The ALMA Spectroscopic Survey in the HUDF: A Search for [CII] Emitters at $6\le z\le 8$

Abstract

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212-272 GHz) covers potential [CII] emission in galaxies at $6\le z\le 8$ throughout a 2.9 arcmin${}^2$ area. By selecting on known Lyman-$\hat{I}\pm$ emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5$\ddot{I}ƒ$ [CII] luminosity depth $L_{[\mathrm{CII}]}\sim 2.0\times 10^8$ L${}_{\odot }$, corresponding roughly to star formation rates (SFRs) of $10$-$20$ M${}_{\odot }$ yr${}^{-1}$ when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [CII] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of $z=6$-$7$ LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between $L_{[\mathrm{CII}]}$ and SFR -- with the exception of a single [CII]-deficient, UV luminous LBG. We also perform a blind search for [CII]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [CII] sources with $L_{[\mathrm{CII}]}>2.0\times 10^8$ L${}_{\odot }$ ($5\ddot{I}ƒ$) to be less than $1.8\times 10^{-4}$ Mpc${}^{-3}$ (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [CII] luminosity function from $z=6$-$8$ to $z\sim 0$ by comparing the ASPECS measurement to literature results at lower redshift.

16 pages, 6 figures, accepted for publication in ApJ