Systematic Effects and a New Determination of the Primordial Abundance of 4He and dY/dZ from Observations of Blue Compact Galaxies

By Y. Izotov, T. Thuan. 2003

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We use spectroscopic observations of a sample of 82 H II regions in 76 blue compact galaxies to determine the primordial helium abundance Yp and the slope dY/dZ from the Y-O/H linear regression. To improve the accuracy of the dY/dZ measurement, we have included new spectrophotometric observations of 33 H II regions that span a large metallicity range, with oxygen abundance 12 + log(O/H) varying between 7.43 and 8.30 (Z☉/30 ≤ Z ≤ Z☉/4). Most of the new galaxies were selected from the First Byurakan, the Hamburg/SAO, and the University of Michigan objective prism surveys. For a subsample of seven H II regions, we derive the He mass fraction taking into account known systematic effects, including collisional and fluorescent enhancements of He I emission lines, collisional excitation of hydrogen emission, underlying stellar He I absorption, and the difference between the temperatures Te(He II) in the He+ zone and Te(O III) derived from the collisionally excited [O III] lines. We find that the net result of all the systematic effects combined is small, changing the He mass fraction by less than 0.6%. By extrapolating the Y versus O/H linear regression to O/H = 0 for seven H II regions of this subsample, we obtain Yp = 0.2421 ± 0.0021 and dY/dO = 5.7 ± 1.8, which corresponds to dY/dZ = 3.7 ± 1.2, assuming the oxygen mass fraction to be O = 0.66Z. In the framework of the standard big bang nucleosynthesis theory, this Yp corresponds to Ωbh2 = 0.012, where h is the Hubble constant in units of 100 km s-1 Mpc-1. This is smaller at the 2 σ level than the value obtained from recent deuterium abundance and microwave background radiation measurements. The linear regression slope dY/dO = 4.3 ± 0.7 (corresponding to dY/dZ = 2.8 ± 0.5) for the whole sample of 82 H II regions is similar to that derived for the subsample of seven H II regions, although it has a considerably smaller uncertainty.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/dcad6c3b5ce1983814884fe51195c58f61b52721

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Citations in the corpus

Galaxy UV-luminosity function and reionization constraints on axion dark matter (2014, background): “The primordial helium and hydrogen abundances are consistent with both CMB measurements (Komatsu et al. 2011) and estimates from low-metallicity extragalactic regions (Izotov & Thuan 2004; Steigman 2007).”
Revised Primordial Helium Abundance Based on New Atomic Data (2007, methodology): “Fukugita & Kawasaki (2006), based on a reanalysis of the Izotov & Thuan (2004) sample of 33 H ii regions, determined a value of Yp ¼ 0:250 0:004.”
The Primordial Abundance of 4He: A Self-consistent Empirical Analysis of Systematic Effects in a Large Sample of Low-Metallicity H II Regions (2007, methodology): “Therefore, for consistency with our previous work, we have adopted the Whitford (1958) reddening law with RV ¼ 3:2, the same as the one used by Izotov et al. (1994, 1997) and Izotov & Thuan (1998a, 2004).”
The Adequacy of Stellar Evolution Models for the Interpretation of the Color-Magnitude Diagrams of Resolved Stellar Populations (2005, background): “Current empirical estimates of Yp based on measurements in low-metallicity extragalactic HII regions agree within 5% with Yp in the range of 0.230–0.242 (see Olive, Steigman & Skillman 1997; Luridiana et al. 2003; Izotov & Thuan 2004).”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: POWER SPECTRA AND WMAP-DERIVED PARAMETERS (2010, background): “…as a function of metallicity can be observed and the relation can be regressed to zero metallicity, which is presumed to give the primordial abundance (Gruenwald et al. 2002; Izotov & Thuan 2004; Olive & Skillman 2004; Fukugita & Kawasaki 2006; Peimbert et al. 2007) as reviewed by Steigman (2007).”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2010, result): “This value is broadly consistent with the helium abundances estimated from observations of low-metallicity extragalactic ionized (HII) regions, Yp ≃ 0.24 − 0.25 (Gruenwald et al. 2002; Izotov & Thuan 2004; Olive & Skillman 2004; Fukugita & Kawasaki 2006; Peimbert et al. 2007).”
THE MASS–METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES (2012, unknown): “…2003b, 2004, 2009, 2011), Hägele et al. (2008), Hawley (1978), Hodge & Miller (1995), Izotov et al. (1994, 1997, 1999, 2001, 2004, 2009, 2011), Izotov & Thuan (1998a, 1998b, 2004), Kehrig et al. (2004, 2011), Kennicutt & Skillman (2001), Kennicutt et al. (2003), Kinkel & Rosa (1994),…”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, background): “…SDSS and a representative sample of metal-rich H ii regions with well-measured electron temperatures (red squares; Garnett et al. 1997; van Zee et al. 1998; Kennicutt et al. 2003a; Kniazev et al. 2004; Bresolin et al. 2004, 2005; Izotov & Thuan 2004; Izotov et al. 2006; Rosolowsky & Simon 2008).”
The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey (2005, methodology): “This sample is the same as in Izotov et al. (2004), with the addition of galaxies from Izotov & Thuan (2004a).”