Comparing X-ray and Dynamical Mass Profiles in the Early-Type Galaxy NGC 4636 (2009)
Johnson, Ria, Chakrabarty, Dalia, O'Sullivan, Ewan, Raychaudhury, Somak
We present the results of an X-ray mass analysis of the early-type galaxy NGC 4636, using Chandra data. We have compared the X-ray mass density profile with that derived from a dynamical analysis of...
Gianniotis, Nikolaos, Tino, Peter, Spreckley, Steve, Raychaudhury, Somak
We present a probabilistic generative approach for constructing topographic maps of light curves from eclipsing binary stars. The model defines a low-dimensional manifold of local noise models...
Fossil Galaxy Groups -- Ideal Laboratories for Studying the Effects of AGN Heating (2009)
Jetha, Nazirah N., Khosroshahi, Habib, Raychaudhury, Somak, Sengupta, Chandreyee, Hardcastle, Martin
We present the first of a sample of fossil galaxy groups with pre-existing Chandra and/or XMM-Newton X-ray observations and new or forthcoming low frequency GMRT data -- RXJ1416.4+2315 (z=0.137)....
Cuevas-Tello, Juan C., Tino, Peter, Raychaudhury, Somak, Yao, Xin, Harva, Markus
We study the problem of estimating the time delay between two signals representing delayed, irregularly sampled and noisy versions of the same underlying pattern. We propose and demonstrate an...
Red star-forming and blue passive galaxies in clusters (2009)
Mahajan, Smriti, Raychaudhury, Somak
We explore the relation between colour and specific star formation rate (derived from optical spectra obtained by SDSS DR4) of over 6,000 galaxies (M_r
Estimating Time Delay in Gravitationally Lensed Fluxes (2009)
Tino, Peter, Cuevas-Tello, Juan C., Raychaudhury, Somak
We study the problem of estimating the time delay between two signals representing delayed, irregularly sampled and noisy versions of the same underlying pattern. We propose a kernel-based technique...
Luminosity functions of LMXBs in Centaurus A: globular clusters versus the field (2009)
Voss, Rasmus, Gilfanov, Marat, Sivakoff, Gregory R., Kraft, Ralph P., Jordan, Andres, Raychaudhury, Somak, ...
an application to gravitational (2008)
Peter Tiňo, Somak Raychaudhury
A kernel-based approach to estimating phase
Mapping the Physical Properties of Cosmic Hot Gas with Hyper-spectral Imaging (2008)
Trevor Ponman, Ela Claridge, Somak Raychaudhury
A novel inversion technique is proposed to compute parametric maps showing the temperature, density and chemical composition of cosmic hot gas from X-ray hyper-spectral images. The parameters are...
Star formation in galaxies falling into clusters along supercluster-scale filaments (2008)
Porter, Scott C., Raychaudhury, Somak, Pimbblet, Kevin A., Drinkwater, Michael J.
With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to...
The Distribution of Dark Matter in the Halo of the early-type galaxy NGC 4636 (2008)
Chakrabarty, Dalia, Raychaudhury, Somak
We present the density structure of dark matter in the outer parts (to about 7 effective radii) of the elliptical galaxy NGC 4636, from the radial velocities of 174 globular clusters, using the...
A Transient Black-Hole Low-Mass X-Ray Binary Candidate in Centaurus A (2008)
Sivakoff, Gregory R., Kraft, Ralph P., Jordán, Andrés, Juett, Adrienne M., Evans, Daniel A., Forman, William R., ...
We report the discovery of a bright transient X-ray source, CXOU J132518.2-430304, towards Centaurus A (Cen A) using six new Chandra X-Ray Observatory observations in 2007 March--May. Between 2003...
On class visualisation for high dimensional data: Exploring scientific data sets (2008)
Ata Kabán, Jianyong Sun, Somak Raychaudhury, Louisa Nolan
Abstract. Parametric Embedding (PE) has recently been proposed as a general-purpose algorithm for class visualisation. It takes class posteriors produced by a mixture-based clustering algorithm and...
Robust Visual Mining of Data with Error Information (2008)
Jianyong Sun, Ata Kabán, Somak Raychaudhury
Abstract. Recent results on robust density-based clustering have indicated that the uncertainty associated with the actual measurements can be exploited to locate objects that are atypical for a...
Ata Kabán, Louisa A. Nolan, Somak Raychaudhury
Elliptical galaxies are believed to consist of a single population of old stars formed together at an early epoch in the Universe, yet recent analyses of galaxy spectra seem to indicate the presence...
Globular Clusters and X-ray Point Sources in Centaurus A (NGC 5128) (2008)
Woodley, Kristin A., Raychaudhury, Somak, Kraft, Ralph P., Harris, William E., Jordan, Andres, Whitaker, Katherine E., ...
