Evolution of N/O abundance ratios and ionization parameters from <i>z</i> ∼ 0 to 2 investigated by the direct temperature method

Kojima, Takashi; Ouchi, Masami; Nakajima, Kengo; Shibuya, Tetsuo; Harikane, Yuichi; Ono, Yoshiyasu

doi:10.1093/pasj/psx017

Cited by 68 publications

(78 citation statements)

References 102 publications

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“…There have been observational studies that indicate the presence of an anticorrelation between U and Z based on a strongline method (Nakajima & Ouchi 2014;Onodera et al 2016). Shapley et al (2015) and Kojima et al (2017) mentioned the anticorrelation by using the stacked measurements based on the direct method from Andrews & Martini (2013). In Figure 4, our data show that U is apparently strongly anticorrelated with Z: a simple power-law fit yields U ∝ Z −1.52±0.04 .…”

Section: Ionization Parametermentioning

confidence: 80%

Disentangling the physical parameters of gaseous nebulae and galaxies

Kashino

Inoue

2019

Monthly Notices of the Royal Astronomical Society

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We present an analysis to disentangle the connection between physical quantities that characterize the conditions of ionized H ii regions -metallicity (Z), ionization parameter (U), and electron density (n e ) -and the global stellar mass (M * ) and specific star formation rate (sSFR = SFR/M * ) of the host galaxies. We construct composite spectra of galaxies at 0.027 ≤ z ≤ 0.25 from Sloan Digital Sky Survey, separating the sample into bins of M * and sSFR, and estimate the nebular conditions from the emission line flux ratios. Specially, metallicity is estimated from the direct method based on the faint auroral lines [O iii]λ4363 and [O ii]λλ7320,7330. The metallicity estimates cover a wide range from 12 + log O/H ∼ 7.6-8.9. It is found that these three nebular parameters all are tightly correlated with the location in the M * -sSFR plane. With simple physically-motivated ansätze, we derive scaling relations between these physical quantities by performing multi regression analysis. In particular, we find that U is primarily controlled by sSFR, as U ∝ sSFR 0.43 , but also depends significantly on both Z and n e . The derived partial dependence of U ∝ Z −0.36 is weaker than the apparent correlation (U ∝ Z −1.52 ). The remaining negative dependence of U on n e is found to be U ∝ n −0.29 e . The scaling relations we derived are in agreement with predictions from theoretical models and observations of each aspect of the link between these quantities. Our results provide a useful set of equations to predict the nebular conditions and emission-line fluxes of galaxies in semi-analytic models.

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Section: Ionization Parametermentioning

confidence: 80%

Disentangling the physical parameters of gaseous nebulae and galaxies

Kashino

Inoue

2019

Monthly Notices of the Royal Astronomical Society

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“…the purple dot-dashed line in Figure 10) examples of highly ionized, high metallicity galaxies are not present in the literature (e.g. Kojima et al 2017).…”

Section: The Correlation Between F Esc (L Yc) and O32mentioning

confidence: 88%

“…A more complex relationship between 12 + log 10 (O/H), q ion , and f esc (L yC) may be required (e.g. by including known correlations between metallicity and ionization parameter, Kojima et al 2017). Confirming this will require a larger sample of LCEs with reliably measured metallicities.…”

mentioning

confidence: 99%

On the lack of correlation between [O iii]/[O ii] and Lyman continuum escape fraction

