We present the discovery of a unique Lyman-continuum (LyC) emitter at z = 3.088. The LyC emission was detected using the Hubble Space Telescope WFC3/UVIS F336W filter, covering a rest-frame wavelength range of 760-900 & Aring;. The peak signal-to-noise ratio of LyC emission is 3.9 in an r = 0.'' 24 aperture and is spatially offset by 0.'' 29 +/- 0.'' 04 (similar to 2.2 +/- 0.3 kpc) from the peak of rest-UV emission (F606W). By combining imaging and spectroscopic data from the James Webb Space Telescope (JWST) JADES, FRESCO, and JEMS surveys, along with VLT/MUSE data from the MXDF survey, we estimate that the probability of random alignment with an interloper galaxy causing the LyC emission is less than 6 x 10(-5). The interstellar medium (ISM) conditions in the galaxy are similar to those in other LyC emitters at high redshift (12 + log(O/H) = 7.79(-0.05)(+0.06), log U = -3.27(-0.12)(+0.14), O32 = 0.63 +/- 0.03), although the single-peaked Ly alpha profile and lack of rest-UV emission lines suggest an optically thick ISM. Our observations indicate that LyC photons are leaking through a narrow cone of optically thin neutral ISM, most likely created by a past merger (as evidenced by medium-band F210M and F182M images). Using the constraints on escape fraction from individual leakers and a simple model, we estimate that the opening half-angle of ionization cones can be as small as 16 degrees (2% ionized fraction) to reproduce some of the theoretical constraints on the average escape fraction for galaxies. The narrow opening angle required can explain the low number density of confirmed LyC leakers.

The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of $36 \times12$-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky ($-90^{\circ} < \delta< +30^{\circ}$) to a redshift of $z \lesssim0.26$, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam−1 per 4 km s−1 channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of $z \sim0.05$ (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

We present the first results of our pilot study of eight photometrically selected Lyman-continuum (LyC) emitting galaxy candidates from the COSMOS field and focus on their optical emission line ratios. Observations were performed in the II and K bands using the Multi-Object Spectrometer for Infra-Red Exploration (MOSHRE) instrument at the Keck Observatory, targeting the [O II], H beta, and [O III] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [O III]/[O II] ratios (O32), with an average ratio for our sample of 2.5 +/- 0.2. Preliminary results of our companion Low-Resolution Imaging Spectrometer (LRIS) observations, targeting LyC and Ly alpha, show that those galaxies with the largest O32 arc typically found to also be Ly alpha emitters. High O32 galaxies are also found to have tentative non-zero LyC escape fractions (f(esc) (LyC)) based on u band photometric detections. These results are consistent with samples of highly ionized galaxies, including confirmed LyC emitting galaxies from the literature. We also perform a detailed comparison between the observed emission line ratios and simulated line ratios from density bounded H II regions modelled using the photoionization code MAPPINGS V. Estimates of f(esc) (LyC) for our sample fall in the range from 0.0 to 0.23 and suggest possible tension with published correlations between O32 and f(esc),(LyC), adding weight to dichotomy of arguments in the literature. We highlight the possible effects of clumpy geometry and mergers that may account for such tension.

For the first time both H alpha and far-ultraviolet (FUV) observations from an HI-selected sample are used to determine the dust-corrected star formation rate density (SFRD: (rho)over dot) in the local Universe. Applying the two star formation rate indicators on 294 local galaxies, we determine log((rho)over dotH alpha) = -1.68(-0.05)(+0.13) [M(circle dot)yr(-1) Mpc(-3)] and log((rho)over dotFUV) = -1.71(-0.13)(+0.12) [M-circle dot yr(-1) Mpc(-3)]. These values are derived from scaling H alpha and FUV observations to the HI mass function. Galaxies were selected to uniformly sample the full HI mass (M-HI) range of the HI Parkes All-Sky Survey (M-HI similar to 10(7) to similar to 10(10.7) M-circle dot). The approach leads to relatively larger sampling of dwarf galaxies compared to optically selected surveys. The low HI mass, low luminosity, and low surface brightness galaxy populations have, on average, lower H alpha/FUV flux ratios than the remaining galaxy populations, consistent with the earlier results of Meurer. The near-identical H alpha-and FUV-derived SFRD values arise with the low H alpha/FUV flux ratios of some galaxies being offset by enhanced H alpha from the brightest and high mass galaxy populations. Our findings confirm the necessity to fully sample the HI mass range for a complete census of local star formation to include lower stellar mass galaxies which dominate the local Universe.

