.

The dust mask is the most obvious of the masks that obscure our view of the Milky Way. But there are others, including the mass mask, kinematical masks, and structural, chemical and dynamical masks. In each case, there are ways to penetrate the mask.

A number of very small isolated HII regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These HII regions appear as tiny emission line objects in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic confirmation of four isolated HII regions in two systems, both systems have tidal HI features. The results are consistent with stars forming in interactive debris due to cloud-cloud collisions. The H-alpha luminosities of the isolated HII regions are equivalent to the ionizing flux of only a few O stars each. They are most likely ionized by stars formed in situ, and represent atypical star formation in the low density environment of the outer parts of galaxies. A small but finite intergalactic star formation rate will enrich and ionize the surrounding medium. In one system, NGC 1533, we calculate a star formation rate of 1.5e-3 msun/yr, resulting in a metal enrichment of ~1e-3 solar for the continuous formation of stars. Such systems may have been more common in the past and a similar enrichment level is measured for the `metallicity floor' in damped Lyman-alpha absorption systems., Comment: accepted for publication in the Astronomical Journal, 19 pages, including 5 figures, some low resolution. Paper with high resolution images can be downloaded from http://astro.ph.unimelb.edu.au/~eryan/publications/eldots.ps.gz

The HI Parkes All-Sky Survey (HIPASS) is a blind 21-cm survey for extragalactic neutral hydrogen, covering the whole southern sky. The HIPASS Bright Galaxy Catalog (BGC; Koribalski et al. 2002) is a subset of HIPASS and contains the 1000 HI-brightest (peak flux density) galaxies. Here we present the 138 HIPASS BGC galaxies, which had no redshift measured prior to the Parkes multibeam HI surveys. Of the 138 galaxies, 87 are newly cataloged. Newly cataloged is defined as no optical (or infrared) counterpart in the NASA/IPAC Extragalactic Database. Using the Digitized Sky Survey we identify optical counterparts for almost half of the newly cataloged galaxies, which are typically of irregular or magellanic morphological type. Several HI sources appear to be associated with compact groups or pairs of galaxies rather than an individual galaxy. The majority (57) of the newly cataloged galaxies lie within ten degrees of the Galactic Plane and are missing from optical surveys due to confusion with stars or dust extinction. This sample also includes newly cataloged galaxies first discovered in the HI shallow survey of the Zone-of-Avoidance (Henning et al. 2000). The other 30 newly cataloged galaxies escaped detection due to their low surface brightness or optical compactness. Only one of these, HIPASS J0546-68, has no obvious optical counterpart as it is obscured by the Large Magellanic Cloud. We find that the newly cataloged galaxies with |b| > 10 are generally lower in HI mass and narrower in velocity width compared with the total HIPASS BGC. In contrast, newly cataloged galaxies behind the Milky Way are found to be statistically similar to the entire HIPASS BGC. In addition to these galaxies, the HIPASS BGC contains four previously unknown HI clouds., 39 pages including 14 figures, to appear in the Oct 2002 issue of AJ

In order to find the best observable diagnostics for the amount of internal extinction within spiral galaxies, we have constructed models for disk galaxies with immersed dust layers. The radiative transfer problem, including both scattering and pure absorption, has been computed for a range of model galaxies. This reveals a set of superior diagnostics for the opacity. These include the behaviour of the radial colour and luminosity distributions, the amplitude of the asymmetry between the near and far sides of the major axis, and their dependence on the orientation of the galaxy with respect to the observer.

Boxy/peanut-shaped bulge galaxies constitute at least 20–30% of all spirals. Distribution functions and numerical simulations studies have shown that the slow decay of the orbit of a companion into a larger spiral can lead to the formation of a boxy/peanut bulge. However, the bar-buckling instability now appears a more likely process. Thin bars either do not form or, as shown by N-body simulations, buckle and settle with an increased thickness, appearing boxy or peanut-shaped when seen edge-on. This project aims to determine the dynamical state of a sample of 30 edge-on spirals, 3/4 of which have boxy/peanut-shaped bulges, half having close-by companions.

