The primordial helium abundance from observations of extragalactic H II regions

Metallicity is a key parameter that controls many aspects in the formation and evolution of stars and galaxies. In this review we focus on the metal deficient galaxies, in particular the most metal-poor ones, because they play a crucial rôle in the cosmic scenery. We first set the stage by discussing the difficult problem of defining a global metallicity and how this quantity can be measured for a given galaxy. The mechanisms that control the metallicity in a galaxy are reviewed in detail and involve many aspects of modern astrophysics: galaxy formation and evolution, massive star formation, stellar winds, chemical yields, outflows and inflows etc. Because metallicity roughly scales as the galactic mass, it is among the dwarfs that the most metalpoor galaxies are found. The core of our paper reviews the considerable progress made in our understanding of the properties and the physical processes that are at work in these objects. The question on how they are related and may evolve from one class of objects to another is discussed. While discussing metal-poor galaxies in general, we present a more detailed discussion of a few very metal-poor blue compact dwarf galaxies like IZw18. Although most of what is known relates to our local universe, we show that it pertains to our quest for primeval galaxies and is connected to the question of the origin of structure in the universe. We discuss what QSO absorption lines and known distant galaxies tell us already? We illustrate the importance of star-forming metal-poor galaxies for the determination of the primordial helium abundance, their use as distance indicator and discuss the possibility to detect nearly metal-free galaxies at high redshift from Lyα emission.

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“…11), a value slightly higher than that of Pagel et al (1992), i.e. more in line with the predictions of the Standard Big Bang nucleosynthesis.…”

Section: The Primordial Helium Abundancesupporting

confidence: 81%

The most metal-poor galaxies

Kunth

Östlin

2000

Astronomy and Astrophysics Review

375

428

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“…As in our previous work (see Izotov et al 2007Izotov et al , 2013Izotov & Thuan 2010, and references therein), we determine the primordial He mass fraction Yp by fitting the data points in the Y -O/H plane with a linear regression line of the form (Peimbert & Torres-Peimbert 1974, 1976Pagel et al 1992)…”

Section: Primordial He Mass Fraction Ypmentioning

confidence: 99%

A new determination of the primordial He abundance using the He i λ10830 Å emission line: cosmological implications

Izotov¹,

Thuan²,

Гусева³

2014

Monthly Notices of the Royal Astronomical Society

254

355

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We present near-infrared spectroscopic observations of the high-intensity He i λ10830Å emission line in 45 low-metallicity H ii regions. We combined these NIR data with spectroscopic data in the optical range to derive the primordial He abundance. The use of the He i λ10830Å line, the intensity of which is very sensitive to the density of the H ii region, greatly improves the determination of the physical conditions in the He + zone. This results in a considerably tighter Y -O/H linear regression compared to all previous studies. We extracted a final sample of 28 H ii regions with Hβ equivalent width EW(Hβ) 150Å, excitation parameter O 2+ /O 0.8, and with helium mass fraction Y derived with an accuracy better than 3%. With this final sample we derived a primordial 4 He mass fraction Y p = 0.2551 ± 0.0022. The derived value of Y p is higher than the one predicted by the standard big bang nucleosynthesis (SBBN) model. Using our derived Y p together with D/H = (2.53±0.04)×10 −5 , and the χ 2 technique, we found that the best agreement between these light element abundances is achieved in a cosmological model with a baryon mass density Ω b h 2 = 0.0240±0.0017 (68% CL), ±0.0028 (95.4% CL), ±0.0034 (99% CL) and an effective number of neutrino species N eff = 3.58±0.25 (68% CL), ±0.40 (95.4% CL), ±0.50 (99% CL). A non-standard value of N eff is preferred at the 99% CL, implying the possible existence of additional types of neutrino species.

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“…Some authors postulate that the interstellar gas in such galaxies may become "contaminated" by nitrogen-rich and helium-rich winds of the evolved stars (Pagel, Terlevich, & Melnick 1986). For this reason, such galaxies are often omitted from studies seeking to use the chemical properties of low-mass galaxies to measure the primordial helium abundance and other fundamental cosmological parameters (Pagel et al 1992;Olive & Steigman 1995).…”

Section: Chemical Abundances In Wolf-rayet Galaxiesmentioning

confidence: 99%

Chemical enrichment from massive stars in starbursts

Kobulnicky

1999

Symp. - Int. Astron. Union

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Abstract.The warm ionized gas in low-mass, metal-poor starforming galaxies is chemically homogeneous despite the prevalence of large H II regions which contain hundreds of evolved massive stars, supernovae, and WolfRayet stars with chemically-enriched winds. Galaxies with large WolfRayet star content are chemically indistinguishable from other vigorously star-forming galaxies. Furthermore, no significant localized chemical fluctuations are present in the vicinity of young star clusters, despite large expected chemical yields of massive stars. An ad-hoc fine-tuning of the release, dispersal and mixing of the massive star ejecta could give rise to the observed homogeneity, but a more probable explanation is that fresh ejecta from massive stars reside in a hard-to-observe hot or cold phase. In any case, the observed chemical homogeneity indicates that heavy elements which have already mixed with the warm interstellar medium (thus accessible to optical spectroscopy) are homogeneously dispersed over scales exceeding 1 kpc. Mixing of fresh ejecta with the surrounding warm ISM apparently requires longer than the lifetimes of typical H II regions (>10 7 yrs). The lack of observed localized chemical enrichments is consistent with a scenario whereby freshly-synthesized metals from massive stars are expelled into the halos of galaxies in a hot, 10 6 K phase by supernova-driven winds before they cool and "rain" back down upon the galaxy, creating gradual enrichments on spatial scales >1 kpc.

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The primordial helium abundance from observations of extragalactic H II regions

Cited by 538 publications

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The most metal-poor galaxies

The most metal-poor galaxies

A new determination of the primordial He abundance using the He i λ10830 Å emission line: cosmological implications

Chemical enrichment from massive stars in starbursts

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