The Herschel-SPIRE Dark Field III: probing the deepest Herschel field with SCUBA-2
File(s)
Published version
Author(s)
Parmar, Ayushi
Clements, David L
Pearson, Chris
Varnish, Thomas WO
Type
Journal Article
Abstract
The Herschel-SPIRE Dark Field (SDF), originally observed for calibration of the SPIRE instrument, is the deepest far-infrared field to date (equivalent exposure time of $\sim 700$ h deg$^{-1}$) at wavelengths 250–$500\,\, \mu$m, probing below the SPIRE confusion limit. We present SCUBA-2 $850\,\, \mu$m observations covering the central Deep Region, detecting 36 sources with number counts consistent with previous surveys at this wavelength. Cross-identification with multiwavelength catalogues reveals 20 SPIRE-dropouts, whose stacked SPIRE fluxes suggest a photometric redshift of $z \sim 4$. Photo-z estimates from the magphys, bagpipes, and mmpz tools are consistent within the uncertainties for 3 sources ($z \sim 1$–2), while 13 are inconsistent, and 20 lack sufficient data due to counterpart ambiguity or non-detections. We flag a total of 9 sources as potentially lensed and 15 as potential multiples. Spectral energy distribution fitting yields average properties for SPIRE-detected sources of log$_{10}(L_{\text{FIR}}$/L$_{\odot }) = 13.6\pm 0.1$, log$_{10}(M_{\text{dust}}$/M$_{\odot }) = 8.1\pm 0.1$, and SFR$_{\text{obsc}} = 7000\pm 1900\,$ M$_{\odot}$ yr$^{-1}$. The stacked dropouts yield log$_{10}(L_{\text{FIR}}$/L$_{\odot }) = 12.8^{+0.5}_{-0.7} [12.5^{+0.4}_{-0.6}]$, log$_{10}(M_{\text{dust}}$/M$_{\odot }) = 6.52^{+0.33}_{-0.41} [6.71^{+0.19}_{-0.23}]$, and SFR$_{\text{obsc}} = 700^{+1500}_{-560} [350^{+420}_{-250}]\,$ M$_{\odot}$ yr$^{-1}$ at a derived $z = 6.7^{+2.4}_{-3.0}$ (at a fixed $z = 4.0^{+0.1}_{-0.6}$) contributing $\sim 15$ ($\sim 2$) per cent of the cosmic star formation rate density (SFRD) at that epoch. We find an excess at $z\sim 1$ in the SFRD of SPIRE-detected sources, consistent with the sub-mJy bump in SPIRE number counts previously identified in this field, possibly tracing large-scale structure.
Date Issued
2026-05-01
Date Acceptance
2026-03-24
Citation
Monthly Notices of the Royal Astronomical Society, 2026, 548 (3)
ISSN
0035-8711
Publisher
Oxford University Press (OUP)
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
548
Issue
3
Copyright Statement
© The Author(s) 2026. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
License URL
Publication Status
Published
Article Number
stag631
Date Publish Online
2026-04-02