Searcharxiv⌕ Search

arXiv subjects

Andrew Blain

Publications and source records attributed to Andrew Blain.

52 records · Page 3Linked to original sources
arXiv2005

Optical and Near-Infrared Integral Field Spectroscopy of the SCUBA Galaxy N2-850.4

We present optical and near-infrared integral field spectroscopy of the SCUBA galaxy SMM J163650.43+405734.5 (ELAIS N2 850.4) at z=2.385. We combine Ly-alpha and H-alpha emission line maps and velocity structure with high resolution HST ACS and NICMOS imaging to probe the complex dynamics of this vigorous star-burst galaxy. The imaging data shows a complex morphology, consisting of at least three components separated by ~1'' (8kpc) in projection. When combined with the H-alpha velocity field from UKIRT UIST IFU observations we identify two components whose redshifts are coincident with the systemic redshift, measured from previous CO observations, one of which shows signs of AGN activity. A third component is offset by 220+/-50km/s from the systemic velocity. The total star formation rate of the whole system (estimated from the narrow-line H-alpha and uncorrected for reddening) is 340+/-50Mo/yr. The Ly-alpha emission mapped by the GMOS IFU covers the complete galaxy and is offset by +270+/-40km/s from the systemic velocity. This velocity offset is comparable to that seen in rest-frame UV-selected galaxies at similar redshifts and usually interpreted as a star-burst driven wind. The extended structure of the Ly-alpha emission suggests that this wind is not a nuclear phenomenon, but is instead a galactic scale outflow. Our observations suggest that the vigorous activity in N2 850.4 is arising as a result of an interaction between at least two dynamically-distinct components, resulting in a strong starburst, a starburst-driven wind and actively-fuelled AGN activity. [abridged]

astro-ph↗
arXiv2005

Molecular Gas in a z~2.5 Triply-Imaged, sub-mJy Submillimetre Galaxy Typical of the Cosmic Far-Infrared Background

We present the results of observations from the IRAM array of the submm galaxy SMMJ16359+6612 lying at z=2.516 behind the massive cluster A2218. The foreground gravitational lens produces 3 images with a total mag. of 45 of this faint submm galaxy, which has an intrinsic submm flux of f_850mic=0.8mJy placing it below the confusion limit of blank-field surveys. The substantial magnification provides a rare opportunity to probe the nature of a distant sub-mJy submm-selected galaxy, part of the population which produces the bulk of the submm cosmic far-infrared background. Our observations detect the CO(3-2) line in all 3 images, as well as the CO(7-6) line and the dust continuum at 1.3mm for the brightest image. The CO(3-2) velocity profile displays a double-peak profile which is well fit by two Gaussians with FWHM of 220km/s and separated by 280km/s. We estimate the dynamical mass of the system to be ~1.5 10^10 M_sun and an H2 gas mass of 2.6 10^9 M_sun. We identify a spatial offset of ~1'' between the two CO(3-2) velocity components, modeling of which indicates that the offset corresponds to just ~3kpc in projection at z=2.5. The spatial and velocity properties of these two components are closely related to features detected in previously published Halpha spectroscopy. We conclude that this source is likely to be a compact merger of 2 fairly typical Ly-break galaxies with a maximal separation between the two nuclei of ~3kpc. This system is much less luminous and massive than other high-z submm galaxies studied to date, but it bears a close similarity to similarly luminous, dusty starburst resulting from lower-mass mergers in the local Universe.

