A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT

Tuning ultrafast electron injection dynamics at organic-graphene/metal interfaces

We compare the ultrafast charge transfer dynamics of molecules on epitaxial graphene and bilayer graphene grown on Ni(111) interfaces through first principles calculations and X-ray resonant photoemission spectroscopy. We use 4,4'-bipyridine as a prototypical molecule for these explorations as the energy level alignment of core-excited molecular orbitals allows ultrafast injection of electrons from a substrate to a molecule on a femtosecond timescale. We show that the ultrafast injection of electrons from the substrate to the molecule is similar to 4 times slower on weakly coupled bilayer graphene than on epitaxial graphene. Through our experiments and calculations, we can attribute this to a difference in the density of states close to the Fermi level between graphene and bilayer graphene. We therefore show how graphene coupling with the substrate influences charge transfer dynamics between organic molecules and graphene interfaces

FIR Measurements of Lyα Emitters at z

One remaining open question regarding the physical properties of Ly alpha emitters (LAEs) is their dust content and evolution with redshift. The variety of results is large and with those reported by now it is difficult to establish clear relations between dust, other fundamental parameters of galaxies (star formation rate, metallicity, or age), and redshift. In this Letter, we report Herschel PACS-100 mu m, PACS-160 mu m, and Spitzer MIPS-24 mu m detections of a sample of spectroscopically GALEX selected LAEs at z similar to 0.3 and similar to 1.0. Five out of ten and one out of two LAEs are detected in, at least, one PACS band at z similar to 0.3 and similar to 1.0, respectively. These measurements have a great importance given that they allow us to quantify, for the first time, the dust content in LAEs from direct FIR observations. MIPS-24 mu m detections allow us to determine the IR properties of the PACS-undetected LAEs. We obtain that mid-IR/FIR-detected star-forming (SF) LAEs at z similar to 0.3 have dust content within 0.75 less than or similar to A(1200 angstrom) less than or similar to 2.0, with a median value of A(1200 angstrom) similar to 1.1. This range broadens up to 0.75 less than or similar to A(1200 angstrom) less than or similar to 2.5 when considering the LAEs at z similar to 1.0. Only one SF LAE is undetected both in MIPS-24 mu m and PACS, with A(1200 angstrom) less than or similar to 0.75. These results seem to be larger than those reported for high-redshift LAEs and, therefore, although an evolutionary trend is not clearly seen, it could point out that low-redshift LAEs are dustier than high-redshift ones. However, the diverse methods used could introduce a systematic offset in the results