Copyright © 2020, © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyHernández Caballero, A.Spoon, H. W. W.Alonso-Herrero, AlmudenaHatziminaoglou, EvanthiaMagdis, Georgios E.Pérez González, Pablo G.Pereira Santaella, MiguelArribas, SantiagoCortzen, I.Labiano, AlvaroPiqueras López, JavierRigopoulou, DimitraUnidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-07372021-04-092021-04-092020-08-05Monthly Notices of the Royal Astronomical Society 497(4): 4614–4625 (2020)0035-8711https://academic.oup.com/mnras/article-abstract/497/4/4614/5881327http://hdl.handle.net/20.500.12666/184We 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.engAttribution-NonCommercial-ShareAlike 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-sa/4.0/DustExtinctionGalaxies: ISMGalaxies: star formationInfrared: galaxiesInfrared: ISMinfo:eu-repo/semantics/article10.1093/mnras/staa22821365-2966info:eu-repo/semantics/openAccess