The global star formation laws of galaxies from a radio continuum perspective

Journal Article · Wed May 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/805/1/31· OSTI ID:22883192

Liu, L.; Gao, Y. ^[1]

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1. Purple Mountain Observatory, Key Lab of Radio Astronomy, 2 West Beijing Road, 210008 Nanjing (China)

We study the global star formation law—the relation between gas and star formation (SF) rates—in a sample of 181 local galaxies with infrared (IR) luminosities spanning almost five orders of magnitude (10{sup 7.8}−10{sup 12.3} L{sub ⊙}), which includes 115 normal spiral galaxies and 66 (ultra)luminous IR galaxies ((U)LIRGs, L{sub IR}⩾ 10{sup 11} L{sub ⊙}). We derive their atomic, molecular gas, and dense molecular gas masses using newly available Hi, CO, and HCN data from the literature, and SF rates are determined both from total IR (81000 μm) and 1.4 GHz radio continuum (RC) luminosities. In order to derive the disk-averaged surface densities of gas and SF rates, we have taken a novel approach and used high-resolution RC observations to measure the radio sizes for all 181 galaxies. In our sample, we find that the surface density of dense molecular gas (as traced by HCN) has the tightest correlation with that of SF rates (Σ{sub SFR}), and is linear in log–log space (power-law slope of N = 1.01 ± 0.02) across the full galaxy sample. The correlation between surface densities of molecular gas (Σ{sub H{sub 2}}, traced by CO) and Σ{sub SFR} is sensitive to the adopted value of the CO-to-H{sub 2} conversion factor (α{sub CO}) used to infer molecular gas masses from CO luminosities. For a fixed Galactic value of α{sub CO}, a power law index of 1.14 ± 0.02 is found. If instead we adopt values for α{sub CO} of 4.6 and 0.8 for disk galaxies and (U)LIRGs, respectively, we find the two galaxy populations separate into two distinct Σ{sub SFR} versus Σ{sub H{sub 2}} relations. Finally, applying a continuously varying α{sub CO} to our sample, we recover a single Σ{sub SFR}–Σ{sub H{sub 2}} relation with slope of 1.60 ± 0.03. The Σ{sub SFR} is a steeper function of total gas Σ{sub gas} (molecular gas with atomic gas) than that of molecular gas Σ{sub H{sub 2}}, and are tighter among low-luminosity galaxies. We find no correlation between global surface densities of SFRs and atomic gas (H i).

• OSTI ID: 22883192
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 805; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON MONOXIDE
COSMIC GASES
DENSITY
GHZ RANGE 01-100
HYDROCYANIC ACID
HYDROGEN
LUMINOSITY
MASS
MILKY WAY
SPACE
STAR EVOLUTION
STARS