Delayed star formation in high-redshift stream-fed galaxies

We propose that star formation is delayed relative to the inflow rate in rapidly-accreting galaxies at very high redshift (z > 2) because of the energy conveyed by the accreting gas. Accreting gas streams provide fuel for star formation, but they stir the disk and increase turbulence above the usual levels compatible with gravitational instability, reducing the star formation efficiency in the available gas. After the specific inflow rate has sufficiently decreased - typically at z < 3 - galaxies settle in a self-regulated regime with efficient star formation. An analytic model shows that this interaction between infalling gas and young galaxies can significantly delay star formation and maintain high gas fractions (>40%) down to z = 2, in contrast to other galaxy formation models. Idealized hydrodynamic simulations of infalling gas streams onto primordial galaxies confirm the efficient energetic coupling at z > 2, and suggest that this effect is largely under-resolved in existing cosmological simulations.Comment: Accepted for publication in MNRAS Letters. 5 pages, 3 figure

Evaluating the Unilateral Price and Variety Effects of Horizontal Mergers

Industrial Organization,

Crafting a Class: The Trade Off Between Merit Scholarships and Enrolling Lower-Income Students

[Excerpt] It is well-known that test scores are correlated with students’ socio-economic backgrounds. Hence to the extent that colleges are successful in “buying” higher test score students, one should expect that their enrollment of students from families in the lower tails of the family income distribution should decline. However, somewhat surprisingly, there have been no efforts to test if this is occurring. Our paper presents such a test. While institutional level data on the dollar amounts of merit scholarships offered by colleges and universities are not available, data are available on the number of National Merit Scholarship (henceforth NMS) winners attending an institution on scholarships that have been funded by the institution itself, rather than the National Merit Scholarship Corporation (henceforth NMSC). These institutional scholarships are awarded to high test score students only if they attend the institution. Our research strategy is to estimate if an increase in the number of recipients of these scholarships at an institution is associated with a decline in the number of students from lower and lower middle income families attending the institution, other factors held constant. We measure the number of these students by the number of Pell Grant recipients attending the institution