9/16: 1st Year Projects: Dooseok Jung, Ben Gregg

LGRT 1033 Lecture Area

Open to everyone

Speaker: Dooseok Jung

Title: Investigation into the Star Formation Laws for Starbusting Centers, Disks of Nearby Spiral Galaxies and Starbusts Galaxies

Abstract: We have conducted an analysis of the correlation between surface density of star formation rate (SFR), hydrogen molecular gas mass density and surface density of total gas in a sample of 13 nearby spiral galaxies within 15 Mpc to focus on centers of the galaxies. We measure depletion time in binned regions throughout each galaxy. The goal of this project is to quantify depletion time in the starbursting central regions (SB centers) of several nearby galaxies and compare its values with those of the more quiescent galaxy disks. We use the multiwavelength data in the far-ultraviolet (FUV) from the Galaxy Evolution Explorer (GALEX), mid-Infrared (mid-IR) 24 micron-m from Spitzer Space Telescope Infrared Nearby Galaxies Survey (SINGS), HI from The HI Nearby Galaxy Survey (THINGS) and CO from HERA CO-Line Extragalactic Survey (HERACLES). In the Kennicutt-Schmidt (KS) law plot, the power-law indices are N = 1.134 with molecular gas and N = 2.153 with total gas. We set the standard to identify SB centers which is the ratio between depletion time of each center to the mean value of depletion time in disks for molecular gas of each galaxy is lower than 1/3 and we find six SB galaxies in our sample. The SB centers do not have a strong offset as starburst galaxies (SBGs) do in the universal KS plane for molecular gas, although all of the six SB centers are above the fitted line by data from disks. The SB stars do not show clear evidence for behaving as universal SBGs.


Speaker: Ben Gregg

Title: Quantifying the Molecular Gas in a z=1.75 Galaxy Cluster

Abstract: We present VLA observations of one of the most robustly detected massive galaxy clusters at high redshift, with z=1.75. We characterize this cluster's molecular gas contents by quantifying the strength of CO(1-0) emission within its central regions. We detect one significant CO emission source with a spatial signal-to-noise ratio of 5.29, which is offset from a photometrically determined cluster member galaxy by 2.5 arcseconds (21.5 kpc at z=1.75). We also place 3 sigma upper limits on undetected candidate cluster member galaxies within the half power of our VLA beam. Assuming the association to be accurate, we find that our CO detected galaxy is forming stars at rates that are consistent or below field galaxies with similar stellar mass and molecular gas mass, and that it has significant levels of offset molecular gas with a gas fraction that is consistent with field galaxies at similar redshift. We find our 3 sigma upper limits to indicate that on average the undetected cluster member galaxies are forming stars either on or likely  below  the  main  sequence,  are  consistent with  a  normal  star formation efficiency,  and  have  gas  fractions  that are similar or likely below that of field galaxies at similar redshift. As a result, we find that our cluster has low molecular gas reservoirs and that its galaxies have low star formation rates and thus we find that our cluster is undergoing the process of quenching. We find our results to be consistent with other blind CO(1-0) surveys of high redshift galaxy clusters, concluding that cluster members galaxies detected in CO have properties resembling that  of  a  star-forming  field  galaxy  with  similar stellar mass, gas mass, and redshift.