Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569^⋆,⋆⋆

¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
e-mail: alessandro.boselli@lam.fr
² CEA/IRFU/SAP, Laboratoire AIM Paris-Saclay, CNRS/INSU, Université Paris Diderot, Observatoire de Paris, PSL Research University, 91191 Gif-sur-Yvette Cedex, France
³ Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany
⁴ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
⁵ Astronomical Institute of the Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany
⁶ Universitá di Milano-Bicocca, piazza della scienza 3, 20100 Milano, Italy
⁷ Coelum Astronomia, via Appia 20, 30173 Venezia, Italy
⁸ International Centre for Radio Astronomy Research, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia
⁹ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
¹⁰ Department of Physiscs and Astronomy, Youngstown State University, Youngstown, OH 44503, USA
¹¹ Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
¹² Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹³ National Astronomy Observatory of Japan, 2-21-1 Osawa, Mitaka-shi, 181-8588 Tokyo, Japan
¹⁴ Physics Department, University of Alabama in Huntsville, Huntsville, AL 35899, USA
¹⁵ UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
¹⁶ Texas Tech University, Physics Department, Box 41051, Lubbock, TX 79409-1051, USA

Received: 20 November 2015
Accepted: 18 January 2016

Abstract

Context. Using MegaCam at the CFHT, we obtained a deep narrow band Hα+[NII] wide-field image of NGC 4569 (M90), the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of long tails of diffuse ionized gas, without any associated stellar component extending from the disc of the galaxy up to ≃80 kpc (projected distance) and with a typical surface brightness of a few 10^-18 erg s^-1 cm^-2 arcsec^-2. These features provide direct evidence that NGC 4569 is undergoing a ram-presure stripping event. The image also shows a prominent 8 kpc spur of ionized gas that is associated with the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Hα surface brightness of these extended low-surface brightness features to derive the density and the mass of the gas that has been stripped during the interaction of the galaxy with the intracluster medium. The comparison with ad hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Hα emitting gas in the tail is a large fraction of that of the cold phase that has been stripped from the disc, suggesting that the gas is ionized within the tail during the stripping process. The lack of star-forming regions suggests that mechanisms other than photoionization are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (M_star ≃ 10^10.5 M_⊙) galaxies located in intermediate-mass (≃10¹⁴ M_⊙) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is only ~1% than that removed during the ram pressure stripping event.Together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism that is responsible for the quenching of the star formation activity of galaxies in high density environments.