Carma survey toward infrared-bright nearby galaxies (STING): Molecular gas star formation law in NGC 4254

Nurur Rahman, Alberto D. Bolatto, Tony Wong, Adam K. Leroy, Fabian Walter, Erik Rosolowsky, Andrewa West, Frank Bigiel, Jürgen Ott, Rui Xue, Rodrigo Herrera-Camus, Katherine Jameson, Leo Blitz, Stuart N. Vogel

Research output: Contribution to journalArticle

Abstract

This study explores the effects of different assumptions and systematics on the determination of the local, spatially resolved star formation law. Using four star formation rate (SFR) tracers (Hα with azimuthally averaged extinction correction, mid-infrared 24 μm, combined Hα and mid-infrared 24 μm, and combined far-ultraviolet and midinfrared 24 μm), several fitting procedures, and different sampling strategies, we probe the relation between SFR and molecular gas at various spatial resolutions (500 pc and larger) and surface densities (ΣH2 ≈ 10-245 MȮ pc-2) within the central ∼6.5 kpc in the disk of NGC 4254. We explore the effect of diffuse emission using an unsharp masking technique with varying kernel size. The fraction of diffuse emission, fDE, thus determined is a strong inverse function of the size of the filtering kernel. We find that in the high surface brightness regions of NGC 4254 the form of the molecular gas star formation law is robustly determined and approximately linear (∼0.8-1.1) and independent of the assumed fraction of diffuse emission and the SFR tracer employed. When the low surface brightness regions are included, the slope of the star formation law depends primarily on the assumed fraction of diffuse emission. In such a case, results range from linear when the fraction of diffuse emission in the SFR tracer is fDE ≲ 30% (or when diffuse emission is removed in both the star formation and the molecular gas tracer) to super-linear (∼1.4) when fDE ≳ 50%. We find that the tightness of the correlation between gas and star formation varies with the choice of star formation tracer. The 24 μm SFR tracer by itself shows the tightest correlation with the molecular gas surface density, whereas the Hα corrected for extinction using an azimuthally averaged correction shows the highest dispersion.We find that for R ≤ 0.5R25 the local star formation efficiency is constant and similar to that observed in other large spirals, with a molecular gas depletion time tdep ∼ 2 Gyr.

Original languageEnglish (US)
Article number72
JournalAstrophysical Journal
Volume730
Issue number2
DOIs
StatePublished - Apr 1 2011

Keywords

  • ISM: molecules
  • galaxies: ISM
  • galaxies: general
  • galaxies: individual (NGC 4254)
  • galaxies: spiral
  • stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Rahman, N., Bolatto, A. D., Wong, T., Leroy, A. K., Walter, F., Rosolowsky, E., West, A., Bigiel, F., Ott, J., Xue, R., Herrera-Camus, R., Jameson, K., Blitz, L., & Vogel, S. N. (2011). Carma survey toward infrared-bright nearby galaxies (STING): Molecular gas star formation law in NGC 4254. Astrophysical Journal, 730(2), [72]. https://doi.org/10.1088/0004-637X/730/2/72