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Ian Smail

Publications and source records attributed to Ian Smail.

At least 307 records · Page 17Linked to original sources
arXiv2006

A Search for Dense Gas in Luminous Submillimeter Galaxies with the 100-m Green Bank Telescope

We report deep K-band (18-27GHz) observations with the 100-m Green Bank Telescope of HCN(1-0) line emission towards the two submillimeter-selected galaxies (SMGs) SMMJ02399-0136 (z=2.81) and SMMJ16359+6612 (z=2.52). For both sources we have obtained spectra with channel-to-channel rms noise of <=0.5mJy, resulting in velocity-integrated line fluxes better than < 0.1 Jy km/s, although we do not detect either source. Such sensitive observations -- aided by gravitational lensing of the sources -- permit us to put upper limits of L_HCN(1-0) < 2x10^10 K km/s pc^2 on the intrinsic HCN(1-0) line luminosities of the two SMGs. The far-infrared (FIR) luminosities for all three SMGs with sensitive HCN(1-0) observations to date are found to be consistent with the tight FIR-HCN luminosity correlation observed in Galactic molecular clouds, quiescent spirals and (ultra) luminous infrared galaxies in the local Universe. Thus, the observed HCN luminosities remain in accordance with what is expected from the universal star formation efficiency per dense molecular gas mass implied by the aforementioned correlation, and more sensitive observations with today's large aperture radio telescopes hold the promise of detecting HCN(1-0) emission in similar objects in the distant Universe.

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arXiv2006

The Link between Submillimetre Galaxies and Luminous Ellipticals: Near-Infrared IFU Spectroscopy of Submillimetre Galaxies

We present two-dimensional spectroscopy covering the rest-frame wavelengths of strong optical emission lines in six luminous submillimetre galaxies at z=1.3--2.5. Together with HST ACS and NICMOS imaging we map the dynamics and morphologies of these systems on scales from 4--11kpc. Four of the systems show multiple components in their spatially-resolved spectra with average velocity offsets of ~180km/s across 8kpc in projection. From the ensemble properties from our survey and the literature, we estimate the typical dynamical masses of bright sub-mm galaxies as (5+/-3) x10^{11}Mo. This is similar to recent estimates of their stellar masses -- suggesting that the dynamics of the central regions of these galaxies are baryon dominated, with a substantial fraction of those baryons in stars by the epoch of observation. Combining our dynamical mass estimates with stellar luminosities for this population we investigate whether submillimetre galaxies can evolve onto the Faber-Jackson relation for local ellipticals. Adopting a typical lifetime of tau_{burst}~300Myr for the submillimetre-luminous phase we find that the stellar populations of sub-mm galaxies should fade to place them on the Faber-Jackson relation, at M_K ~ -25.1. Furthermore, using the same starburst lifetime we correct the observed space density of submillimetre galaxies for the duty cycle to derive a volume density of the progenitors of ~1x10^{-4} Mpc^{-3}. This is consistent with the space density of local luminous early-type galaxies with M_K ~ -25.1, indicating that submillimetre galaxies can evolve onto the scaling relations observed for local early-type galaxies, and the observed population at z~2 is then sufficient to account for the formation of the whole population of >~3 L^{*} ellipticals seen at z~0.

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arXiv2006

A Panoramic Mid-infrared Survey of Two Distant Clusters

(abridged) We present panoramic Spitzer MIPS 24um observations covering 9x9Mpc (25'x25') fields around two massive clusters, Cl0024+16 and MS0451-03, at z=0.39 and z=0.55. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turn-around radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24um members. The much more significant excess is associated with Cl0024+16, whereas MS0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A_V~1-2 mags) rather than emission from dusty tori around active galactic nuclei (AGN) in early-type hosts. The inferred total-infrared star-formation rates in Cl0024+16 are typically >5x greater than those found from a similar Halpha survey, indicating significant obscured activity in the cluster population. We find evidence for strong evolution of the level of dust-obscured star-formation in dense environments out to z=0.5, analogous to the rise in fraction of optically-selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.

