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Upcoming Seminar/Colloqium


Associated HI 21 cm absorption towards radio AGNs of different accretion modes

Speaker : Dr. Yogesh Chandola
Affiliation : Purple Mountain Observatory (PMO), Nanjing, China
Date & Time :
Venue : Auditorium/ zoom
Abstract :

Associated HI 21 cm absorption studies towards compact radio sources provide details of gas kinematics in central regions of radio active galactic nuclei (AGNs) which help us to understand feeding and feedback in these sources. Depending upon their accretion efficiencies, AGNs are broadly classified as radiatively efficient and inefficient accretion mode AGNs. Among the radio AGNs, efficient accretion mode AGNs with strong optical emission lines are called High-Excitation Radio Galaxies (HERGs) and inefficient accretion mode AGNs with weak optical emission lines are called Low-Excitation Radio Galaxies (LERGs). In this talk, I will present the results of GMRT observations of a sample of HERGs and LERGs at low redshift (z < 0.3) and low to intermediate radio luminosity (~10^23-10^26 W/Hz at 1.4 GHz). Combined with other sources from the literature, we find HERGs have higher HI absorption detection rates compared to LERGs, mainly due to the gas and dust-rich nature of their host galaxies. We find this to be also reflected in the WISE colours where those with W2-W3>2 have a higher detection rate of HI absorption, with the HERGs also tending to have similar WISE colours. I will also discuss how the SKA precursor radio telescopes such as FAST, with excellent spectral line sensitivity, would help enlarge the samples of different luminosities for such studies, and clarify the different accretion modes and nature of feedback for different types of AGNs.

About Speaker :

Dr. Chandola obtained Ph.D. in 2013 from NCRA, Pune. He worked as a FAST postdoctoral fellow at Purple Mountain Observatory (PMO), Nanjing, China, until  October 2022. Prior to that, he was a postdoctoral fellow at NAOC, Beijing, China (October 2013-June 2017) and IUCAA, Pune, India (August 2017-July 2019). He works mainly on HI 21cm absorption line towards radio AGNs using FAST, GMRT, MeerKAT, and earlier Arecibo.