Pizza Lunch: Laurel Farris
Apr 24 @ 12:30 pm – 1:30 pm
Pizza Lunch: Laurel Farris @ AY 119

Determining the size of coronal bright points using cross-correlation methods

Laurel Farris


Colloquium: Isak Wold (Host: Moire Prescott)
Sep 1 @ 3:15 pm – 4:15 pm
Colloquium: Isak Wold (Host: Moire Prescott) @ BX102

A Faint Flux-Limited LAE Sample at z = 0.3

Isak Wold, UT Austin

Observational surveys of Lya emitters (LAEs) have proven to be an efficient method to identify and study large numbers of galaxies over a wide redshift range. To understand what types of galaxies are selected in LAE surveys – and how this evolves with redshift – it is important to establish a low-redshift reference sample that can be directly compared to high-redshift samples.  The lowest redshift where a direct Lya survey is currently possible is at a redshift of z~0.3 via the Galaxy Evolution Explorer (GALEX ) FUV grism data. Using the z~0.3 GALEX sample as an anchor point, it has been suggested that at low redshifts high equivalent width (EW) LAEs become less prevalent and that the amount of escaping Lya emission declines rapidly.  A number of explanations for these trends have been suggested including increasing dust content, increasing neutral column density, and/or increasing metallicity of star-forming galaxies at lower redshifts. However, the published z~0.3 GALEX sample is pre-selected from bright NUV objects.  Thus, objects with strong Lya emission but faint continuum (high-EW LAEs) could be missed.  In this talk, I will present my efforts to re-reduce the deepest archival GALEX FUV grism data and obtain a sample that is not biased against high-EW LAEs.  I will discuss the implications of this new sample on the evolutionary trends listed above.

Pizza Lunch: Karen Kinemuchi
Dec 4 @ 12:30 pm – 1:30 pm
Pizza Lunch: Karen Kinemuchi @ AY 119

Life at Apache Point Observatory

Colloquium Thesis Defense: Lauren Kahre
Jan 23 @ 3:00 pm – 4:00 pm
Colloquium Thesis Defense: Lauren Kahre

Extinction Mapping and Dust-to-Gas Ratios of Nearby Galaxies

Lauren Kahre, NMSU

We present a study of the dust{to{gas ratios in 31 nearby (D >
10 Mpc) galaxies. Using Hubble Space Telescope broad band WFC3/UVIS UV and
optical images from the Treasury program LEGUS (Legacy ExtraGalactic UV
Survey) combined with archival HST/ACS data, we correct thousands of
individual stars for extinction across these galaxies using an
isochrone-matching (reddening-free Q) method. We generate extinction maps
for each galaxy from the individual stellar extinctions using both
adaptive and fixed resolution techniques, and correlate these maps with
neutral HI and CO gas maps from literature, including The HI Nearby Galaxy
Survey (THINGS) and the HERA CO-Line ExtraGalactic Survey (HERACLES). We
calculate dust-to-gas ratios and investigate variations in the dust-to-gas
ratio with galaxy metallicity. We find a power law relationship between
dust-to-gas ratio and metallicity. The single power law is consistent with
other studies of dust-to-gas ratio compared to metallicity, while the
broken power law shows a significantly shallower slope for low metallicity
galaxies than previously observed. We find a change in the relation when
H_2 is not included. This implies that underestimation of N_H2 in
low-metallicity dwarfs from a too-low CO-to-H2 conversion factor X_CO
could have produced too low a slope in the derived relationship between
dust-to-gas ratio and metallicity. We also
compare our extinctions to those derived from fitting the spectral energy
distribution (SED) using the Bayesian Extinction and Stellar Tool (BEAST)
for NGC 7793 and and systematically lower extinctions from SED-fitting as
compared to isochrone matching. Finally, we compare our extinction maps of
NGC 628 to maps of the dust obtained via IR emission from Aniano et al.
(2012) and find a factor of 2 difference in dust-to-gas ratios determined
from the two maps, consistent with previous work.

Remote Colloquium: Fuyan Bian (Host: Kristian Finlator)
Apr 17 @ 3:00 pm – 4:00 pm
Remote Colloquium: Fuyan Bian (Host: Kristian Finlator) @ Online

Evolution of Ionized Interstellar Medium across Cosmic Time

Fuyan Bian, European Southern Observatory

The ionized interstellar medium (ISM) provides essential information on the star-forming environments, metal enrichment, and underlying ionizing radiation field in galaxies. It is crucial to understand how the ionized ISM evolves with Cosmic time. In this talk, I will present a sample of local galaxies that closely resemble the properties of high-redshift galaxies at high redshift. These local analogs of high-redshift galaxies provide a unique local laboratory to study high-redshift galaxies. I will discuss how to use these analogs to improve our understanding of the high-redshift metallicity empirical calibrations and physical mechanism(s) to drive the evolution of optical diagnostics lines from high redshift to low redshift.