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Star Formation Rates, Ages and Masses
of Massive Galaxies in the
FORS Deep and GOODS South fields
R. Bender, A. Bauer, N. Drory, G. Feulner, A. Gabasch, U. Hopp, M.
Pannella, R.P. Saglia, M. Salvato
(Universitäts-Sternwarte München, Max-Planck Institut für
Extraterrestrische Physik, University of Texas)
Map out galaxy assembly: Luminosity functions
Stellar mass functions, Star formation rates as a function
of mass.
Star Formation Rates, Ages and Masses
of Massive Galaxies in the
FORS Deep and GOODS South fields
• Study evolution of galaxies with broadband deep U to K surveys.
• LFs, Mass Functions, SFRs do not require spectroscopy but can
be derived with accurate photometric redshifts.
• Advantage of photo z: no color selection bias, fainter luminosities,
larger sample (~10000 galaxies in FDF and GOODS S sub-sample)
• FORS Deep Field (IAB=26.8): 98% of all galaxies with dz/(1+z)<0.03;
GOODS S (KAB=25.4): dz/(1+z)<0.055
• Deep I-selection misses only a small fraction of deep K selected
objects. Surveys to IAB=27 also cover a large fraction of submm gals.
• Derive masses from broadband SEDs by fitting exponential SFH +
bursts (with extinction); exp. SFHs only do NOT work for large
l-range (check via comparison with local SDSS+2MASS sample).
• Further check: compare FDF I-selected with GOODS K-selected.
The FORS Deep Field (FDF, GTO project)
• FDF goals: evolution of galaxies: their luminosity
functions, star formation rates, morphologies,
chemical abundances, dark halo properties, TullyFisher , FP relations etc...
• Imaging in U,B,g,R,I,z,J,K (to AB ~ 27 in optical).
• Depths within 0.5 ... 1 mag of Hubble Deep Fields.
• Area ~5 times HDFs together (6.8‘ x 6.8‘).
• 8000 objects with photometric z and type.
• Spectroscopy available for ~360 galaxies.
• HST Advanced Camera observations obtained.
• FORS partners: Observatories in Heidelberg, Göttingen and
Munich built two FORS spectrographs for the VLT.
• FDF science team: Appenzeller, Bender, Böhm, Drory, Gabasch,
Heidt, Hopp, Mehlert, Noll, Saglia, Seitz, Ziegler et al.
FDF field selection: DSS image
QSO 0103-260
z=3.36
FDF
Criteria: z>3 QSO in field, minimize foreground of stars and (z<0.2)
galaxies, high Galactic latitude, good accessibility from VLT
FORS Deep Field
FDF BRI real color image
FWHM = 0.45”
QSO 0103-260
z=3.36
~1’x1’ enlargements
FDF BRI
HST ACS
~1’x1’ enlargements
K-band (26.3) selection (FIRES) vs I-band (26.8) selection (FDF)
FDF as well
FIRES only
The Goods-South Field
• J, H, K VLT images,
50 arcmin2, (8 tiles),
seeing 0.4-0.5”
• K-selected catalog:
3297 galaxies to
KAB=25.4
• U, I: GOODS/EIS
public survey
• B, V, R: Garching/
Bonn deep survey
Salvato et al. 2006,
A&A, submitted
K-band
2.5’x2.5’
Global galaxy parameters
from photometric redshifts
• Advantages:
- large samples of ‘normal’ galaxies
- redshifts for faint objects
- full spectral energy distribution
- ‘cheap’ in telescope time
- modest amount of spectroscopy
needed to test reliability
• Potential problems:
- accurate photometry needed
- calibrating galaxies are bright
- larger errors in redshift
- catastrophic failures in z
Observed vs. synthetic color-color diagrams of
stars used to check photometric calibration
Semi-empirical SEDs
derived from broad-band fluxes of galaxies with spectroscopic z by
fitting them with SEDs of Bruzual&Charlot, Maraston and spectra from FDF, Kinney&Calzetti, Manucci
=> used as templates to determine photometric redshifts
Examples of template fits to FDF broad band photometry I
Examples of template fits to FDF broad band photometry II
check:
photo z
vs.
spec z
180 galaxies used
to derive semiempirical SEDs
180 galaxies in
the control sample
QSO
Only ~ 1% catastrophic failures on normal galaxies! (mostly
very blue, faint dwarf objects with almost power-law SEDs)
check:
photo z
vs.
spec z
for
MB > -20
Photometric z for faint objects: o.k.!!
FDF: distributions of photometric redshift errors and c2
FDF redshift distribution: extends to z ~ 6 (similar to HDFs)
another check:
peaks in
photometric
z distribution
well consistent
with peaks in
spectroscopic
z distribution
at: 0.22, 0.33,
0.39, 0.45,
0.77, 2.35,
3.38 (QSO)
MB distribution in FDF vs z
completeness
limits in FDF:
red massive
galaxies to
z~2
blue starforming
galaxies to
z~6
Most luminous
galaxies in
optical bands
tend to have
oldest SEDs
clustering in
redshift space
very obvious!
