As previously noted, the James Webb Space Telescope (JWST) has seen the earliest detected galaxies, far earlier than should be possible in the LambdaCDM Standard Model of Cosmology.
A new paper spells out how the JWST improves on the Hubble Space Telescope in capabilities to see such galaxies and recognizes that the "impossible early galaxies" problem is a severe one for the LambdaCDM paradigm.
Modified gravity theories that seek to explain dark matter (including efforts to explain dark matter with non-Newtonian General Relativistic effects) generically result in earlier galaxy formation than in LambdaCDM.
On July 13, 2022, NASA released to the whole world the data obtained by the James Webb Space Telescope (JWST) Early Release Observations (ERO). These are the first set of science-grade data from this long-awaited facility, marking the beginning of a new era in astronomy. Many critical questions unanswered in the past several decades now see the hope of being addressed. JWST will push the redshift boundary far beyond what has been reached by the Hubble Space Telescope (HST), and in so doing it will lead to the understanding of how the first luminous objects - first stars and first galaxies - were formed in the early universe.
The red wavelength cut-off at 1.6 micron limits HST to redshift around 11, which is when the age of the universe was only ~420 million years. The NIRCam instrument, the most sensitive camera onboard JWST, extends to 5 micron and will allow for the detection of early objects only several tens of million years after the Big Bang should they exist.
Among the JWST ERO targets there is a nearby galaxy cluster SMACS 0723-73, which is a massive cluster and has been long recognized as a good "cosmic telescope" to amplify the background, far-away galaxies through its gravitational lensing effect. The NIRCam field-of-view is large enough that the ERO observations have covered not only the cluster but also a flanking field not boosted by gravitational lensing. JWST is so sensitive that the flanking field also sees far beyond HST.
Here we report the result from our search of candidate galaxies at redshift larger than 11 using these ERO data. We have a total of 88 such candidates spreading over the two fields, some of which could be at redshifts as high as 20. Neither the high number of such objects found nor the high redshifts they reside at are expected from the previously favored predictions.
Haojing Yan, et al., "First Batch of Candidate Galaxies at Redshifts 11 to 20 Revealed by the James Webb Space Telescope Early Release Observations" arXiv:2207.11558 (July 23, 2022).
Another paper also discusses the finds and suggests that JWST may be approaching the limits of finding the oldest galaxies because the oldest galaxies found by the JWST also appear to be very young galaxies.
One of the main goals of the JWST is to study the first galaxies in the Universe. We present a systematic photometric analysis of very distant galaxies in the first JWST deep field towards the massive lensing cluster SMACS0723. As a result, we report the discovery of two galaxy candidates at z∼16, only 250 million years after the Big Bang. We also identify two candidates at z∼12 and 11 candidates at z∼10−11.
Our search extended out to z≲21 by combining color information across seven NIRCam and NIRISS filters. By modelling the Spectral Energy Distributions (SEDs) with EAZY and BEAGLE, we test the robustness of the photometric redshift estimates. While their intrinsic (un-lensed) luminosity is typical of the characteristic luminosity L∗ at z>10, our high-redshift galaxies typically show small sizes and their morphologies are consistent with disks in some cases. The highest-redshift candidates have extremely blue UV-continuum slopes −3<β<−2.5, young ages ∼10−100 Myr, and stellar masses log(M⋆/M⊙)=8.4−8.8 inferred from their SED modeling which indicate a rapid build-up of their stellar mass. Our search clearly demonstrates the capabilities of JWST to uncover robust photometric candidates up to very high redshifts, and peer into the formation epoch of the first galaxies.
Hakim Atek, et al., "Revealing Galaxy Candidates out to z∼16 with JWST Observations of the Lensing Cluster SMACS0723" arXiv:2207.12338 (July 25, 2022).
Yet another paper looks at early galaxies seen by the JWST at arXiv:2207.12356.