Rohit Kondapally

LoTSS Deep DR1 - Value added catalogues

As part of the LOFAR Two-Metre Sky Survey (LoTSS), the LOFAR radio telescope is undertaking one of the deepest wide-field radio-continuum surveys to date at 150 MHz, known as the LoTSS Deep Fields (led by Philip Best). Over the past few years, deep, repeated observations have been obtained of some of the best-studied extra-galactic fields in the Northern Sky: ELAIS-N1, Lockman Hole, and Bootes, totalling 100s of hours per field and reaching rms noise levels of 20µJy/beam for the first data release. The figure on the left shows the full field-of-view of the deepest field, ELAIS-N1, compared to the full moon (to-scale) -- the deep observations show not just extended radio-AGN but also many distant star-forming galaxies (image credit: Philip Best & Jose Sabater).

The LoTSS Deep Fields also benefit from having deep, wide-area panchromatic imaging from a host of ground and space-based telescopes, making them ideal for studying determining physical properties. For the first data release, I generated new multi-wavelength photometry catalogues in ELAIS-N1 and Lockman Hole, which incorporated new deeper imaging datasets and improvements to the catalogues than those available in the literature that facilitate more robust photometric redshifts. Using these new photometry catalogues, I led the process of identifying the host-galaxies of the LOFAR-detected sources using a combination of statistical and visual classification processes. This resulted in a value-added catalogue of > 80,000 radio-sources, with host-galaxies identified for > 97% of these sources (Kondapally et al. 2021). This process was vital for a wide range of scientific studies, including determining the photometric redshifts (Duncan et al. 2021) and the SED-fitting and source classification process (Best et al. 2023).

More information about the LoTSS Deep Fields DR1 and the dataset can be accessed here: LoTSS Deep DR1 .

Cosmic evolution of jet-mode AGN out to z ~ 2.5

Using the LoTSS Deep Fields dataset (see above), I recently led a paper which presented the first measurement of the evolution of the jet-mode AGN out to z ~ 2.5. These AGN are thought to be particularly important in the lifecycle massive galaxies, however their cosmic evolution was previously not well constrained. Through this analysis, I found that jet-mode AGN luminosity function shows surprisingly little evolution with redshift. These AGN are found to be hosted by massive quiescent galaxies in the local Universe, therefore the lack of evolution in this population is surprising! We investigated the host galaxy properties to find a significant new population of jet-mode AGN hosted by star-forming galaxies at higher redshifts, in contrast to expectations in the local Universe. This previously unstudied population has interesting implications for the triggering of jet-mode AGN and the amount of feedback across cosmic time.

Cosmic evolution of radio-AGN feedback: comparison with simulations

In a recent paper that I led, we studied the amount of heating performed by radio-AGN throughout cosmic history and compared this to predictions in various cosmological hydrodynamical and semi-analytical simulations. We find that compared to a semi-analytical model for galaxy evolution, the radio-AGN output more than enough energy to offset radiative cooling losses across cosmic time, providing evidence for a self-regulating AGN feedback cycle since z ~ 2.5. Overall, there is a broad consistency between the observations and simulations, however, they do not agree in detail; this will be studied in more detail in upcoming works.