arXiv subjects

Alastair Edge

Publications and source records attributed to Alastair Edge.

47 records · Page 3Linked to original sources

arXiv2008

The 2dF-SDSS LRG and QSO Survey: The spectroscopic QSO catalogue

We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG and QSO (2SLAQ) Survey. This is a deep, 18<g<21.85 (extinction corrected), sample aimed at probing in detail the faint end of the broad line AGN luminosity distribution at z<2.6. The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg^2 and contains new spectra of 16326 objects, of which 8764 are QSOs, and 7623 are newly discovered (the remainder were previously identified by the 2QZ and SDSS surveys). The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission line galaxies with a median redshift of z=0.22. We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host galaxy contributions. This calculation shows that at g~21.85 QSO colours are significantly affected by the presence of a host galaxy up to redshift z~1 in the SDSS ugriz bands. In particular we see a significant reddening of the objects in g-i towards fainter g-band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2-3 Gyr. The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/

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arXiv2008

An Infrared Survey of Brightest Cluster Galaxies. II: Why are Some Brightest Cluster Galaxies Forming Stars?

Quillen et al.(2007) presented an imaging survey with the {\it Spitzer Space Telescope} of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters. They found that at least half of these sources have signs of excess infrared emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star forming galaxies. The gas depletion time scale is about 1 Gyr. The physical extent of the infrared excess is consistent with that of the optical emission line nebulae. This supports the hypothesis that the star formation occurs in molecular gas associated with the emission line nebulae and with evidence that the emission line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates (${\dot M}_X$) estimated from the X-ray emission and the star formation rate estimated from the infrared luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates suggesting that the re-heating of the ICM is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.

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arXiv2008

First-Year Spectroscopy for the SDSS-II Supernova Survey

This paper presents spectroscopy of supernovae discovered in the first season of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for and measures multi-band light curves of supernovae in the redshift range z = 0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the supernova population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our supernova spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the supernova and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host galaxy contamination existing in the majority of our SN spectra.

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arXiv2007

An infrared survey of brightest cluster galaxies: Paper I

We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8 micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.

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arXiv2006

MegaZ-LRG: A photometric redshift catalogue of one million SDSS Luminous Red Galaxies

We describe the construction of MegaZ-LRG, a photometric redshift catalogue of over one million luminous red galaxies (LRGs) in the redshift range 0.4 < z < 0.7 with limiting magnitude i < 20. The catalogue is selected from the imaging data of the Sloan Digital Sky Survey Data Release 4. The 2dF-SDSS LRG and Quasar (2SLAQ) spectroscopic redshift catalogue of 13,000 intermediate-redshift LRGs provides a photometric redshift training set, allowing use of ANNz, a neural network-based photometric-redshift estimator. The rms photometric redshift accuracy obtained for an evaluation set selected from the 2SLAQ sample is sigma_z = 0.049 averaged over all galaxies, and sigma_z = 0.040 for a brighter subsample (i < 19.0). The catalogue is expected to contain ~5 per cent stellar contamination. The ANNz code is used to compute a refined star/galaxy probability based on a range of photometric parameters; this allows the contamination fraction to be reduced to 2 per cent with negligible loss of genuine galaxies. The MegaZ-LRG catalogue is publicly available on the World Wide Web from http://www.2slaq.info .

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arXiv2003

A Chandra Study of the Complex Structure in the Core of 2A 0335+096

We present a Chandra observation of the central (r< 200kpc) region of the cluster of galaxies 2A 0335+096, rich in interesting phenomena. On large scales (r> 40kpc), the X-ray surface brightness is symmetric and slightly elliptical. The cluster has a cool dense core; the radial temperature gradient varies with position angle. The radial metallicity profile shows a pronounced central drop and an off-center peak. Similarly to many clusters with dense cores, 2A 0335+096 hosts a cold front at r\approx 40kpc south of the center. The gas pressure across the front is discontinuous by a factor A_P=1.6\pm 0.3, indicating that the cool core is moving with respect to the ambient gas with a Mach number M\approx 0.75\pm 0.2. The central dense region inside the cold front shows an unusual X-ray morphology, which consists of a number of X-ray blobs and/or filaments on scales \gtrsim 3kpc, along with two prominent X-ray cavities. The X-ray blobs are not correlated with either the optical line emission (Hα+[NII]), member galaxies or radio emission. Deprojected temperature of the dense blobs is consistent with that of the less dense ambient gas, so these gas phases do not appear to be in thermal pressure equilibrium. An interesting possibility is a significant, unseen non-thermal pressure component in the inter-blob gas, possibly arising from the activity of the central AGN. We discuss two models for the origin of the gas blobs -- hydrodynamic instabilities caused by the observed motion of the gas core, or ``bubbling'' of the core caused by multiple outbursts of the central AGN.

