Sushant Dutta - Academia.edu (original) (raw)

Papers by Sushant Dutta

Research paper thumbnail of Detection of radio-AGN in dust-obscured galaxies using deep uGMRT radio continuum observations

Journal of Astrophysics and Astronomy, Nov 3, 2022

Research paper thumbnail of Characteristics of remnant radio galaxies detected in the deep radio continuum observations from the SKA pathfinders

arXiv (Cornell University), Jul 16, 2022

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no... more The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The timescale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of lowsurface-brightness in all five remnants with 400 MHz surface brightness in the range of 36−201 mJy arcmin −2. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off model (CI OFF), that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages (t s) in the range of 20.3 Myr to 41.4 Myr with t OFF /t s distributed in the range of 0.16 to 0.63, which in turn suggests them to belong to different evolutionary phases. We note that, in comparison to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments.

Research paper thumbnail of Characteristics of remnant radio galaxies detected in deep radio continuum observations from SKA pathfinders

Journal of Astrophysics and Astronomy

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no... more The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The timescale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of lowsurface-brightness in all five remnants with 400 MHz surface brightness in the range of 36−201 mJy arcmin −2. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off model (CI OFF), that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages (t s) in the range of 20.3 Myr to 41.4 Myr with t OFF /t s distributed in the range of 0.16 to 0.63, which in turn suggests them to belong to different evolutionary phases. We note that, in comparison to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments.

Research paper thumbnail of Search and characterization of remnant radio galaxies in the XMM$-$LSS deep field

arXiv (Cornell University), Dec 20, 2022

The remnant phase of a radio galaxy is characterized by the cessation of AGN activity resulting i... more The remnant phase of a radio galaxy is characterized by the cessation of AGN activity resulting in the stoppage of jets supplying plasma to radio lobes. In this paper, we present the search and characterization of remnant candidates in 12.5 deg 2 of the XMM−Newton Large−Scale Structure (XMM−LSS) field by using deep radio observations at 325 MHz from the Giant Metrewave Radio Telescope (GMRT), at 150 MHz from the LOw Frequency ARray (LOFAR), at 1.4 GHz from the Jansky Very Large Array (JVLA), and at 3 GHz from the VLA Sky Survey (VLASS). By using both morphological criteria viz., undetected radio core as well as spectral criteria viz., high spectral curvature, and ultra−steep spectrum, we identify 21 remnant candidates that are found to reside mostly in non−cluster environments, and exhibit diverse properties in terms of morphology, spectral index (α 1400 150 in the range of −1.71 to −0.75 with a median of −1.10), and linear radio size (ranging from 242 kpc to 1.3 Mpc with a median of 469 kpc). Our study attempts to identify remnant candidates down to the flux density limit of 6.0 mJy at 325 MHz, and yields an upper limit on the remnant fraction (f rem) to be around 5%. The observed f rem seems consistent with the predictions of an evolutionary model assuming power law distributions of the duration of active phase and jet kinetic power with index −0.8 to −1.2.

Research paper thumbnail of Remnant Radio Galaxy Candidates of Small Angular Sizes

Galaxies, 2021

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-... more Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy’s life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes (<30′′) in the XMM−LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature i.e., α150MHz325MHz−α325MHz1.4GHz≥ 0.5. Spectral characteristics at higher frequency regime (>1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction (frem) to be 3.9%, which increases to 5.4% if flux cutoff limit of S150MHz≥ 10 mJy is considered. Our study unveils, hitherto unexplored, a new population of s...

Research paper thumbnail of Detection of radio-AGN in dust-obscured galaxies using deep uGMRT radio continuum observations

Journal of Astrophysics and Astronomy, Nov 3, 2022

Research paper thumbnail of Characteristics of remnant radio galaxies detected in the deep radio continuum observations from the SKA pathfinders

arXiv (Cornell University), Jul 16, 2022

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no... more The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The timescale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of lowsurface-brightness in all five remnants with 400 MHz surface brightness in the range of 36−201 mJy arcmin −2. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off model (CI OFF), that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages (t s) in the range of 20.3 Myr to 41.4 Myr with t OFF /t s distributed in the range of 0.16 to 0.63, which in turn suggests them to belong to different evolutionary phases. We note that, in comparison to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments.

Research paper thumbnail of Characteristics of remnant radio galaxies detected in deep radio continuum observations from SKA pathfinders

Journal of Astrophysics and Astronomy

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no... more The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The timescale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of lowsurface-brightness in all five remnants with 400 MHz surface brightness in the range of 36−201 mJy arcmin −2. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off model (CI OFF), that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages (t s) in the range of 20.3 Myr to 41.4 Myr with t OFF /t s distributed in the range of 0.16 to 0.63, which in turn suggests them to belong to different evolutionary phases. We note that, in comparison to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments.

Research paper thumbnail of Search and characterization of remnant radio galaxies in the XMM$-$LSS deep field

arXiv (Cornell University), Dec 20, 2022

The remnant phase of a radio galaxy is characterized by the cessation of AGN activity resulting i... more The remnant phase of a radio galaxy is characterized by the cessation of AGN activity resulting in the stoppage of jets supplying plasma to radio lobes. In this paper, we present the search and characterization of remnant candidates in 12.5 deg 2 of the XMM−Newton Large−Scale Structure (XMM−LSS) field by using deep radio observations at 325 MHz from the Giant Metrewave Radio Telescope (GMRT), at 150 MHz from the LOw Frequency ARray (LOFAR), at 1.4 GHz from the Jansky Very Large Array (JVLA), and at 3 GHz from the VLA Sky Survey (VLASS). By using both morphological criteria viz., undetected radio core as well as spectral criteria viz., high spectral curvature, and ultra−steep spectrum, we identify 21 remnant candidates that are found to reside mostly in non−cluster environments, and exhibit diverse properties in terms of morphology, spectral index (α 1400 150 in the range of −1.71 to −0.75 with a median of −1.10), and linear radio size (ranging from 242 kpc to 1.3 Mpc with a median of 469 kpc). Our study attempts to identify remnant candidates down to the flux density limit of 6.0 mJy at 325 MHz, and yields an upper limit on the remnant fraction (f rem) to be around 5%. The observed f rem seems consistent with the predictions of an evolutionary model assuming power law distributions of the duration of active phase and jet kinetic power with index −0.8 to −1.2.

Research paper thumbnail of Remnant Radio Galaxy Candidates of Small Angular Sizes

Galaxies, 2021

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-... more Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy’s life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes (<30′′) in the XMM−LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature i.e., α150MHz325MHz−α325MHz1.4GHz≥ 0.5. Spectral characteristics at higher frequency regime (>1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction (frem) to be 3.9%, which increases to 5.4% if flux cutoff limit of S150MHz≥ 10 mJy is considered. Our study unveils, hitherto unexplored, a new population of s...