Galaxies and Cosmology Seminar

Mabel Stephenson, The University of Texas at Austin

Evolution of Electron Densities of Galaxies Across Cosmic Epochs

We investigate the electron density in the interstellar medium of galaxies across 0 < z < 8, derived with the [O II] 3727,3730 and [S II] 6718,6733 doublets, using both deep JWST NIRCam/grism and NIRSpec/MSA spectroscopy, and ancillary samples reported in the literature. We assemble three samples containing a total of 703 galaxies spanning 3.7 < z < 7.8; 691 galaxies in the luminosity-complete NIRCam/grism programs CONGRESS and FRESCO, and 12 galaxies with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs. Combining these measurements with literature samples, we find that median ne increases from 0 < z < 4, which agrees well with previous studies and those using JWST observations. However, we find that beyond z ~ 4 median ne decreases with increasing redshift, following a trend best described by a double-power law, which is inconsistent within 3 sigma of other JWST studies of ne across redshift past z > 4. We find a positive, but shallow, correlation between O32 (a proxy for the ionization parameter) and ne, and confirm a positive correlation between O32 and z. We also find correlations between median O32 and median stellar mass, specific SFR, and SFR surface density, which further support the prevalence of increasingly clumpy and inhomogeneous ISM conditions at high-z. We suggest that these trends are possibly due to an evolving ISM gas density and ionization structure, and propose an inhomogeneous density model of galaxies at z > 4 to explain our findings. This would dramatically impact how nebular properties of galaxies are measured and interpreted across cosmic time.

Joshua Oppor, The University of Texas at Austin

Kinematics of Multi-Phase Gas in the Disks of 10 LADUMA Spiral Galaxies

Within the Looking at the Deep Universe with the MeerKat Array (LADUMA) field, we investigate differences between neutral and ionized gas rotation curves in a subset of 10 well resolved galaxies. Using spectroscopic data from RSS-VIS on SALT, we extract rotation curves of ionized gas and compare them to unresolved HI line-width measurements and HI envelope-fit rotation curves. Using full-spectrum spectral energy distribution fitting, we measure H𝛼, H𝛽, [SII], [NII], and [OIII] emission lines to differentiate HII-region associated ionized gas from extra-planar diffuse ionized gas (DIG) that can be associated with other ionization sources such as older stellar populations or shocks. We explore whether kinematic differences are more pronounced in regions with elevated emission line ratios, in particular [NII]/H𝛼 and [SII]/H𝛼. Our results indicate that HI envelope-fit rotational velocities are consistent with turbulence corrected HI W₂₀ from previous literature. HI rotation curves generally match that of the ionized gas but do present evidence of lagging DIG as a function of inclination. We inspect other potential trends in lagging DIG as a function of observables including H𝛼 equivalent width, stellar age, and total baryonic mass. Finally, we show that this optical-morphologically selected sample lie tightly on a Tully-fisher Relation and conclude that integral field spectroscopic data is required to make progress in disentangling the spatial and kinematic signature of extra-planar diffuse ionized gas.