Galaxy Evolution
Bulges of Galaxies
With my collaborators, I studied the bulges of spiral, elliptical, and lenticular galaxies (ApJ Letter, MNRAS paper). Related work has explored the bar fraction in lenticulars as a function of luminosity and environment.
We reported systematic differences in the star formation history of bright and faint lenticular galaxies. My short review article (now rather dated) summarises early work in this area.
Our more recent papers cover pseudo bulge fraction versus environment, S0s in high-density environments, age bimodality in pseudo bulges, why classical bulges are more common in lenticulars, and spectral studies of pseudobulges using SALT.
Star-formation in and around Galaxies
I used WFPC2 parallels of the Hubble Ultra Deep Field to study star-forming galaxies at z < 2 and Lyman break galaxies at higher redshifts (AAS Poster, AJ paper). We investigated the importance of morphological K correction in UV-bright galaxies.
For blue cloud galaxies (0 < z < 1), we studied the radio-FIR correlation and the dependence of star formation on morphology and environment.
Other related studies include outlying H-alpha emitters, the discovery of a giant hydrogen ring, star-forming S0 galaxies in SDSS-MaNGA, structure and kinematics of star-forming ellipticals, and low-metallicity warm plasma discovery with HST/COS.
Low-surface Brightness Features
We serendipitously discovered a galaxy with the longest known tidal tail.
High Redshift Galaxies
We discovered the highest redshift disk-dominated spiral galaxy known using JWST data. Our recent submitted work using JWST includes studies of massive quiescent galaxies at cosmic noon and optically invisible galaxies at cosmic noon and beyond.
Radio Properties of Galaxies
Radio Continuum Emission from AGN
For my doctoral thesis, I studied radio emission from Quasars. A companion paper discussed radio emission from Seyfert galaxies. My thesis was titled "Optical studies of VLA FIRST Survey radio sources" (PDF).
Later work includes GMRT observations of an AGN cum luminous type IIn supernova, kiloparsec-scale radio emission in Seyfert and LINER galaxies, and the discovery of rare double-lobed radio AGN in spiral galaxies.
Giant radio galaxy discoveries by me and my collaborators include a relic giant at z~1.3, a giant at z~0.57, and double-double radio galaxies. My remnant radio galaxy studies cover the Lockman Hole field, an overview paper, new XMM-LSS remnants, and small angular size remnants.
Galaxy Clusters
My postdoc - Lijo George - developed an upper limit calculator for extended cluster radio haloes and used GMRT archival observations to detect and characterise radio haloes in 39 galaxy clusters.
Nearby Spirals
Another postdoc - Aritra Basu - studied the radio continuum emission of 6 nearby spirals to constrain cosmic ray electron generation, diffusion, and energy losses at ~1 kpc scales.
High Redshift Radio Galaxies
We used deep GMRT observations to identify high-redshift radio sources with the steep spectrum technique, combined with optical/IR data to characterise steep-spectrum sources. Discoveries include a relic high-z giant radio galaxy and another high-z giant, along with studies of infrared-faint radio sources and dust-obscured radio-AGN.
Software and Technology Development
Square Kilometre Array (SKA)
Since 2010, I have been part of the NCRA group working on SKA-related activities, with a focus on the Monitoring and Control System. Our URSI 2011 paper and concept design documents (zip) describe our work, and the technologies we developed were implemented in the GMRT monitoring and control system.
Recent work includes a SPIE paper and 2023 overview. For the S20 policy webinar on Astroinformatics, I led a panel on Large projects in Astronomy. I am a member of the SKA-India continuum science group (science interests paper).
SKA Regional Centre
I was a member of the SKA Regional Centre Steering Committee, until it was disbanded in 2024, coordinating efforts to build a regional centre in India. I contributed to SRCNet documents and the overview paper.
Astronomy Software
I developed fitgal (bulge-disk decomposition), contributed to building PyMorph (GitHub) for galaxy morphology measurements, built the APPP data processing for HST data, a telescope scheduler for GMRT data, and NAPS (NCRA Archive & Proposal System).
Machine Learning in Astronomy
I have worked on star-galaxy classification using the Difference Boosting Neural Network (DBNN), which was used to classify SDSS DR7 detections. I proposed a new approach to photometric redshift estimation using Support Vector Machines, and more recently I helped develop a scaled ensemble framework for photo-z estimation up to z~4.
My deep learning applications include predicting star formation properties, the bulge-to-total ratio, and radio galaxy morphological classification. I have also contributed to the ASI Vision Document chapter on AI/ML in Astronomy.