The Search for Forming Galaxies
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Transcript of The Search for Forming Galaxies
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The Search for Forming The Search for Forming GalaxiesGalaxies
Chris O’Dea
Space Telescope Science Institute
Acknowledgements:•Mauro Giavalisco•Harry Ferguson
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OutlineOutline
Hierarchical Galaxy Formation Star Formation & Stellar Evolution Searches for Forming Galaxies
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
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Hierarchical Galaxy FormationHierarchical Galaxy Formation
(Virgo consortium)
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Hierarchical Galaxy Formation: Hierarchical Galaxy Formation: The ParadigmThe 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
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Jenkins etal 1998, ApJ, 499, 20
Blow up of dark matter density in the region around a rich cluster in a simulation of a ΛCDM universe at z=0.
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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.
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Star Formation & Stellar EvolutionStar Formation & Stellar Evolution
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Star FormationStar 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).
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Star FormationStar 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).
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SED of Instantaneous BurstSED 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
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Star Formation in a MergerStar Formation in a Merger
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).
N-Body simulation of evolution of galaxies with dusty starbursts showing old stellar population.
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Star Formation in a MergerStar Formation in a Merger
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).
N-Body simulation of evolution of galaxies with dusty starbursts showing gas and new stars.
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Star Formation in a MergerStar Formation in a Merger
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 rate depends on the accumulation of dense gas in the central region.
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Star Formation in a MergerStar Formation in a Merger
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.
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.
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Star Formation in a MergerStar Formation in a Merger
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.
Effect of dust is to remove UV light and re-radiate in the IR.
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Integrated Spectra of GalaxiesIntegrated Spectra of Galaxies
Fluxes Normalized at 5500 Å. (Kennicutt 1992, ApJS, 79, 255)
Spectra reflect the large difference in SFR as a function of Hubble type.
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SRF vs Hubble TypeSRF vs Hubble Type
From a large sample of nearby spiral galaxies (Kennicutt 1998, ARAA,36, 189).
Line EQW scales with stellar birthrate parameter (b) and Hubble type.
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Narrow Band Searches 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.
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Extended LyExtended Lyαα Emission 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 cooling-flows.
(Steidel etal, 2000, ApJ, 532, 170)
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High z GPS QuasarsHigh z GPS Quasars
A significant fraction of radio-loud 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)
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Radio GalaxiesRadio Galaxies
(Carilli 2000)
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Radio Galaxies at High z Radio Galaxies at High z
Van Breugel etal. 1999, ApJ, 518, L61
Powerful radio galaxies are detectable out to high z.
They are generally bright L* Ellipticals with old stellar populations rather than proto galaxies.
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The Hubble Deep FieldsThe Hubble Deep Fields
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HDF Census HDF Census ~3000 Galaxies at U,B,V,I
~1700 Galaxies at J, H
~300 Galaxies at K
~9 Galaxies at 3.2m
~50 Galaxies at 6.7 or 15m
~5 Sources at 850m
0 Sources at 450m or 2800m
~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
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Advantages and Advantages and disadvantages disadvantages
of a pencil-beam of a pencil-beam surveysurvey
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)
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Galaxy CountsGalaxy Counts
Galaxy number counts favor ΛCDM cosmologies.
Galaxies are more numerous than simple no-evolution models (esp at U)
Ferguson etal 2000, ARAA, 38,667
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WFPC2 & NICMOS ImagingWFPC2 & 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
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Galaxy MorphologiesGalaxy 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…
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Galaxy Sizes at z~3Galaxy 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)
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F814WF814W
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F606WF606W
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F450WF450W
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F300WF300W
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STIS 2300STIS 2300ǺǺ
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STIS 1600STIS 1600ÅÅ
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Lyman Break GalaxiesLyman Break Galaxies
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Lyman-Break GalaxiesLyman-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
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Spectral Features due to Spectral Features due to HydrogenHydrogen
(Valenti 2001)
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Lyman-Break selection
(Giavalisco 2001)
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Lyman-Break selectionLyman-Break selection
(Giavalisco 2001)
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Steidel etal 1999, ApJ, 519, 1
Expected colors of high z Lyman break galaxies are well defined, and not sensitive to reddening.
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Steidel etal 1999, ApJ, 519, 1
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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.
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Lyman-Break TechniqueLyman-Break Technique
NOT photometric redshiftJust effective set of selection criteriaRequires follow-up spectroscopic
identification to be useful
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Keck-LRIS spectra
Rs<25.5Texp~2-4 hrΔλ~12 Å
•Similar to local SF galaxies•Richness of features from:
•Interstellar gas•Nebular gas•Stars
•Presence of OB stars•Varying Lyα
Giavalisco 2001
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Keck-LRIS spectra
Rs<25.5Texp~2-4 hrΔλ~12 Å
•Similar to local SF galaxies•Richness of features from:
•Interstellar gas•Nebular gas•Stars
•Presence of OB stars•Varying Lyα
Giavalisco 2001
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Large surveyLarge survey
Steidel etal 1999, ApJ, 519, 1
Results of spectroscopic follow up of color selected LBGs.
The two samples are consistent with having similar colors.
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The Nature of LBGs 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?
