The ABC of dEs First results of the MAGPOP-ITP Dolf Michielsen Centre for Astronomy & Particle Theory School for Physics & Astronomy University of Nottingham

Introduction Dwarf elliptical galaxies (dEs) M B > -18 mag gas- and dust-less (or -poor) exponential surface brightness profiles very difficult to observe!

Introduction Dwarf elliptical galaxies (dEs) M B > -18 mag gas- and dust-less (or -poor) exponential surface brightness profiles most abundant type of galaxy in nearby clusters in hierarchical structure formation, dwarf galaxy-size DM halos are the first to form  dEs probe early universe? In the last years reasonable samples became available (e.g. with kinematic information)

Introduction L-σ relation for dEs (Faber-Jackson) De Rijcke, Michielsen et al., 2005

Introduction Formation and evolution of dEs Isolated formation – SN-driven galactic winds

Introduction Formation and evolution of dEs Isolated formation – SN-driven galactic winds Impact of environment –Ram pressure stripping

Introduction Formation and evolution of dEs Isolated formation – SN-driven galactic winds Impact of environment –Ram pressure stripping –Harassment

Introduction Formation and evolution of dEs –Harassment Moore et al., 1998

Introduction Formation and evolution of dEs Isolated formation – SN-driven galactic winds Impact of environment –Ram pressure stripping –Harassment Evidence for transformation –Disk/spiral structures in dEs –Ionized/neutral gas in dEs

Introduction Transformation: distribution of dEdis in Virgo Lisker et al., 2006

MAGPOP-ITP MAGPOP European Marie-Curie Training Network (including IAC) Aim: study galaxy formation and evolution Focus on population synthesis through multiwavelength observations

MAGPOP-ITP MAGPOP International Time Programme (ITP) 5% of telescope time on Canary telescopes is dedicated to large, international programmes “Star formation history of dwarf galaxies” (PI: Peletier) Survey of dwarf galaxies in Virgo and field Optical/NIR imaging/spectroscopy of dIrrs/dEs

MAGPOP-ITP Sample selection –UV / optical imaging from GALEX / SDSS available –Virgo: complete sample dEs : m B > 16 mag – 43 objects dIrrs: m B > 15.5 mag – 50 objects –Field: dEs ~15 objects difficult to find dEs in field – faint + residual star formation dIrrs ~25 objects –Archival data from HST and GOLDMine

MAGPOP-ITP 70 nights allocated on 4 large telescopes on La Palma ( ) dIrr part almost completed dE part suffered from bad weather –5/6 nights on NOT with ALFOSC –2/3 nights on WHT with WYFFOS –½/5 nights on WHT with ISIS –0/6 nights on NOT with NOTCAM

NOT observations 25 dEs: 18 cluster (Virgo) and 7 field Long-slit 3500 – A (FWHM) S/N = 20 – 40 (per resolution element) Field dEs Virgo dEs

Lick indices Break age-metallicity degeneration of optical colors Use age and metallicity sensitive lines –Age: H-balmer series –Metallicity: Mg, Fe lines

Lick indices SSP models Single-age Single-metallicity Population or Simple Stellar Population

Ages and Metallicities [MgFe] versus Hβ for field and cluster dEs Field M32 Virgo Cluster Cancer

α/Fe abundance Measures star formation history α-elements produced in SNII on rapid timescales (α-elements : O, Si, Ca, Mg,…) Fe mainly produced in SNIa on long timescales SSP models constructed with solar abundance resulting from continuous star formation Normal Es form in a rapid burst, and exhibit α/Fe overabundance

α/Fe abundance Mgb versus for field and cluster dEs Virgo Cluster Cancer Field M32

Normal Es: SAURON dEs versus Es: age/met and α/Fe SAURON Es Our dEs

Consequences dEs are not just small Es dEs are not simple, old, metalpoor objects as predicted by naive interpretation of hierarchical merging scenario Like Local Group dSphs, dEs have a prolonged star formation history Need to try and disentangle old underlying stellar population from dominating (in light) young population

Special case VCC 21 SDSS g-band HST/ACS F450 band

Special case VCC 21 Nuclei younger than host Right nucleus more metal-rich + solar abundance Blue-core dE (Lisker et al., 2006)

Conclusions Field and cluster dEs have the same properties (but sample problems : very few field dEs) (Mean, luminosity-weighted) ages and metallicities : dEs are younger than normal Es dEs are less metal-rich than normal Es dEs show α/Fe underabundance whereas Es show α/Fe overabundance Galactic winds combined with prolonged star formation can explain the low metallicities and underabundance dEs probably are a mixed population of ‘original’ dEs + transformed dIrrs Intermediate-type dE/dIrrs : galaxies in transition?

Invitation There is a lot of data to analyse… Anyone interested in working with the MAGPOP-ITP data contact –Alexandre Vazdekis –Javier Cenarro –Marc Balcells