Prathamesh Tamhane

Prathamesh Tamhane

Postdoc at the University of Alabama in Huntsville.

Publications

You can also find my articles on Google Scholar.

My publication list is also available on NASA ADS.

XRISM constraints on unidentified X-ray emission lines, including the 3.5 keV line, in the stacked spectrum of ten galaxy clusters

Published in The Astrophysical Journal Letters, 2025

This work, led by Prof. Ming Sun, combined approximately 4 million seconds of XRISM telescope observations of 10 galaxy clusters to search for faint, unidentified emission lines in their X-ray spectra. By stacking the de-redshifted spectra of these clusters, we specifically looked for the previously reported 3.5 keV line associated with sterile neutrino warm dark matter. We did not detect any emission at 3.5 keV. While the current data lack the depth needed to reach the sensitivity of the earlier XMM-Newton claims, our results demonstrate the promise of high–spectral resolution instruments. The stacked spectrum also reveals several rarely observed emission features, including sulfur and charge exchange lines.

Recommended citation: XRISM Collaboration (2025). "XRISM constraints on unidentified X-ray emission lines, including the 3.5 keV line, in the stacked spectrum of ten galaxy clusters." ApJL. https://arxiv.org/abs/2510.24560

Constraining Star Formation in M87 Using Deep Hubble Space Telescope UV Data

Published in The Astrophysical Journal, 2025

We analyzed one of the deepest HST UV data in the F275W filter of M87 and provide the most accurate estimate of its low-level star formation rate and history. We found that the star formation rate in M87 is extremely low at ~$2 \times 10^{-5} \, M_\odot \, {\rm yr}^{-1}$ with a burst-like star formation history, with a primary burst around 125 Myr ago that formed approximately 1000 $M_\odot$ stars. This bust is not associated with the current and previous AGN outburst and likely corresponds to an even earlier episode of AGN activity. The last two outbursts have not triggered any star formation. We also did not detect star formation related to the UV-optical filaments detected in M87 indicating that the star formation in M87 has been suppressed for ~200 Myr. We also detected a hotspot created by the counterjet of M87 in the UV images and constrain its spectral index. The data from this work will be publicly released at: https://archive.stsci.edu/hlsp/m87-hst-uv/ Watch a journal club-like discussion of this work here: https://youtu.be/ItZfa9VgYck?si=B1yp-08jPmv6Km-I

Recommended citation: Prathamesh Tamhane; William Waldron; Ming Sun; Silvia Martocchia; Claudia Maraston; Alessandro Boselli; William Forman; Massimo Gaspari; Juhi Tiwari; Megan Donahue; G. Mark Voit; Tim Edge; Grant Tremblay; Daniel Thomas, (2025). "Constraining Star Formation in M87 Using Deep Hubble Space Telescope UV Data." ApJ, 990, 1. https://iopscience.iop.org/article/10.3847/1538-4357/adf20d

Constraining gas motion and non-thermal pressure beyond the core of the Abell 2029 galaxy cluster with XRISM

Published in Publications of the Astronomical Society of Japan, 2025

This work presents a spectroscopic analysis of gas dynamics and hydrostatic mass bias in the cool-core cluster Abell 2029 using XRISM Resolve observations. Measurements out to the scale radius (670 kpc) reveal low bulk and turbulent velocities, with non-thermal pressure contributing less than 2% at all radii and decreasing outward. These results imply minimal departures from hydrostatic equilibrium, yielding a hydrostatic mass bias of only ~2%, in contrast to predictions from many simulations.

Recommended citation: XRISM Collaboration (2025). "Constraining gas motion and non-thermal pressure beyond the core of the Abell 2029 galaxy cluster with XRISM." PASJ. https://academic.oup.com/pasj/advance-article/doi/10.1093/pasj/psaf055/8237182

Velocity Structure Correlations between the Nebular, Molecular, and Atmospheric Gases in the Cores of Four Cool Core Clusters

Published in The Astrophysical Journal, 2025

We analyzed the velocity structure function (VSF), a tool for quantifying turbulence, of nebular gas in the central galaxies of four galaxy clusters using Keck Cosmic Web Imager data, and compared it to molecular gas traced by ALMA. In most systems, the extended filamentary nebular gas shows steep VSF slopes, likely influenced by gravity and AGN-driven motions. Comparisons to X-ray-derived turbulence from Chandra observations support condensation-driven gas motions in some clusters. We also highlighted challenges in comparing VSFs across wavelengths due to instrumental, projection, and resolution-related effects.

Recommended citation: Li, Muzi ; McNamara, B. R.; Coil, Alison L.; Marie-Joëlle Gingras ; Brighenti, Fabrizio; Russell, H. R.; Tamhane, Prathamesh D.; Oh, S. Peng ; Perrotta, (2025). "Velocity Structure Correlations between the Nebular, Molecular, and Atmospheric Gases in the Cores of Four Cool Core Clusters." ApJ, 984, 22L. https://iopscience.iop.org/article/10.3847/1538-4357/ad9b7f

XRISM Reveals Low Nonthermal Pressure in the Core of the Hot, Relaxed Galaxy Cluster A2029

Published in The Astrophysical Journal Letters, 2025

I co-authored one of the first publications using early data from the XRISM telescope. In this study, we analyzed the extremely massive and relaxed galaxy cluster Abell 2029, one of the XRISM Performance Verification (PV) targets. Using XRISMs high spectral resolution, we measured bulk motions in the intracluster medium below 100 km/s and a velocity dispersion of ~170 km/s. If the dispersion is due to turbulence, it implies that non-thermal pressure contributes only ~3% of the thermal pressure, confirming Abell 2029s remarkably relaxed dynamical state.

