Description: We present the high-angular-resolution catalogue for the Australia Telescope 20 GHz (AT20G) survey, using the high-angular-resolution 6-km antenna data at the baselines of ~4500 m of the Australia Telescope Compact Array. We have used the data to produce the visibility catalogue that separates the compact active galactic nuclei (AGNs) from the extended radio sources at the 0.15 arcsec angular scale, corresponding to the linear size scale of 1  kpc at redshifts higher than 0.7. We find the radio population at 20 GHz to be dominated by compact AGNs constituting 77 per cent of the total sources in the AT20G. We introduce the visibility-spectra diagnostic plot, produced using the AT20G cross-matches with lower frequency radio surveys at 1 GHz [the NRAO VLA Sky Survey (NVSS) and the Sydney University Molonglo Sky Survey (SUMSS)], that separates the 20 GHz population into distinct sub-populations of the compact AGNs, the compact steep-spectrum (CSS) sources, the extended AGN-powered sources and extended flat-spectrum sources. The extended flat-spectrum sources include a local thermal emitting population of high-latitude planetary nebulae and also gravitational lens and binary black hole candidates among the AGNs. We find a smooth transition in properties between the CSS sources and the AGN populations. The visibility catalogue, together with the main AT20G survey, provides an estimate of angular size scales for sources in the AT20G and an estimate of the flux arising from central cores of extended radio sources. The identification of the compact AGNs in the AT20G survey provides high-quality calibrators for high-frequency radio telescope arrays and very large baseline interferometry observations.

Description: Photometric instruments operating at far-infrared to millimetre wavelengths often have broad spectral passbands (/ ~ 3 or less), especially those operating in space. A broad passband can result in significant variation of the beam profile and aperture efficiency across the passband, effects which thus far have not generally been taken into account in the flux calibration of such instruments. With absolute calibration uncertainties associated with the brightness of primary calibration standards now in the region of 5 per cent or less, variation of the beam properties across the passband can be a significant contributor to the overall calibration accuracy for extended emission. We present a calibration framework which takes such variations into account for both antenna-coupled and absorber-coupled focal plane architectures. The scheme covers point source and extended source cases, and also the intermediate case of a semi-extended source profile. We apply the new method to the Spectral and Photometric Imaging Receiver (SPIRE) photometer on board the Herschel Space Observatory.

Description: Recent simulation work has successfully captured the formation of the star clusters that have been observed in merging galaxies. These studies, however, tend to focus on studying extreme starbursts, such as the Antennae galaxies. We aim to establish whether there is something special occurring in these extreme systems or whether the mechanism for cluster formation is present in all mergers to a greater or lesser degree. We undertake a general study of merger-induced star formation in a sample of 5 pc resolution adaptive mesh refinement simulations of low-redshift equal-mass mergers with randomly chosen orbital parameters. We find that there is an enhanced mass fraction of very dense gas that appears as the gas density probability density function evolves during the merger. This finding has implications for the interpretation of some observations; a larger mass fraction of dense gas could account for the enhanced HCN/CO ratios seen in ultraluminous infrared galaxies and predict that α CO is lower in mergers, as for a given mass of H 2 , CO emission will increase in a denser environment. We also find that as the star formation rate increases, there is a correlated peak in the velocity dispersion of the gas, which we attribute to increasing turbulence driven by the interaction itself. Star formation tends to be clumpy: in some cases there is extended clumpy star formation, but even when star formation is concentrated within the inner kpc (i.e. what may be considered a nuclear starburst) it still often has a clumpy, rather than a smooth, distribution. We find no strong evidence for a clear bimodality in the Kennicutt–Schmidt relation for the average mergers simulated here. Instead, they are typically somewhat offset above the predicted quiescent relation during their starbursts.

