Transcript Observing the Assembly of Galaxies Hans-Walter Rix Max-Planck-Institute for Astronomy Heidelberg HWR Princeton, 2005 Overview I.

Observing the Assembly of Galaxies
Hans-Walter Rix
Max-Planck-Institute for Astronomy
Heidelberg
HWR
Princeton, 2005
Overview
I. The Build-Up of the Stellar Mass in Galaxies
II. The Formation and Evolution of Massive Galaxies
Thursday May 5, 2:00PM
III. The Evolution of (Internal) Galaxy Structure
Wednesday May 11, 2:00PM
IV. Archeo-Cosmology in the Local Group
Friday, May 13, 2:00PM
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I. The Build-Up of Stellar Mass
1. Casting the problem into specific questions
2. Diagnostic Tools
3. A brief survey of surveys
4. Estimating the star-formation rate = f(z)
5. Estimating the stellar mass density = f(z)
6. Results
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1. Re-phrasing “the build-up of stellar mass”
•
What is <SFR(z)> and
<r*(z) >?
• What epoch encloses the formation of most stars?
• How to best measure <SFR (z)r
> and <r*(z) > ?
• How much important are mergers in triggering SF and in
setting the present-day mass function?
• What are the expectations from models?
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2. Diagnostic tools for
star-formation rates and stellar masses
• Star formation rate estimates are
based on UV luminosity produced by
hot, massive, short-lived stars
– Observe the UV
– Observe Ha
– Observe absorbed UV flux, reradiated by dust in thermal IR
! LIR(re-radiated) >> LUV(escaped) !
– Mtot estimate is based on stars >10Mo,
which are small fraction of Mtot
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Kroupa 2002
Starlight and
Re-processed Starlight
Single-age, dust-free stellar population
Devriend et al 2000
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ground
Herschel
(2007)
Spitzer
SED of an ageing stellar
population of solar
metalicity with dust
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f(24mm) vs Lbol
Papovich and Bell 2003
Given that Spitzer
can only observe well
at 24 mm, what are
the bolometric
corrections?
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Mass measurements in cosmologically distant
galaxies
• Dynamics:
– OK to z~1, but quite expensive.
– Very limited spatial resolution conceptually problematic
– Currently not feasible for most galaxies z>1.5
• Clustering:
– Measures halo mass, not stellar mass
• M* = L x (M/L)* with M/L from SEDs
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Stellar Masses from Spectral Energy Distributions
Near-degeneracy of age,
metallicity and dust
Source of despair or
opportunity?
tstars =
[Gyrs]
B
K
Bell and de Jong 2001
Optical/near-IR spectra of galaxies
are a nearly 1D sequence
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• Mapping one or few integrated galaxy colors to
– age
– dust extinction
– metallicity
is poor!
• Mapping (optical -- across 4000A break)
color to M/L should be robust!
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M/L from Colors? Compare to Mdyn!
Van der Wel, Franx, can Dokkum and Rix, 2004
at z~1
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Look-back Galaxy Surveys: Desiderata
•
•
Select SFR surveys by SFR, and mass surveys by stellar mass
–
SFR: assure most of the intense star-burst are not missing due to
dust
–
Stellar mass: select galaxies lobs > (1+z) 4000A break
Number of galaxies as a function of
–
–
Epoch  redshift (few %)
Luminosity/stellar mass
–
Color/stellar age
1,000 – 10,000 galaxies
•
Measure galaxy sizes/internal structure ~0.3” resolution
•
Either Nfield >> 1 or qfield > 2xcorrelation length ~10’
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A Survey Survey
Name
Nfield
Field
size
HST
imaging
# of
bands
Depth
Nredshift
HDFs/UDF
3
2.5’
+
7
R=29
700
GOODS
2
12’
+
10
i=27.5
400
3000 (5%)
FIRES
2
5’
+
10
KAB=26
600
(5%)
COMBO-17
GEMS
3
30’
+
22
R=24
30,000
(1%)
MUNICS
3
30’
-
7
K=19.5
20.000 (5%)
GDDS/LCIRS
2
30’
-
7
H=21.5
500(2000)
SUBARU
RestUV
Steidel et al
RestUV
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COMBO-17
Wolf, Meisenheimer, Rix et al. 01/03
Heidelberg, Oxford,Potsdam,Edinburgh
•
•
•
3 fields @ 30’x30’
17 filters to mr~23.6
~10.000 redshifts (1.5%)+ SEDs per field
Z
Wavelength
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[nm]
MB
Comparison of COMBO-17 with VIMOS Spectra
(data from Le Fevre et al 2004)
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A quick Tour through Redshift Space
GEMS(CDFS)
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Abell 901
S11 (random)
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Stellar Masses from the COMBO-17 Survey
Borch, Rix, Meisenheimer et al 2005
• Stellar masses to z~1 can
be estimated for 10.000s
of galaxies
• Flux limit (R-band) is
VERY different from
mass limits.
0.65<z<0.75
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FIRES: FaintInfra-Red-Extragalactic-Survey
ultra-deep VLT survey
*HDF-south
100 hours in JHK
FWHM=0.45”
*MS1054:
5xlarger area
25 hours in JHK
per pointing
Franx, Rix, Rudnick, Labbe, van
Dokkum, Foerster-Schreiber,
Trujillo, Moorwood, et al.
