We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman α system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected ...from the SDSS DR5 DLA sample in a uniform way. We analyse the metallicities and kinematic diagnostics, including the velocity width of 90 per cent of the optical depth, Δv
90, and the equivalent widths of the Si ii λ1526 (W
λ1526), C iv λ1548 and Mg ii λ2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM ∼ 71 km s−1), we derived metallicities from metal transitions which absorbed at most 35 per cent of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample, 〈Z〉 = (−0.04 ± 0.13)z − (1.06 ± 0.36), consistent with no evolution over the redshift range z ∼ 2.2, 4.4, but note that the majority of our sample falls at z ∼ 2.2, 3.5. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median Δv
90 and W
λ1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. who found 〈Z〉 = (−0.22 ± 0.03)z − (0.65 ± 0.09) over z ∼ 0, 5, several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. estimate.
Loss of skeletal integrity during ageing and disease is associated with an imbalance in the opposing actions of osteoblasts and osteoclasts
. Here we show that intrinsic ageing of skeletal stem cells ...(SSCs)
in mice alters signalling in the bone marrow niche and skews the differentiation of bone and blood lineages, leading to fragile bones that regenerate poorly. Functionally, aged SSCs have a decreased bone- and cartilage-forming potential but produce more stromal lineages that express high levels of pro-inflammatory and pro-resorptive cytokines. Single-cell RNA-sequencing studies link the functional loss to a diminished transcriptomic diversity of SSCs in aged mice, which thereby contributes to the transformation of the bone marrow niche. Exposure to a youthful circulation through heterochronic parabiosis or systemic reconstitution with young haematopoietic stem cells did not reverse the diminished osteochondrogenic activity of aged SSCs, or improve bone mass or skeletal healing parameters in aged mice. Conversely, the aged SSC lineage promoted osteoclastic activity and myeloid skewing by haematopoietic stem and progenitor cells, suggesting that the ageing of SSCs is a driver of haematopoietic ageing. Deficient bone regeneration in aged mice could only be returned to youthful levels by applying a combinatorial treatment of BMP2 and a CSF1 antagonist locally to fractures, which reactivated aged SSCs and simultaneously ablated the inflammatory, pro-osteoclastic milieu. Our findings provide mechanistic insights into the complex, multifactorial mechanisms that underlie skeletal ageing and offer prospects for rejuvenating the aged skeletal system.
During progression of atherosclerosis, myeloid cells destabilize lipid-rich plaques in the arterial wall and cause their rupture, thus triggering myocardial infarction and stroke. Survivors of acute ...coronary syndromes have a high risk of recurrent events for unknown reasons. Here we show that the systemic response to ischaemic injury aggravates chronic atherosclerosis. After myocardial infarction or stroke, Apoe-/- mice developed larger atherosclerotic lesions with a more advanced morphology. This disease acceleration persisted over many weeks and was associated with markedly increased monocyte recruitment. Seeking the source of surplus monocytes in plaques, we found that myocardial infarction liberated haematopoietic stem and progenitor cells from bone marrow niches via sympathetic nervous system signalling. The progenitors then seeded the spleen, yielding a sustained boost in monocyte production. These observations provide new mechanistic insight into atherogenesis and provide a novel therapeutic opportunity to mitigate disease progression.
Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous group of diseases with approximately 45 different causative genes described. The aims of this study were to determine ...the frequency of different genes in a large cohort of patients with CMT and devise guidelines for genetic testing in practice.
The genes known to cause CMT were sequenced in 1607 patients with CMT (425 patients attending an inherited neuropathy clinic and 1182 patients whose DNA was sent to the authors for genetic testing) to determine the proportion of different subtypes in a UK population.
A molecular diagnosis was achieved in 62.6% of patients with CMT attending the inherited neuropathy clinic; in 80.4% of patients with CMT1 (demyelinating CMT) and in 25.2% of those with CMT2 (axonal CMT). Mutations or rearrangements in PMP22, GJB1, MPZ and MFN2 accounted for over 90% of the molecular diagnoses while mutations in all other genes tested were rare.
