Large Population of ALMA Galaxies at z &gt; 6 with Very High [O iii] 88 μm to [C ii] 158 μm Flux Ratios: Evidence of Extremely High Ionization Parameter or PDR Deficit?

Harikane, Yuichi; Ouchi, Masami; Inoue, Akio; Matsuoka, Yoshiki; Tamura, Motohide; Bakx, Tom J. L. C.; Fujimoto, Seiji; Moriwaki, Kana; Ono, Yoshiyasu; Nagao, Tohru; Tadaki, Ken-ichi; Kojima, Takashi; Shibuya, Tetsuo; Egami, Eiichi; Ferrara, Andrea; Gallerani, S.; Hashimoto, T.; Kohno, Kotaro; Matsuda, Yoshihisa; Matsuo, Hiroshi; Pallottini, Andrea; Sugahara, Yuma; Vallini, L.

doi:10.3847/1538-4357/ab94bd

Cited by 174 publications

(374 citation statements)

References 137 publications

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“…Since the [O iii]/[C ii] has been observed to also be similarly extreme in many high-z galaxies (e.g. Laporte et al 2019;Hashimoto et al 2019;Tamura et al 2019;Harikane et al 2020), the results presented here, where we focus on low-Z star-forming galaxies, may eventually be relevant to the understanding of the total molecular gas content and structure in some high-z galaxies.…”

Section: Dwarf Galaxy Survey: Extreme Properties In Low-metallicity Ementioning

confidence: 79%

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

Madden

Cormier

Hony

et al. 2020

A&A

138

128

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Context. Molecular gas is a necessary fuel for star formation. The CO (1−0) transition is often used to deduce the total molecular hydrogen but is challenging to detect in low-metallicity galaxies in spite of the star formation taking place. In contrast, the [C ii]λ158 µm is relatively bright, highlighting a potentially important reservoir of H 2 that is not traced by CO (1−0) but is residing in the C +-emitting regions. Aims. Here we aim to explore a method to quantify the total H 2 mass (M H 2) in galaxies and to decipher what parameters control the CO-dark reservoir. Methods. We present Cloudy grids of density, radiation field, and metallicity in terms of observed quantities, such as [O i], [C i], CO (1−0), [C ii], L TIR , and the total M H 2. We provide recipes based on these models to derive total M H 2 mass estimates from observations. We apply the models to the Herschel Dwarf Galaxy Survey, extracting the total M H 2 for each galaxy, and compare this to the H 2 determined from the observed CO (1−0) line. This allows us to quantify the reservoir of H 2 that is CO-dark and traced by the [C ii]λ158 µm. Results. We demonstrate that while the H 2 traced by CO (1−0) can be negligible, the [C ii]λ158 µm can trace the total H 2. We find 70 to 100% of the total H 2 mass is not traced by CO (1−0) in the dwarf galaxies, but is well-traced by [C ii]λ158 µm. The CO-dark gas mass fraction correlates with the observed L [C ii] /L CO(1−0) ratio. A conversion factor for [C ii]λ158 µm to total H 2 and a new CO-to-total-M H 2 conversion factor as a function of metallicity are presented. Conclusions. While low-metallicity galaxies may have a feeble molecular reservoir as surmised from CO observations, the presence of an important reservoir of molecular gas that is not detected by CO can exist. We suggest a general recipe to quantify the total mass of H 2 in galaxies, taking into account the CO and [C ii] observations. Accounting for this CO-dark H 2 gas, we find that the star-forming dwarf galaxies now fall on the Schmidt-Kennicutt relation. Their star-forming efficiency is rather normal because the reservoir from which they form stars is now more massive when introducing the [C ii] measures of the total H 2 compared to the small amount of H 2 in the CO-emitting region.

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Section: Dwarf Galaxy Survey: Extreme Properties In Low-metallicity Ementioning

confidence: 79%

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

Madden

Cormier

Hony

et al. 2020

A&A

138

128

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“…We analyze the sample of six Lyman break galaxies with [OIII]88 μm detections compiled by Harikane et al (2020), spanning z=7.1-9.1. The relevant measurements and original literature references are given in Table 1.…”

Section: Z > 7 Galaxy Samplementioning

confidence: 99%

The Mass–Metallicity Relation at z ≃ 8: Direct-method Metallicity Constraints and Near-future Prospects

Jones

Roberts-Borsani

Ellis

et al. 2020

ApJ

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Physical properties of galaxies at z>7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization. Chemical abundance measurements offer valuable information on the integrated star formation history, and hence ionizing photon production, as well as the rapid gas accretion expected at such high redshifts. We use reported measurements of [OIII]88 μm emission and star formation rate to estimate gasphase oxygen abundances in five galaxies at z=7.1-9.1 using the direct T e method. We find typical abundances + 12 log O H ( )=7.9 (∼0.2 times the solar value) and an evolution of 0.9±0.5 dex in oxygen abundance at fixed stellar mass from z;8 to 0. These results are compatible with theoretical predictions, albeit with large (conservative) uncertainties in both mass and metallicity. We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter/submillimeter Array (ALMA) and the James Webb Space Telescope (JWST). In particular we highlight [OIII]52 μm as a valuable feature for robust metallicity measurements. Precision of 0.1-0.2 dex in T e -based O/H abundance can be reasonably achieved for galaxies at z≈5-8 by combining [OIII]52 μm with rest-frame optical strong lines. It will also be possible to probe gas mixing and mergers via resolved T e -based abundances on kiloparsec scales. With ALMA and JWST, direct metallicity measurements will thus be remarkably accessible in the reionization epoch.

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“…A complementary approach to obtaining accurate redshifts is searching for the [CII]158 µm or the [OIII]88 µm line in spectroscopic observations at (sub-)mm frequencies (e.g., Decarli et al 2017;Hashimoto et al 2019;Harikane et al 2020). This approach is particularly promising as it allows for a redshift estimate in those LBG candidates with absent or weak Lyα (Decarli et al 2019) or a fall in redshift windows covered by sky lines (see Fig.…”

Section: Environment Of Early Black Holes: Future Prospectsmentioning

confidence: 99%

Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524

Mignoli

Gilli

Decarli

et al. 2020

A&A

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We report on the spectroscopic confirmation of a large-scale structure around the luminous z = 6.31 quasi-stellar object (QSO) SDSS J1030+0524, powered by a one billion solar mass black hole. The structure is populated by at least six members, namely, four Lyman-break galaxies (LBGs), and two Lyman alpha emitters (LAEs). The four LBGs were identified among a sample of 21 i-band dropouts with zAB < 25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts were determined through multi-object spectroscopic observations at 8−10 m class telescopes lasting up to eight hours. The two LAEs were identified in a 6 h VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range between 6.129−6.355. Assuming that the peculiar velocities are negligible, this range corresponds to radial separations of ±5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at a level > 3.5σ and that the level of the galaxy overdensity is at least 1.5−2 within the large volume sampled (∼780 physical Mpc3). The spectral properties of the six member galaxies (Lyα strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>1012 M⊙) dark matter halos in large-scale structures and that the absence of earlier detections of such systems is likely due to observational limitations.

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Large Population of ALMA Galaxies at z > 6 with Very High [O iii] 88 μm to [C ii] 158 μm Flux Ratios: Evidence of Extremely High Ionization Parameter or PDR Deficit?

Cited by 174 publications

References 137 publications

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

The Mass–Metallicity Relation at z ≃ 8: Direct-method Metallicity Constraints and Near-future Prospects

Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524

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