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dwarf elliptical galaxies (again)

dwarf elliptical galaxies (again). Dolf Michielsen School of Physics & Astronomy. dwarf elliptical galaxies (dEs). first observations in the 1940s of the dSphs and dEs in the Local Group detailed observations since the 1980s with CCDs & large telescopes

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dwarf elliptical galaxies (again)

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  1. dwarf elliptical galaxies(again) Dolf MichielsenSchool of Physics & Astronomy

  2. dwarf elliptical galaxies (dEs) • first observations inthe 1940s of the dSphs and dEs in the Local Group • detailed observations since the 1980s with CCDs & large telescopes • dwarf galaxies aremost common typeof galaxy • whole ‘zoo’ of dwarf galaxies what is their connection (if any) ? Ferguson & Binggeli 1994

  3. dwarf elliptical galaxies (dEs) • first observations inthe 1940s of the dSphs and dEs in the Local Group • detailed observations since the 1980s with CCDs & large telescopes • dwarf galaxies aremost common typeof galaxy • whole ‘zoo’ of dwarf galaxies what is their connection (if any) ? ? Ferguson & Binggeli 1994

  4. dEs & environment • dEs are (almost) only found in dense environments: in clusters and around giant galaxies • morphology-density relation for dwarfs • environment veryimportant in formationand evolution Binggeli et al.1987

  5. stellar populations in dEs • Not many studies done yet  dEs have low surface brightness high S/N needed for population studies • Some work using  narrow-band filters (Rakos et al. 2001, 2004, 2006) surface brightness fluctuations (Jerjen, 2004) spectra of compact objects and nuclei (higher surface brightness) (Mieske, 2006) 2D spectroscopy (Chilingarian, 2007) • dEs seem to form a heterogeneous population with a wide spread in ages and metallicities • More, consistent, age/metallicity estimates are needed, preferably using (optical) spectroscopy • MAGPOP-ITP on dwarf galaxies (Virgo & field) • VLT FORS spectroscopy of dEs (Fornax & groups)

  6. ITP – optical spectroscopy • 26 dEs in Virgo &field • ages, metallicities,enhancement H Balmer – Mg,Fe

  7. ITP – C/N/Ca vs Fe • compare to Es, GCs of an E,GCs of a dE

  8. ITP – structural parameters • C,A,S – age, met, ZMgb/Z<Fe> • selection effect on field dEs

  9. ITP – environment Virgocentricdistance ‘special’ cases • bluenuclei • disks • rotation

  10. ITP – future • more data available • spectroscopy: see talks of Elisa & Javier • imaging: see talk of Reynier

  11. VLT – the calcium puzzle I CaT* -  anti-correlation Too high CaT values for expected age & metallicity Michielsen et al. 2003

  12. VLT – the calcium puzzle II • Ages & metallicities based on • low-resolution spectroscopy (Held&Mould 94) • narrow-band imaging (Rakos et al. 2001) • New optical spectroscopy with VLT FORS • Michielsen, Koleva, Prugniel, Zeilinger, De Rijcke, Dejonghe, Pasquali, Ferreras & Debattista, ApJL, accepted

  13. VLT – the calcium puzzle IIIa • SSP spectral fit with Pegase-HR + Elodie FCC 043 ‘normal’ - 12

  14. VLT – the calcium puzzle IIIb • SSP spectral fit with Pegase-HR + Elodie FCC 046 emission - 3

  15. VLT – the calcium puzzle IIIc • SSP spectral fit with Pegase-HR + Elodie FCC 150 very weakemission - 1

  16. VLT – the calcium triplet IV • SSP results

  17. VLT – the calcium puzzle V Solving the puzzle… Consistent with use of CaT as metallicity indicator in Local Group GCs & dSphs

  18. conclusions • dEs have a range in ages & metalliticies • in general younger and less metal-rich than Es, and have solar /Fe ratios • age and assymmetry seem to correlate with environment, suggesting an infall scenario of dIrr  dE transformation. • new age/metallicity estimates solve the calcium puzzle, at least for dEs.

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