Download Metallicity, Age, and Mass of Star Forming Galaxies at z~3

The Search for Forming
Galaxies
Chris O’Dea
Space Telescope Science Institute
Acknowledgements:
•Mauro Giavalisco
•Harry Ferguson
Outline
 Hierarchical Galaxy Formation
 Star Formation & Stellar Evolution
 Searches for Forming Galaxies


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
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
Narrow Band Optical Searches
GPS Quasars
High-Z Radio Galaxies
The Hubble Deep Fields
Lyman-Break Galaxies
Sub-mm/IR
 Star Formation History of the Universe
Hierarchical Galaxy Formation
(Virgo consortium)
Hierarchical Galaxy Formation:
The Paradigm
 At recombination (z~1160), the universe is very
homogeneous & smooth
There is a spectrum of density perturbations – gravitational
potential fluctuations are independent of length scale
Low mass clumps collapse first and merge to form galaxies
Larger scale structure builds slowly as galaxies form groups, clusters, super clusters.
e.g., Kauffmann etal. 1993, MNRAS, 264, 201
Blow up of dark
matter density in the
region around a rich
cluster in a
simulation of a
ΛCDM universe at
z=0.
Jenkins etal 1998,
ApJ, 499, 20
Numerical models of
structure formation in 4
cosmologies. (dark matter
density is plotted).
All simulations are
normalized to reproduce
the abundance of rich
galaxy clusters today.
However, the power
spectrum of the simulated
dark matter distribution is
not consistent with that of
observed galaxies.
Jenkins etal 1998, ApJ, 499, 20
Star Formation & Stellar Evolution
Star Formation
Evolution of the
UV-Optical SED of a
continuous star burst.
The SED brightens
in the UV around 3
Myr and then reddens
only slightly with
time.
1 solar mass/yr with
solar metals and Salpeter
IMF 1-100 M⊙
(Starburst99 code).
Star Formation
Evolution of the
UV-Optical SED of
an instantaneous star
burst.
The SED brightens
in the UV around 2
Myr and then reddens
and fades as the stars
evolve.
106 M⊙ burst with solar
metals and Salpeter IMF
1-100 M⊙ (Starburst99
code).
SED of Instantaneous Burst
Broadband
spectrum of
instantaneous burst
reddens and dims
are the population
evolves (massive
hot stars die first).
Devriendt etal. 1999,
A&A, 350, 381
Star Formation in a Merger
N-Body simulation of evolution of
galaxies with dusty starbursts
showing old stellar population.
Mass distribution of old stars projected
onto (x,y) plane at each time T for the
merger model. Each frame is 105 kpc.
Merger is prograde-retrograde. (Bekki &
Shioya 2001, ApJS, 134, 241).
Star Formation in a Merger
N-Body simulation of evolution of
galaxies with dusty starbursts
showing gas and new stars.
Mass distribution of gas and new stars
projected onto (x,y) plane at each time T
for the merger model. Each frame is 105
kpc. Merger is prograde-retrograde.
(Bekki & Shioya 2001, ApJS, 134, 241).
Star Formation in a Merger
Star formation rate depends on the
accumulation of dense gas in the central
region.
Time evolution of star formation rate
in solar masses/yr in the merger.
(Bekki & Shioya 2001, ApJS, 134, 241).
Time evolution of gas
mass accumulated
within the central
regions.
Star Formation in a Merger
Time dependence of SED depends
on time dependence of star formation
rate.
IR and sub-mm luminosity
increases during peak of star
formation (when gas is efficiently
transported to galaxy center).
 In later stages, gas is rapidly
consumed, and UV and IR luminosity
declines.
Spectral energy distribution of a merger as
a function of time. Model includes gas and
dust. Time given in Gyr. (Bekki & Shioya
2001, ApJS, 134, 241). 104 Å = 1μ.
Star Formation in a Merger
Effect of dust is to remove
UV light and re-radiate in the
IR.
Spectral energy distribution of a merger
(top) with gas and dust, and (bottom)
without. Corresponds to maximum SFR in
the merger. Bekki & Shioya 2001, ApJS,
134, 241. 104 Å = 1μ.
Integrated Spectra of Galaxies
 Spectra reflect the
large difference in
SFR as a function of
Hubble type.
Fluxes Normalized at 5500 Å. (Kennicutt 1992, ApJS, 79, 255)
SRF vs Hubble Type
 Line EQW scales
with stellar birthrate
parameter (b) and
Hubble type.
From a large sample of nearby spiral galaxies (Kennicutt 1998, ARAA,36, 189).
Narrow Band Searches