Description: Simulations of the formation of galaxies, as well as ionization models used to interpret observations of quasar absorption lines, generally either assume ionization equilibrium or ignore the presence of the extragalactic background (EGB) radiation. We introduce a method to compute the non-equilibrium ionization and cooling of diffuse gas exposed to the EGB. Our method iterates the ionization states of the 11 elements that dominate the cooling (H, He, C, N, O, Ne, Si, Mg, S, Ca and Fe) and uses tabulated ion-by-ion cooling and photo-heating efficiencies to update the temperature of the gas. Our reaction network includes radiative and di-electric recombination, collisional ionization, photoionization, Auger ionization and charge transfer. We verify that our method reproduces published results for collisional equilibrium, collisional non-equilibrium and photoionized equilibrium. Non-equilibrium effects can become very important in cooling gas, particularly below 10 6 K. Photoionization and non-equilibrium effects both tend to boost the degree of ionization and to reduce cooling efficiencies. The effect of the EGB is larger for lower densities (i.e. higher ionization parameters). Hence, photoionization affects (equilibrium and non-equilibrium) cooling more under isochoric than under isobaric conditions. Non-equilibrium effects are smaller in the presence of the EGB and are thus overestimated when using collisional-only processes. The inclusion of the EGB alters the observational diagnostics of diffuse, metal-enriched gas (e.g. metal absorption lines probed in quasar sight lines) even more significantly than the cooling efficiencies. We argue that the cooling efficiency should be considered if ionization models are used to infer physical conditions from observed line ratios, as the a priori probability of observing gas is lower if its cooling time is shorter. We provide online tables of ionization fractions and cooling efficiencies, as well as other data, for equilibrium and non-equilibrium scenarios, and both with and without an EGB. Cooling efficiencies and diagnostics of the physical state of diffuse gas can become highly inaccurate if ionization equilibrium is assumed or if the existence of the ionizing background is ignored.

Description: All models for the formation of multiple populations in globular clusters (GCs) imply an initial mass of the systems several times greater than the present mass. A recent study of the dwarf spheroidal galaxy Fornax, where the low-metallicity ([Fe/H]  –2) stars contained in GCs appear to account for ~20 per cent of the total number, seems to constrain the initial mass of the four low-metallicity GCs in Fornax to be at most a factor of 5–6 greater than their present mass. We examine the photometric data for Fornax clusters, focusing our attention on their horizontal branch (HB) colour distribution and, when available, on the fraction and period distribution of RR Lyrae variables. Based on our understanding of the HB morphology in terms of varying helium content (and red giant mass-loss rate) in the context of multiple stellar generations, we show that the clusters F2, F3 and F5 must contain substantial fractions of second-generation stars (~54–65 per cent). On the basis of a simple chemical evolution model we show that the helium distribution in these clusters can be reproduced by models with cluster initial masses ranging from values equal to ~4 to ~10 times greater than the current masses. Models with a very short second-generation star formation episode can also reproduce the observed helium distribution but require greater initial masses up to about 20 times the current mass. While the lower limit of this range of possible initial GC masses is consistent with those suggested by observations of the low-metallicity field stars, we also discuss the possibility that the metallicity scale of field stars (based on Ca  ii triplet spectroscopy) and the metallicities derived for the clusters in Fornax may not be consistent with each other. In this case, observational constraints would allow greater initial cluster masses. Two interesting hypotheses are needed in order to reproduce the HB morphology of the clusters F2, F3 and F5. (i) The first-generation HB stars all lie at ‘red’ colours; that is, they populate only the RR Lyraes and the red HB region. According to this interpretation, the low-metallicity stars in the field of Fornax, populating the HB at colours bluer than the blue side [( V – I ) 0 0.3 or ( B – V ) 0 0.2] of the RR Lyraes, should be second-generation stars born in the clusters. A preliminary analysis of available colour surveys of Fornax field provides a fraction ~20 per cent of blue HB stars, in the low-metallicity range. (ii) The mass loss from individual second-generation red giants is a few per cent of a solar mass larger than the mass loss from first-generation stars.

Description: We have used medium-resolution spectra to search for evidence that proto-stellar objects accrete at high rates during their early ‘assembly phase’. Models predict that depleted lithium and reduced luminosity in T-Tauri stars are key signatures of ‘cold’ high-rate accretion occurring early in a star's evolution. We found no evidence in 168 stars in NGC 2264 and the Orion nebula cluster for strong lithium depletion through analysis of veiling-corrected 6708 Å lithium spectral line strengths. This suggests that ‘cold’ accretion at high rates ( M ≥ 5 x 10 –4 M  yr –1 ) occurs in the assembly phase of fewer than 0.5 per cent of 0.3 ≤ M *  ≤ 1.9 M stars. We also find that the dispersion in the strength of the 6708 Å lithium line might imply an age spread that is similar in magnitude to the apparent age spread implied by the luminosity dispersion seen in colour–magnitude diagrams. Evidence for weak lithium depletion (〈10 per cent in equivalent width) that is correlated with luminosity is also apparent, but we are unable to determine whether age spreads or accretion at rates less than 5  x 10 –4 M  yr –1 are responsible.