The MACHO microlensing experiment’s time-sampled photometry database contains blue and red lightcurves for nearly 9 million stars in the central bar region of the Large Magellanic Cloud (LMC). We have identified known LMC Planetary Nebulae (PN) in the database and find one, Jacoby 5, to be variable. We additionally present data on the “parent populations” of LMC PN, and discuss the star formation history of the LMC bar.

The MACHO Project is searching for galactic dark matter in the form of massive compact halo objects (Machos). Millions of stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge are photometrically monitored in an attempt to detect rare gravitational microlensing events caused by otherwise invisible Machos. Analysis of two years of photometry on 8.5 million stars in the LMC reveals 8 candidate microlensing events, far more than the $\sim1$ event expected from lensing by low-mass stars in known galactic populations. From these eight events we estimate the optical depth towards the LMC from events with $2 < \that < 200$ days to be $��_2^{200} \approx 2.9 ^{+1.4}_{-0.9} \ten{-7}$. This exceeds the optical depth of $0.5\ten{-7}$ expected from known stars and is to be compared with an optical depth of $4.7\ten{-7}$ predicted for a ``standard'' halo composed entirely of Machos. The total mass in this lensing population is $\approx 2^{+1.2}_{-0.7} \ten{11} \msun$ (within 50 kpc from the Galactic center). Event timescales yield a most probable Macho mass of $0.5^{+0.3}_{-0.2}\msun$, although this value is quite model dependent., 10 pages, 6 epsf figures and style file included, 451k, also at http://wwwmacho.mcmaster.ca/Pubs/Pubs.html; To appear in the Proceedings of "Sources and Detection of Dark Matter in the Universe", Santa Monica, CA, Feb., 1996

The rotation curves of spiral galaxies indicate that most of them have massive dark coronas, and it seems likely that our Galaxy also has a dark corona. Our position in the galactic disk makes it difficult to measure the galactic rotation curve beyond about 20 kpc from the galactic center, but it does allow us to use several other indicators of the total galactic mass out to very large distances. I will review some of these indicators. The conclusion is that the Galaxy does indeed have a massive dark corona: the data are consistent with the enclosed mass within radius R increasing like M(R) ≈, R(kpc) × 1010 M ⊙, out to a radius of more than 100 kpc, and a total galactic mass of at least 12 × 1011 M⊙.

We present K-band integrated photometry of a class of interacting galaxies with a spheroidal and irregular components. These systems are Arp 118 (NGC 1143/44), Arp 140 (NGC 0274/75), Arp 142 (NGC 2936/37), Arp 144 (NGC 7828/29), Arp 146 and Arp 147 (IC 298/IC 298A). Two of these systems are found to have very high internal velocities within the irregular component: Arp 118 has an internal velocity of ~1100 km/s (Hippelein, 1989; McCain et al., 1995), while Arp 142 has ~900 km/s.

We present our study of Arp 142, an interacting system which consists of irregular (NGC 2936) and spheroidal (NGC 2937) components. We discovered that NGC 2936 has very high internal motions, much higher than what is expected from the dynamics of interaction of such galaxies.

Real-time detection of microlensing has moved from proof of concept in 1994 (Udalski et al. 1994a, Alcock et al.1994) to a steady stream of events this year. Global dissemination of these events by the MACHO and OGLE collaborations has made possible intensive photometric and spectroscopic follow up from widely dispersed sites confirming the microlensing hypothesis (Benetti 1995). Improved photometry and increased temporal resolution from follow up observations greatly increases the possibility of detecting deviations from the standard point-source, point-lens, inertial motion microlensing model. These deviations are crucial in understanding individual lensing systems by breaking the degeneracy between lens mass, position and velocity. We report here on GMAN (Global Microlensing Alert Network), the coordinated follow up of MACHO alerts.