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arXiv2006

Galaxies Under the Cosmic Microscope: Resolved Spectroscopy and New Constraints on the z=1 Tully-Fisher relation

We exploit the gravitational potential of massive cluster lenses to probe the emission line properties of six z=1 galaxies which appear as highly magnified luminous arcs. Using the GMOS integral field spectrograph together with detailed cluster lens models we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to \~0.5kpc (unlensed) at z=1. Four of the galaxies have stable disk-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I-band Tully-Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B-band, the observations suggest 0.5+/-0.3mag of brightening, consistent with increased star-formation activity at z=1. However, the galaxies with stable disk kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counter-parts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high redshift Universe than possible with conventional surveys.

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arXiv2005

The Las Campanas/AAT Rich Cluster Survey III: Spectroscopic Studies of X-ray Bright Galaxy Clusters at z~0.1

[abridged] We present the analysis of the spectroscopic and photometric catalogues of 11 X-ray luminous clusters at z=0.07-0.16 from the Las Campanas / Anglo-Australian Telescope Rich Cluster Survey. Our spectroscopic dataset consists of over 1600 galaxy cluster members, of which two thirds are outside r_200. We assign cluster membership using a detailed mass model and expand on our previous work on the cluster colour-magnitude relation where membership was inferred statistically. We confirm that the modal colours of galaxies on the colour magnitude relation become progressively bluer with increasing radius and decreasing local galaxy density. Interpreted as an age effect, we hypothesize that these trends in galaxy colour should be reflected in mean Hdelta equivalent width. We confirm that passive galaxies in the cluster increase in Hdelta line strength as dHdelta / d r_p = 0.35 +/- 0.06. A variation of star formation rate, as measured by [OII], with increasing local density of the environment is discernible and is shown to be in broad agreement with previous studies from 2dFGRS and SDSS. We find that clusters at z~0.1 are less active than their higher redshift analogues. We also investigate unusual populations of blue and very red nonstarforming galaxies and we suggest that the former are likely to be the progenitors of galaxies which will lie on the colour-magnitude relation, while the colours of the latter possibly reflect dust reddening. The cluster galaxies at large radii consist of both backsplash ones and those that are infalling to the cluster for the first time. We make a comparison to the field population at z~0.1 and examine broad differences between the two populations. Individually, the clusters show significant variation in their galaxy populations which reflects their recent infall histories.

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arXiv2005

A robust sample of submillimetre galaxies: constraints on the prevalence of dusty, high-redshift starbursts

The modest significance of most sources detected in current submm surveys can potentially compromise some analyses due to the inclusion of spurious sources in catalogues typically selected at >3.0-3.5sigma. Here, we develop and apply a dual-survey extraction technique to SCUBA and MAMBO images of the Lockman Hole. Cut above 5sigma, our catalogue of SMGs is more robust than previous samples, with a reduced likelihood of real, but faint SMGs (beneath and around the confusion limit) entering via superposition with noise. The effective flux limit of the survey is well matched to our deep 1.4-GHz image. The former is sensitive to luminous, dusty galaxies at extreme redshifts whilst the latter probes the z<3 regime. A high fraction of our robust SMGs (~80%) have radio counterparts which, given the ~10% contamination by spurious sources, suggests that very distant SMGs (z>>3) are unlikely to make up more than ~10% of the bright SMG population. This implies that almost all of the bright SMG population is amenable to study via the deepest current radio imaging. We use these radio counterparts to provide an empirical calibration of the positional uncertainty in SMG catalogues. We then go on to outline the acquisition of redshifts for radio-identified SMGs, from sample selection in the submm, to counterpart selection in the radio and optical/IR, to slit placement on spectrograph masks. We determine a median of z=2.05 +/- 0.41 from a sample of six secure redshifts for unambigious radio-identified submm sources and z=2.14 +/- 0.27 when we include submm sources with multiple radio counterparts and/or less reliable redshifts. These figures are consistent with previous estimates, suggesting that our knowledge of the median redshift of bright SMGs population has not been biased by the low significance of the source catalogues employed.

