JWST reveals a population of ultra-red, flattened disk galaxies at 2<z<6 previously missed by HST


With just a month of data, JWST is already transforming our view of the Universe, revealing and resolving starlight in unprecedented populations of galaxies. Although ``HST-dark’’ galaxies have previously been detected at long wavelengths, these observations generally suffer from a lack of spatial resolution which limits our ability to characterize their sizes and morphologies. Here we report on a first view of starlight from a subset of the HST- dark population that are bright with JWST/NIRCam (4.4$μ$m<24.5mag) and very faint or even invisible with HST ($<$1.6$μ$m). In this Letter we focus on a dramatic and unanticipated population of physically extended galaxies ($rsim$0.17’’). These 12 galaxies have photometric redshifts $2<z<6$, high stellar masses $M_⋆rsim 10^10~M_ødot$, and significant dust-attenuated star formation. Surprisingly, the galaxies have elongated projected axis ratios at 4.4$μ$m, suggesting that the population is disk-dominated or prolate. Most of the galaxies appear red at all radii, suggesting significant dust attenuation throughout. We refer to these red, disky, HST-dark galaxies as Ultra-red Flattened Objects (UFOs). With $r_e$(F444W)$∼1-2$åisebox-0.5ex~kpc, the galaxies are similar in size to compact massive galaxies at $z∼2$ and the cores of massive galaxies and S0s at $z∼0$. The stellar masses, sizes, and morphologies of the sample suggest that some could be progenitors of lenticular or fast- rotating galaxies in the local Universe. The existence of this population suggests that our previous censuses of the universe may have missed massive, dusty edge-on disks, in addition to dust-obscured starbursts.

arXiv e-prints