arXiv subjects

Andrew W. Blain

Publications and source records attributed to Andrew W. Blain.

69 records · Page 4Linked to original sources

arXiv1999

Future millimeter, submillimeter and far-infrared surveys and their successful follow up

The first unbiased surveys for high-redshift galaxies in the submillimeter (submm) and far-infrared (FIR) wavebands have been made over the last two years. When combined with the intensity of extragalactic background radiation in the same wavebands, we have a reasonable first view of the dust enshrouded Universe. Limited spatial resolution hampers the identification of the submm galaxies, and follow-up observations currently consume much larger amounts of telescope time than the initial submm-wave detections. Here the prospects for future submm/FIR surveys are discussed, highlighting the importance of planning careful multiwaveband radio/submm/FIR observations. These can be used to yield photometric redshift information. Radio observations are vital to give accurate positions for the detected sources.

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arXiv1999

Galactic morning: the Atacama Large Millimeter Array (ALMA) and the evolution of galaxies

The importance of the Atacama Large Millimeter Array (ALMA) to the study of high-redshift dusty gas-rich galaxies is described. ALMA will have dramatically greater sensitivity and angular resolution than existing millimetre(mm) and submm-wave telescopes. Two key areas are emphasized: i) extremely deep galaxy surveys down to flux densities of about 10 microJy, two orders of magnitude deeper than can be reached using existing telescopes; ii) the study of known high-redshift galaxies, quasars and gravitational lenses. The sensitivity of ALMA will allow very faint galaxies to be detected, while its angular resolving power avoids the problem of source confusion. Dust continuum emission, molecular rotational line emission and atomic fine-structure line emission will all be detected from high-redshift galaxies. Both the spatial structure of continuum emission and the spatial and velocity structure of line emission will be resolved, revealing the astrophysical processes at work in detail. These programs are very complementary to surveys using the Next Generation Space Telescope (NGST) and Planck Surveyor.

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arXiv1999

Dust-obscured star formation and AGN fuelling in hierarchical models of galaxy evolution

A large fraction of the luminous distant submm-wave galaxies recently detected using SCUBA on the JCMT appear to be associated with interacting optical counterparts. We investigate these systems using a simple hierarchical clustering model of galaxy evolution, in which the large luminosity of the SCUBA galaxies is assumed to be generated at the epoch of galaxy mergers in a burst of either star formation activity or the fuelling of an active galactic nucleus (AGN). The models are well constrained by the observed spectrum of the FIR/submm background radiation and the 60-micron counts of low-z IRAS galaxies. The ratio between the total amount of energy released during mergers and the mass of dark matter involved must increase sharply with z at z<1, and then decrease at higher z, independent of the fraction of the luminosity of mergers that is produced by starbursts and AGN. One additional parameter - the reciprocal of the product of the duration of the enhanced luminosity produced by the merger and the fraction of mergers that induce an enhanced luminosity, which we call the activity parameter - is introduced, to allow the relationship between merging dark matter haloes and the observed counts of distant dusty galaxies to be investigated. The observed counts can only be reproduced if the activity parameter is greater by a factor of about 5 and 100 at redshifts of 1 and 3 respectively, compared with the present epoch. Hence, if mergers account for the SCUBA galaxies, then the merger process must have been much more violent at high redshifts. We discuss the counts of galaxies and the intensity of background radiation in the optical/near-IR wavebands in the context of these hierarchical models, and thus investigate the relationship between the populations of SCUBA and Lyman-break galaxies.

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arXiv1999

Dust temperture and the submillimetre-radio flux density ratio as a redshift indicator for distant galaxies

It is difficult to identify the distant galaxies selected in existing submillimetre-wave surveys, because their positions are known at best to only several arcseconds. Centimetre-wave VLA observations are required in order to determine positions to subarcsecond accuracy, and so to allow reliable optical identifications to be made. Carilli & Yun pointed out that the ratio of the radio to submillimetre-wave flux densities provides a redshift indicator for dusty star-forming galaxies, when compared with the tight correlation between the far-infrared and radio flux densities observed in low-redshift galaxies. This method does provide a useful, albeit imprecise, indication of the distance to a submillimetre-selected galaxy. Unfortunately, it does not provide an unequivocal redshift estimate, as the degeneracy between the effects of increasing the redshift of a galaxy and decreasing its dust temperature is not broken.

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arXiv1999

Submillimeter-selected galaxies

The first generation of submillimeter(submm)-wave surveys are being carried out using the 450/850-micron SCUBA camera at the JCMT on Mauna Kea. These surveys are potentially sensitive to galaxies at very high redshift, and the galaxies that have been detected so far appear to contribute the greater fraction of the mm/submm-wave background radiation intensity measured by COBE. In order to understand this new population of galaxies, individual examples must be studied in detail across many wavebands; in particular their redshifts must be determined. We discuss the potential selection effects at work in submm-wave surveys and describe the spectral energy distributions of galaxies selected or luminous in the submm waveband. We also describe the general procedure for, and emphasize the difficulty of, identifying optical counterparts to submm-selected galaxies. Finally, we summarize what is known about the redshifts of these galaxies and the source of their luminosity.