We present the first detection of parallax effects in a gravitational microlensing event. Parallax in a gravitational microlensing event observed only from the Earth appears as a distortion of the lightcurve due to the motion of the Earth around the Sun. This distortion can be detected if the event duration is not much less than a year and if the projected velocity of the lens is not much larger than the orbital velocity of the Earth about the Sun. The event presented here has a duration of 220 days and clearly shows the distortion due to the Earth's motion. We find that the projected velocity of the lens is 75+/-5 km/s at an angle of 28+/-4 deg from the direction of increasing galactic longitude, as expected for a lens in the galactic disk. A likelihood analysis yields estimates of the distance to and mass of the lens: D_{lens} = 1.7 (+1.1/-0.7) kpc and M = 1.3 (+1.3/-0.6) Msun, suggesting that the lens is a remnant such as a white dwarf or neutron star. A less likely possibility is that the lens is a main sequence star. If so, we can add our upper limit on the observed flux from the lens to the analysis. This modifies the estimates to: D_{lens} = 2.8 (+1.1/-0.6) kpc, and M = 0.6 (+0.4/-0.2) Msun., Comment: 11 pages, 3 figs in uuencoded, compressed, tared postscript files

In the past few years, the Magellanic Clouds have been the targets for several major variable star surveys. The results of these surveys are now becoming available and it is clear that a Renaissance in LMC and SMC variable star research will result. In this review, I will describe the results of such surveys and review the questions that are likely to be answered by further work. With respect to results, I will concentrate on LMC MACHO Project data, including beat Cepheids, discovery statistics, mode identification, Fourier decomposition of lightcurves, and the differences between the LMC and galactic sample., Comment: uuencoded, compressed PostScript, 8 pages, 2 figures (in text). Invited review for proceedings of IAU Colloquium #155: Astrophysical Applications of Stellar Pulsation (Cape Town, February 1995), ASP Conference Series, ed. R. Stobie

The recent spectroscopic observations of Planetary Nebulae (PNe) with the ESO New Technology Telescope (NTT) in the multi-object spectroscopy (MOS) mode have achieved very important results for understanding the dark matter content and the formation mechanism of the cD giant elliptical galaxy NGC 1399 in the Fornax cluster. The telescopes of the new generation will revolutionise the use of PNe as mass tracers for the dynamics of the outer regions of early type galaxies. With an 8-m telescope, a spectrograph similar to EMMI with the MOS mode, and a wavelength resolution of about 1.0 A/pix, it will possible to detect and measure velocities of PNe as faint as log F5007 (ergs cm-2 s-1) = -18.0. At the distance of the Virgo and Fornax clusters, this will allow us to measure about 600 PNe in the outer regions of the giant galaxies NGC 1399 and M87, which will give a good sampling of their potential wells. It will also be possible to measure at least 100 PNe in the outer regions of smaller ellipticals, down to 2.8 mag fainter than the cluster giants.

We have developed an astronomical imaging system tailored to our search for gravitational microlensing by compact objects in the halo and disk of the Galaxy. The challenge of detecting rare microlensing events is to monitor ∼10 million stars per night and distinguish genuine events from other sources of variability. The Large Magellanic Cloud and the Galactic bulge provide the high surface density of resolvable stars necessary for this task. A dedicated 50 inch telescope at Mt. Stromlo Observatory has been producing science data since the fall of 1992. Our system incorporates eight 2048 x 2048 CCDs into two focal planes for simultaneous imaging in two passbands (4500-6300 and 6300-8100 A). Each focal plane consists of four ‘edge-buttable’ CCDs in a custom mounted 2 x 2 array. The 0.62 arcsecond pixel scale (15 μ) yields a 40 x 40 arcminute square field of view in each frame. A sophisticated point spread fitting photometry package extracts up to 600,000 useful magnitudes per color per frame. The data collection rate we need is obtained by simultaneously reading out all sixteen CCD outputs (two per chip) at 34 KHz with 16 bit digitization. With exposure times of 150-300 seconds and a 70 second readout time we can collect up to 100 fields per night. These rates are designed to allow us to detect or rule out massive compact halo objects (MACHOs) in the 10-6 - 10 1 M⊙range.

Without attempting to cover all of the topics discussed at this meeting, I plan to talk briefly about some of the major achievements and ideas that came up here, and then mention a few of the important open questions and some work that might be done to answer them.

The main components of our Galaxy are (1) the disk (thin and thick), which is rapidly rotating; (2) the bulge; (3) the metal weak halo, which rotates very slowly, and (4) the dark corona, which provides most of the mass. Near the sun, there is no rotationally intermediate population.

The MACHO microlensing experiment's time-sampled photometry database contains blue and red lightcurves for nearly 9 million stars in the central bar region of the Large Magellanic Cloud (LMC). We have identified known LMC Planetary Nebulae (PN) in the database and find one, Jacoby 5, to be variable. We additionally present data on the “parent populations” of LMC PN, and discuss the star formation history of the LMC bar.

