The ALMA Frontier Fields Survey

IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACS J0416.1–2403 and MACS J1149.5+2223

¹ Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
e-mail: alejandra.munozar@uv.cl
² Instituto de Astrofísica y Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
³ Núcleo de Astronomía de la Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
⁴ Millennium Institute of Astrophysics, Santiago, Chile
⁵ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
⁶ Zentrum für Astronomie, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany
⁷ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁸ Departamento de Ciencias Físicas, Universidad Andres Bello, Av. República 252, Santiago, Chile
⁹ Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
¹⁰ Department of Astronomy, Universidad de Concepción, Casilla 160-C, Concepción, Chile
¹¹ Carnegie Institution for Science, Las Campanas Observatory, Casilla 601, Colina El Pino S/N, La Serena, Chile
¹² Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla, 19001 Santiago, Chile
¹⁴ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, PR China
¹⁵ Universidad Autónoma de Chile, Av. Pedro de Valdivia 425, Santiago, Chile
¹⁶ Physics Department, Ben-Gurion University of the Negev, PO Box 653, Be’er-Sheva 8410501, Israel

Received: 8 December 2017
Accepted: 20 August 2018

Abstract

Context. Characterizing the number counts of faint (i.e., sub-mJy and especially sub-100 μJy), dusty star-forming galaxies is currently a challenge even for deep, high-resolution observations in the FIR-to-mm regime. They are predicted to account for approximately half of the total extragalactic background light at those wavelengths. Searching for dusty star-forming galaxies behind massive galaxy clusters benefits from strong lensing, enhancing their measured emission while increasing spatial resolution. Derived number counts depend, however, on mass reconstruction models that properly constrain these clusters.

Aims. We aim to estimate the 1.1 mm number counts along the line of sight of three galaxy clusters, Abell 2744, MACS J0416.1–2403, and MACS J1149.5+2223, which are part of the ALMA Frontier Fields Survey. We have performed detailed simulations to correct these counts for lensing effects, probing down to the sub-mJy flux density level.

Methods. We created a source catalog based on ALMA 1.1 mm continuum detections. We used several publicly available lensing models for the galaxy clusters to derive the intrinsic flux densities of these sources. We performed Monte Carlo simulations of the number counts for a detailed treatment of the uncertainties in the magnifications and adopted source redshifts.

Results. We estimate lensing-corrected number counts at 1.1 mm using source detections down to S/N = 4.5. In each cluster field, we find an overall agreement among the number counts derived for the different lens models, despite their systematic variations regarding source magnifications and effective areas. Combining all cluster fields, our number counts span ∼2.5 dex in demagnified flux density, from several mJy down to tens of μJy. Both our differential and cumulative number counts are consistent with recent estimates from deep ALMA observations at a 3σ level. Below ≈0.1 mJy, however, our cumulative counts are lower by ≈1 dex, suggesting a flattening in the number counts.

Conclusions. We derive 1.1 mm number counts around three well-studied galaxy clusters following a statistical approach. In our deepest ALMA mosaic, we estimate number counts for intrinsic flux densities ≈4 times fainter than the rms level. This highlights the potential of probing the sub-10 μJy population in larger samples of galaxy cluster fields with deeper ALMA observations.