arXiv subjects

Ian Smail

Publications and source records attributed to Ian Smail.

At least 361 records · Page 20Linked to original sources

arXiv2002

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: III. A Multiply-imaged Extremely Red Galaxy at z=1.6

We present near-infrared spectroscopy and Hubble Space Telescope (HST) imaging of EROJ003707+0909.5, the brightest of three gravitationally-lensed images of an Extremely Red Object (ERO) at z=1.6, in the field of the massive cluster A68 (z=0.255). We exploit the superlative resolution of our HST data and the enhanced spatial resolution and sensitivity afforded by the lens amplification to reconstruct the source-plane properties of this ERO. Our morphological and photometric analysis reveals that EROJ003707 is an L* early-type disk-galaxy and we estimate that ~10 per cent of EROs with (R-K)>=5.3 and K<=21 may have similar properties. The unique association of passive EROs with elliptical galaxies therefore appears to be too simplistic. We speculate on the evolution of EROJ003707: if gas continues to cool onto this galaxy in the manner predicted by hierarchical galaxy formation models, then by the present day, EROJ003707 could evolve into a very luminous spiral galaxy.

astro-ph↗

arXiv2002

An H-alpha survey of the rich cluster A1689

(Abridged) We present results of an H-alpha survey in the rich cluster A1689 at z=0.18, using the LDSS++ spectrograph on the AAT. We obtained spectra covering redshifted H-alpha for 522 galaxies brighter than I=22.5, covering a field of 8.7'X8.7'. We detect H-alpha emission in 46 of these galaxies; accounting for selection effects due to sampling and cluster membership, we determine that 24% of cluster members brighter than M_R=-16.5+5log(h) are detected with H-alpha flux greater than 4h^{-2}X 10^{38} ergs/s. This corresponds to a limiting star formation rate of 0.008 h^{-2} Msun/yr, assuming 1 magnitude of dust extinction. From a Hubble Space Telescope mosaic covering 7.5' X 10.0', we determine morphologies for 199 galaxies brighter than I=21, and find that 20% of the cluster members are of type Sa or later. More than 90% of cluster spirals show H-alpha emission, compared with less than 10% of E and S0 galaxies. The cluster H-alpha luminosity function has a low normalisation relative to the z~0.2 field, by ~50%, after accounting for the different fraction of spiral galaxies in the two environments. When compared with local field galaxies, this suggests that star formation activity is suppressed in early-type cluster galaxies, relative to their field counterparts. Our sample includes 29 galaxies previously observed with ISOCAM at 6 and 15 microns. We detect all 15-micron sources at H-alpha, so there is no evidence for any star formation completely hidden at H-alpha. Comparing the 15-micron and H-alpha fluxes, we find evidence that some mid-infrared-detected galaxies could be obscured by as much as 3 magnitudes of extinction at H-alpha, although this depends on the largely unknown contribution from any AGN-heated dust to the mid-infrared flux.

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

The nature of faint submm-selected galaxies

We present the source catalogue for the SCUBA Lens Survey. We summarise the results of extensive multi-wavelength observations of the 15 submillimetre-selected galaxies in the catalogue, from X-rays to radio. We discuss the main observational characteristics of faint submillimetre galaxies as a population, and consider their interpretation within the framework of our understanding of galaxy formation and evolution.

astro-ph↗

arXiv2001

The Las Campanas/AAT Rich Cluster Survey II: The Environmental Dependance of Galaxy Colours in Clusters at z~0.1

(Abridged) We present a photometric investigation of the variation in galaxy colour with environment in 11 X-ray luminous clusters at 0.07<z<0.16 taken from the Las Campanas/AAT Rich Cluster Survey. We study the properties of the galaxy populations in individual clusters and take advantage of the homogeneity of the sample to combine the clusters together to investigate weaker trends in the composite sample. We find that modal colours of galaxies lying on the colour-magnitude relation in the clusters become bluer by d(B-R)/dr_p=-0.022 \pm 0.004 from the cluster core out to a projected radius of r_p=6 Mpc; further out in radius than any previous study.....

astro-ph↗

arXiv2001

The Transformation of Galaxies within the Large Scale Structure around a z=0.41 Cluster

We present deep, panoramic multi-color imaging of the distant rich cluster A851 (Cl0939+4713, z=0.41) using Suprime-Cam on Subaru. These images cover a 27' field of view, ~11 Mpc at z=0.41, and by exploiting photometric redshifts estimated from our BVRI imaging we can isolate galaxies in a narrow redshift slice at the cluster redshift. Using a sample of ~2700 probable cluster members brighter than 0.02 Lv*, we trace the network of filaments and subclumps around the cluster core. The depth of our observations, combined with the identification of filamentary structure, gives us an unprecedented opportunity to test the influence of the environment on the properties of low luminosity galaxies. We find an abrupt change in the colors of < 0.1 Lv* galaxies at a local density of 100 gal. per sq. Mpc, with the population in lower density regions being predominantly blue, while those in higher density regions are red. The transition in the color-local density behavior occurs at densities corresponding to subclumps within the filaments surrounding the cluster. Identifying the sites where the transition occurs brings us much closer to understanding the mechanisms which are responsible for establishing the present-day relationship between environment and galaxy characteristics.

