Measuring Star Formation and Black Hole Accretion Rates in Tandem Using Mid-infrared Spectra of Local Infrared Luminous Galaxies
Abstract
We present the results of a stacking analysis performed on Spitzer/Infrared Spectrograph high-resolution mid-infrared (mid-IR) spectra of luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. By binning in relation to mid-IR active galactic nucleus (AGN) fraction and stacking spectra, we detect bright emission lines [Ne ii] and [Ne iii], which trace star formation, and fainter emission lines [Ne v] and [O iv], which trace AGN activity, throughout the sample. We find that the [Ne ii] luminosity is fairly constant across all AGN fraction bins, while the [O iv] and [Ne v] luminosities increase by over an order of magnitude. Our measured average line ratios, [Ne v]/[Ne ii] and [O iv]/[Ne ii], at low AGN fraction are similar to H II galaxies, while the line ratios at high AGN fraction are similar to LINERs and Seyferts. We decompose the [O iv] luminosity into star formation and AGN components by fitting the [O iv] luminosity as a function of the [Ne ii] luminosity and the mid-IR AGN fraction. The [O iv] luminosity in LIRGs is dominated by star formation for mid-IR AGN fractions ≲ 0.3. With the corrected [O iv] luminosity, we calculate black hole accretion rates (BHARs) ranging from 10⁻⁵ M_⊙ yr⁻¹ at low AGN fractions to 0.2 M_⊙ yr⁻¹ at the highest AGN fractions. We find that using the [O iv] luminosity, without correcting for star formation, can lead to overestimation of the BHAR by up to a factor of 30 in starburst-dominated LIRGs. Finally, we show that the BHAR/star formation rate ratio increases by more than three orders of magnitude as a function of mid-IR AGN fraction in LIRGs.
Additional Information
© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 December 14; revised 2022 April 15; accepted 2022 June 8; published 2022 July 21. We thank the referee for the constructive comments that improved this work. We thank Krista Gile for advice regarding statistics and error analysis. M.S. is grateful for support from the Massachusetts Space Grant consortium, the Commonwealth Honors College, and the Five College Astronomy Department. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. We thank the IRSA staff for help with the GOALS IRS data products.Attached Files
Published - Stone_2022_ApJ_934_27.pdf
Accepted Version - 2206.05301.pdf
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Additional details
- Eprint ID
- 115858
- Resolver ID
- CaltechAUTHORS:20220726-997759000
- Massachusetts Space Grant Consortium
- Commonwealth Honors College
- Five College Astronomy Department
- NASA/JPL/Caltech
- Created
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2022-07-27Created from EPrint's datestamp field
- Updated
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2022-07-27Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)