Ajit Kembhavi

Correlations among global photometric properties of disk galaxies

Using a two-dimensional galaxy image decomposition technique, we extract global bulge and disk parameters for a complete sample of early-type disk galaxies in the near-infrared K band. We find significant correlation of the bulge parameter n with the central bulge surface brightness μb(0) and with effective radius re. Using bivariate analysis techniques, we find that log n, log re, and μb(0) are distributed in a plane with small scatter. We do not find a strong correlation of n with bulge-to-disk luminosity ratio, contrary to earlier reports. For these early-type disk galaxies, re and the disk scale length rd are well correlated, but with large scatter. We examine the implications of our results for various bulge formation scenarios in disk galaxies.

A Near-Infrared Photometric Plane for Elliptical Galaxies and Bulges of Spiral Galaxies.

We report the existence of a single plane in the space of global photometric parameters describing elliptical galaxies and the bulges of early-type spiral galaxies. The three parameters that define the plane are obtained by fitting the Sersic form to the brightness distribution obtained from near-infrared K-band images. We find, from the range covered by their shape parameters, that the elliptical galaxies form a more homogeneous population than the bulges. Known correlations like the Kormendy relation are projections of the photometric plane. The existence of the plane has interesting implications for bulge formation models.

Broadening of the Iron Emission Line in MCG–6-30-15 by Comptonization

We show that the iron K emission line from MCG-6-30-15 could be broadened through Comptonization by a surrounding highly ionized cloud with radius ~1014 cm. We calculate the temperature of the cloud to be ~0.21 keV, provided that a reasonable estimate of the UV flux is made. The X-ray/γ-ray emission observed from the source is compatible with this model. Such a cloud should be highly ionized, and strong absorption edges are not expected from the source. For a 106 M☉ black hole the size of the cloud corresponds to about 300 Schwarzschild radii. The intrinsic line could then be emitted far from the black hole, and gravitational redshift and Doppler effects would be negligible. If the black hole mass is much larger than 106 M☉, gravitational/Doppler redshifts would also contribute significantly to the broadening. We argue that the broad red wing observed in the source does not by itself imply emission from regions close (R < 5rS) to the black hole. However, Comptonization cannot produce a double peak. The presence of such a feature is a clear sign of inner disk emission influenced by gravitational and Doppler effects, perhaps broadened by the Comptonization. We note that simultaneous broadband (2-100 keV) study of this source can also reveal (or rule out) the presence of such a Comptonizing cloud.

Near-infrared bulge-disc correlations of lenticular galaxies

We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a 2D galaxy image decomposition technique, we extract bulge and disc structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterize the bulge and the disc as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disc parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars (MT > −24.5) formed via secular formation processes that likely formed the pseudo-bulges of late-type disc galaxies, while brighter lenticulars (MT < −24.5) formed through a different formation mechanism most likely involving major mergers. On probing variations in lenticular properties as a function of environment, we find that faint cluster lenticulars show systematic differences with respect to faint field lenticulars. These differences support the idea that the bulge and disc components fade after the galaxy falls into a cluster, while simultaneously undergoing a transformation from spiral to lenticular morphologies.

Two-dimensional Galaxy Image Decomposition

We propose a two-dimensional galaxy fitting algorithm to extract parameters of the bulge, disk, and a central point source from broadband images of galaxies. We use a set of realistic galaxy parameters to construct a large number of model galaxy images, which we then use as input to our galaxy decomposition program to test it. We elucidate our procedure by extracting parameters for three disk galaxies—NGC 5326, 5587, and 7311—and compare our results with those previously reported in the literature.

A Difference boosting neural network for automated star-galaxy classification

In this paper we describe the use of a new articial neural network, called the dierence boosting neural network (DBNN), for automated classication problems in astronomical data analysis. We illustrate the capabilities of the network by applying it to star galaxy classication using recently released, deep imaging data. We have compared our results with classication made by the widely used Source Extractor (SExtractor) package. We show that while the performance of the DBNN in star-galaxy classication is comparable to that of SExtractor, it has the advantage of signicantly higher speed and flexibility during training as well as classication.

Warm absorbers in X-rays (WAX), a comprehensive high-resolution grating spectral study of a sample of Seyfert galaxies – I. A global view and frequency of occurrence of warm absorbers.

We present results from a homogeneous analysis of the broadband 0.3-10 keV CCD resolution as well as of soft X-ray high-resolution grating spectra of a hard X-ray flux-limited sample of 26 Seyfert galaxies observed with XMM-Newton. Our goal is to characterise the warm absorber (WA) properties along the line-of-sight to the active nucleus. We significantly detect WAs in

Properties of warm absorbers in active galaxies: a systematic stability curve analysis

65\%

Toward a robust estimate of the merger rate evolution using near-IR photometry

of the sample sources. Our results are consistent with WAs being present in at least half of the Seyfert galaxies in the nearby Universe, in agreement with previous estimates . We find a gap in the distribution of the ionisation parameter in the range

The Nonlinear Behavior of the Black Hole System GRS 1915+105

0.5<\log\xi<1.5