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Title: Extinction in the 11.2 mu m PAH band and the low L-11.2/L-IR in ULIRGs
Authors: Hernández Caballero, A.
Spoon, H. W. W.
Alonso Herrero, A.
Hatziminaoglou, Evanthia
Magdis, Georgios E.
Pérez González, P. G.
Pereira Santaella, M.
Arribas, S.
Cortzen, I.
Labiano, Á.
Piqueras, J.
Rigopoulou, D.
Keywords: Dust;Extinction;Galaxies: ISM;Galaxies: star formation;Infrared: galaxies;Infrared: ISM
Issue Date: 5-Aug-2020
Publisher: Oxford Academics: Blackwell Publishing
DOI: 10.1093/mnras/staa2282
Published version:
Citation: Monthly Notices of the Royal Astronomical Society 497(4): 4614–4625 (2020)
Abstract: 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.
E-ISSN: 1365-2966
ISSN: 0035-8711
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