We report optical extinction properties of dust for a sample of 26 early-type galaxies based on the analysis of their multicolour CCD observations. The wavelength dependence of dust extinction for these galaxies is determined and the extinction curves are found to run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic environment are quite similar to those of the Milky Way. For the sample galaxies, value of the parameter R V , the ratio of total extinction in V band to selective extinction in B and V bands, lies in the range 2.03−3.46 with an average of 3.02, compared to its canonical value of 3.1 for the Milky Way. A dependence of R V on dust morphology of the host galaxy is also noticed in the sense that galaxies with a well defined dust lane show tendency to have smaller R V values compared to the galaxies with disturbed dust morphology. The dust content of these galaxies estimated using total optical extinction is found to lie in the range 10 4 to 10 6 M , an order of magnitude smaller than those derived from IRAS flux densities, indicating that a significant fraction of dust intermixed with stars remains undetected by the optical method. We examine the relationship between dust mass derived from IRAS flux and the X-ray luminosity of the host galaxies.The issue of the origin of dust in early-type galaxies is also discussed.

We present results based on the systematic analysis of currently available Chandra archive data on the brightest galaxy in the Draco constellation, NGC 6338, in order to investigate the properties of the X‐ray cavities. In the central ∼6 kpc, at least two, possibly three, X‐ray cavities are evident. All these cavities are roughly of ellipsoidal shape and show a decrement in surface brightness of several tens of per cent. In addition to these cavities, a set of X‐ray bright filaments are also noticed which are spatially coincident with the Hα filaments over an extent of 15 kpc. The Hα emission‐line filaments are perpendicular to the X‐ray cavities. Spectroscopic analysis of the hot gas in the filaments and cavities reveals that the X‐ray filaments are cooler than the gas contained in the cavities. The emission‐line ratios and the extended, asymmetric nature of the Hα emission‐line filaments seen in this system require a harder ionizing source than that produced by star formation and/or young, massive stars. Radio emission maps derived from the analysis of 1.4‐GHz Very Large Array Faint Images of the Radio Sky at Twenty‐Centimeters survey data failed to show any association of these X‐ray cavities with radio jets; however, the cavities are filled by radio emission. The total power of the cavities is 17 × 1042 erg s−1 and the ratio of radio luminosity to cavity power is ∼10−4, implying that most of the jet power is mechanical.

We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counters (LAXPC) and Soft X-ray Telescope (SXT) on-board AstroSat, when the source was in the hard spectral state as revealed by the broad band spectra. The spectra obtained from all the observations can be described by a single temperature Comptonizing region with disk and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional root mean square (rms) and time-lag at different frequencies which we fit with empirical functions. We invoke a fluctuation propagation model for a simple geometry of a truncated disk with a hot inner region. Unlike other propagation models, the hard X-ray emission (> 4 keV) is assumed to be from the hot inner disk by a single temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disk and then the temperature of the inner disk after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.

We present the results obtained from a total of 123 ks X-ray (Chandra) and 8 hrs of 1.4 GHz radio (Giant Metrewave Radio Telescope -GMRT) observations of the cool core cluster ZwCl 2701 (z = 0.214). These observations of ZwCl 2701 showed the presence of an extensive pair of ellipsoidal cavities along the East and West directions within the central region < 20 kpc. Detection of bright rims around the cavities suggested that the radio lobes displaced Xray emitting hot gas forming shell-like structures. The total cavity power (mechanical power) that directly heated the surrounding gas and cooling luminosity of the cluster were estimated to be ∼ 2.27 × 10 45 erg s −1 and 3.5× 10 44 erg s −1 , respectively. Comparable values of cavity power and cooling luminosity of ZwCL 2701 suggested that the mechanical power of the AGN outburst is large enough to balance the radiative cooling in the system. The star formation rate derived from the Hα luminosity was found to be ∼ 0.60 M yr −1 which is about three orders of magnitude lower than the cooling rate of ∼ 196 M yr −1 . Detection of the floor in entropy profile of ZwCl 2701 suggested the presence of an alternative heating mechanism at the centre of the cluster. Lower value of the ratio (∼10 −2 ) between black hole mass accretion rate and Eddington mass accretion rate suggested that launching of jet from the super massive black hole is efficient in ZwCl 2701. However, higher value of ratio (∼10 3 ) between black hole mass accretion rate and Bondi accretion rate indicated that the accretion rate required to create cavities is well above the Bondi accretion rate.

We present results based on the systematic analysis of high resolution 95 ks Chandra observations of the strong cool core cluster Abell 2390 at the redshift of z = 0.228 that hosts an energetic radio AGN. This analysis has enabled us to investigate five X-ray deficient cavities in the atmosphere of Abell 2390 within central 30′′ . Presence of these cavities have been confirmed through a variety of image processing techniques like, the surface brightness profiles, unsharp masked image, as well as 2D elliptical model subtracted residual map. Temperature profile as well as 2D temperature map revealed structures in the distribution of ICM, in the sense that ICM in the NW direction is cooler than that on the SE direction. Temperature jump in all directions is evident near 25 ′′ (90.5 kpc) corresponding to the average Mach number 1.44±0.05, while another jump from 7.47 keV to 9.10 keV at 68 ′′ (246 kpc) in the north-west direction, corresponding to Mach number 1.22±0.06 and these jumps are associated with the cold fronts. Tricolour map as well as hardness ratio map detects cool gas clumps in the central 30 kpc region of temperature 4.45 +0.16 −0.10 keV. The entropy profile derived from the X-ray analysis is found to fall systematically inward in a power-law fashion and exhibits a floor near 12.20±2.54 keV cm 2 in the central region. This flattening of the entropy profile in the core region confirms the intermittent heating at the centre by AGN. The diffuse radio emission map at 1.4 GHz using VLA L-band data exhibits highly asymmetric morphology with an edge in the north-west direction coinciding with the X-ray edge seen in the unsharp mask image. The mechanical power injected by the AGN in the form of X-ray cavities is found to be 5.94×1045 erg s −1 and is roughly an order of magnitude higher than the energy lost by the ICM in the form of X-ray emission, confirming that AGN feedback is capable enough to quench the cooling flow in this cluster.