Distant Star-forming Galaxies Research Articles

A very energetic supernova associated with the gamma-ray burst of 29 March 2003.

Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.

On Measuring the Infrared Luminosity of Distant Galaxies with the [ITAL]Space Infrared Telescope Facility[/ITAL

The Space Infrared Telescope Facility (SIRTF) will revolutionize the study of dust-obscured star formation in distant galaxies. Although deep images from the Multiband Imaging Photometer for SIRTF (MIPS) will provide coverage at 24, 70, and 160 μm, the bulk of MIPS-detected objects may only have accurate photometry in the shorter wavelength bands because of the confusion noise. Therefore, we have explored the potential for constraining the total infrared (IR) fluxes of distant galaxies solely with the 24 μm flux density and for the combination of 24 and 70 μm data. We also discuss the inherent systematic uncertainties in making these transitions. Under the assumption that distant star-forming galaxies have IR spectral energy distributions (SEDs) that are represented somewhere in the local universe, the 24 μm data (plus optical and X-ray data to allow the redshift estimation and AGN rejection) constrain the total IR luminosity to within a factor of 2.5 for galaxies with 0.4 z 1.6. Incorporating the 70 μm data substantially improves this constraint by a factor 6. Lastly, we argue that if the shape of the IR SED is known (or well constrained, e.g., because of a high IR luminosity or a low ultraviolet/IR flux ratio), then the IR luminosity can be estimated with more certainty.

Submillimetre sources in rich cluster fields: source counts, redshift estimates and cooling flow limits

Recent submillimetre surveys have revealed a population of dusty, high-redshift sources of great cosmological significance for understanding dust-enshrouded star formation in distant galaxies, and for determining the origin of the far-infrared background. In this paper, we analyse nine rich cluster fields mapped at 850 and 450μm with the SCUBA array on the James Clerk Maxwell Telescope. Lensing models of the clusters are developed in order to derive accurate source counts for our sample. VLA maps of the same clusters are used to help constrain the redshift distribution of our SCUBA detections. Implications for high-redshift galaxies and for the far-infrared background are discussed. We also provide limits on distributed dust produced by cooling flows in these clusters.

The Nature of Radio Emission from Distant Galaxies: The 1.4 GHz Observations

We have conducted a deep radio survey with the Very Large Array at 1.4 GHz of a region containing the Hubble Deep Field. This survey overlaps previous observations at 8.5 GHz allowing us to investigate the radio spectral properties of microjansky sources to flux densities greater than 40 $\mu$Jy at 1.4 GHz and greater than 8 $\mu$Jy at 8.5 GHz. A total of 371 sources have been catalogued at 1.4 GHz as part of a complete sample within 20\arcmin ~of the HDF. The differential source count for this region is only marginally sub-Euclidean and is given by $n(S) = (8.3 \pm 0.4) S^{-2.4 \pm 0.1}$ sr$^{-1}$Jy$^{-1}$. Above about 100 $\mu$Jy the radio source count is systematically lower in the HDF as compared to other fields. We conclude that there is clustering in our radio sample on size scales of 1\arcmin - 40\arcmin \. The 1.4 GHz selected sample shows that the radio spectral indices are preferentially steep ($\bar{\alpha}_{1.4} = 0.85 $) and the sources are moderately extended with average angular size $\theta$ = 1.8\arcsec . Optical identification with disk-type systems at $z \sim $ 0.5-0.8 suggests that synchrotron emission, produced by supernovae remnants, is powering the radio emission in the majority of sources. The 8.5 GHz sample contains primarily moderately flat spectrum sources ($\bar{\alpha}_{8.5} = 0.35$), with less than 15% inverted. We argue that we may be observing an increased fraction of optically thin bremsstrahlung over synchrotron radiation in these distant star-forming galaxies.

15 MicronInfrared Space ObservatoryObservations of the 1415+52 Canada‐France Redshift Survey Field: The Cosmic Star Formation Rate as Derived from Deep Ultraviolet, Optical, Mid‐Infrared, and Radio Photometry

