NuSTAR Observations of Heavily Obscured Quasars at z ~ 0.5

We present NuSTAR hard X-ray observations of three Type 2 quasars at z ≈ 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O III] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N_H) are poorly known. In this analysis, (1) we study X-ray emission at >10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N_H. (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at >8 keV with a no-source probability of <0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N_H≳5 × 10^(23) cm^(–2). The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N_H≳10^(24) cm^(–2)). We find that for quasars at z ~ 0.5, NuSTAR provides a significant improvement compared to lower energy (<10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained

Observation of metastable Aβ amyloid protofibrils by atomic force microscopy

AbstractBackground: Brain amyloid plaque, a diagnostic feature of Alzheimer's disease (AD), contains an insoluble fibrillar core that is composed primarily of variants of the β-amyloid protein (Aβ). As Aβ amyloid fibrils may initiate neurodegeneration, the inhibition of fibril formation is a possible therapeutic strategy. Very little is known about the early steps of the process, however.Results: Atomic force microscopy was used to follow amyloid fibril formation in vitro by the Aβ variants Aβ1-40 and Aβ1-42. Both variants first form small ordered aggregates that grow slowly and then rapidly disappear, while prototypical amyloid fibrils of two discrete morphologies appear. Aβ1-42 aggregates much more rapidly than Aβ1-40, which is consistent with its connection to early-onset AD. We propose that the metastable intermediate species be called Aβ amyloid protofibrils.Conclusions: Aβ protofibrils are likely to be intermediates in the in vitro assembly of Aβ amyloid fibrils, but their in vivo role has yet to be determined. Numerous reports of a nonfibrillar form of Aβ aggregate in the brains of individuals who are predisposed to AD suggest the existence of a precursor form, possibly the protofibril. Thus, stabilization of Aβ protofibrils may be a useful therapeutic strategy

Heavy X-ray obscuration in the most-luminous galaxies discovered by WISE

Hot Dust-Obscured Galaxies (Hot DOGs) are hyperluminous ($L_{\mathrm{8-1000\,\mu m}}>10^{13}\,\mathrm{L_\odot}$) infrared galaxies with extremely high (up to hundreds of K) dust temperatures. The sources powering both their extremely high luminosities and dust temperatures are thought to be deeply buried and rapidly accreting supermassive black holes (SMBHs). Hot DOGs could therefore represent a key evolutionary phase in which the SMBH growth peaks. X-ray observations can be used to study their obscuration levels and luminosities. In this work, we present the X-ray properties of the 20 most-luminous ($L_{\mathrm{bol}}\gtrsim10^{14}\, L_\odot$) known Hot DOGs at $z=2-4.6$. Five of them are covered by long-exposure ($10-70$ ks) Chandra and XMM-Newton observations, with three being X-ray detected, and we study their individual properties. One of these sources (W0116$-$0505) is a Compton-thick candidate, with column density $N_H=(1.0-1.5)\times10^{24}\,\mathrm{cm^{-2}}$ derived from X-ray spectral fitting. The remaining 15 Hot DOGs have been targeted by a Chandra snapshot (3.1 ks) survey. None of these 15 is individually detected; therefore we applied a stacking analysis to investigate their average emission. From hardness-ratio analysis, we constrained the average obscuring column density and intrinsic luminosity to be log$N_H\,\mathrm{[cm^{-2}]}>23.5$ and $L_X\gtrsim10^{44}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$, which are consistent with results for individually detected sources. We also investigated the $L_X-L_{6\mu\mathrm{m}}$ and $L_X-L_{bol}$ relations, finding hints that Hot DOGs are typically X-ray weaker than expected, although larger samples of luminous obscured QSOs are needed to derive solid conclusions.Comment: MNRAS, accepted 2017 November 29 . Received 2017 November 29 ; in original form 2017 October 11. 15 pages, 6 figure

The Inequitable Burden of Infectious Diseases Among Remote-living Aboriginal and Torres Strait Islander Australians: A Product of History

Insufficient and poorly maintained housing and plumbing in many remote Australian Indigenous communities in Australia results in reduced capacity to maintain personal hygiene, contributing to infectious disease inequalities. Infections from Streptococcus pyogenes (Strep A) and sequalae are often noted to be the result of contextual poverty; a product of over 230 years of discriminatory practice that has excluded Indigenous people from the basic human rights of healthy, maintained housing afforded to most in the nation. The solutions for eliminating diseases of inequity among Australian Indigenous population are known, their success is historically documented, and yet they are to be comprehensively implemented in the remote Indigenous communities. This paper explores how decades of inequitable policy has permeated contemporary Australian Indigenous wellbeing with specific regards to infectious disease rates; a deviation from thousands of years with limited exposure to such illnesses

Resolving the cosmic X-ray background with a next-generation high-energy X-ray observatory

