A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

XII. Ionised gas emission in the inner regions of lenticular galaxies^⋆,⋆⋆

¹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
e-mail: alessandro.boselli@lam.fr
² Universitá di Milano-Bicocca, piazza della scienza 3, 20100 Milano, Italy
³ Instituto Tecnológico de Aeronáutica (ITA), São José dos Campos, Sao Paolo, Brazil
⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁵ Centro de Astronomiá (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁶ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
⁷ International Centre for Radio Astronomy Research, The University of Western Australia, 35 Stirling Hw, 6009 Crawley, Australia
⁸ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁹ National Research Council of Canada, Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁰ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, Observatoire de Paris, PSL University, 91191 Gif-sur-Yvette Cedex, France
¹¹ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
¹² Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹³ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹⁴ Department of Astronomy, Peking University, Beijing 100871, PR China
¹⁵ University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada
¹⁶ Osservatorio Astronomico di Cagliari, Via della scienza 5, 09047 Selargius, Cagliari, Italy
¹⁷ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20159 Milano, Italy

Received: 19 October 2021
Accepted: 9 November 2021

Abstract

As part of the Virgo Cluster Survey Tracing Ionised Gas Emission, a blind narrow-band Hα+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered eight massive (10¹⁰ ≲ M_star ≲ 10¹¹ M_⊙) lenticular galaxies with prominent ionised gas emission features in their inner (a few kiloparsec) regions. These features are either ionised gas filaments similar to those observed in cooling flows (two galaxies), or they are thin discs with sizes 0.7 ≲ R(Hα)≲2.0 kpc (six galaxies), thus significantly smaller than those of the stellar disc (R(Hα)≃7 − 22%R_iso(r)). The morphological properties of these discs are similar to those of the dust seen in absorption in high-resolution HST images. Using a unique set of multifrequency data, including new or archival ASTROSAT/UVIT, GALEX, HST, CFHT, Spitzer, and Herschel imaging data, combined with IFU (MUSE, ALMA) and long-slit (SOAR) spectroscopy, we show that while the gas that is located within these inner discs is photoionised by young stars, which signals ongoing star formation, the gas in the filamentary structures is shock ionised. The star formation surface brightness of these discs is similar to that observed in late-type galaxies. Because of their reduced size, however, these lenticular galaxies are located below the main sequence of unperturbed or cluster star-forming systems. By comparing the dust masses measured from absorption maps in optical images, from the Balmer decrement, or estimated by fitting the UV-to-far-IR spectral energy distribution of the target galaxies, we confirm that the dust masses derived from optical attenuation maps are heavily underestimated because of geometrical effects due to the relative distribution of the absorbing dust and the emitting stars. We also show that these galaxies have gas-to-dust ratios of G/D ≃ 80₃₀³²⁰, and that the star formation within these discs follows the Schmidt relation, but with an efficiency that is reduced by a factor of ∼2.5. Using our unique set of multifrequency data, we discuss the possible origin of the ionised gas in these objects, which suggests multiple and complex formation scenarios for massive lenticular galaxies in clusters.