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arXiv · 2410.16354

Galaxy Size and Mass Build-up in the First 2 Gyrs of Cosmic History from Multi-Wavelength JWST NIRCam Imaging

Natalie Allen·Pascal A. Oesch·Sune Toft·Jasleen Matharu·Conor J. R. McPartland·Andrea Weibel·Gabe Brammer·Rebecca A. A. Bowler·Kei Ito·Rashmi Gottumukkala·Francesca Rizzo·Francesco Valentino·Rohan G. Varadaraj·John R. Weaver·Katherine E. Whitaker
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Abstract

The evolution of galaxy sizes in different wavelengths provides unique insights on galaxy build-up across cosmic epochs. Such measurements can now finally be done at $z>3$ thanks to the exquisite spatial resolution and multi-wavelength capability of the JWST. With the public data from the CEERS, PRIMER-UDS, and PRIMER-COSMOS surveys, we measure the sizes of $\sim 3500$ star-forming galaxies at $3 \leqslant z<9$, in 7 NIRCam bands using the multi-wavelength model fitting code GalfitM. The size-mass relation is measured in four redshift bins, across all NIRCam bands. We find that, the slope and intrinsic scatter of the rest-optical size-mass relation are constant across this redshift range and consistent with previous HST-based studies at low-z. When comparing the relations across different wavelengths, the average rest-optical and rest-UV relations are consistent with each other up to $z=6$, but the intrinsic scatter is largest in rest-UV wavelengths compared to rest-optical and redder bands. This behaviour is independent of redshift and we speculate that it is driven by bursty star-formation in $z>4$ galaxies. Additionally, for $3\leqslant z<4$ star-forming galaxies at $\rm M_* > 10^{10} M_{\odot}$, we find smaller rest-$\rm 1\rm\,μm$ sizes in comparison to rest-optical (and rest-UV) sizes, suggestive of colour gradients. When comparing to simulations, we find agreement over $\rm M_* \approx 10^{9} - 10^{10} M_{\odot}$ but beyond this mass, the observed size-mass relation is significantly steeper. Our results show the power of JWST/NIRCam to provide new constraints on galaxy formation models.

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Natalie Allen, Pascal A. Oesch, Sune Toft, Jasleen Matharu, Conor J. R. McPartland, Andrea Weibel, Gabe Brammer, Rebecca A. A. Bowler, Kei Ito, Rashmi Gottumukkala, Francesca Rizzo, Francesco Valentino, Rohan G. Varadaraj, John R. Weaver, Katherine E. Whitaker. 2024-10-21. Galaxy Size and Mass Build-up in the First 2 Gyrs of Cosmic History from Multi-Wavelength JWST NIRCam Imaging. https://doi.org/10.1051/0004-6361%2F202452690

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