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HST morphology
•Observed mostly only faint LBGs (m>m*)
•Small size: r1/2~1-3 kpc
•Dispersion of properties: both disk-like and spheroid-like observed
•Rest-UV and rest-optical morphologies similar
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Radial Profile: WFPC2 & NICMOSRadial Profile: WFPC2 & NICMOS
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The HDF-N
HST + WFPC2 & NICMOS-3
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The HDF-N
HST + WFPC2 & NICMOS-3
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Results From MorphologyResults 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
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Observing the Rest-Frame Observing the Rest-Frame Optical SEDOptical SED
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
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Keck + NIRSPEC K-band spectra of LBGsKeck + NIRSPEC K-band spectra of LBGs
Wavelength (μm)
R~7-14 Å
Texp~5-18 Ksec
Pettini et al. 2001
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ISAAC K-band spectra of LBGsISAAC K-band spectra of LBGs
Wavelength (μm)
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NIRSPEC H-band spectra of LBGsNIRSPEC H-band spectra of LBGs
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Detecting the continuum in K-band…Detecting the continuum in K-band…
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The metallicity of LBGsThe 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
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The Metallicity of LBGs vs Normal GalaxiesThe 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).
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The Metallicity of LBGsThe 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
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Dynamics from the nebular Dynamics from the nebular lineslines
Idea is to use velocity width of nebular lines as dynamical indicator
It is found:
50<σ<115 km/sReturns masses in the range
M ~ a few 1010 M⊙
within r1/2~2-3 kpc
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Are the nebular lines good dynamical Are the nebular lines good dynamical indicators?indicators?
No correlation with with either LUV or MB
raises serious doubts that N.L.s are reliable dynamical tracers
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Spatially resolved velocity profiles - 1Spatially resolved velocity profiles - 1
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HST image, F702WHST image, F702W
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Spatially resolved velocity profiles - 2Spatially resolved velocity profiles - 2
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Keck + NIRC K-band image, ~0.5”Keck + NIRC K-band image, ~0.5”
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Gas outflowsGas outflows
Vout ~ 200 - 400 km/s
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Results from the near-IR Results from the near-IR spectroscopyspectroscopy
Estimate of metallicity: 0.1<[O/H] <~1 solar
Insight into the extinction law: Calzetti law OK
Mass unconstrainedEvidence of high-speed outflows (300
km/s)
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The rest-frame B-band LFThe rest-frame B-band LF
Dickinson, Papovich & Ferguson 2001
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Fitting age and stellar massFitting age and stellar mass
Papovich, Dickinson& Ferguson 2001
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Fitting SED with Broad-band photometryFitting SED with Broad-band photometry
Papovich, Dickinson& Ferguson 2001
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Stellar Mass and Burst AgeStellar Mass and Burst Age
Papovich, Dickinson & Ferguson 2001
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Stuffing in old starsStuffing in old stars
Papovich, Dickinson & Ferguson 2001
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Stuffing In Old StarsStuffing In Old Stars
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LBGs at z~3 and z>4LBGs at z~3 and z>4
The z~3 galaxiesdo not seem to be the same ones seen at z>4
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LBGs at z~3 and z>4LBGs at z~3 and z>4
Aging z>4 ex-LBG should bevisible in the HDF images asred sources. There are no suchgalaxies. But we do see z>4 LBGs.Where are they atZ~3?Recurrent SF? Just bad luck in The HDF?
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Conclusions from SED FittingConclusions from SED Fitting
The forming population (the one observed) is younger than ~ 1 Gyr
Unconstrained for how long SF will go onStellar mass smaller, but not too smaller
than m* today: M ~ a few 1010 M⊙ (nebular
line mass really dubious)Maybe recurrent SF activity?
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High-z Galaxy ClusteringHigh-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 clusteringAngular clustering seems reliable and safe
measure
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The Clustering of LBGsThe 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
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Clustering in the redshift spaceClustering in the redshift space
The Westphal Field
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Star Formation History of the Star Formation History of the Universe Universe
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UV luminosity and UV luminosity and star-formation ratesstar-formation rates
SFR is very important parameter for galaxy evolution
If there is no dust obscuration, UV luminosity is good tracer of the star-formation rate:
SFR (M⊙/yr) = 1.4x10-28 x LUV(1500 Å)
(Kennicutt 1998)
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UV luminosity and UV luminosity and star-formation ratesstar-formation rates
Star formation rates estimated using UV and Hβ luminosities are roughly consistent in LBGs.
(Pettini etal 2001, ApJ, 554, 981)
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High-z Galaxy Stellar High-z Galaxy Stellar Populations and ExtinctionPopulations and Extinction
E(B-V)=0.4
0.2
0.0
Ferguson etal 2000, ARAA, 38,667
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Evidence of dust reddening
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The star-formation rates
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Luminosity Function of LBGs Luminosity Function of LBGs
Luminosity function of LBGs at z=3&4. (Steidel et al. 1999, ApJ, 519, 1)
Data are consistent with similar LF at z~3 and z~4.
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Rest-Frame Luminosity Function of LBGsRest-Frame Luminosity Function of LBGs
Luminosity function of LBGs at z=3&4. (Steidel et al. 1999, ApJ, 519, 1)
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.
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Star Formation History of the Star Formation History of the UniverseUniverse
UV luminosity density as a function of z. (Steidel et al. 1999, ApJ, 519, 1)
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 ?
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Radio and Sub-mm SearchesRadio and Sub-mm Searches
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Radio to IR Spectrum of Radio to IR Spectrum of Luminous IR Galaxies Luminous IR Galaxies
Carilli & Yun 2000, ApJ, 530, 618
“K-correction” increases flux density for high-z objects.
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SED of Instantaneous BurstSED 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
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Obscured high-redshift Obscured high-redshift galaxies in the HDFgalaxies 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
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ConclusionsConclusions
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The EndThe End