Photometry in [OIII] emission of Planetary Nebulae in external galaxies can be used to determine distances as great as that of the Virgo cluster and beyond, as forcefully argued elsewhere during this conference (G.H. Jacoby, invited talk). In addition, measurement of the radial velocities of the PN allows dynamical behaviour to be probed to much greater distance from the galaxian centre than integrated light techniques (e.g. Arnaboldi 1994).

We describe a procedure for the efficient measurement of large quantities of PN radial velocities (RVs) in early-type galaxies, using the Focal Reducer and Spectrograph (FORS) at the Cassegrain foci of the ESO Very Large Telescope. The PNs are detected using the classic on-band/off-band filter technique. The radial velocity is obtained by measuring and calibrating the displacement of a PN image on the CCD produced by the insertion of a grism in the light path. Since no slits are used, it is possible to measure RVs for all the detected PNs, irrespective of their number and distribution in the field. All the images needed to find the PNs and measure their brightness and RVs can be collected in just one observing run, without the complicated preparation procedures typical of multi-object slit spectroscopy. The RVs have errors of about 40 km/s.

We report the discovery of two new R Coronae Borealis (RCB) stars in the LMC using the MACHO project photometry database. The identification of both stars has been confirmed spectroscopically. One is a cool RCB star ({ital T}{sub eff}{approximately}5000 K), characterized by very strong Swan bands of C{sub 2} and violet bands of CN, and weak or absent Balmer lines, G band, and {sup 12}C{sup 13}C bands. The second star is an example of a hot RCB star, of which only three were previously known to exist in the Galaxy and none in the LMC. Its spectrum is characterized by several CII lines in emission. Both stars have shown deep declines of {Delta}{ital V}{ge}4 mag in brightness. The new stars are significantly fainter at maximum light than the three previously known LMC RCB stars. The amount of reddening toward these stars is somewhat uncertain, but both seem to have absolute magnitudes, {ital M}{sub {ital V}}, {approximately}0.5 mag fainter than the other three stars. Estimates of {ital M}{sub bol} find that the hot RCB star lies in the range of the other three stars, while the cool RCB star is fainter. The two cool LMC RCB stars are the faintest atmore » {ital M}{sub bol}. The discovery of these two new stars brings to five the number of known RCB stars in the LMC, and it demonstrates the utility of the MACHO photometric database for the discovery of new RCB stars. {copyright} {ital 1996 The American Astronomical Society.}« less

In order to find the best observable diagnostics for the amount of internal extinction within spiral galaxies, we have constructed realistic models for disk galaxies with immersed dust layers. The radiative transfer including both scattering and absorption has been computed for a range of model galaxies in various orientations. Standard galaxy surface photometry techniques were then applied to the numerical data to illustrate how different observables such as total magnitude, color and luminosity distribution behave under given conditions of dust distribution. This work reveals a set of superior diagnostics for the dust in the disk. These include not only the integrated parameters, but also the apparent disk structural parameters, the amplitude of the asymmetry between the near and far sides of the galaxy as divided by the apparent major axis and their dependence on the orientation of the galaxy with respect to the observer. Combining the above diagnostics with our impressions of real galaxies, we arrive at the qualitative conclusion that galaxy disks are generally optically thin. Quantitative conclusions will appear in subsequent work.

We have measured the diameters of a large number of disk galaxies on various Sky Surveys in order to examine the problem of the apparent uniformity of the central surface brightness in disk galaxies. From the ratio of diameters on the various surveys we find that at least 55% of the disk galaxies follow this rule. Another 26% of the galaxies have only a very modest increase in diameters on the SRC-J survey when compared to the Palomar survey prints, indicating the presence of a cutoff in the outer disk. 19% of the galaxies measured have a large increase in diameter. From their integrated H I profiles, these turn out to be mostly dynamically giant galaxies. Several examples are shown

The young globular star clusters in the LMC offer us insights into the formation and early dynamical evolution of globular clusters which are unobtainable from the old globular clusters in our Galaxy. Because these young clusters are so young and populous, they provide an opportunity to measure the upper end of the initial mass function by direct means and also through the dynamical effects of stellar mass loss on the structure of the clusters.

