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Title: STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING

Abstract

Recent observational results indicate that the functional shape of the spatially resolved star formation-molecular gas density relation depends on the spatial scale considered. These results may indicate a fundamental role of sampling effects on scales that are typically only a few times larger than those of the largest molecular clouds. To investigate the impact of this effect, we construct simple models for the distribution of molecular clouds in a typical star-forming spiral galaxy and, assuming a power-law relation between star formation rate (SFR) and cloud mass, explore a range of input parameters. We confirm that the slope and the scatter of the simulated SFR-molecular gas surface density relation depend on the size of the sub-galactic region considered, due to stochastic sampling of the molecular cloud mass function, and the effect is larger for steeper relations between SFR and molecular gas. There is a general trend for all slope values to tend to {approx}unity for region sizes larger than 1-2 kpc, irrespective of the input SFR-cloud relation. The region size of 1-2 kpc corresponds to the area where the cloud mass function becomes fully sampled. We quantify the effects of selection biases in data tracing the SFR, either as thresholds (i.e.,more » clouds smaller than a given mass value do not form stars) or as backgrounds (e.g., diffuse emission unrelated to current star formation is counted toward the SFR). Apparently discordant observational results are brought into agreement via this simple model, and the comparison of our simulations with data for a few galaxies supports a steep (>1) power-law index between SFR and molecular gas.« less

Authors:
;  [1];  [2]
  1. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
  2. Department of Physics and Astronomy, State University of New York at Stony Brook, New York, NY (United States)
Publication Date:
OSTI Identifier:
22037037
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 752; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; EMISSION; GALAXIES; MASS; STAR EVOLUTION; STARS; STOCHASTIC PROCESSES

Citation Formats

Calzetti, D., Liu, G., and Koda, J., E-mail: calzetti@astro.umass.edu. STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING. United States: N. p., 2012. Web. doi:10.1088/0004-637X/752/2/98.
Calzetti, D., Liu, G., & Koda, J., E-mail: calzetti@astro.umass.edu. STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING. United States. doi:10.1088/0004-637X/752/2/98.
Calzetti, D., Liu, G., and Koda, J., E-mail: calzetti@astro.umass.edu. Wed . "STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING". United States. doi:10.1088/0004-637X/752/2/98.
@article{osti_22037037,
title = {STAR FORMATION LAWS: THE EFFECTS OF GAS CLOUD SAMPLING},
author = {Calzetti, D. and Liu, G. and Koda, J., E-mail: calzetti@astro.umass.edu},
abstractNote = {Recent observational results indicate that the functional shape of the spatially resolved star formation-molecular gas density relation depends on the spatial scale considered. These results may indicate a fundamental role of sampling effects on scales that are typically only a few times larger than those of the largest molecular clouds. To investigate the impact of this effect, we construct simple models for the distribution of molecular clouds in a typical star-forming spiral galaxy and, assuming a power-law relation between star formation rate (SFR) and cloud mass, explore a range of input parameters. We confirm that the slope and the scatter of the simulated SFR-molecular gas surface density relation depend on the size of the sub-galactic region considered, due to stochastic sampling of the molecular cloud mass function, and the effect is larger for steeper relations between SFR and molecular gas. There is a general trend for all slope values to tend to {approx}unity for region sizes larger than 1-2 kpc, irrespective of the input SFR-cloud relation. The region size of 1-2 kpc corresponds to the area where the cloud mass function becomes fully sampled. We quantify the effects of selection biases in data tracing the SFR, either as thresholds (i.e., clouds smaller than a given mass value do not form stars) or as backgrounds (e.g., diffuse emission unrelated to current star formation is counted toward the SFR). Apparently discordant observational results are brought into agreement via this simple model, and the comparison of our simulations with data for a few galaxies supports a steep (>1) power-law index between SFR and molecular gas.},
doi = {10.1088/0004-637X/752/2/98},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 752,
place = {United States},
year = {2012},
month = {6}
}