Extinction in the 11.2 mu m PAH band and the low L-11.2/L-IR in ULIRGs
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We present a method for recovering the intrinsic (extinction-corrected) luminosity of the 11.2 mu m PAH band in galaxy spectra. Using 105 high S/N Spitzer/IRS spectra of star-forming galaxies, we show that the equivalent width ratio of the 12.7 and 11.2 mu m PAH bands is independent on the optical depth (tau), with small dispersion (similar to 5 percent) indicative of a nearly constant intrinsic flux ratio R-int = (f(12.7)/f(11.2))(int) = 0.377 +/- 0.020. Conversely, the observed flux ratio, R-obs = (f(12.7)/f(11.2))(obs), strongly correlates with the silicate strength (S-sil) confirming that differences in R-obs reflect variation in tau. The relation between R-obs and S-sil reproduces predictions for the Galactic Centre extinction law but disagrees with other laws. We calibrate the total extinction affecting the 11.2 mu m PAH from R-obs, which we apply to another sample of 215 galaxies with accurate measurements of the total infrared luminosity (L-IR) to investigate the impact of extinction on L-11.2/L-IR. Correlation between L-11.2/L-IR and R-obs independently on L-IR suggests that increased extinction explains the well-known decrease in the average L-11.2/L-IR at high L-IR. The extinction-corrected L-11.2 is proportional to L-IR in the range L-IR = 10(9)-10(13) L-circle dot. These results consolidate L-11.2 as a robust tracer of star formation in galaxies.
Original language | English |
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Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 497 |
Issue number | 4 |
Pages (from-to) | 4614-4625 |
Number of pages | 12 |
ISSN | 0035-8711 |
DOIs | |
Publication status | Published - 5 Aug 2020 |
- dust, extinction, galaxies: ISM, galaxies: star formation, infrared: galaxies, infrared: ISM, POLYCYCLIC-AROMATIC-HYDROCARBON, ACTIVE GALACTIC NUCLEI, STAR-FORMATION RATES, INFRARED-EMISSION, MIDINFRARED SPECTROSCOPY, INTERSTELLAR DUST, GALAXIES, FEATURES, DISTRIBUTIONS, SPECTROGRAPH
Research areas
Links
- https://arxiv.org/pdf/2009.00676.pdf
Submitted manuscript
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