Abstract
Galaxies The most massive galaxies in the Universe are all giant ellipticals, formed in major merger events. Spiral galaxies form more quiescently, by accreting gas from the intergalactic medium. Ogle et al. observed a sample of the most massive spiral galaxies known. For each galaxy, they separately determined the mass of stars and the mass of the surrounding dark matter halo. At the highest masses, the sample diverges from well-known scaling laws that describe lower-mass spiral galaxies, implying a maximum spiral galaxy stellar mass of about 1011.8 solar masses. These galaxies are very efficient at converting gas into stars, which may relate to the apparent mass limit. Astrophys. J. Lett. 884 , L11 (2019).
Highlights
Candidate drug testing using standard preclinical models cannot accurately predict which compounds are likely to cause drug-induced liver injury in humans
To improve selection of promising drug candidates, Jang et al developed Liver-Chips, which consist of rat, dog, or human hepatocytes, endothelial cells, Kupffer cells, and stellate cells
Rivera-Thorsen et al took advantage of a gravitational lensing system to observe 12 images of the same star-forming region in a distant galaxy and determined the fraction of ultraviolet photons that escape into the intergalactic medium
Summary
Nitrogen oxides (NOx) have a central role in controlling air quality, so designing effective strategies to combat air pollution, especially by ozone and particulate matter, depends on knowing their atmospheric abundances. Those abundances depend on NOx production rates and on their lifetimes. Laughner and Cohen report that NOx lifetimes can be measured directly from satellite observations of nitrogen dioxide. They used data on 49 North American cities to show how NOx lifetimes there changed between 2005 and 2014. Accounting for this change in lifetime should help to reconcile conflicting trends between bottom-up and topdown emissions estimates. —HJS
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