arXiv subjects

A. W. Blain

Publications and source records attributed to A. W. Blain.

At least 91 records · Page 5Linked to original sources

arXiv2005

MIPS J142824.0+352619: A Hyperluminous Starburst Galaxy at z=1.325

Using the SHARC-II camera at the Caltech Submillimeter Observatory to obtain 350 micron images of sources detected with the MIPS instrument on Spitzer, we have discovered a remarkable object at z=1.325+/-0.002 with an apparent Far-Infrared luminosity of 3.2(+/-0.7) x 10^13 Lsun. Unlike other z>1 sources of comparable luminosity selected from mid-IR surveys, MIPS J142824.0+352619 lacks any trace of AGN activity, and is likely a luminous analog of galaxies selected locally by IRAS, or at high redshift in the submillimeter. This source appears to be lensed by a foreground elliptical galaxy at z=1.034, although the amplification is likely modest (~10). We argue that the contribution to the observed optical/Near-IR emission from the foreground galaxy is small, and hence are able to present the rest-frame UV through radio Spectral Energy Distribution of this galaxy. Due to its unusually high luminosity, MIPS J142824.0+352619 presents a unique chance to study a high redshift dusty starburst galaxy in great detail.

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arXiv2005

The Relationship Between Stellar and Black-Hole Mass in Submillimeter Galaxies

We analyze deep X-ray, optical and mid-infrared Spitzer observations of the CDF-N/GOODS-N region to study 13 submillimeter-detected galaxies (SMGs) with spectroscopic redshifts (median z=2.2). We find a correlation between the estimated stellar and X-ray luminosity, implying that masses of the black holes may be related to the stellar masses of their host galaxies. Although the submillimeter emission implies that these galaxies are undergoing an epoch of intense star-formation, the Spitzer data reveal a massive stellar population already in place. These stellar masses are then compared to previously published black hole mass estimates derived from the X-ray luminosities under the assumption of Eddington-limit accretion. We find that the black hole masses for our high-redshift sample are approximately 1-2 orders of magnitude smaller than galaxies of comparable stellar mass in the local Universe. Although our estimates of black hole masses will increase if the accretion is sub-Eddington, and our stellar masses will decrease if we assume a much younger stellar population or a different initial mass function, we find that only through a combination of effects is it possible to shift the high redshift galaxies such that they lie on the local relation. This suggests that the black holes need to grow substantially between z=2.2 and the present-day, with much of the black hole growth occurring after the current obscured, far-infrared luminous phase of activity which is likely associated with the formation of the spheroid. This interpretation supports a scenario where SMGs pass through a subsequent accretion-dominated phase, where they would appear as optically bright quasars. (ABRIDGED)

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arXiv2005

The X-ray Spectral Properties of SCUBA Galaxies

Deep SCUBA surveys have uncovered a large population of massive submm galaxies (SMGs) at z>~1. Although it is generally believed that these galaxies host intense star-formation activity, there is growing evidence that a substantial fraction also harbor an AGN. We present here possibly the strongest evidence for this viewpoint to date: the combination of ultra-deep X-ray observations (the 2 Ms CDF-N) and deep Keck spectroscopic data. We find that the majority (~75%) of the spectroscopically identified SMGs host AGN activity; the other ~25% have X-ray properties consistent with star formation (X-ray derived SFRs of ~1300-2700 solars/yr). The AGNs have properties generally consistent with those of nearby luminous AGNs (L_X~1E43-3E44) and the majority (~80%) are heavily obscured. We construct composite rest-frame 2-20 keV spectra for three different obscuration classes. An ~1 keV equivalent width FeK-alpha emission line is seen in the composite X-ray spectrum of the most heavily obscured AGNs (N_H>5x10^{23}), suggesting Compton-thick or near Compton-thick absorption. Even taking into account the effects of absorption, we find that the average X-ray-FIR ratio of the AGN-classified SMGs is approximately one order of magnitude below that found for typical quasars. This result suggests that intense star-formation activity dominates the bolometric output; however, we also explore whether the X-ray-FIR ratio is intrinsically less than that found for typical quasars and postulate that some SMGs may be AGN dominated. We investigate the growth of massive black holes, discuss prospects for deeper observations, and explore the potential of the next generation of X-ray observatories. (ABRIDGED).