A proto galaxy forming stars at a rate of 100 M⊙/yr should
produce a Lyα luminosity ~ 1043 ergs/s (e.g., Thompson etal, 1995,
AJ, 110, 963).
Yet, with some exceptions (see next viewgraph) Lyα from possible
proto galaxies is rarely detected in deep narrow band searches
(Thompson etal 1995; Stern & Spinrad, 1999, PASP, 111, 1475)
This implies that the galaxies are obscured by dust.
Extended Lyα Emission



Two large, bright, diffuse
Lyα blobs in a protocluster
region at z~3.09
The blobs are similar to
those seen around
powerful radio galaxies,
but these are radio-weak.
They could be excited by
obscured AGN or they
could be large coolingflows.
(Steidel etal, 2000, ApJ, 532, 170)
High z GPS Quasars

A significant fraction of radioloud quasars at high z (>2) tend
to be GPS.
 GPS quasars tend to be at high
z (>2)
 Possibly, the high z quasars are
GPS because the radio sources
are confined to small scales
(<100 pc) due to dense gas in
the host circumnuclear region.
 The presence of the dense gas
necessary to confine a
powerful quasar (> 1010 M⊙),
suggests that the host is a proto
galaxy.
(O’Dea 1998, PASP,110, 493)
Radio Galaxies
(Carilli 2000)
Radio Galaxies at High z
Powerful radio
galaxies are detectable
out to high z.
They are generally
bright L* Ellipticals
with old stellar
populations rather than
proto galaxies.
Van Breugel etal. 1999, ApJ, 518, L61
The Hubble Deep Fields
HDF Census
~3000 Galaxies at U,B,V,I
~1700 Galaxies at J, H
~300
Galaxies at K
~9 Galaxies at 3.2mm
~50
Galaxies at 6.7 or 15mm
~5 Sources at 850mm
0
Sources at 450mm or 2800mm
~16
Sources at 8.5 GHz
~150
Measured redshifts
~30
Galaxies with spectroscopic z > 2
<20
Main-sequence stars to I = 26.3
~2 Supernovae
0-2
Strong gravitational lenses
6
X-ray sources
Ferguson, Dickinson & Williams 2000,
ARAA, 38, 667
Advantages and
disadvantages
of a pencil-beam
survey
Normalized by
galaxy luminosity
function. Shows the
number of L*
volumes.
Volume is smallest
at low z where most
of cosmic time
passes.
(Ferguson etal. 2000, ARAA,
38, 667)
Galaxy Counts
Galaxy number
counts favor
ΛCDM
cosmologies.
Galaxies are
more numerous
than simple noevolution models
(esp at U)
Ferguson etal 2000,
ARAA, 38,667
WFPC2 & NICMOS Imaging
Selected galaxies from
the HDF-N at a range of
z. Left – B, V, I; Right –
I, J, H.
Morphologies are
similar in both optical
and near-IR.
Ferguson etal. 2000, ARAA, 38,
667
Galaxy Morphologies



Higher fraction of irregular & peculiar galaxies than seen
locally.
Qualitatively supports hierarchical galaxy formation.
LSB galaxies and bursting dwarf galaxies don’t dominate the
counts.
Abraham et al. 1996, Baugh et al. 1996, Ferguson & Babul 1998…
Galaxy Sizes at z~3

The galaxies at z~3 are
small but luminous,
with half-light radii 1.8
<r1/2< 6.5 h kpc and
absolute magnitudes 21.5 > M(B) > -23.
Blue magnitude vs half-light
radius for High-Z HDF galaxies
and a representative sample of
local galaxies. (Lowenthal etal
1997, ApJ, 481, 673)
F814W
F606W
F450W
F300W
STIS 2300Ǻ
STIS 1600Å
Lyman Break Galaxies
Lyman-Break Galaxies
Color selection of star-forming galaxies from the
912 Å continuum discontinuity
 Effects of cosmic opacity…
– Photoelectric absorption
– Line blanketing
… and moderate dust obscuration
 Makes identification of distant galaxies “easy” with
optical/near-IR multi-band imaging
 Very efficient: ~90% at z~3,
50% at z~4
 Current best way to test ideas on galaxy formation

