MOLECULAR GAS, CO, AND STAR FORMATION IN GALAXIES: EMERGENT EMPIRICAL RELATIONS, FEEDBACK, AND THE EVOLUTION OF VERY GAS-RICH SYSTEMS

Journal Article · Sun Dec 20 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/707/2/954· OSTI ID:21392600

Pelupessy, Federico I ^[1]; Papadopoulos, Padelis P ^[2]

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1. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
2. Argelander Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)

We use time-varying models of the coupled evolution of the H I, H{sub 2} gas phases and stars in galaxy-sized numerical simulations to (1) test for the emergence of the Kennicutt-Schmidt (K-S) and the H{sub 2}-pressure relation, (2) explore a realistic H{sub 2}-regulated star formation recipe which brings forth a neglected and potentially significant SF-regulating factor, and (3) go beyond typical galactic environments (for which these galactic empirical relations are deduced) to explore the early evolution of very gas-rich galaxies. In this work, we model low-mass galaxies (M{sub baryon} <= 10{sup 9} M{sub sun}), while incorporating an independent treatment of CO formation and destruction, the most important tracer molecule of H{sub 2} in galaxies, along with that for the H{sub 2} gas itself. We find that both the K-S and the H{sub 2}-pressure empirical relations can robustly emerge in galaxies after a dynamic equilibrium sets in between the various interstellar medium (ISM) states, the stellar component and its feedback (T approx> 1 Gyr). The only significant dependence of these relations seems to be for the CO-derived (and thus directly observable) ones, which show a strong dependence on the ISM metallicity. The H{sub 2}-regulated star formation recipe successfully reproduces the morphological and quantitative aspects of previous numerical models while doing away with the star formation efficiency parameter. Most of the H I -> H{sub 2} mass exchange is found taking place under highly non-equilibrium conditions necessitating a time-dependent treatment even in typical ISM environments. Our dynamic models indicate that the CO molecule can be a poor, nonlinear, H{sub 2} gas tracer. Finally, for early evolutionary stages (T approx< 0.4 Gyr), we find significant and systematic deviations of the true star formation from that expected from the K-S relation, which are especially pronounced and prolonged for metal-poor systems. The largest such deviations occur for the very gas-rich galaxies, where deviations of a factor approx3-4 in global star formation rate (SFR) can take place with respect to those expected from the CO-derived K-S relation. This is particularly important since gas-rich systems at high redshifts could appear as having unusually high SFRs with respect to their CO-bright H{sub 2} gas reservoirs. This points to a possibly serious deficiency of K-S relations as elements of the sub-grid physics of star formation in simulations of structure formation in the early universe.

• OSTI ID: 21392600
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 707; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COMPUTERIZED SIMULATION
ELEMENTS
EVOLUTION
FEEDBACK
GALACTIC EVOLUTION
GALAXIES
HYDROGEN
MASS
METALS
NONLINEAR PROBLEMS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
RED SHIFT
SIMULATION
STARS
TIME DEPENDENCE
UNIVERSE