ABSTRACT
We present an improved measurement of the Hubble constant (H0) using the ‘inverse distance ladder’ method, which adds the information from 207 Type Ia supernovae (SNe Ia) from the Dark ...Energy Survey (DES) at redshift 0.018 < z < 0.85 to existing distance measurements of 122 low-redshift (z < 0.07) SNe Ia (Low-z) and measurements of Baryon Acoustic Oscillations (BAOs). Whereas traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia. We find H0 = 67.8 ± 1.3 km s−1 Mpc−1 (statistical and systematic uncertainties, 68 per cent confidence). Our measurement makes minimal assumptions about the underlying cosmological model, and our analysis was blinded to reduce confirmation bias. We examine possible systematic uncertainties and all are below the statistical uncertainties. Our H0 value is consistent with estimates derived from the Cosmic Microwave Background assuming a ΛCDM universe.
W. R. Brown and C. R. Thore (2011) Neuropathology and Applied Neurobiology37, 56–74 Cerebral microvascular pathology in ageing and neurodegeneration
This review of age‐related brain microvascular ...pathologies focuses on topics studied by this laboratory, including anatomy of the blood supply, tortuous vessels, venous collagenosis, capillary remnants, vascular density and microembolic brain injury. Our studies feature thick sections, large blocks embedded in celloidin, and vascular staining by alkaline phosphatase. This permits study of the vascular network in three dimensions, and the differentiation of afferent from efferent vessels. Current evidence suggests that there is decreased vascular density in ageing, Alzheimer's disease and leukoaraiosis, and cerebrovascular dysfunction precedes and accompanies cognitive dysfunction and neurodegeneration. A decline in cerebrovascular angiogenesis may inhibit recovery from hypoxia‐induced capillary loss. Cerebral blood flow is inhibited by tortuous arterioles and deposition of excessive collagen in veins and venules. Misery perfusion due to capillary loss appears to occur before cell loss in leukoaraiosis, and cerebral blood flow is also reduced in the normal‐appearing white matter. Hypoperfusion occurs early in Alzheimer's disease, inducing white matter lesions and correlating with dementia. In vascular dementia, cholinergic reductions are correlated with cognitive impairment, and cholinesterase inhibitors have some benefit. Most lipid microemboli from cardiac surgery pass through the brain in a few days, but some remain for weeks. They can cause what appears to be a type of vascular dementia years after surgery. Donepezil has shown some benefit. Emboli, such as clots, cholesterol crystals and microspheres can be extruded through the walls of cerebral vessels, but there is no evidence yet that lipid emboli undergo such extravasation.
Brown carbon aerosol consists of light‐absorbing organic particulate matter with wavelength‐dependent absorption. Aerosol optical extinction, absorption, size distributions, and chemical composition ...were measured in rural Alabama during summer 2013. The field site was well located to examine sources of brown carbon aerosol, with influence by high biogenic organic aerosol concentrations, pollution from two nearby cities, and biomass burning aerosol. We report the optical closure between measured dry aerosol extinction at 365 nm and calculated extinction from composition and size distribution, showing agreement within experiment uncertainties. We find that aerosol optical extinction is dominated by scattering, with single‐scattering albedo values of 0.94 ± 0.02. Black carbon aerosol accounts for 91 ± 9% of the total carbonaceous aerosol absorption at 365 nm, while organic aerosol accounts for 9 ± 9%. The majority of brown carbon aerosol mass is associated with biomass burning, with smaller contributions from biogenically derived secondary organic aerosol.
Key Points
Aerosol optical extinction in the southeastern U.S. is dominated by scattering
Black carbon is a more significant absorber than organic carbon at 365 nm
Biomass burning makes the largest contribution to organic aerosol absorption
Galaxy And Mass Assembly (GAMA): stellar mass estimates Taylor, Edward N.; Hopkins, Andrew M.; Baldry, Ivan K. ...