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arXiv2005

Rapid Growth of Black Holes in Massive Star-Forming Galaxies

The tight relationship between the masses of black holes and galaxy spheroids in nearby galaxies implies a causal connection between the growth of these two components. Optically luminous quasars host the most prodigious accreting black holes in the Universe and can account for >30% of the total cosmological black-hole growth. As typical quasars are not, however, undergoing intense star formation and already host massive black holes [>10^(8) M(Sun)], there must have been an earlier pre-quasar phase when these black holes grew [mass range ~10^(6)-10^(8) M(Sun)]. The likely signature of this earlier stage is simultaneous black-hole growth and star formation in distant (i.e., z>1; >8 billion light years away) luminous galaxies. Here we report ultra-deep X-ray observations of distant star-forming galaxies that are bright at submillimetre wavelengths. We find that the black holes in these galaxies are growing almost continuously throughout periods of intense star formation. This activity appears to be more tightly associated with these galaxies than any other coeval galaxy populations. We show that the black-hole growth from these galaxies is consistent with that expected for the pre-quasar phase.

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arXiv2005

An interferometric CO survey of luminous submm galaxies

In this paper we present results from an IRAM Plateau de Bure millimetre-wave Interferometer (PdBI) survey for CO emission towards radio-detected submillimetre galaxies (SMGs) with known optical and near-infrared spectroscopic redshifts. Five sources in the redshift range z~1-3.5 were detected, nearly doubling the number of SMGs detected in CO. We summarise the properties of all 12 CO-detected SMGs, as well as 6 sources not detected in CO by our survey, and use this sample to explore the bulk physical properties of the SMG population as a whole. The median CO line luminosity of the SMGs is = (3.8 +- 2.0) x 10^10 K km/s pc^2. Using a CO-to-H_2 conversion factor appropriate for starburst galaxies, this corresponds to a molecular gas mass = (3.0 +- 1.6) x 10^10 Msun within a ~2kpc radius, about four times greater than the most luminous local ultraluminous infrared galaxies (ULIRGs) but comparable to that of the most extreme high-redshift radio galaxies and QSOs. The median CO fwhm linewidth is broad, = 780 +- 320 km/s, and the SMGs often have double peaked line profiles, indicative of either a merger or a disk. From their median gas reservoirs (~3 x 10^10 Msun) and star-formation rates (>700 Msun/yr) we estimate a lower limit on the typical gas-depletion time scale of >40Myr in SMGs. This is marginally below the typical age expected for the starbursts in SMGs, and suggests that negative feedback processes may play an important role in prolonging the gas consumption time scale. We find a statistically-significant correlation between the far-infrared and CO luminosities of the SMGs which extends the observed correlation for local ULIRGs to higher luminosities and higher redshifts. [ABRIDGED]

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arXiv2004

A Redshift Survey of the Submillimeter Galaxy Population

We have obtained spectroscopic redshifts using the Keck-I telescope for a sample of 73 submillimeter (submm) galaxies for which precise positions are available. The galaxies lie at redshifts out to z=3.6, with a median redshift of 2.2. The dust-corrected ultraviolet (UV) luminosities of the galaxies rarely hint at their huge bolometric luminosities indicated by their radio/submm emission, underestimating the true luminosity by a median factor of ~100 for SMGs with pure starburst spectra. The 850mu, radio, and redshift data is used to estimate the dust temperatures ( =36+-7 K), and characterize photometric redshifts. We calculate total infrared and bolometric luminosities, construct a luminosity function, and quantify the strong evolution of the submm population across z=0.5-3.5, relative to local IRAS galaxies. We conclude that bright submm galaxies contribute a comparable star formation density to Lyman-break galaxies at z=2-3 and including galaxies below our submm flux limit this population may be the dominant site of massive star formation at this epoch. The rapid evolution of submm galaxies and QSO populations contrasts with that seen in bolometrically lower luminosity galaxy samples selected in the restframe UV, and suggests a close link between submm galaxies and the formation and evolution of the galactic halos which host QSOs. [Abridged].

