Jun 17, 2020
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?
The Astrophysical Journal
- Volume
- 896
- Number
- 2
- First page
- 93
- Last page
- 93
- Language
- Publishing type
- Research paper (scientific journal)
- DOI
- 10.3847/1538-4357/ab94bd
- Publisher
- American Astronomical Society
We present our new Atacama Large Millimeter/Submillimeter Array (ALMA) observations targeting [O iii]88 μm, [C ii]158 μm, [N ii]122 μm, and dust-continuum emission for three Lyman break galaxies at z = 6.0293-6.2037, identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [O iii] and [C ii] lines from all of the galaxies at 4.3-11.8σ levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z > 6, we confirm that all the nine z = 6-9 galaxies have high [O iii]/[C ii] ratios of, ∼10 times higher than z ∼ 0 galaxies. We also find a positive correlation between the [O iii]/[C ii] ratio and the Lyα equivalent width (EW) at the ∼90% significance level. We carefully investigate physical origins of the high [O iii]/[C ii] ratios at z = 6-9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6-9 galaxies. Instead, the observed high [O iii]/[C ii] ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0%-10%, both of which are consistent with our [N ii] observations. The latter scenario can be reproduced with a density-bounded nebula with PDR deficit, which would enhance the Lyα, Lyman continuum, and C+ ionizing photons escape from galaxies, consistent with the [O iii]/[C ii]-Lyα EW correlation we find.
- Link information
-
- DOI
- https://doi.org/10.3847/1538-4357/ab94bd
- arXiv
- http://arxiv.org/abs/arXiv:1910.10927
- URL
- https://iopscience.iop.org/article/10.3847/1538-4357/ab94bd/pdf
- URL
- https://iopscience.iop.org/article/10.3847/1538-4357/ab94bd
- Arxiv Url
- http://arxiv.org/abs/1910.10927v1
- Arxiv Url
- http://arxiv.org/pdf/1910.10927v1 Open access
- Scopus
- https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85086878460&origin=inward
- Scopus Citedby
- https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85086878460&origin=inward
- ID information
-
- DOI : 10.3847/1538-4357/ab94bd
- ISSN : 0004-637X
- eISSN : 1538-4357
- ORCID - Put Code : 68652847
- arXiv ID : arXiv:1910.10927
- SCOPUS ID : 85086878460
- BibTex Code : 2019arXiv191010927H