ALBERT

Description: We report the discovery of an extremely long (~110 Mpc h –1 ) and dark ( eff   7) Lyα trough extending down to z ~= 5.5 towards the z em ~= 6.0 quasar ULAS J0148+0600. We use these new data in combination with Lyα forest measurements from 42 quasars at 4.5 ≤  z em  ≤ 6.4 to conduct an updated analysis of the line-of-sight variance in the intergalactic Lyα opacity over 4 ≤  z  ≤ 6. We find that the scatter in transmission among lines of sight near z  ~ 6 significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near z ~= 5.6–5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone. We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by z ~= 5.6, however, a large fraction of the data are consistent with a uniform UVB, and by z  ~ 5 the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at z  ~ 6, it has fully completed by z  ~ 5.

Description: The flow of baryons to and from a galaxy, which is fundamental for galaxy formation and evolution, can be studied with galaxy-metal absorption system pairs. Our search for galaxies around C iv absorption systems at z  ~ 5.7 showed an excess of photometric Lyman α emitter (LAE) candidates in the fields J1030+0524 and J1137+3549. Here, we present spectroscopic follow-up of 33 LAEs in both fields. In the first field, three out of the five LAEs within 10 h –1 projected comoving Mpc from the C iv system are within ±500 km s –1 from the absorption at $z_{{\rm C\,{\small iv}}}=5.7242\pm 0.0001$ . The closest candidate (LAE 103027+052419) is robustly confirmed at $212.8^{+14}_{-0.4}\;h^{-1}$ physical kpc from the C iv system. In the second field, the LAE sample is selected at a lower redshift ( z  ~ 0.04) than the C iv absorption system as a result of the filter transmission and, thus, do not trace its environment. The observed properties of LAE 103027+052419 indicate that it is near the high-mass end of the LAE distribution, probably having a large H i column density and large-scale outflows. Therefore, our results suggest that the C iv system is likely produced by a star-forming galaxy which has been injecting metals into the intergalactic medium since z  〉 6. Thus, the C iv system is either produced by LAE 103027+052419, implying that outflows can enrich larger volumes at z  〉 6 than at z  ~ 3.5, or an undetected dwarf galaxy. In either case, C iv systems like this one trace the ionized intergalactic medium at the end of cosmic hydrogen reionization and may trace the sources of the ionizing flux density.

Description: 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 $U_nG{\cal R}$ -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 per cent that of the LBG population. We define R obs ( U n ) as the relative fraction of observed LyC flux, integrated from 912 Å to the shortest rest-frame wavelength probed by the U n filter, to the observed non-ionizing flux (here measured at 1500 Å). We use the 794 spectra as a statistical sample for the full z  ~ 3 LBG population, and find ${{R_{\rm obs}(U_n)}=5.0^{+1.0}_{-0.4} (4.1^{+0.5}_{-0.3})}$  per cent, which corresponds to an intrinsic LyC escape fraction of ${{f_{\rm esc}^{\rm LyC}}=10.5^{+2.0}_{-0.8} (8.6^{+1.0}_{-0.6})}$  per cent (contamination corrected). From the composite spectral distributions we estimate ${{R_{\rm obs}(U_n)}\sim 16\pm 3,\ {f_{\rm esc}^{\rm LyC}}\sim 33\pm 7}$  per cent for LCGs and ${{R_{\rm obs}(U_n)}\sim 8\pm 3,\ {f_{\rm esc}^{\rm LyC}}\sim 16\pm 4}$  per cent for the combined LBG+LCG z  ~ 3 sample. All values are measured in apertures defined by the ultraviolet continuum and do not include extended and/or offset LyC flux. A complete galaxy census and the total emergent LyC flux at high redshift are essential to quantify the contribution of galaxies to the ionizing photon budget of the Universe, particularly during the epoch of reionization.

Description: We examine the effects of magnitude, colour and Lyα equivalent width (EW) on the spatial distribution of z  ~ 3 Lyman break galaxies (LBGs) and report significant differences in the two-point autocorrelation functions. The results are obtained using samples of ~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 (1 $h^{-1}_{70}$ Mpc, the one-halo term) and that colour is more influential on large scales (1 $h^{-1}_{70}$ Mpc, the two-halo term). We find the most significant differences between autocorrelation functions for LBGs with dominant net Lyα EW in absorption (aLBGs) and dominant net Lyα EW in emission (eLBGs) determined from 95 per cent pure samples of each population using a photometric technique calibrated from ~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 ~1 $h^{-1}_{70}$ Mpc, corresponding to the virial radii of M DM ~ 10 13 M dark matter haloes. In contrast, the eLBG autocorrelation function has a one-halo term departure at ~0.12 $h^{-1}_{70}$ Mpc, suggesting parent haloes of M DM ~ 10 11 M 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 Lyα 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  ~ 3 and that Lyα 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.

Description: Metal absorption systems are products of star formation. They are believed to be associated with massive star-forming galaxies, which have significantly enriched their surroundings. To test this idea with high column density C iv absorption systems at z  ~ 5.7, we study the projected distribution of galaxies and characterize the environment of C iv systems in two independent quasar lines of sight: J103027.01+052455.0 and J113717.73+354956.9. Using wide-field photometry (~80 60 h –1 comoving Mpc), we select bright ( M UV (1350 Å)  –21.0 mag.) Lyman break galaxies (LBGs) at z  ~ 5.7 in a redshift slice z  ~ 0.2 and we compare their projected distribution with z  ~ 5.7 narrow-band selected Lyman alpha emitters (LAEs, z  ~ 0.08). We find that the C iv systems are located more than 10  h –1 projected comoving Mpc from the main concentrations of LBGs and no candidate is closer than ~5 h –1 projected comoving Mpc. In contrast, an excess of LAEs – lower mass galaxies – is found on scales of ~10 h –1 comoving Mpc, suggesting that LAEs are the primary candidates for the source of the C iv systems. Furthermore, the closest object to the system in the field J1030+0524 is a faint LAE at a projected distance of 212 h –1 physical kpc. However, this work cannot rule out undiscovered lower mass galaxies as the origin of these absorption systems. We conclude that, in contrast with lower redshift examples ( z 3.5), strong C iv absorption systems at z  ~ 5.7 trace low-to-intermediate density environments dominated by low-mass galaxies. Moreover, the excess of LAEs associated with high levels of ionizing flux agrees with the idea that faint galaxies dominate the ionizing photon budget at this redshift.

