Abundance scaling in stars, nebulae and galaxies

Nicholls, David C.; Sutherland, Ralph S.; Dopita, M. A.; Kewley, Lisa J.; Groves, Brent

doi:10.1093/mnras/stw3235

Cited by 108 publications

(129 citation statements)

References 101 publications

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“…Second, there is limited knowledge on how iron abundances relative to α−element (e.g, O, Mg, Si, S and Ca) abundance change over cosmic time and in different galactic environments (eg., Wolfe et al 2005;Kobayashi et al 2006;Yuan et al 2015). In addition, there is a lack of consistency in abundance scale used in stellar atmosphere modelling, stellar evolutionary tracks and nebular models (Nicholls et al 2016 (2016), then we would reach the same conclusion as Steidel et al (2016) that our stellar abundance is [Fe/H] ∼ −1.0. In this case, we cannot completely rule out extremely low metallicity scenarios to explain the distribution of galaxies in the Hα EW vs [340] − [550] colour space.…”

Section: Stellar Metallicitysupporting

confidence: 68%

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Nanayakkara

Glazebrook

Kacprzak

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We use the ZFIRE a survey to investigate the high mass slope of the initial mass function (IMF) for a mass-complete (log 10 (M * /M ) ∼ 9.3) sample of 102 star-forming galaxies at z ∼ 2 using their Hα equivalent widths (Hα-EW) and rest frame optical colours. We compare dust-corrected Hα-EW distributions with predictions of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic stellar population models. We find an excess of high Hα-EW galaxies that are up to 0.3-0.5 dex above the model-predicted Salpeter IMF locus and the Hα-EW distribution is much broader (10-500Å) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity, and the IMF upper-mass cutoff. IMF variations and/or highly rotating extreme metal poor stars (Z∼ 0.1Z ) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest Hα-EWs would require very shallow slopes (Γ > −1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z 2 show distinct differences from local populations and there is no simple physical model to explain the large variation in Hα-EWs at z ∼ 2.

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Section: Stellar Metallicitysupporting

confidence: 68%

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Nanayakkara

Glazebrook

Kacprzak

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…These models are applied to the study of Herbig-Haro (HH) objects in the second paper in this series (Dopita & Sutherland, 2017: in press). -The X-ray and Ionising efficiency factors.…”

Section: Discussionmentioning

confidence: 99%

“…This much improved MAPPINGS V code 2 will be discussed in detail in a forthcoming paper (Sutherland & Dopita, 2017) which provides new cooling function computations for optically thin plasmas. This is based on greatly expanded atomic data of the CHIANTI 8 database.…”

Section: The Mappings Codementioning

confidence: 99%

Effects of Preionization in Radiative Shocks. I. Self-consistent Models

Sutherland

Dopita

2017

ApJS

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In this paper we treat the pre-ionisation problem in shocks over the velocity range 10 < v s < 1500 km/s in a self-consistent manner. We identify four distinct classes of solution controlled by the value of the shock precursor parameter, Ψ = Q/v s , where Q is the ionization parameter of the UV photons escaping upstream. This parameter determines both the temperature and the degree of ionisation of the gas entering the shock. In increasing velocity the shock solution regimes are cold neutral precursors (v s 40 km/s), warm neutral precursors (40 v s 75 km/s), warm partly-ionized precursors (75 v s 120 km/s), and fast shocks in which the pre-shock gas is in photoionisation equilibrium, and is fully ionized. The main effect of a magnetic field is to push these velocity ranges to higher values, and to limit the post-shock compression. In order to facilitate comparison with observations of shocks, we provide a number of convenient scaling relationships for parameters such as post-shock temperature, compression factors, cooling lengths, and Hβ and X-ray luminosity.

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“…For our nebular models, we adopt the solar reference abundances of Anders & Grevesse (1989), corresponding to a solar value of Z = 0.020 ≡ 12 + log(O/H) = 8.93. Abundances at other metallicities of Z = 0.001, Z = 0.004, Z = 0.008, and Z = 0.040 are obtained by applying the Local Galactic Concordance (LGC) abundance scaling prescription described by Nicholls et al (2017). Typically nebular models adopt a linear scaling for abundances with metallicity, with the exception of a few elements (e.g.…”

Section: Abundance Setsmentioning

confidence: 99%

“…These abundances account for the nonlinear scaling of alpha elements (including oxygen) with iron and account for primary and secondary production mechanisms for carbon and nitrogen. The variation with O/H of several elements, such as C, N, and Fe, is shown in Nicholls et al (2017). We note that this abundance scale is calibrated from MW stellar abundances and may not be appropriate for dwarf galaxies or galaxies with instantaneous SFHs (see Nicholls et al 2017, for a detailed explanation of abundance scaling with metallicity).…”

Section: Abundance Setsmentioning

confidence: 99%

Comparison of Theoretical Starburst Photoionization Models for Optical Diagnostics

D'Agostino

Kewley

Groves

et al. 2019

ApJ

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We study and compare different examples of stellar evolutionary synthesis input parameters used to produce photoionisation model grids using the mappings v modelling code. The aim of this study is to (a) explore the systematic effects of various stellar evolutionary synthesis model parameters on the interpretation of emission lines in optical strong-line diagnostic diagrams, (b) characterise the combination of parameters able to reproduce the spread of local galaxies located in the star-forming region in the Sloan Digital Sky Survey, and (c) investigate the emission from extremely metal-poor galaxies using photoionisation models. We explore and compare the stellar input ionising spectrum (stellar population synthesis code [Starburst99, SLUG, BPASS], stellar evolutionary tracks, stellar atmospheres, star-formation history, sampling of the initial mass function) as well as parameters intrinsic to the H ii region (metallicity, ionisation parameter, pressure, H ii region boundedness). We also perform a comparison of the photoionisation codes mappings and cloudy. On the variations in the ionising spectrum model parameters, we find that the differences in strong emission-line ratios between varying models for a given input model parameter are small, on average ∼0.1 dex. An average difference of ∼0.1 dex in emission-line ratio is also found between models produced with mappings and cloudy. Large differences between the emission-line ratios are found when comparing intrinsic H ii region parameters. We find that low-metallicity galaxies are better explained by a density-bounded H ii region and higher pressures better encompass the spread of galaxies at high redshift.

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Abundance scaling in stars, nebulae and galaxies

Cited by 108 publications

References 101 publications

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

Effects of Preionization in Radiative Shocks. I. Self-consistent Models

Comparison of Theoretical Starburst Photoionization Models for Optical Diagnostics

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