Publications by Philip James Marshall

Nomads of the Galaxy

Monthly Notices of the Royal Astronomical Society 423 (2012) 1856-1865

LE Strigari, M Barnabè, PJ Marshall, RD Blandford

We estimate that there may be up to ∼10 5 compact objects in the mass range 10 -8-10 -2M ⊙ per-main-sequence star that are unbound to a host star in the Galaxy. We refer to these objects as nomads; in the literature a subset of these are sometimes called free-floating or rogue planets. Our estimate for the number of Galactic nomads is consistent with a smooth extrapolation of the mass function of unbound objects above the Jupiter-mass scale, the stellar mass density limit and the metallicity of the interstellar medium. We analyse the prospects for detecting nomads via Galactic microlensing. The Wide-Field Infrared Survey Telescope will measure the number of nomads per-main-sequence star greater than the mass of Jupiter to ∼13per cent, and the corresponding number greater than the mass of Mars to ∼25per cent. All-sky surveys such as Gaia and Large Synoptic Survey Telescope can identify nomads greater than about the mass of Jupiter. We suggest a dedicated drift scanning telescope that covers approximately 100deg 2 in the Southern hemisphere could identify nomads via microlensing of bright stars with characteristic time-scales of tens to hundreds of seconds. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

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