A New Star Formation Rate Calibration From Polycyclic Aromatic Hydrocarbon Emission Features and Application to High-Redshift Galaxies

Abstract

We calibrate the integrated luminosity from the polycyclic aromatic hydrocarbon (PAH) features at 6.2, 7.7, and 11.3 μm in galaxies as a measure of the star formation rate (SFR). These features are strong (containing as much as 5%-10% of the total infrared luminosity) and suffer minimal extinction. Our calibration uses Spitzer Infrared Spectrograph (IRS) measurements of 105 galaxies at 0<z<0.4, infrared (IR) luminosities of 10 9 -10 12 L  , combined with other well-calibrated SFR indicators. The PAH luminosity correlates linearly with the SFR as measured by the extinction-corrected Hα luminosity over the range of luminosities in our calibration sample. The scatter is 0.14 dex, comparable to that between SFRs derived from the Paα and extinction-corrected Hα emission lines, implying that the PAH features may be as accurate an SFR indicator as hydrogen recombination lines. The PAH SFR relation depends on gas-phase metallicity, for which we supply an empirical correction for galaxies with 0.2Z  <Z  0.7 Z  . We present a case study in advance of the James Webb Space Telescope (JWST), which will be capable of measuring SFRs from PAHs in distant galaxies at the peak of the SFR density in the universe (z∼2) with SFRs as low as ∼10M yr 1 - . We use Spitzer/IRS observations of the PAH features and Paα emission plus Hα measurements in lensed star-forming galaxies at 1<z<3 to demonstrate the ability of the PAHs to derive accurate SFRs. We also demonstrate that because the PAH features dominate the mid-IR fluxes, broadband mid-IR photometric measurements from JWST will bothtracethe SFR and provide a way to exclude galaxies dominated by an active galactic nucleus.

VLA AND ALMA IMAGING OF INTENSE GALAXY-WIDE STAR FORMATION IN z ∼ 2 GALAXIES

“…These submm galaxies have median SFRs 3-8 times those of our sample, hence an explanation is that the more compact star formation could be a characteristic of this higher SFR regime, but not for main-sequence SFGs (Figure 3). The increasing compactness of SFGs at SFR300 M e yr −1 is independently indicated by the decreasing ratio of midinfrared aromatic luminosity to the total infrared luminosity (L 6.2 μm /L IR trend shown in Figure 3; Nordon et al 2012;Pope et al 2013;Shipley et al 2016). Consistent with this trend, the two most intense SFGs in our sample (UDF1 and 2) are also the most compact.…”

“…Right: main-sequence SFGs (this work) are ∼2× larger than submillimeter galaxies that form stars ∼8× more rapidly (the large symbols represent median for each sample). Above an SFR of 200-300 M e yr −1 , SFGs become more compact; the dotted line shows a compactness trend inferred independently of the ratio of the 6.2 μm aromatic feature luminosity and the total infrared luminosity (Shipley et al 2016, normalized to this work's median size).…”

A star formation study of the ATLAS3Dearly-type galaxies with the AKARI all-sky survey

“…To convert L PAH to a SFR, we adopted the method described in Shipley et al (2016), in which the sum of the 6.2, 7.7 and 11.3 µm features is used to estimate the SFR. The ratio of these PAH bands to the total PAH emission is 0.65 in the PAH template adopted for our SED fits (a value typical of star-forming galaxies; Smith et al 2007), so we simply propagate this fraction in our calculations.…”

The complex evolutionary paths of local infrared bright galaxies: a high-angular resolution mid-infrared view

“…Using the calibrations of the SFR in terms of the luminosity of the 11.3 µm PAH luminosity (see Diamond-Stanic & Rieke 2012;Shipley et al 2016) we find nuclear (not corrected for extinction) SFR 3 for the nuclei of IR-bright galaxies (see Table 5) between 0.6 M⊙ yr Comparison between the nuclear 11.3 µm PAH luminosities as measured from high angular resolution ground-based spectroscopy and kpc-scales 11.3 µm PAH luminosities as measured from Spitzer/IRS spectroscopy for the IR-bright galaxy sample. Symbols are color-coded by the AGN fractional contribution at 12 µm within the ground-based slits.…”