Search for cold and hot gas in the ram pressure stripped Virgo dwarf galaxy IC 3418 ^⋆,⋆⋆

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 00 Prague, Czech Republic
e-mail: jachym@ig.cas.cz
² Department of Astronomy, Yale University, 260 Whitney Ave., New Haven, CT 06511, USA
e-mail: jeff.kenney@yale.edu
³ Eureka Scientific, 2452 Delmer Street Suite 100, Oakland, CA 94602, USA
e-mail: mingsun.cluster@gmail.com
⁴ Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France
e-mail: francoise.combes@obspm.fr

Received: 4 October 2012
Accepted: 30 April 2013

Abstract

We present IRAM 30 m sensitive upper limits on CO emission in the ram pressure stripped dwarf Virgo galaxy IC 3418 and in a few positions covering H ii regions in its prominent 17 kpc UV/Hα gas-stripped tail. In the central few arcseconds of the galaxy, we report a possible marginal detection of about 1 × 10⁶  M_⊙ of molecular gas (assuming a Galactic CO-to-H₂ conversion factor) that could correspond to a surviving nuclear gas reservoir. We estimate that there is less molecular gas in the main body of IC 3418, by at least a factor of 20, than would be expected from the pre-quenching UV-based star formation rate assuming the typical gas depletion timescale of 2 Gyr. Given the lack of star formation in the main body, we think the H₂-deficiency is real, although some of it may also arise from a higher CO-to-H₂ factor typical in low-metallicity, low-mass galaxies. The presence of H ii regions in the tail of IC 3418 suggests that there must be some dense gas; however, only upper limits of <1 × 10⁶  M_⊙ were found in the three observed points in the outer tail. This yields an upper limit on the molecular gas content of the whole tail <1 × 10⁷  M_⊙, which is an amount similar to the estimates from the observed star formation rate over the tail. We also present strong upper limits on the X-ray emission of the stripped gas in IC 3418 from a new Chandra observation. The measured X-ray luminosity of the IC 3418 tail is about 280 times lower than that of ESO 137-001, a spiral galaxy in a more distant cluster with a prominent ram pressure stripped tail. Non-detection of any diffuse X-ray emission in the IC 3418 tail may be due to a low gas content in the tail associated with its advanced evolutionary state and/or due to a rather low thermal pressure of the surrounding intra-cluster medium.