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arXiv2005

A Catalogue of Potential Adaptive Optics Survey Fields from the UKIRT Archive

We present a multicolour catalogue of faint galaxies situated close to bright stars, V<15, with the aim of identifying high-redshift galaxies suitable for study with adaptive optics-equipped near-infrared imagers and spectrographs. The catalogue is constructed from archival calibration observations of UKIRT Faint Standard stars with the UFTI camera on UKIRT. We have analysed the deepest 16 fields from the archive to provide a catalogue of galaxies brighter than K~20.3 lying within 25" of the guide stars. We identify 111 objects in a total survey area of 8.7 sq. arcmin, of these 87 are classified as galaxies based on their light profiles in our ~0.5" median seeing K-band images. Of these, 12 galaxies have (J-K)>2.0 consistent with them lying at high-redshifts, z~2. These 12 very red galaxies have K-band magnitudes of K=18.1-20.1 and separations from the guide stars of 4-20" and hence are very well-suited to adaptive optics studies to investigate their morphologies and spectral properties on sub-kpc scales. We provide coordinates and JHK photometry for all catalogued objects.

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arXiv2005

A submm survey of Lyman-alpha haloes in the SA22 protocluster at z=3.1

We present the results from a submm survey of a sample of 23 giant Lya emitting nebulae in the overdensity at z=3.09 in the SA22 field. These objects, which have become known as Lya Blobs (LABs) have a diverse range of morphology and surface brightness, but the nature of their power source is unclear - with cooling flows and/or AGN/starburst ionised winds being possibilities. Using the SCUBA submm camera we measure the 850um flux of a sample of LABs, detecting four LABs at >3.5sigma individually, and a modest statistical detection of the full sample at about 3mJy. These fluxes correspond to bolometric luminosities in the ultraluminous regime, with star-formation rates of about 1e3 Msun/yr. We show there is a trend between Lya luminosity and bolometric output, which suggests that a galactic scale superwind generated from starbursts of age 10-100Myr may be responsible for the Lya emission. We estimate the star-formation rate density in SA22 to be >3 Msun/yr/Mpc^3 - greater than the field at this epoch, and note that there are now 7 submm galaxies in the SA22 structure, making this region the richest association of these intensely active galaxies. Finally we suggest that Lya haloes may be a common feature of the submm population in general, and have an important role in the heating and enrichment of the intergalactic medium.

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arXiv2005

A Wide-field Hubble Space Telescope Survey of the Cluster Cl 0024+16 at z=0.4. III: Spectroscopic Signatures of Environmental Evolution in Early Type Galaxies

We report results from a panoramic spectroscopic survey of 955 objects in the field of the rich cluster Cl 0024+1654 (z~0.4), complementing the HST imaging presented in the first paper in this series. Our new spectroscopic sample includes over 200 high quality spectra of cluster members, spread across an area 10 Mpc in diameter. We examine the properties of a large sample of 104 cluster early-types as a function of cluster radius and local density, using them as sensitive tracers of the various physical processes that may be responsible for galaxy evolution. By constructing the Fundamental Plane of Cl 0024, we infer an evolution in the mean mass to light ratio of early-types equal to Δ = -0.14 +- 0.02. In the cluster center, we detect a significantly increased scatter in the relationship compared to that seen in local clusters. Moreover, we observe a clear radial trend in the mass to light ratios of individual early types, with the oldest galaxies located in the cluster core. Galaxies are apparently younger at larger radius, with E+S0s in the periphery having M/L_V ratios that nearly match values seen in the field at a similar redshift. Independent spectral indicators used in combination reveal an abrupt interaction with the cluster environment which occurs near the virial radius of Cl 0024, revealed by small bursts of star formation in a population of dim early-types, as well as by enhanced Balmer absorption for a set of larger E+S0s closer to the cluster core. We construct a simple infall model used to compare the timescales and strengths of the observed interactions in this cluster. We examine the possibility that bursts of star formation are triggered when galaxies suffer shocks as they encounter the intra-cluster medium, or by the onset of galaxy harassment.

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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

Rest-frame optical and far-infrared observations of extremely bright Lyman-break galaxy candidates at z ~ 2.5

We have investigated the rest-frame optical and far-infrared properties of a sample of extremely bright candidate Lyman-break galaxies (LBG) identified in the Sloan Digital Sky Survey. Their high ultraviolet luminosities and lack of strong ultraviolet emission lines are suggestive of massive starbursts, although it is possible that they are more typical luminosity LBGs which have been highly magnified by strong gravitational lensing. Alternatively, they may be an unusual class of weak-lined quasars. If the ultraviolet and submillimetre properties of these objects mirror those of less luminous, starburst LBGs, then they should have detectable rest-frame far-infrared emission. However, our submm photometry fails to detect such emission, indicating that these systems are not merely scaled-up (either intrinsically or as a result of lensing) examples of typical LBGs. In addition we have searched for the morphological signatures of strong lensing, using high-resolution, near-infrared imaging, but we find none. Instead, near-infrared spectroscopy reveals that these systems are, in fact, a rare class of broad absorption-line (BAL) quasars.

