The Evolution of Bias - Generalized

Fry (1996) showed that galaxy bias has the tendency to evolve towards unity, i.e. in the long run, the galaxy distribution tends to trace that of matter. Generalizing slightly Fry's reasoning, we show that his conclusion remains valid in theories of modified gravity (or equivalently, complex clustered dark energy). This is not surprising: as long as both galaxies and matter are subject to the same force, dynamics would drive them towards tracing each other. This holds, for instance, in theories where both galaxies and matter move on geodesics. This relaxation of bias towards unity is tempered by cosmic acceleration, however: the bias tends towards unity but does not quite make it, unless the formation bias were close to unity. Our argument is extended in a straightforward manner to the case of a stochastic or nonlinear bias. An important corollary is that dynamical evolution could imprint a scale dependence on the large scale galaxy bias. This is especially pronounced if non-standard gravity introduces new scales to the problem: the bias at different scales relaxes at different rates, the larger scales generally more slowly and retaining a longer memory of the initial bias. A consistency test of the current (general relativity + uniform dark energy) paradigm is therefore to look for departure from a scale independent bias on large scales. A simple way is to measure the relative bias of different populations of galaxies which are at different stages of bias relaxation. Lastly, we comment on the possibility of directly testing the Poisson equation on cosmological scales, as opposed to indirectly through the growth factor.Comment: 8 pages, 2 figures. References added. Accepted for publication in Physical Review

Dual Supermassive Black Hole Candidates in the AGN and Galaxy Evolution Survey

Dual supermassive black holes (SMBHs) with kiloparsec scale separations in merger-remnant galaxies are informative tracers of galaxy evolution, but the avenue for identifying them in large numbers for such studies is not yet clear. One promising approach is to target spectroscopic signatures of systems where both SMBHs are fueled as dual active galactic nuclei (AGNs), or where one SMBH is fueled as an offset AGN. Dual AGNs may produce double-peaked narrow AGN emission lines, while offset AGNs may produce single-peaked narrow AGN emission lines with line-of-sight velocity offsets relative to the host galaxy. We search for such dual and offset systems among 173 Type 2 AGNs at z<0.37 in the AGN and Galaxy Evolution Survey (AGES), and we find two double-peaked AGNs and five offset AGN candidates. When we compare these results to a similar search of the DEEP2 Galaxy Redshift Survey and match the two samples in color, absolute magnitude, and minimum velocity offset, we find that the fraction of AGNs that are dual SMBH candidates increases from z=0.25 to z=0.7 by a factor of ~6 (from 2/70 to 16/91, or 2.9% to 18%). This may be associated with the rise in the galaxy merger fraction over the same cosmic time. As further evidence for a link with galaxy mergers, the AGES offset and dual AGN candidates are tentatively ~3 times more likely than the overall AGN population to reside in a host galaxy that has a companion galaxy (from 16/173 to 2/7, or 9% to 29%). Follow-up observations of the seven offset and dual AGN candidates in AGES will definitively distinguish velocity offsets produced by dual SMBHs from those produced by narrow-line region kinematics, and will help sharpen our observational approach to detecting dual SMBHs.Comment: 10 pages, 8 figures, accepted for publication in Ap

User's guide for the Nimbus 7 ERB Solar Analysis Tape (ESAT)

Five years of Nimbus 7 ERB solar data is available in compact form on a single ERB solar analysis tape (ESAT). The period covered is November 16, 1978 through October 31, 1983. The Nimbus 7 satellite performs just under 14 orbits a day and the ERB solar telescope observe the Sun once per orbit as the satellite passes + or - near the south pole. The data were carefully calibrated and screened. Mean orbital and daily values are given for the total solar irradiance plus selected spectral intervals. In addition, selected solar activity indicators are on the tape. The ERB experiment, the solar data calibration and screening procedures, the solar activity indicators, and the tape format are described briefly

A fast, low-memory, and stable algorithm for implementing multicomponent transport in direct numerical simulations

Implementing multicomponent diffusion models in reacting-flow simulations is computationally expensive due to the challenges involved in calculating diffusion coefficients. Instead, mixture-averaged diffusion treatments are typically used to avoid these costs. However, to our knowledge, the accuracy and appropriateness of the mixture-averaged diffusion models has not been verified for three-dimensional turbulent premixed flames. In this study we propose a fast,efficient, low-memory algorithm and use that to evaluate the role of multicomponent mass diffusion in reacting-flow simulations. Direct numerical simulation of these flames is performed by implementing the Stefan-Maxwell equations in NGA. A semi-implicit algorithm decreases the computational expense of inverting the full multicomponent ordinary diffusion array while maintaining accuracy and fidelity. We first verify the method by performing one-dimensional simulations of premixed hydrogen flames and compare with matching cases in Cantera. We demonstrate the algorithm to be stable, and its performance scales approximately with the number of species squared. Then, as an initial study of multicomponent diffusion, we simulate premixed, three-dimensional turbulent hydrogen flames, neglecting secondary Soret and Dufour effects. Simulation conditions are carefully selected to match previously published results and ensure valid comparison. Our results show that using the mixture-averaged diffusion assumption leads to a 15% under-prediction of the normalized turbulent flame speed for a premixed hydrogen-air flame. This difference in the turbulent flame speed motivates further study into using the mixture-averaged diffusion assumption for DNS of moderate-to-high Karlovitz number flames.Comment: 36 pages, 14 figure

Ecological and taxonomic variation among human RNA viruses

AbstractOnly a minority of RNA viruses that can infect humans are capable of spreading in human populations independently of a zoonotic reservoir. This is especially true of vector-borne RNA viruses; the majority of these are not transmissible (via the vector) between humans at all. Understanding the biology underlying this observation will help us evaluate the public health risk associated with novel vector-borne RNA viruses