2001-2005
Selecting and studying
galaxies z>2 in their
rest-frame optical bands
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Not a Ly-break!!
Just a red SED
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What kind of galaxies are found in such a search?
• Galaxies without many (really) young stars won’t be found by
their Ly-break or their sub-mm dust emission.
• Ditto for galaxies with significant dust extinction that are
not powerful enough for a sub-mm detection.
• Remember: both UV searches (dust) and sub-mm searches
(fainter galaxies) have ~10 corrections to get total SFR
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SED fits for DRGs
Near-IR selected
UV selected
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Förster-Schreiber, Franx, Rix et al; FIRES
Improving Mass, SFR and Av Estimates at z~2.5
through IRAC (3.6mm-8mm) data
Labbe, Franx, Rix et al 2005
Förster-Schreiber, Rix et al 2005; FIRES
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Comparing dynamical (?) with SED masses
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Van Dokkum, Franx, Rix, et al. 2004
Results I: Cosmic Star-Formation Rate
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SFR’s from thermal-IR flux 0<z<1
Zheng, Rix, Rieke, Bell et al 2004
Stacking galaxy classes (z,L) from
COMBO-17 and measuring the 24mm flux
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SFR’s from thermal-IR flux 0<z<1
Zheng, Rix, Rieke, Bell et al 2004
• Through stacking,
(single source) confusion limit
LIR/LSpitzer’s
UV = f(SFR) @ all z,Lopt
can be beat by >10 to <10mJy
• IR flux dominates in all galaxies (to 3% of L*) to z~1.2;
–
large majority of UV photons absorbed.
Local relation
• Mean LIR/LUV drops with galaxy luminosity
 faint galaxies contribute hardly to SF integral
• “Correction” seems to be a function of (absolute) SFR only
– Insensitive to stellar luminosity, redshift
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State of Affairs: Star-fomration rate
Borch, Rix, Meisenheimer et al 2005
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Why the drop of the SFR since z~1?
or
In what type of galaxies did stars form back then?
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Whence the UV flux at z~0.7?
j280 (z~0.7) ~ 4 x j280nm (now)
[not necessarily true in massive,
old systems]
Explore “morphology” of
galaxies that give rise to
these photons
Subjective – use 6 eyes
[Morphologies from GEMS, see
Thursday]
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UV luminous
“blue”
Pick f(2800A) as a proxy
for young stars (t<tdyn)
UV-to-optical flux (M280nm – V)
Wolf, Bell, Rix et al 2004
0.65<z<0.75
UV-light contribution by
•
At MV>-19 and z~0.75
– ½ the flux comes from
seemingly normal spirals
– 20% from visibly interacting
systems
• only minority of UV flux from
manifestly interacting
systems at z~0.75
• drop in (major) merger
rate not cause of SFR drop
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Galaxy type at z~0.75
z~0.75
Normal
spirals
Results II:
Evolution of the Stellar Mass Density with Redshift
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The Evolution of the Stellar Mass Function
over the Last 7 Gyrs
COMBO-17 survey; 30,000 galaxies
Mean stellar mass Build-Up
Present-day
stellar mass
function
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Borch, Meisenheimer, Rix, Bell et al 2005, COMBO-17
Where is the stellar mass at z=2-3.5?
DRGs (“distant red galaxies”) vs Ly-Break Galaxies
Distant red galaxies
likely dominate the
mass budget
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<r*(z)>: State of Affairs
Borch, Meisenheimer, Rix et al 2005
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…half the mass since z~1.5…
Borch et al 2005
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Putting it together
Borch, Meisenheimer, Rix et al 2005
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Summary
• Waning SFR not a consequence of waning major mergers
– Waning cold gas supply
• SED-based stellar mass estimates now available for 1000’s
of galaxies to z~3
– Need to observe at least to lrest>4000A
– Available testing against dynamics OK
• “Distant red galaxies”, between Ly-break and sub-mm
galaxies, may contain the bulk of stellar mass 2<z<3.5
– Found through near-IR surveys
– Quite frequent objects with SFR x tSFR ~1010-11M
• <r*(z) > can be traced from z~3.5 to 0
– enclosing ~90% of all stars formed
• Integral over SFR estimate agrees with <r*(z)
– Assuming diet-Salpeter IMF (e.g. Kroupa 2002)
– Leaves not much room for overlooked SFR
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> to < 2
Where do we go from here?
• Role of merging in the build-up of the galaxy mass
function is observationally barely constrained
• Comprehensive linkeage of SED-based and
dynamical masses
• Beat field-to-field variations at z>2
• Relate stellar masses at different z to halo
masses
– Lensing, clustering
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Improving Mass, SFR and Av Estimates at z~2.5
through IRAC (3.6mm-8mm) data
Labbe, Franx, Rix et al 2005
Förster-Schreiber, Rix et al 2005; FIRES
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SED Fitting of FIRES Galaxies
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Where is the stellar masses at z=2-3.5
DRGs (“distant red galaxies”) vs Ly-Break Galaxies
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Förster-Schreiber, Franx, Rix et al 2005