We detect 353 X-ray point sources, mostly low-mass X-ray binaries (LMXBs), in four Chandra observations of Centaurus A (NGC 5128), the nearest giant early-type galaxy, and correlate this point source...
Star formation in galaxies falling into clusters along supercluster-scale filaments (2008)
Porter, Scott C., Raychaudhury, Somak, Pimbblet, Kevin A., Drinkwater, Michael J.
With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to...
The nature of the ghost cavity in the NGC 741 group (2007)
Jetha, Nazirah N., Hardcastle, Martin J., Babul, Arif, O'Sullivan, Ewan, Ponman, Trevor J., Raychaudhury, Somak, ...
We discuss the effects of energy injection into the intra-group medium of the group of galaxies associated with NGC 741. The X-ray emission reveals a large bubble, which in the absence of a currently...
Gary M. Bernstein, Puragra Guhathakurta, Somak Raychaudhury, Riccardo Giovanelli, Martha P. Haynes, Terry Herter, ...
We examine the precision of the Tully-Fisher relation (TFR) using a sample of galaxies in the Coma region of the sky, and find that it is good to 5 % or better in measuring relative distances. Total...
Tests of the Tully-Fisher Relation II: Scatter Using Optical Rotation Curves (2007)
Somak Raychaudhury, Kaspar Von Braun, Gary M. Bernstein, Puragra Guhathakurta
We investigate the amount of scatter in the Tully-Fisher relation (TFR) when using optical long-slit Hff rotation curves to determine the velocity widths of spiral galaxies. We study a sample of 25...
Low-Mass X-ray Binaries and Globular Clusters in Centaurus A (2007)
Jordan, Andres, Sivakoff, Gregory R., McLaughlin, Dean E., Blakeslee, John P., Evans, Daniel A., Kraft, Ralph P., ...
We present results of Hubble Space Telescope and Chandra X-ray Observatory observations of globular clusters (GCs) and low-mass X-ray binaries (LMXBs) in the central regions of Centaurus A. Out of...
Robust mixtures in the presence of measurement errors (2007)
Sun, Jianyong, Kaban, Ata, Raychaudhury, Somak
We develop a mixture-based approach to robust density modeling and outlier detection for experimental multivariate data that includes measurement error information. Our model is designed to infer...
The Mass Assembly of Fossil Groups of Galaxies in the Millennium Simulation (2007)
Dariush, Ali, Khosroshahi, Habib G., Ponman, Trevor J., Pearce, Frazer, Raychaudhury, Somak, Hartley, Will
The evolution of present-day fossil galaxy groups is studied in the Millennium Simulation. Using the corresponding Millennium gas simulation and semi-analytic galaxy catalogues, we select fossil...
Robust mixtures in the presence of measurement errors (2007)
Jianyong Sun, Ata Kabán, Somak Raychaudhury
We develop a mixture-based approach to robust density modeling and outlier detection for experimental multivariate data that includes measurement error information. Our model is designed to infer...
Star formation in galaxies along the Pisces-Cetus Supercluster filaments (2006)
Porter, Scott C., Raychaudhury, Somak
We investigate the variation of current star formation in galaxies as a function of distance along three supercluster filaments, each joining pairs of rich clusters, in the Pisces-Cetus supercluster,...
Differences in the AGN Populations of Groups and Clusters: Clues to AGN Evolution (2006)
Shen, Yue, Mulchaey, John S., Raychaudhury, Somak, Rasmussen, Jesper, Ponman, Trevor J.
We combine optical and X-ray data for eight low redshift ($z\sim 0.06$) poor groups of galaxies from the {\it XI}({\it XMM/IMACS}) Groups Project to study the AGN population in the group environment....
Miles, Trevor A., Raychaudhury, Somak, Russell, Paul A.
We present J and K-band luminosity functions (LF) for the Group Evolution Multiwavelength Study (GEMS) sample of 60 nearby groups of galaxies, with photometry from the 2MASS survey. We find that, as...
First results of the XI Groups Project: Studying an unbiased sample of galaxy groups (2006)
Rasmussen, Jesper, Ponman, Trevor J., Mulchaey, John S., Miles, Trevor A., Raychaudhury, Somak
X-ray observations of hot, intergalactic gas in galaxy groups provide a useful means of characterizing the global properties of groups. However, X-ray studies of large group samples have typically...
On class visualisation for high dimensional data: Exploring scientific datasets (2006)
Kaban, Ata, Sun, Jianyong, Raychaudhury, Somak, Nolan, Louisa
Parametric Embedding (PE) has recently been proposed as a general-purpose algorithm for class visualisation. It takes class posteriors produced by a mixture-based clustering algorithm and projects...
