The Survival of Planetary Nebulae in the Intracluster Medium

The stellar population stripped from galaxies in clusters evolve under the extreme conditions imposed by the intracluster (IC) medium. Intracluster stars generally suffer very high systemic velocities, and evolve within a rarefied and extremely hot IC medium. We present numerical simulations which aim to explore the evolution and survival of IC Asymptotic Giant Branch (AGB) envelopes and Planetary Nebula (PN) shells. Our models reflect the evolution of a low-mass star under the observed conditions in the Virgo IC medium. We find that the integrated hydrogen-recombination line emission of a PN is dominated by the inner dense shell, whose evolution is unaffected by the environment. Ram pressure stripping affects mainly the outermost IC PN shell, which hardly influences the emission when the PN is observed as a point source. More importantly, we find that a PN with progenitor mass of 1M⊙ fades to ∼30% and ∼10% of its maximum emission, in 5 000 and 10 000 yr respectively, disclosing an actual PN lifetime (tPN) several times shorter to what is usually adopted (25 000 yr). This result affects the theoretical calculation of the luminosity-specific density of IC PNe, which scales with tPN . For tPN=10 000 yr, our more conservative estimate, we obtain that the luminosity-specific density of PNe is in fair agreement with the value obtained from Red Giants. With our more realistic PN lifetime we infer a higher fraction (above 15%) of IC starlight in the Virgo core than current estimates. Affiliated with the Hubble Space Telescope Division of the European Space Agency On leave from INAF-Bologna Observatory