We present a theoretical study of intergalactic metal absorption lines imprinted in the spectra of distant quasars during and after the Epoch of Reionization (EoR). We use high-resolution hydrodynamical simulations at high redshift (4 < z < 8), assuming a uniform UV background Haardt-Madau 12, post-processing with CLOUDY photoionization models and Voigt profile fitting to accurately calculate column densities of the ions C II, C IV, Si II, Si IV and OI in the intergalactic medium (IGM). In addition, we generate mock observations of neutral hydrogen (H I) at z < 6. Our simulations successfully reproduce the evolution of the cosmological mass density (Omega) of CII and C IV, with Omega(CII) exceeding Omega(CIV) at z > 6, consistent with the current picture of the tail of the EoR. The simulated C II exhibits a bimodal distribution with large absorptions in and around galaxies, and some traces in the lower density IGM. We find some discrepancies between the observed and simulated column density relationships among different ionic species at z = 6, probably due to uncertainties in the assumed UV background. Finally, our simulations are in good agreement with observations of the HI column density distribution function at z = 4 and the HI cosmological mass density Omega(HI) at 4 < z < 6.

We identify gravitationally bound structures in the Ursa Major region using positions, velocities and photometry from the Sloan Digital Sky Survey (SDSS DR7) and the Third Reference Catalogue of Bright Galaxies (RC3). A friends-of-friends algorithm is extensively tested on mock galaxy lightcones and then implemented on the real data to determine galaxy groups whose members are likely to be physically and dynamically associated with one another. We find several galaxy groups within the region that are likely bound to one another and in the process of merging. We classify 6 galaxy groups as the Ursa Major `supergroup', which are likely to merge and form a poor cluster with a mass of ~8x10^13 Msun. Furthermore, the Ursa Major supergroup as a whole is likely bound to the Virgo cluster, which will eventually form an even larger system in the context of hierarchical structure formation. [abridged]

Lyman break galaxies (LBGs) at z ~ 3-4 are targeted to measure the fraction of Lyman continuum (LyC) flux that escapes from high redshift galaxies. However, z ~ 3-4 LBGs are identified using the Lyman break technique which preferentially selects galaxies with little or no LyC. We re-examine the standard LBG selection criteria by performing spectrophotometry on composite spectra constructed from 794 U_nGR-selected z ~ 3 LBGs from the literature while adding LyC flux of varying strengths. The modified composite spectra accurately predict the range of redshifts, properties, and LyC flux of LBGs in the literature that have spectroscopic LyC measurements while predicting the existence of a significant fraction of galaxies outside the standard selection region. These galaxies, termed Lyman continuum galaxies (LCGs), are expected to have high levels of LyC flux and are estimated to have a number density ~30-50 percent that of the LBG population. We define R_obs(U_n) as the relative fraction of observed LyC flux, integrated from 912A to the shortest restframe wavelength probed by the U_n filter, to the observed non-ionising flux (here measured at 1500A). We use the 794 spectra as a statistical sample for the full z ~ 3 LBG population, and find R_obs(U_n) = 5.0 +1.0/-0.4 (4.1 +0.5/-0.3) percent, which corresponds to an intrinsic LyC escape fraction of f_esc = 10.5 +2.0/-0.8 (8.6 +1.0/-0.6) percent (contamination corrected). From the composite spectral distributions we estimate R_obs(U_n) ~16 +/-3, f_esc ~33 +/-7 percent for LCGs and R_obs(U_n) ~8 +/-3, f_esc ~16 +/-4 percent for the combined LBG + LCG z ~ 3 sample. All values are measured in apertures defined by the UV continuum and do not include extended and/or offset LyC flux. A complete high redshift galaxy census and total emergent LyC flux is essential to quantify the contribution of galaxies to the epoch of reionisation.

