The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619

TL;DR

This study reports a precise measurement of the primordial deuterium-to-hydrogen ratio toward the QSO HS 0105+1619, using a high-column-density Lyman limit system at $z\approx2.536$ where D I is detected in five Lyman series transitions. The absorber is predominantly neutral with metallicity around 1% solar, supporting the interpretation that the measured D/H reflects primordial values. Combining this result with previous D/H measurements yields a weighted primordial value of $D/H=(3.0\pm0.4)\times10^{-5}$, translating to $\eta=(5.6\pm0.5)\times10^{-10}$ and $\Omega_b h^{2}=0.0205\pm0.0018$, in good agreement with CMB constraints and BBN predictions. The HS 0105+1619 data provide a notably secure, environment-diverse check on primordial D/H, reinforcing the standard cosmological model and constraining light-element synthesis during the early universe.

Abstract

We report the measurement of the primordial D/H abundance ratio towards QSO \object. The column density of the hydrogen in the $z \simeq 2.536$ Lyman limit system is high, \lnhi $= 19.422 \pm 0.009$ \cmm, allowing for the deuterium to be seen in 5 Lyman series transitions. The measured value of the D/H ratio towards QSO \object is found to be D/H$ = 2.54 \pm 0.23 \times 10^{-5}$. The metallicity of the system showing D/H is found to be $\simeq 0.01$ solar, indicating that the measured D/H is the primordial D/H within the measurement errors. The gas which shows D/H is neutral, unlike previous D/H systems which were more highly ionized. Thus, the determination of the D/H ratio becomes more secure since we are measuring it in different astrophysical environments, but the error is larger because we now see more dispersion between measurements. Combined with prior measurements of D/H, the best D/H ratio is now D/H$ = 3.0 \pm 0.4 \times 10^{-5}$, which is 10% lower than the previous value. The new values for the baryon to photon ratio, and baryonic matter density derived from D/H are $η= 5.6 \pm 0.5 \times 10^{-10} $ and \ob $=0.0205 \pm 0.0018$ respectively.

Figures (12)

• Figure 1: Spectrum of HS 0105+1619 . The upper panel shows the low resolution flux calibrated spectrum obtained with the Kast spectrograph. The lower panel shows the flux calibrated HIRES spectrum. The flux calibration was noisy at wavelengths less than 3800 Å and was not applied to the Lyman limit, which is not shown above for the HIRES spectrum.
• Figure 2: Lyman series absorption in the $z \simeq 2.536$ Lyman limit system towards HS 0105+1619 . The velocities shown are relative to the H I redshift of $z=2.535998$. The vertical scales are linear flux, from zero, and the lower traces are the $1\sigma$ error. The D I absorption is seen at $-82$ km s$^{-1}$ in Ly$\beta$ , Ly$\gamma$ , Ly-5, Ly-6 and Ly-7.
• Figure 3: Observed metal line absorption associated with the $z \simeq 2.536$ Lyman limit system. The metals are grouped according to ionization state and are organized by atomic mass. The low ionization lines have simple, narrow profiles centered near 0 km s$^{-1}$ .
• Figure 4: Spectral regions used to measure the H I column density. The upper panel shows the Ly$\alpha$ line, with the core and damping wing regions used in the fit shaded grey. The lower panel shows the absorption near the Lyman limit. Over-layed is the single component fit to the hydrogen with a column density of $\log N_{HI}$$=19.422$ cm$^{-2}$ from Table \ref{['dhlinetab']} .
• Figure 5: Ly$\alpha$ region of the $z \simeq 2.536$ Lyman limit system. Over-layed is the continuum fit (solid line) and the approximate $1 \sigma$ error to the continuum fit (dashed line).