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arXiv2004

The Rest-Frame Optical Properties of SCUBA Galaxies

We present optical and near-IR photometry of 96 dusty, far-IR luminous galaxies. We have precise spectroscopic redshifts for all these galaxies yielding a median redshift of z=2.2. The majority, 78, are submm-detected galaxies lying at z=0.2-3.6, while the remaining 18 are optically-faint uJy radio galaxies at z=0.9-3.4 which are proposed to be similarly luminous, dusty galaxies whose dust emission is too hot to be detected in the submm. We compare the photometric and morphological properties of these distant, ultraluminous galaxies to local samples. We confirm that spectroscopically-identified far-IR luminous galaxies at z>1 display a wide variety in their optical-near-IR and near-IR colors, with only a modest proportion red enough to classify as unusually red. We show that on average luminous, high-z dusty galaxies are both brighter and redder in restframe optical passbands than UV-selected star-forming galaxies at similar z. HST ACS imaging of 20 sources demonstrates both indications of mergers and interactions, which may have triggered their activity, and structured dust within these galaxies. We derive a near-IR Hubble diagram for far-IR luminous galaxies, showing that they are typically fainter than high luminosity radio galaxies at similar z and exhibit more scatter in their K-band magnitudes. The typical extinction-corrected optical luminosity of the high-z population, assuming passive evolution, provides a good fit to the bright end of the luminosity function of luminous spheroidal galaxies seen in rich clusters at z<1. This adds to the growing evidence that these high z, far-infrared luminous sources identify star-formation and AGN fueling events in the early life of massive galaxies. [Abridged]

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arXiv2004

A population of hot, dusty ultra-luminous galaxies at z~2

We report spectroscopic redshifts for 18 microJy-radio galaxies at mean redshift of z=2.2 that are faint at both submmillimeter (submm) and optical wavelengths. While the radio fluxes of these galaxies could indicate far-infrared (far-IR) luminosities comparable to high-redshift submillimeter-selected galaxies (>10^12 Lsun), none are detected in the submm. We propose that this new population of galaxies represents an extension of the high-redshift submm galaxy population, but with hotter characteristic dust temperatures that shift the peak of their far-IR emission to shorter wavelengths, reducing the submm flux below the sensitivity of current instruments. Therefore, surveys in the submm waveband may miss up to half of the most luminous, dusty galaxies at z~2. Mid-infrared observations with Spitzer will be a powerful tool to test this hypothesis.

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arXiv2004

The submm properties of GRB host galaxies

Long duration gamma-ray bursts (GRBs) accompany the deaths of some massive stars and hence, since massive stars are short lived, are a tracer of star formation activity. Given that GRBs are bright enough to be seen to very high redshifts, and detected even in dusty environments, they should therefore provide a powerful probe of the global star formation history of the universe. The potential of this approach can be investigated via submm photometry of GRB host galaxies. Submm luminosity also correlates with star formation rate, so the distribution of host galaxy submm fluxes should allow us to test the two methods for consistency. Here, we report new JCMT/SCUBA 850 micron measurements for 15 GRB hosts. Combining these data with results from previous studies we construct a sample of 21 hosts with <1.4 mJy errors. We show that the distribution of apparent 850 micron flux densities of this sample is reasonably consistent with model predictions, but there is tentative evidence of a dearth of submm bright (>4 mJy) galaxies. Furthermore, the optical/infrared properties of the submm brightest GRB hosts are not typical of the galaxy population selected in submm surveys, although the sample size is still small. Possible selection effects and physical mechanisms which may explain these discrepancies are discussed.