We examine the effects of magnitude, colour and Ly alpha equivalent width (EW) on the spatial distribution of z similar to 3 Lyman break galaxies (LBGs) and report significant differences in the two-point autocorrelation functions. The results are obtained using samples of similar to 10 000-55 000 LBGs from the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. We find that magnitude has a larger effect on the autocorrelation function amplitude on small scales (less than or similar to 1 h(70)(-1) Mpc, the one-halo term) and that colour is more influential on large scales (greater than or similar to 1 h(70)(-1) Mpc, the two-halo term). We find the most significant differences between autocorrelation functions for LBGs with dominant net Ly alpha EW in absorption (aLBGs) and dominant net Ly alpha EW in emission (eLBGs) determined from greater than or similar to 95 per cent pure samples of each population using a photometric technique calibrated from similar to 1000 spectra. The aLBG autocorrelation function has a higher two-halo amplitude than the full LBG sample and has a one-halo term departure from a power-law fit near similar to 1 h(70)(-1) Mpc, corresponding to the virial radii of M-DM similar to 10(13) M-circle dot dark matter haloes. In contrast, the eLBG autocorrelation function has a one-halo term departure at similar to 0.12 h(70)(-1) Mpc, suggesting parent haloes of M-DM similar to 10(11) M-circle dot and a two-halo term that exhibits a curious 'hump' on intermediate scales that we localize to the faintest, bluest members. The aLBG-eLBG cross-correlation function exhibits an anticorrelation component that reinforces different physical locations for a significant fraction of aLBGs and eLBGs. We introduce a 'shell' model for the eLBG autocorrelation function and find that the form can be reproduced assuming that a significant fraction of eLBGs have a shell-like spatial distribution. Based on the analysis of all LBG subsamples, and considering the natural asymmetric distribution of LBGs on the colour-magnitude diagram, we conclude that aLBGs are more likely to reside in group-like environments hosting multiple luminous (i(') < 26.4) LBGs whereas eLBGs are more likely to be found on group outskirts and in the field. Because Ly alpha is a tracer of several intrinsic properties, including morphology, the results presented here imply that the mechanisms behind the morphology-density relation at low redshift are in place at z similar to 3 and that Ly alpha EW may be a key environment diagnostic. Finally, our results show that the LBG autocorrelation function amplitude is lower than the true average as a result of the spatial anticorrelation of the spectral types. This result holds broad consequences for all autocorrelation functions measured for any population that contains members residing in different environments as the average amplitude, and hence the inferred average dark matter mass, will always be underestimated.

We present the results of a deep, near-infrared, narrow-band imaging survey at a central wavelength of 1.062 mu m (FWHM = 0.01 mu m) in the GOODS-South field using the ESO VLT instrument, HAWK-I. The data are used to carry out the highest redshift search for [O ii] lambda 3727 A emission line galaxies to date. The images reach an emission line flux limit (5 Sigma) of 1.5 x 10-17 erg cm-2 s-1, additionally making the survey the deepest of its kind at high redshift. In this paper we identify a sample of [O ii] lambda 3727 A emission line objects at redshift z similar to 1.85 in a comoving volume of similar to 4100 Mpc-3. Objects are selected using an observed equivalent width (EWobs) threshold of EWobs > 50A. The sample is used to derive the space density and constrain the luminosity function of [O ii] emitters at z = 1.85. We find that the space density () of objects with observed [O ii] luminosities in the range is log() = -2.45 +/- 0.14 Mpc-3, a factor of 2 greater than the observed space density of [O ii] emitters reported at z similar to 1.4. After accounting for completeness and assuming an internal extinction correction of A(H alpha) = 1 mag (equivalent to = 1.87), we report a star formation rate density of M-circle dot yr-1 Mpc-3. We independently derive the dust extinction of the sample using 24-mu m fluxes and find a mean extinction of magnitudes (A(H alpha) = 0.52). This is significantly lower than the A(H alpha) = 1 ( = 1.86) mag value widely used in the literature. Finally, we incorporate this improved extinction correction into the star formation rate density measurement and report M-circle dot yr-1 Mpc-3.

