Abstract Details

Name: Pratik Dabhade
Affiliation: IUCAA
Conference ID: ASI2016_601
Title : Discovery and multiwavelength analysis of Giant Radio Galaxies
Authors and Co-Authors : Madhuri Gaikwad (NCRA)& Joydeep Bagchi (IUCAA)
Abstract Type : Poster
Abstract Category : Extragalactic astronomy
Abstract : Giant radio galaxies (GRGs) are a class of radio galaxies with linear sizes greater than 0.7 Mpc thus making them the largest single object known to us in the Universe. They are rare among the entire population of radio galaxies (RGs). Their physical evolution is not well understood so far. Most of the sources show bright hot spots at the edges and hence are classified as FR-II type radio sources. These radio sources host an active galactic nuclei (AGN) at the centre. It is believed that the “central engine”in the AGN is responsible for the production of bipolar relativistic jets. Largest known GRG is about 5 Mpc in projected linear size. In the past 60 years thousands of radio galaxies have been found, but less than 150 GRGs are only known so far which makes them very rare. GRGs owing to their large sizes and relatively low surface brightness, makes it difficult for their detection via automated search algorithms in various radio surveys. We have carried out non automated systematic search for GRGs. As a result we have found about 30 giant radio galaxies (GRGs) from the NRAO VLA SKY SURVEY (NVSS). Our discovery sample of GRGs have contributed to this field significantly. Questions about their rarity and exceptional large sizes have not been answered so far. In an attempt to answer one these questions we have started to study the host galaxy properties of these GRG in greater details. We have for the first time attempted to study the black hole properties of hosts of the GRGs. Studies in past three decades has provided strong evidences about black holes being the central engine responsible for powering these long and highly collimated radio jets in these GRGs. Interesting results of this study will be presented. The host galaxies of the GRGs were also studied for the first in mid-IR using the WISE telescope data. This has enabled us to classify for the very first time the GRGs into high & low excitation (LERGS & HERGS). WISE has unique capabilities of picking up high redshift AGNs as well as dust obscured AGNs. We also have developed a new technique of identifying radio loud quasars using WISE data along with radio data. This has enabled us to identify some of our GRGs as Giant radio quasars (GRQs) which are even more rarer than GRGs. These GRQs challenge the existing AGN unification scheme. These all results will be presented in greater details.