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arXiv1999

Galaxy counts at 450 and 850 microns

Surveys of the distant Universe have been made using the SCUBA submillimeter(submm)-wave camera at the JCMT. 450- and 850-micron data is taken simultaneously by SCUBA in the same 5-square-arcmin field. Deep 850-micron counts of high-redshift dusty galaxies have been published; however, at 450 microns both the atmospheric transmission and antenna efficiency are lower, and the atmospheric noise is higher, and so only upper limits to the 450-micron counts have been reported so far. Here we apply the methods used by Blain et al. (1999) to derive deep 850-micron counts from SCUBA images of lensing clusters to the 450-micron images that were obtained in parallel, in which four sources were detected. We present the first 450-micron galaxy count. This analysis has only just become possible because the volume of data and the difficulty of calibration are both greater for the 450-micron array. In light of recent work, in which the identification of two of the galaxies in our sample was clarified, we also update our deep 850-micron counts.

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arXiv1999

Dust temperature and the submillimeter-radio flux density ratio as a redshift indicator

It is difficult to identify the distant galaxies selected in existing submillimeter (submm)-wave surveys, because their positional accuracy is only several arcseconds. Currently, centimeter-wave VLA observations are required in order to determine sub-arcsec positions, and so to make reliable optical identifications. Carilli & Yun (1999) pointed out that the ratio of the radio and submm-wave flux densities provides a redshift indicator for dusty star-forming galaxies, when compared with the tight correlation observed between the far-infrared and radio flux densities for low-redshift galaxies. This method provides a useful, albeit imprecise, indication of the distance to a submm-selected galaxy. However, because the degeneracy between the effects of increasing the redshift of a galaxy and decreasing its dust temperature is not broken, it does not provide an unequivocal redshift estimate.

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arXiv1999

The differential magnification of high-redshift ultraluminous infrared galaxies

This proceeding discusses the potential modifications to the mid-infrared spectral energy distribution (SED) of a high-redshift dusty AGN that is graviationally lensed by a foreground galaxy. The mid-infrared colour of a lensed galaxy would typically be bluer than that of the same galaxy in the absence of magnification. This effect would make it more difficult to interpret the very small sample of high-redshift dusty AGN for which broad-band SEDs are known in terms of the viewing angle of an obscuring dust torus, as all are known to be lensed by galaxies.

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arXiv1999

The differential magnification of high-redshift ultraluminous infrared galaxies

A class of extremely luminous high-redshift galaxies has recently been detected in unbiased submillimetre-wave surveys using the Submillimetre Common-User Bolometer Array (SCUBA) camera at the James Clerk Maxwell Telescope. Most of the luminosity of these galaxies is emitted from warm interstellar dust grains, and they could be the high-redshift counterparts of the low-redshift ultraluminous infrared galaxies (ULIRGs). Only one - SMM J02399-0136 - has yet been studied in detail. Three other very luminous high-redshift dusty galaxies with well determined spectral energy distributions in the mid-infrared waveband are known - IRAS F10214+4724, H1413+117 and APM 08279+5255. These were detected serendipitously rather than in unbiased surveys, and are all gravitationally lensed by a foreground galaxy. Two - H 1413+117 and APM 08279+5255 - appear to emit a significantly greater fraction of their luminosity in the mid-infrared waveband as compared with both low-redshift ULIRGs and high-redshift submillimetre-selected galaxies. This can be explained by a systematically greater lensing magnification of hotter regions of the source as compared with cooler regions: differential magnification. This effect can confuse the interpretation of the properties of distant ultraluminous galaxies that are lensed by intervening galaxies, but offers a possible way to investigate the temperature distribution of dust in their nuclei on scales of tens of parsecs.

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arXiv1999

Deep counts of submillimeter galaxies

We present the counts of luminous submillimeter (sub-mm) galaxies from an analysis of our survey of the distant Universe through lensing clusters, which uses massive cluster lenses with well-constrained mass models to magnify the background sky. This both increases the sensitivity and reduces the effects of source confusion. Accurate lens models are used to correct the observed sub-mm source counts. The associated uncertainties do not dominate the final errors. We derive counts by two independent methods: a direct inversion of the observed sources, corrected individually for lens amplification; and a Monte-Carlo simulation of our observations using a parametric model for the background counts, which is folded through the lens models and incompleteness estimates to determine best-fitting values of the count parameters. Both methods agree well and confirm the robustness of our analysis. Detections that are optically identified with galaxies in the lensing clusters are removed prior to our analysis, and the results are insensitive both to the details of the correction and to the redshift distribution of the detections. We present 850-micron counts between 0.5 and 8 mJy. The most accurate count is determined at 1 mJy: 7900 +- 3000 deg^-2, including both Poisson and systematic errors. These are the deepest sub-mm counts published, and are not subject to source confusion because the detected galaxies are separated and magnified by the lens. Down to the 0.5-mJy limit, the resolved 850-micron background radiation intensity is (0.5 +- 0.2) nW m^{-2} sr^{-1}, comparable to the current COBE estimate of the background, and so the bulk of the 850-micron background radiation originated in distant ultraluminous galaxies.