The Canada-France Redshift Survey 1452+52 field has been deeply imaged with the Infrared Space Observatory using ISOCAM through the LW3 filter (12-18 μm). Careful data analysis and comparison with deep optical and radio data have allowed us to generate a catalog of 78 15 μm sources with both radio and optical identifications. They are redder and lie at higher redshift than I-band-selected galaxies, with most of them being star-forming galaxies. We have considered the galaxies detected at radio and 15 μm wavelengths, which potentially include all strong and heavily extincted starbursts, up to z=1. Spectral energy distributions (SEDs) for each of the sources have been derived using deep radio, mid-IR, near-IR, optical, and UV photometry. The sources were then spectrally classified by comparing with SEDs of well-known nearby galaxies. By deriving their far-IR luminosities by interpolation, we can estimate their star formation rate (SFR) in a way that does not depend sensitively on the extinction. Between 35% and 85% of the star formation at z≤1 is related to IR emission, and the global extinction is in the range AV=0.5-0.85. While heavily extincted starbursts with SFRs in excess of 100 M☉ yr-1 constitute less than 1% of all galaxies, they contribute about 18% of the SFR density out to z=1. Their morphologies range from S0 to Sab, and more than a third are interacting systems. The SFR derived by far-IR fluxes is likely to be ~2.9 times higher than those previously estimated from UV fluxes. The derived stellar mass formed since the redshift of 1 could be too high when compared with the present-day stellar mass density. This might be due to an initial mass function in distant star-forming galaxies different from the solar neighborhood one or an underestimate of the local stellar mass density.

On Measuring Nebular Chemical Abundances in Distant Galaxies Using Global Emission‐Line Spectra

The advent of 8-10 m class telescopes enables direct measurement of the chemical properties in the ionized gas of cosmologically distant galaxies with the same nebular analysis techniques used in local H II regions. We show that spatially unresolved (i.e., global) emission-line spectra can reliably indicate the chemical properties of distant star-forming galaxies. However, standard nebular chemical abundance measurement methods (those with a measured electron temperature from [O III] λ4363) may be subject to small systematic errors when the observed volume includes a mixture of gas with diverse temperatures, ionization parameters, and metallicities. To characterize these systematic effects, we compare physical conditions derived from spectroscopy of individual H II regions with results from global galaxy spectroscopy. We consider both low-mass, metal-poor galaxies with uniform abundances and larger galaxies with internal chemical gradients. For low-mass galaxies, standard chemical analyses using global spectra produce small systematic errors in that the derived electron temperatures are 1000-3000 K too high due to nonuniform electron temperatures and large variations in the ionization parameter. As a result, the oxygen abundances derived from direct measurements of the electron temperatures are too low, but it is possible to compensate for this effect by applying a correction of Δ(O/H)≤+0.1 dex to the oxygen abundances derived from global spectra. For more massive metal-rich galaxies like local spiral galaxies, direct measurements of electron temperatures are seldom possible from global spectra. Well-established empirical calibrations using strong-line ratios can serve as reliable (±0.2 dex) indicators of the overall systemic oxygen abundance even when the signal to noise of the Hβ and [O III] emission lines is as low as 8:1. We present prescriptions, directed toward high-redshift observers, for using global emission-line spectra to trace the chemical properties of star-forming galaxies in the distant universe.

Ultraviolet spectral libraries of massive stars at low metallicity

Three new ultraviolet spectral libraries of massive, hot stars using high and medium resolution spectra of objects located in the solar neighbourhood and the Magellanic Clouds are presented. Massive stars display unique wind signatures which are relatively easy to study in the ultraviolet. These libraries are crucial tools when investigating the massive stellar population of distant star-forming galaxies.

Extremely red and dusty galaxies

Preliminary results of a project aiming at unveiling the nature ofthe extremely red galaxies (ERGs) found in deep optical-NIR surveys are presented.Very little is known about these objects, the critical issue beingwhether they are old ellipticals at z > 1 or distant star-forminggalaxies strongly reddened by dust extinction.We expect to shed light onto the unknown nature of these galaxiesby completing our three-step project:(1) the construction of two very deep optical/NIR surveys to select ERGs,(2) subsequent VLT/NIR spectroscopy; (3)observations in the smm region with SCUBA at the JCMT and withMPIfRbolo at the IRAM 30m antenna.

The Norris Survey of the Corona Borealis Supercluster. II. Galaxy Evolution with Redshift and Environment

