Abstract / Description of output
The ultraviolet (UV) continuum slope β, typically observed at z
≈ 7 in Hubble Space Telescope (HST) WFC3/IR bands via the J - H
colour, is a useful indicator of the age, metallicity and dust content
of high-redshift stellar populations. Recent studies have shown that the
redward evolution of β with cosmic time from redshift 7 to 4 can be
largely explained by a buildup of dust. However, initial claims that
faint z ≈ 7 galaxies in the Hubble Ultra Deep Field WFC3/IR imaging
(HUDF09) were blue enough to require stellar populations of zero
reddening, low metallicity and young ages, hitherto unseen in
star-forming galaxies, have since been refuted and revised. Here we
revisit the question of how best to measure the UV slope of z ≈ 7
galaxies through source recovery simulations, within the context of
present and future ultra-deep imaging from HST. We consider how source
detection, selection and colour measurement have each biased the
measurement of β in previous studies. After finding a robust method
for measuring β in the simulations (via a power-law fit to all the
available photometry), we remeasure the UV slopes of a sample of
previously published low-luminosity z ≈ 7 galaxy candidates. The mean
UV slope of faint galaxies in this sample appears consistent with an
intrinsic distribution of normal star-forming galaxies with β ≈
-2, although properly decoding the underlying distribution will require
further imaging from the ongoing HUDF12 programme. We therefore go on to
consider strategies for obtaining better constraints on the underlying
distribution of UV slopes at z ≈ 7 from these new data, which will
benefit particularly from the addition of imaging in a second J-band
filter: F140W. We find that a precise and unbiased measurement of β
should then be possible.
Original language | English |
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Pages (from-to) | 2456-2468 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 429 |
Publication status | Published - 1 Mar 2013 |
Keywords / Materials (for Non-textual outputs)
- galaxies: evolution
- galaxies: formation
- galaxies: high-redshift
- early Universe
- ultraviolet: galaxies