Galaxies and Cosmology Seminar

Oct

2025

12:00 pm – 1:00 pm

In Person (view details)

Two talks by UT Astronomy speakers

Description

Archana Aravindan, The University of Texas at Austin

Big Impact in Small Galaxies: AGN-Driven Outflows in Dwarf Galaxies

Dwarf galaxies in our local universe provide a unique window into the formation and evolution of galaxies at high redshifts, allowing us to understand how processes like star formation and the presence of black holes influence their growth. While stellar feedback has long been considered the primary process in regulating dwarf galaxy properties, recent discoveries of black holes and galaxy-wide AGN-driven outflows in dwarf galaxies challenge this outlook. I will talk about some recent results using near-infrared coronal lines in AGN-hosting dwarfs that sensitively trace the effects of AGN feedback. These diagnostics provide compelling evidence that AGN in low-mass galaxies can produce energetic feedback capable of influencing the structure and evolution of their host galaxies.

Zorayda Martinez, The University of Texas at Austin

Decoding the Effect of High Densities on Derived Nebular Properties

Recent JWST observations have uncovered a population of compact, high-redshift (z > 6) galaxies exhibiting extreme nebular conditions and enhanced nitrogen abundances that challenge standard chemical evolution paradigms. We present a joint UV and optical abundance analysis using a new suite of Cloudy photoionization models covering a wide density range (n_e = 10² - 10⁹ cm^-3), combined with HST and JWST spectroscopy for a sample of star-forming galaxies across 0.0 ≲ z ≲ 10.6. We find that assuming uniform, low-density conditions (n_e ~ 10² cm^-3) in high-density environments (n_e ~ 10⁵ cm^-3) can bias nebular diagnostics by overestimating T_e (up to 1800 K), over predicting log U (by > 1 dex), and underestimating O/H (up to 0.67 dex), while only modestly inflating N/O. Therefore, robust abundance determinations at high-z require a multi-phase density model. Using this model, we recalculate O/H and N/O abundances for our sample and present the first log U diagnostics and ICFs for high-ionization UV N lines. We find that the UV tracers systematically overestimate N/O by ~ 0.3 - 0.4 dex relative to the optical benchmark. We find that N/O increases with redshift, correlating with both n_e and star formation rate surface density (Σ_SFR), suggesting that N/O is temporarily enhanced in compact, high-pressure environments. However, the n_e evolution with z is more gradual than the (1 + z)³ scaling of virial halo densities, suggesting that n_e evolution is shaped by both cosmological structure growth and baryonic processes. These trends point to prompt N/O enrichment potentially driven by very massive stars, with key implications for interpreting UV emission and determining reliable chemical abundances from JWST observations of the early universe.