Copyright © 2021, Oxford University PressFontani, F.Barnes, A. T.Caselli, P.Henshaw, J. D.Cosentino, G.Jiménez Serra, I.Tan, J. C.Pineda, J. E.Law, C. Y.2022-02-112022-02-112021-03-22Monthly Notices of the Royal Astronomical Society 503(3): 4320–4335(2021)0035-8711https://academic.oup.com/mnras/article-abstract/503/3/4320/6179871http://hdl.handle.net/20.500.12666/530The 14N/15N ratio in molecules exhibits a large variation in star-forming regions, especially when measured from N2H+ isotopologues. However, there are only a few studies performed at high-angular resolution. We present the first interferometric survey of the 14N/15N ratio in N2H+ obtained with Atacama Large Millimeter Array observations towards four infrared-dark clouds harbouring 3 mm continuum cores associated with different physical properties. We detect N15NH+ (1–0) in ∼20−40 per cent of the cores, depending on the host cloud. The 14N/15N values measured towards the millimetre continuum cores range from a minimum of ∼80 up to a maximum of ∼400. The spread of values is narrower than that found in any previous single-dish survey of high-mass star-forming regions and than that obtained using the total power data only. This suggests that the 14N/15N ratio is on average higher in the diffuse gaseous envelope of the cores and stresses the need for high-angular resolution maps to measure correctly the 14N/15N ratio in dense cores embedded in IRDCs. The average 14N/15N ratio of ∼210 is also lower than the interstellar value at the Galactocentric distance of the clouds (∼300–330), although the sensitivity of our observations does not allow us to unveil 14N/15N ratios higher than ∼400. No clear trend is found between the 14N/15N ratio and the core physical properties. We find only a tentative positive trend between 14N/15N and H2 column density. However, firmer conclusions can be drawn only with higher sensitivity measurements.engStars: formationISM: CloudsISM: moleculesinfo:eu-repo/semantics/article10.1093/mnras/stab7001365-2966http://dx.doi.org/10.13039/501100000781http://dx.doi.org/10.13039/501100011033info:eu-repo/semantics/restrictedAccess