We measure the field galaxy luminosity function (LF) as a function of color and redshift from z = 0 to z = 0.5 using galaxies from the Norris Survey of the Corona Borealis Supercluster. The data set consists of 603 field galaxies with 0 < z ? 0.5 and spans a wide range in apparent magnitude (14.0 r 21.5), although our field galaxy LF analysis is limited to 493 galaxies with r ? 20.0 mag. We use the observed g-r colors of the galaxies to compute accurate corrections to the rest BAB and r bands. We find that our local r-band LF, when normalized to counts in high galactic latitude fields, agrees well with the local LF measured in the Las Campanas Redshift Survey. Our BAB-band local LF, however, does not match the bj-band LF from the Stromlo/APM survey, having a normalization 1.6 times higher. We see compelling evidence that the BAB-band field galaxy LF evolves with redshift. The evolution is strongest for the population of star-forming galaxies with [O II] ?3727 rest-frame equivalent widths greater than 10 ?. The population of red, quiescent galaxies shows no sign of evolution to z = 0.5. The evolution of the LF that we observe is consistent with the findings of other faint galaxy redshift surveys. The fraction of galaxies with [O II] emission increases rapidly with redshift, but the fraction of galaxies with strong H? absorption, a signature of a burst of star formation, does not. We thus conclude that the star formation in distant galaxies is primarily long-lived. We also compute the LFs of the Corona Borealis supercluster (z ? 0.07, 419 galaxies with 14.1 ? r ? 20.0 mag) and the Abell 2069 supercluster (z ? 0.11, 318 galaxies with 15.1 ? r ? 20.0 mag). The shapes of the two supercluster luminosity functions are broadly similar to the shape of the local luminosity function. However, there are important differences. Both supercluster LFs have an excess of very bright galaxies. In addition, the characteristic magnitude of the Corona Borealis supercluster LF is roughly half a magnitude brighter than that of the local field galaxy LF, and there is a suggestion of an upturn in the LF for galaxies fainter than M(BAB) ~ -17 + 5 log10 h mag, where h is the Hubble constant in units of 100 km s-1 Mpc-1.

Gravitational lensing by clusters of galaxies in the millimetre/submillimetre waveband

Rich clusters of galaxies are observed to produce strongly magnified arcs and multiple images of background galaxies in the optical waveband. Here the properties of the equivalent images in the submillimetre waveband are discussed. Carefully designed submillimetre-wave surveys preferentially select galaxies at large redshifts, because the flux density-redshift relations for distant dusty star-forming galaxies are expected to be flat in this waveband, and so distant galaxies are much brighter as compared with observations in the optical waveband. For the same reason, submillimetre-wave observations are also ideally suited to detect the lensed images of very distant galaxies in clusters. Here we combine a model of a lensing cluster with predicted source counts of distant galaxies in the submillimetre waveband in order to investigate the form of the magnification bias introduced into the population of faint galaxies by lensing. A positive magnification bias corresponds to an increase in the surface density of galaxies. In the submillimetre waveband magnification biases can be large and positive, and depend strongly on the form of evolution of distant galaxies. New submillimetre-wave instruments and telescopes will allow galaxies at redshifts z ~ 10 to be observed in as much detail as galaxies at z = 0.5, and we assess the practicality of detecting a useful sample of lensed images in the fields of clusters using both single-antenna telescopes and large interferometer arrays. The surface and flux densities of the lensed images in the submillimetre waveband are expected to exceed those of galaxies within the lensing cluster, and their values can be used to infer the form of evolution of star-forming galaxies since redshifts of about 10.

Observing strategies for blank-field surveys in the submillimetre waveband

The coming generation of submillimetre bolometer array detectors, such as the Submillimetre Common-User Bolometer Array (SCUBA) instrument currently being constructed for the James Clerk Maxwell Telescope (JCMT), offer opportunities for searching for distant star-forming galaxies in the submillimetre waveband. The special features of observing in the submillimetre waveband requirea careful assessment of the optimum observing strategy, aimed both at maximizing the probabilities of detecting distant galaxies and at discriminating between different models of galaxy formation and evolution. The distinctive feature of faint submillimetre sources is that their predicted source counts are inverted at low flux densities and this strongly influences the observing strategy. We illustrate how the strategy differs for distinct models of the evolution of the population of star-forming galaxies. In all cases the preferred observing wavelength is 850 μn. plausible models of the evolution of IRAS galaxies suggest that the best strategy would be to observe an area of about 0.1 deg2 for an observing time of 3 × 105 s. In a hierarchical clustering picture, it would be preferable to observe a much smaller area of 0.01 deg2 for the same time to a deeper limiting flux density of 0.3 mJy, at which the extremely steep source counts expected in these models should be detected. It is argued that both types of survey should be carried out.

Giant H II Regions in M81

Giant HII regions are important tracers of recent star formation in distant galaxies. For a selection of HII regions in our galaxy where the exciting stars can be identified, Rumstay (1985) finds that the measured Hα and radio continuum luminosities of an HII region correlate with the stellar ionizing flux derived from model atmospheres and the known exciting stars. Therefore, we use flux measurements of giant HII regions as an index of the distribution of O stars in M81.