astro-ph↗

arXiv2001

Distinguishing Local and Global Influences on Galaxy Morphology: An HST Comparison of High and Low X-ray Luminosity Clusters

(Abridged) We present a morphological analysis of 17 X-ray selected clusters at z~0.25, imaged uniformly with HST WFPC2. Eight of these clusters have low X-ray luminosities (<10^{44} erg/s), while the remaining nine clusters have L_x>10^{45} ergs/s. The clusters cover a relatively small range in redshift and the data are homogeneous in terms of depth, resolution and rest wavelength observed. We use GIM2D to fit the two dimensional surface brightness profiles of galaxies down to M(702)<=-18.2 (Ho=50; roughly 0.01 L*) with parametric models, and quantify their morphologies using the fractional bulge luminosity (B/T). Within a single WFPC2 image we find that the Low-Lx clusters are dominated by galaxies with low B/T (~0), while the High-Lx clusters are dominated by galaxies with intermediate B/T (~0.4). We test whether this difference could arise from a universal morphology-density relation due to differences in the typical galaxy densities in the two samples. We find that small differences in the B/T distributions of the two samples persist with marginal statistical significance even when we restrict the comparison to galaxies in environments with similar projected local galaxy densities. From the correlations with the bulge and disk luminosity functions, we argue that the global environment affects the population of bulges, over and above trends seen with local density. We conclude that the destruction of disks through ram pressure stripping or harassment is not solely responsible for the morphology-density relation, and that bulge formation is less efficient in low mass clusters.

astro-ph↗

arXiv2001

History of mass assembly and star formation in clusters

We present deep, panoramic multi-color imaging of the distant rich cluster A851 (z=0.41) using Suprime-Cam on Subaru. These images cover a 27' field of view (~11 h_{50}^{-1}Mpc), and by exploiting photometric redshifts, we can isolate galaxies in a narrow redshift slice at the cluster redshift. Using a sample of ~2700 probable cluster members ( M*+1) at a local density of 100 gal. Mpc^{-2}. The transition in the color-local density behavior occurs at densities corresponding to subclumps within the filaments surrounding the cluster. Identifying the sites where the transition occurs brings us much closer to understanding the mechanisms which are responsible for establishing the present-day relationship between environment and galaxy characteristics.

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↗

arXiv2001

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: II. A Search for Gravitationally Lensed EROs

We present the results of a survey for Extremely Red Objects (EROs) in the fields of ten galaxy cluster lenses at z~0.2, combining high-resolution Hubble Space Telescope imaging with deep K-band imaging from UKIRT. We detect 60 EROs with R-K>=5.3, of which 26 have R-K>=6.0 in a total image plane survey area of 49arcmin^2 down to K=20.6. We use detailed models of the cluster lenses to quantify the lens amplification and thus correct the observed number counts and survey area for the effects of gravitational lensing. After making these corrections, we estimate surface densities at K<=21.6 of 2.5+/-0.4 and 1.2+/-0.3 arcmin^-2 for EROs with R-K>=5.3 and 6.0 respectively. These ERO number counts agree with previous shallower surveys at K<~19 and flatten significantly at magnitudes fainter than K~19-20. This flattening may be due to a transition from an ERO population dominated by evolved galaxies at z~1-2 (K<~19.5) to one dominated by dusty starburst galaxies at z>1 (K>~19.5). We also compare our results with various model predictions, including a model that attempts to explain EROs in terms of a single population of elliptical galaxies formed at high redshift. We find that a formation epoch of z_f~2.5 for this population matches the observed surface density of R-K>=5.3 EROs quite well, and the R-K>=6.0 sample less well. More sophisticated models, including semi-analytic prescriptions, under-predict the ERO surface density by approximately an order of magnitude, suggesting that these models produce insufficient stars and/or dust at high redshift.

