Simon P. Driver

New Upper Limit on the Total Neutrino Mass from the 2 Degree Field Galaxy Redshift Survey

We constrain f(nu) identical with Omega(nu)/Omega(m), the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2 Degree Field Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos, and a cosmological constant. Adding constraints from independent cosmological probes we find f(nu)<0.13 (at 95% confidence) for a prior of 0.1<Omega(m)<0.5, and assuming the scalar spectral index n=1. This translates to an upper limit on the total neutrino mass m(nu,tot)<1.8 eV for concordance values of Omega(m) and the Hubble constant.

Morphological number counts and redshift distributions to I <26 from the Hubble deep field: Implications for the evolution of ellipticals, spirals, and irregulars

We combine the photometric redshift data of Fern?ndez-Soto et al. with the morphological data of Odewahn et al. for all galaxies with I 24. The breadth of the redshift distribution at faint magnitudes implies strong clustering or an extended epoch of formation commencing at z>3. 2.?Spiral galaxies are present in numbers consistent with zero-evolution predictions to I=22. Beyond this magnitude some net positive evolution is required. Although the number counts are consistent with the passive-evolution predictions to I=26.0, the redshift distributions favor number and luminosity evolution, although few obvious mergers are seen (possibly classified as irregulars). We note that beyond z~2 very few ordered spirals are seen suggesting a formation epoch of spiral galaxies at z~1.5-2. 3.?There is no obvious explanation for the late-type/irregular class, and this category requires further subdivision. While a small fraction of the population lies at low redshift (i.e., true irregulars), the majority lie at redshifts 1 1.5 mergers are frequent and, taken in conjunction with the absence of normal spirals at z>2, the logical inference is that they represent the progenitors of normal spirals that form via hierarchical merging.

Herschel-ATLAS: counterparts from the ultraviolet-near-infrared in the science demonstration phase catalogue

We present a technique to identify optical counterparts of 250-μm-selected sources from theu2002Herschel–ATLAS survey. Of the 6621 250 μm > 32-mJy sources in our science demonstration catalogue we find that ∼60 per cent have counterparts brighter thanu2002ru2002 = 22.4 mag in the Sloan Digital Sky Survey. Applying a likelihood ratio technique we are able to identify 2423 of the counterparts with a reliabilityu2002Ru2002> 0.8. This is approximately 37 per cent of the full 250-μm catalogue. We have estimated photometric redshifts for each of these 2423 reliable counterparts, while 1099 also have spectroscopic redshifts collated from several different sources, including the GAMA survey. We estimate the completeness of identifying counterparts as a function of redshift, and present evidence that 250-μm-selectedu2002Herschel–ATLAS galaxies have a bimodal redshift distribution. Those with reliable optical identifications have a redshift distribution peaking atu2002zu2002≈ 0.25 ± 0.05, while submillimetre colours suggest that a significant fraction with no counterpart above theu2002r-band limit haveu2002zu2002 > 1. We also suggest a method for selecting populations of strongly lensed high-redshift galaxies. Our identifications are matched to UV–NIR photometry from the GAMA survey, and these data are available as part of theu2002Herschel–ATLAS public data release.

Automated Morphological Classification in Deep Hubble Space Telescope UBVI Fields: Rapidly and Passively Evolving Faint Galaxy Populations

We analyze deep Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) images in U, B, V, I using artificial neural network (ANN) classifiers, which are based on galaxy surface brightness and light profile (but not on color nor on scale length, rhl). The ANN distinguishes quite well between E/S0, Sabc, and Sd/Irr+M galaxies (M for merging systems) for BJ 27 mag. We discuss effects from the cosmological surface brightness (SB) dimming and from the redshifted UV morphology on the classifications, and we correct for the latter. We present classifications in UBVI from (a) four independent human classifiers; (b) ANNs trained on V606 and I814 images; and (c) an ANN trained on images in the rest-frame UBV according to the expected redshift distribution as a function of BJ. For each of the three methods, we find that the fraction of galaxy types does not depend significantly on wavelength, and that they produce consistent counts as a function of type. The median scale length at BJ 27 mag is rhl 025-03 (1-2 kpc at z ≈ 1-2). Early- and late-type galaxies are fairly well separated in BVI color-magnitude diagrams for B 27 mag, with E/S0 galaxies being the reddest and Sd/Irr+M galaxies generally blue. We present the B-band galaxy counts for five WFPC2 fields as a function of morphological type for BJ 27 mag. E/S0 galaxies are only marginally above the no-evolution predictions, and Sabc galaxies are at most 0.5 dex above the nonevolving models for BJ 24 mag. The faint blue galaxy counts in the B band are dominated by Sd/Irr+M galaxies and can be explained by a moderately steep local luminosity function (LF) undergoing strong luminosity evolution. We suggest that these faint late-type objects (24 mag BJ 28 mag) are a combination of low-luminosity lower redshift dwarf galaxies, plus compact star-forming galaxies and merging systems at z 1-3, possibly the building blocks of the luminous early-type galaxies seen today.

