Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Desika Narayanan, Daniel P. Stark, Steven L. Finkelstein, Paul Torrey, Qi Li
| Summary:
JWST has enabled the detection of the UV continuum of galaxies at z>10,
evidencing a population of extremely blue, potentially dust-free galaxies.
Interpreting the UV spectra of galaxies as they redden is complicated by the
well-known degeneracy between stellar ages, dust, and nebular continuum. The
main goal of this paper is to develop a theoretical model for the relationship
between galaxy UV slopes, bursty star formation histories, dust evolution, and
the contribution from nebular regions. We accomplish this via cosmological
zoom-in simulations, and in specific, build a layered model where we simulate
the UV slopes of galaxies with increasingly complex physics. Our main results
follow. (i) Unattenuated stellar populations with no nebular emission exhibit a
diverse range of intrinsic UV slopes, with values ranging from beta ~ -3 –>
-2.2 due to long delays between bursts. This is manifested by an inverse
correlation between the intrinsic UV slope and sSFR for early galaxies such
that higher sSFR corresponds to bluer UV slopes. (ii) When including dust, our
model galaxies demonstrate a rapid rise in dust obscuration between z ~ 8-10.
This increase in dust mass is due to high grain-grain shattering rates, and
enhanced growth per unit dust mass in very small grains, resulting in
UV-detected galaxies at z ~ 12 descending into ALMA-detectable galaxies by z ~
6. The rapid rise in dust content at z ~ 8-10 leads to a systematic reddening
of the UV slopes during this redshift range. (iii) The inclusion of nebular
continuum reddens the UV slope by a median factor Delta beta ~ 0.2-0.4.
However, when including nebular continuum, our highest redshift galaxies (z~12)
are insufficiently blue compared to observations; this may imply an evolving
escape fraction from HII regions with redshift.
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