Improving Predictions for Helium Emission Lines

Benjamin, Robert A.; Skillman, Evan D.; Smits, Derck P.

doi:10.1086/306923

Cited by 272 publications

(412 citation statements)

References 67 publications

(80 reference statements)

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“…Third, the He i emission lines should be corrected for fluorescent excitation, parametrised by the optical depth τ (λ3889) of the He i λ3889 emission line. We used the correction factors for fluorescent excitation derived by Benjamin et al (1999Benjamin et al ( , 2002.…”

Section: Adjustment Of Nir To Optical Spectramentioning

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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Section: Adjustment Of Nir To Optical Spectramentioning

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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“…The abundances of He i and He ii were computed using the equations of Benjamin et al (1999) in two density regimes, that is Ne > 1,000 and 1,000 cm −3 . Clegg's collisional populations were taken into account (Clegg 1987).…”

Section: Spectral Analysis and Determination Of The Physical And Chemmentioning

confidence: 99%

NGC 55: a disc galaxy with flat abundance gradients

Magrini

Gonçalves

Vajgel

2016

Mon. Not. R. Astron. Soc.

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We present new spectroscopic observations obtained with GMOS@Gemini-S of a sample of 25 H ii regions located in NGC 55, a late-type galaxy in the nearby Sculptor group. We derive physical conditions and chemical composition through the T e -method for 18 H ii regions, and strong-line abundances for 22 H ii regions. We provide abundances of He, O, N, Ne, S, Ar, finding a substantially homogenous composition in the ionised gas of the disc of NGC 55, with no trace of radial gradients. The oxygen abundances, both derived with T e -and strong-line methods, have similar mean values and similarly small dispersions: 12+log(O/H)=8.13±0.18 dex with the former and 12+log(O/H)=8.17±0.13 dex with the latter. The average metallicities and the flat gradients agree with previous studies of smaller samples of H ii regions and there is a qualitative agreement with the blue supergiant radial gradient as well. We investigate the origin of such flat gradients comparing NGC 55 with NGC 300, its companion galaxy, which is also twin of NGC 55 in terms of mass and luminosity. We suggest that the differences in the metal distributions in the two galaxies might be related to the differences in their K-band surface density profile. The flatter profile of NGC 55 probably causes in this galaxy higher infall/outflow rates than in similar galaxies. This likely provokes a strong mixing of gas and a re-distribution of metals.

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“…A new grid of emissivities improving the predictions for He emission lines are now available (Benjamin et al 1999). Problems inherent to the observations and reduction processes have also been considered and have led to at least two distinct approaches.…”

Section: The Primordial Helium Abundancementioning

confidence: 99%

The most metal-poor galaxies

Kunth

Östlin

2000

Astronomy and Astrophysics Review

375

428

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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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Improving Predictions for Helium Emission Lines

Cited by 272 publications

References 67 publications

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

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

NGC 55: a disc galaxy with flat abundance gradients

The most metal-poor galaxies

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