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Title: A SIMPLE LAW OF STAR FORMATION

Abstract

We show that supersonic MHD turbulence yields a star formation rate (SFR) as low as observed in molecular clouds, for characteristic values of the free-fall time divided by the dynamical time, t{sub ff}/t{sub dyn}, the Alfvenic Mach number, M{sub a}, and the sonic Mach number, M{sub s}. Using a very large set of deep adaptive-mesh-refinement simulations, we quantify the dependence of the SFR per free-fall time, {epsilon}{sub ff}, on the above parameters. Our main results are (1) that {epsilon}{sub ff} decreases exponentially with increasing t{sub ff}/t{sub dyn}, but is insensitive to changes in M{sub s}, for constant values of t{sub ff}/t{sub dyn} and M{sub a}. (2) Decreasing values of M{sub a} (stronger magnetic fields) reduce {epsilon}{sub ff}, but only to a point, beyond which {epsilon}{sub ff} increases with a further decrease of M{sub a}. (3) For values of M{sub a} characteristic of star-forming regions, {epsilon}{sub ff} varies with M{sub a} by less than a factor of two. We propose a simple star formation law, based on the empirical fit to the minimum {epsilon}{sub ff}, and depending only on t{sub ff}/t{sub dyn}: {epsilon}{sub ff} Almost-Equal-To {epsilon}{sub wind}exp (- 1.6 t{sub ff}/t{sub dyn}). Because it only depends on the mean gas densitymore » and rms velocity, this law is straightforward to implement in simulations and analytical models of galaxy formation and evolution.« less

Authors:
 [1];  [2];  [3]
  1. ICREA and ICC, University of Barcelona, Marti i Franques 1, E-08028 Barcelona (Spain)
  2. Centre for Star and Planet Formation, University of Copenhagen, Oestervoldgade 5-7., DK-1350, Copenhagen (Denmark)
  3. Centre for Star and Planet Formation and Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100, Copenhagen (Denmark)
Publication Date:
OSTI Identifier:
22078450
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 759; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; COMPUTERIZED SIMULATION; DENSITY; GALACTIC EVOLUTION; GALAXIES; MACH NUMBER; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; STARS; TURBULENCE

Citation Formats

Padoan, Paolo, Haugbolle, Troels, and Nordlund, Ake, E-mail: ppadoan@icc.ub.edu, E-mail: haugboel@nbi.dk, E-mail: aake@nbi.dk. A SIMPLE LAW OF STAR FORMATION. United States: N. p., 2012. Web. doi:10.1088/2041-8205/759/2/L27.
Padoan, Paolo, Haugbolle, Troels, & Nordlund, Ake, E-mail: ppadoan@icc.ub.edu, E-mail: haugboel@nbi.dk, E-mail: aake@nbi.dk. A SIMPLE LAW OF STAR FORMATION. United States. doi:10.1088/2041-8205/759/2/L27.
Padoan, Paolo, Haugbolle, Troels, and Nordlund, Ake, E-mail: ppadoan@icc.ub.edu, E-mail: haugboel@nbi.dk, E-mail: aake@nbi.dk. Sat . "A SIMPLE LAW OF STAR FORMATION". United States. doi:10.1088/2041-8205/759/2/L27.
@article{osti_22078450,
title = {A SIMPLE LAW OF STAR FORMATION},
author = {Padoan, Paolo and Haugbolle, Troels and Nordlund, Ake, E-mail: ppadoan@icc.ub.edu, E-mail: haugboel@nbi.dk, E-mail: aake@nbi.dk},
abstractNote = {We show that supersonic MHD turbulence yields a star formation rate (SFR) as low as observed in molecular clouds, for characteristic values of the free-fall time divided by the dynamical time, t{sub ff}/t{sub dyn}, the Alfvenic Mach number, M{sub a}, and the sonic Mach number, M{sub s}. Using a very large set of deep adaptive-mesh-refinement simulations, we quantify the dependence of the SFR per free-fall time, {epsilon}{sub ff}, on the above parameters. Our main results are (1) that {epsilon}{sub ff} decreases exponentially with increasing t{sub ff}/t{sub dyn}, but is insensitive to changes in M{sub s}, for constant values of t{sub ff}/t{sub dyn} and M{sub a}. (2) Decreasing values of M{sub a} (stronger magnetic fields) reduce {epsilon}{sub ff}, but only to a point, beyond which {epsilon}{sub ff} increases with a further decrease of M{sub a}. (3) For values of M{sub a} characteristic of star-forming regions, {epsilon}{sub ff} varies with M{sub a} by less than a factor of two. We propose a simple star formation law, based on the empirical fit to the minimum {epsilon}{sub ff}, and depending only on t{sub ff}/t{sub dyn}: {epsilon}{sub ff} Almost-Equal-To {epsilon}{sub wind}exp (- 1.6 t{sub ff}/t{sub dyn}). Because it only depends on the mean gas density and rms velocity, this law is straightforward to implement in simulations and analytical models of galaxy formation and evolution.},
doi = {10.1088/2041-8205/759/2/L27},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 759,
place = {United States},
year = {2012},
month = {11}
}