THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3*

Sanders, Ryan L.; Shapley, Alice E.; Kriek, Mariska; Reddy, Naveen A.; Freeman, William R.; Coil, Alison L.; Siana, Brian; Mobasher, Bahram; Shivaei, Irene; Price, Sedona H.; Groot, Laura de

doi:10.3847/0004-637x/816/1/23

Cited by 316 publications

(660 citation statements)

References 120 publications

(225 reference statements)

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“…This ne value at z = 2-3 is about an order of magnitude higher than the typical value of local galaxies, ne ∼ 25 cm −3 , which is derived by Sanders et al (2016) from the sample of the Sloan Digital Sky Survey (SDSS; York et al 2000). Although there is a large difference of the ne values between z = 2-3 and local SFGs, photoionization models indicate that this ne difference can increase [O III] λ5007/Hβ and [N II] λ6584/Hα values only by ∼ 0.01, 0.05, and 0.1 dex for SFGs with the oxygen abundances of 12+log(O/H) =8.0, 8.3, and 8.5, respectively (Sanders et al 2016). These small changes cannot explain the BPT offset, suggesting that the ne evolution is not the major source of the BPT offset.…”

Section: Introductionmentioning

confidence: 66%

“…Our calculations are terminated when the hydrogen ionization fractions reach ≤ 1%. (Shimakawa et al 2015;Sanders et al 2016). Thus, the dependence of ne is negligible in our Te estimates.…”

Section: Discussionmentioning

confidence: 82%

“…Local SFGs make a tight relation in the BPT diagram, which is caused by the anticorrelation between the oxygen abundance, 12+log(O/H), and the ionization parameter, qion (Dopita & Evans 1986;Dopita et al 2000Dopita et al , 2006a. Recent studies have revealed that z ∼ 2 galaxies have [N II] λ6584/Hα (N2) values higher than those of the local SFGs for a given [O III] λ5007/Hβ (O3) on average (Shapley et al 2005;Erb et al 2006;Brinchmann et al 2008;Liu et al 2008;Kewley et al 2013b;Steidel et al 2014;Masters et al 2014;Yabe et al 2014;Hayashi et al 2015;Shapley et al 2015;Sanders et al 2016;Kashino et al 2017). The z = 2 galaxies observed in the Keck Baryonic Structure Survey (KBSS; Steidel et al 2014) show the average of ∼ 0.4 dex excesses in [N II] λ6584/Hα.…”

Section: Introductionmentioning

confidence: 99%

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

Kojima

Ouchi

Nakajima

et al. 2017

Publications of the Astronomical Society of Japan

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We present N/O abundance ratios, ionization parameters q ion , and oxygen abundance O/H for a total of 41 galaxies (11 individual galaxies and a 30-galaxy stack) including Lyα emitters and Lyman break galaxies at z ∼ 2, and investigate galaxy evolution from z ∼ 0 to 2 in conjunction with 208,529 local SDSS galaxies and 9 green pea galaxies (GPs). In contrast with most of the recent studies, we obtain the N/O ratio, q ion , and O/H measurements by direct T e methods with [O III] λ4363 and O III] λ1665 lines. Based on these reliable measurements, we find that there exist z ∼ 2 galaxies with an excess of N/O falling beyond the local average of N/O-O/H relation, while the majority of the z ∼ 2 galaxies have the N/O ratios nearly comparable with z ∼ 0 galaxies in the N/O-stellar mass relation. Our galaxies place the upper limit of N/O ratio log(N/O) ≤ −1.26 on average, suggesting that the N/O ratio evolves, if at all, by < 0.17 dex. Exploiting our reliable measurements free from the N/O-q ion -O/H degeneracies, we identify, for the first time, that z ∼ 2 galaxies with offsets in the BPT diagram indicate either 1) only an N/O excess, 2) only a q ion excess, or 3) both N/O and q ion excesses. We argue that the BPT offsets at z ∼ 2 are not made by one of 1)-3) galaxy populations alone, but the composite of 1)-3) populations. We confirm that these 1)-3) populations also exist at z ∼ 0, such as GPs and SDSS low-mass and high-SFR galaxies (LMHSs).