A workshop on 'The Early Universe' was held at Mount Stromlo Observatory, near Canberra, in June 1989. The discussion topics included a wide range of theoretical and observational aspects of the astrophysics of the early universe, from the origin of primordial fluctuations to the properties of high red shift galaxies. This issue of the Australian Journal of Physics presents most of the formal papers given by astrophysicists from the USSR and Australia at this workshop

In the Milky Way, the globular clusters are all very old, and we are accustomed to think of them as the oldest objects in the Galaxy. The clusters cover a wide range of chemical abundance, from near solar down to about [Fe/H] ⋍ −2.3. However there are field stars with abundances significantly lower than −2.3 (eg Bond, 1980); this implies that the clusters formed during the active phase of chemical enrichment, with cluster formation beginning at a time when the enrichment processes were already well under way.

What are the characteristic scale lengths and densities for the dark halos of galaxies, and the typical ratios of dark to luminous mass? For elliptical galaxies, the best estimates come from X-ray data which will be discussed in a later session. For spirals, the best estimates come from rotation curves. I will concentrate on the halo parameters for disk galaxies. At the end, there will be a few comments on stellar dynamical data for ellipticals, and on the unique information available for the dark halo of our Galaxy.

Observations made at Las Campanas Observatory and at the Anglo-Australian Observatory have been used to determine line-of-sight velocities with an average accuracy of 3 kms−1 for 135 member stars in the globular cluster 47 Tucanae. The velocities were derived from cross-correlation techniques applied to 30 A/mm spectra obtained with digital sky-subtracting detectors. The spectra themselves have been used to analyze the cyanogen anomalies on the red giant branch in this cluster (Norris et al., 1984). When combined with the velocities published by the CORAVEL group (Mayor et al., 1983), these observations yield velocities for 212 stars with projected distances from the cluster center ranging from 3 to 68 core radii. After radial binning and analysis these observations yield the following results:(i) The inner parts of the cluster show appreciable differential rotation with a maximum projected rotation velocity of approximately 6 kms−1 in the region 6–18 core radii. However, at larger radii the rotation declines rapidly and is essentially zero for radii greater than 30 core radii. This result is illustrated in Figure 1. To within the errors of the determinations, the position angle of the maximum rotation and that of the major axis of the stellar density distribution coincide.(ii) In contrast to M3 (Gunn and Griffin 1979), “thermal equilibrium” multimass models (c.f. Da Costa and Freeman 1976) can ONLY reproduce the observed velocity dispersion values by including a substantial amount of “dark matter”; i.e. unlike M3, there is “missing mass” in 47 Tuc. In order to retain a fit to the surface brightness profile of the cluster, this “dark mass” (which provides perhaps 30 to 40 percent of the total cluster mass) cannot have a distribution much different from that of the cluster giants if it is in the form of stars and “thermal equilibrium” is maintained. In this case the obvious candidates for the dark matter are the white dwarf remnants of the stars more massive than the current turnoff mass, though many more such remnants are required than the number expected from extrapolating the present mass function. The difference between M3 and 47 Tuc in this case then implies that the 47 Tuc initial mass function had many more massive stars than did that for M3. The work of Freeman (1977), who demonstrated large IMF variations in the 8 − 1.5 solar mass range in young Magellanic Cloud clusters, provides observational support for this interpretation.

We review the kinematical and chemical properties of the old population of our Galaxy. Comparison is made with the properties of the old population in other disk galaxies.

In tills review, I will talk about some galactic problems for which stellar radial velocities are important. I will not attempt to be comprehensive, but will just pick out some problems which are being actively studied and which I find particularly interesting.This is a classical problem. The aim is to estimate the total matter density near the Sun from the distribution and kinematics of a tracer population towards the galactic poles. Recently Bahcall (1984a,b,c) has made a major attack on this problem, using F stars and W giants. He finds that about half the total matter density near the Sun is unaccounted for. This is important. We know from work on other diek galaxies that about half their mass lies in a dark corona and the other half in the disk; the nature of this dark matter is not yet understood. If we also see that about half the mass of the disk itself is dark, then that is certainly worth knowing, because this dark matter has dissipated to the disk. That may help us to understand the nature of the dark matter.