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Title: The Physical Origin of Long Gas Depletion Times in Galaxies

We present a model that elucidates why gas depletion times in galaxies are long compared to the time scales of the processes driving the evolution of the interstellar medium. We show that global depletion times are not set by any "bottleneck" in the process of gas evolution towards the star-forming state. Instead, depletion times are long because star-forming gas converts only a small fraction of its mass into stars before it is dispersed by dynamical and feedback processes. Thus, complete depletion requires that gas transitions between star-forming and non-star-forming states multiple times. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in galaxy simulations. In particular, the model explains the mechanism by which feedback self-regulates star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated $$L_*$$-sized disk galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is close to linear on kiloparsec scales, even though a non-linear relation is adopted in simulation cells. Furthermore, this difference is due to stellar feedback, which breaks the self-similar scaling of the gas density PDF with the average gas surface density.
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [2]
  1. The Univ. of Chicago, Chicago, IL (United States)
  2. The Univ. of Chicago, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Publication Date:
Report Number(s):
FERMILAB-PUB-17-125-A; arXiv:1704.04239
Journal ID: ISSN 1538-4357; 1591602
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 845; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: evolution; ISM: kinematics and dynamics; methods: numerical; stars: formation
OSTI Identifier:
1354866

Semenov, Vadim A., Kravtsov, Andrey V., and Gnedin, Nickolay Y.. The Physical Origin of Long Gas Depletion Times in Galaxies. United States: N. p., Web. doi:10.3847/1538-4357/aa8096.
Semenov, Vadim A., Kravtsov, Andrey V., & Gnedin, Nickolay Y.. The Physical Origin of Long Gas Depletion Times in Galaxies. United States. doi:10.3847/1538-4357/aa8096.
Semenov, Vadim A., Kravtsov, Andrey V., and Gnedin, Nickolay Y.. 2017. "The Physical Origin of Long Gas Depletion Times in Galaxies". United States. doi:10.3847/1538-4357/aa8096. https://www.osti.gov/servlets/purl/1354866.
@article{osti_1354866,
title = {The Physical Origin of Long Gas Depletion Times in Galaxies},
author = {Semenov, Vadim A. and Kravtsov, Andrey V. and Gnedin, Nickolay Y.},
abstractNote = {We present a model that elucidates why gas depletion times in galaxies are long compared to the time scales of the processes driving the evolution of the interstellar medium. We show that global depletion times are not set by any "bottleneck" in the process of gas evolution towards the star-forming state. Instead, depletion times are long because star-forming gas converts only a small fraction of its mass into stars before it is dispersed by dynamical and feedback processes. Thus, complete depletion requires that gas transitions between star-forming and non-star-forming states multiple times. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in galaxy simulations. In particular, the model explains the mechanism by which feedback self-regulates star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated $L_*$-sized disk galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is close to linear on kiloparsec scales, even though a non-linear relation is adopted in simulation cells. Furthermore, this difference is due to stellar feedback, which breaks the self-similar scaling of the gas density PDF with the average gas surface density.},
doi = {10.3847/1538-4357/aa8096},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 845,
place = {United States},
year = {2017},
month = {8}
}