Ages, Metallicities and Abundances of Dwarf Early-Type Galaxies in the Coma Cluster by Ana Matkovic (STScI)

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Ages, Metallicities and Abundances of Dwarf
Early-Type Galaxies in the Coma ClusterbyAna
Matkovic (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)
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Dwarf Elliptical Galaxies

• 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.

• Coma cluster 100 Mpc away.

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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.
• FWHM1.91 Å ? measure velocity dispersion, ?,
  down to 30 km/s.
• Note MB lt -17 mag cannot distinguish between
  dEs and dS0s.

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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?

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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 (?
  gt100 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)

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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

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Deriving Ages, Metallicities and ?? - ratios

• Stellar population models from Thomas, Maraston
  and Korn (2004).
• Used a combination of
• H?MgFe, and ltFegtMgb to derive ages,
  metallicities and
• ?/Fe.
• To reduce correlated errors, used average value
  of each index is binned by ?.

? high-? galaxies (??gt100 km/s) ? low-? galaxies
(? 100 km/s)
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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).

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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
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SP parameters vs. ?

• 3 groups of galaxies with high ?/Fe
• Old ages and low metallicities.

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SP parameters vs. ?

• 3 groups of galaxies with high ?/Fe
• Old ages and low metallicities.
• Young ages and high metallicities.

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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.

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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 ??gt100 kim/s ? Center with
50 ??lt100 km/s ? Center with 30 ??lt50 km/s ?
Outer galaxies with ??gt100 km/s ? Outer with 50
??lt100 km/s ? Outer with 30 ??lt50 km/s
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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 average younger 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.

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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.

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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 GCs? or UCDs?
• Distribution of nucleated dEs in the cluster.

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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.