dwarf elliptical galaxies(again)

Dolf MichielsenSchool of Physics &

Astronomy

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

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

?

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

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)

ITP – optical spectroscopy

• 26 dEs in Virgo &field

• ages, metallicities,enhancement H Balmer – Mg,Fe

ITP – C/N/Ca vs Fe

• compare to Es, GCs of an E,GCs of a dE

ITP – structural parameters

• C,A,S – age, met, ZMgb/Z<Fe>

• selection effect on field dEs

ITP – environment

Virgocentricdistance

‘special’ cases• bluenuclei• disks• rotation

ITP – future

• more data available

• spectroscopy: see talks of Elisa & Javier

• imaging: see talk of Reynier

Michielsen et al. 2003

VLT – the calcium puzzle I

CaT* - anti-correlation Too high CaT values for expected age & metallicity

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

VLT – the calcium puzzle IIIa

• SSP spectral fit with Pegase-HR + Elodie

FCC 043

‘normal’ - 12

VLT – the calcium puzzle IIIb

• SSP spectral fit with Pegase-HR + Elodie

FCC 046

emission - 3

VLT – the calcium puzzle IIIc

• SSP spectral fit with Pegase-HR + Elodie

FCC 150

very weakemission - 1

VLT – the calcium triplet IV

• SSP results

VLT – the calcium puzzle V

Solving the puzzle…

Consistent with use of CaT as metallicity indicator in Local Group GCs & dSphs

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.