arXiv subjects

Pratik Dabhade

Publications and source records attributed to Pratik Dabhade.

39 records · Page 3Linked to original sources

arXiv2017

Saraswati: An Extremely Massive ~ 200 Megaparsec Scale Supercluster

Here we report the discovery of an extremely massive and large supercluster (called Saraswati) found in the Stripe 82 region of SDSS. This supercluster is a major concentration of galaxies and galaxy clusters, forming a wall-like structure spanning at least 200 Mpc across at the redshift $z \approx 0.3$. This enormous structure is surrounded by a network of galaxy filaments, clusters, and large, $\sim40 - 170$ Mpc diameter, voids. The mean density contrast $δ$ (relative to the background matter density of the universe) of Saraswati is $\gtrsim 1.62$ and the main body of the supercluster comprises at least 43 massive galaxy clusters (mean $z = 0.28$) with a total mass of $\sim 2 \times 10^{16} M_{\odot}$. The spherical collapse model suggests that the central region of radius $\sim20$ Mpc and mass at least $ 4 \times 10^{15} M_{\odot}$ may be collapsing. This places it among the few largest and most massive superclusters known, comparable to the most massive `Shapley Concentration' ($z \approx 0.046$) in the nearby universe. The Saraswati supercluster and its environs reveal that some extreme large-scale, prominent matter density enhancements had formed $\sim4$ Gy in the past when dark energy had just started to dominate structure formation. This galactic concentration sheds light on the role of dark energy and cosmological initial conditions in supercluster formation, and tests the competing cosmological models.

astro-ph.CO↗

arXiv2017

Discovery of Giant Radio Galaxies from NVSS: Radio & Infrared Properties

Giant radio galaxies (GRGs) are one of the largest astrophysical sources in the Universe with an overall projected linear size of ~0.7 Mpc or more. Last six decades of radio astronomy research has led to the detection of thousands of radio galaxies. But only ~ 300 of them can be classified as GRGs. The reasons behind their large size and rarity are unknown. We carried out a systematic search for these radio giants and found a large sample of GRGs. In this paper, we report the discovery of 25 GRGs from NVSS, in the redshift range (z) ~ 0.07 to 0.67. Their physical sizes range from ~0.8 Mpc to ~4 Mpc. Eight of these GRGs have sizes greater than 2Mpc which is a rarity. In this paper, for the first time, we investigate the mid-IR properties of the optical hosts of the GRGs and classify them securely into various AGN types using the WISE mid-IR colours. Using radio and IR data, four of the hosts of GRGs were observed to be radio loud quasars that extend up to 2 Mpc in radio size. These GRGs missed detection in earlier searches possibly because of their highly diffuse nature, low surface brightness and lack of optical data. The new GRGs are a significant addition to the existing sample that will contribute to better understanding of the physical properties of radio giants.

astro-ph.GA↗

arXiv2016

Tracking galaxy evolution through low frequency radio continuum observations using SKA and Citizen-science Research using Multi-wavelength data

We present a review on galaxy black hole co-evolution through merger, star formation and AGN-jet feedback. We highlight results on transitional galaxies (e.g. NGC1482, NGC6764, NGC3801, Speca, RAD-18 etc.) which has data from Giant Meterwave Radio Telescope (GMRT) and other sub-mm, IR, optical, UV and X-ray telescopes. The `smoking gun' relic-evidences of past AGN-jet feedback which is believed to have quenched star formation in transitional galaxies are still missing. Relic radio lobes, as old as a few hundred Myr, can be best detected at low radio frequencies with the GMRT, LOFAR and in future SKA. However, similar relic evidences of quasar activities, known as `Hanny's Voorwerp' discovered by Galaxy Zoo in optical data, are only around a few tens of thousand years old. More discoveries are needed to match these time-scales with time since the decline of star formation in transitional galaxies. Such faint fuzzy relic emissions in optical and angular-scale sensitive radio interferometric images can be discovered most efficiently by citizen-scientists but with a formal training. We describe RAD@home, the only Indian citizen-science research project in astronomy which takes such a modified approach. We present interesting objects, discovered from the TIFR GMRT Sky Survey (TGSS) by 69 trained citizen-scientists or e-astronomers, like relic radio lobes, episodic radio galaxies, jet-galaxy interaction, bent radio galaxy in filament etc.. This model can provide an equal opportunity of academic-growth to people even in the under-developed regions where we always need to establish our optical and radio telescopes. This can expand the research-activity of city-based research-institutes beyond their four brick walls, and alleviate various socio-economic and geo-political constraints on growth of citizens located in remote areas. #RADatHomeIndia #ABCDresearch

astro-ph.GA↗