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Section: Introductionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

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

Kojima

Ouchi

Nakajima

et al. 2017

Publications of the Astronomical Society of Japan

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show abstract

“…After iterating over the parent sample several times, the selection converges, yielding a reference sample of 475 objects that we refer to as the "reference H ii region sample." Objects in this sample have detections of [O ii] Electron temperatures are calculated using a fivelevel atom approximation and up-to-date atomic data (Sanders et al 2016). For the transition probabilities, we use values from the NIST MCHF database (Fischer & Tachiev 2014) for all ions.…”

Section: Abundances and Line Emission Of H II Regionsmentioning

confidence: 99%

“…Correcting strongline MZRs for biases can thus provide more robust determinations of the evolution of the MZR. However, potential evolution of physical conditions of star-forming regions with redshift may ultimately require a reevaluation of strong-line calibrations at high redshift (Steidel et al 2014;Sanders et al 2015;Shapley et al 2015). Even so, eliminating observational biases from z ∼ 0 strongline MZR measurements provides a more robust baseline relative to which metallicity evolution can be inferred.…”

Section: Application To the Z ∼ 0 Mzr And Fmrmentioning

confidence: 99%

Biases in Metallicity Measurements from Global Galaxy Spectra: The Effects of Flux Weighting and Diffuse Ionized Gas Contamination

Sanders

Shapley

Zhang

et al. 2017

ApJ

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142

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Galaxy metallicity scaling relations provide a powerful tool for understanding galaxy evolution, but obtaining unbiased global galaxy gas-phase oxygen abundances requires proper treatment of the various line-emitting sources within spectroscopic apertures. We present a model framework that treats galaxies as ensembles of H ii and diffuse ionized gas (DIG) regions of varying metallicities. These models are based upon empirical relations between line ratios and electron temperature for H ii regions, and DIG strong-line ratio relations from SDSS-IV MaNGA IFU data. Flux-weighting effects and DIG contamination can significantly affect properties inferred from global galaxy spectra, biasing metallicity estimates by more than 0.3 dex in some cases. We use observationally-motivated inputs to construct a model matched to typical local star-forming galaxies, and quantify the biases in strong-line ratios, electron temperatures, and direct-method metallicities as inferred from global galaxy spectra relative to the median values of the H ii region distributions in each galaxy. We also provide a generalized set of models that can be applied to individual galaxies or galaxy samples in atypical regions of parameter space. We use these models to correct for the effects of flux-weighting and DIG contamination in the local direct-method mass-metallicity and fundamental metallicity relations, and in the mass-metallicity relation based on strong-line metallicities. Future photoionization models of galaxy line emission need to include DIG emission and represent galaxies as ensembles of emitting regions with varying metallicity, instead of as single H ii regions with effective properties, in order to obtain unbiased estimates of key underlying physical properties.

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Observations of Ly$$\alpha $$ Emitters at High Redshift

Ouchi

2019

Lyman-Alpha as an Astrophysical and Cosmological Tool

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In this series of lectures, I review our observational understanding of highz Lyα emitters (LAEs) and relevant scientific topics. Since the discovery of LAEs in the late 1990s, significant progresses in LAE studies have been made over the past two decades by deep multi-wavelength observations. More than ten (one) thousand(s) of LAEs have been identified photometrically (spectroscopically) in optical and near-infrared data, and the redshifts of these LAEs range from z ∼ 0 to z ∼ 10. These large samples of LAEs are useful to address two major astrophysical issues, galaxy formation and cosmic reionization. Statistical studies have revealed the general picture of LAEs' physical properties: young stellar populations, remarkable luminosity function evolutions, compact morphologies, highly ionized inter-stellar media (ISM) with low metal/dust contents, low masses of dark-matter halos. Typical LAEs represent low-mass high-z galaxies, high-z analogs of dwarf galaxies, some of which are thought to be candidates of population III galaxies. These observational studies have also pinpointed rare bright Lyα sources extended over ∼ 10 − 100 kpc, dubbed Lyα blobs, whose physical origins are under debate. LAEs are used as probes of cosmic reionization history through the Lyα damping wing absorption given by the neutral hydrogen of the inter-galactic medium (IGM), which complement the cosmic microwave background radiation and 21cm observations targeting the epoch of reionization. The low-mass and highly-ionized population of LAEs can be major sources of cosmic reionization, and physical parameters including the ionizing photon escape fraction have been extensively investigated. The budget of ionizing photons for cosmic reionization has been constrained, although there remain large observational uncertainties in the parameters. Beyond these two established topics of LAEs, galaxy formation and cosmic reionization, several new usages of LAEs for science frontiers have been suggested such as the distribution of HI gas in the circum-galactic medium and filaments of large-scale structures. Ongoing 10 mclass optical telescope programs and future telescope projects, such as JWST, ELTs,

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THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3*

Cited by 316 publications

References 120 publications

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

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

Biases in Metallicity Measurements from Global Galaxy Spectra: The Effects of Flux Weighting and Diffuse Ionized Gas Contamination

Observations of Ly$$\alpha $$ Emitters at High Redshift

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