Hα Equivalent widths from the 3D-HST survey: evolution with redshift and dependence on stellar mass
Date
2012
Authors
Fumagalli, Mattia
Patel, Shannon
Franx, Marijn
Brammer, Gabriel
van Dokkum, P.G.
da Cunha, Elisabete
Kriek, Mariska
Lundgren, Britt
Momcheva, Ivelina
Rix, Hans-Walter
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Volume Title
Publisher
Institute of Physics Publishing Ltd.
Abstract
We investigate the evolution of the Hα equivalent width, EW(Hα), with redshift and its dependence on stellar
mass, using the first data from the 3D-HST survey, a large spectroscopic Treasury program with the Hubble Space
Telescope Wide Field Camera 3. Combining our Hα measurements of 854 galaxies at 0.8 < z < 1.5 with those
of ground-based surveys at lower and higher redshift, we can consistently determine the evolution of the EW(Hα)
distribution from z = 0 to z = 2.2. We find that at all masses the characteristic EW(Hα) is decreasing toward the
present epoch, and that at each redshift the EW(Hα) is lower for high-mass galaxies. We find EW(Hα) ∼ (1 + z)1.8
with little mass dependence. Qualitatively, this measurement is a model-independent confirmation of the evolution
of star-forming galaxies with redshift. A quantitative conversion of EW(Hα) to specific star formation rate (sSFR)
is model dependent because of differential reddening corrections between the continuum and the Balmer lines. The
observed EW(Hα) can be reproduced with the characteristic evolutionary history for galaxies, whose star formation
rises with cosmic time to z ∼ 2.5 and then decreases to z = 0. This implies that EW(Hα) rises to 400 Å at z =
8. The sSFR evolves faster than EW(Hα), as the mass-to-light ratio also evolves with redshift. We find that the
sSFR evolves as (1 + z)3.2, nearly independent of mass, consistent with previous reddening insensitive estimates.
We confirm previous results that the observed slope of the sSFR–z relation is steeper than the one predicted by
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Source
Astrophysical Journal Letters
Type
Journal article
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Open Access