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arXiv2004

Searching for gravitational lenses in the distant universe

The ESA cornerstone mission The Far-Infrared and Submillimetre Sapce Telescope (FIRST) has the ideal combination of sensitivity and angular resolving power to determine the bright counts of galaxies over a large area of sky in the submillimetre (submm) waveband. Important information about the evolution of galaxies at moderate redshifts will be provided by the analysis of these counts, and the effects of gravitational lensing will make the counts even more significant for observational cosmology. This paper describes the flux and surface densities of lensed galaxies in the submm waveband and explains how FIRST could be used to discover several tens of lenses. The Planck Surveyor and FIRST missions are very well suited to cooperate in this programme, and together could compile a larger sample of several hundred lenses. FIRST will be able to detect the signal due to the Sunyaev--Zel'dovich effect in a large sample of clusters. These observations could also be used to investigate submm-wave lensing by clusters, and to infer the properties of the population of faint distant galaxies.

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arXiv2004

The very bright SCUBA galaxy count: looking for SCUBA galaxies with the Mexican Hat Wavelet

We present the results of a search for bright high-redshift galaxies in two large SCUBA scan-maps of Galactic regions. A Mexican Hat Wavelet technique was used to locate point sources in these maps, which suffer high foreground contamination as well as typical scan-map noise signatures. A catalogue of point source objects was selected and observed again in the submillimetre continuum, and in HCO+ (3->2) at zero redshift to rule out Galactic sources. No extragalactic sources were found. Simulations show that the survey was sensitive to sources with fluxes > 50 mJy, depending on the local background. These simulations result in upper limits on the 850-micron counts of SCUBA galaxies of 53 per square degree at 50 mJy and 2.9 per square degree at 100 mJy.

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arXiv2004

Submillimeter Galaxies as Tracers of Mass Assembly at Large M

Luminous submillimeter galaxies (SMGs) have been known for some time to produce a substantial fraction of the far-IR/submillimeter background. New observations show that these systems are not only very luminous, but also very massive. Here we present results from (a) a survey of SMGs' molecular line emission, which has confirmed Keck optical redshifts and revealed their high gas and dynamical masses; and (b) a detailed case study of the rest-frame optical emission from one SMG, which has revealed its high metallicity and old stellar population. We infer a high z~2.7 comoving number density of galaxies with baryonic masses greater than 10^11 solar masses; this is not accounted for in current semi-analytic models of galaxy evolution.

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arXiv2004

Fact: Many SCUBA galaxies harbour AGNs

Deep SCUBA surveys have uncovered a large population of ultra-luminous galaxies at z>1. These sources are often assumed to be starburst galaxies, but there is growing evidence that a substantial fraction host an AGN (i.e., an accreting super-massive black hole). We present here possibly the strongest evidence for this viewpoint to date: the combination of ultra-deep X-ray observations (the 2 Ms Chandra Deep Field-North) and deep optical spectroscopic data. We argue that upward of 38% of bright (f850um>=5mJy) SCUBA galaxies host an AGN, a fraction of which are obscured QSOs (i.e., L_X>3x10^{44} erg/s). However, using evidence from a variety of analyses, we argue that in almost all cases the AGNs are not bolometrically important (i.e., <20%). Thus, star formation appears to dominate their bolometric output. A substantial fraction of bright SCUBA galaxies show evidence for binary AGN activity. Since these systems appear to be interacting and merging at optical/near-IR wavelengths, their super-massive black holes will eventually coalesce.

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arXiv2003

A 1200 micron MAMBO Survey of the ELAIS N2 and Lockman Hole East Fields

Using the MPIfR Max Planck Millimeter Bolometer array (MAMBO) on the IRAM 30m Telescope we have mapped the ELAIS N2 and Lockman Hole East Fields at 1200 micron to a rms noise level of 0.8-1.0 mJy per 11" beam. The areas surveyed are 326 arcmin^2 in the ELAIS N2 field and 212 arcmin^2 in the Lockman Hole,and cover the 260 arcmin^2 previously observed by SCUBA [5].

