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On the Molecular Gas Content of z~1 Galaxies and the Origin of Ultra-Diffuse Galaxies

Timothy Carleton - UC Irvine

Friday, December 1, 2017
  2:10–3 p.m.

Location: Physics Building 3035
  Parking Information

Category: Seminar


I will present results from two projects investigating two different puzzles in galaxy evolution. First, I will address the question of why star-formation rates in z~1 galaxies are elevated compared with their z~0 counterparts: is this a result of an increased supply of molecular gas to galaxies or a more efficient conversion of existing molecular gas into stars? With new sensitive mm and sub-mm facilities such as NOEMA and ALMA, we are able to directly probe signatures of the molecular gas reservoir in high-z galaxies; however, extracting a measurement of the molecular gas content of these objects relies on an uncertain conversion from the observed tracer (typically Carbon Monoxide) luminosity to the molecular gas mass. Motivated by the dependence of this conversion factor (alpha_CO) on ISM properties observed locally, I will present an investigation of the variation between alpha_CO and integrated galaxy properties, in particular mass surface density, in 38 massive star-forming galaxies at z~1. Overall, I find that the molecular gas conditions at z~1 are remarkably consistent with those at z=0, suggesting that the process of converting molecular gas to stars in z~1 galaxies is similar to that identified in local galaxies.

Additionally, I will discuss a model for the formation of Ultra-Diffuse Galaxies (UDGs). These dwarf galaxies, with half-light radii similar to that of the Milky Way, but only 1% of its stellar mass, present a significant challenge to our understanding of dwarf-galaxy evolution. Motivated by the environmental dependence of UDG abundance, I investigate the effects of tidal stripping on the dwarf galaxy population using a semi-analytic model for the influence of tidal-stripping on the stellar mass and half-light radius of dwarf galaxies applied to dark-matter halos in the Bolshoi simulation. In particular, simulations show that dwarf galaxies occupying cored dark-matter halos expand significantly as a result of tidal heating as they pass through a massive cluster. By applying this relatively simple model, I am able to reproduce the observed stellar mass and half-light radii distributions of UDGs, as well as the observed UDG abundance across a range of environments remarkably well.

Additional Information:

Open to: General Public
Admission: Free
Sponsor: Physics and Astronomy

Contact Information:
Naveen Reddy