Recommended citation: Xrism collaboration et al, (2025). "XRISM Reveals Low Nonthermal Pressure in the Core of the Hot, Relaxed Galaxy Cluster A2029." ApJL. https://iopscience.iop.org/article/10.3847/2041-8213/ada7cd

Can Active Galactic Nuclei Activity Be Enhanced by Ram Pressure Stripping?—X-Ray Perspective

Published in The Astrophysical Journal, 2025

This study investigated the potential connection between ram pressure stripping (RPS) and active galactic nuclei (AGN) activity in cluster galaxies from an X-ray perspective, analyzing a sample of RPS galaxies in four nearby clusters. The results show no significant enhancement in X-ray AGN activity among RPS galaxies compared to non-RPS galaxies, suggesting that any potential effect is weak or occurs on a short timescale

Recommended citation: Tiwari, Juhi; Sun, Ming; Luo, Rongxin; Fossati, Matteo; Chen Chien-Ting, Chen J.; Tamhane, Prathamesh, (2025). "Can Active Galactic Nuclei Activity Be Enhanced by Ram Pressure Stripping?—X-Ray Perspective." ApJ. https://iopscience.iop.org/article/10.3847/1538-4357/ad9b7f

A massive multiphase plume of gas in Abell 2390’s brightest cluster galaxy

Published in Monthly Notices of the Royal Astronomical Society, 2024

We studied the origin of massive (>10^10 solar masses) molecular gas plume in Abell 2390 brightest cluster galaxy also observed in the X-ray and optical wavelengths. We discuss different mechanisms that could have led to the formation of the plume based on its observed properties. We also report detection of molecular gas absorption against the nucleus and somple models to explain its origin.

Recommended citation: Rose, Tom; McNamara, B. R.; Combes, F.; Edge, A. C.; Russell, H.; Salomé, P.; Tamhane, P. ; Fabian, A. C.; Tremblay, G., (2024). "A massive multiphase plume of gas in Abell 2390s brightest cluster galaxy." MNRAS. https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stae213/7581997

Radio jet-ISM interaction and positive radio-mechanical feedback in Abell 1795

Published in Monthly Notices of the Royal Astronomical Society, 2023

We studied the positive radio mechanical feedback and the interaction between radio jets and the interstellar medium in the brightest cluster galaxy of the Abell 1795 galaxy cluster. We found that radio-jet triggered star formation has a lower efficiency compared to the efficiency of star formation in the central regions of nearby spiral galaxies.

Recommended citation: Prathamesh D. Tamhane, Brian R. McNamara, Helen R. Russell, Francoise Combes, Yu, Qiu, Alastair C. Edge, Roberto Maiolino, Andrew Fabian, Paul E. J. Nulsen, R. Johnstone, Stefano Carniani, (2022). "Radio jet-ISM interaction and positive radio-mechanical feedback in Abell 1795." MNRAS, Volume 519, Issue 3. https://academic.oup.com/mnras/article-abstract/519/3/3338/6965357?redirectedFrom=fulltext

Molecular Flows in Contemporary Active Galaxies and the Efficacy of Radio-Mechanical Feedback

Published in Monthly Notices of the Royal Astronomical Society, 2022

We studied molecular flows in brightest cluster galaxies (BCGs) and compared them with molecular flows in early type galaxies. Molecular flows in BCGs powered by radio-mechanical feedback are larger, heavier and slower. We found that radio feedback is generally more effective at lifting gas in galaxies compared to quasars and starburst winds. Star formation in BCGs is quenched compared to other galaxies.

Recommended citation: Prathamesh D. Tamhane, Brian R. McNamara, Helen R. Russell, Alastaire C. Edge, Andrew C. Fabian, Paul E. J. Nulsen, Iurii V. Babyk et. al, (2022). "Molecular Flows in Contemporary Active Galaxies and the Efficacy of Radio-Mechanical Feedback." MNRAS, Volume 516, Issue 1. https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stac2168/6653098

Thermally Unstable Cooling Stimulated by Uplift: The Spoiler Clusters

Published in The Astrophysical Journal, 2020

In this paper we studied clusters with low atmospheric cooling time but no warm/cold gas. We propose that the clusters lack cold gas because their central radio jets fail to lift low-entropy gas to large altitudes.

Recommended citation: C. G. Martz, B. R. McNamara, P. E. J. Nulsen, A. N. Vantyghem, M-J. Gingras, Iu. V. Babyk, H. R. Russell, A. C. Edge, M. McDonald, P. D. Tamhane et. al, (2020). "Thermally Unstable Cooling Stimulated by Uplift: The Spoiler Clusters." ApJ. 897. https://iopscience.iop.org/article/10.3847/1538-4357/ab96cd

Origins of Molecular Clouds in Early-type Galaxies

Published in The Astrophysical Journal, 2019

In this paper we show that the molecular gas in early type galaxies most likely originates from cooling of the hot gas in their atmospheres, and that the thermodynamic properties of early type galaxies are similar to that of cluster center galaxies.

Recommended citation: Babyk, Iu. V., McNamara, B. R., Tamhane, P. D. et. al. (2019). "Origins of Molecular Clouds in Early-type Galaxies." ApJ. 887. https://iopscience.iop.org/article/10.3847/1538-4357/ab54ce