Ho = 70 km s-1 Mpc-1
Wm = 0.3, WL = 0.7
Type classification: Sersic n vs. T vs. SED Type
Type dependent angular clustering at 0.2 < zphot < 0.4
all types
irregulars
early types
ellipticals
Estimating Schechter parameters F*, M*, a:
parameter coupling in luminosity function fits
V/Vmax and completeness
corrections applied
The LF faint end slope a in the FDF:
2800 A
1500 A
z
FDF
constraints
on a and M*
between
z ~ 0.6
(low M*)
and
z ~ 3.5
(high M*)
u’
g’
(some low z
bins have large
errors because
scaling with c2
was applied)
What about Steidel et al. 1999:
a ~ –1.6 ?
FDF
(galaxies selected by drop out technique)
Steidel et al. 1999
FDF
The faint
end slope
at 1700A:
Steidel et al. 1999
FDF
FDF:
z~3
FDF
z~4
• cannot be settled definitely yet,
but a ~ –1.6 pretty unlikely
Measured faint end slopes of the LFs in FDF:
adopted in
the following:
Evolution
of LF
in g’ band:
z = 0.3
to
z = 5.5
Evolution
of LF
at 2800 A:
z = 0.3
to
z = 5.5
1500 A
2800 A
F*
vs.
M*
for
u’
g’
z = 0.6
to
z = 4.5
Evolution of M* and F* for fixed a
Fits based on FDF alone predict SDSS values reasonably well.
provides
SF history
consistent
with Madau
diagram
same B-band
evolution as
observed for
bright cluster
ellipticals:
DB ~ z
a and b values for 1500 A and
2800 A imply SFR ~ constant
The UV-luminosity density and SFR
Schechter Luminosity Function:
a
  L 
 L
 ( L) =    exp  - 
L  L 
 L 
Ltot =  L ( M )dM = L(2 - a )
For the FDF, the extrapolation to L=0 in the calculation
of Ltot amounts to only 2%-20%, depending on redshift.
SFR1500 = 1.25 10-28 Ltot M yr -1Mpc -3
(no correction for dust)
Adelberger & Steidel (2000)
dust corrected
a
= -1.6
a
GALEX
= -1.1
Evolution
of Star
Formation
Rate
• Cosmic variance
between FDF and
GOODS <0.1dex
• Luminous galaxies
immune to wavelength dependent
selection effects.
•Luminous galaxies
(B- to K-selected,
L>L*) contribute
only ~1/3 to total
star formation rate
at all redshifts.
Gabasch et al. 2004b,
ApJ Lett. in press
Broadband galaxy
masses from SED-fits: I. check by
application to combined SDSS+2MASS data set (exp.SFH+bursts)
Drory, Bender, & Hopp, ApJL, 616, 103
Kauffmann + 2003
SDSS spectral feature mass
… and by
comparison
with masses
from spectral
analysis of
SDSS data
by Kauffmann
et al. (2003)
(17000 obj.):
o.k.!
Mass from SED fitting
Drory + 2004
Residuals of photometric and spectroscopic masses
against a dynamical mass indicator: o.k.!
Evolution of
the galaxy
mass
function
at low z:
MUNICS
(photo z)
and
K20
(mostly
spectra)
Stellar
masses of
galaxies in
FDF and
GOODS S:
red=old
blue=young
at all z,
massive
galaxies
are older
than low
mass
objects!
Drory et al. 2005, ApJL, 619, 131
Evolution of the galaxy stellar mass function
with redshift:
Drory et al. 2005, ApJL, 619, 131
See poster by Pannella et al. for MF as function of morphology
Evolution of total stellar mass density.
Drory et al. 2005, ApJL, 619, 131
Number density evolution of massive galaxies.
Drory et al. 2005, ApJL, 619, 131
Specific star formation rates (from [OII]) to z ~ 1.5:
Bauer et al. 2005, ApJL, 621, 89
Bauer et al. 2006
Study star formation as a function of mass and
redshift.
Specific star formation rates (from UV cont.) z ~ 4.5:
Feulner et al. 2005, ApJL, 633, 9
Study star formation as a function of mass and
redshift: strong constraints on models of galaxy formation.
Specific star formation rates (from UV cont.) z ~ 4.5:
• More massive galaxies
form their stars earlier.
• Stars are formed by z~2
• More massive galaxies
show a steeper decline
in SSFR.
Summary:
• faint end slope of luminosity function is shallow at high z
• LF evolution stronger at shorter wavelength
• F* decreases, L* increases with redshift in all bands
• analysis of cosmic SFH not very sensitive to l-selection
• at all z, L>L* galaxies contribute ~1/3 to total SFR, but less
to SSFR
• at all z, massive galaxies are older than low mass galaxies
• high mass galaxies form their stars earlier and faster
Papers:
FDF+GOODS LFs, SFH: Gabasch et al. 2004, 2005
FDF+GOODS+MUNICS+SDSS+2MASS masses:
Drory et al. 2001, 2003, 2004, 2005