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Thorbjørn Clausen

Publications and source records attributed to Thorbjørn Clausen.

2 recordsLinked to original sources

Performance of Photometric Template Fitting for Ultra-High Redshift Galaxies

The James Webb Space Telescope (JWST) has enabled the discovery of a significant population of galaxies at z > 10. Our understanding of the astrophysical properties of these galaxies relies on fitting templates developed using models predicting the differences between these first galaxies and lower-redshift counterparts. In this work, tests are performed on several of these high-redshift template sets in order to determine how successful they are at predicting both photometric redshifts and full spectral energy distributions (SEDs). Our work shows that the best templates for photometric redshift estimation differ from the best templates for predicting the full SED. Overall, some templates perform adequately at photometric redshift estimation, while all are generally poor predictors of the full SED. A few objects in particular are poorly fit by all the template sets tested. We conclude that although photometric redshifts can be reliable when given a high enough observational depth and adequate filters, models are not yet able to produce robust astrophysical properties for these ultra-high-redshift galaxies.

astro-ph.IM↗

The Highest-Redshift Balmer Breaks as a Test of $Λ$CDM

Recent studies have reported tension between the presence of luminous, high-redshift galaxies and the halo mass functions predicted by standard cosmology. Here, an improved test is proposed using the presence of high-redshift Balmer breaks to probe the formation of early $10^4 - 10^5 M_\odot$ baryonic minihalos. Unlike previous tests, this does not depend upon the mass-to-light ratio, stellar initial mass function, or star-formation history, which are all weakly constrained at high redshift. We show that the strongest Balmer breaks allowed at $z = 9$ using the simplest $Λ$CDM cosmological model have $D_{4000} \leq 1.26$ under idealized circumstances and $D_{4000} \leq 1.14$ including realistic feedback models. Since current photometric template fitting to JWST sources infers the existence of stronger Balmer breaks out to $z \gtrsim 11$, upcoming spectroscopic followup will either demonstrate those templates are invalid at high redshift or imply new physics beyond `vanilla' $Λ$CDM.

astro-ph.GA↗