astro-ph↗
arXiv2004

The Rest-frame Optical Spectra of SCUBA Galaxies

We present near-infrared spectroscopy and narrow-band imaging at the wavelength of redshifted H-alpha for a sample of 30 high-redshift, far-infrared luminous galaxies. This sample is selected from surveys in the sub-millimeter, millimeter and radio wavebands and has complete redshift coverage with a median redshift of z~2.4. Removing obvious AGN, we find that the predicted H-alpha star formation rates in this diverse population are suppressed (by ~10x) compared to those derived from their far-infrared luminosities. We estimate that AGN are present in at least 40% of the galaxies in our sample. To further investigate this, we construct a composite rest-frame spectrum for both the entire sample and for those galaxies which individually show no signs of nuclear activity. We find [NII]/H-alpha ratios for both composite spectra which suggest that the energy output of the galaxies is star-formation- rather than AGN-dominated. The median H-alpha line width for our sample (removing obvious AGN) is 400+/-70km/s (FWHM), and the typical spatial extent of the H-alpha emission in our narrow-band observations is < 4-8kpc, which indicates a dynamical mass of 1-2 x 10^11 Mo. This estimate is larger than recent estimates of the dynamical masses of UV-selected galaxies at similar redshifts derived in an identical manner. We also compared our H-alpha and far-infrared luminosities with deep Chandra observations of a subset of our survey fields and use these data to further assess their AGN content. We conclude that these high-redshift, far-infrared luminous galaxies represent a population of massive, metal-rich, merging systems with high instantaneous star formation rates, strong dust obscuration and actively-fueled AGN which are likely to be the progenitors of massive local elliptical galaxies. (abridged)

astro-ph↗
arXiv2004

Multiply-imaged submm galaxy in a z~2.5 group

We present observations of a remarkable submillimetre-selected galaxy, SMMJ16359+6612. This distant galaxy lies behind the core of a massive cluster of galaxies, A2218, and is gravitationally lensed by the foreground cluster into three discrete images which were identified in deep submillimetre maps of the cluster core at both 450 and 850micron. Subsequent follow-up using deep optical and NIR images identify a faint counterpart to each of the 3 images, with similar red optical--NIR colours and HST morphologies. By exploiting a detailed mass model for the cluster lens we estimate that the combined images of this galaxy are magnified by a factor of ~45, implying that this galaxy would have un-lensed magnitudes K_s=22.9 and I=26.1, and an un-lensed 850micron flux density of only 0.8mJy. Moreover, the highly constrained lens model predicted the redshift of SMMJ16359+6612 to be z=2.6+/-0.4. We confirm this estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of z=2.516. SMMJ16359+6612 is the faintest submm-selected galaxy so far identified with a precise redshift. Thanks to the large gravitational magnification of this source, we identify 3 sub-components in this submm galaxy, which are also seen in the NIRSPEC data, arguing for either a strong dust (lane) absorption or a merger. Interestingly, there are 2 other highly-amplified galaxies at almost identical redshifts in this field (although neither is a strong submm emitter). The 3 galaxies lie within a ~100kpc region on the background sky, suggesting this submm galaxy is located in a dense high-redshift group.

astro-ph↗
arXiv2002

Deep radio imaging of the SCUBA 8-mJy survey fields: sub-mm source identifications and redshift distribution

The SCUBA 8-mJy survey is the largest submm extragalactic mapping survey undertaken to date, centred on the Lockman Hole and ELAIS N2 regions. Here, we present new 1.4-GHz imaging of the depth and resolution necessary to reliably identify radio counterparts for 18 of 30 submm sources. Armed with this greatly improved positional information, we present and analyse new optical, near-IR and XMM-Newton X-ray imaging to identify optical/IR host galaxies to half of the submm-selected sources in those fields. As many as 15% of the submm sources detected at 1.4 GHz are resolved by the 1.4'' beam and a further 25% have more than one radio counterpart, suggesting that radio and submm emission arise from extended starbursts and that interactions are common. We note that less than a quarter of the submm-selected sample would have been recovered by targeting optically faint radio sources, underlining the selective nature of such surveys. At least 60% of the radio-confirmed optical/IR host galaxies appear to be morphologically distorted; many are composite systems - red galaxies with relatively blue companions; just over half are found to be very red or extremely red; contrary to popular belief, most are sufficiently bright to be tackled with spectrographs on 8-m telescopes. We estimate the median redshift of the S(850um) ~ 8 mJy submm galaxy population: if the radio/far-IR correlation holds at high redshift, and our sample is unbiased, we derive a conservative median z >= 2.0, or >= 2.4 using spectral templates more representative of known submm galaxies [abridged].

astro-ph↗
arXiv2002

Gigamasers: the key to the dust-obscured star-formation history of the Universe?

