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Register a new userThe cosmological baryon density from the deuterium to hydrogen ratio towards QSO absorption systems: D/H towards Q1243+3047
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We report the detection of Deuterium absorption at redshift 2.525659 towards Q1243+3047. We describe improved methods to estimate the Deuterium to Hydrogen abundance ratio (D/H) in absorption systems, including improved modeling of the continuum level, the Ly-alpha forest and the velocity structure of the absorption. Together with improved relative flux calibration, these methods give D/H = 2.42^+0.35_-0.25 x 10^-5 cm^-2 from our Keck-I HIRES spectra of Q1243+3047, where the error is from the uncertainty in the shape of the continuum level and the amount of D absorption in a minor second component. The measured D/H is likely the primordial value because the [O/H] = -2.79 +/- 0.05. This absorption system has a neutral Hydrogen column density of 19.73 +/- 0.04 cm^-2, it shows five D lines and is mostly ionized. The best estimate of the primordial D/H is 2.78^+0.44_-0.38 x 10^-5, from the log D/H values towards five QSOs. The dispersion in the five values is larger than we expect from their individual measurement errors and we suspect this is because some of these errors were underestimated. We observe a trend in D/H with neutral H column density that we also suspect is spurious. The D/H corresponds to a baryon-to-photon ratio ETA = 5.9 +/- 0.5 x 10^-10 and a cosmological baryon density Omega_b h^2 = 0.0214 +/- 0.0020 (9.3%) that agrees with values from the pre-MAP measurements of the anisotropy of the Cosmic Microwave Background.
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We present a measurement of the D/H abundance ratio in a metal-poor damped Lyman alpha (DLA) system along the sightline of QSO SDSS1558-0031. The DLA system is at redshift z = 2.70262, has a neutral column density of log(NHI)=20.67+/-0.05 cm^2, and a gas-phase metallicity [O/H]= -1.49 which indicates that deuterium astration is negligible. Deuterium absorption is observed in multiple Lyman series with a column density of log(NDI)=16.19+/-0.04 cm^2, best constrained by the deuterium Lyman-11 line. We measure log(D/H) = -4.48+/-0.06, which when combined with previous measurements along QSO sightlines gives a best estimate of log(D/H) = -4.55+/-0.04, where the 1-sigma error estimate comes from a jackknife analysis of the weighted means. Using the framework of standard big bang nucleosynthesis, this value of D/H translates into a baryon density of Omega_b h^2 = 0.0213 +/- 0.0013 +/- 0.0004 where the error terms represent the 1-sigma errors from D/H and the uncertainties in the nuclear reaction rates respectively. Combining our new measurement with previous measurements of D/H, we no longer find compelling evidence for a trend of D/H with NHI.
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 $eta = 5.6 pm 0.5 times 10^{-10} $ and ob $=0.0205 pm 0.0018$ respectively.
We have discovered a third quasar absorption system which is consistent with a low deuterium to hydrogen abundance ratio, D/H = 3.4 times 10^-5. The z ~ 2.8 partial Lyman limit system towards QSO 0130-4021 provides the strongest evidence to date against large D/H ratios because the H I absorption, which consists of a single high column density component with unsaturated high order Lyman series lines, is readily modeled -- a task which is more complex in other D/H systems. We have obtained twenty-two hours of spectra from the HIRES spectrograph on the W.M. Keck telescope, which allow a detailed description of the Hydrogen. We see excess absorption on the blue wing of the H I Lyman alpha line, near the expected position of Deuterium. However, we find that Deuterium cannot explain all of the excess absorption, and hence there must be contamination by additional absorption, probably H I. This extra H I can account for most or all of the absorption at the D position, and hence D/H = 0 is allowed. We find an upper limit of D/H < 6.7 times 10^-5 in this system, consistent with the value of D/H ~ 3.4 times 10^-5 deduced towards QSO 1009+2956 and QSO 1937-1009 by Burles and Tytler (1998a, 1998b). This absorption system shows only weak metal line absorption, and we estimate [Si/H] < -2.6 -- indicating that the D/H ratio of the system is likely primordial. All four of the known high redshift absorption line systems simple enough to provide useful limits on D are consistent with D/H = 3.4 +/- 0.25 times 10^-5. Conversely, this QSO provides the third case which is inconsistent with much larger values.
We report the detection of H2 in a zabs= 0.0963 Damped Lyman-{alpha} (DLA) system towards zem = 0.4716 QSO J1619+3342. This DLA has log N(H I) = 20.55 (0.10), 18.13 < log N(H2) < 18.40, [S/H] = -0.62 (0.13), [Fe/S] = -1.00 (0.17) and the molecular fraction -2.11 < log f(H2) < -1.85. The inferred gas kinetic temperature using the rotational level population is in the range 95 - 132 K. We do not detect C I or C II* absorption from this system. Using R- and V-band deep images we identify a sub-L* galaxy at an impact parameter of 14 kpc from the line of sight, having consistent photometric redshift, as a possible host for the absorber. We use the photoionization code CLOUDY to get the physical conditions in the H2 component using the observational constrains from H2, C I, C II* and Mg I. All the observations can be consistently explained if one or more of the following is true: (i) Carbon is underabundant by more than 0.6 dex as seen in halo stars with Z ~ 0.1 Z_sun, (ii) H I associated with H2 component is less than 50% of the H I measured along the line of sight and (iii) the H2 formation rate on the dust grains is at least a factor two higher than what is typically used in analytic calculations for Milky Way interstellar medium. Even when these are satisfied, the gas kinetic temperature in the models are much lower than what is inferred from the ortho-to-para ratio of the molecular hydrogen. Alternatively the high kinetic temperature could be a consequence of contribution to the gas heating from non-radiative heating processes seen in hydrodynamical simulations.
We report a further analysis of the ratio of deuterium to hydrogen (D/H) using HST spectra of the z=0.701 Lyman limit system towards the QSO PG1718+481. Initial analyses of this absorber found it gave a high D/H value, 1.8 - 3.1 times 10^{-4} (Webb et al. 1998), inconsistent with several higher redshift measurements. It is thus important to critically examine this measurement. By analysing the velocity widths of the DI, HI and metal lines present in this system, Kirkman et al. (2001) report that the additional absorption in the blue wing of the lya line can not be DI, with a confidence level of 98%. Here we present a more detailed analysis, taking into account possible wavelength shifts between the three sets of HST spectra used in the analysis. We find that the constraints on this system are not as strong as those claimed by Kirkman et al. The discrepancy between the parameters of the blue wing absorption and the parameters expected for DI is marginally worse than 1 sigma. Tytler et al.(1999) commented on the first analysis of Webb et al.(1997,1998), reporting the presence of a contaminating lower redshift Lyman limit system, with log[N(HI)] = 16.7 at z=0.602, which biases the N(HI) estimate for the main system. Here we show that this absorber actually has log[N(HI)] < 14.6 and does not impact on the estimate of N(HI) in the system of interest at z = 0.701. The purpose of the present paper is to highlight important aspects of the analysis which were not explored in previous studies, and hence help refine the methods used in future analyses of D/H in quasar spectra.
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