Sameer

About

Hello, I am a postdoctoral research associate in the Department of Physics and Astronomy at the University of Notre Dame who studies observational galaxy evolution. I grew up in Hyderabad, India, and received my bachelor's degree in Astronomy from the Indian Institute of Space Science and Technology, Thiruvananthapuram, India, before assuming a scientist position at the Physical Research Laboratory (PRL), Gujarat, India. I then moved overseas to pursue my PhD from Penn State, where my advisor was Jane Charlton. While I am broadly interested in many aspects of observational galaxy formation, summed up in one sentence, my main research goal is using absorption spectroscopy to learn about the physicochemical properties of the diffuse gas surrounding galaxies called the circumgalactic medium (CGM). I observe this CGM gas using both ground and space-based telescopes like the Keck and Hubble. Much of my work involves the development and application of software and novel methods that utilize the tools of ionization modeling, Bayesian inference, and high-performance computing.

My CV is available here

Recent Research

Concise videos summarizing key aspects of my recent research.

In this talk, I present an absorption line investigation of the inner circumgalactic medium (CGM) of M31, a region that previously has been too sparsely sampled to characterize the most complex and influential region for galaxy evolution. Using absorption spectroscopy acquired by HST/COS, we empirically determine column densities of important ions using the apparent optical depth method to understand the radial and azimuthal distribution of metals. Coupled with ionization modeling using the photoionization code Cloudy, we are able to place constraints on the metal mass of the cool CGM as traced by several dozen sightlines and compare with that of the outer CGM, yielding valuable insights into the disk-halo connection of M31.

This video summarizes key findings from the Halo21 absorption modelling challenge Hafen, Sameer, Hummels et al. (2024), which tested how well observational methods can recover the properties of circumgalactic medium (CGM) gas from synthetic absorption spectra. The study analyzed three samples of increasing complexity: uniform clouds, multiple uniform clouds, and a turbulent mixing zone. Overall, parameter estimation accurately recovered the bulk properties of the absorbing gas across all samples. For the turbulent mixing scenario, properties of the strongest absorption components were retrieved with high accuracy, while weaker components were weakly constrained. The study highlights both the strengths and limitations of current CGM analysis techniques, providing valuable insights for future observational work in this field.

This video presents an absorption line study by Sameer et al. (2022) of the physical and chemical properties of the Leo HI Ring and the Leo I Group as traced by 11 quasar sightlines. Using HST/COS G130/G160 archival observations as constraints, we couple cloud-by-cloud, multiphase, Bayesian ionization modeling with galaxy property information to determine the plausible origin of the absorbing gas along these sightlines. We find that the metallicities associated with the Leo Ring are generally high, with values between solar and several times solar. The inferred high metallicities are consistent with the origin of the ring as tidal debris from a galaxy-galaxy interaction.

This video presents an absorption line study by Sameer et al. (2021). We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of CLOUDY and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium.

Publications

TALKS & COLLOQUIA

Galaxy Group at UMich Mar 27, 2025

Galaxies Seminar University of Michigan, MI

ND Astro Seminar Mar 25, 2025

Astrophysics Seminar University of Notre Dame, IN

Discussion Lead - Bridging CGM observations and simulations Sept 11, 2024

A Holistic Understanding of the Multi-scale, Multiphase CGM Aspen Center for Physics, CO

Discussion Lead - Cold Gas in the CGM Sept 10, 2024

A Holistic Understanding of the Multi-scale, Multiphase CGM Aspen Center for Physics, CO

Participant Sept 1-15, 2024

A Holistic Understanding of the Multi-scale, Multiphase CGM Aspen Center for Physics, CO

Contributed Talk Aug 21, 2024

Resolving the CGM in Theory & Observations Harvard University, MA

Participant Jul 15-19, 2024

Code/Astro Northwestern University, IL

Contributed Talk May 07, 2024

FOGGIE Retreat Michigan State, MI

Invited Talk Feb 20, 2024

Astro Seminar University of Washington, WA

ND Astro Seminar Oct 31, 2023

Astrophysics Seminar University of Notre Dame, IN

Contributed Talk Feb 21, 2023

Structure of the Circumgalactic Medium Arizona State University, AZ

ND Astro Seminar Nov 22, 2022

Astrophysics Seminar University of Notre Dame, IN

Dissertation Talk June 16, 2022

AAS 240 Meeting Pasadena Convention Center, CA

Dissertation Defense June 10, 2022

Department Talk Penn State

Invited Talk January 27, 2022

Carnegie Tea Talk Carnegie Science Observatories

Contributed Talk November 5, 2021

STARs Lab Meeting Online, Arizona State University

Contributed Talk October 15, 2021

Milky Way Halo Research Group Meeting Online, STScI

Contributed Talk September 21, 2021

Lunch Talk Online, Penn State

Invited Talk August 19, 2021

Baltimore Winds Workshop Johns Hopkins University

Contributed Talk April 5, 2021

Galread Extragalactic Discussion Group Online, Princeton University

Contributed Talk March 25, 2021

High Energy Astro Group Seminar Online, MIT

Tutorial contributor & presenter Jan 20, 2021

Fundamentals of Gaseous Halos Workshop Online, UCSB

Invited Talk Oct 29, 2020

Data Science Consortium Online, University of Michigan

Department Colloquium June 19, 2020

Astronomy & Astrophysics Department Online, New Mexico State University

Gallery

This is a small collection of photos from various conferences I have attended recently.

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Contact

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Elements

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