Survival of molecular gas in Virgo’s hot intracluster medium: CO near M 86

¹ Observatoire de Paris, LERMA, CNRS, 61 avenue de l’Observatoire, 75014 Paris, France
e-mail: kalliopi.dasyra@obspm.fr
² Univ. Bordeaux, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, 33270 Floirac, France
³ CNRS, LAB, UMR 5804, 33270 Floirac, France

Received: 4 January 2012
Accepted: 9 February 2012

Abstract

We carried out ¹²CO(1−0) and ¹²CO(2−1) observations of 21 different regions in the vicinity of M 86, NGC 4438, and along the 120 kpc-long,  Hα-emitting filamentary trail that connects them, aiming to test whether molecular gas can survive to be transferred from a spiral to an elliptical galaxy in Virgo’s 10⁷ K intracluster medium (ICM). We targeted  Hα-emitting regions that could be associated with the interface between cold molecular clouds and the hot ionized ICM. The data, obtained with the 30 m telescope of the Institut de Radioastronomie Millimétrique, led to the detection of molecular gas close to M 86. CO gas with a recession velocity that is similar to that of the stars,  −265 km s^-1, and with a corresponding H₂ mass of 2  ×  10⁷ M_⊙, was detected  ~10 kpc southeast of the nucleus of M 86, near the peak of its  H i emission. We argue that it is possible for this molecular gas either to have formed in situ from  H i, or to have been stripped from NGC 4438 directly in molecular form. In situ formation is nonetheless negligible for the 7 × 10⁶ M_⊙ of gas detected at 12:26:15.9+12:58:49, at  ~10 kpc northeast of M 86, where no (strong)  H i emission is present. This detection provides evidence for the survival of molecular gas in filaments for timescales of  ~100 Myr. An amount equivalent to 5 × 10⁷ M_⊙ of H₂ gas that could be lost to the ICM or to neighboring galaxies was also discovered in the tidal tail northwest of NGC 4438. A scenario in which gas was alternatively brought to M 86 from NGC 4388 was also examined but it was considered unlikely because of the non-detection of CO below or at the H I stream velocities, 2000–2700 km s^-1.