Bassett

Ryan-Weber

Cooke

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present the first results of our pilot study of 8 photometrically selected Lyman continuum (LyC) emitting galaxy candidates from the COSMOS field and focus on their optical emission line ratios. Observations were performed in the H and K bands using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) instrument at the Keck Observatory, targeting the [OII], Hβ, and [OIII] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [OIII]/[OII] ratios (O32), with an average ratio for our sample of 2.5±0.2. Preliminary results of our companion Low Resolution Imaging Spectrometer (LRIS) observations, targeting LyC and Lyα, show that those galaxies with the largest O32 are typically found to also be Lyα emitters. High O32 galaxies are also found to have tentative non-zero LyC escape fractions ( f esc (L yC)) based on u band photometric detections. These results are consistent with samples of highly ionized galaxies, including confirmed LyC emitting galaxies from the literature. We also perform a detailed comparison between the observed emission line ratios and simulated line ratios from density bounded H ii regions modeled using the photoionization code MAPPINGS V. Estimates of f esc (L yC) for our sample fall in the range from 0.0-0.23 and suggest possible tension with published correlations between O32 and f esc (L yC), adding weight to dichotomy of arguments in the literature. We highlight the possible effects of clumpy geometry and mergers that may account for such tension.

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“…The T e method provides the most reliable ways to measure the N/O ratio and oxygen abundance. However, it is extremely challenging to measure the N/O ratio and oxygen abundance using the T e method in high-redshift galaxies (e.g., Kojima et al 2017;Strom et al 2017;Sanders et al 2016b), because it requires a detection of the weak emission line [O iii]λ4363, which is more than 10 times weaker than Hβ . However, such measurements are possible in this work, thanks to the high S/N in the stacked spectra of both the local analogues and the SDSS reference galaxies.…”

Section: N-to-o Ratiosmentioning

confidence: 99%

“…Four competing interpretations have been proposed: (1) higher nitrogen-to-oxygen ratio (N/O ratio, e.g. Masters et al 2014Masters et al , 2016Jones et al 2015;Shapley et al 2015;Kojima et al 2017), (2) harder stellar radiation field (e.g., Steidel et al 2014Steidel et al , 2016, (3) higher ionisation parameter and/or electron density in high-redshift galaxies (e.g., Liu et al 2008;Brinchmann et al 2008;Bian et al 2010;Kewley et al 2013a,b;Kojima et al 2017;Dopita et al 2016), and (4) selection effects (e.g., Juneau et al 2014;Salim et al 2015). Bian et al (2016) found that selection effects cannot fully account for the offset between low-and high-redshift galaxies on the BPT diagram.…”

Section: Introductionmentioning

confidence: 99%

What drives the redshift evolution of strong emission line ratios?

Bian

Kewley

Groves

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We study the physical mechanisms that cause the offset between low-redshift and highredshift galaxies on the [O iii]λ5007/Hβ versus [N ii]λ6584/Hα "Baldwin, Phillips & Terlevich" (BPT) diagram using a sample of local analogues of high-redshift galaxies. These high-redshift analogue galaxies are selected from the Sloan Digital Sky Survey. Located in the same region on the BPT diagram as the ultra-violet selected galaxies at z ∼ 2, these high-redshift analogue galaxies provide an ideal local benchmark to study the offset between the local and high-redshift galaxies on the BPT diagram. We compare the nitrogen-to-oxygen ratio (N/O), the shape of the ionising radiation field, and ionisation parameters between the high-redshift analogues and a sample of local reference galaxies. The higher ionisation parameter in the high-redshift analogues is the dominant physical mechanism driving the BPT offset from low-to high-redshift, particularly at high [N ii]λ6584/Hα. Furthermore, the N/O ratio enhancement also plays a minor role to cause the BPT offset. However, the shape of the ionising radiation field is unlikely to cause the BPT offset because the high-redshift analogues have a similar hard ionising radiation field as local reference galaxies. This hard radiation field cannot be produced by the current standard stellar synthesis models. The stellar rotation and binarity may help solve the discrepancy.

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Evolution of N/O abundance ratios and ionization parameters from z ∼ 0 to 2 investigated by the direct temperature method

Cited by 68 publications

References 102 publications

Disentangling the physical parameters of gaseous nebulae and galaxies

Disentangling the physical parameters of gaseous nebulae and galaxies

On the lack of correlation between [O iii]/[O ii] and Lyman continuum escape fraction

What drives the redshift evolution of strong emission line ratios?

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