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We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae(SNe) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopyfor a sample of 36 events at intermediate redshift (z=0.5) discoveredby the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). Weintroduce a new method for removing host galaxy contamination in our spectra,exploiting the comprehensive photometric coverage of the SNLS SNe and theirhost galaxies, thereby providing the first quantitative view of the UV spectralproperties of a large sample of distant SNe Ia. Although the mean SN Ia spectrumhas not evolved significantly over the past 40 percent of cosmic history, preciseevolutionary constraints are limited by the absence of a comparable sample ofhigh quality local spectra. The mean UV spectrum of our z 0.5 SNe Ia and itsdispersion is tabulated for use in future applications. Within the high-redshiftsample, we discover significant UV spectral variations and exclude dust extinctionas the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see aremuch larger than predicted in recent models and do not follow expected patterns.An interesting new result is a variation seen in the wavelength of selected UVfeatures with phase. We also demonstrate systematic differences in the SN Iaspectral features with SN lightcurve width in both the UV and the optical. Weshow that these intrinsic variations could represent a statistical limitation in thefuture use of high-redshift SNe Ia for precision cosmology. We conclude thatfurther detailed studies are needed, both locally and at moderate redshift wherethe rest-frame UV can be studied precisely, in order that future missions canconfidently be planned to fully exploit SNe Ia as cosmological probes.

This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described.

Stars with initial asses such that 10[M.sub.[??]] ≤ [M.sub.initial] ≤ 100[M.sub.[??]], where [M.sub.[??]] is the solar mass, fuse progressively heavier elements in their centres, until the core is inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion--an iron-core-collapse supernova (1,2). By contrast, extremely massive stars with [M.sub.initial] ≥ 140 [M.sub.[??]](if such exist) develop oxygen cores with masses, [M.sub.core], that exceed 50[M.sub.[??]], where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion (3-5) that unbinds the star in a pair-instability supernova. Transitional objects with 100[M.sub.[??]]3[M.sub.[??]] of radioactive [sup.56]Ni was synthesized during the explosion and that our observations are well fitted by models of pair-instability supernovae (9,10). This indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic stellar mass limit (11), which perhaps result from processes similar to those that created the first stars in the Universe., We identified a new optical transient (SNF20070406-008) on 2007 April 6.5 UT (universal time is used for all dates in this paper) at right ascension 13 h 19 min 20.2 [...]

Large numbers of distant supernovae can now be found, and their redshifts and apparent brightnesses can be measured. The most distant spectroscopically confirmed supernova is reported, which is similar to nearby, recent type Ia supernovae. The new measurements indicate a low-mass-density universe.

The study of faint galaxies has inspired cosmologists since Edwin Hubble's pioneering observations in the 1920s. Appropriately, the successfully refurbished Space Telescope named after Hubble now holds the key to unravelling many of the outstanding questions in modern extragalactic astronomy, including how galaxies form and evolve in the expanding cosmos. The combination of Hubble Space Telescope's exquisite imaging and spectroscopy from ground-based telescopes is being used to resolve a major puzzle concerning a population of low mass galaxies which was particularly abundant a few billion years ago but which has mysteriously vanished by the present epoch. The solution to the puzzle may shed new light on the physical processes which produce the rich variety of galaxy types we see today.

Researchers show that multiple deep probes can solve several of the statistical problems related to single pencil beams. Results from cross correlations of multiple pencil beams consisting of more than 1200 galaxies suggest that the strong peak in the power spectrum is because of structures of large transverse size.

We compute the bispectrum of the 2dF Galaxy Redshift Survey (2dFGRS) and use it to measure the bias parameter of the galaxies. This parameter quantifies the strength of clustering of the galaxies relative to the mass in the Universe. By analysing 80 × 10[sup 6] triangle configurations in the wavenumber range 0.1 < k < 0.5 h Mpc[sup -1] (i.e. on scales roughly between 5 and 30 h[sup -1] Mpc) we find that the linear bias parameter is consistent with unity: b[sub 1]= 1.04 ± 0.11, and the quadratic (non-linear) bias is consistent with zero: b[sub 2]=-0.054 ± 0.08. Thus, at least on large scales, optically selected galaxies do indeed trace the underlying mass distribution. The bias parameter can be combined with the 2dFGRS measurement of the redshift distortion parameter β≃Ω[sub m][sup 0.6]/b[sub 1], to yield Ω[sub m]= 0.27 ± 0.06 for the matter density of the Universe, a result that is determined entirely from this survey, independent of other data sets. Our measurement of the matter density of the Universe should be interpreted as Ω[sub m] at the effective redshift of the survey (z= 0.17). [ABSTRACT FROM AUTHOR]