We discuss the possibility of using OH and H2O gigamasers to trace the redshift distribution of luminous, dust-obscured, star-forming galaxies. It has long been thought that ultraluminous, interacting galaxies should host gigamasers due to their vast pumping IR luminosity, the large column density of molecules available to populate the maser states and the turbulent motion of the gas in these dynamically complex systems which allows unsaturated maser emission. OH masers may thus be well-suited to the redshift-blind detection of ultraluminous and hyperluminous infrared galaxies (L_FIR >= 10^12 L_sun) such as those uncovered by the SCUBA submillimetre camera. The bandwidth requirement is low, <1 GHz for z=1-10 (lower still if additional redshift constraints are available) and the dual-line 1665-/1667-MHz OH spectral signature can act as a check on the reality of detections.

astro-ph↗
arXiv2001

Probing the mass distribution in groups of galaxies using gravitational lensing

In this paper, we study gravitational lensing by groups of galaxies. Since groups are abundant and therefore have a large covering fraction on the sky, lensing by groups is likely to be very important observationally. Besides, it has recently become clear that many lens models for strong lensing by individual galaxies require external shear to reproduce the observed image geometries; in many cases a nearby group is detected that could provide this shear. In this work, we study the expected lensing behavior of galaxy groups in both the weak and strong lensing regime. We examine the shear and magnification produced by a group and its dependence on the detailed mass distribution within the group. We find that the peak value of the weak lensing shear signal is of the order of 3 per cent and varies by a factor of about 2 for different mass distributions. These variations are large enough to be detectable in the Sloan Digital Sky Survey (SDSS). In the strong lensing regime we find that the image geometries and typical magnifications are sensitive to the group properties and that groups can easily provide enough external shear to produce quadruple images. We investigate the statistical properties of lensing galaxies that are near or part of a group and find that statistical lens properties, like the distribution of time delays, are affected measurably by the presence of the group which can therefore introduce an additional systematic error in the measurement of the Hubble constant from such systems. We conclude that both the detection of weak lensing by groups and accurate observations of strong galaxy lens systems near groups could provide important information on the total mass and matter distribution within galaxy groups.

astro-ph↗
arXiv2001

Locating the starburst in the SCUBA galaxy, SMM J14011+0252

We present new, multi-wavelength, high-resolution imaging of the luminous, submillimeter galaxy, SMM J14011+0252, an interacting starburst at z = 2.56. Our observations comprise optical imaging from the HST, sensitive radio mapping from the VLA and CO observations from OVRO and BIMA. Aided by well-constrained gravitational amplification, we use these new data to map the distribution of gas and both obscured and unobscured starlight. The maps show that the gas and star formation are extended on scales of >= 10 kpc, much larger than starbursts seen in local ultraluminous galaxies, and larger than the rest-frame UV-bright components of SMM J14011+0252, J1/J2. The most vigorous star formation is marked by peaks in both the molecular gas and radio emission, ~1'' north of J1/J2, in the vicinity of J1n, an apparent faint extension of J1. Using new sub-0.5'' K-band imaging from UKIRT, we identify J1n as an extremely red object (ERO). We suggest that while J1 and J2 are clearly associated with the submm source, they are merely windows through the dust, or unobscured companions to a large and otherwise opaque star-forming system. Hence, their rest-frame UV properties are unlikely to be relevant for understanding the detailed internal physics of the starburst.

