SPITZER IRS spectra of Virgo early-type galaxies: detection of stellar silicate emission Laura Silva (INAF-TS) Alessandro Bressan (INAF-PD), Pasquale Panuzzo (INAF-PD), Lucio Buson (INAF-PD), Marcel Clemens (INAF-PD) GianLuigi Granato (INAF-PD), Roberto Rampazzo (INAF-PD), Jose- Ramon Valdes (IANOE), Olga Vega (IANOE) AGB dusty envelopes as a tool to disentangle age and metallicity effects in the SEDs of E galaxies MIR observations: 10  m feature and SF signatures Bressan, Granato, Silva 1998, A&A, 332, 135 Bressan et al. 2006, ApJL, accepted (astro-ph/ ) Panuzzo et al. 2006, in preparation

The brightest stars in intermediate age (  100 Myr to a few Gyrs) stellar populations are AGB stars AGB stars are embedded within dusty envelopes originated by very strong stellar winds (  Mo/yr) We included the effect of AGB dusty envelopes in SSP: Spherical symmetry and v exp independent of r   =  (M,R,L,Z). Radiative transfer of the photospheric SED through the envelope computed with the Granato & Danese 94 code. (Bressan, Granato, Silva 1998) Modeling intermediate and old stellar populations: the effect of AGB dusty envelopes

SSP with AGBs

Age & Metallicity degeneracy hampers reconstructing the history of baryon assembly in the early universe, recorded in the fossil stellar populations (early type galaxies) Old & Metal Poor = Young & Metal Rich NO Dusty AGBs Lot of Dusty AGBs OPT: MIR: Age & metallicity Age Metallicity 

10  m bump: 13 (76%) N4339 N4365 N4371 N4377 N4382 N4442 N4473 N4474 N4551 N4564 N4570 N4621 N4660 Signs of MIR activity: 4 (24%) N4486 (M87), N4636, N4435, N4550 Systematic spectroscopic study with Spitzer IRS of 17 Early type galaxies along CM relation in Virgo Cluster (PID 3419 cycle 1 - PI A. Bressan ) + 50 hours in cycle 2 with IRS Blue Peak Up: fainter virgo and bright Coma…

13 galaxies (76%) with a broad and spatially extended 10  m emission feature 10Gyr SSP models with Z=0.008, 0.02, 0.05 SSP with 5Gyr Z=0.008 Dashed: mean outflow AGB star Dotted: C-rich star U Cam

M giant sed model + circumstellar envelope model

Old Stellar Populations MIR emission from dusty (silicates) AGB Stars (Bressan, Granato & Silva 98) Degeneracy in the Optical Degeneracy in the MIR MIR + Optical NIR Removes degeneracy

4 galaxies (24%) with MIR signatures of activity (M87)

NGC 4435 S0 Liner-HII (Ho et al 97) GRASIL fit (Silva et al 98, Vega et al 05) MODEL Post starburst 10 8 yr Current SFR 0.14 M Ÿ /yr 2.8 M Ÿ /yr Formed stars M Ÿ Mgas M Ÿ Fmol = 70% t 1 =43 NGC7331 Smith et al 05

Summarizing: 17 E-type galaxies in Virgo observed with SL1 SL2 LL2 Signature of AGB stars well detected by Spitzer IRS In the majority (76%) of galaxies no other features The bump is in very good agreement with model predictions OPT and NIR follow-up is underway to break the age-Z degeneracy 2 galaxies show emission lines but no PAHs NGC4486 (M87) NGC 4636 (E/S0 Liner ) 2 galaxies show PAHs ( NGC 4550-SB0 Liner, NGC 4435-SB0 Liner HII) N4435 MIR SED remarkably similar to N7331 (Spiral) - Model suggests a post-starburst with residual SFR