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arXiv2003

A measurement of H_0 from Ryle Telescope, ASCA and ROSAT observations of Abell 773

We present new Ryle Telescope (RT) observations of the Sunyaev Zel'dovich (SZ) decrement from the cluster Abell 773. The field contains a number of faint radio sources that required careful subtraction. We use ASCA observations to measure the gas temperature and a ROSAT HRI image to model the gas distribution. Normalising the gas distribution to fit the RT visibilities returns a value of H_0 of 77 (+19,-15) km/s/Mpc (1-sigma errors) for an Einstein-de-Sitter universe, or 85 (+20,-17) km/s/Mpc for a flat model with Omega_Lambda = 0.7. The errors quoted include estimates of the effects of the principal errors: noise in the SZ measurement, gas temperature uncertainty, and line-of sight depth uncertainty.

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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.

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arXiv2001

Determining the Hubble Constant from Ryle Telescope observations

We describe our algorithm for measuring the Hubble constant from Ryle Telescope (RT) interferometric observations of the Sunyaev-Zel'dovich (SZ) effect from a galaxy cluster and observation of the cluster X-ray emission. We analyse the error budget in this method: as well as radio and X-ray random errors, we consider the effects of clumping and temperature differences in the cluster gas, of the kinetic SZ effect, of bremsstrahlung emission at radio wavelengths, of the gravitational lensing of background radio sources and of primary calibration error. Using RT, ASCA and ROSAT observations of the cluster Abell 1413, we find that random errors dominate over systematic ones, and estimate H_0 = 57^{+23}_{-16} km/s/Mpc (1-sigma errors).

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arXiv2000

MACS: The evolution and properties of massive clusters of galaxies

We present first results from the MAssive Cluster Survey (MACS), a new large-scale X-ray survey designed to find and characterize very massive, distant clusters of galaxies. Based on X-ray detections in the ROSAT All-Sky Survey, MACS aims to compile a sample of more than 200 X-ray luminous clusters at z>0.3, about 50 times the number of EMSS clusters in the same redshift and luminosity range. The MACS sample is uniquely suited to investigate cluster evolution at redshifts and luminosities poorly sampled by all existing surveys. At the time of writing the MACS sample comprises 41 clusters with measured redshifts of 0.3 0.3 are scheduled for spectroscopic observation. From a preliminary analysis of a statistically well defined subsample of the 25 X-ray brightest MACS clusters we conclude tentatively that negative evolution is not significant at the highest X-ray luminosities (Lx>10^45 erg/s) out to redshifts of z~0.4. Our findings thus extend the no-evolution result obtained by many serendipitous ROSAT cluster surveys at lower luminosities.

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arXiv1996

Detection of a CMB decrement towards the z = 3.8 quasar pair PC1643+4631A&B

In a 15-GHz Ryle-Telescope observation of PC1643+4631 A & B, a pair of quasars at redshifts z = 3.79 and 3.83 separated by 198 arcsec on the sky, we find a decrement in the cosmic microwave background (CMB) of -380 +/- 64 uJy in a 110 arcsec x 175 arcsec beam. Assuming this to be a Sunyaev-Zel'dovich effect due to an intervening cluster, the minimum magnitude of the central temperature decrement is 560 uK. A serendipitous ROSAT observation shows that there is no X-ray-luminous cluster in the direction of the decrement at z < 1. The implied gas mass is >~ 2 x 10^{14} solar masses (assuming a temperature of ~ 5 keV), indicating a total mass of > 10^{15} solar masses. This result demonstrates the existence of a massive system too distant to be detected by its emission, but which can be found via its imprint on the CMB.

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