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Dwarf Elliptical Galaxies

Investigating ages, metallicities, and abundances of dwarf galaxies in the Coma Cluster, comparing properties, and analyzing environmental effects. Study uses spectroscopic observations to derive ages, metallicities, and α-ratios, revealing formation scenarios and differences in central and outer galaxies. Results show variations in star formation histories and environmental influences on galaxy properties.

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Dwarf Elliptical Galaxies

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  1. Ages, Metallicities and Abundances of Dwarf Early-Type Galaxies in the Coma ClusterbyAna Matković (STScI) Rafael Guzmán (U. of Florida)Patricia Sánchez-Blázquez (U. of Central Lancashire)Javier Gorgas (U. Complutense de Madrid)Nicolas Cardiel (U. Complutense de Madrid) Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  2. Coma cluster ~100 Mpc away. Ideal test-beds for galaxy formation models Galaxy Harassment: higher metallicities, more nucleated dE/dS0s and less spiral remnants in the center of a cluster than in lower-density environments. Hierarchical model: older ages and lower metallicities for dE/dS0s in high density environments. Accreted field galaxies older ages and lower metallicities in the center. Dwarf Elliptical Galaxies Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  3. Spectroscopic Observations • 2 fields: 30’ diameter in center and 1 just outside the Virial core of the Coma cluster (outer/infall region). • Center: 74 early-type galaxies (out of which 36 are dE/dS0). • Outskirts: 48 early-types (out of which 37 are dEs) • Sample selection from Color-Magnitude relation. • 3.5 m WIYN/HYDRA on Kitt Peak. • =4120-5600 Å  H, Mg2, Fe5335. • FWHM=1.91 Å measure velocity dispersion, , down to 30 km/s. • Note: MB < -17 mag; cannot distinguish between dEs and dS0s. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  4. Motivation • How do the stellar populations of dE/dS0s compare to gEs? • Which formation scenario(s) best reproduce properties of dEs in clusters? • Do cluster dwarf galaxies have homogenous formation? • What is the role of environment in shaping the properties of the dE/dS0 population? Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  5. I -Relations for Central Region • Line strength index = difference in flux between the spectral feature and continuum. Used Lick/IDS indices. • Different shapes for low- and high- galaxies ( >100 km/s). • No connection between age, metallicity and [/Fe]with the shape of the I -  relations. • Group III independent of micro-turbulent velocity of stellar atmospheres (Tripicco & Bell 1995). • Center dE/dS0s  Off- model grids dE/dS0  Bins of   NFPS galaxies (Nelan et al. 2005) Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  6. Environmental Effects on I - • Confirm different shapes of I- relations. • Outer dE/dS0s show a larger scatter than central galaxies. Infall dE/dS0s Infall dE/dS0s with emission • Center dE/dS0  NFPS galaxies Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  7. Deriving Ages, Metallicities and  - ratios • Stellar population models from Thomas, Maraston and Korn (2004). • Used a combination of H–[MgFe]’, and <Fe>–Mgb to derive ages, metallicities and [/Fe]. • To reduce correlated errors, used average value of each index is binned by . high- galaxies (>100 km/s)  low- galaxies (≥100 km/s) Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  8. SP parameters vs.for Central Galaxies • Weak trend where low- galaxies display younger ages than high- early-types. • Metallicity increases with where the more massive elliptical galaxies are more metal rich than the dE/dS0s. • [/Fe] decreases for low- galaxies. • Overall good agreement with NOAO Fundamental Plane Survey (); (Smith et al. 2005). Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  9. Environmental Effects on SP parameters vs. • Hint toward younger ages and lower metallicities for outer dEs. • Larger scatter in all parameters for outer/infall galaxies.  heterogeneity? • Largest environmental effect is in the -ratios, where infall dE/dS0s have on average higher [/Fe]! Center galaxies  Infall/outer galaxies Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  10. SP parameters vs. • 3 groups of galaxies with high [/Fe]: • Old ages and low metallicities. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  11. SP parameters vs.  • 3 groups of galaxies with high [/Fe]: • Old ages and low metallicities. • Young ages and high metallicities. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  12. SP parameters vs. • 3 groups of galaxies with high [/Fe]: • Old ages and low metallicities. • Young ages and high metallicities. • Young ages and low metallicities. • Heterogeneous star formation histories for dE/dS0s in the infall region. • Can be explained with different scenarios, e.g. dIs falling into the cluster. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  13. Age - Metallicity Relation? • The age-metallicity anti-correlation is due to correlated errors in age and metallicity! • dE/dS0s show a relation with the same slope, but are offset toward younger ages and lower metallicities. • Outer dE/dS0s are on average younger and less metal rich than the galaxies in the center. Center galaxies with >100 kim/s Center with 50 ≤<100 km/s  Center with 30 ≤<50 km/s Outer galaxies with >100 km/s Outer with 50 ≤<100 km/s Outer with 30 ≤<50 km/s Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  14. Conclusions • Index- relations for most metalic indices show a change of slope in the dwarf regime. • Galaxies in the lower density region of Coma cluster are on averageyounger and have slightly lower metallicities. • More galaxies in the low- region have high [/Fe] suggesting short time scales in their star formation histories, where some dE/dS0 experience a short burst long time ago, and others very recently. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  15. The Next Step • Use photometry to determine the morphology of early-type galaxies in the Coma cluster (dS0s or dEs). • Are dS0s “contaminating” the relations between  and line strengths or ages, metallicities and [/Fe]? • Test spiral remnant and nucleation prediction of galaxy harassment model. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  16. Nucleated dwarf ellipticals in the Coma clustercollaboration with Henry Ferguson (STScI) and the ACS/HST Coma Cluster survey team • ACS/HST Coma Cluster survey (P.I. David Carter). • Observed ~30% of planned fields most in the center of cluster and some in a less dense region. • What are dE nuclei? • How do they relate to black holes in more massive galaxies? • Are they progenitors of some GC’s? or UCDs? • Distribution of nucleated dEs in the cluster. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

  17. Nucleated dwarf ellipticals in the Coma clustercollaboration with Henry Ferguson (STScI) and the ACS/HST Coma Cluster survey team • Are there trends in color, or age between nucleated and non-nucleated dEs? What would this tell us about their formation? • Do Coma dE,Ns follow trends found in Virgo and Fornax? • brighter dEs tend to have nuclei; • dE,N population is strongly concentrated toward the cluster center; • bright dE population is less strongly concentrated. Matkovic, Extreme SF in Dwarf Galaxies Ann Arbor 29 July 2009

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