The ALMA Patchy Deep Survey: A blind search for [CII] emitters at z~4.5

TL;DR

This study conducted a blind search for [CII] emitters at z~4.5 using ALMA archival data, setting upper limits on their luminosity function, but did not detect any new emitters, highlighting the need for more data to understand dusty galaxy contributions.

Contribution

First blind search for [CII] emitters at z~4.5 using extensive ALMA archival data, establishing upper limits on luminosity functions and demonstrating the potential of the ALMA Patchy Deep Survey.

Findings

No new [CII] emitters detected above 6-sigma significance.

Upper limits set on [CII] luminosity function at z~4.5.

Current limits are two orders of magnitude above theoretical expectations.

Abstract

We present a result of a blind search for [CII] 158 $\mu$m emitters at $z\sim 4.5$ using ALMA Cycle~0 archival data. We collected extra-galactic data covering at 330-360 GHz (band~7) from 8 Cycle~0 projects from which initial results have been already published. The total number of fields is 243 and the total on-source exposure time is 19.2 hours. We searched for line emitters in continuum-subtracted data cubes with spectral resolutions of 50, 100, 300 and 500 km/s. We could not detect any new line emitters above a 6-$\sigma$ significance level. This result provides upper limits to the [CII] luminosity function at $z\sim 4.5$ over $L_{\rm [CII]} \sim 10^8 - 10^{10} L_{\odot}$ or star formation rate, SFR $\sim$ 10-1000 M$_{^\odot}$/yr. These limits are at least 2 orders of magnitude larger than the [CII] luminosity functions expected from the $z \sim 4$ UV luminosity function or from numerical simulation. However, this study demonstrates that we would be able to better constrain the [CII] luminosity function and to investigate possible contributions from dusty galaxies to the cosmic star-formation rate density by collecting Cycle~1+2 archival data as the ALMA Patchy Deep Survey.