A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

IV. A tail of ionised gas in the merger remnant NGC4424

¹ Aix-Marseille Univ., CNRS, CNES, LAM, Marseille, France
e-mail: alessandro.boselli@lam.fr
² Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
³ Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
e-mail: matteo.fossati@durham.ac.uk
⁴ Universitá di Milano-Bicocca, Piazza della scienza 3, 20100 Milano, Italy
e-mail: guido.consolandi@mib.infn.it
⁵ Department of Physics and Astronomy, University of Alabama in Huntsville, Huntsville, AL 35899, USA
⁶ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
⁷ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁸ International Centre for Radio Astronomy Research, The University of western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
⁹ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
¹⁰ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹¹ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Observatoire de Paris, PSL University, 91191 Gif-sur-Yvette Cedex, France
¹² Department of Physiscs and Astronomy, Youngstown State University, Youngstown, OH, USA
¹³ PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA
¹⁴ Department of Astrophysics, University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria
¹⁵ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, 20014 Finland
¹⁶ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, 20014 Finland
¹⁷ Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidadede São Paulo, Cidade Universitária, CEP 05508-900 São Paulo, SP, Brazil
¹⁸ Cerro Tololo Inter-American Observatory, SOAR Telescope, Casilla 603, La Serena, Chile
¹⁹ Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
²⁰ Instituto de Astronomía, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Ciudad de México 04510, Mexico
²¹ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
²² UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
²³ Texas Tech University, Physics Department, Box 41051, Lubbock, TX 79409-1051, USA
²⁴ INAF-Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
²⁵ Observatoire Astronomique de Strasbourg, UMR 7750, 11 rue de l’Université, 67000 Strasbourg, France

Received: 20 July 2018
Accepted: 22 October 2018

Abstract

We observed the late-type peculiar galaxy NGC 4424 during the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band Hα+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii Telescope (CFHT). The presence of a ∼110 kpc (in projected distance) HI tail in the southern direction indicates that this galaxy is undergoing a ram pressure stripping event. The deep narrow-band image revealed a low surface brightness (Σ(Hα) ≃ 4 × 10⁻¹⁸ erg s⁻¹ cm⁻² arcsec⁻²) ionised gas tail ∼10 kpc in length extending from the centre of the galaxy to the north-west, thus in the direction opposite to the HI tail. Chandra and XMM X-rays data do not show a compact source in the nucleus or an extended tail of hot gas, while IFU spectroscopy (MUSE) indicates that the gas is photo-ionised in the inner regions and shock-ionised in the outer parts. Medium-resolution (MUSE) and high-resolution (Fabry-Perot) IFU spectroscopy confirms that the ionised gas is kinematically decoupled from the stellar component and indicates the presence of two kinematically distinct structures in the stellar disc. The analysis of the SED of the galaxy indicates that the activity of star formation was totally quenched in the outer disc ∼250–280 Myr ago, while only reduced by ∼80% in the central regions. All this observational evidence suggests that NGC 4424 is the remnant of an unequal-mass merger that occurred ≲500 Myr ago when the galaxy was already a member of the Virgo cluster, and is now undergoing a ram pressure stripping event that has removed the gas and quenched the activity of star formation in the outer disc. The tail of ionised gas probably results from the outflow produced by a central starburst fed by the collapse of gas induced by the merging episode. This outflow is sufficiently powerful to overcome the ram pressure induced by the intracluster medium on the disc of the galaxy crossing the cluster. This analysis thus suggests that feedback can participate in the quenching process of galaxies in high-density regions.