The Direct Detectability of Giant Exoplanets in the Optical

Motivated by the possibility that a coronagraph will be put on WFIRST/AFTA, we explore the direct detectability of extrasolar giant planets (EGPs) in the optical. We quantify a planet's detectability by the fraction of its orbit for which it is in an observable configuration ($f_\mathrm{obs}$). Using a suite of Monte Carlo experiments, we study the dependence of $f_\mathrm{obs}$ upon the inner working angle (IWA) and minimum achievable contrast ($C_\mathrm{min}$) of the direct-imaging observatory; the planet's phase function, geometric albedo, single-scattering albedo, radius, and distance from Earth; and the semi-major axis distribution of EGPs. We calculate phase functions for a given geometric or single-scattering albedo, assuming various scattering mechanisms. We find that the Lambertian phase function can predict significantly larger $f_\mathrm{obs}$'s with respect to the more realistic Rayleigh phase function. For observations made with WFIRST/AFTA's baseline capabilities ($C_\mathrm{min}\sim10^{-9}$, $\mathrm{IWA}\sim0.2''$), Jupiter-like planets orbiting stars within 10, 30, and 50 parsecs of Earth have volume-averaged observability fractions of ${\sim}$12%, 3%, and 0.5%, respectively. At 10 parsecs, such observations yield $f_\mathrm{obs}>1\%$ for low- to modest-eccentricity planets with semi-major axes in the range ${\sim}2 - 10$ AU. If $C_\mathrm{min}=10^{-10}$, this range extends to ${\sim}35$ AU. We find that, in all but the most optimistic configurations, the probability for detection in a blind search is low (${<}\,5\%$). However, with orbital parameter constraints from long-term radial-velocity campaigns and Gaia astrometry, the tools we develop in this work can be used to determine both the most promising systems to target and when to observe them.Comment: 16 pages, 16 figures. Accepted for publication in Ap

Discovery of a red backsplash galaxy candidate near M81

Understanding quenching mechanisms in low-mass galaxies is essential for understanding galaxy evolution overall. In particular, isolated galaxies are important tools to help disentangle the complex internal and external processes that impact star formation. Comparisons between quenched field and satellite galaxies in the low mass regime offer a substantial opportunity for discovery, although very few quenched galaxies with masses below $M_{\star}$$\sim$$10^{9} M_{\odot}$ are known outside the virial radius, $R_{vir}$, of any host halo. Importantly, simulations and observations suggest that an in-between population of backsplash galaxies also exists that may complement interpretations of environmental quenching. Backsplash galaxies -- like field galaxies -- reside outside the virial radius of a host halo, but their star formation can be deeply impacted by previous interactions with more massive systems. In this paper, we report the discovery of a low-mass ($M_{\star}$$\sim$$10^{7} M_{\odot}$) quenched galaxy approximately $1 R_{vir}$ in projection from the M81 group. We use surface brightness fluctuations (SBF) to investigate the possibility that the new galaxy, dubbed dw0910p7326 (nicknamed Blobby), is a backsplash galaxy or a more distant field galaxy. The measured SBF distance of $3.21\substack{+0.15 +0.41 \\ -0.15 -0.36}$ Mpc indicates that Blobby likely lies between $1.0 < R/R_{vir} < 2.7$ outside the combined M81--M82 system. Given its distance and quiescence, Blobby is a good candidate for a backsplash galaxy and could provide hints about the formation and evolution of these interesting objects.Comment: 15 pages, 8 figures, to be submitted to MNRAS, comments welcome