Revised Primordial Helium Abundance Based on New Atomic Data

Abstract

We have derived a primordial helium abundance of Yp = 0.2477 +- 0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Yp by 0.0086, a very significant amount. By combining our Yp result with the predictions made by the standard Big Bang nucleosynthesis model, we find a baryon-to-photon ratio, \eta, in excellent agreement both with the \eta value derived by the primordial deuterium abundance value observed in damped Lyman-\alpha systems and with the one obtained from the WMAP observations.Comment: 35 pages, 1 figure. AAS LaTeX. Accepted for publication in the Astrophysical Journal. The accepted version is more explicit in the description of the procedure and in the treatment of errors with respect to the first version, and the final numerical result is slightly changed. Scheduled for ApJ, Vol. 667, Sept 20, 200

Simulating the growth of intermediate-mass black holes

“…Here, T is the gas temperature, R is the gas constant and µ is the mean molecular weight which, for a primordial gas with helium fraction Yp = 0.2477 (Peimbert et al 2007) and no metals Zp = 0, is equal to µ = 1.15. The gas thermal pressure is given by the usual equation for ideal gases:…”

Galactic evolution of D, 3He and 4He

“…(1) Cyburt et al (2008); (2) Pettini et al (2008); (3) Geiss & Gloeckler (1998); (4) Linsky et al (2006); (5) Hébrard et al (2005); (6) Prodanović et al (2009); (7) Bania et al (2002); (8) Gloeckler & Geiss (1996); (9) Peimbert et al (2007); (10) Steigman (2007); (11) Asplund et al (2009). can not be reproduced by the models, independently of how many low-mass stars burn their 3 He on the RGB.…”

“…The vertical band crossing all panels corresponds to the η10 value derived from analysis of five-years WMAP data on the CMB anisotropy (Dunkley et al 2009). Also shown are the most recent estimates of the primordial abundances of D, 3 He and 4 He from observations, along with the allowed ranges of values for η10 (boxes; Bania et al 2002, Peimbert et al 2007, Steigman 2007, Pettini et al 2008). …”

Uncertainties in nebular helium abundances

“…This was, in part, in response to recent improvements to the atomic data (Porter, Ferland, & MacAdam 2007) which have resulted in significant changes to the derived helium abundances of HII regions (Izotov et al 2007;Peimbert, Luridiana, & Peimbert 2007). Additionally, we have investigated combining the minimizations, previously based on the hydrogen lines and the helium lines separately, into a single minimization, which is inherently self-consistent.…”

“…One well known effect shown in the plot is the small error bars relative to the differences between determinations and relative to the currently favored value. In 2004, Keith Olive and I (Olive & Skillman 2004, hereafter OS04) attempted to account for most of the important statistical and systematic uncertainties, and, in a reanalysis of data from the literature (Izotov & Thuan 1998;Peimbert, Peimbert, & Ruiz 2000), found significantly larger uncertainties for helium abundance determinations for individual objects and a resulting larger uncertainty in the primordial helium abundance. In the plot, this result appears as a giant step backwards as the uncertainty in the primordial helium abundance is comparable to uncertainties associated with determinations from the 1980's.…”