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Search Results: 1 - 10 of 53086 matches for " David Crampton "
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The High Redshift Universe with Adaptive Optics: Recent results from CFHT
David Crampton
Physics , 1998,
Abstract: The CFHT Adaptive Optics Bonnette (AOB) has been used to obtain high spatial resolution (0.1") observations of several extragalactic targets including the nuclei of nearby galaxies, high redshift galaxies, AGN, radiogalaxies, the host galaxies of quasars and gravitational lenses. Examples of these are discussed and the role of adaptive optics in exploring the high redshift universe is critically assessed in light of these results.
Searching for z = 6.5 Galaxies with Multislit Windows
David Crampton,Simon Lilly
Physics , 1999,
Abstract: A method for searching for emission-line objects in "windows" between atmospheric emission lines using multislits is described. A search for Ly alpha emitters at z = 6.5 in the 9130A window using this technique is being carried out with the multi-object spectrograph on CFHT. This technique could be extended to similar windows at longer wavelengths, aided by the (1 + z) factor in observed equivalent widths. In the J band there are windows corresponding to Ly alpha at z = 7.7, 8.7 and 9.3; in the H band, there are two at z = 11.9 and 13.4. Multislit window observations in these bands coupled with photometric redshift information offer perhaps the best method of the detecting extremely high redshift galaxies.
Dark matter distribution in galaxy groups from combined strong lensing and dynamics analysis
Karun Thanjavur,David Crampton,Jon Willis
Physics , 2010, DOI: 10.1088/0004-637X/714/2/1355
Abstract: Using a combined analysis of strong lensing and galaxy dynamics, we characterize the mass distributions and M/L ratios of galaxy groups, which form an important transition regime in Lambda-CDM cosmology. By mapping the underlying mass distribution, we test whether groups are dark matter dominated as hypothesized by the standard cosmogony, or isothermal as observed in baryon rich field galaxies. We present our lensing + galaxy dynamics formalism built around the dark matter dominant NFW and Hernquist distributions, compared against the Isothermal Sphere observed in galaxy scale objects. We show that mass measurement in the core of the group (r ~ 0.2 r_{vir}), determined jointly from a lens model and from differential velocity dispersion estimates, may effectively distinguish between these density distributions. We apply our method to MOS observations of two groups, SL2SJ1430+5546 and SL2SJ1431+5533, drawn from our CFHTLS lens catalog. With the measured lensing and dynamical masses, combined with a maximum likelihood estimator built around our model, we estimate the concentration index characterizing each density distribution and the corresponding virial mass of each group. Our results indicate that both groups are dark matter dominant, and reject the Isothermal distribution at >>3 sigma level. For both groups, the estimated i-band M/L ratios of ~260 Msun/Lsun, are similar to other published values for groups. The Gaussian distributions of the velocities of their member galaxies support a high degree of virialization. The differences in their virial masses, 2.8 and 1.6 x 10^14 Msun, and velocity dispersions, 720 and 560 km/s respectively, may indicate however that each group is at a different stage of transition to a cluster. We aim to populate this important transition regime with additional results from ongoing observations of the remaining lensing groups in our catalog.
Photometric Redshifts in the CFDF
Mark Brodwin,Simon Lilly,David Crampton
Physics , 1999,
Abstract: The Canada-France Deep Fields (CFDF) is a large, deep, multi-colour imaging survey undertaken primarily at CFHT. It is about 10 times fainter than the CFRS (Lilly et al 1995a) and contains over 100 times as many galaxies. With three common fields, CFDF redshifts will be estimated photometrically using the CFRS spectroscopic catalogue as a training set. The project will yield large numbers of galaxies and will extend many of the CFRS results to higher redshifts and fainter flux levels.
A Relationship between Supermassive Black Hole Mass and the Total Gravitational Mass of the Host Galaxy
Kaushala Bandara,David Crampton,Luc Simard
Physics , 2009, DOI: 10.1088/0004-637X/704/2/1135
Abstract: We investigate the correlation between the mass of a central supermassive black hole and the total gravitational mass of the host galaxy (M_tot). The results are based on 43 galaxy-scale strong gravitational lenses from the Sloan Lens ACS (SLACS) Survey whose black hole masses were estimated through two scaling relations: the relation between black hole mass and Sersic index (M_bh - n) and the relation between black hole mass and stellar velocity dispersion (M_bh - sigma). We use the enclosed mass within R_200, the radius within which the density profile of the early type galaxy exceeds the critical density of the Universe by a factor of 200, determined by gravitational lens models fitted to HST imaging data, as a tracer of the total gravitational mass. The best fit correlation, where M_bh is determined from M_bh - sigma relation, is log(M_bh) = (8.18 +/- 0.11) + (1.55 +/- 0.31) (log(M_tot) - 13.0) over 2 orders of magnitude in M_bh. From a variety of tests, we find that we cannot reliably infer a connection between M_bh and M_tot from the M_bh - n relation. The M_bh - M_tot relation provides some of the first, direct observational evidence to test the prediction that supermassive black hole properties are determined by the halo properties of the host galaxy.