astro-ph↗

arXiv2001

Near-infrared Spectroscopy and HST Imaging of a Dusty Starburst ERO

We present near-IR spectroscopy and HST imaging of EROJ164023, an Extremely Red Object (ERO) with R-K=5.9 at z=1.05. EROJ164023 is a disk galaxy, with an optical/IR spectral energy distribution which is strongly reddened by dust (L_FIR/L_B<~200; A_V~5). The narrow emission lines (~300km/s) and the high [NII]/Halpha line ratio indicate that this is a ``composite'' starburst-Seyfert galaxy. Assuming that star formation dominates, we constrain the SFR to be 10-700Mo/yr from a variety of indicators. We compare EROJ164023 with the only other spectroscopically identified dusty EROs: HR10 (z=1.44) and ISOJ1324-2016 (z=1.50). EROJ164023 and HR10 have similar disk-like morphologies, and both exhibit a variation in the apparent dust obscuration depending upon the diagnostic used, suggesting that there is a complex spatial mix of stellar populations and dust in these galaxies. In contrast, the compact morphology and spectral properties of ISOJ1324-2016 indicate that it is a dusty quasar. Our results demonstrate that dusty galaxies identified using photometric ERO criteria include pure starbursts, composite systems such as EROJ164023 and dusty quasars. We suggest that the classification of EROs into these sub-classes cannot be reliably achieved from optical/near-IR photometry and instead requires mid/far-IR or sub-mm photometry and near-IR spectroscopy. The advent of efficient multi-object spectrographs working in the near-IR as well as the imminent launch of SIRTF therefore promise the opportunity of rapid progress in our understanding of the elusive ERO population. [Abridged]

astro-ph↗

arXiv2001

The Las Campanas/AAT Rich Cluster Survey I: Precision and Reliability of the Photometric Catalogue

The Las Campanas Observatory and Anglo--Australian Telescope Rich Cluster Survey (LARCS) is a panoramic imaging and spectroscopic survey of an X-ray luminosity-selected sample of 21 clusters of galaxies at 0.07<z<0.16. CCD imaging was obtained in B and R of typically 2-degree wide regions centred on the 21 clusters, and the galaxy sample selected from the imaging is being used for an on-going spectroscopic survey of the clusters with the 2dF spectrograph on the Anglo-Australian Telescope. This paper presents the reduction of the imaging data and the photometric analysis used in the survey. Based on an overlapping area of 12.3 square degrees, we compare the CCD-based LARCS catalogue with the photographic-based galaxy catalogue used for the input to the 2dF Galaxy Redshift Survey (2dFGRS) from the APM, to the completeness of the GRS/APM catalogue, b_J=19.45. This comparison confirms the reliability of the photometry across our mosaics and between the clusters in our survey. This comparison also provides useful information about the properties of the GRS/APM. The stellar contamination in the GRS/APM galaxy catalogue is confirmed to be around 5-10 percent, as originally estimated. However, using the superior sensitivity and spatial resolution in the LARCS survey, we find evidence for four distinct populations of galaxies that are systematically omitted from the GRS/APM catalogue. The characteristics of the `missing' galaxy populations are described, reasons for their absence examined and the impact they will have on the conclusions drawn from the 2dF Galaxy Redshift Survey are discussed.

astro-ph↗

arXiv2001

Testing the Hypothesis of the Morphological Transformation from Field Spiral to Cluster S0

Hubble Space Telescope observations of distant clusters have suggested a steep increase in the proportion of S0 galaxies between clusters at high redshifts and similar systems the present-day. It has been proposed that this increase results from the transformation of the morphologies of accreted field galaxies from spirals to S0s. We have simulated the evolution of the morphological mix in clusters based on a simple phenomenological model where the clusters accrete a mix of galaxies from the surrounding field, the spiral galaxies are transformed to S0s (through an unspecified process) and are added to the existing cluster population. We find that in order to reproduce the apparently rapid increase in the ratio of S0 galaxies to ellipticals in the clusters, our model requires that: (1) galaxy accretion rate has to be high (typically, more than half of the present-day cluster population must have been accreted since z~0.5), and (2) most of the accreted spirals, with morphological types as late as Scdm, must have transformed to S0's. Although the latter requirement may be difficult to meet, it is possible that such bulge-weak spirals have already been `pre-processed' into the bulge-strong galaxies prior to entering the cluster core and are eventually transformed into S0's in the cluster environment. On the basis of the evolution of the general morphological mix in clusters our model suggests that the process responsible for the morphological transformation takes a relatively long time (1-3Gyr) after the galaxy has entered the cluster environment.

astro-ph↗

arXiv2000

A low global star formation rate in the rich galaxy cluster AC114 at z=0.32

We present the results of a wide-field survey for H-alpha emitting galaxies in the cluster AC114 at z=0.32. Spectra centred on H-alpha at the cluster redshift have been obtained for 586 galaxies to I~22 out to a radius around 2Mpc. At most, only ~10% of these were found to be H-alpha-emitting cluster members. These objects are predominantly blue and of late-type spiral morphology, consistent with them hosting star formation. However, ~65% of the cluster members classified morphologically as spirals (with HST), have no detectable H-alpha emission; star-formation and morphological evolution in cluster galaxies appear to be largely decoupled. Changes in the H-alpha detection rate and the strength of H-alpha emission with environment are found to be weak within the region studied. Star formation within the cluster members is also found to be strongly and uniformly suppressed, with the rates inferred from the H-alpha emission not exceeding 4Mo/yr, and AC114's H-alpha luminosity function being an order of magnitude below that observed for field galaxies at the same redshift. None of the galaxies detected have the high star formation rates associated with `starburst' galaxies; however, this may still be reconciliable with the known (8+/-3%) fraction of `post-starburst' galaxies within AC114, given the poorly determined but short lifetimes of starbursts and the possibility that much of the associated star formation is obscured by dust.