We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at z∼0.05 that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of σ>1000 km s[sup -1] clusters of 3.6×10[sup -6] h[sup 3] Mpc[sup -3]. This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum. [ABSTRACT FROM AUTHOR]

We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 deg[sup 2] (about 20 per cent of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications – the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range z=0.005 to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star formation density of 0.022±0.004 M[sub ⊙] yr[sup -1] Mpc[sup -3] (H[sub 0]=50 km s[sup -1] Mpc[sup -1]). [ABSTRACT FROM AUTHOR]

We present a deep H-band image of the region in the vicinity of the cluster Abell 1942 containing the puzzling dark matter concentration detected in an optical weak lensing study by Erben et al. We demonstrate that our limiting magnitude, H=22, would be sufficient to detect clusters of appropriate mass out to redshifts comparable with the mean redshift of the background sources. Despite this, our infrared image reveals no obvious overdensity of sources at the location of the lensing mass peak, nor an excess of sources in the I-H versus H colour–magnitude diagram. We use this to constrain further the luminosity and mass-to-light ratio of the putative dark clump as a function of its redshift. We find that for spatially flat cosmologies, background lensing clusters with reasonable mass-to-light ratios lying in the redshift range 0

We present the bivariate brightness distribution (BBD) for the 2dF Galaxy Redshift Survey (2dFGRS) based on a preliminary subsample of 45 000 galaxies. The BBD is an extension of the galaxy luminosity function, incorporating surface brightness information. It allows the measurement of the local luminosity density, jB, and of the galaxy luminosity and surface brightness distributions, while accounting for surface brightness selection biases. The recovered 2dFGRS BBD shows a strong luminosity–surface brightness relation MB∝(2.4±0.51.5)μe], providing a new constraint for galaxy formation models. In terms of the number density, we find that the peak of the galaxy population lies at MB≥-16.0 mag. Within the well-defined selection limits (-24B<-16.0 mag, 18.0<μe<24.5 mag arcsec-2) the contribution towards the luminosity density is dominated by conventional giant galaxies (i.e., 90 per cent of the luminosity density is contained within -22.5e<23.0). The luminosity-density peak lies away from the selection boundaries, implying that the 2dFGRS is complete in terms of sampling the local luminosity density, and that luminous low surface brightness galaxies are rare. The final value we derive for the local luminosity density, inclusive of surface brightness corrections, is jB=2.49±0.20×108 h100 L⊙ Mpc-3. Representative Schechter function parameters are M*=-19.75±0.05, φ*=2.02±0.02×10-2 and α=-1.09±0.03. Finally, we note that extending the conventional methodology to incorporate surface brightness selection effects has resulted in an increase in the luminosity density of ∼37 per cent. Hence surface brightness selection effects would appear to explain much of the discrepancy between previous estimates of the local luminosity density. [ABSTRACT FROM AUTHOR]

We investigate the dispersion in the internal colours of faint spheroidals in the Hubble Deep Fields North and South. In high-redshift rapid-collapse scenarios, the dispersion in internal colours should be small at moderate redshift apart from a small metallicity induced reddening in the enriched cores. However, recently assembled spheroidals are likely to show non-homologous internal colours, at least until younger stellar populations become fully mixed. Here we find that a remarkably large fraction (&gsim;30 per cent) of the morphologically classified spheroidals with I814W<24 mag show strong variations in internal colour, which we take as evidence for recent episodes of star formation. In most cases these colour variations manifest themselves via the presence of blue cores, an effect of opposite sign to that expected from metallicity gradients. Examining similarly selected ellipticals in five rich clusters with 0.37SFR). Although the samples are currently small, we find evidence for an increase in ρSFR between z=0 and 1. We discuss the implications of this rise in the context of that observed in the similar rise in the abundance of galaxies with irregular morphology. Regardless of whether there is a connection our results provide strong evidence for the continued formation of field spheroidals over 0

We present further spectroscopic observations for a sample of galaxies selected in the vacuum ultraviolet (UV) at 2000 Å from the FOCA balloon-borne imaging camera of Milliard et al. This work represents an extension of the initial study by Treyer et al. Our enlarged catalogue contains 433 sources (≃3 times as many as in our earlier study) across two FOCA fields. 273 of these are galaxies, nearly all with redshifts z≃0–0.4. Nebular emission-line measurements are available for 216 galaxies, allowing us to address issues of excitation, reddening and metallicity. The UV and Hα luminosity functions strengthen our earlier assertions that the local volume-averaged star formation rate is higher than indicated from earlier surveys. Moreover, internally within our sample, we do not find a steep rise in the UV luminosity density with redshift over 0