We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha measurements for star forming regions in 21 galaxies, in order to characterise the properties of their discs at radii beyond the main optical radius (R25). In our representative sample of extended and non-extended UV discs we find that half of the extended UV discs also exhibit extended Halpha emission. We find that extended UV discs fall into two categories, those with a sharp truncation in the Halpha disc close to the optical edge (R25), and those with extended emission in Halpha as well as in the ultraviolet. Although most galaxies with strong Halpha truncations near R25 show a significant corresponding falloff in UV emission (factor 10--100), the transition tends to be much smoother than in Halpha, and significant UV emission often extends well beyond this radius, confirming earlier results by Thilker et al. (2007) and others. After correcting for dust attenuation the median fraction of total FUV emission from regions outside of R25 is 1.7%, but it can be as high as 35% in the most extreme cases. The corresponding fractions of Halpha emission are approximately half as large on average. This difference reflects both a slightly lower ratio of Halpha to UV emission in the HII regions in the outer discs, as well as a lower fraction of star clusters showing HII regions. Most HII regions in the extended disc have fluxes consistent with small numbers of ionising O-type stars, and this poor sampling of the upper initial mass function in small clusters can probably account for the differences in the emission properties, consistent with earlier conclusions by Zaritsky & Christlein (2007), without needing to invoke a significant change in the stellar IMF itself. Consistent Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and extended discs across our whole galaxy sample demonstrate no evidence for a change in the cluster luminosity function or the IMF in the low gas density outer disc.

Many results in modern astrophysics rest on the notion that the Initial Mass Function (IMF) is universal. Our observations of HI selected galaxies in the light of H-alpha and the far-ultraviolet (FUV) challenge this notion. The flux ratio H-alpha/FUV from these two star formation tracers shows strong correlations with the surface-brightness in H-alpha and the R band: Low Surface Brightness (LSB) galaxies have lower ratios compared to High Surface Brightness galaxies and to expectations from equilibrium star formation models using commonly favored IMF parameters. Weaker but significant correlations of H-alpha/FUV with luminosity, rotational velocity and dynamical mass are found as well as a systematic trend with morphology. The correlated variations of H-alpha/FUV with other global parameters are thus part of the larger family of galaxy scaling relations. The H-alpha/FUV correlations can not be due to dust correction errors, while systematic variations in the star formation history can not explain the trends with both H-alpha and R surface brightness. LSB galaxies are unlikely to have a higher escape fraction of ionizing photons considering their high gas fraction, and color-magnitude diagrams. The most plausible explanation for the correlations are systematic variations of the upper mass limit and/or slope of the IMF at the upper end. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars form. Our results imply that the star formation rate measured in a galaxy is highly sensitive to the tracer used in the measurement. A non-universal IMF also calls into question the interpretation of metal abundance patterns in dwarf galaxies and star formation histories derived from color magnitude diagrams. Abridged.

