arXiv subjects

Rudrani Kar Chowdhury

Publications and source records attributed to Rudrani Kar Chowdhury.

9 recordsLinked to original sources

arXiv2026

Gravitational Wave Signatures of Quasi-Periodic Eruptions: LISA Detection Prospects for RX J1301.9+2747

Quasiperiodic eruptions (QPEs) are intense, recurring outbursts of X-ray radiation originating from the nuclei of distant galaxies. One of the promising models of QPE explains these eruptions using extreme-mass-ratio inspirals (EMRIs), in which a stellar-mass object-such as a star or a stellar-mass black hole-orbits a central massive black hole (MBH) and periodically plows through its accretion disk. In this work, we compute the gravitational wave (GW) signals emitted by such EMRI systems. We find that the physical drag and perturbations due to shock caused by the orbiter-disk collisions leave a distinct imprint on the emitted waveforms. Rather than the smooth, monochromatic evolution observed in vacuum systems, these interactions excite non-discrete modes that manifest as subtle shifts in the orbital frequency and as high-frequency ``tails'' in the signal spectrum. We demonstrate as an example outcome of our model that a specific QPE source RX J1301.9+2747 could be detectable by future space-based GW detectors, provided the orbiter maintains a moderate eccentricity of approximately $0.25$ and a mass exceeding $35\;M_\odot$. Our analysis shows that the signal-to-noise ratio for these events would be high enough to clearly distinguish them from standard vacuum EMRIs. Consequently, GW observations offer a powerful tool to probe the dense environments surrounding MBHs and could give further insight into the elusive origins of QPEs.

astro-ph.HE↗

arXiv2026

Merger Driven or Internal Evolution? A New Morphological Study of Tidal Disruption Event Host Galaxies

The host galaxies of tidal disruption events (TDEs) show enhanced central stellar concentration and are preferentially found in poststarburst and green valley populations. This connection has led to the proposal that TDE host galaxies likely have gone through recent mergers. We conduct a new morphological study of 14 TDE host galaxies, using the r-band images from the Sloan Digital Sky Survey (SDSS), Dark Energy Camera Legacy Survey, and Ultraviolet Near-Infrared Optical Northern Survey, with the images from the latter two surveys having much higher depth and resolution than SDSS. We examine galaxy structures using conventional methods and also apply diagnostics of merger activity from a suite of machine learning models. Consistent with previous studies, our results show that TDE host galaxies are ~16% more centrally concentrated when compared to non-TDE-host controls. However, surprisingly, TDE hosts lack any indication of significant recent merger activity from both morphological analysis and the machine learning merger classifier. Instead, our results reveal that TDE host galaxies in the green valley are approximately 1.5-3 times more likely to have bar-like or ringlike structures compared to their controls. Based on these results, we propose that bar-driven secular evolution, instead of mergers, likely dominates the recent evolution of the TDE hosts found in the green valley, which can simultaneously explain their distinctive nuclear properties and enhanced TDE rates.

astro-ph.HE↗

arXiv2026

TDEs on FIRE: Illuminating the Cosmic Evolution of Tidal Disruption Rates

Tidal disruption events have been extensively studied in the local universe, but their prevalence at high redshifts remains largely unexplored. Using the FIRE-2 cosmological zoom-in simulations, we compute the per-galaxy tidal disruption rate (TDR) over $z=1-10$, covering black holes from IMBHs to SMBHs. The averaged TDR rises from the early universe, peaks at $\sim 4 \times 10^{-4} \, \text{yr}^{-1}$ near $z \sim 2.5$, and declines to $\sim 10^{-5} \, \text{yr}^{-1}$ at $z=1$. The TDR correlates strongly with host galaxy star formation rate and central stellar density at all redshifts. Qualitatively, the TDR trends with the $M_{\rm BH}$ and $M_{\rm gal}$ persist from high redshift to the local universe, suggesting similar BH-galaxy scaling across cosmic time. Satellite galaxies exhibit comparably high TDRs, with their fractional contribution increasing significantly at high redshifts, highlighting their potential for probing IMBHs and early galaxy assembly. This work demonstrates that cosmological simulations offer a promising avenue for constraining the cosmic evolution of the TDR, paving the way for future comparisons with next-generation observations.

astro-ph.HE↗

arXiv2025

Rates of Stellar Tidal Disruption Events around Intermediate-Mass Black Holes

Rates of stellar tidal disruption events (TDEs) around supermassive black holes (SMBHs) have been extensively calculated using the loss cone theory, while theoretical work on TDE rates around intermediate-mass black holes (IMBHs) has been lacking. In this work, we aim to accurately calculate the IMBH TDE rates based on their black hole (BH) masses and the stellar profiles of their host galaxies obtained from the latest observations. We find that the TDE rate per galaxy for IMBHs in the center of small galaxies is similar to that of SMBH TDEs, while the TDE rate per cluster from IMBHs in globular clusters is much lower. Very interestingly, we show that the rate of IMBH TDEs generally increases with the BH mass, which is opposite to the trend seen in SMBH TDEs. As a result, the volumetric TDE rate peaks around a BH mass of 10^6 M. The IMBH TDEs from galactic nuclei have an overall volumetric rate comparable to SMBH TDEs at ~10^-7 Mpc^-3 yr^-1, and off-center IMBH TDEs from globular clusters have a volumetric rate that is one or two orders of magnitude lower, assuming that their occupation fraction varies within 10%-100%. Furthermore, we report that IMBH TDEs typically occur in the pinhole regime, which means that deeply plunging events are more likely for IMBH TDEs compared to SMBH TDEs.

