Galaxy Build-up in the first 1.5 Gyr of Cosmic History: Insights from the Stellar Mass Function at z∼4-9 from JWST NIRCam Observations
arxiv(2024)
摘要
Combining the public JWST/NIRCam imaging programs CEERS, PRIMER and JADES,
spanning a total area of ∼500 arcmin^2, we obtain a sample of >30,000
galaxies at z∼4-9 that allows us to perform a complete, rest-optical
selected census of the galaxy population at z>3. Comparing the stellar mass
M_* and the UV-slope β distributions between JWST- and HST-selected
samples, we generally find very good agreement and no significant biases.
Nevertheless, JWST enables us to probe a small population of UV-red galaxies
that was missing from previous HST-based LBG samples. We measure galaxy stellar
mass functions (SMFs) at z∼4-9 and show that they are broadly consistent
with existing literature results. However, UV-red galaxies dominate the
high-mass end of the SMF at least out to z∼6. In particular the most
massive galaxies typically show very red colors between
λ_obs∼1.5μm and ∼4.5μm, and thus JWST's unprecedented
resolution and sensitivity at these wavelengths yields more accurate
constraints on their abundance and masses. The implied redshift evolution of
the high-mass end of the SMF suggests a rapid build-up of massive dust-obscured
as well as quiescent galaxies from z∼6 to z∼4 as well as an enhanced
efficiency of star formation towards earlier times (z≳6). We find the
SMFs to be steep over the entire redshift range, and slightly steepening with
redshift from z∼ 4-6, reaching values of ≈-2 at z≳6.
Finally, we show that the galaxy mass density grows by a factor ∼20×
in the ∼1 Gyr of cosmic time from z∼9 to z∼4. Our results
emphasize the importance of rest-frame optically-selected samples in inferring
accurate distributions of physical properties and studying the mass build-up of
galaxies in the first 1.5 Gyr of cosmic history.
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