The H I Parkes all-sky survey (HIPASS) galaxy catalogue is cross-correlated with known low redshift, low column density (N-H < 10(15) cm(-2)) Lyman alpha (Ly alpha) absorbers from the literature. The redshift-space correlation is found to be similar in strength to HIPASS galaxy self-clustering (correlation length s(0,ag)= 6 +/- 4 h(100)(-1) Mpc and s(0,gg)= 3.1 +/- 0.5 h(100)(-1) Mpc, respectively). In real space the cross-correlation is stronger than the galaxy auto-correlation (correlation length r(0,ag)= 7.2 +/- 1.4 h(100)(-1) Mpc and r(0,gg)= 3.5 +/- 0.7 h(100)(-1) Mpc, respectively) on scales from 1 to 10 h(100)(-1) Mpc, ruling out the minihalo model for the confinement Ly alpha absorbers at the 99 per cent confidence level. Provided that the cause of the strong cross-correlation is purely gravitational, the ratio of correlation lengths suggest that absorbers are embedded in dark matter haloes with masses log(M/M-circle dot) = 14.2 h(100)(-1), similar to those of galaxy groups. The flattening of the cross-correlation at separations less than similar to 600 h(100)(-1) kpc could correspond to the thickness of filaments in which absorbers are embedded. This work provides indirect statistical evidence for the notion that galaxy groups and large-scale filaments, particularly those that comprise gas-rich galaxies, are the dominant environments of low column density Ly alpha absorbers at z = 0.

AbstractIntergalactic HII regions, far from the confines of a galactic disk, represent a mode of star formation in low-density gas outside of galaxies. The figure below (left) shows an R-band continuum image of NGC 1533 from the SINGG Hα survey (Meurer et al. 2006) overlaid with HI contours and the location of three intergalactic HII regions discovered by Ryan-Weber et al. (2004). The HI contours are 1.6, 2.0, 2.4, 2.8, 3.2 and 4.0 ×1020 cm−2 and have a resolution of ~1′. ACS/HRC images of the intergalactic HII regions (right) are composites of UV, V, and I bands. The half-light radii of the clusters associated with regions 1, 2, and 5 are 24.7, 21.7, and 17.0 pc, respectively, at the distance to NGC 1533 (21 Mpc; Tonry et al. 2001). Assuming a Salpeter IMF with Mup = 100, Hα/UV ratios indicate a small number of ionizing O stars relative to the total number of UV-emitting O and B stars. These young (4-6 Myr), intergalactic stellar populations lend valuable insight to our understanding of the methods by which star formation is triggered and may even represent the first episodes of star formation in emerging galaxies.

We have found the peculiar galaxy NGC 922 to be a new drop-through ring galaxy using multiwavelength (ultraviolet-radio) imaging and spectroscopic observations. Its 'C'-shaped morphology and tidal plume indicate a recent strong interaction with its companion which was identified with these observations. Using numerical simulations we demonstrate that the main properties of the system can be generated by a high-speed off-axis drop-through collision of a small galaxy with a larger disc system, thus making NGC 922 one of the nearest known collisional ring galaxies. While these systems are rare in the local Universe, recent deep Hubble Space Telescope images suggest they were more common in the early Universe.

We derive observed H alpha and R-band luminosity densities of an H I-selected sample of nearby galaxies using the SINGG sample to be l'(H alpha) = (9.4 +/- 1.8) x 10(38) h(70) ergs s(-1) Mpc(-3) for H alpha and l'(R) = (4.4 +/- 9.7) x 10(37) h(70) ergs s(-1) angstrom(-1) Mpc(-3) in the R band. This R-band luminosity density is approximately 70% of that found by the Sloan Digital Sky Survey. This leads to a local star formation rate density of log ((rho)over dot(SFR) [M-circle dot yr(-1) Mpc(-3)]) = -1.80(-0.07)(+0.13)(random) +/- 0.03(systematic) + log (h(70)) after applying a mean internal extinction correction of 0.82 mag. The gas cycling time of this sample is found to be t(gas) = 7.5(-2.1)(+1.3) Gyr, and the volume-averaged equivalent width of the SINGG galaxies is EW(H alpha) = 28.8(-4.7)(+7.2) angstrom (21.2-3.5+4.2 angstrom without internal dust correction). As with similar surveys, these results imply that (rho)over dot(SFR)(z) decreases drastically from z similar to 1.5 to the present. A comparison of the dynamical masses of the SINGG galaxies evaluated at their optical limits with their stellar and H I masses shows significant evidence of downsizing: the most massive galaxies have a larger fraction of their mass locked up in stars compared with H I, while the opposite is true for less massive galaxies. We show that the application of the Kennicutt star formation law to a galaxy having the median orbital time at the optical limit of this sample results in a star formation rate decay with cosmic time similar to that given by the. (rho)over dot(SFR)(z) evolution. This implies that the (rho)over dot(SFR)(z) evolution is primarily due to the secular evolution of galaxies, rather than interactions or mergers. This is consistent with the morphologies predominantly seen in the SINGG sample.

