Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape

By K. Nakajima, M. Ouchi. 2013

266 citations recorded by the source corpus.

We present a systematic study for ionization state of inter-stellar medium in galaxies at z=0-3 with ~140,000 SDSS galaxies and 108 intermediate to high redshift galaxies from the literature, using an ionization-parameter sensitive line ratio of [OIII]5007/[OII]3727 and photoionization models. We confirm that z=2-3 galaxies show an [OIII]/[OII] ratio significantly higher than a typical star-forming galaxy of SDSS by a factor of >~10, and the photoionization models reveal that these high-z galaxies have an ionization parameter of log(qion/cm s^{-1})~7.6-9.0, a factor of ~4-10 higher than local galaxies. For galaxies at any redshift, we identify a correlation between the [OIII]/[OII] ratio and galaxy global properties of star-formation rate (SFR), stellar mass (M_star), and metallicity (Z). We extend the fundamental metallicity relation (FMR) and develop the fundamental ionization relation (FIR), a four-dimensional relation of ionization parameter, SFR, M_star, and Z. The intermediate and high-z galaxies up to z~3 follow the FIR defined with the local galaxies, in contrast with the FMR whose possible evolution from z~2 to 3 is reported. We find that the FMR evolution of z~2-3 appears, if one omits ionization parameter differences, and that the FMR evolution does not exist for an average metallicity solution of z~3 galaxies with a high-ionization parameter. Interestingly, all of two local Lyman-continuum emitting galaxies (LyC leakers) have a high [OIII]/[OII] ratio, indicating a positive correlation between [OIII]/[OII] and ionizing photon escape fraction (fesc), which is successfully explained by our photoionization models. Because [OIII]/[OII] ratios of z~2-3 galaxies, especially Ly-alpha emitters (LAEs), are comparable to, or higher than, those of the local LyC leakers, these high-z galaxies are candidates of Lyman-continuum emitting objects. (abridged)

Subfields: Astronomy and Astrophysics, Biophysics, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/ec6c44a1e7e3e882edbb5a46895c103fbbbc67a8

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In Astronomy and Astrophysics

1. P. Hopkins
2. M. Ouchi
3. Naveen A. Reddy
4. R. Dav'e
5. A. Shapley
6. L. Hernquist
7. Richard S. Ellis
8. C. Steidel

In Biophysics

1. A. Verhamme
2. I. Orlitová
3. Naveen A. Reddy
4. A. Shapley

In Global and Planetary Change

1. Naveen A. Reddy
2. A. Shapley
3. C. Steidel
4. M. Pettini
5. A. Verhamme
6. I. Orlitová
7. B. Siana
8. M. Oguri

Citations in the corpus

• The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at z ∼ 3 (2018, background): “…with LyC escape but are more amenable to measurement at very high redshift where direct measurements of LyC flux become difficult (e.g., Steidel et al. 2011; Heckman et al. 2011; Zackrisson et al. 2013; Nakajima & Ouchi 2014; Erb et al. 2014; Trainor et al. 2015, 2016; Verhamme et al. 2017).”
• Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, background): “…selected for follow-up based on very high observed or inferred ionizing environments, typically constrained via the ratio of [O III]/[O II] line emission, which has been proposed as a predictor of strong ionizing photon escape (e.g., Jaskot & Oey 2013; Nakajima & Ouchi 2014; Stasińska et al. 2015).”
• J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons (2017, background): “…(FUV) and a high enough redshift (z & 0.3) to allow direct LyC observations with the COS; and 2) a high extinction-corrected O32 & 5, which may indicate the presence of density-bounded H ii regions, i.e. escaping LyC radiation (Jaskot & Oey 2013; Nakajima & Ouchi 2014; Izotov, Thuan & Guseva 2017).”
• THE MOSDEF SURVEY: EXCITATION PROPERTIES OF z ∼ 2.3 STAR-FORMING GALAXIES (2014, methodology): “The O32R23 diagram has long been known as a probe of both ionization parameter and metallicity (Kewley & Dopita 2002), and has even been used to estimate oxygen abundances at z ∼ 2 (Nakajima et al. 2013; Nakajima & Ouchi 2014).”
• SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14–21 deg2 sky (2017, background): “From these observations, it has been revealed that LAEs are in an early phase of galaxy evolution, i.e., LAEs are young, less massive, less dusty, and in highly ionized state (e.g., Ono et al. 2010b; Ono et al. 2010a; Nakajima & Ouchi 2014; Kusakabe et al. 2015; Inoue et al. 2016).”
• An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “We compare the metallicity and the ionization parameter with the results presented in Nakajima & Ouchi (2014) in Figure 7.”
• Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios (2018, background): “A fair fraction of compact SFGs is characterised by high line ratios O32 = [O iii]λ5007/[O ii]λ3727 > ∼ 5 (Stasińska et al. 2015) indicating that they may contain density-bounded H ii regions and be potential LyC leakers as suggested e.g. by Jaskot & Oey (2013) and Nakajima & Ouchi (2014).”
• Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). I. Program strategy and clustering properties of ∼2000 Lyα emitters at z = 6–7 over the 0.3–0.5 Gpc2 survey area (2017, background): “LAEs have strong high-ionization lines such as [O III]5007, indicative of the high ionization state of the inter-stellar medium (ISM) given by intense ionizing radiation from young massive stars (Nakajima & Ouchi 2014).”
• Using Lyman-α to detect galaxies that leak Lyman continuum (2014, background): “13 in Nakajima & Ouchi 2014), but they may be rare (Vanzella et al. 2010).”
• Lyman-α spectral properties of five newly discovered Lyman continuum emitters (2016, methodology): “Comparison of Lyα and [O iii]/[O ii] diagnostics for LyC escape As discussed above, high [O iii]/[O ii] ratios have been proposed to trace density-bounded H ii regions in galaxies (Jaskot & Oey 2013; Nakajima & Ouchi 2014).”
• The mass–metallicity and the fundamental metallicity relation revisited on a fully Te-based abundance scale for galaxies (2019, unknown): “, metallicity and SFR has been observed and confirmed by several authors (Yates et al. 2012; Andrews & Martini 2013; Nakajima & Ouchi 2014; Salim et al. 2014; Grasshorn Gebhardt et al. 2016; Hunt et al. 2016; Hirschauer et al. 2018).”
• THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, methodology): “The Strömgren sphere definition of the ionization parameter also assumes that the nebula is radiation-bounded (i.e. no hydrogen-ionizing photons escape) instead of density-bounded (Nakajima & Ouchi 2014), which may not hold true at high redshifts.”
• JWST Census for the Mass–Metallicity Star Formation Relations at z = 4–10 with Self-consistent Flux Calibration and Proper Metallicity Calibrators (2023, methodology): “…of lower-redshift samples of continuum-selected galaxies ( Nakajima & Ouchi 2014; Troncoso et al. 2014; Sanders et al. 2016; Onodera et al. 2016; Strom et al. 2017 ) and Ly α emitting galaxies ( LAEs; Nakajima & Ouchi 2014; Erb et al. 2016; Nakajima et al. 2020 ) , as indicated in the legend.”
• Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies (2016, background): “3) with that of high-redshift LAEs that are potentially leaking ionizing radiation (Nakajima & Ouchi 2014), and that of known low-redshift LyC leakers.”