My career as an observational astronomer began by studying Giant X-shaped Radio Galaxies. People believe that the X-shape of these sources is due to multiple epochs of activity, with something happening between the epochs to change the spin axis of the central supermassive black hole of the host galaxy. However, no one knows for sure if this is the principle mechanism for the formation of the "wings", or if back flows due to the interaction of the lobes with the intergalactic environment are responsible for the strange shape of these sources. With Ravi Subrahmanyan and Lakshmi Saripalli at the Raman Research Institute, Bangalore, I prepared high-resolution radio images of J2018-556, the largest X-shaped radio galaxy known, revealing an inner-double in the core, implying a new period of activity! Read the full story here.

For my next observational project, I worked with Dave Soderblom at the Space Telescope Science Institute, Baltimore, studying the fascinating pre-main sequence (PMS) stellar system HD98800. PMS evolution is an ill-understood phase of a star's life. We set out to pin down the metallicity of this system using optical stellar spectroscopy, aiming eventually to help stellar astrophycists refine their evolutionary models.

Moving further up in energy, I worked with Andy Fabian at the Institute of Astronomy, Cambridge University on inverse-Compton scattering of the Cosmic Microwave Background (ICCMB) by relativistic electrons in Giant Radio Galaxies. ICCMB is great because it is not redshift-dimmed, and we can see this effect in sources out to the edge of the visible Universe. Having both x-ray and radio data from such sources enables us to break a degeneracy between electron density and magnetic field, allowing us to constrain the electron energy spectrum and obtain an independent estimate of the magnetic field in the lobes of radio-loud AGN. I used x-ray observations with XMM-Newton to study ICCMB from radio galaxies at z ~ 1. The results are here.

To fill in the holes in wavelength-coverage, I have just finished (Feb 2011) working on gamma-ray bursts and infrared observations with Spitzer (yes, in one project). Edo Berger and I looked at the stellar mass - gas metallicity relationship in early galaxies (z ~ 3 - 5). We used GRB afterglows as backlights shining through the hosts to provide us with a spectrum of the host galaxy, which used to determine the gas-phase metallicity. Simlutaneously, we hunted for the hosts in Spitzer images to estimate the total stellar mass. Our work was the first statistical study that put host galaxies of long-duration GRBs in context at z > 3. This study also pioneered the investigation of the mass-metallicity relation with GRBs, which may well be the only way to envestigate this relation at even higher redshift!

It is believed that supernovae produce much of the dust that we see floating about in giant molecular clouds, sites of future star-formation. But do they really? It is possible that much of the dust we believe to be produced in a typical supernova explosion is destroyed by the shock waves that result from the interaction of the cooling ejecta and the environment. With Biman Nath at RRI, I studied the effect of the reverse shock on the formation of dust grains in supernovae. This is one of the few analytical treatments of the subject. Why not check it out?

With Tarun Deep Saini at the Indian Institute of Science, Bangalore, I have dabbled a bit in cosmology. We looked carefully at the supernova Ia data that tells us that the expansion of the Universe is acelerating, leading people to postulate the existence of Dark Energy. We studied the possibility that there were direction-dependent systematics in this data. We did find some interesting evidence that the errors in these data were not Gaussian in nature.