Testing the pressure-confined Ly alpha cloud model

The Ly-alpha absorption line forest, seen in quasar spectra, is generally interpreted as being due to cosmologically distributed 'clouds' of primordial gas. Analyses of the observations reveal that the number distribution can be described by power laws: dN/dz is proportional to (1 + z)(sup gamma) and dN/dN(sub HI) is proportional to N(sub HI)(sup -beyda), where N(sub HI) is the HI column density. The typical values for power law indices range between 2 is approximately less than gamma is approximately less than 2.6 and 1.7 is approximately less than gamma is approximately less than 1.9. One model postulates that the Ly-alpha clouds are optically thin entities, photoionized by the background UV flux, J(sub nu) is proportional to (1 + z)(sup j), and confined by an adiabatically evolving intercloud medium (ICM): P(z) is proportional to (1 + z)(sup 5). Analytic studies of this model suggest that the ensuing Ly-alpha line statistics can account for the observations (in particular, the dN/dz and the dN/dN(sub HI) distributions) if the cloud mass spectrum is a power law dN/dN is proportional to M(sup -delta), delta is approximately 1.9, and j is approximately 4. One of the simplifying assumptions incorporated into these studies is the existence of a large mass range for the clouds at all epochs, the validity of which is questionable. The pressure-confined model is investigated using a 1-D spherically symmetric hydrodynamical code to simulate cloud evolution over the epoch 1.8 less than z less than 6. This enables us to relax many of the assumptions incorporated in the analytic studies

Low-Metallicity Gas Clouds in a Galaxy Proto-Cluster at Redshift 2.38

We present high resolution spectroscopy of a QSO whose sight-line passes through the halo of a pair of elliptical galaxies at redshift 2.38. This pair of galaxies probably lies at the center of a galaxy proto-cluster, and is embedded in a luminous extended Ly-alpha nebula. The QSO sight-line intersects two small gas clouds within this halo. These clouds have properties similar to those of high velocity clouds (HVCs) seen in the halo of the Milky Way. The gas is in a cool (< 2 x 10^4 K) and at least 20% neutral phase, with metallicities in the range -3.0 < [Fe/H] < -1.1 and neutral hydrogen column densities of ~10^19.5 /cm^2. The origin of these clouds is unclear. The presence of low metallicity gas within this possible proto-cluster implies either that the intra-cluster medium has not been enriched with metals at this redshift, or the clouds are embedded within a hot, ionized, metal-rich gas phase.Comment: Accepted to appear in ApJ Letter

The Distribution of Lya-Emitting Galaxies at z=2.3

We present the detection of 34 Ly-alpha emission-line galaxy candidates in a 80x80x60 co-moving Mpc region surrounding the known z=2.38 galaxy cluster J2143-4423. The space density of Ly-alpha emitters is comparable to that found by Steidel et al. when targeting a cluster at redshift 3.09, but is a factor of 5.8 +/- 2.5 greater than that found by field samples at similar redshifts. The distribution of these galaxy candidates contains several 5-10 Mpc scale voids. We compare our observations with mock catalogs derived from the VIRGO consortium Lambda-CDM n-body simulations. Fewer than 1% of the mock catalogues contain voids as large as we observe. Our observations thus tentatively suggest that the galaxy distribution at redshift 2.38 contains larger voids than predicted by current models. Three of the candidate galaxies and one previously discovered galaxy have the large luminosities and extended morphologies of "Ly-alpha blobs".Comment: 10 pages, 8 figures, emulateapj5, Accepted for publication in Ap

Ultraviolet-Bright, High-Redshift ULIRGS

We present Spitzer Space Telescope observations of the z=2.38 lya-emitter over-density associated with galaxy cluster J2143-4423, the largest known structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within the filament-like structure, using the MIPS 24um band. We detected 6 of the lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG energies. Lya blobs frequently show evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lya cloud. This connection suggests that interaction or even mergers may be related to the production of Lya blobs. A connection to mergers does not in itself help explain the origin of the Lya blobs, as most of the suggested mechanisms for creating Lya blobs (starbursts, AGN, cooling flows) could also be associated with galaxy interactions.Comment: 12 pages, 3 figures, accepted by ApJ Letter

Polycyclic Aromatic Hydrocarbon Emission within Lyα Blobs

We present Spitzer observations of Lyα blobs (LABs) at z = 2.38-3.09. The mid-infrared ratios (4.5 μm/8 μm and 8 μm/24 μm) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGNs). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850 μm or rest-frame far-infrared) also indicates that a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with submillimeter detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of six infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^(11) M_⊙. There is a weak trend of mass upper limit with the Lyα luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs

PAH Emission Within Lyman Alpha Blobs

We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.Comment: 34 pages, 5 figures, accepted by Ap

HST Imaging of the Globular Clusters in the Fornax Cluster: NGC 1399 and NGC 1404

The Fornax cluster galaxies NGC 1399 and NGC 1404 are ideal for studying the effects of a cluster environment on globular cluster systems. Here we present new optical imaging of these two galaxies from both the Hubble Space Telescope's Wide Field and Planetary Camera 2 and the Cerro Tololo Inter-American Observatory's 1.5m telescope. The combination of both data sets provides unique insight on the spatial and colour distribution of globular clusters. From B-I colours, we find that both galaxies have a broad globular cluster metallicity distribution that is inconsistent with a single population. Two Gaussians provide a reasonable representation of the metallicity distribution in each galaxy. The metal-rich subpopulation is more centrally concentrated than the metal-poor one. We show that the radial metallicity gradient can be explained by the changing relative mix of the two globular cluster subpopulations. We derive globular cluster surface density profiles, and find that they are flatter (i.e. more extended) than the underlying starlight. The total number of globular clusters and specific frequency are calculated to be N = 5700 +/- 500, S_N = 11.5 +/- 1.0 for NGC 1399 and N = 725 +/- 145, S_N = 2.0 +/- 0.5 for NGC 1404. Our results are compared to the expectations of globular cluster formation scenarios.Comment: 21 pages, Latex, 13 figures, submitted to MNRA

Compatibility of the large quasar groups with the concordance cosmological model

We study the compatibility of large quasar groups with the concordance cosmological model. Large quasar groups are very large spatial associations of quasars in the cosmic web, with sizes of 50–250 h−1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ∼860 h−1 Mpc, larger than the scale of homogeneity (∼260 Mpc), which has been noted as a possible violation of the cosmological principle. Using mock catalogues constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 ± 1 times larger than the one currently studied

Correlated orientations of the axes of large quasar groups on Gpc scales

Abstract Correlated orientations of quasar optical and radio polarisation, and of radio jets, have been reported on Gpc scales, possibly arising from intrinsic alignment of spin axes. Optical quasar polarisation appears to be preferentially either aligned or orthogonal to the host large-scale structure, specifically large quasar groups (LQGs). Using a sample of 71 LQGs at redshifts 1.0 ≤ z ≤ 1.8, we investigate whether LQGs themselves exhibit correlated orientation. We find that LQG position angles (PAs) are unlikely to be drawn from a uniform distribution (p-values 0.008 ≲ p ≲ 0.07). The LQG PA distribution is bimodal, with median modes at $\bar{\theta }\sim 45\pm 2^{\circ }, 136\pm 2^{\circ }$, remarkably close to the mean angles of quasar radio polarisation reported in two regions coincident with our LQG sample. We quantify the degree of alignment in the PA data, and find that LQGs are aligned and orthogonal across very large scales. The maximum significance is $\simeq 0.8\%$ (2.4σ) at typical angular (proper) separations of ∼30○ (1.6 Gpc). If the LQG orientation correlation is real, it represents large-scale structure alignment over scales larger than those predicted by cosmological simulations and at least an order of magnitude larger than any so far observed, with the exception of quasar-polarisation / radio-jet alignment. We conclude that LQG alignment helps explain quasar-polarisation / radio-jet alignment, but raises challenging questions about the origin of the LQG correlation and the assumptions of the concordance cosmological model

The Distribution of Ly-alpha-Emitting Galaxies at z=2.38: Paper 2, Spectroscopy

In Paper 1 of this series we identified an 80 co-moving Mpc filament of candidate Lyman-alpha emitting galaxies at redshift 2.38. In this paper we present spectroscopy of the 37 galaxy candidates. Our spectroscopy reached a surface brightness limit of 5.0E-17 erg/cm^2/s/arcsec^2. Of the 14 candidates down to this limit, 12 were confirmed to be Lyman-alpha emitting galaxies at the filament redshift. We also obtained spectral confirmation for six of the lower surface brightness candidates, all of which also lay at the filament redshift. In addition, we identify a foreground cluster of QSOs at z=1.65.Comment: Accepted for publication in the Astrophysical Journa