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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

We present the first results from the COLA (Compact Objects in Low-power AGN) project which aims to determine the relationship between one facet of AGN activity, the compact radio core, with star formation in the circumnuclear region of the host galaxy. This will be accomplished by the comparison of the multi-wavelength properties of a sample of AGN with compact radio cores to those of a sample of AGN without compact cores and a matched sample of galaxies without AGN. In this paper we discuss the selection criteria for our galaxy samples and present the initial radio observations of the 107 Southern galaxies in our sample. Low-resolution ATCA observations at 4.8, 2.5 and 1.4 GHz and high resolution, single baseline snapshots at 2.3 GHz with the Australian LBA are presented. We find that for the majority of the galaxies in our sample, the radio luminosity is correlated with the FIR luminosity. Compact radio cores are detected in 9 galaxies. The majority (8/9) of these galaxies exhibit a significant radio excess and 50% (7/14) of the galaxies which lie above the radio-FIR correlation by more than 1 sigma have compact radio cores. The emission from the cores is too weak to account for this radio excess and there is no evidence that the radio luminosity of the compact cores is correlated with the FIR galaxy luminosity. The galaxies with compact cores tend to be classified optically as AGN, with two thirds (6/9) exhibiting Seyfert-like optical emission line ratios, and the remaining galaxies classified either as composite objects (2/9) or starburst (1/9). (Abridged), 25 pages, including 6 figures and 4 tables, in Latex (uses emulateapj5.sty). Accepted for publication in ApJ

We present the results of our major HST study of the evolution of PN in the Magellanic Clouds. This consists of imaging studies in [O III] and FOS UV spectroscopy. These data are then used in theoretical photoionisation models in conjuction with ground-based spectrophotometry, absolute flux and expansion velocity and density to derive self consistent diameters, ages, masses, and nebular abundances and to accurately place the central stars on the H-R Diagram. We find that observed sizes and ages can be reconciled with evolutionary theory provided that the He-burners outnumber the H-burners in the approximate ratio 2:1. For the LMC observed abundance patterns are qualitatively consistent with the (mass-dependent) operation of the various chemical dredge-up processes as predicted by theory. However, the observed dredge-up efficiencies do not agree with current theory. Finally, since core masses are determined with adequate precision, we are able to derive, for the first time, the metallicity age relation for of the LMC. We find that the base metallicity of the LMC rapidly increased ∼ 2 Gyr ago, consistent with the age of the burst of star formation inferred from field stars and clusters.

Gamma-ray bursts (GRBs) serve as powerful probes of the early Universe, with their luminous afterglows revealing the locations and physical properties of star forming galaxies at the highest redshifts, and potentially locating first generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal to noise spectroscopy, or photometry. Here we present a photometric redshift of z~9.4 for the Swift-detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a majority of GRB sight-lines), the 90% likelihood range for the redshift is 9.06 < z < 9.52, although there is a low-probability tail to somewhat lower redshifts. Adopting Milky Way or Large Magellanic Cloud dust laws leads to very similar conclusions, while a Maiolino law does allow somewhat lower redshift solutions, but in all cases the most likely redshift is found to be z>7. The non-detection of the host galaxy to deep limits (Y_AB >~ 28 mag, which would correspond roughly to 0.001 L* at z=1) in our late time optical and infrared observations with the Hubble Space Telescope strongly supports the extreme redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs, and suggest that its progenitor is not greatly different to those of lower redshift bursts., Accepted for publication on The Astrophysical Journal

Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approximately 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

We present a simple two-wind model for the evolution of the Magellanic Cloud planetary nebulae (PN) which reproduces the observed density / radius / ionised mass relationships, and serves to define the geometrical relationship between the ionised nebula and the star. From self-consistent photoionisation modelling of 78 Magellanic Cloud PN, we have constructed the H-R Diagram for the central stars, and have derived both the chemical abundances and the nebular parameters. We find that the central stars have masses generally between 0.55 and 0.7 M⊙. Type I PN have more massive precursors, and show clear evidence for the Third dredge-up episode and for the dredge-up of ON processed material. The expansion velocity of the nebula is closely correlated with the position of the central star on the H-R Diagram, proving that the nebula undergoes continuous acceleration. Excluding Type I PN, the mean abundances derived for the LMC and the SMC agree with those derived from H II regions and evolved, radiative SNR.