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arXiv2003

Interferometric Observations of Powerful CO Emission from the three Submillimeter Galaxies at z=2.30, 2.51 and 3.35

We report IRAM Plateau de Bure, millimeter interferometry of three z=~2.4 to 3.4, SCUBA deep field galaxies. Our CO line observations confirm the rest-frame UV/optical redshifts, thus more than doubling the number of confirmed, published redshifts of the faint submillimeter population and proving their high-z nature. In all three sources our measurements of the intrinsic gas and dynamical mass are large (1e10 to 1e11 Msun). In at least two cases the data show that the submillimeter sources are part of an interacting system. Together with recent information gathered in the X-ray, optical and radio bands our observations support the interpretation that the submm-population consists of gas rich (gas to dynamical mass ratio ~0.5) and massive, composite starburst/AGN systems, which are undergoing a major burst of star formation and are evolving into m*-galaxies.

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arXiv2003

Near-Infrared Colors of Submillimeter-Selected Galaxies

We report on deep near-infrared (NIR) observations of submillimeter-selected galaxies (SMGs) with the Near Infrared Camera (NIRC) on the Keck I telescope. We have identified K-band candidate counterparts for 12 out of 15 sources in the SCUBA Cluster Lens Survey. Three SMGs remain non-detections with K-band limits of K>23 mag, corrected for lensing. Compensating for lensing we find a median magnitude of K=22+/-1 mag for the SMG population, but the range of NIR flux densities spans more than a factor of 400. For SMGs with confirmed counterparts based on accurate positions from radio, CO, and/or millimeter continuum interferometric observations, the median NIR color is J-K=2.6+/-0.6 mag. The NIR-bright SMGs (K<19 mag) have colors of J-K =~ 2 mag, while the faint SMGs tend to be extremely red in the NIR (J-K>3 mag). We argue that a color selection criterion of J-K>~3 mag can be used to help identify counterparts of SMGs that are undetected at optical and radio wavelengths. The number density of sources with J-K>3 mag is 5 arcmin^{-2} at K<22.5 mag, greater than that of SMGs with S(850um)>2 mJy. It is not clear if the excess represents less luminous infrared-bright galaxies with S(850um)<~2 mJy, or if the faint extremely red NIR galaxies represent a different population of sources that could be spatially related to the SMGs.

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arXiv2003

The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003

Many past studies of cosmological gamma-ray bursts (GRBs) have been limited because of the large distance to typical GRBs, resulting in faint afterglows. There has long been a recognition that a nearby GRB would shed light on the origin of these mysterious cosmic explosions, as well as the physics of their fireballs. However, GRBs nearer than z=0.2 are extremely rare, with an estimated rate of localisation of one every decade. Here, we report the discovery of bright optical afterglow emission from GRB 030329. Our prompt dissemination and the brilliance of the afterglow resulted in extensive followup (more than 65 telescopes) from radio through X-ray bands, as well as measurement of the redshift, z=0.169. The gamma-ray and afterglow properties of GRB 030329 are similar to those of cosmological GRBs (after accounting for the small distance), making this the nearest known cosmological GRB. Observations have already securely identified the progenitor as a massive star that exploded as a supernova, and we anticipate futher revelations of the GRB phenomenon from studies of this source.

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arXiv2003

Discs in early-type lensing galaxies: effects on magnification ratios and measurements of $H_0$

Observations of early-type galaxies, both in the local universe and in clusters at medium redshifts, suggest that these galaxies often contain discs or disc-like structures. Using the results of Kelson et al. (2000) for the incidence of disc-components among the galaxies in the redshift z=0.33 cluster CL 1358+62, we investigate the effect of disc structures on the lensing properties of early-type galaxies. Statistical properties, like magnification cross sections and the expected number of quad (four-image) lens systems, are not affected greatly by the inclusion of discs that contain less than about 10 per cent of the total stellar mass. However, the properties of individual lens systems are affected. We estimate that 10-30 per cent of all quad lens systems, with early-type deflector galaxies, would be affected measurably by the presence of disc components. Intriguingly, the image magnification ratios are altered significantly. The amplitude of the predicted change is sufficient to explain the observed magnification ratios in systems like B1422+231 without requiring compact substructure. Furthermore, time delays between images also change; fitting a bulge-only model to early-type lenses that in fact contain a disc would yield a value of the Hubble constant H_0 that is systematically too low by about 25 per cent.

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