We calculate in detail the expected properties of low redshift DLAs under the assumption that they arise in the gaseous disks of galaxies like those in the to the present time. We conclude that the local galaxy population can explain all properties of low redshift DLAs.

A comprehensive analysis of 355 high-quality Westerbork Synthesis Radio Telescope (WSRT) HI 21-cm line maps of nearby galaxies shows that the properties and incident rate of damped Lyman alpha absorption systems (DLAs) observed in the spectra of high-redshift QSOs are in good agreement with DLAs originating in gas discs of galaxies like those in the z approximate to 0 population. Comparison of low-z DLA statistics with the HI incidence rate and column density distribution f(N (HI)) for the local galaxy sample shows no evidence for evolution in the integral 'cross-section density' = l(-1) (l = mean free path between absorbers) below z approximate to 1.5, implying that there is no need for a hidden population of galaxies or H I clouds to contribute significantly to the DLA cross-section. Compared with z approximate to 4, our data indicate evolution of a factor of 2 in the comoving density along a line of sight. We find that dN/dz(z = 0) = 0.045 +/- 0.006. The idea that the local galaxy population can explain the DLAs is further strengthened by comparing the properties of DLAs and DLA galaxies with the expectations based on our analysis of local galaxies. The distribution of luminosities of DLA host galaxies, and of impact parameters between QSOs and the centres of DLA galaxies, is in good agreement with what is expected from local galaxies. Approximately 87 per cent of low-z DLA galaxies are expected to be fainter than L-*, and 37 per cent have impact parameters less than 1 arcsec at z = 0.5. The analysis shows that some host galaxies with very low impact parameters and low luminosities are expected to be missed in optical follow-up surveys. The well-known metallicity-luminosity relation in galaxies, in combination with metallicity gradients in galaxy discs, causes the expected median metallicity of low-z DLAs to be low (similar to 1/7 solar), which is also in good agreement with observations of low-z DLAs. We find that f(N H I) can be fitted satisfactorily with a gamma distribution, a single power law is not a good fit at the highest column densities N H I > 10(21) cm(-2). The vast majority (approximate to 81 per cent) of the H I gas in the local Universe resides in column densities above the classical DLA limit (N (H I) > 2 x 10(20) cm(-2)), with N (H I) similar to 10(21) cm(-2) dominating the cosmic H I mass density.

We have investigated the effect of spatial resolution on determining pencil-beam-like velocity widths and column densities in galaxies. Three 21-cm data sets are used, the H i Parkes All Sky Survey (HIPASS) galaxy catalogue, a subset of HIPASS galaxies with Australia Telescope Compact Array maps and a high-resolution image of the Large Magellanic Cloud. Velocity widths measured from 21-cm emission in local galaxies are compared with those measured in intermediate-redshift damped Lyman α (DLA) absorbers. We conclude that spatial resolution has a severe effect on measuring pencil-beam like velocity widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase the median velocity width by a factor of 2. Thus any difference between velocity widths measured from global profiles or low spatial resolution 21-cm maps at z= 0 and DLAs at z > 1 cannot unambiguously be attributed to galaxy evolution. The effect on column density measurements is less severe and the values of dNDLA/dz from local low-resolution 21-cm measurements are expected to be overestimated by only ∼10 per cent.