We combine archival ALMA data targeting the Hubble Ultra Deep Field (HUDF) to
produce the deepest currently attainable 1-mm maps of this key, extragalactic
survey field. Combining all existing data in Band 6, our deepest map covers
4.2arcmin^2, with a beamsize of 1.49"x1.07" at an effective frequency of 243GHz
(1.23mm). It reaches an rms of 4.6uJy/beam, with 1.5arcmin^2 below 9.0uJy/beam,
an improvement of >5% over the best previously published map and 50%
improvement in some regions. We also make a wider, but shallower map, covering
25.4arcmin^2. We detect 45 galaxies in the deep map down to 3.6sigma, including
10 more 1-mm sources than previously detected. 38 of these galaxies have a JWST
ID from the JADES NIRCam imaging and the new sources are typically faint and
red. A stacking analysis on the positions of ALMA-undetected JADES galaxies
yields detections for z<4 and stellar masses from 10^(8.4) to 10^(10.4)Msun,
extracting 10% of additional stacked signal from our map compared to previous
analyses. Detected sources and stacking contribute (10.0+/-0.5)Jy/deg^2 of the
cosmic infrared background (CIB) at 1.23mm. Although this is short of the
(uncertain) background level of about 20Jy/deg^2, after taking into account
intrinsic fluctuations in the CIB, our measurement is consistent with the
background if the HUDF is a mild (~2sigma) negative fluctuation. This suggests
that within the HUDF, JWST may have detected essentially all of the galaxies
that contribute to the CIB. Our stacking analysis predicts that the field
contains around 60 additional galaxies with 1.23mm flux densities averaging
around 15uJy, and over 300 galaxies at the few uJy level. However, the
contribution of these fainter more modestly-obscured objects to the background
is small, and converging, as anticipated from the now well-established strong
correlation between galaxy stellar mass and obscured star formation.Comment: Submitted to MNRA