The cosmic X-ray background (CXB), which peaks at an energy of ~30 keV, is produced primarily by emission from accreting supermassive black holes (SMBHs). The CXB therefore serves as a constraint on the integrated SMBH growth in the Universe and the accretion physics and obscuration in active galactic nuclei (AGNs). This paper gives an overview of recent progress in understanding the high-energy (>~10 keV) X-ray emission from AGNs and the synthesis of the CXB, with an emphasis on results from NASA's NuSTAR hard X-ray mission. We then discuss remaining challenges and open questions regarding the nature of AGN obscuration and AGN physics. Finally, we highlight the exciting opportunities for a next-generation, high-resolution hard X-ray mission to achieve the long-standing goal of resolving and characterizing the vast majority of the accreting SMBHs that produce the CXB.Comment: Science White paper submitted to Astro2020 Decadal Survey; 5 pages, 3 figures, plus references and cover pag

Explorations in anatomy: the remains from Royal London Hospital

This paper considers the faunal remains from recent excavations at the Royal London Hospital. The remains date to the beginning of the 19th century and offer an insight into the life of the hospital's patients and practices of the attached medical school. Many of the animal remains consist of partially dissected skeletons, including the unique finds of Hermann's tortoise (Testudo hermanni) and Cercopithecus monkey. The hospital diet and developments in comparative anatomy are discussed by integrating the results with documentary research. They show that zooarchaeological study of later post-medieval material can significantly enhance our understanding of the exploitation of animals in this perio

Peering through the Dust: Nustar Observations of Two First-2mass Red Quasars

Some reddened quasars appear to be transitional objects in the merger-induced black hole growth/galaxy evolution paradigm, where a heavily obscured nucleus starts to be unveiled by powerful quasar winds evacuating the surrounding cocoon of dust and gas. Hard X-ray observations are able to peer through this gas and dust, revealing the properties of circumnuclear obscuration. Here, we present NuSTAR and XMM-Newton/Chandra observations of FIRST-2MASS selected red quasars F2M 0830+3759 and F2M 1227+3214. We find that though F2M 0830+3759 is moderately obscured (NH,Z=2.1±0.2×1022 cm−2) and F2M 1227+3214 is mildly absorbed (NH,Z=3.4+0.8−0.7×1021 cm−2) along the line-of-sight, heavier global obscuration may be present in both sources, with NH,S=3.7+4.1−2.6×1023 cm−2 and \u3c5.5×1023 cm−2, for F2M 0830+3759 and F2M 1227+3214, respectively. F2M 0830+3759 also has an excess of soft X-ray emission below 1 keV which is well accommodated by a model where 7% of the intrinsic AGN X-ray emission is scattered into the line-of-sight. While F2M 1227+3214 has a dust-to-gas ratio (E(B−V)/NH) consistent with the Galactic value, the E(B−V)/NH value for F2M 0830+3759 is lower than the Galactic standard, consistent with the paradigm that the dust resides on galactic scales while the X-ray reprocessing gas originates within the dust-sublimation zone of the broad-line-region. The X-ray and 6.1μm luminosities of these red quasars are consistent with the empirical relations derived for high-luminosity, unobscured quasars, extending the parameter space of obscured AGN previously observed by NuSTAR to higher luminosities

The AllWISE Motion Survey, Part 2

We use the AllWISE Data Release to continue our search for WISE-detected motions. In this paper, we publish another 27,846 motion objects, bringing the total number to 48,000 when objects found during our original AllWISE motion survey are included. We use this list, along with the lists of confirmed WISE-based motion objects from the recent papers by Luhman and by Schneider et al. and candidate motion objects from the recent paper by Gagne et al. to search for widely separated, common-proper-motion systems. We identify 1,039 such candidate systems. All 48,000 objects are further analyzed using color-color and color-mag plots to provide possible characterizations prior to spectroscopic follow-up. We present spectra of 172 of these, supplemented with new spectra of 23 comparison objects from the literature, and provide classifications and physical interpretations of interesting sources. Highlights include: (1) the identification of three G/K dwarfs that can be used as standard candles to study clumpiness and grain size in nearby molecular clouds because these objects are currently moving behind the clouds, (2) the confirmation/discovery of several M, L, and T dwarfs and one white dwarf whose spectrophotometric distance estimates place them 5-20 pc from the Sun, (3) the suggestion that the Na 'D' line be used as a diagnostic tool for interpreting and classifying metal-poor late-M and L dwarfs, (4) the recognition of a triple system including a carbon dwarf and late-M subdwarf, for which model fits of the late-M subdwarf (giving [Fe/H] ~ -1.0) provide a measured metallicity for the carbon star, and (5) a possible 24-pc-distant K5 dwarf + peculiar red L5 system with an apparent physical separation of 0.1 pc.Comment: 62 pages with 80 figures, accepted for publication in The Astrophysical Journal Supplement Series, 23 Mar 2016; second version fixes a few small typos and corrects the footnotes for Table