Reconstructing the Observed Ionizing Photon Production Efficiency at z ∼ 2 Using Stellar Population Models

Nanayakkara, Themiya; Brinchmann, Jarle; Glazebrook, Karl; Kewley, Lisa J.; Tran, Kim‐Vy H.; Cowley, Michael J.; Fisher, David B.; Kacprzak, Glenn G.; Labbé, Ivo; Straatman, Caroline

doi:10.3847/1538-4357/ab65eb

Cited by 23 publications

(22 citation statements)

References 94 publications

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“…This could reflect a harder ionizing radiation field associated with young, hot, and metal-poor stars, as well as a much higher ionizing photon production efficiency at high redshift (Sect. 4.4 of Nanayakkara et al 2020). We also have not yet detected a less extreme population of z 6 faint and low mass galaxies exhibiting spectral properties similar to the average ones of faint LAEs at 3 ≤ z ≤ 4.6, probably because of the selection methods (e.g., Du et al 2020).…”

Section: Comparison With the Literaturementioning

confidence: 65%

The MUSE Hubble Ultra Deep Field Survey

Feltre

Maseda

Bacon

et al. 2020

A&A

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We investigated the ultraviolet (UV) spectral properties of faint Lyman-α emitters (LAEs) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint Universe. We used data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M UV of −18 and down to M UV of −16), low stellar mass (median value of 10 8.4 M and down to 10 7 M) LAEs at redshift z 3. We computed various averaged spectra of LAEs, subsampled on the basis of their observational (e.g., Lyα strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and starformation rate) properties. We searched for UV spectral features other than Lyα, such as higher ionization nebular emission lines and absorption features. We successfully observed the O iii]λ1666 and [C iii]λ1907+C iii]λ1909 collisionally excited emission lines and the He iiλ1640 recombination feature, as well as the resonant C ivλλ1548,1551 doublet either in emission or P-Cygni. We compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Lyα equivalent widths, fainter UV magnitudes, bluer UV spectral slopes, and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z > 2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, lowmass, and faint LAEs. We publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.

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Section: Comparison With the Literaturementioning

confidence: 65%

The MUSE Hubble Ultra Deep Field Survey

Feltre

Maseda

Bacon

et al. 2020

A&A

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“…Moreover, cleaning the SFG samples from sources powered by AGNs is fundamental in order to measure with high accuracy the Lyman continuum photon production efficiency. Present renditions of ξ ion at lower redshifts (Nanayakkara et al 2020), indeed, could be biased high due to the presence of unrecognized AGNs, especially the sources dominated by high ionization lines in emission, e.g. those characterized by high OIII/OII line ratio or large EWs in HeII or Hα.…”

Section: Discussionmentioning

confidence: 92%

On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5

Grazian,

Giallongo,

Fiore

et al. 2020

Preprint

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It is a widespread opinion that hydrogen reionization is mainly driven by primeval star-forming galaxies, with a minor role of high-z active galactic nuclei. Recent observations, however, challenge this notion, indicating a number of issues related to a galaxy-driven reionization scenario. We provide here an updated assessment of the space density of relatively faint (M 1450 ∼ −22.5) AGNs at z spec ∼ 5.5 in order to improve the estimate of the photo-ionization rate contribution from accreting super massive black holes. Exploiting deep UV rest-frame ground-based spectra collected at the Very Large Telescope on the CANDELS/GOODS-South field and deep Chandra X-ray images in the CANDELS/GOODS-North and EGS areas, we find two relatively bright (M 1450 ∼ −22.5) AGNs at z spec ∼ 5.5. We derive an AGN space density of Φ = 1.29 × 10 −6 cM pc −3 at z ∼ 5.5 and M 1450 ∼ −22.5 by simply dividing their observed number by the cosmological volume in the range 5.0 < z < 6.1. Our estimate does not consider corrections for incompleteness, therefore it represents a lower limit, although uncertainties due to cosmic variance can still be significant. This value supports a high space density of AGNs at z > 5, in contrast with previous claims mostly based on standard color selection, possibly affected by significant incompleteness. Our estimate for the AGN photo-ionization rate at z ∼ 5.5 is in agreement with the observed values at similar redshifts, which are needed to keep the intergalactic medium highly ionized. Upcoming JWST and giant ground based telescopes observations will improve the study of high-z AGNs and their contribution to the reionization of the Universe.

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“…If these galaxies did indeed have top heavy IMFs in their star-formation phase (e.g. as formulated by Lacey et al (2016), also see Gunawardhana et al (2011);Nanayakkara et al (2017Nanayakkara et al ( , 2020), this would lead to differences in the number of ionizing photons produced, the chemical enrichment and stellar wind and supernovae feedback processes. Such changes would be crucial to the re-ionization timescales of the Universe, thus, the reconstruction of the relic IMF in the 𝑧 > 6 Universe is important to constrain the cosmological evolutionary models of the Universe.…”

Section: The Imfmentioning

confidence: 99%

Massive High-Redshift Quiescent Galaxies With JWST

Nanayakkara,

Esdaile,

Glazebrook

et al. 2021

Preprint

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Recent ground based deep observations of the Universe have discovered populations of massive quiescent galaxies at 𝑧 ∼ 3 − 5. The observed number density of sources are higher than predicted by cosmological models. Thus, constraining the formation and evolutionary mechanisms of these galaxies is crucial to determine how the Universe built such massive galaxies early in the Universe and what mechanisms drove the cessation of star-formation. With the scheduled launch of the James Webb Space Telescope, observations of rest-frame optical features of 𝑧 ∼ 3 − 5 galaxies will be enabled through the continuous 0.6 − 5.3𝜇𝑚 coverage of the on-board NIRSpec instrument. Here we perform mock JWST/NIRSpec observations to determine optimal observing strategies to efficiently recover the completeness, star-formation histories, element abundances, and the initial mass function of massive quiescent galaxies in this cosmic window. We show that through smart grism/filter choices, NIRSpec slit and integral field spectroscopy observations can be used to constrain formation pathways of these galaxies to high accuracy with high efficiency. Such observations could revolutionize our understanding of galaxy evolution in the early Universe providing much needed constraints to galaxy evolutionary models in the early Universe.

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Reconstructing the Observed Ionizing Photon Production Efficiency at z ∼ 2 Using Stellar Population Models

Cited by 23 publications

References 94 publications

The MUSE Hubble Ultra Deep Field Survey

The MUSE Hubble Ultra Deep Field Survey

On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5

Massive High-Redshift Quiescent Galaxies With JWST

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