MEASURING STAR FORMATION RATES AND FAR-INFRARED COLORS OF HIGH-REDSHIFT GALAXIES USING THE CO(7–6) AND [N II] 205 μm LINES

Journal Article · Fri Mar 20 00:00:00 EDT 2015 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/802/1/L11· OSTI ID:22518820

Lu, Nanyao; Zhao, Yinghe; Xu, C. Kevin; Howell, Justin; Mazzarella, Joseph M.; Schulz, Bernhard ^[1]; Gao, Yu; Liu, Lijie ^[2]; Díaz-Santos, Tanio; Armus, Lee ^[3]; Charmandaris, Vassilis ^[4]; Inami, Hanae ^[5]; Privon, George C. ^[6]; Lord, Steven D. ^[7]; Sanders, David B. ^[8]

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1. Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125 (United States)
2. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
3. Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States)
4. Department of Physics, University of Crete, GR-71003 Heraklion (Greece)
5. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
6. Departamento de Astronomía, Universidad de Concepción, Casilla 160 C, Concepción (Chile)
7. The SETI Institute, 189 Bernardo Avenue Suite 100, Mountain View, CA 94043 (United States)
8. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

To better characterize the global star formation activity in a galaxy, one needs to know not only the star formation rate (SFR) but also the rest-frame, far-infrared color (e.g., the 60–100 μm color, C(60/100)) of the dust emission. The latter probes the average intensity of the dust heating radiation field and scales statistically with the effective SFR surface density in star-forming galaxies including (ultra-)luminous infrared galaxies ((U)LIRGs). To this end, here we exploit a new spectroscopic approach involving only two emission lines: CO(7–6) at 372 μm and [N ii] at 205 μm([N ii]{sub 205μm}). For local (U)LIRGs, the ratios of the CO(7–6) luminosity (L{sub CO(7–6)}) to the total infrared luminosity (L{sub IR}; 8–1000 μm) are fairly tightly distributed (to within ∼0.12 dex) and show little dependence on C(60/100). This makes L{sub CO(7–6)} a good SFR tracer, which is less contaminated by active galactic nuclei than L{sub IR} and may also be much less sensitive to metallicity than L{sub CO(1–0)}. Furthermore, the logarithmic [N ii]{sub 205μm}/CO(7–6) luminosity ratio depends fairly strongly (at a slope of ∼ −1.4) on C(60/100), with a modest scatter (∼0.23 dex). This makes it a useful estimator on C(60/100) with an implied uncertainty of ∼0.15 (or ≲4 K in the dust temperature (T{sub dust}) in the case of a graybody emission with T{sub dust} ≳ 30 K and a dust emissivity index β ≥ 1). Our locally calibrated SFR and C(60/100) estimators are shown to be consistent with the published data of (U)LIRGs of z up to ∼6.5.

• OSTI ID: 22518820
• Journal Information: Astrophysical Journal Letters, Vol. 802, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON MONOXIDE
COLOR
DENSITY
EMISSIVITY
GALAXIES
GALAXY NUCLEI
HEATING
LUMINOSITY
METALLICITY
MOLECULES
NITROGEN
PROBES
RED SHIFT
STAR EVOLUTION
STARS