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Abstract We report the discovery of 15 exceptionally luminous 10 ≲z≲ 14 candidate galaxies discovered in the first 0.28 deg2of JWST/NIRCam imaging from the COSMOS-Web survey. These sources span rest-frame UV magnitudes of −20.5 >MUV> −22, and thus constitute the most intrinsically luminousz≳ 10 candidates identified by JWST to date. Selected via NIRCam imaging, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuinez≳ 10 sources and 3/15 (20%) likely low-redshift contaminants. Three of ourz∼ 12 candidates push the limits of early stellar mass assembly: they have estimated stellar masses ∼ 5 × 109M⊙, implying an effective stellar baryon fraction ofϵ⋆∼ 0.2−0.5, whereϵ⋆≡M⋆/(fbMhalo). The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales < 100 Myr where the star formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred forM⋆∼ 1010M⊙galaxies relative toM⋆∼ 109M⊙—both about 10−6Mpc−3—implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UV luminosity function from a double power law to a Schechter function atz≈ 8. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understand how, and if, such early massive galaxies push the limits of galaxy formation in the Lambda cold dark matter paradigm.
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Stress testing ΛCDM with high-redshift galaxy candidates
Abstract Early data from the James Webb Space Telescope (JWST) have revealed a bevy of high-redshift galaxy candidates with unexpectedly high stellar masses. An immediate concern is the consistency of these candidates with galaxy formation in the standardΛCDM cosmological model, wherein the stellar mass (M⋆) of a galaxy is limited by the available baryonic reservoir of its host dark matter halo. The mass function of dark matter haloes therefore imposes an absolute upper limit on the number densityn(>M⋆, z) and stellar mass densityρ⋆(>M⋆, z) of galaxies more massive thanM⋆at any epochz. Here I show that the most massive galaxy candidates in JWST observations atz ≈ 7–10 lie at the very edge of these limits, indicating an important unresolved issue with the properties of galaxies derived from the observations, how galaxies form at early times inΛCDM or within this standard cosmology itself.
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- PAR ID:
- 10406675
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Astronomy
- Volume:
- 7
- Issue:
- 6
- ISSN:
- 2397-3366
- Page Range / eLocation ID:
- p. 731-735
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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