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Measuring Star Formation and Black Hole Accretion Rates In Tandem using Mid-Infrared Spectra of Local Infrared-Luminous Galaxies

Presentation #343.14 in the session Potpourri of Galaxies — iPoster Session.

Published onJun 29, 2022
Measuring Star Formation and Black Hole Accretion Rates In Tandem using Mid-Infrared Spectra of Local Infrared-Luminous Galaxies

We present the results of a spectral stacking analysis of Spitzer/Infrared Spectrograph high-resolution spectra of luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey (GOALS). We separate the sample of ~200 galaxies into 6 bins according to the mid-IR AGN fraction: the fraction of the mid-IR light coming from the central supermassive black hole, known as an active galactic nucleus (AGN). We stack the mid-IR spectra and detect a rich array of spectral lines including the star-formation tracers [Ne II] and [Ne III], and fainter AGN tracers [Ne V] and [O IV] throughout the sample. We decompose the [O IV] luminosity into components from star formation and AGN using [Ne II], [Ne V] and the AGN fraction. The [O IV] luminosity in LIRGs is dominated by star formation for AGN fractions of ≲0.3 and will over-predict the black hole accretion rate (BHAR) by multiple orders of magnitude at the lowest AGN fractions if not corrected. We calculate the BHARs using the AGN component of the [O IV] luminosity and compare to the star formation rates as a function of AGN fraction, finding that the relative growth of supermassive black holes to star formation increases by more than three orders of magnitude as a function of AGN fraction in LIRGs. We discuss the incidence of mergers in GOALS and the role that merger stage may play in driving our results. Our study, which probes lines below the noise in Spitzer data, provides the groundwork for future JWST/MIRI observations.

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