Spectral Features due to
Hydrogen
(Valenti 2001)
Lyman-Break selection
(Giavalisco 2001)
Lyman-Break selection
(Giavalisco 2001)
Expected
colors of high z
Lyman break
galaxies are
well defined,
and not
sensitive to
reddening.
Steidel etal 1999, ApJ, 519, 1
Steidel etal 1999, ApJ, 519, 1
Color color plot
of real data.
 207/29,000
satisfy the color
selection criteria.
Blue circles are
objects with
spectroscopic
3.7<z<4.8. And
yellow objects are
interlopers.
Steidel etal 1999, ApJ, 519, 1
Lyman-Break Technique

NOT photometric redshift
 Just effective set of selection criteria
 Requires follow-up spectroscopic
identification to be useful
Keck-LRIS spectra
Rs<25.5
Texp~2-4 hr
Δλ~12 Å
•Similar to local SF galaxies
•Richness of features from:
•Interstellar gas
•Nebular gas
•Stars
•Presence of OB stars
•Varying Lyα
Giavalisco 2001
Keck-LRIS spectra
Rs<25.5
Texp~2-4 hr
Δλ~12 Å
•Similar to local SF galaxies
•Richness of features from:
•Interstellar gas
•Nebular gas
•Stars
•Presence of OB stars
•Varying Lyα
Giavalisco 2001
Large survey
Results of
spectroscopic
follow up of
color selected
LBGs.
The two
samples are
consistent with
having similar
colors.
Steidel etal 1999, ApJ, 519, 1
The Nature of LBGs

What is the link between LBGs and the local
populations?
– Are LBGs small sub-galactic systems that will
merge to form more massive galaxies, as
predicted by hierarchical cosmologies (CDM)?
– What is their mass distribution?

Regardless, their stars must be old
– Can they be the progenitors of the spheroids?
– What is their metallicity?
– What are their stellar mass and age?
HST morphology
•Observed mostly
only faint LBGs
(m>m*)
•Small size: r1/2~13 kpc
•Dispersion of
properties: both
disk-like and
spheroid-like
observed
•Rest-UV and restoptical
morphologies
similar
Radial Profile: WFPC2 & NICMOS
The HDF-N
HST +
WFPC2 &
NICMOS-3
The HDF-N
HST +
WFPC2 &
NICMOS-3
Results From Morphology





Disk-like and spheroid-like structures observed
Compact and fragmented/irregular/diffuse
structures observed. Merging?
Sizes smaller than present-day L* galaxies; similar
to big bulges and intermediate-luminosity
Ellipticals
No obvious evidence for much older, larger
structures. UV morph. ~ Opt morph.
NOTE: HST has mostly imaged faint (m>m*)
LBGs
Observing the Rest-Frame
Optical SED



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

MOTIVATIONS
Estimate metallicity (O abundance) from optical
nebular lines
Estimate dynamics (hence mass)
Estimate reddening (hence SFR)
Estimate age and stellar mass
Two complementary samples: GB & HDF…
…and two methods: Keck near-IR spectroscopy
and HST multi-band photometry
Keck + NIRSPEC K-band spectra of LBGs
R~7-14 Å
Texp~5-18 Ksec
Pettini et al. 2001
Wavelength (μm)
ISAAC K-band spectra of LBGs
Wavelength (μm)
NIRSPEC H-band spectra of LBGs
Detecting the continuum in K-band…
The metallicity of LBGs







Key measure: if progenitors of spheroids, LBGs
must be metal rich
Measures from the O23 index:
R23=([OII]+[OIII])/Hβ
Measures are double-valued
Rest-frame optical spectroscopy to target
[OII], Hbeta, and [OIII] lines (in the near-IR)
Keck+NIRSPEC and VLT+ISAAC spectra in H
and K band
VERY DIFFICULT observations
The Metallicity of LBGs vs Normal Galaxies
Metallicity-luminosity for local galaxies from Kobulnicky & Koo (2000) adjusted for
cosmology. Purple box shows the location of the LBGs where are over luminous for their
metallicity. (Pettini etal. 2001, ApJ, 554, 981).
The Metallicity of LBGs
0.1<~[O/H]/[O/H]⊙<~ 1
In two cases: [O/H]/[O/H]⊙~0.3

(see Kobulniky and Koo 2001)
LBGs are relatively metal rich systems
– More metal enriched than DLAs
– Less enriched than inner regions of AGNs

Metallicity comparable to the Solar
neighborhood
Dynamics from the nebular
lines

Idea is to use velocity width of nebular lines
as dynamical indicator
 It is found:
50<σ<115 km/s
 Returns masses in the range
M ~ a few 1010 M⊙
within r1/2~2-3 kpc
Are the nebular lines good dynamical
indicators?
No correlation with with either LUV or MB
raises serious doubts that N.L.s are reliable dynamical tracers
Spatially resolved velocity profiles - 1
HST image, F702W
Spatially resolved velocity profiles - 2
Keck + NIRC K-band image, ~0.5”
Gas outflows
Vout ~ 200 - 400 km/s
Results from the near-IR
spectroscopy