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arXiv2005

The Intrinsic Properties of SMMJ14011+0252

We discuss the properties of the bright submillimeter source SMMJ14011+0252 at z=2.56 which lies behind the central regions of the z=0.25 lensing cluster A1835. This system has a complex optical morphology consisting of at least five separate components. We reassess the extensive multiwavelength observations of this system and find strong support for the suggestion that one of these five components represents a foreground galaxy. The spectral and morphological properties of the foreground galaxy indicate that it is a low-luminosity, passive early-type disk member of the A1835 cluster. We estimate the likely properties of the dark matter halo of this galaxy from its stellar distribution. Based on these estimates we suggest that, contrary to earlier claims, this foreground galaxy is unlikely to significantly magnify the background submillimeter source. Thus SMMJ14011+0252 probably represents an intrinsically luminous submillimeter galaxy.

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arXiv2005

Submillimetre photometry of X-ray absorbed QSOs: their formation and evolutionary status

We present an analysis of the submillimetre/X-ray properties of 19 X-ray absorbed, Compton-thin quasi-stellar objects (QSOs) selected to have luminosities and redshifts which represent the peak of cosmic QSO activity. i.e. ~L* objects at 1 1.5, the high star formation rates are consistent with a scenario in which the QSOs evolve to become local luminous elliptical galaxies. Combining these results with previously published data for X-ray unabsorbed QSOs and submillimetre-selected galaxies we propose the following evolutionary sequence: the forming galaxy is initially far-infrared luminous but X-ray weak similar to the sources discovered by the Submillimetre Common-User Bolometer Array; as the black hole and spheroid grow with time a point is reached when the central QSO becomes powerful enough to terminate the star formation and eject the bulk of the fuel supply (the Compton-thin absorbed QSO phase); this transition is followed by a period of unobscured QSO activity which subsequently declines to leave a quiescent spheroidal galaxy.

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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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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]

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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.

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arXiv2005

On the evolutionary status of early-type galaxies in clusters at z~0.2 - I. The Fundamental Plane

We investigate a spectroscopic sample of 48 early-type (E+S0) galaxies in the rich cluster Abell 2390 (z=0.23) and 48 E+S0 galaxies from a previously published survey of Abell 2218 (z=0.18). The A2390 spectra are based on Multi Object Spectroscopy with MOSCA at the Calar Alto 3.5-m, complemented by ground-based and HST F555W and F814W observations. Our investigation spans a broad range in luminosity (-20.5>M_r>-23.0) and a wide FOV of 1.5x1.5 Mpc^2. Since the A2218 and A2390 samples are very similar, we can combine them and analyse a total of 96 E+S0 galaxies at z~0.2. We construct the Faber-Jackson relation (FJR) for all E+S0s and detect a modest luminosity evolution. The average offset from the local FJR in Gunn r-band is (DeltaM_r)=0.32+-0.22^m. Less-massive galaxies show a trend for a larger evolution than more-massive galaxies. HST/WFPC2 surface brightness profile fits were used to derive structural parameters. For 34 E+S0 galaxies which enter the Fundamental Plane (FP) we deduce a mild evolution in Gunn r with a zero-point offset of 0.10+-0.06, corresponding to 0.31+-0.18^m. Elliptical and lenticular galaxies are uniformly distributed along the FP with a similar scatter of 0.1 dex. We find little evidence for differences between the populations of ellipticals and S0s. Lenticulars induce on average a larger evolution of 0.44+-0.18^m than ellipticals with 0.02+-0.21^m. The M/L ratios at z=0.2 are offset by (Deltalog(M/L_r))=-0.12+-0.06 dex compared to those of Coma. Our results can be reconciled with a passive evolution of the stellar populations and a high formation redshift for the bulk of the stars in E+S0 galaxies. However, our findings are also consistent with the hierarchical formation picture for rich clusters. [abridged]

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