Broad Emission Lines in Optical Spectra of Hot, Dust-obscured Galaxies Can Contribute Significantly to JWST/NIRCam Photometry

McKinney, Jed and Finnerty, Luke and Casey, Caitlin M. and Franco, Maximilien and Long, Arianna S. and Fujimoto, Seiji and Zavala, Jorge A. and Cooper, Olivia and Akins, Hollis and Pope, Alexandra and Armus, Lee and Soifer, B. T. and Larson, Kirsten and Matthews, Keith and Melbourne, Jason and Cushing, Michael (2023) Broad Emission Lines in Optical Spectra of Hot, Dust-obscured Galaxies Can Contribute Significantly to JWST/NIRCam Photometry. The Astrophysical Journal Letters, 946 (2). L39. ISSN 2041-8205

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Selecting the first galaxies at z > 7 − 10 from JWST surveys is complicated by z < 6 contaminants with degenerate photometry. For example, strong optical nebular emission lines at z < 6 may mimic JWST/NIRCam photometry of z > 7–10 Lyman-break galaxies (LBGs). Dust-obscured 3 < z < 6 galaxies in particular are potentially important contaminants, and their faint rest-optical spectra have been historically difficult to observe. A lack of optical emission line and continuum measures for 3 < z < 6 dusty galaxies now makes it difficult to test their expected JWST/NIRCam photometry for degenerate solutions with NIRCam dropouts. Toward this end, we quantify the contribution by strong emission lines to NIRCam photometry in a physically motivated manner by stacking 21 Keck II/NIRES spectra of hot, dust-obscured, massive ($\mathrm{log}{M}_{* }/{M}_{\odot }\gtrsim 10\mbox{--}11$) and infrared (IR) luminous galaxies at z ∼ 1–4. We derive an average spectrum and measure strong narrow (broad) [O iii]5007 and Hα features with equivalent widths of 130 ± 20 Å (150 ± 50 Å) and 220 ± 30 Å (540 ± 80 Å), respectively. These features can increase broadband NIRCam fluxes by factors of 1.2 − 1.7 (0.2–0.6 mag). Due to significant dust attenuation (AV ∼ 6), we find Hα+[N ii] to be significantly brighter than [O iii]+Hβ and therefore find that emission-line dominated contaminants of high −z galaxy searches can only reproduce moderately blue perceived UV continua of Sλ ∝ λβ with β > − 1.5 and z > 4. While there are some redshifts (z ∼ 3.75) where our stack is more degenerate with the photometry of z > 10 LBGs at λrest ∼ 0.3–0.8 μm , redder filter coverage beyond λobs > 3.5 μm and far-IR/submillimeter follow-up may be useful for breaking the degeneracy and making a crucial separation between two fairly unconstrained populations, dust-obscured galaxies at z ∼ 3–6 and LBGs at z > 10.

Item Type: Article
Subjects: Eprints STM archive > Physics and Astronomy
Depositing User: Unnamed user with email admin@eprints.stmarchive
Date Deposited: 27 Apr 2023 07:57
Last Modified: 26 Dec 2023 04:54

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