Series: Astronomy Colloquium
Date: Wednesday 04-Nov-2009
Time: 16:00-17:00 (4:00-5:00 pm)
Location: CSS 2400
Speaker: Dr. Gerhardt Meuerer (JHU)
Title: Star Formation Laws in HI Selected Galaxies
Star formation is complex, and very hard to model even with the fastest computers. Instead, simulations of galaxy evolution usually resort to emprical based prescriptions to set the amount of ISM that is converted into stars (the Star Formation Law - SFL) and the mass distribution of stars formed (the Initial Mass Function - IMF). These "laws" have proved remarkably resilient, having been proposed over 50 years ago. I will show results from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and the Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of galaxies as traced by H-alpha and Ultraviolet emission. Our simple neutral hydrogen (HI) only selection criteria results in a sample that captures all types of star forming galaxies, while the use of two star formation tracers and integrated HI fluxes provide new constraints on both the SFL and IMF. We find strong correlations between the Halpha/FUV flux ratio and the optical surface brightness of galaxies. The only plausible explanation of this result is that the IMF is not constant. This result has enormous implications for galaxy evolution. Meanwhile strong correlations between the HI, star-formation, and old stellar population properties of galaxies are tighter than the Kennicutt-Schmidt SFL. The existence of an HI - star formation connection has been somewhat of a mystery since stars form in the molecular not the neutral ISM, while the highest mass stars and the HI have very different distributions in galaxies. I will argue that the IMF and the other star formation scaling relations result from pressure-regulated star-formation in a disk maintained at near critical dynamical stability.
I will show results and ongoing work from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and the Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of galaxies as traced by H-alpha and Ultraviolet emission, respectively. Our simple HI only selection criteria results in a sample that captures all types of star forming galaxies, while the use of two star formation tracers gives us sensitivity to the Initial Mass Function. Our team has found strong correlations between the Halpha/FUV flux ratio and the optical surface brightness of galaxies. The only plausible explanation of this result is that the IMF is not constant. This result has enormous implications for galaxy evolution in both the near and distant universe. Our sample also shows strong correlations between the HI, star-formation, and old stellar population properties of galaxies. These scaling relations are tighter than the Kennicutt-Schmidt Star Formation Law. The existence of an HI - star formation connection has been somewhat of a mystery since stars form in the molecular not the neutral ISM, while the highest mass stars and the HI have very different distributions in galaxies. I will argue that the IMF and the other star formation scaling relations result from pressure-regulated star-formation in a disk maintained at near critical dynamical stability.
Colloquia are usually preceded by espresso and ice cream at 1:45 pm in the first floor lobby of the Astronomy Department and followed by an informal reception in room CSS 0254. Anyone interested in having lunch or talking with the speaker should contact the colloquium organizer given below. The hour immediately after lunch will normally be reserved for the speaker to talk to graduate students. Students are urged to contact the coordinator to arrange this.
Colloquium Organizer:
Prof. Richard Mushotzky
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.
