Abstract
The spectrum of the zem = 2.63 quasar Q1009+2956 has been observed extensively on the Keck telescope. The Lyman limit absorption system zabs = 2.504 was previously used to measure D/H by ...Burles & Tytler using a spectrum with signal to noise (S/N) approximately 60 per pixel in the continuum near Ly α at zabs = 2.504. The larger data set now available combines to form an exceptionally high S/N spectrum, around 147 per pixel. Several heavy element absorption lines are detected in this Lyman limit system, providing strong constraints on the kinematic structure. We explore a suite of absorption system models and find that the deuterium feature is likely to be contaminated by weak interloping Ly α absorption from a low column density Hi cloud, reducing the expected D/H precision. We find D/H $=2.48^{+0.41}_{-0.35} \times 10^{-5}$ for this system. Combining this new measurement with others from the literature and applying the method of Least Trimmed Squares to a statistical sample of 15 D/H measurements results in a ‘reliable’ sample of 13 values. This sample yields a primordial deuterium abundance of (D/H)p = (2.545 ± 0.025) × 10−5. The corresponding mean baryonic density of the Universe is Ωbh2 = 0.02174 ± 0.00025. The quasar absorption data are of the same precision as, and marginally inconsistent with, the 2015 CMB Planck (TT+lowP+lensing) measurement, Ωbh2 = 0.02226 ± 0.00023. Further quasar and more precise nuclear data are required to establish whether this is a random fluctuation.
Abstract
The primordial deuterium abundance probes fundamental physics during the big bang nucleosynthesis and can be used to infer cosmological parameters. Observationally, the abundance can be ...measured using absorbing clouds along the lines of sight to distant quasars. Observations of the quasar PKS1937–101 contain two absorbers for which the deuterium abundance has previously been determined. Here, we focus on the higher redshift one at z
abs = 3.572. We present new observations with significantly increased signal-to-noise ratio that enable a far more precise and robust measurement of the deuterium to hydrogen column density ratio, resulting in D i/H i = 2.62 ± 0.05 × 10−5. This particular measurement is of interest because it is amongst the most precise assessments to date and it has been derived from the second lowest column-density absorber N(H i) = 17.9 cm−2 that has so-far been utilized for deuterium abundance measurements. The majority of existing high-precision measurements were obtained from considerably higher column density systems i.e. N(H i) > 19.4 cm−2. This bodes well for future observations as low column density systems are more common.
The primordial deuterium abundance is an important tracer of the fundamental physics taking place during big bang nucleosynthesis. It can be determined from absorption features along the line of ...sight to distant quasars. The quasar PKS 1937-1009 contains two absorptions systems that have been used to measure the primordial deuterium abundance, the lower redshift one being at zabs = 3.256. New observations of this absorber are of a substantially higher signal-to-noise ratio and thus permit a significantly more robust estimate of the primordial deuterium abundance, leading to a D I/H I ratio of 2.45 plus or minus 0.28 x 10 super( -5). Whilst the precision of the new measurement presented here is below that obtained from the recent cosmological parameter measurements by the Planck Surveyor, our analysis illustrates how a statistical sample obtained using similarly high spectral signal-to-noise ratio can make deuterium a competitive and complementary cosmological parameter estimator and provide an explanation for the scatter seen between some existing deuterium measurements.
Oxidative maturation of secretory and membrane proteins in the endoplasmic reticulum (ER) is powered by Ero1 oxidases. To prevent cellular hyperoxidation, Ero1 activity can be regulated by ...intramolecular disulphide switches. Here, we determine the redox‐driven shutdown mechanism of Ero1α, the housekeeping Ero1 enzyme in human cells. We show that functional silencing of Ero1α in cells arises from the formation of a disulphide bond—identified by mass spectrometry—between the active‐site Cys94 (connected to Cys99 in the active enzyme) and Cys131. Competition between substrate thiols and Cys131 creates a feedback loop where activation of Ero1α is linked to the availability of its substrate, reduced protein disulphide isomerase (PDI). Overexpression of Ero1α‐Cys131Ala or the isoform Ero1β, which does not have an equivalent disulphide switch, leads to augmented ER oxidation. These data reveal a novel regulatory feedback system where PDI emerges as a central regulator of ER redox homoeostasis.