We describe the ROSAT International X-ray/Optical Survey (RIXOS), a medium-sensitivity survey and optical identification of X-ray sources discovered in ROSAT high Galactic latitude fields (|b|>28°) and observed with the Position Sensitive Proportional Counter (PSPC) detector. The survey made use of the central 17 arcmin of each ROSAT field. A flux limit of 3×10[sup -14] erg cm[sup -2] s[sup -1] (0.5–2 keV) was adopted for the survey, and a minimum exposure time of 8000 s was required for qualifying ROSAT observations. X-ray sources in the survey are therefore substantially above the detection threshold of each field used, and many contain enough counts to allow the X-ray spectral slope to be estimated. Spectroscopic observations of potential counterparts were obtained of all sources down to the survey limit in 64 fields, totalling a sky area of 15.77 deg[sup 2]. Positive optical identifications are made for 94 per cent of the 296 sources thus examined. A further 18 fields (4.44 deg[sup 2]), containing 105 sources above the 3×10[sup -14] erg cm[sup -2] s[sup -1] survey limit, are completely optically identified to a higher flux of 8×10[sup -14] erg cm[sup -2] s[sup -1] (0.5–2 keV). Optical spectroscopic data are supplemented by deep CCD imaging of many sources to reveal the morphology of the optical counterparts, and objects too faint to register on Sky Survey plates. The faintest optical counterparts have R∼22. This paper describes the survey method, and presents a catalogue of the RIXOS sources and their optical identifications. Finding charts based on Sky Survey data are given for each source, supplemented by CCD imaging where necessary. [ABSTRACT FROM AUTHOR]

Hubble Space Telescope images of a sample of 285 galaxies with measured redshifts from the Canada–France Redshift Survey (CFRS) and Autofib–Low Dispersion Spectrograph Survey (LDSS) redshift surveys are analysed to derive the evolution of the merger fraction out to redshifts z∼1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences δm≤1.5 mag. We find that the pair fraction increases with redshift, with up to ∼20 per cent of the galaxies being in physical pairs at z∼0.75–1. We derive a merger fraction varying with redshift as ∝(1+z)[sup 3.2±0.6], after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m=3.4±0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as ∝(1+z)[sup 2.7±0.6]. This implies that an average L* galaxy will have undergone 0.8–1.8 merger events from z=1 to z=0, with 0.5 to 1.2 merger events occuring in a 2-Gyr time-span at around z∼0.9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple coaddition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average [O ii] equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z∼1. [ABSTRACT FROM AUTHOR]

In hierarchical models, where spheroidal galaxies are primarily produced via a continuous merging of disc galaxies, the number of intrinsically red systems at faint limits will be substantially lower than in ‘traditional’ models where the bulk of star formation was completed at high redshifts. In this paper we analyse the optical–near-infrared colour distribution of a large flux-limited sample of field spheroidal galaxies identified morphologically from archival Hubble Space Telescope data. The I[sub 814]-HK′ colour distribution for a sample jointly limited at I[sub 814]<23 mag and HK′<19.5 mag is used to constrain their star formation history. We compare visual and automated methods for selecting spheroidals from our deep HST images and, in both cases, detect a significant deficit of intrinsically red spheroidals relative to the predictions of high-redshift monolithic-collapse models. However, the overall space density of spheroidals (irrespective of colour) is not substantially different from that seen locally. Spectral synthesis modelling of our results suggests that high-redshift spheroidals are dominated by evolved stellar populations polluted by some amount of subsidiary star formation. Despite its effect on the optical–infrared colour, this star formation probably makes only a modest contribution to the overall stellar mass. We briefly discuss the implications of our results in the context of earlier predictions based on models where spheroidals assemble hierarchically. [ABSTRACT FROM AUTHOR]