astro-ph.HE↗

arXiv2024

Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman

The first generation metal-free stars, referred to as population III (Pop III) stars, are believed to be the first objects to form out of the pristine gas in the very early Universe. Pop III stars have different structures from current generation of stars and are important for generating heavy elements and shaping subsequent star formation. However, it is very challenging to directly detect Pop III stars given their high redshifts and short life-times. In this paper, we propose a novel method for detecting Pop III stars through their tidal disruption events (TDEs) by massive black holes. We model the emission properties and calculate the expected rates for these unique TDEs in the early Universe at z ~ 10. We find that Pop III star TDEs have much higher mass fallback rates and longer evolution timescales compared to solar-type star TDEs in the local universe, which enhances the feasibility of their detection, although a good survey strategy will be needed for categorizing these sources as transients. We further demonstrate that a large fraction of the flare emissions are redshifted to infrared wavelengths, which can be detected by the James Webb Space Telescope and the Nancy Grace Roman Space Telescope. Last but not least, we find a promising Pop III star TDE detection rate of up to a few tens per year using the Nancy Grace Roman Space Telescope, based on our current understanding of the black hole mass function in the early Universe.

astro-ph.HE↗

arXiv2023

Cosmological Simulations of Galaxy Groups and Clusters-III: Constraining Quasar Feedback Models with the Atacama Large Millimeter Array

The thermal Sunyaev-Zeldovich (SZ) effect serves as a direct potential probe of the energetic outflows from quasars that are responsible for heating the intergalactic medium. In this work, we use the GIZMO meshless finite mass hydrodynamic cosmological simulation SIMBA (Dave et al. 2019), which includes different prescriptions for quasar feedback, to compute the SZ effect arising from different feedback modes. From these theoretical simulations, we perform mock observations of the Atacama Large Millimeter Array (ALMA) in four bands (320 GHz, 135 GHZ, 100 GHz and 42 GHz) to characterize the feasibility of direct detection of the quasar SZ signal. Our results show that for all the systems we get an enhancement of the SZ signal, when there is radiative feedback, while the signal gets suppressed when the jet mode of feedback is introduced in the simulations. Our mock ALMA maps reveal that, with the current prescription of jet feedback, the signal goes below the detection threshold of ALMA. We also find that the signal is higher for high redshift systems, making it possible for ALMA and cross SZ-X-ray studies to disentangle the varying modes of quasar feedback and their relative importance in the cosmological context.

astro-ph.CO↗

arXiv2022

Cosmological Simulation of Galaxy Groups and Clusters-II: Studying Different Modes of Feedback through X-ray Observations

The impact of feedback from Active Galactic Nuclei (AGN) on the cosmological evolution of the large scale structure is a long studied problem. However, it is still not well understood how the feedback energy couples to the ambient medium to influence the properties of AGN host galaxies and dark matter halos. In this work we investigate different modes of AGN feedback and their effect on the surrounding medium by probing the diffuse X-ray emission from the hot gas inside galaxy groups and clusters. For this purpose, we use the cosmological hydrodynamic simulation SIMBA to theoretically calculate the X-ray emission from simulated galaxy clusters/groups with the help of the Astrophysical Plasma Emission Code (APEC). We also perform synthetic observations of these systems with the Chandra X-ray telescope using the ray-tracing simulator Model of AXAF Response to X-rays (MARX). Our results show that in addition to the radiative wind mode of feedback from the AGN, jet and X-ray mode of feedback play significant roles in suppressing the X-ray emission from the diffuse gas in the vicinity of the black hole. Our mock observational maps suggest that the signatures of AGN feedback from the high redshift objects may not be detected with the instrumental resolution of current X-ray telescopes like Chandra, but provide promising prospect for detection of these features with potential X-ray missions such as Lynx.

astro-ph.CO↗

arXiv2020

Simulated X-ray Emission in Galaxy Clusters with Feedback from Active Galactic Nuclei

To investigate the effect of feedback from active galactic nuclei (AGN) on their surrounding medium, we study the diffuse X-ray emission from galaxy groups and clusters by coupling the Astrophysical Plasma Emission Code (APEC) with the cosmological hydrodynamic simulation involving AGN feedback. We construct a statistical sample of synthetic Chandra X-ray photon maps to observationally characterize the effect of AGN on the ambient medium. We show that AGN are effective in displacing the hot X-ray emitting gas from the centers of groups and clusters, and that these signatures remain evident in observations of the X-ray surface brightness profiles.

astro-ph.GA↗

arXiv2019

Cosmological Simulation of Galaxy Groups and Clusters-I: Global Effect of Feedback from Active Galactic Nuclei

In this study we quantify the properties of the gas and dark matter around active galactic nuclei (AGN) in simulated galaxy groups and clusters and analyze the effect of AGN feedback on the surrounding intra-cluster (group) medium. Our results suggest downsizing of AGN luminosity with host halo mass, supporting the results obtained from clustering studies of AGN. By examining the temperature and density distribution of the gas in the vicinity of AGN we show that due to feedback from the central engine, the gas gets displaced from the centre of the group/cluster resulting in a reduction of the density but an enhancement of temperature. We show that these effects are pronounced at both high and low redshifts and propose new observables to study the effect of feedback in higher redshift galaxies. We also show that the average stellar mass is decreased in halos in the presence of AGN feedback confirming claims from previous studies. Our work for the first time uses a fully cosmological-hydrodynamic simulation to evaluate the global effects of AGN feedback on their host dark matter halos as well as galaxies at scales of galaxy groups and clusters.

astro-ph.GA↗