astro-ph↗

arXiv2000

An HST Lensing Survey of X-ray Luminous Galaxy Clusters: I. A383

We analyse the mass distribution in the core of A383 (z=0.188), one of 12 X-ray luminous clusters at z~0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Deep HST imaging reveals a wide variety of gravitationally lensed features in A383, including a giant arc formed from the strongly-lensed images of 2 background galaxies, 2 radial arcs, several multiply-imaged arcs and numerous arclets. Based upon the constraints from the various lensed features, we construct a detailed mass model for the central regions of the cluster, taking into account both the cluster-scale potential and perturbations from individual cluster galaxies. Keck spectroscopy of one component of the giant arc identifies it as a star-forming galaxy at z=1.01 and provides an accurate measurement of the cluster mass within the radius of the giant arc (65kpc) of (3.5+/-0.1)*10^13 Mo. Using the weak shear measured from our HST observations we extend our mass model to determine a mass of (1.8+/-0.2)*10^14 Mo within a radius of 250kpc. On smaller scales we employ the radial arcs as probes of the shape of the mass distribution in the cluster core (r<20kpc), and find that the mass profile is more peaked than a single NFW profile. The optical and X-ray properties of A383 indicate the presence of a central cooling flow, for which we derive a mass deposition rate of >200 Mo/yr. We also use the X-ray emission from A383 to obtain independent estimates of the total mass within projected radii of 65 and 250kpc: (4.0+/-1.4)*10^13 Mo and (1.2+/-0.5)*10^14 Mo, which are consistent with the lensing measurements. [Abridged]

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↗

arXiv2000

A Photometric Study of the Ages and Metallicities of Early-type Galaxies in A2218

We present deep optical and near-infrared imaging of the rich cluster A2218 at z=0.17. Our optical imaging comes from new multicolour Hubble Space Telescope WFPC2 observations in the F450W (B), F606W (V) and F814W (I) passbands. These observations are complemented by deep near-infrared, Ks-band, imaging from the new INGRID imager on the 4.2-m William Herschel Telescope. This combination provides unique high-precision multicolour optical-infrared photometry and morphological information for a large sample of galaxies in the core of this rich cluster at a lookback time of ~3Gyrs. We analyse the (B-I), (V-I) and (I-Ks) colours of galaxies spanning a range of a factor of 100 in K-band luminosity in this region and compare these with grids of stellar population models. We find that the locus of the colours of the stellar populations in the luminous (>0.5L*) early-type galaxies, both ellipticals and S0s, traces a sequence of varying metallicity at a single age. At fainter luminosities (<0.1L*), this sequence is extended to lower metallicities by the morphologically-classified ellipticals. However, the faintest S0s exhibit very different behaviour, showing a wide range in colours, including a large fraction (30%) with relatively blue colours which appear to have younger luminosity-weighted ages for their stellar populations, 2-5Gyrs. We show that the proportion of these young S0s in the cluster population is consistent with the observed decrease in the S0 population seen in distant clusters when interpreted within the framework of a two-step spectroscopic and morphological transformation of accreted spiral field galaxies into cluster S0s.

astro-ph↗

arXiv2000

A strategy for finding gravitationally-lensed distant supernovae

Distant Type Ia and II supernovae (SNe) can serve as valuable probes of the history of the cosmic expansion and star formation, and provide important information on their progenitor models. At present, however, there are few observational constraints on the abundance of SNe at high redshifts. A major science driver for the Next Generation Space Telescope (NGST) is the study of such very distant supernovae. In this paper we discuss strategies for finding and counting distant SNe by using repeat imaging of super-critical intermediate redshift clusters whose mass distributions are well-constrained via modelling of strongly-lensed features. For a variety of different models for the star formation history and supernova progenitors, we estimate the likelihood of detecting lensed SNe as a function of their redshift. In the case of a survey conducted with HST, we predict a high probability of seeing a supernova in a single return visit with either WFPC-2 or ACS, and a much higher probability of detecting examples with z>1 in the lensed case. Most events would represent magnified SNe II at z~1, and a fraction will be more distant examples. We discuss various ways to classify such events using ground-based infrared photometry. We demonstrate an application of the method using the HST archival data and discuss the case of a possible event found in the rich cluster AC 114 (z=0.31).

astro-ph↗