GEMS:
The Evolution of Disc Galaxies
Marco Barden
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Galaxy Evolution
• Archaeology  Look-back approach
• Galaxy evolution  Population evolution
• Important because:
– Even in local universe 60-80% discs
– Most of all stars form in discs
– Most of the stars of the MW formed since z~1
 measure structural parameters of discs
as a function of time
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Theoretical Models
• Expectation from models (e.g. Mo, Mao,
White 1998, Bouwens & Silk 2002):
Discs in the early universe
– were more compact
– were on average brighter
– had higher surface brightness
– had lower stellar masses
than disc galaxies today
 large redshift surveys to constrain models
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Observations
• Several surveys (e.g.
CFRS, DEEP, GOODS)
 controversy
• Strong SB evolution (result
of higher overall SFR,
Schade et al. 1996)
• No evolution in SB
(selection effects, Simard et
al. 1999)
• At z~1 a new class of high
SB galaxies (0,e<17.7 mag
arcsec-2) appears (Simard
et al. 1999)
Ravindranath et al. 2004
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Observations
• Restricted luminosity range
 interpretation
• Surface brightness dimming
 selection effects dominate a high-z
• Objects are small
 high spatial resolution needed
• Distribution of surface brightness is wide
 large samples
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
GEMS: Galaxy Evolution from
Morphology and SEDs
MPIA: Barden, Bell, Borch, Häußler,
Heymans, Meisenheimer, Rix (P.I.)
STScI: Beckwith, Caldwell, Jogee,
Somerville
AIP: Jahnke, Sanchez, Wisotzki
Oxford: Wolf
UMass: McIntosh
U. Arizona: Peng
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
GEMS: Galaxy Evolution from
Morphology and SEDs
• E-CDFS
• Largest HST colour
mosaic: ~30’x30’, 9x9
ACS tiles, ~150 HDF
• 125 (GEMS) + 50
(GOODS) orbits
• 2 filters:
– F606W (mAB<28.3)
– F850LP (mAB<27.1)
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
GEMS: Galaxy Evolution from
Morphology and SEDs
• ~10000
redshifts from
COMBO-17
(Wolf, Meisenheimer et al.
2003)
• 5 broad / 12
medium band
filters
• z~0.02,
0.1<z<1.3,
mr<24
• SEDs (35009250Å)
18/05/2004
z=1.25
z=0.69
z=0.46
z=0.24
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Disc Sample
• Sersic fits to F850LP
images with GALFIT
(Peng et al. 2002)
• Selection of discs
with n<2.5
• Completeness 
simulations (Häußler
et al. 2004)
• Size correction (de
Jong 1996)
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Completeness & Selection Effects
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Magnitude-Size Relation
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Magnitude-Size Relation
V(z)=(20.790.08) - (1.050.11) z
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Magnitude-Size Relation
Trujillo et al. 2004
FIRES
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
V(z)=(20.790.08) - (1.050.11) z
HDF
The Magnitude-Size Relation
V(z)=(21.240.08) - (1.790.11) z
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Magnitude-Size Relation
Bouwens & Silk 2002
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Mass-Size Relation
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Mass-Size Relation
log (z) = 8.240.02
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
The Mass-Size Relation
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies
Conclusions
• The magnitude-size relation of disc galaxies
changes as a function of redshift
 average SB increases
• The appearance of high SB galaxies at high-z is
a result of the increasing average SB
• Disc galaxies at different redshifts follow the
same mass-size relation
 galaxies form inside-out
• Mass densities stay roughly constant with
redshift
18/05/2004
Ringberg Workshop: Secular
Evolution of Disc Galaxies