Estimate of metallicity: 0.1<[O/H] <~1
solar
 Insight into the extinction law: Calzetti law
OK
 Mass unconstrained
 Evidence of high-speed outflows (300 km/s)
The rest-frame B-band LF
Dickinson, Papovich & Ferguson 2001
Fitting age and stellar mass
Papovich, Dickinson
& Ferguson 2001
Fitting SED with Broad-band photometry
Papovich, Dickinson
& Ferguson 2001
Stellar Mass and Burst Age
Papovich, Dickinson
& Ferguson 2001
Stuffing in old stars
Papovich, Dickinson
& Ferguson 2001
Stuffing In Old Stars
LBGs at z~3 and z>4
The z~3 galaxies
do not seem to be
the same ones seen
at z>4
LBGs at z~3 and z>4
Aging z>4 exLBG should be
visible in the
HDF images as
red sources.
There are no such
galaxies. But we
do see z>4 LBGs.
Where are they at
Z~3?
Recurrent SF?
Just bad luck in
The HDF?
Conclusions from SED Fitting

The forming population (the one observed)
is younger than ~ 1 Gyr
 Unconstrained for how long SF will go on
 Stellar mass smaller, but not too smaller
than m* today: M ~ a few 1010 M⊙
(nebular line mass really dubious)
 Maybe recurrent SF activity?
High-z Galaxy Clustering

Clustering links mass distribution and
physics of star formation. Key observable
 Samples are large enough to attempt the
measure
 Possible to estimate spatial clustering
 Angular clustering seems reliable and safe
measure
The Clustering of LBGs





LBGs are strongly clustered in space
Correlation lengths rivals that of local galaxies
Clustering of mass cannot have grown to such an
extent at z~3 in “reasonable” cosmologies
Bias: galaxies form in biased regions of the mass
distribution
In principle, it can constrain the mass spectrum
Clustering in the redshift space
The Westphal Field
Star Formation History of the
Universe
UV luminosity and
star-formation rates

SFR is very important parameter for galaxy
evolution
 If there is no dust obscuration, UV
luminosity is good tracer of the starformation rate:
SFR (M⊙/yr) = 1.4x10-28 x LUV(1500 Å)
(Kennicutt 1998)
UV luminosity and
star-formation rates

Star formation
rates estimated
using UV and Hβ
luminosities are
roughly consistent
in LBGs.
(Pettini etal 2001, ApJ, 554, 981)
High-z Galaxy Stellar
Populations and Extinction
E(B-V)=0.4
0.2
0.0
Ferguson etal
2000, ARAA,
38,667
Evidence of dust reddening
The star-formation rates
Luminosity Function of LBGs
Data are consistent
with similar LF at
z~3 and z~4.
Luminosity function of
LBGs at z=3&4. (Steidel
et al. 1999, ApJ, 519, 1)
Rest-Frame Luminosity Function of LBGs
GB and HDF give
similar results.
Data are consistent
with similar LF at
z~3 and z~4.
Possible drop at
faint mags at z~4.
Luminosity function of
LBGs at z=3&4. (Steidel
et al. 1999, ApJ, 519, 1)
Star Formation History of the
Universe
Extinction
corrected emissivity
of star formation is
~constant for z>1
Onset of substantial
star formation occurs
at z> 4.5 ?
Star formation does
not show strong peak
at z~2 as for quasar
activity ?
UV luminosity density as
a function of z. (Steidel et
al. 1999, ApJ, 519, 1)
Radio and Sub-mm Searches
Radio to IR Spectrum of
Luminous IR Galaxies
“K-correction”
increases flux density
for high-z objects.
Carilli & Yun 2000,
ApJ, 530, 618
SED of Instantaneous Burst
IR sub-mm
remains bright as a
dusty starburst
spectrum is
redshifted.
Thus, it is
relatively easy to
detect these objects
in the sub-mm.
Devriendt etal. 1999,
A&A, 350, 381
Obscured high-redshift
galaxies in the HDF
ISO: Rowan-Robinson et al. 1997;
Desert et al. 1999, Aussel et al, 1999
SCUBA: Hughes et al. 1998,
Peacock et al. 2000
Conclusions
The End