The optical and near-infrared properties of nearby groups of galaxies (2006)
Raychaudhury, Somak, Miles, Trevor A.
We present a study of the optical (BRI) and near-infrared (JHK) luminosity fuctions (LFs) of the GEMS sample of 60 nearby groups of galaxies between 0
Young stellar populations in early-type galaxies in the Sloan Digital Sky Survey (2006)
Nolan, Louisa A., Raychaudhury, Somak, Kaban, Ata
We use a purely data-driven rectified factor analysis to identify early-type galaxies with recent star formation in DR4 of the SDSS Spectroscopic Catalogue. We compare the spectra and environment of...
Chandra Observations of the X-ray Point Source Population in NGC 4636 (2006)
Posson-Brown, Jennifer, Raychaudhury, Somak, Forman, William, Donnelly, R. Hank, Jones, Christine
We present the X-ray point source population in the nearby Virgo elliptical galaxy NGC 4636 from 3 Chandra/ACIS observations, totaling 193 ks, taken over 3 years. Using wavelet decomposition, we...
How accurate are the time delay estimates in gravitational lensing? (2006)
Cuevas-Tello, Juan C., Tino, Peter, Raychaudhury, Somak
We present a novel approach to estimate the time delay between light curves of multiple images in a gravitationally lensed system, based on Kernel methods in the context of machine learning. We...
The Group Evolution Multiwavelength Study (GEMS): the Sample and Datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia, Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some the balance. Here we describe the GEMS...
The Group Evolution Multiwavelength Study (GEMS) : the sample and datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia A., Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some of the balance. Here we describe the...
The Group Evolution Multiwavelength Study (GEMS) : the sample and datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia A., Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some of the balance. Here we describe the...
The Group Evolution Multiwavelength Study (GEMS) : the sample and datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia A., Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some of the balance. Here we describe the...
The Group Evolution Multiwavelength Study (GEMS) : the sample and datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia A., Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some of the balance. Here we describe the...
The Group Evolution Multiwavelength Study (GEMS): the sample and datasets (2006)
Forbes, Duncan A., Ponman, Trevor, Pearce, Frazer, Osmond, John, Kilborn, Virginia A., Brough, Sarah, ...
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some of the balance. Here we describe the...
Porter, Scott C., Raychaudhury, Somak
The Pisces-Cetus supercluster (redshift z~0.06) is one of the richest nearby (z4.7 and delta_M>1.3 for the two filaments making up the supercluster.
X-ray observations of the edge-on star-forming galaxy NGC891 and its supernova SN1986J (2005)
Temple, Rowan, Raychaudhury, Somak, Stevens, Ian
We present XMM-Newton observations of NCG891, a nearby edge-on spiral galaxy. We analyse the extent of the diffuse emission emitted from the disk of the galaxy, and find that it has a single...
Mapping the Physical Properties of Cosmic Hot Gas with Hyper-spectral Imaging (2005)
O'Dwyer, Mark, Ponman, Trevor, Claridge, Ela, Raychaudhury, Somak
A novel inversion technique is proposed to compute parametric maps showing the temperature, density and chemical composition of cosmic hot gas from X-ray hyper-spectral images. The parameters are...
Kaban, Ata, Nolan, Louisa A., Raychaudhury, Somak
Elliptical galaxies are believed to consist of a single population of old stars formed together at an early epoch in the Universe, yet recent analyses of galaxy spectra seem to indicate the presence...
Louisa A. Nolan, Markus O. Harva, Ata Kabán, Somak Raychaudhury
Efficient predictive models and data analysis techniques for the analysis of photometric and spectroscopic observations of galaxies are not only desirable, but also required, in view of the...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera
We present B and R-band luminosity functions (LF) for a sample of 25 nearby groups of galaxies. We find that the LFs of the groups with low X-ray luminosity (L_X < 10^{41.7} erg/s) are significantly...
Scaling relations in early-type galaxies belonging to groups (2004)
Khosroshahi, Habib G., Raychaudhury, Somak, Ponman, Trevor J., Miles, Trevor A., Forbes, Duncan A.
We present a photometric analysis of a large sample of early-type galaxies in 16 nearby groups, imaged with the Wide-Field Camera on the Isaac Newton Telescope. Using a two-dimensional surface...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera, ...
Not available.
Scaling relations in early-type galaxies belonging to groups (2004)
Khosroshahi, Habib G., Raychaudhury, Somak, Ponman, Trevor J., Miles, Trevor A., Forbes, Duncan A.
We present a photometric analysis of a large sample of early-type galaxies in 16 nearby groups, imaged with the Wide-Field Camera on the Isaac Newton Telescope. Using a two-dimensional surface...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera
Not available.
