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SPITZER IRS spectra of Virgo early-type galaxies: detection of stellar silicate emission

SPITZER IRS spectra of Virgo early-type galaxies: detection of stellar silicate emission Laura Silva (INAF-TS)

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SPITZER IRS spectra of Virgo early-type galaxies: detection of stellar silicate emission

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  1. 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 envelopesas 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/0602014) Panuzzo et al. 2006, in preparation

  2. Modeling intermediate and old stellar populations: the effect of AGB dusty envelopes 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 (10-7-10-4 Mo/yr) We included the effect of AGB dusty envelopes in SSP: Spherical symmetry and vexp 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)

  3. SSP with AGBs

  4. NO Dusty AGBs Lot of Dusty 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 OPT:  MIR: Age Metallicity Age & metallicity

  5. Systematic spectroscopic study with Spitzer IRS of 17 Early type galaxies along CM relation in Virgo Cluster (PID 3419 cycle 1 - PI A. Bressan ) 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 + 50 hours in cycle 2 with IRS Blue Peak Up: fainter virgo and bright Coma…

  6. 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

  7. M giant sed model + circumstellar envelope model

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

  9. 4 galaxies (24%) with MIR signatures of activity (M87)

  10. NGC7331 Smith et al 05 NGC 4435S0 Liner-HII (Ho et al 97) GRASIL fit (Silva et al 98, Vega et al 05) MODEL Post starburst 108 yr Current SFR 0.14 MŸ/yr <SFR> 2.8 MŸ/yr Formed stars 3 108 MŸ Mgas 2.5 108 MŸ Fmol = 70% t1=43

  11. Summarizing: • 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 • 17 E-type galaxies in Virgo observed with SL1 SL2 LL2 • 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

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