# Detection of a Lensed z$\approx$11 Galaxy in the Rest-Optical with Spitzer/IRAC and the Inferred SFR, Stellar Mass, and Physical Size

Daniel Lam, Rychard J. Bouwens, Dan Coe, Adi Zitrin, Christopher Barber, Ivo Labbe, Themiya Nanayakkara, Megan Donahue, Renske Smit, Xinwen Shu, Ranga-Ram Chary, John Moustakas, Mario Nonino, Daniel D. Kelson, Tom Broadhurst, Larry Bradley, Mauricio Carrasco, Piero Rosati

Research output: Contribution to journalArticle

## Abstract

We take advantage of new 100-hour Spitzer/IRAC observations available for MACS0647-JD, a strongly lensed $z\approx11$ galaxy candidate, to provide improved constraints on its physical properties. Probing the physical properties of galaxies at $z>8$ is challenging due to the inherent faintness of such sources and the limited wavelength coverage available. Thanks to the high $\approx$2-6$\times$ lensing magnification of the multiple images of MACS0647-JD, we can use the sensitive Spitzer/IRAC data to probe the rest-frame optical fluxes of MACS0647-JD and investigate its physical properties including the age and the stellar mass. In deriving Spitzer/IRAC fluxes for MACS0647-JD, great care is taken in coping with the impact of three bright ($\approx$8-16 mag) stars in our field to ensure robust results. Assuming a constant star formation rate, the age, stellar mass, and rest-frame UV slope we estimate for MACS0647-JD based on a stack of the photometry are log$_{10}$(age/yr) = 8.6$^{+0.1}_{-2.1}$, log$_{10}$(M$_{*}$/M$_{\odot}$) = 9.1$^{+0.2}_{-1.4}$, and $\beta = -$1.3$\pm$0.6, respectively. We compare our results with expectations from the EAGLE simulation and find that MACS0647-JD has properties consistent with corresponding to the most massive and rapidly star-forming galaxies in the simulation. We also find that its radius, 105$\pm$28 pc, is a factor of $\approx$2 smaller than the mean size in a separate simulation project DRAGONS. Interestingly enough, the observed size is similar to the small sizes seen in very low-luminosity $z\approx$6-10 galaxies behind lensing clusters.
Original language English GB Arxiv preprint arXiv:1903.08177 Published - 2019

## Keywords

• Astrophysics - Astrophysics of Galaxies

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