High Equivalent Width of Hα+[N ii] Emission in z ∼ 8 Lyman-break Galaxies from IRAC 5.8 μm Observations: Evidence for Efficient Lyman-continuum Photon Production in the Epoch of Reionization

Stefanon, Mauro; Bouwens, Rychard; Illingworth, G. D.; Labbé, Ivo; Oesch, Pascal; González, Valentino

doi:10.3847/1538-4357/ac7e44

Cited by 34 publications

(46 citation statements)

References 163 publications

(279 reference statements)

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“…For star-forming galaxies, we assume an average conversion factor from ρ UV to ionizing emissivity of ξ ion = 25.6. This value is motivated by increasing evidence that ξ ion increases with increasing redshift (e.g., Bouwens et al 2016;Stark et al 2017;Endsley et al 2021;Stefanon et al 2022), and is consistent with the results of the empirical model of Finkelstein et al (2019) for the redshift range considered here. The intrinsic ionizing emissivity from galaxies is thus:…”

Section: Ionizing Emissivitysupporting

confidence: 82%

On the Coevolution of the AGN and Star-forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9

Finkelstein

Bagley

2022

ApJ

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Studies of the rest-frame ultraviolet (UV) luminosity functions (LFs) typically treat star-forming galaxies and active galactic nuclei (AGNs) separately. However, modern ground-based surveys now probe volumes large enough to discover AGNs at depths sensitive enough for fainter galaxies, bridging these two populations. Using these observations as constraints, we present a methodology to empirically jointly model the evolution of the rest-UV LFs at z = 3–9. Our critical assumptions are that both populations have LFs well described by double power laws modified to allow for a flattening at the faint-end, and that all LF parameters evolve smoothly with redshift. This methodology provides a good fit to the observations and makes predictions to volume densities not yet observed, finding that the volume density of bright (M UV = −28) AGNs rises by ∼105 from z = 9 to z = 3, while bright (M UV = −21) star-forming galaxies rise by only ∼102 across the same epoch. The observed bright-end flattening of the z = 9 LF is unlikely to be due to AGN activity, and rather is due to a shallowing of the bright-end slope, implying a reduction of feedback in bright galaxies at early times. The intrinsic ionizing emissivity is dominated by star-forming galaxies at z > 3, even after applying a notional escape fraction. We find decent agreement between our AGN LFs and predictions based on different black hole seeding models, though all models underpredict the observed abundance of bright AGNs. We show that the wide-area surveys of the upcoming Euclid and Roman observatories should be capable of discovering AGNs to z ∼ 8.

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Section: Ionizing Emissivitysupporting

confidence: 82%

On the Coevolution of the AGN and Star-forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9

Finkelstein

Bagley

2022

ApJ

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“…Alternatively, strong Balmer emission lines can also be produced from star-forming galaxies. Such high values of EW Hα ; 1000 Å have been reported in z > 6 star-forming galaxies based on Spitzer and JWST (e.g., Endsley et al 2021;Chen et al 2023;Stefanon et al 2022). However, those galaxies show a significantly steeper continuum slopes (α λ ; −2.0), compared to that of CEERS-AGN-z5-1.…”

Section: Broadband/mediumband Excesssupporting

confidence: 70%

A Candidate for the Least-massive Black Hole in the First 1.1 Billion Years of the Universe

Onoue¹,

Inayoshi²,

Ding³

et al. 2023

ApJL

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We report a candidate of a low-luminosity active galactic nucleus (AGN) at z = 5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named CEERS-AGN-z5-1 at absolute 1450 Å magnitude M 1450 = −19.5 ± 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at z > 4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, Hubble Space Telescope, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted Hβ+[O iii] and Hα are covered. The estimated line luminosity is L Hβ+[O III] = 1043.0 erg s−1 and L Hα = 1042.9 erg s−1 with the corresponding rest-frame equivalent width EWHβ+[O III] = 1100 Å and EWHα = 1600 Å, respectively. Our spectral energy distribution fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity, L bol = 2.5 ± 0.3 × 1044 erg s−1, is consistent with those of z < 0.35 broad-line AGNs with M BH ∼ 106 M ⊙ accreting at the Eddington limit. This new AGN population in the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.

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“…Using the relations found at low-z and z ∼ 1−2 (see Tang et al 2019;Izotov et al 2021a), we estimate log(ξ ion ) ≈ 25.1−25.5 erg −1 Hz, up to a factor of ∼2 higher than the "canocical" value often assumed in ionizing photon budget calculations (Robertson et al 2013). This is comparable to other estimates of ξ ion at high redshift (e.g., Stefanon et al 2022).…”

Section: Emission Line Propertiessupporting

confidence: 69%

First look with JWST spectroscopy: Resemblance among z ∼ 8 galaxies and local analogs

Schaerer

Marques-Chaves

Barrufet

et al. 2022

A&A

107

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Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3−7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O iii]λ4363 auroral line (see JWST PR 2022-035). We present an analysis of the emission line properties of these galaxies, finding that these galaxies have a high excitation (as indicated by high, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H) ≈ 7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H) ≈ 7.4−7.5 (∼5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z ∼ 2 mass-metallicity relation. Overall, these first galaxy spectra at z ∼ 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

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High Equivalent Width of Hα+[N ii] Emission in z ∼ 8 Lyman-break Galaxies from IRAC 5.8 μm Observations: Evidence for Efficient Lyman-continuum Photon Production in the Epoch of Reionization

Cited by 34 publications

References 163 publications

On the Coevolution of the AGN and Star-forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9

On the Coevolution of the AGN and Star-forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9

A Candidate for the Least-massive Black Hole in the First 1.1 Billion Years of the Universe

First look with JWST spectroscopy: Resemblance among z ∼ 8 galaxies and local analogs

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