Nova LMC 1990A was a very fast Ne-O-Mg nova, for which a particularly dense coverage of spectral observation in both the UV and optical was obtained. The data for the nebular phase were subjected to an analysis by the photoionisation modelling code MAPPINGS 2. The following parameters were obtained: Lmax = 8×104L⊙, Teff = 2×105K and the mass of ejecta = 5.5×10−5M⊙. The abundance ratios in the ejecta were similar to those obtained by Williams et al. (1985) in the case of V693 CrA 1981. The N/O ratio and the overabundance of Al is consistent with outburst on a ONeMg white dwarf of mass ∽1.2M⊙, but the super-Eddington luminosity, and amount of mass ejected presents some problems to theory.

We present results of a self-consistent model of the spectral energy distribution (SED) of starburst galaxies. Two parameters control the IR SED, the mean pressure in the ISM and the destruction timescale of molecular clouds. Adding a simplified AGN spectrum provides mixing lines on IRAS color : color diagrams. This reproduces the observed colors of both AGNs and starbursts., Comment: Poster Paper for IAU 222: The Interplay among Black Holes, Stars and ISM in Galactic Nuclei

The prospects for future advances in understanding the chemical evolution of the Magellanic Clouds is reviewed on the basis of results presented at IAU Symposium #148. These are divided into three areas, the metallicity - age relationships, the current abundance set, and the theory of the chemical evolution of the Clouds.

The production rate of ionizing photons in young (≤8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass to investigate the upper end of the stellar initial mass function (IMF). We have found that within the uncertainties the upper end of the stellar IMF appears to be universal in this galaxy, and that deviations from a universal IMF can be attributed to stochastic sampling of stars in clusters with masses ≾ 10^3 M_☉. Furthermore, we have found that there does not seem to be a dependence of the maximum stellar mass on the cluster mass. We have also found that for massive clusters, feedback may cause an underrepresentation in Hα luminosities, which needs to be taken into account when conducting this type of analysis.

Recently a number of new planetary nebulae (PN) have been found in the outer field of the LMC using deep objective-prism J plates taken with a Schmidt Telescope at the AAO. For a number of these PN, we have obtained spectrophotometry on the 2.3m ATT and for a sub-sample, determined the radial velocities using the Echelle Spectrograph of the 2.3m Telescope. All this data is to appear in the ApJ.

Progress in developing theories concerning the evolution of the central star and the surrounding planetary nebula requires a large, uniform set of data (monochromatic images, isophotes) which CCD imaging of PN can supply at present (Kaler, 1985; Balick 1987). One of the unknown parameters remains the mass budget of the (PN + central star) system. As a matter of fact, existing inventories of the measured ionised mass in PN reveal a shortfall as compared with theory. Nonetheless, since the major portion of the total mass loss occurs in the earlier ejection phases, a main objective was to detect the faint brightness peripheral nebular emissions and to provide quantitative measurement when possible of the global ionised mass.

We have obtained Hubble Space Telescope (HST) Planetary Camera (PC) images of a number of Magellanic Cloud planetary nebulae. The objects, except for SMP 83 were observed as part of the Cycle I GO program. The observations were made in the [O III] λ5007Å line. The object SMP 83, was observed as part of the GTO program, and in this case observations were also made in the Hα line using the F650N filter. In order to characterise the point spread function, a star was placed at the same point on the chip as the PN. This allowed us to determine the diameters of barely resolved PN in an accurate manner, by convolving the PSF with a function until it matched the appearance of the PN image. The results are given in Table 1.

We report the optical identification of four Balmer-dominated supernova remnants (SNRs) in the Large Magellanic Cloud. Both the Balmer-dominated spectra and the presence of a broad Hα component in one remnant can be understood in terms of a very high velocity non-radiative shock encountering gas which is partially neutral, as proposed originally by Chevalier and Raymond to account for the similar spectra of the galactic remnants, Tycho and SN1006. From a consideration of the optical and X-ray luminosities of the SNR with broad Hα emission, we infer that the fraction of neutral gas in the medium is ≲ 30%. Radio observations of the LMC remnants show that their surface brightnesses are anomalously low; this could be intrinsic to the supernova themselves, or a result of their environment. Finally, we argue that the four SNRs all resulted from Type I supernovae, in which case they are the first such remnants to be identified outside the Galaxy.

Empirical calibrations based on prior studies of Galactic OB Stars are used to determine the integrated stellar wind mechanical luminosity (Lw) and the integrated Lyman continuum photon luminosity (S*) for 10 OB clusters in the L.M.C. These values of Lw and S*, together with narrow band H-α surface photometry of an overlapping sample of 15 L.M.C. HII regions, are used to show that the large shell-like HII regions, in the L.M.C. are stellar wind bubbles 3 to 5 million years old. In order to reproduce the general properties of these HII shells, a thick cushion of shocked stellar wind gas must have been present on the inside of the shell for most of the life time of the nebula, and the shell itself must be ram pressure confined by the HI/molecular cloud out of which it formed.