There is a long-standing discrepancy between galaxy cluster masses determined from X-ray and gravitational lensing observations of which Abell 1689 is a well studied example. In this work, we take ...advantage of 180 ks of Chandra X-ray observations and a new weak gravitational study based on a Hubble Space Telescope mosaic covering the central 1.8 Mpc X 1.4 Mpc to eliminate the mass discrepancy. In contrast to earlier X-ray analyses where the very circular surface brightness has been inferred as Abell 1689 being spherically symmetric and in hydrostatic equilibrium, a hardness ratio map analysis reveals a regular and symmetric appearing main clump with a cool core plus some substructure in the northeastern part of the cluster. The gravitational lensing mass model supports the interpretation of Abell 1689 being composed of a main clump, which is possibly a virialized cluster, plus some substructure. In order to avoid complications and misinterpretations due to X-ray emission from the substructure, we exclude it from the mass reconstruction. Comparing X-ray and lensing mass profiles of the regular main part only, shows no significant discrepancy between the two methods and the obtained mass profiles are consistent over the full range where the mass can be reconstructed from X-rays (out to 1Mpc). The obtained cluster mass within 875 kpc derived from X-rays alone is (6.4 ± 2.1) X 1014 M compared to a weak lensing mass of (8.6 ± 3.0) X 1014 M within the same radius.
ABSTRACT Some dark matter candidates, e.g., sterile neutrinos, provide observable signatures in the form of mono-energetic line emission. We present the first search for dark matter line emission in ...the range in a pointed observation of the Bullet Cluster with NuSTAR. We do not detect any significant line emission and instead we derive upper limits (95% CL) on the flux, and interpret these constraints in the context of sterile neutrinos and more generic dark matter candidates. NuSTAR does not have the sensitivity to constrain the recently claimed line detection at , but improves on the constraints for energies of .
Context. The sterile neutrino is an excellent dark matter candidate, which can be searched for in a wide range of astrophysical sites. It has previously been shown that the optimal search strategy is ...to consider dwarf galaxies belonging to the Milky Way. Aims. We search for line emission from decaying dark matter. Methods. We analyse publicly available Chandra X-ray observations of the dwarf galaxy Draco. Results. The Draco and blank sky (background) spectra are nearly identical in shape, which allows us to conclude: i) dwarf spheroidals are ideal for studying dark matter X-ray emission since the baryonic noise is impressively low; ii) there is very little room for line emission, which leads to constraints in the mass-mixing angle parameter space of the sterile neutrino. We compare the standard flux derivation method to a very conservative rebinning approach. The resulting constraints are strongly dependent on the chosen method.
The z abs = 2.504 Lyman Limit absorption system (LLS) towards Q1009+2956 has previously been used to estimate the primordial deuterium abundance. Since the initial measurement by Burles & Tytler 1, ...this quasar has been observed extensively with the Keck telescope, providing a substantial increase in signal-to-noise (from 60 to 147 at continuum level of Ly-α at z abs = 2.504). We explore a set of different models for the absorption system and find that the deuterium feature is contaminated by Ly-α absorption from a low column density HI cloud. This significantly limits precision to which one can estimate the D/H ratio in this LLS. Our final result for this system \(\text{D/H}=2.48_{-0.35}^{+0.41}\times {{10}^{-5}}\) has the same relative uncertainty of 17% as the previous estimate by 1 despite the far higher signal-to-noise of our dataset. A weighted mean of 13 D/H measurements available in the literature (including our result) gives the primordial deuterium abundance of (D/H)p = (2.545 ± 0.025) × 10−5 and the corresponding baryon density of the Universe of Ωb h 2 = 0.02174 ± 0.00025 marginally inconsistent with the 2015 Planck CMB data. More measurements of the deuterium abundance in quasar spectra are needed to check this tension.
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