Scaling relations in early-type galaxies belonging to groups (2004)
Khosroshahi, Habib G., Raychaudhury, Somak, Ponman, Trevor J., Miles, Trevor A., Forbes, Duncan A.
We present a photometric analysis of a large sample of early-type galaxies in 16 nearby groups, imaged with the Wide-Field Camera on the Isaac Newton Telescope. Using a two-dimensional surface...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera
Not available.
Scaling relations in early-type galaxies belonging to groups (2004)
Khosroshahi, Habib G., Raychaudhury, Somak, Ponman, Trevor J., Miles, Trevor A., Forbes, Duncan A.
We present a photometric analysis of a large sample of early-type galaxies in 16 nearby groups, imaged with the Wide-Field Camera on the Isaac Newton Telescope. Using a two-dimensional surface...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera
Not available.
An evolutionary approach to modeling radial brightness distributions in elliptical galaxies (2004)
Jin Li, Xin Yao, Colin Frayn, Habib G. Khosroshahi, Somak Raychaudhury
Abstract. A reasonably good description of the luminosity profiles of galaxies is needed as it serves as a guide towards understanding the process of galaxy formation and evolution. To obtain a...
Scaling relations in early-type galaxies belonging to groups (2004)
Khosroshahi, Habib G., Raychaudhury, Somak, Ponman, Trevor J., Miles, Trevor A., Forbes, Duncan A.
We present a photometric analysis of a large sample of early-type galaxies in 16 nearby groups, imaged with the Wide-Field Camera on the Isaac Newton Telescope. Using a two-dimensional surface...
Miles, Trevor A., Raychaudhury, Somak, Forbes, Duncan A., Goudfrooij, Paul, Ponman, Trevor J., Kozhurina-Platais, Vera
Not available.
Is B1422+231 a Golden Lens? (2003)
Raychaudhury, Somak, Saha, Prasenjit, Williams, Liliya L. R.
B1422+231 is a quadruply-imaged QSO with an exceptionally large lensing contribution from group galaxies other than the main lensing galaxy. We detect diffuse X-rays from the galaxy group in archival...
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
FLASH redshift survey - I. Observations and catalogue (2003)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, B.A.
not available
Bagchi, Joydeep, Ensslin, Torsten A., Miniati, Francesco, Stalin, C. S., Singh, M., Raychaudhury, Somak, ...
We report the discovery of large-scale diffuse radio emission from what appears to be a large-scale filamentary network of galaxies in the region of cluster ZwCl 2341.1+0000, and stretching over an...
FLASH redshift survey - I. Observations and Catalogue (2001)
Kaldare, Raven, Colless, Matthew, Raychaudhury, Somak, Peterson, Bruce A.
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of 4613 galaxies brighter than $\bJ = 16.7$ (corrected for Galactic extinction) over a 605 sq. degree region of sky in the general...
Observing high-redshift Supernovae in lensed galaxies (2000)
Saini, Tarun Deep, Raychaudhury, Somak, Shchekinov, Yuri A.
Supernovae in distant galaxies that are gravitationally lensed by foreground galaxy clusters make excellent cosmological candles for measuring quantities like the density of the Universe in its...
A Lens Mapping Algorithm for Weak Lensing (2000)
Saini, Tarun Deep, Raychaudhury, Somak
We develop an algorithm for the reconstruction of the two-dimensional mass distribution of a gravitational lens from the observable distortion of background galaxies. From the measured reduced shear,...
Reconstructing the Cosmic Equation of State from Supernova distances (1999)
Saini, Tarun Deep, Raychaudhury, Somak, Sahni, Varun, Starobinsky, A. A.
Observations of high-redshift supernovae indicate that the universe is accelerating. Here we present a {\em model-independent} method for estimating the form of the potential $V(\phi)$ of the scalar...
Tests of the Tully-Fisher Relation II: Scatter Using Optical Rotation Curves (1997)
Raychaudhury, Somak, Von Braun, Kaspar, Bernstein, Gary M., Guhathakurta, Puragra
We investigate the amount of scatter in the Tully-Fisher relation (TFR) when using optical long-slit H-alpha rotation curves to determine the velocity widths of spiral galaxies. We study a sample of...
The observed distribution function of peculiar velocities of galaxies (1996)
Raychaudhury, Somak, Saslaw, William C.
We give the first determination of the observed peculiar velocity distribution function for a representative sample of galaxies (within 50 Mpc (H=100) of the Local Group), which includes a wide range...
Gravity, galaxies and the 'Great Attractor' survey. (1990)
Thesis (Ph. D.)--University of Cambridge, 1990.