NIKA2 Cosmological Legacy Survey. First measurement of the confusion noise at the IRAM 30 m telescope

Ponthieu, N., Desert, F.-X., Beelen, A., Adam, R., Ade, Peter ORCID: https://orcid.org/0000-0002-5127-0401, Ajeddig, H., Amarantidis, S., Andre, P., Aussel, H., Benoit, A., Berta, S., Bethermin, M., Bing, L. J., Bongiovanni, A., Bounmy, J., Bourrion, O., Calvo, M., Catalano, A., Chérouvrier, D., De Petris, M., Doyle, S. ORCID: https://orcid.org/0000-0002-9054-986X and Tucker, C. ORCID: https://orcid.org/0000-0002-1851-3918 2026. NIKA2 Cosmological Legacy Survey. First measurement of the confusion noise at the IRAM 30 m telescope. Astronomy & Astrophysics 705 , A213. 10.1051/0004-6361/202554530

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Abstract

The NIKA2 Cosmological Legacy Survey (N2CLS) is a large programme using the NIKA2 dual-band camera on the IRAM 30 m telescope. Its goal is to improve our understanding of the physics of distant Dusty Star Forming Galaxies (DSFGs) by carrying out deep surveys of two fields, GOODS-North and COSMOS. This work is focussed on GOODS-North, which was observed for 78.2 hours, simultaneously at 1.2 and 2 mm, with a field of view of ∼240 arcmin 2 . With such a deep integration, we were able to measure, for the first time, the confusion noise limits at the 30 m telescope using the best sampled ∼62 arcmin 2 and masking sources with a flux greater than 0.54 or 0.17 mJy at 1.2 or 2 mm, respectively. We found a confusion noise of 139.1 −19.2 +15.9 ±11.9 μJy/beam at 1.2 mm and 38.6 −13.1 +9.6 ±3.7 μJy/beam at 2 mm (the first uncertainty is statistical, the second is the cosmic variance). In this region, this corresponds to half the instrumental noise. To derive these estimates, we devised a novel estimator, referred to as the cross variance, which also enabled us to estimate the correlated confusion noise between the two bands. Thus, we obtained a result of 49.6 −24.8 +15.9 ±6.4 μJy/beam. These values are consistent with the state of the art Simulated Infrared Dusty Extragalactic Sky (SIDES) model.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	For the full list of authors, please see article webpage https://doi.org/10.1051/0004-6361/202554530
Publisher:	EDP Sciences
ISSN:	0004-6361
Date of First Compliant Deposit:	13 February 2026
Date of Acceptance:	17 June 2025
Last Modified:	13 Feb 2026 12:24
URI:	https://orca.cardiff.ac.uk/id/eprint/184814

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