JWST's first glimpse of a z > 2 forming cluster reveals a top-heavy stellar mass function
The Astrophysical Journal Letters(2024)
摘要
Clusters and their progenitors (protoclusters) at z = 2-4, the peak epoch of
star formation, are ideal laboratories to study the formation process of both
the clusters themselves and their member galaxies. However, a complete census
of their member galaxies has been challenging due to observational
difficulties. Here we present new JWST/NIRCam observations targeting the
distant cluster CLJ1001 at z = 2.51 from the COSMOS-Webb program, which, in
combination with previous narrow-band imaging targeting H-alpha emitters and
deep millimeter surveys of CO-emitters, provide a complete view of massive
galaxy assembly in CLJ1001. In particular, JWST reveals a population of
massive, extremely red cluster members in the long-wavelength bands that were
invisible in previous HST/F160W imaging (HST-dark). Based on this highly
complete spectroscopic sample of member galaxies, we show that the spatial
distribution of galaxies in CLJ1001 exhibits a strong central concentration,
with the central galaxy density already resembling that of low-z clusters.
Moreover, we reveal a "top-heavy" stellar mass function for the star-forming
galaxies (SFGs), with an overabundance of massive SFGs piled up in the cluster
core. These features strongly suggest that CLJ1001 is caught in a rapid
transition, with many of its massive SFGs likely soon becoming quiescent. In
the context of cluster formation, these findings suggest that the earliest
clusters form from the inside out and top to bottom, with the massive galaxies
in the core assembling first, followed by the less-massive ones in the
outskirts.
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关键词
Galaxies,Protoclusters,High-redshift galaxy clusters
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