Direct Far-infrared Metal Abundances (FIRA). I. M101 Academic Article uri icon


  • Abstract Accurately determining gas-phase metal abundances within galaxies is critical as metals strongly affect the physics of the interstellar medium. To date, the vast majority of widely used gas-phase abundance indicators rely on emission from bright optical lines, whose emissivities are highly sensitive to the electron temperature. Alternatively, direct-abundance methods exist that measure the temperature of the emitting gas directly, though these methods usually require challenging observations of highly excited auroral lines. Low-lying far-infrared (FIR) fine structure lines are largely insensitive to electron temperature and thus provide an attractive alternative to optically derived abundances. Here, we introduce the far-infrared abundance (FIRA) project, which employs these FIR transitions, together with both radio freefree emission and hydrogen recombination lines, to derive direct, absolute gas-phase oxygen abundances. Our first target is M101, a nearby spiral galaxy with a relatively steep abundance gradient. Our results are consistent with the O++ electron temperatures and absolute oxygen abundances derived using optical direct-abundance methods by the CHemical Abundance Of Spirals (CHAOS) program, with a small difference (1.5) in the radial abundance gradients derived by the FIR/freefree-normalized versus CHAOS/direct-abundance techniques. This initial result demonstrates the validity of the FIRA methodologywith the promise of determining absolute metal abundances within dusty star-forming galaxies, both locally and at high redshift.

published proceedings


altmetric score

  • 8.33

author list (cited authors)

  • Lamarche, C., Smith, J. D., Kreckel, K., Linden, S. T., Rogers, N., Skillman, E., ... Ferkinhoff, C.

citation count

  • 1

complete list of authors

  • Lamarche, C||Smith, JD||Kreckel, K||Linden, ST||Rogers, NSJ||Skillman, E||Berg, D||Murphy, E||Pogge, R||Donnelly, GP||Kennicutt, R Jr||Bolatto, A||Croxall, K||Groves, B||Ferkinhoff, C

publication date

  • February 2022