Description: We report CCD V and I time series photometry of the globular cluster NGC 6333 (M9). The technique of difference image analysis has been used, which enables photometric precision better than 0.05 mag for stars brighter than V ~ 19.0 mag, even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RRc stars, three eclipsing binaries, seven long-term variables and one field RRab star behind the cluster. A detailed identification chart and equatorial coordinates are given for all the variable stars in the field of our images of the cluster. Our data together with the literature V -data obtained in 1994 and 1995 allowed us to refine considerably the periods for all RR Lyrae stars. The nature of the new variables is discussed. We argue that variable V12 is a cluster member and an Anomalous Cepheid. Secular period variations, double-mode pulsations and/or the Blazhko-like modulations in some RRc variables are addressed. Through the light-curve Fourier decomposition of 12 RR Lyrae stars we have calculated a mean metallicity of [Fe/H] ZW = –1.70 ± 0.01(statistical) ± 0.14(systematic) or $[\mathrm{Fe/H}]_{\text{UVES}}=-1.67 \pm 0.01{\rm (statistical)} \pm 0.19{\rm (systematic)}$ . Absolute magnitudes, radii and masses are also estimated for the RR Lyrae stars. A detailed search for SX Phe stars in the Blue Straggler region was conducted but none were discovered. If SX Phe exist in the cluster then their amplitudes must be smaller than the detection limit of our photometry. The colour–magnitude diagram has been corrected for heavy differential reddening using the detailed extinction map of the cluster of Alonso-García et al. This has allowed us to set the mean cluster distance from two independent estimates; from the RRab and RRc absolute magnitudes, we find 8.04 ± 0.19 and 7.88 ± 0.30 kpc, respectively.

Description: Nuclear stellar cusps are defined as central excess light component in the stellar light profiles of galaxies and are suggested to be stellar relics of intense compact starbursts in the central ~100–500 pc region of gas-rich major mergers. Here, we probe the build-up of nuclear cusps during the actual starburst phase for a complete sample of luminous infrared galaxy (LIRG) systems (85 LIRGs, with 11.4 〈 log [ L IR /L ] 〈 12.5) in the Great Observatories All-sky LIRG Survey sample. Cusp properties are derived via 2D fitting of the nuclear stellar light imaged in the near-infrared (NIR) by the Hubble Space Telescope and have been combined with mid-infrared (IR) diagnostics for active galactic nucleus (AGN)/starburst characterization. We find that nuclear stellar cusps are resolved in 76 per cent of LIRGs (merger and non-interacting galaxies). The cusp strength and luminosity increase with far-IR luminosity (excluding AGN) and merger stage, confirming theoretical models that starburst activity is associated with the build-up of nuclear stellar cusps. Evidence for ultracompact nuclear starbursts is found in ~13 per cent of LIRGs, which have a strong unresolved central NIR light component but no significant contribution of an AGN. The nuclear NIR surface density (measured within 1 kpc radius) increases by a factor of ~5 towards late merger stages. A careful comparison to local early-type galaxies with comparable masses reveals (a) that local (U)LIRGs have a significantly larger cusp fraction and (b) that the majority of the cusp LIRGs have host galaxy luminosities ( H band) similar to core ellipticals which are roughly one order in magnitude larger than those for cusp ellipticals.

Description: We derive an M BH - relation between supermassive black hole mass and stellar velocity dispersion in galaxy bulges that results from self-regulated, energy-conserving feedback. The relation is of the form M BH v w   5 , where v w is the velocity of the wind driven by the black hole. We take a sample of quiescent early-type galaxies and bulges with measured black hole masses and velocity dispersions and use our model to infer the wind speeds they would have had during an active phase. This approach, in effect, translates the scatter in the observed M BH - relation into a distribution of v w . There are some remarkable similarities between the distributions of black hole wind speeds that we obtain and the distributions of outflow speeds observed in local active galactic nuclei, including a comparable median of v w  = 0.035 c .

Description: We study the properties of the straight segments forming in N -body simulations of the galactic discs. The properties of these features are consistent with the observational ones summarized by Chernin et al. Unlike some previous suggestions to explain the straight segments as gas dynamical instabilities, they form in our models in the stellar system. We suggest that the straight segments are forming as a response of the rotating disc to a gravity of the regions of enhanced density (overdensities) corotating with the disc. The kinematics of stars near the prominent overdensities is consistent with this hypothesis.