VENUS: A Strongly Lensed Clumpy Galaxy at $z\sim 11-12$ behind the Galaxy Cluster MACS J0257.1-2325

Abstract

We present the discovery of a strongly lensed galaxy at $z\sim 11-12$, dubbed the ``Misty Moons'', identified in the JWST Treasury Survey, Vast Exploration for Nascent, Unexplored Sources (VENUS). The Misty Moons is gravitationally lensed by the galaxy cluster MACS J0257.1-2325 at $z=0.505$, and has five multiple images suggested by two independent lensing models. Two of the five images, ID1 and ID2 ($\hat{I}¼\sim 20-30$), are very bright (F200W$\sim 26$ AB mag) and exhibit blue SEDs with prominent Ly$\hat{I}\pm$ breaks. In the source plane, the Misty Moons is a sub-$L^{\ast }$ galaxy ($M_{\mathrm{UV}}\sim -18.0$ mag) resolved into multiple stellar clumps, each of which has an effective radius of $r_{\mathrm{eff}}\sim 10-70$ pc and a stellar mass of $\sim 10^7{M}_{\odot }$. These clumps dominate the stellar mass budget of the Misty Moons ($\gtrsim 80\%$), similar to other high-$z$ clumps, which suggests a highly clustered mode of star formation in the early Universe, unlike seen in local dwarf galaxies. We convolve the source-plane image with the JWST/NIRCam point-spread function to produce a mock NIRCam image of the Misty Moons without lensing magnification, and find that the intrinsic galaxy has a radial surface-brightness profile comparable to those of $z\gtrsim 10$ faint galaxies, such as JADES-GS-z13-0 and JADES-GS-z14-1, indicating that the Misty Moons represents a typical $z\gtrsim 10$ faint galaxy. The Misty Moons, a lensed galaxy with resolved internal structures, provides an ideal laboratory for exploring the early stages of galaxy formation at $z\gtrsim 10$.

25 pages, 12 figures, accepted for publication in ApJ