Astronomy Colloquium for 2020-02-05


Series: Astronomy Colloquium
Date: Wednesday 05-Feb-2020
Time: 16:05-17:00 (4:05-5:00 pm)
Location: ATL 2400
Speaker: Dr. Vadim Semenov (Harvard-Smithsonian Center for Astrophysics)
Title: The Origin of Inefficient Star Formation in Galaxies

Observed star-forming galaxies convert their gas into stars surprisingly inefficiently. Available gas in galaxies is depleted on the timescale of several Gyr which is orders of magnitude longer than any physical timescale relevant for star formation. The origin of long gas depletion times is a long-standing puzzle. Many galaxy simulations can reproduce observed long depletion times but the physical mechanism controlling their values is not well understood. In addition, some of the simulations show a rather counter-intuitive behavior: global depletion times appear to be almost insensitive to the assumptions about local star formation in individual star-forming regions, a phenomenon described as "self-regulation." Yet another part of the puzzle is the observed tight and near-linear correlation between star formation rates and the amount of molecular gas on kiloparsec and larger scales. A linear correlation implies that depletion time of molecular gas is almost independent of molecular gas density on >kiloparsec scales, while popular models of star formation in galaxies predict a strong dependence. I will present results from a suite of isolated disk galaxy simulations in which we systematically explored the behavior of depletion times. Using insights from these simulations we formulated a physical model that explains both the origin of long gas depletion times in observed galaxies and the results of galaxy formation simulations. This model and our simulation results also provide major insights into the origin of the observed linear correlation between star formation rates and molecular gas.


Colloquia are usually preceded by espresso and ice cream at 1:45 pm outside room PSC 1150 and are followed by an informal reception at 5:15 pm in that room. Anyone interested in talking with the speaker, or being added to the colloquium announcement email list, should contact the colloquium organizer. Lunch will normally be reserved for the speaker to talk to graduate students. Anyone asking a question during a talk is asked to raise their hand and be acknowledged before speaking.

Colloquium Organizer: Prof. Richard Mushotzy

SPECIAL ACCOMMODATIONS:

Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.

DIRECTIONS, PARKING, AND OTHER INFORMATION FOR VISITORS

Directions and information about parking can be found here.

This page was automatically generated on: 23-Jan-2020.