Optical identifications of 32 X-ray sources in the Magellanic Clouds confirm that they are SNRs. They are separated into four classes: the evolved, the oxygen-rich, the Balmer-dominated and the Crab-like. High velocity HI emission is observed from an extended region near 0525–66.0. It is suggested that this is produced by a possible Type III supernova which occurred out of the plane of the LMC and on the far side of the disk. The cumulative number-diameter relation for the LMC SNRs shows that they have evolved much faster than expected from the Sedov theory. It is suggested that this apparent “free-expansion” up to quite large diameters is due to the gradual conversion of the kinetic energy of the ejecta into thermal energy as they overtake the decelerating blast wave.

When first asked to contribute to this volume to mark Professor Kopal’s retirement after thirty years as Head of the Department of Astronomy at Manchester, my mind cast back to my first meeting with him, a scant ten years ago. Like most things connected with this man, this could never be classified as commonplace. Having applied to undertake a post-graduate course at Manchester, I received a letter in London asking me to attend at a certain date and time at the tomb of Isaac Newton in Westminster Abbey. This I did, to find several others milling about, eyeing the stone work, inscriptions and each other. At five minutes past the appointed hour in swept Prof. Kopal up the main aisle, resplendent in fur coat and accompanied by two or three of his staff, and proceeded to interview us hopeful candidates in a very business-like manner in the front pew. This lasted until the winter’s light faded and a verger appeared before us to end the interview by enquiring “whether the gentlemen would be staying for Evensong”. Thus began a very warm professional association!

The problem of the interaction of a strong stellar wind with a massive collapsing neutral hydrogen cloud has been considered and a new class of steady flow solutions found.

From models of plane-parallel radiating shock waves and the observations of Osterbrock and Dufour, the abundances of oxygen, nitrogen, neon and sulfur (and indirectly, or carbon) are derived for the Large Magellanic Cloud supernova remnant N49. These are somewhat smaller than solar values, and it is concluded that the discrepancies between these and values derived for the LMC H II regions reflect the composition of ''ice'' grains with low sublimation temperatures which are destroyed in the supernova event. (AIP)

A planetary nebula has been identified near the center of the Fornax dwarf elliptical galaxy. Quantitative spectrophotometry reveals that it is slightly reddened, and belongs to an intermediate-excitation class, with a normal helium abundance. Since the abundances of all 2 to 3 times lower than in the Orion nebula, the material in the nebula which has a mass ≥ 0.1 M probably represents at least a second generation of processed matter. The implications of this conclusion are briefly discussed from the point of view of heavy element enrichment in low mass systems such as Fornax whose mass is 2×107 M. (Paper will appear in The Astrophysical Journal.)

Extensive absolute spectrophotometry of HH objects has been obtained with the 3.9 m AAT and the 1.9 m Mount Stromlo telescopes. Systematic trends in their spectral characteristics have been found. All the observations can be explained in a quantitative manner using a theory of radiating shock waves traveling into a partially preionized medium.There are probably two classes of stellar objects driving the shocks. These are either B-type protostars in the process of breaking up optically thick dust cocoons, or FU Orionis-type stars losing mass. In either case, high luminosities and/or high mass-loss rates are required. If the stellar object is an FU Orionis object, these must be maintained over time scales of order 100 years.

We have computed an extensive, homogeneous grid of theoretical photoionization models with conditions appropriate to observed H II regions. This grid has been used to develop a comprehensive set of theoretical diagnostic diagrams for H II regions which employ ratios of prominent emission lines to determine the ionization parameter within the nebula, and the ionization temperature of its exciting star(s). It is also possible to estimate the element-averaged metallicity in the nebula and stars from these diagnostics.

Because X-ray luminosities of most SNRs are dominated by emission from heavy elements, estimates of the X-ray emitting mass based on cosmic abundances may be incorrect. Here we investigate the apparent density evolution of a SNR when substantial amounts of processed material are ejected by the supernova. If this material is shock heated, it will dominate X-ray emission from the remnant long after the SNR has swept up the equivalent amount of interstellar matter (ISM). Emission from metal-rich ejecta may explain why ISM densities of young remnants far from the galactic plane, deduced from standard analysis, are higher than expected, as well as why larger SNRs appear to be lying in regions of lower ISM density. It should be included in detailed calculations of SNR surface brightness distributions, along with effects due to departures from ionization equilibrium and cloudlet evaporation in a multiphase ISM which may also contribute to the apparent evolution of density with radius.