Description: Hα observations centred on galaxies selected from the H i Parkes All-Sky Survey (H i PASS) typically show one and sometimes two star-forming galaxies within the ~15 arcmin beam of the Parkes 64 m H i detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of H i PASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in H i PASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total H i mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, Hα equivalent width and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly H i deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190 kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to H i mass), showing an increasing trend in SFE with stellar mass.

Description: We report results from a programme aimed at investigating the temperature of neutral gas in high-redshift damped Lyman α absorbers (DLAs). This involved (1) H i 21 cm absorption studies of a large sample of DLAs towards radio-loud quasars, (2) very long baseline interferometric studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and the velocity widths of low-ionization metal lines. Including literature data, our sample consists of 37 DLAs with estimates of the harmonic mean spin temperature T s . We find a statistically significant (4) difference between the T s distributions in the high- z ( z  〉 2.4) and low- z ( z  〈 2.4) DLA samples. The high- z sample contains more systems with high spin temperature, T s 1000 K. The T s distributions in DLAs and the Galaxy are also significantly (6) different, with more high- T s sightlines in DLAs than in the Milky Way. The high T s values in the high- z DLAs of our sample arise due to low fractions of the cold neutral medium (CNM). Only 2 of 23 DLAs at z  〉 1.7 have T s values indicating CNM fractions 〉20 per cent, comparable to the median value (27 per cent) in the Galaxy. We tested whether the H i column density measured towards the optical quasar might be systematically different from that towards the radio core by comparing the H i column densities inferred from H i 21 cm emission studies at different spatial resolutions (15 pc-1 kpc) in the Large Magellanic Cloud. The high-resolution N H i values are, on average, larger than the smoothed ones for N H i 〉 10 21 cm –2 , but lower than the smoothed N H i estimates for N H i 〈 10 21 cm –2 . Since there are far more DLAs with low N H i values than high ones, the use of the optical N H i value for the radio sightline results in a statistical tendency to underestimate DLA spin temperatures. For 29 DLAs with metallicity estimates, we confirm the presence of an anticorrelation between T s and metallicity [ Z /H], at 3.5 significance via a non-parametric Kendall-tau test. This result was obtained with the assumption that the DLA covering factor is equal to the core fraction. However, Monte Carlo simulations show that the significance of the result is only marginally decreased if the covering factor and the core fraction are uncorrelated, or if there is a random error in the inferred covering factor. We also find statistically significant evidence for redshift evolution in DLA spin temperatures even for the DLA sub-sample at z  〉 1. Since all DLAs at z  〉 1 have angular diameter distances comparable to or larger than those of their background quasars, they have similar efficiency in covering the quasars. We conclude that low covering factors in high- z DLAs cannot account for the observed redshift evolution in spin temperatures.

Description: We present a new optical spectroscopic survey of 1777 ‘star-forming’ (‘SF’) and 366 ‘non-star-forming’ (‘non-SF’) galaxies at redshifts z ~ 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope ( HST ) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 ‘strong’ (10 14 ≤ N H I 10 17 cm –2 ) and 496 ‘weak’ (10 13 N H I 〈 10 14 cm –2 ) intervening H i (Lyα) absorption-line systems at z 1 (669 in total), observed in the spectra of eight QSOs at z ~ 1 by the Cosmic Origins Spectrograph and the Faint Object Spectrograph on the HST . Combining these new data with previously published galaxy catalogues such as the Very Large Telescope Visible Multi-Object Spectrograph Deep Survey and the Gemini Deep Deep Survey, we have gathered a sample of 654 H i absorption systems and 17 509 galaxies at transverse scales 50 Mpc, suitable for a two-point correlation function analysis. We present observational results on the H i –galaxy ( ag ) and galaxy–galaxy ( gg ) correlations at transverse scales r 10 Mpc, and the H i –H i autocorrelation ( aa ) at transverse scales r 2 Mpc. The two-point correlation functions are measured both along and transverse to the line of sight, ( r , r || ). We also infer the shape of their corresponding ‘real-space’ correlation functions, ( r ), from the projected along the line-of-sight correlations, assuming power laws of the form ( r ) = ( r / r 0 ) – . Comparing the results from ag , gg and aa , we constrain the H i –galaxy statistical connection, as a function of both H i column density and galaxy star formation activity. Our results are consistent with the following conclusions: (i) the bulk of H i systems on ~ Mpc scales have little velocity dispersion (120 km s –1 ) with respect to the bulk of galaxies (i.e. no strong galaxy outflow/inflow signal is detected); (ii) the vast majority (~100 per cent) of ‘strong’ H i systems and ‘SF’ galaxies are distributed in the same locations, together with 75 ± 15 per cent of ‘non-SF’ galaxies, all of which typically reside in dark matter haloes of similar masses; (iii) 25 ± 15 per cent of ‘non-SF’ galaxies reside in galaxy clusters and are not correlated with ‘strong’ H i systems at scales 2 Mpc; and (iv) 〉50 per cent of ‘weak’ H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting ‘strong’ systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales 2 Mpc.