Direct Far-Infrared Metal Abundances (FIRA) I: M101. (arXiv:2111.10385v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Lamarche_C/0/1/0/all/0/1">C. Lamarche</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_J/0/1/0/all/0/1">J. D. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kreckel_K/0/1/0/all/0/1">K. Kreckel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Linden_S/0/1/0/all/0/1">S. T. Linden</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rogers_N/0/1/0/all/0/1">N. S. J. Rogers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Skillman_E/0/1/0/all/0/1">E. Skillman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berg_D/0/1/0/all/0/1">D. Berg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Murphy_E/0/1/0/all/0/1">E. Murphy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pogge_R/0/1/0/all/0/1">R. Pogge</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Donnelly_G/0/1/0/all/0/1">G. P. Donnelly</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kennicutt_R/0/1/0/all/0/1">R. Kennicutt Jr.</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bolatto_A/0/1/0/all/0/1">A. Bolatto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Croxall_K/0/1/0/all/0/1">K. Croxall</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Groves_B/0/1/0/all/0/1">B. Groves</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ferkinhoff_C/0/1/0/all/0/1">C. Ferkinhoff</a>
Accurately determining gas-phase metal-abundances within galaxies is critical
as metals strongly affect the physics of the interstellar medium (ISM). 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 abundances
(FIRA) project, which employs these FIR transitions, together with both radio
free-free 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 ($sim$ 1.5$sigma$) in the radial
abundance-gradients derived by the FIR/free-free-normalized vs.
CHAOS/direct-abundance techniques. This initial result demonstrates the
validity of the FIRA methodology $-$ with the promise of determining absolute
metal-abundances within dusty star-forming galaxies, both locally and at high
redshift.
Accurately determining gas-phase metal-abundances within galaxies is critical
as metals strongly affect the physics of the interstellar medium (ISM). 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 abundances
(FIRA) project, which employs these FIR transitions, together with both radio
free-free 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 ($sim$ 1.5$sigma$) in the radial
abundance-gradients derived by the FIR/free-free-normalized vs.
CHAOS/direct-abundance techniques. This initial result demonstrates the
validity of the FIRA methodology $-$ with the promise of determining absolute
metal-abundances within dusty star-forming galaxies, both locally and at high
redshift.
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