Letter to the Editor

Sub-arcsecond imaging of Arp 299-A at 150 MHz with LOFAR: Evidence for a starburst-driven outflow

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: naimro@iaa.es
² Jodrell Bank Centr for Astrophysics, Alan Turing Building, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³ Visiting Scientist: Facultad de Ciencias, Univ. de Zaragoza, Zaragoza, Spain
⁴ Centro de Astrobiología (CSIC-INTA), ESAC Campus, 28692 Villanueva de Cañada, Madrid, Spain
⁵ Centre for Astrophysics & Supercomputing Swinburne University of Technology, John St, Hawthorn VIC 3122, Australia
⁶ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁷ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁸ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁹ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden

Received: 23 December 2017
Accepted: 2 February 2018

Abstract

We report on the first sub-arcsecond (0.44 × 0.41 arcsec²) angular resolution image at 150 MHz of the A-nucleus in the luminous infrared galaxy Arp 299, from International Low Frequency Array (LOFAR) Telescope observations. The most remarkable finding is that of an intriguing two-sided, filamentary structure emanating from the A-nucleus, which we interpret as an outflow that extends up to at least 14 arcsec from the A-nucleus in the N–S direction ( ≈5 kpc deprojected size) and accounts for almost 40% of the extended emission of the entire galaxy system. We also discuss HST/NICMOS [FeII] 1.64 μm and H₂ 2.12 μm images of Arp 299-A, which show similar features to those unveiled by our 150 MHz LOFAR observations, providing strong morphological support for the outflow scenario. Finally, we discuss unpublished Na I D spectra that confirm the outflow nature of this structure. From energetic arguments, we rule out the low-luminosity active galactic nucleus in Arp 299-A as a driver for the outflow. On the contrary, the powerful, compact starburst in the central regions of Arp 299-A provides plenty of mechanical energy to sustain an outflow, and we conclude that the intense supernova (SN) activity in the nuclear region of Arp 299-A is driving the observed outflow. We estimate that the starburst wind can support a mass-outflow rate in the range (11–63 M_⊙ yr⁻¹) at speeds of up to 370–890 km s⁻¹, and is relatively young, with an estimated kinematic age of 3–7 Myr. Those results open an avenue to the use of low-frequency (150 MHz), sub-arcsecond imaging with LOFAR to detect outflows in the central regions of local luminous infrared galaxies.