Monthly notices of the Royal Astronomical Society,
December 2011, Letnik:
418, Številka:
3
Journal Article
Recenzirano
Odprti dostop
This paper describes the first catalogue of photometrically derived stellar mass estimates for intermediate-redshift (z < 0.65; median z= 0.2) galaxies in the Galaxy And Mass Assembly (GAMA) ...spectroscopic redshift survey. These masses, as well as the full set of ancillary stellar population parameters, will be made public as part of GAMA data release 2. Although the GAMA database does include near-infrared (NIR) photometry, we show that the quality of our stellar population synthesis fits is significantly poorer when these NIR data are included. Further, for a large fraction of galaxies, the stellar population parameters inferred from the optical-plus-NIR photometry are formally inconsistent with those inferred from the optical data alone. This may indicate problems in our stellar population library, or NIR data issues, or both; these issues will be addressed for future versions of the catalogue. For now, we have chosen to base our stellar mass estimates on optical photometry only. In light of our decision to ignore the available NIR data, we examine how well stellar mass can be constrained based on optical data alone. We use generic properties of stellar population synthesis models to demonstrate that restframe colour alone is in principle a very good estimator of stellar mass-to-light ratio, M
*/Li
. Further, we use the observed relation between restframe (g−i) and M
*/Li
for real GAMA galaxies to argue that, modulo uncertainties in the stellar evolution models themselves, (g−i) colour can in practice be used to estimate M
*/Li
to an accuracy of ≲0.1 dex (1σ). This 'empirically calibrated' (g−i)-M
*/Li
relation offers a simple and transparent means for estimating galaxies' stellar masses based on minimal data, and so provides a solid basis for other surveys to compare their results to z≲0.4 measurements from GAMA.
We present the Dark Energy Camera (DECam) discovery of the optical counterpart of the first binary neutron star merger detected through gravitational-wave emission, GW170817. Our observations ...commenced 10.5 hr post-merger, as soon as the localization region became accessible from Chile. We imaged 70 deg2 in the i and z bands, covering 93% of the initial integrated localization probability, to a depth necessary to identify likely optical counterparts (e.g., a kilonova). At 11.4 hr post-merger we detected a bright optical transient located from the nucleus of NGC 4993 at redshift z = 0.0098, consistent (for km s−1 Mpc−1) with the distance of 40 8 Mpc reported by the LIGO Scientific Collaboration and the Virgo Collaboration (LVC). At detection the transient had magnitudes of and , and thus an absolute magnitude of , in the luminosity range expected for a kilonova. We identified 1500 potential transient candidates. Applying simple selection criteria aimed at rejecting background events such as supernovae, we find the transient associated with NGC 4993 as the only remaining plausible counterpart, and reject chance coincidence at the 99.5% confidence level. We therefore conclude that the optical counterpart we have identified near NGC 4993 is associated with GW170817. This discovery ushers in the era of multi-messenger astronomy with gravitational waves and demonstrates the power of DECam to identify the optical counterparts of gravitational-wave sources.
We present UV, optical, and near-infrared (NIR) photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced Laser Interferometer Gravitational-wave Observatory ...(LIGO)/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at 0.47-18.5 days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-South/FLAMINGOS-2 (GS/F2), and the Hubble Space Telescope (HST). The spectral energy distribution (SED) inferred from this photometry at 0.6 days is well described by a blackbody model with T 8300 K, a radius of R 4.5 × 10 14 cm (corresponding to an expansion velocity of v 0.3 c ), and a bolometric luminosity of L bol 5 × 10 41 erg s−1. At 1.5 days we find a multi-component SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands and significant reddening of the optical/NIR colors. Modeling the entire data set, we find that models with heating from radioactive decay of 56Ni, or those with only a single component of opacity from r-process elements, fail to capture the rapid optical decline and red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data; the resulting "blue" component has M ej blue 0.01 M and v ej blue 0.3 c , and the "red" component has M ej red 0.04 M and v ej red 0.1 c . These ejecta masses are broadly consistent with the estimated r-process production rate required to explain the Milky Way r-process abundances, providing the first evidence that binary neutron star (BNS) mergers can be a dominant site of r-process enrichment.
We present griz light curves of 251 SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program's (DES-SN) spectroscopically classified sample. The photometric pipeline described in ...this paper produces the calibrated fluxes and associated uncertainties used in the cosmological parameter analysis by employing a scene modeling approach that simultaneously models a variable transient flux and temporally constant host galaxy. We inject artificial point sources onto DECam images to test the accuracy of our photometric method. Upon comparison of input and measured artificial supernova fluxes, we find that flux biases peak at 3 mmag. We require corrections to our photometric uncertainties as a function of host galaxy surface brightness at the transient location, similar to that seen by the DES Difference Imaging Pipeline used to discover transients. The public release of the light curves can be found at https://des.ncsa.illinois.edu/releases/sn.
The newly commissioned Orion laser system has been used to study dense plasmas created by a combination of short pulse laser heating and compression by laser driven shocks. Thus the plasma density ...was systematically varied between 1 and 10 g/cc by using aluminum samples buried in plastic foils or diamond sheets. The aluminum was heated to electron temperatures between 500 and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. The K-shell spectra show the effect of the ionization potential depression as a function of density. The data are compared to simulated spectra which account for the change in the ionization potential by the commonly used Stewart and Pyatt prescription and an alternative due to Ecker and Kröll suggested by recent x-ray free-electron laser experiments. The experimental data are in closer agreement with simulations using the model of Stewart and Pyatt.
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