What Determines Star Formation Rates?
The relations between star formation and properties of molecular cloudsare studied based on a sample of star forming regions in the Galactic Plane. Sources were selected by having radio recombination lines toprovide identification of associated molecular clouds and dense clumps.Radio continuum and mid-infrared emission were used to determine star formation rates, while 13CO and submillimeter dust continuum emissionwere used to obtain masses of molecular and dense gas, respectively.We test whether total molecular gas or dense gasprovides the best predictor of star formation rate. We also test twospecific theoretical models, one relying on the molecular mass dividedby the free-fall time, the other using the free-fall time divided bythe crossing time. Neither is supported by the data.The data are also compared to those from nearbystar forming regions and extragalactic data. The star formation``efficiency," defined as star formation rate divided by mass, spreadsover a large range when the mass refers to molecular gas; thestandard deviation of the log of the efficiency decreases by a factorof three when the mass of relatively dense molecular gas is usedrather than the mass of all the molecular gas.
Dr. Neal Evans earned his bachelor's degree and doctorate in physics, at the University of California, Berkeley and did a year and a half of post-doctoral work at Caltech before coming to Texas. Although initially interested in high-energy and particle physics, he shifted his focus to astrophysics and worked with a research group started at Berkeley by Nobel laureate Charles Townes. Evans joined The University of Texas faculty in 1975, where he taught for 40 years, including classes about the search for extraterrestrial life, and a seminar on the origin of the Universe and life. He was the Randall Centennial Professor of Astronomy before becoming an Emeritus Professor in Sept. 2016. Evans has led large groups in programs on both the Spitzer and Herschel space telescopes, studying the formation of stars and planet-forming disks. He is a member of the ALMA Board.