paper

On the observability of individual Population III stars and their stellar-mass black hole accretion disks through cluster caustic transits

arXiv:1801.03584 · doi:10.3847/1538-4365/aaa760

Abstract

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z7-17. Theoretical predictions and recent near-infrared power-spectra provide tighter constraints on their sky-signal. We outline the physical properties of zero metallicity Population III stars from MESA stellar evolution models through helium-depletion and of BH accretion disks at z7. We assume that second-generation non-zero metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be 10-10, with rise times of hours and decline times of 1 year for cluster transverse velocities of 1000 km s. Microlensing by intracluster medium objects can modify transit magnifications, but lengthen visibility times. Depending on BH masses, accretion-disk radii and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require to monitor 3-30 lensing clusters to AB29 mag over a decade.

53 pages, 5 figures, Accepted for publication in ApJS

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