PhD thesis: Gravitational lensing as a probe of the first stars and galaxies
Friday 30 January 2015
to 17:00 at
Claes-Erik Rydberg (Department of Astronomy)
Simulations indicate that the first Population III stars should appear in minihalos of mass M =
105-106 Msol at z ≈ 10-30. To assess the detectability of these objects, theoretical models of these
stars and their surrounding HII regions are used. We assess the plausibility of detection with the
upcoming James Webb Space Telescope (JWST), using the gravitational lensing provided by the
galaxy cluster MACSJ0717.5+3745. The conclusion is that the detection of these objects is highly
improbable but not impossible.
To investigate the prospects of detecting and identifying the first galaxies, the spectral synthesis
code Yggdrasil is introduced. According to this code, JWST may be able to detect Population III
galaxies with stellar masses as low as 105 Msol at z ≈ 10 in unlensed fields. We find that, over
limited redshift intervals, it could be possible to use Hubble Space Telescope (HST) and/or JWST
broadband color criteria to single out Population III galaxy candidates.
The prospects of detecting gravitationally lensed Population III galaxies with JWST and HST is
investigated. A lower limit to detect ≈1 Population III galaxy of ε ≈ 10-2 (HST/CLASH) and ε ≈ 10-3
(JWST using MACS J0717.5+3745 as lens) is derived, where ε is the baryon fraction converted
to Population III stars in a host halo.
By fitting HST/CLASH data to Yggdrasil and comparison grids, two Population III galaxy
candidates are discovered. These two candidates are the first Population III galaxy candidates
discovered at z > 6.5. A highly-magnified and doubly lensed extremely high-redshift (z ≈ 7.8)
object is also identified.
Finally the prospects of detecting core-collapse (CC) supernovae (SN) from the first galaxies
at z ≈ 5-12 are investigated. The prediction is that no primordial SN is detectable, but 2-3 CC SN
should be discovered by the HST/CLASH.