Abstract Details
| Name: Pratik Dabhade Affiliation: IUCAA Conference ID: ASI2017_601 Title : SAGAN - Search & Analysis of GRGs with Associated Nuclei Authors and Co-Authors : Madhuri Gaikwad(MPIFR, Germany) Joydeep Bagchi (IUCAA, India) Huub Rottgering (Observatory of Leiden,Netherlands) Francoise Combes (Observatory of Paris, France), Shishir Sankhayayan (IISER, Pune-India) Abstract Type : Oral Abstract Category : Extragalactic astronomy Abstract : In this talk we will present about Giant Radio Galaxies (GRGs) and highlight the importance of their studies and our efforts to solve major standing problems related to growth and evolution of GRGs and their host AGN. The GRGs represent an extreme class of active galaxies which have linear sizes in the range of ~ 0.5 Mpc to 5 Mpc which places them among the largest single astrophysical objects known to us. From the past four decades only ~ 300 GRGs are known as oppose to thousands of normal sized radio galaxies (> 450-500 Kpc). It is unsettled if the large sizes of GRGs indicate the high efficiency of radio jets ejected from the central AGN, or they grow to enormous sizes due to their location in sparser cluster environments. In spite of various studies of GRGs, there is still not a single tested unified model which might explain the immense physical scale and other extreme properties of GRGs. Moreover, till now only a small fraction of these GRGs have been studied in sufficient detail in multiple wavebands for achieving a good understanding of their unusual nature. This puts a restriction on carrying out statistical studies of their properties. We under our project SAGAN (Search & Analysis of GRGs with Associated Nuclei) aim to firstly make a complete sample of all known GRGs with same cosmological parameters for uniformity, secondly find more GRGs from existing radio and optical surveys, thirdly study the hosts of GRGs in multiwavelength to understand the nature of accretion, feedback and their excitation types. Lastly we aim to study the environments of these GRGs and explore the effects of environment on morphology and other properties. All the above listed goals are not attempted before anyone. We have already discovered nearly 200 new GRGs (Dabhade et al-2016 and Dabhade et al-in prep) from NVSS. These numerous GRGs were missed before due to their very low surface brightness features: they were just at the sensitivity limits of existing surveys like NVSS. I will describe the methods used and results of their analysis. GMRT which provides sufficient high resolution and sensitivity at low frequencies has enabled us to decipher and study their morphologies which extend over megaparsec scales. Nearly 10 new GRGs were mapped with GMRT which has unveiled stunning new feature of these GRGs which most likely host the most massive black holes known in the Universe. Our mid-infrared studies of the hosts of GRGs too suggests this possibility. We will present our study of these AGN which emit and sustain powerful radio jets for 100s of kpc scale. |