Galaxy and mass assembly (GAMA) : AUTOZ spectral redshift measurements, confidence and errors

The Galaxy And Mass Assembly (GAMA) survey has obtained spectra of over 230 000 targets using the Anglo-Australian Telescope. To homogenize the redshift measurements and improve the reliability, a fully automatic redshift code was developed (AUTOZ). The measurements were made using a cross-correlation method for both the absorption- and the emission-line spectra. Large deviations in the high-pass-filtered spectra are partially clipped in order to be robust against uncorrected artefacts and to reduce the weight given to single-line matches. A single figure of merit (FOM) was developed that puts all template matches on to a similar confidence scale. The redshift confidence as a function of the FOM was fitted with a tanh function using a maximum likelihood method applied to repeat observations of targets. The method could be adapted to provide robust automatic redshifts for other large galaxy redshift surveys. For the GAMA survey, there was a substantial improvement in the reliability of assigned redshifts and in the lowering of redshift uncertainties with a median velocity uncertainty of 33kms −1 .

Luminosity distributions within rich clusters — III. A comparative study of seven Abell/ACO clusters

ABSTRA C T We recover the luminosity distributions over a wide range of absolute magnitude (π24:5 < MR < π16:5) for a sample of seven rich southern galaxy clusters. We find a large variation in the ratio of dwarf to giant galaxies, DGR: 0:8# DGR #3:1. This variation is shown to be inconsistent with a ubiquitous cluster luminosity function. The DGR shows a smaller variation from cluster to cluster in the inner regions (r & 0:56 Mpc). Outside these regions we find the DGR to be strongly anticorrelated with the mean local projected galaxy density, with the DGR increasing towards lower densities. In addition, the DGR in the outer regions shows some correlation with Bautz‐Morgan type. Radial analysis of the clusters indicates that the dwarf galaxies are less centrally clustered than the giants, and they form a significant halo around clusters. We conclude that measurements of the total cluster luminosity distribution based on the inner core alone are likely to be severe underestimates of the dwarf component, the integrated cluster luminosity and the contribution of galaxy masses to the cluster’s total mass. Further work is required to quantify this. The observational evidence that the unrelaxed, lower density outer regions of clusters are dwarf-rich adds credence to the recent evidence and conjecture that the field is a predominantly dwarf-rich environment, and that the dwarf galaxies are under-represented in measures of the local field luminosity function.

The Luminosity Distribution in Galaxy Clusters: A Dwarf Population-Density Relation?

Recent work suggests that rich clusters of galaxies commonly have large populations of dwarf (i.e., low-luminosity) members, that is, their luminosity function turns up to a steep slope at the faint end. This population, or more particularly the relative numbers of dwarfs to giants, appears to be very similar for clusters of similar morphology but may vary between cluster types. We have previously suggested that dwarfs may be more common in less compact, spiral-rich clusters. Similarly, we have found evidence for population gradients across clusters, in that the dwarf population appears more spatially extended. In the present Letter, we summarize the current evidence and propose, in an analogy to the well-known morphology-density relation, that what we are seeing is a dwarf population-density relation: dwarfs are more common in lower density environments. Finally, we discuss recent semianalytic models of galaxy formation in the hierarchical clustering picture, which may give clues as to the origin of our proposed relation.

Luminosity distributions within rich clusters — I. A ubiquitous dwarf-rich luminosity function?

From deep CCD observations of the cluster Abell 2554 we recover the luminosity distribution of the cluster over a wide range of magnitude ( - 24 < MR < -16). We compare the derived A 2554 cluster luminosity function (at redshift 0.1) with that of the local Coma Cluster (A1656) and the more distant (z = 0.2) cluster A963. The distribution is remarkably similar for these three clusters of comparable richness and morphology. All show a flat (0( = - 1.0) luminosity function for the giant galaxies ( - 24 <MR < -19.5) which exhibits a sharp upturn (0( ~ -1.7) at some intermediate magnitude (MR ~ -19) and continues to rise to the limits of existing data. We suggest that such a luminosity function may be ubiquitous among rich clusters, and that a similar form may apply for poorer clusters and possibly the field as well. The three cluster dwarf luminosity functions are seen over a range of lookback times covering a quarter of the age of the Universe. Therefore the similarity between the three measured luminosity functions seems to rule out strong evolution of the dwarf populations in rich cluster environments, at least out to z = 0.2, unless richness effects conspire to conceal evolutionary changes.

Is the luminosity distribution of field galaxies really flat

Recent observations of the galaxy population within rich clusters have found a characteristic luminosity distribution described by a flat (alpha = -1.0) Schechter function which exhibits an upturn at faint absolute magnitudes (B Mag = -18). Here we discuss whether such a form for the field luminosity distribution is ruled out by local and/or faint magnitude limited redshift surveys (MLRS). nOur conclusions are that existing redshift surveys provide little constraints on the volume-density distribution of field galaxies faintwards of B Mag = -18. The local MLRS suffer from poor statistics over inhomogeneous volumes, while the faint MLRS are ambiguous because of the unknown nature of the ``faint blue excess and the ``normalization problem. nAdopting a functional form similar to that seen in rich clusters we find that the maximum allowable faint end slope, based on the Mt Stromlo-APM redshift survey, is

Luminosity distributions within rich clusters — II. Demonstration and verification via simulation

alpha approx -1.8