We describe the construction of the QDOT survey, which is publicly available from an anonymous FTP account. The catalogue consists of infrared properties and redshifts of an all-sky sample of 2387 IRAS galaxies brighter than the IRAS PSC 60-μm completeness limit (S[sub 60]>0.6 Jy), sparsely sampled at a rate of one-in-six. At |b|>10°, after removing a small number of Galactic sources, the redshift completeness is better than 98 per cent (2086/2127). New redshifts for 1401 IRAS sources were obtained to complete the catalogue; the measurement and reduction of these are described, and the new redshifts tabulated here. We also tabulate all sources at |b|>10° with no redshift so far, and sources with conflicting alternative redshifts either from our own work, or from published velocities. A list of 95 ultraluminous galaxies (i.e. with L[sub 60 μm]>10[sup 12] L[sub ⊙]) is also provided. Of these, ∼20 per cent are AGN of some kind; the broad-line objects typically show strong Fe ii emission. Since the publication of the first QDOT papers, there have been several hundred velocity changes: some velocities are new, some QDOT velocities have been replaced by more accurate values, and some errors have been corrected. We also present a new analysis of the accuracy and linearity of IRAS 60-μm fluxes. We find that the flux uncertainties are well described by a combination of 0.05-Jy fixed size uncertainty and 8 per cent fractional uncertainty. This is not enough to cause the large Malmquist-type errors in the rate of evolution postulated by Fisher et al. We do, however, find marginal evidence for non-linearity in the PSC 60-μm flux scale, in the sense that faint sources may have fluxes overestimated by about 5 per cent compared with bright sources. We update some of the previous scientific analyses to assess the changes. The main new results are as follows. (1) The luminosity function is very well determined overall but is uncertain by a factor of several at the very highest luminosities (L[sub 60 μm]>5×10[sup 12] L[sub ⊙]), as this is where the remaining unidentified objects are almost certainly concentrated. (2) The best-fitting rate of evolution is somewhat lower than our previous estimate; expressed as pure density evolution with density varying as (1+z)[sup p], we find p=5.6±2.3. Making a rough correction for the possible (but very uncertain) non-linearity of fluxes, we find p=4.5±2.3. (3) The dipole amplitude decreases a little, and the implied value of the density parameter, assuming that IRAS galaxies trace the mass, is Ω=0.9(+0.45, -0.25). (4) Finally, the estimate of density variance on large scales changes negligibly, still indicating a significant discrepancy from the predictions of simple cold dark matter cosmogonies. [ABSTRACT FROM AUTHOR]

The frequency of barred spiral galaxies as a function of redshift contains important information on the gravitational influence of stellar discs in their dark matter haloes and may also distinguish between contemporary theories for the origin of galactic bulges. In this paper we present a new quantitative method for determining the strength of barred spiral structure, and verify its robustness to redshift-dependent effects. By combining galaxy samples from the Hubble Deep Field North with newly available data from the Hubble Deep Field South, we are able to define a statistical sample of 46 low-inclination spiral systems with I[sub 814 W]<23.2 mag. Analysing the proportion of barred spiral galaxies seen as a function of redshift, we find a significant decline in the fraction of barred spirals with redshift. The redshift distribution of 22 barred and 24 non-barred spirals with suitable inclinations is inconsistent with their being drawn from the same distribution at the 99 per cent confidence level. The physical significance of this effect remains unclear, but several possibilities include dynamically hotter (or increasingly dark-matter-dominated) high-redshift discs, or an enhanced efficiency in bar destruction at high redshifts. By investigating the formation of the ‘orthogonal’ axis of Hubble’s classification tuning fork, our result complements studies of evolution in the early–late sequence, and pushes to later epochs the redshift at which the Hubble classification sequence is observed to be in place. [ABSTRACT FROM AUTHOR]

We describe the 2dF Galaxy Redshift Survey (2dFGRS) and the current status of the observations. In this exploratory paper, we apply a principal component analysis to a preliminary sample of 5869 galaxy spectra and use the two most significant components to split the sample into five spectral classes. These classes are defined by considering visual classifications of a subset of the 2dF spectra, and also by comparison with high-quality spectra of local galaxies. We calculate a luminosity function for each of the different classes and find that later-type galaxies have a fainter characteristic magnitude, and a steeper faint-end slope. For the whole sample we find M*=-19.7 (for Ω=1, H[sub 0]=100 km s[sup -1] Mpc[sup -1]), α=-1.3, φ*=0.017. For class 1 (‘early-type’) we find M*=-19.6, α=-0.7, while for class 5 (‘late-type’) we find M*=-19.0, α=-1.7. The derived 2dF luminosity functions agree well with other recent luminosity function estimates. [ABSTRACT FROM AUTHOR]

Discusses confliction results of previous attempts to determine the cosmological curvature from the asymptotic surface density of faint galaxies. Proposes to resolve the conflict with an evolutionary model in which galaxies merge at recent look-back times. Excess of blue galaxies seen at optical wavelengths; More.

Reports on a cosmology meeting at which scientists identified a disappearing population of remote galaxies. Importance of remote galaxies' fate; Edwin Hubble's test; Galaxy counting; Measurement of galaxy distances; Overabundance of galaxies; Mergers; Dwarf galaxies.