| Name: | Abhijit Kayal |
| Affiliation: | Physical Research Laboratory, Ahmdebad |
| Conference ID : | ASI2024_215 |
| Title : | Unveiling a new population of obscured Active Galactic Nuclei in deep field surveys |
| Authors : | Abhijit Kayal1, Veeresh Singh1, Sushant Dutta1, C. H. Ishwara Chandra2, Yogesh Wadadekar2, Santosh Vadawale1, N.P.S. Mithun1, Claudio Ricci3,4, Gulab C. Dewangan5, Poshak Gandhi6 |
| Authors Affiliation: | 1 Physical Research Laboratory, Ahmedabad 380009, India.
2 National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411007, India.
3 Núcleo de Astronomı́a de la Facultad de Ingenierı́a, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile.
4 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China.
5 Inter-University Centre for Astronomy and Astrophysics (IUCAA), SPPU Campus, Pune 411007, India.
6 School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK |
| Mode of Presentation: | Oral |
| Abstract Category : | Thesis |
| Abstract : | Obscuration poses a challenge for uncovering the complete population of active galactic nuclei (AGN) and understanding their cosmic evolution, particularly at high redshifts. The dust-obscured galaxies (DOGs), containing large reservoir of dust and gas, can be the potential hosts for obscured AGN. Due to obscuration, a significant population of AGN hosted in DOGs can be missed by several optical and UV surveys. However, radio, infrared (IR) and X-ray surveys, being less susceptible to absorption, can detect obscured AGN. My thesis work delves into the detection and understanding the nature of the obscured population of AGN hosted in DOGs using the deepest available multi-frequency radio, mid-IR and X-ray surveys in the XMM-LSS field. With deep band-3 uGMRT observations (noise-rms ~30 microJy/beam), we found the radio-detection rate of DOGs to be nearly 28%, the highest among all other radio surveys. The multi-frequency radio observations (band-3 uGMRT, 1.5GHz VLA and 144MHz LOFAR) revealed that the radio-detected DOGs are mainly compact steep spectrum and peaked spectrum radio sources, indicating the presence of young AGN in DOGs. Unlike the radio, the deep XMM-Newton observations of DOGs are limited only to a small fraction (~7%). We studied the X-ray properties of DOGs by utilizing all the available XMM-Newton and Chandra/ACIS observations in the XMM-SERVS field. Our study revealed DOGs host moderate to heavily obscured but luminous AGN belonging to an early evolutionary phase. In my thesis, I also reported a case study of heavily obscured (Compton-thick) AGN in the Circinus galaxy using all the available hard X-ray (> 10 keV) observations taken from BeppoSAX, Suzaku, NuSTAR and AstroSat, at ten different epochs across 22 years (1998-2020). We found tentative evidence for the variable line-of-sight column density on various time scales, suggesting a clumpy circumnuclear material located at sub-parsec to tens of parsec scales. |