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arXiv1998

Statistical lensing by galactic discs

The high-magnification gravitational lensing cross-section of a galaxy is enhanced significantly if a baryonic disc is embedded in its dark matter halo. We investigate the effects of a population of such disks on the probability of detecting strongly lensed images of distant galaxies and quasars. The optical depth to lensing is always more than doubled. The effects are particularly significant at magnifications greater than about 50, for which the optical depth typically increases by a factor greater than 5. If either the fraction of discs or the typical disc-to-halo mass ratio increases with redshift, then the optical depth is expected to be increased even further. Obscuration by dust in the lensing disc is expected to counteract the associated enhanced magnification bias for surveys in the optical waveband, but not in the radio and millimetre/submillimetre wavebands. The presence of galactic discs should hence lead to a significant increase in the number of lensed galaxies and quasars detected in both radio- and millimetre/submillimetre-selected surveys. An increase by a factor of about 3 is expected, enhancing the strong case for millimetre/submillimetre-wave lens surveys using the next generation of ground-based telescopes and the FIRST and Planck Surveyor space missions.

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arXiv1998

Infrared galaxies

To study large-scale structure in the Universe a full census of the contents are required. This is even more important when the processes of galaxy formation are being investigated. In the last year the population of distant galaxies that emit most of their energy in the infrared waveband have been studied in unprecedented detail. The intensity of background radiation at wavelengths between 3 mm and 10 microns has been determined to within a factor of about 2, and much of this background radiation has been resolved into individual galaxies. These galaxies are largely hidden from view in the optical waveband by absorption due to interstellar dust. By combining this new knowledge with the ever growing body of information gathered using optical telescopes, the process of galaxy formation is slowly being revealed. Great opportunities for studying the distant Universe are promised by advances in instrumentation in the millimeter (mm), submm and far-infrared wavebands over the next decade.

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arXiv1998

Submillimetre-wave surveys: first results and prospects

The population of distant dusty submm-luminous galaxies was first detected last year (Smail, Ivison and Blain 1997). Forms of evolution required to account for both this population and the intensity of background radiation have now been determined (Blain, Smail, Ivison and Kneib 1998), and are used to investigate the most efficient observing strategies for future surveys.

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arXiv1998

Gravitational lensing and the Sunyaev-Zel'dovich effect in the millimetre/submillimetre waveband

The intensity of the cosmic microwave background radiation in the fields of clusters of galaxies is modified by inverse Compton scattering in the hot intracluster gas - the Sunyaev-Zel'dovich (SZ) effect. The effect is expected to be most pronounced at a frequency of about 350 GHz (a wavelength of about 800 microns), and has been detected in the centimetre and millimetre wavebands. In the millimetre/submillimetre waveband, the gravitationally-lensed images of distant dusty star-forming galaxies in the background of the cluster are predicted to dominate the appearance of clusters on scales of several arcseconds, and could confuse observations of the SZ effect at frequencies greater than about 200 GHz (wavelengths shorter than about 1.5 mm). Recent observations by Smail, Ivison & Blain (1997) confirm that a significant population of confusing sources are present in this waveband. Previous estimates of source confusion in observations of the millimetre/submillimetre-wave SZ effect did not include the effects of lensing by the cluster, and so the accuracy of such measurements could be lower than expected. Source subtraction may be required in order to measure the SZ effect accurately, and a careful analysis of the results of an ensemble of SZ measurements could be used to impose limits to the form of evolution of distant star-forming galaxies.

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arXiv1998

The Planck Surveyor mission and gravitational lenses

An extremely sensitive all-sky survey will be carried out in the millimetre/submillimetre waveband by the forthcoming ESA mission Planck Surveyor. The main scientific goal of the mission is to make very accurate measurements of the spatial power spectrum of primordial anisotropies in the cosmic microwave background radiation; however, hundreds of thousands of distant dusty galaxies and quasars will also be detected. These sources are much more likely to be gravitationally lensed by intervening galaxies as compared with sources discovered in surveys in other wavebands. Here the number of lenses expected in the survey is estimated, and techniques for discriminating between lensed and unlensed sources are discussed. A practical strategy for this discrimination is presented, based on exploiting the remarkable sensitivity and resolving power of large ground-based millimetre/submillimetre-wave interferometer arrays. More than a thousand gravitational lenses could be detected: a sample that would be an extremely valuable resource in observational cosmology.

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