Swetha Sankar Swetha Sankar

“In some strange way, any new fact or insight that I may have found has not seemed to me as a ‘discovery’ of mine, but rather something that had always been there and that I had chanced to pick up.”

— Subrahmanyan Chandrasekhar

Research Highlights

My research asks how supermassive black holes grow, change, and transfer energy into their surroundings. I focus on systems caught during brief transitional phases—when gas is flowing inward, accretion structures are changing, or winds and jets are beginning to interact with the host galaxy.

Across these projects, I use infrared spectroscopy, integral-field observations, radio imaging, and molecular-gas measurements to connect black hole activity to shocks, outflows, gas reservoirs, and star formation.

Gemini GNIRS near-infrared spectrum of a blue low-excitation radio galaxy

Radio AGN • Molecular Gas • Galaxy Transitions

When Do Radio Jets Begin to Affect a Gas-Rich Galaxy?

Radio jets are often associated with massive, quiescent galaxies, yet some low-excitation radio galaxies retain blue colors, substantial gas reservoirs, and signs of recent activity. These unusual systems may reveal what happens before jet-driven feedback becomes globally effective.

Using Gemini/GNIRS spectroscopy, radio imaging, and host-galaxy morphology, I find warm molecular hydrogen in several systems, with the strongest emission preferentially appearing in disturbed galaxies. The radio sources are generally compact, and the H2 emission does not show a clear positive trend with radio power. Together, these results suggest that merger-driven gas inflows and shocks can coexist with young or recently restarted jets before the jets fully couple to the galaxy-wide interstellar medium.

Why it matters: These galaxies may capture an early stage of mechanical feedback, when black hole fueling, disturbed molecular gas, and compact radio activity overlap rather than forming a simple sequence from star formation to quenching.

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Spatially resolved iron emission and gas kinematics in a red quasar observed with JWST

Obscured Quasars • Outflows • Shock Excitation

Catching a Quasar Outflow as It Strikes the Host Galaxy

Quasar winds can carry enormous amounts of energy, but detecting an outflow does not by itself show where that energy is deposited. The central challenge is to identify the locations where the wind physically interacts with the surrounding interstellar medium.

With JWST/NIRSpec integral-field spectroscopy, I map near-infrared [Fe II] emission around an obscured quasar at z = 0.435. Some of the [Fe II]-emitting gas shares the extreme velocities and broad line widths of the ionized outflow, while another region has substantially narrower kinematics and emission-line ratios consistent with shock excitation. This spatial separation distinguishes gas carried by the wind from gas shocked where the wind encounters the host galaxy.

Why it matters: The result provides direct evidence of where quasar feedback begins to couple to multiphase gas, connecting a powerful nuclear outflow to its physical impact on the galaxy.

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Molecular gas and star formation relation for interacting dwarf galaxies

Dwarf Galaxies • Molecular Gas • Star Formation

Does an Interaction Make Dwarf Galaxies Form Stars More Efficiently?

Dwarf galaxies provide an important laboratory for understanding star formation in low-mass, metal-poor environments resembling conditions common in the early universe. Yet their molecular gas is difficult to detect, leaving the role of interactions poorly constrained.

As part of the TiNy Titans program, I use ALMA observations of CO(1–0) in isolated dwarf-galaxy pairs to measure their molecular gas reservoirs. We detect CO emission in seven of nineteen galaxies. Their inferred molecular-gas masses and star-formation efficiencies do not show compelling evidence for a strong interaction-driven enhancement relative to isolated dwarf systems.

Why it matters: The results suggest that close interactions do not automatically produce the dramatic increases in star-formation efficiency seen in some massive mergers, emphasizing the importance of galaxy mass, metallicity, and interaction stage.

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Spectral energy distribution of the dusty planetary system V488 Per

Circumstellar Dust • Planetary Systems • Infrared Spectroscopy

The Unusual Dust Around V488 Per

Before focusing on black hole and galaxy evolution, I studied the unusually dusty planetary system V488 Per. Despite hosting one of the strongest infrared excesses known around a main-sequence star, its warm dust spectrum lacks the prominent solid-state features typically seen in debris disks.

By combining infrared spectroscopy, far-infrared measurements, high-resolution imaging, and radial-velocity monitoring, we found no evidence for a stellar or substellar companion capable of producing the excess. The featureless spectrum instead points toward unusually large grains or an uncommon dust composition, potentially associated with major collisions in the inner planetary system.

Why it matters: V488 Per demonstrates how time-variable and transitional systems can expose physical processes that are difficult to infer from mature, stable planetary architectures.

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Have questions? Feel free to Email Me

ssanka10@jh.edu
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