The ALMA Frontier Fields Survey

III. 1.1 mm emission line identifications in Abell 2744, MACSJ 0416.1-2403, MACSJ 1149.5+2223, Abell 370, and Abell S1063

¹ Instituto de Astrofísica and Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
e-mail: jgonzal@astro.puc.cl
² Millennium Institute of Astrophysics, MAS, Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago de Chile, Chile
³ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, 80301 Colorado, USA
⁴ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁶ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
⁷ Zentrum für Astronomie, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany
⁸ Department of Astronomy, Universidad de Concepcion, Casilla 160-C, Concepción, Chile
⁹ Carnegie Institution for Science, Las Campanas Observatory, Casilla 601, Colina El Pino S/N, La Serena, Chile
¹⁰ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, 19001 Casilla, Santiago, Chile
¹² Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹³ Universidad Autónoma de Chile, Chile. Av. Pedro de Valdivia 425, Santiago, Chile
¹⁴ Physics Department, Ben-Gurion University of the Negev, PO Box 653, 8410501 Be’er- Sheva, Israel

Received: 9 April 2017
Accepted: 22 September 2017

Abstract

Context. Most sub-mm emission line studies of galaxies to date have targeted sources with known redshifts where the frequencies of the lines are well constrained. Recent blind line scans circumvent the spectroscopic redshift requirement, which could represent a selection bias.

Aims. Our aim is to detect emission lines present in continuum oriented observations. The detection of these lines provides spectroscopic redshift information and yields important properties of the galaxies.

Methods. We perform a search for emission lines in the Atacama Large Millimeter/submillimeter Array observations of five clusters which are part of the Frontier Fields and assess the reliability of our detection. We additionally investigate plausibility by associating line candidates with detected galaxies in deep near-infrared imaging.

Results. We find 26 significant emission lines candidates, with observed line fluxes between 0.2–4.6 Jy kms^-1and velocity dispersions (FWHM) of 25–600kms^-1. Nine of these candidates lie in close proximity to near-infrared sources, boosting their reliability; in six cases the observed line frequency and strength are consistent with expectations given the photometric redshift and properties of the galaxy counterparts. We present redshift identifications, magnifications, and molecular gas estimates for the galaxies with identified lines. We show that two of these candidates likely originate from starburst galaxies, one of which is a so-called jellyfish galaxy that is strongly affected by ram pressure stripping, while another two are consistent with being main sequence galaxies based in their depletion times.

Conclusions. This work highlights the degree to which serendipitous emission lines can be discovered in large mosaic continuum observations when deep ancillary data are available. The low number of high-significance line detections, however, confirms that such surveys are not as optimal as blind line scans. We stress that Monte Carlo simulations should be used to assess the line detection significances since using the negative noise suffers from stochasticity and incurs significantly larger uncertainties.