astro-ph↗
arXiv2000

The Nature of Faint Submillimeter Galaxies

We summarise the main results on the faint submillimeter (submm) galaxy population which have come from the SCUBA Cluster Lens Survey. We detail our current understanding of the characteristics of these submm-selected galaxies across wavebands from X-rays to radio. After presenting the main observational properties of this population we conclude by discussing the nature of these distant, ultraluminous infrared galaxies and their relationship to other high-redshift populations.

astro-ph↗
arXiv1999

The diversity of SCUBA-selected galaxies

We present extensive observations of a sample of distant, submm galaxies detected in the field of the massive cluster lens, A1835, using SCUBA. Taken in conjunction with earlier observations of other submm-selected sources (Ivison et al. 1998; Smail et al. 1999; Soucail et al. 1999) we now have detailed, multi-wavelength observations of 7 examples of the submm population, having exploited the combination of achromatic amplification by cluster lenses and lavish archival datasets. These sources, all clearly at z > 1, illustrate the wide range in the radio and optical properties of distant submm-selected galaxies. We include detailed observations of the first candidate `pure' starburst submm galaxy at high redshift, a z=2.56 interacting galaxy which shows no obvious sign of hosting an AGN. The remaining sources have varying degrees of inferred AGN activity (3 from 7 of the most luminous show some evidence of the presence of an AGN) although even when an AGN is obviously present it is still not apparent if reprocessed radiation from this source dominates the submm emission. In contrast with the variation in the spectral properties, we see relatively homogeneous morphologies for the population, with a large fraction of merging or interacting systems. Our study shows that virtually identical SEDs are seen for galaxies which exhibit strikingly different opt/UV spectral-line characteristics. We conclude that standard opt/UV spectral classifications are misleading when applied to distant, highly obscured galaxies and that we must seek other means of determining the various contributions to the overall energy budget of submm galaxies and hence to the far-IR extragalactic background.

astro-ph↗
arXiv1999

Submm Continuum Surveys for Obscured Galaxies

We discuss deep surveys in the submm regime using the SCUBA bolometer array on the JCMT. At 850um SCUBA has resolved the bulk of the submm background (SMBR) detected by COBE into discrete sources brighter than 0.5mJy. The on-going identification and characterisation of this population at other wavelengths suggests that the bulk of the submm sources brighter than ~1mJy lie at z>1, with a median redshift for the population of ~2-3. The optical/near-infrared properties of the counterparts to the submm sources breakdown as follows: roughly two-thirds have reliable identifications with the others being more ambiguous. Of those with identifications about half are optically bright (I<23) mergers or interactions with a high proportion showing signatures of AGN activity and the other half are optically faint (I>25) including both blank fields and Extremely Red Objects (EROs). We conclude that a population of distant, highly obscured ultraluminous infrared galaxies (ULIRGs) dominates the SMBR. The wide range in the characteristics of the optical counterparts is consistent with the dispersion in the restframe UV properties of local ULIRGs. We suggest that the faint submm population comprises a class of high redshift dusty, mergers associated with the formation of present day luminous elliptical galaxies.

astro-ph↗
arXiv1999

SCUBA's first-born: SMM J02399-0136

We discuss observations of the submm-selected galaxy, SMM J02399-0136, and what has been learnt about it during the year following its discovery. SMM J02399-0136 was the first distant galaxy detected in submm surveys with SCUBA. Its association with a massive, gas-rich starburst/AGN at z=2.8 has lead to suggestions that the prevalence of AGN in the early Universe may be high and that these AGN may account for a significant fraction of the far-IR background.

