Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Justus L. Gibson, Erica Nelson, Christina C. Williams, Sedona H. Price, Katherine E. Whitaker
| Summary:
One of the more surprising findings after the first year of JWST observations
is the large number of spatially extended galaxies (ultra-red flattened
objects, or UFOs) among the optically-faint galaxy population otherwise thought
to be compact. Leveraging the depth and survey area of the JADES survey, we
extend observations of the optically-faint galaxy population to an additional
112 objects, 56 of which are well-resolved in F444W with effective sizes, $R_e
> 0.25”$, more than tripling previous UFO counts. These galaxies have
redshifts around $2 < z < 4$, high stellar masses ($mathrm{log(M_*/M_{odot})}
sim 10-11$), and star-formation rates around $sim 100-1000
mathrm{M_{odot}/yr}$. Surprisingly, UFOs are red across their entire extents
which spatially resolved analysis of their stellar populations shows is due to
large values of dust attenuation (typically $A_V > 2$ mag even at large radii).
Morphologically, the majority of our UFO sample tends to have low S’ersic
indices ($n sim 1$) suggesting these large, massive, optically faint galaxies
have little contribution from a bulge in F444W. Further, a majority have
axis-ratios between $0.2 < q < 0.4$, which Bayesian modeling suggests that
their intrinsic shapes are consistent with being a mixture of inclined disks
and prolate objects with little to no contribution from spheroids. While
kinematic constraints will be needed to determine the true intrinsic shapes of
UFOs, it is clear that an unexpected population of large, disky or prolate
objects contributes significantly to the population of optically faint
galaxies.
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