K2: A new method for the detection of galaxy clusters based on CFHTLS multicolor images
Karun Thanjavur,Jon Willis,David Crampton
Physics , 2009, DOI: 10.1088/0004-637X/706/1/571
Abstract: We have developed a new method, K2, optimized for the detection of galaxy clusters in multicolor images. Based on the Red Sequence approach, K2 detects clusters using simultaneous enhancements in both colors and position. The detection significance is robustly determined through extensive Monte-Carlo simulations and through comparison with available cluster catalogs based on two different optical methods, and also on X-ray data. K2 also provides quantitative estimates of the candidate clusters' richness and photometric redshifts. Initially K2 was applied to 161 sq deg of two color gri images of the CFHTLS-Wide data. Our simulations show that the false detection rate, at our selected threshold, is only ~1%, and that the cluster catalogs are ~80% complete up to a redshift of 0.6 for Fornax-like and richer clusters and to z ~0.3 for poorer clusters. Based on Terapix T05 release gri photometric catalogs, 35 clusters/sq deg are detected, with 1-2 Fornax-like or richer clusters every two square degrees. Catalogs containing data for 6144 galaxy clusters have been prepared, of which 239 are rich clusters. These clusters, especially the latter, are being searched for gravitational lenses -- one of our chief motivations for cluster detection in CFHTLS. The K2 method can be easily extended to use additional color information and thus improve overall cluster detection to higher redshifts. The complete set of K2 cluster catalogs, along with the supplementary catalogs for the member galaxies, are available on request from the authors.
Internal Kinematics of Blue CFRS Galaxies at z ~ 0.6
Gabriela Mallen-Ornelas,Simon Lilly,David Crampton,David Schade
Physics , 1999,
Abstract: We present the results of a study of the internal kinematics of luminous starforming galaxies in the 0 < z < 0.8 range, with the aim of investigating the nature of the blue galaxies which cause the largest changes in the luminosity function at z > 0.5. New kinematic data are analysed for a sample of 24 galaxies from the Canada-France Redshift Survey, most of them with rest-frame (U-V)_{AB}< 1.14. Unlike most previous studies, target galaxies were selected regardless of size and morphology, from a well-studied magnitude-limited survey (the CFRS). Our sample is therefore representative of the most rapidly changing 1/3 of the galaxy population in the 0 < z < 0.8 range. The 15 galaxies at z > 0.45 have sizes (from HST images) and velocity widths sigma_{v} (from emission lines) similar to those of typical local Irregulars. This is consistent with their morphologies and rest-frame colors; however, these galaxies are as bright as the brightest local Irregulars, and roughly 2 magnitudes brighter than typical Irregulars known nearby. We conclude that the increase in the number density of luminous blue galaxies at z > 0.5 is mainly due to a population of small and unusually-bright late-type galaxies.
The CANADA-FRANCE REDSHIFT SURVEY XIII: The luminosity density and star-formation history of the Universe to z ~ 1
S. J. Lilly,O. Le Fevre,F. Hammer,David Crampton
Physics , 1996, DOI: 10.1086/309975
Abstract: The comoving luminosity density of the Universe is estimated from the CFRS faint galaxy sample in three wavebands (2800A, 4400A and 1 micron) over the redshift range 0 < z < 1. In all three wavebands, the comoving luminosity density increases markedly with redshift. For a (q_0 = 0.5, Omega = 1.0) cosmological model, the comoving luminosity density increases as $(1+z)^{2.1 \pm 0.5}$ at 1 micron, as $(1+z)^{2.7 \pm 0.5}$ at 4400A and as $(1+z)^{3.9 \pm 0.75}$ at 2800A, these exponents being reduced by 0.43 and 1.12 for (0.05,0.1) and (-0.85,0.1) cosmological models respectively. The variation of the luminosity density with epoch can be reasonably well modelled by an actively evolving stellar population with a Salpeter initial mass function (IMF) extending to 125 M_sun, a star-formation rate declining with a power 2.5, and a turn-on of star-formation at early epochs. A Scalo (1986) IMF extending to the same mass limit produces too many long-lived low mass stars. This rapid evolution of the star-formation rate and comoving luminosity density of the Universe is in good agreement with the conclusions of Pei and Fall (1995) from their analysis of the evolving metallicity of the Universe. One consequence of this evolution is that the physical luminosity density at short wavelengths has probably declined by two orders of magnitude since z ~ 1.
The gravitational lens CFRS14.1311 = HST 14176+5226
David Crampton,O. Le Fevre,F. Hammer,S. J. Lilly
Physics , 1996,
Abstract: Ratnatunga et al. (1995) have recently proposed that an object, HST 14176+5226, in the "Groth-Westphal" HST survey strip is an "Einstein cross" gravitational lens. By chance, this object has been previously observed in the Canada-France Redshift Survey. The candidate lens, catalogued as CFRS14.1311, is an elliptical galaxy at z = 0.81. In addition, the spectrum shows a strong, spatially-extended, emission feature at 5342A that almost certainly originates from two of the four "lensed" images. We tentatively identify this emission line as Ly alpha at z =3.4. A less prominent emission feature at 6822A may be C IV 1549. Our data thus support the identification of this system as a new quadruple-image lens.
THE CANADA-FRANCE REDSHIFT SURVEY IV: Spectroscopic Selection Effects and 0300+00 Field Spectroscopic Data
F. Hammer,David Crampton,O. Le Fevre,S. J. Lilly
Physics , 1995, DOI: 10.1086/176558
Abstract: Possible surface brightness selection effects in the redshift catalogs of the Canada-France Redshift Survey are investigated through comparisons of subsamples of the data. Our analyses demonstrate that the securing of redshifts is independent of possible biases arising from surface brightness effects and/or differing galaxy morphologies and orientations. The unusual geometry of the mask designs for our spectroscopic observations also do not produce any significant bias. There is however a bias at the highest and lowest redshifts, especially for absorption-line galaxies at z > 1 and z < 0.2, due to the adopted spectral range (4250A to 8500A). Apart from the latter, we conclude that our sample of identified galaxies is an unbiased subsample of the original photometric catalogue and is essentially limited by I-band flux density ($17.5 \leq I_{AB} \leq 22.5$). Finally, spectroscopic data for 273 objects in the 0300+00 CFRS field are presented.
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