astro-ph↗
arXiv1998

Deep sub-mm surveys with SCUBA

We review published deep surveys in the submillimeter (sub-mm) regime from the new Sub-millimetre Common User Bolometer Array (SCUBA) on the 15-m James Clerk Maxwell Telescope (JCMT), Mauna Kea, Hawaii. Summarising the number counts of faint sub-mm sources determined from the different surveys we show that the deepest counts from our completed SCUBA Lens Survey, down to 0.5mJy at 850um fully account for the far-infrared background (FIRB) detected by COBE. We conclude that a population of distant, dust-enshrouded ultraluminous infrared galaxies dominate the FIRB emission around 1mm. We go on to discuss the nature of this population, starting with the identification of their optical counterparts, where we highlight the important role of deep VLA radio observations in this process. Taking advantage of the extensive archival Hubble Space Telescope (HST) observations of our fields, we then investigate the morphological nature of the sub-mm galaxy population and show that a large fraction exhibit disturbed or interacting morphologies. By employing existing broadband photometry, we derive crude redshift limits for a complete sample of faint sub-mm galaxies indicating that the majority lie at z<5, with at most 20% at higher redshifts. We compare these limits to the initial spectroscopic results from various sub-mm samples. Finally we discuss the nature of the sub-mm population, its relationship to other classes of high-redshift galaxies and its future role in our understanding of the formation of massive galaxies.

astro-ph↗
arXiv1998

A Submillimetre Survey of the Hubble Deep Field: Unveiling Dust-Enshrouded Star Formation in the Early Universe

The advent of sensitive sub-mm array cameras now allows a proper census of dust-enshrouded massive star-formation in very distant galaxies, previously hidden activity to which even the deepest optical images are insensitive. We present the deepest sub-mm survey, taken with the SCUBA camera on the James Clerk Maxwell Telescope (JCMT) and centred on the Hubble Deep Field (HDF). The high source density on this image implies that the survey is confusion-limited below a flux density of 2 mJy. However within the central 80 arcsec radius independent analyses yield 5 reproducible sources with S(850um) > 2 mJy which simulations indicate can be ascribed to individual galaxies. These data lead to integral source counts which are completely inconsistent with a no evolution model, whilst the combined brightness of the 5 most secure sources in our map is sufficient to account for 30-50% of the previously unresolved sub-mm background, and statistically the entire background is resolved at about the 0.3 mJy level. Four of the five brightest sources appear to be associated with galaxies which lie in the redshift range 2 < z < 4. With the caveat that this is a small sample of sources detected in a small survey area, these submm data imply a star-formation density over this redshift range that is at least five times higher than that inferred from the rest-frame ultraviolet output of HDF galaxies.

astro-ph↗
arXiv1998

Unveiling Dust-enshrouded Star Formation in the Early Universe: a Sub-mm Survey of the Hubble Deep Field

The advent of sensitive sub-mm array cameras now allows a proper census of dust-enshrouded massive star-formation in very distant galaxies, previously hidden activity to which even the faintest optical images are insensitive. We present the deepest sub-mm survey of the sky to date, taken with the SCUBA camera on the James Clerk Maxwell Telescope and centred on the Hubble Deep Field. The high source density found in this image implies that the survey is confusion-limited below a flux density of 2 mJy. However, within the central 80 arcsec radius independent analyses yield 5 reproducible sources with S(850um) > 2 mJy which simulations indicate can be ascribed to individual galaxies. We give positions and flux densities for these, and furthermore show using multi-frequency photometric data that the brightest sources in our map lie at redshifts z~3. These results lead to integral source counts which are completely inconsistent with a no-evolution model, and imply that massive star-formation activity continues at redshifts > 2. The combined brightness of the 5 most secure sources in our map is sufficient to account for 30 - 50% of the previously unresolved sub-mm background, and we estimate statistically that the entire background is resolved at about the 0.3 mJy level. Finally we discuss possible optical identifications and redshift estimates for the brightest sources. One source appears to be associated with an extreme starburst galaxy at z~1, whilst the remaining four appear to lie in the redshift range 2 < z < 4. This implies a star-formation density over this redshift range that is at least five times higher than that inferred from the ultraviolet output of HDF galaxies.

astro-ph↗