Is the Galactic Bulge Devoid of Planets?

Is the Galactic Bulge Devoid of Planets? Matthew Penny Ohio State University penny@astronomy.ohio-state.edu

There's Something Going On with Our Distance Estimates

31 Planet hosts Event discovered <= 2014 Event published <= 2015 q <= 0.03

The Data

The Model Henderson et al. (2014) KMTNet simulations Used 13 field simulation (32 min cadence) Covers a large fraction of microlensing events

Is it significant? Anderson-Darling Test statistic Bulge + Disk: A2 = 6.6 p-value = 5x10-4 Just Disk: A2 = 1.5 p-value = 0.18

Is it significant? Binomial Statistics: Data: N(Dl<5kpc) = 17 Model: N(Dl<5kpc) = 9 +/- 2.5

Relative bulge-disk planet abundance Bulge planet abundance < 0.54 disk abundance

Why might Planet Abundance depend on Galactic environment? Metallicity/Host mass [Fe/H] differs between disk and bulge Stellar Dynamics? Fischer & Valenti (2005) Post-formation shaping Stellar Density? Pre-formation destruction Disk truncation Johnson+2010

Why might Planet Abundance depend on Galactic environment? Metallicity/Host mass Stellar Dynamics? [Fe/H] differs between disk and bulge Post-formation shaping Stellar Density? Pre-formation destruction Disk truncation

Well let's test it: df/dx~x α [Fe/H] Mass Semimajor axis α

Including a Mass/Metallicity Dependence

Re-examine the Distances Bayesian If no info, return peak θe: Not much distance info alone, but large (>0.8 mas) indicates disk Parallax Unimpeachable? Degenerate with OM Often subtle

A Closer Look

A Closer Look ~Good agreement between model and data, except for events with Dl<2 kpc

a) OGLE-06-BLG-109 (Gaudi+08, Bennett+10) 2 planets OM+Pllx+Terr. Pllx Blended light consistent with Pllx+FS solution

b) MOA-2007-BLG-192 (Bennett+08, Kubas+12) Poorly sampled anomaly, multiple solutions Extremely low-mass host Xallarap solution, but argued improbable AO follow-up reveals blended light, but poor color constraint.

c) MOA-2010-BLG-328 (Furusawa+13) Large θe could be in bulge but would be bright Xallarap solution fits slightly better than Parallax, but special orientation points to parallax

d) OGLE-2012-BLG-0563 (Fukui+15) Large θe, but suprisingly small error (10%) given no caustic crossing Parallax detection, but argue caused by systematics Excess flux (H~17.8) + large θe constrains distance <~2 kpc

e) OGLE-2013-BLG-0341 (Gould et al. 2014) Triple lens (wide binary) Very wide binary, hard to confuse OM with parallax Large θe won't work with xallarap

f) OGLE-2013-BLG-0723 (Udalski+2015) Venus-mass planet in very-low-mass binary Xallarap not considered, despite low θe and low proper motion Fine-tuned pllx trajectory?

Concluding Results All at face value: Account for metallicity & mass dependent planet abundance fbulge < 0.54 fbulge < 0.70 Remove 2 potentially bad events fbulge < 0.96

OK, what's next? This sample was very inhomogeneous Microlensing has entered the survey era Wide-field, high-cadence surveys (MOA, OGLE-IV, KMTNet) can find planets without follow up Controlled experiments without human decisions are much more easily modeled Spitzer and K2 campaign 9 will get high-quality parallaxes for many planets

Where are the Known Exoplanets Microlensing searches probe a range of stellar populations that will be unique for the next decade