Dwarf Elliptical Galaxies
kinematics and stellar populations
Santos Pedraz (UCM-CAHA)
Javier Gorgas (UCM)
Nicolás Cardiel (UCM-CAHA)
Dwarf Elliptical or Bright Spheroidal
NGC 205
• Dwarf elliptical galaxies (dEs) are the dominant galaxy
population in nearby clusters
• dEs are characterized by low effective surface brightness
(µ>21 mag/arcsec2), faint luminosities (MV > -18) and
Sérsic surface brightness profiles (n = 1-3)
• Studying their kinematics and stellar populations will help
us to understand the processes involved in the formation
and evolution of galaxies
HOWEVER, their origin and true nature are a mystery
• Dwarf elliptical galaxies (dEs) are the dominant galaxy
population in nearby clusters
• dEs are characterized by low effective surface brightness
(µ>21 mag/arcsec2), faint luminosities (MV > -18) and
Sérsic surface brightness profiles (n = 1-3)
• Studying their kinematics and stellar populations will help
us to understand the processes involved in the formation
and evolution of galaxies
HOWEVER, their origin and true nature are a mystery
Our aim:
To compare the kinematics and stellar populations of
dEs in the Virgo cluster with those of the classical
elliptical galaxies
Spectroscopic observations
Telescope
Spectrograph
INT 2.5m
IDS
Spectral range
(Å)
4750 - 6050
INT 2.5m
IDS
3670 – 4440
Shane(Lick) 3.0m
KAST
3500 - 5840
CAHA 3.5m
TWIN
4670 - 5560
WHT 4.2m
AF2/WYFFOS
4000 - 5600
Are dEs and classical Es completely different objects?
Are dEs and classical Es completely different objects?
• Luminosity profiles
dEs: exponential
Es: de Vaucouleurs
Bender, Burstein & Faber (1993)
Are dEs and classical Es completely different objects?
• Luminosity profiles
dEs: exponential
Es: de Vaucouleurs
Bender, Burstein & Faber (1993)
cES
LG dSphs
dEs
Es
Are dEs and classical Es completely different objects?
• Luminosity profiles
dEs: exponential
Es: de Vaucouleurs
Are dEs and classical Es completely different objects?
• Luminosity profiles
dEs: exponential
Es: de Vaucouleurs
• The Fundamental
Plane
Or are dEs the true extension of the classical Es to
lower luminosities?
• Similarity in global properties
• Colour – Magnitude relation
• Mg2 – σ relation
• Continuity in luminosity profile parameters
When a Sérsic law is fitted:
µ(r) = µ0+ C log (r/r 0)n
Binggeli & Jerjen (1998) ; Graham & Guzmán (2003)
What is the origin of dEs in clusters?
• Primordial cluster members (White & Frenk 91)
• Clustering properties (Conselice et al. 01)
• The result of environmental effects
• e.g. galaxy harassment (Moore et al. 98)
What is the origin of dEs in clusters?
• Primordial cluster members (White & Frenk 91)
• Clustering properties (Conselice et al. 01)
• The result of environmental effects
• e.g. galaxy harassment (Moore et al. 98)
9Rotation
9Stellar populations
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
De Rijcke et al. (2001)
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
De Rijcke et al. (2001)
Geha et al. (2002)
Velocity dispersions (σ) and rotation curves for dwarfs ellipticals
σ
V
σ
V
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
De Rijcke et al. (2001)
Geha et al. (2002)
Pedraz et al (2002)
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
De Rijcke et al. (2001)
Geha et al. (2002)
Pedraz et al (2002)
Simien & Prugniel (2002)
Are dwarf Es rotationally supported?
(like low-luminosity Es)
Predictions for isotropic oblate
galaxies flattened by rotation
(from Binney 1978)
Bender & Nieto (1990)
De Rijcke et al. (2001)
Geha et al. (2002)
Pedraz et al (2002)
Simien & Prugniel (2002)
Geha et al (2003)
Evidence of fast rotation in some dEs
* Es from Bender,
Burstein & Faber (93)
Rotationally supported
Correlations with
other parameters?
• Core properties
• Isophote shapes
• Luminosity profiles
• Stellar populations
Stellar populations of dEs versus classical Es:
Crucial to discriminate between different formation
and evolution models
If cluster dEs were
primordial cluster
members
Coeval, old and
low metallicities
formed from
accreted spirals
range of ages
and metallicities
Stellar populations of dEs versus classical Es
Vazdekis (99) models
Stellar population
dichotomy?
ƒ Lower metallicities
ƒ Solar [Mg/Fe] ratios
ƒ Shallower stellar
population gradients
González 93 Es
‫ ە‬Trager 2000 Es
X
Galactic GCs
* M31 GCs
Es
cEs
dEs
Stellar populations of dEs versus classical Es
Breaking the age-metallicity degeneracy
Vazdekis (99) models
ƒ A range of mean
ages
ƒ A mass-metallicity
relation?
ƒ Coincidence with
GCs positions?
González 93 Es
dEs
X
GCs BBF-93
Stellar populations of dEs versus classical Es
Es: high metall.
No σ correlation
dEs: wide metall.
range
Stellar populations of dEs versus classical Es
Es: correlation
with σ
dEs: wide age
range
dEs span a wide range in:
• Rotational support
• Metallicities
• Ages
Different formation and/or evolution histories ?