Four commonly available genes account for over 90% of all CMT molecular diagnoses; a diagnostic algorithm is proposed based on these results for use in clinical practice. Any patient with CMT without a mutation in these four genes or with an unusual phenotype should be considered for referral for an expert opinion to maximise the chance of reaching a molecular diagnosis.
A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require ...measurements of Doppler velocity drifts of ~1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of ~9 meters per second at ~1.5 micrometers--beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.
We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z < 0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar ...spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T ∼ 104 K) CGM gas. We also use HST images to determine host-galaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a H i column density range of 13.8 cm−2 < < 19.9 cm−2. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4 ). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of H i column density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z < 0.7. The presence of low-metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.
Abstract
Though the global atmospheres of hot Jupiters have been extensively studied using phase curve observations, the level of time variability in these data is not well constrained. To ...investigate possible time variability in a planetary phase curve, we observed two full-orbit phase curves of the hot Jupiter WASP-43b at 4.5
μ
m using the Spitzer Space Telescope, and reanalyzed a previous 4.5
μ
m phase curve from Stevenson et al. We find no significant time variability between these three phase curves, which span timescales of weeks to years. The three observations are best fit by a single phase curve with an eclipse depth of 3907 ± 85 ppm, a dayside-integrated brightness temperature of 1479 ± 13 K, a nightside integrated brightness temperature of 755 ± 46 K, and an eastward-shifted peak of 10.°4 ± 1.°8. To model our observations, we performed 3D general circulation model simulations of WASP-43b with simple cloud models of various vertical extents. In comparing these simulations to our observations, we find that WASP-43b likely has a cloudy nightside that transitions to a relatively cloud-free dayside. We estimate that any change in WASP-43b’s vertical cloud thickness of more than three pressure scale heights is inconsistent with our observed upper limit on variation. These observations, therefore, indicate that WASP-43b’s clouds are stable in their vertical and spatial extent over timescales up to several years. These results strongly suggest that atmospheric properties derived from previous, single Spitzer phase curve observations of hot Jupiters likely show us the equilibrium properties of these atmospheres.
ABSTRACT
Solar twins are stars of key importance to the field of astronomy and offer a multitude of science applications. Only a small number (≲200) of solar twins are known today, all of which are ...relatively close to our Sun (${\lesssim}{800}\, {\rm pc}$). The goal of our Survey for Distant Solar Twins (SDST) is to identify many more solar twin and solar analogue stars out to much larger distances (${\sim}{4}\, {\rm kpc}$). In this paper, we present a new method to identify solar twins using relatively low S/N, medium resolving power ($R\sim 28\, 000$) spectra that will be typical of such distant targets observed with HERMES on the ${3.9}\, {\rm m}$ Anglo-Australian Telescope (AAT). We developed a novel approach, namely epic, to measure stellar parameters (SPs) which we use to identify stars similar to our Sun. epic determines the stellar atmospheric parameters (effective temperature Teff, surface gravity log g, and metallicity Fe/H) using differential equivalent width (EW) measurements of selected spectroscopic absorption features and a simple model, trained on previously analysed spectra, that connects these EWs to the SPs. The reference for the EW measurements is a high S/N solar spectrum which is used to minimize several systematic effects. epic is fast, optimized for Sun-like stars and yields SP measurements with small enough uncertainties to enable spectroscopic identification of solar twin and analogue stars up to ${\sim}{4}\, {\rm kpc}$ away using AAT/HERMES, i.e. $\sigma \left(T_{\mathrm{eff}}, \log g, \textrm {Fe/H}\right) = \left({50}\, {\rm K}, {0.08}\, {\rm dex}, {0.03}\, {\rm dex}\right)$ on average at S/N = 25.
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