the search for forming galaxies

The Search for Forming The Search for Forming GalaxiesGalaxies

Chris O’Dea

Space Telescope Science Institute

Acknowledgements:•Mauro Giavalisco•Harry Ferguson

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

Hierarchical Galaxy FormationHierarchical Galaxy Formation

(Virgo consortium)

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

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.

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.

Star Formation & Stellar EvolutionStar Formation & Stellar Evolution

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).

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).

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

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.


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.


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.


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.


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.

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.

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.

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.

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)

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)

Radio GalaxiesRadio Galaxies

(Carilli 2000)

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.

The Hubble Deep FieldsThe Hubble Deep Fields

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

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)

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

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

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…

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)

F814WF814W

F606WF606W

F450WF450W

F300WF300W

STIS 2300STIS 2300ǺǺ

STIS 1600STIS 1600ÅÅ

Lyman Break GalaxiesLyman Break Galaxies

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

Spectral Features due to Spectral Features due to HydrogenHydrogen

(Valenti 2001)

Lyman-Break selection

(Giavalisco 2001)

Lyman-Break selectionLyman-Break selection

(Giavalisco 2001)

Steidel etal 1999, ApJ, 519, 1

Expected colors of high z Lyman break galaxies are well defined, and not sensitive to reddening.


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.

Lyman-Break TechniqueLyman-Break Technique

NOT photometric redshiftJust effective set of selection criteriaRequires follow-up spectroscopic

identification to be useful

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

Large surveyLarge survey


Results of spectroscopic follow up of color selected LBGs.

The two samples are consistent with having similar colors.

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?

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

Radial Profile: WFPC2 & NICMOSRadial Profile: WFPC2 & NICMOS

The HDF-N

HST + WFPC2 & NICMOS-3

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

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

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

ISAAC K-band spectra of LBGsISAAC K-band spectra of LBGs

Wavelength (μm)

NIRSPEC H-band spectra of LBGsNIRSPEC H-band spectra of LBGs

Detecting the continuum in K-band…Detecting the continuum in K-band…

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

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).

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

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

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

Spatially resolved velocity profiles - 1Spatially resolved velocity profiles - 1

HST image, F702WHST image, F702W

Spatially resolved velocity profiles - 2Spatially resolved velocity profiles - 2

Keck + NIRC K-band image, ~0.5”Keck + NIRC K-band image, ~0.5”

Gas outflowsGas outflows

Vout ~ 200 - 400 km/s

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)

The rest-frame B-band LFThe rest-frame B-band LF

Dickinson, Papovich & Ferguson 2001

Fitting age and stellar massFitting age and stellar mass

Papovich, Dickinson& Ferguson 2001

Fitting SED with Broad-band photometryFitting SED with Broad-band photometry

Papovich, Dickinson& Ferguson 2001

Stellar Mass and Burst AgeStellar Mass and Burst Age

Papovich, Dickinson & Ferguson 2001

Stuffing in old starsStuffing in old stars

Papovich, Dickinson & Ferguson 2001

Stuffing In Old StarsStuffing In Old Stars

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

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?

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?

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

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

Clustering in the redshift spaceClustering in the redshift space

The Westphal Field

Star Formation History of the Star Formation History of the Universe Universe

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)

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)

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

Evidence of dust reddening

The star-formation rates

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.

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.

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 ?

Radio and Sub-mm SearchesRadio and Sub-mm Searches

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.

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

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

ConclusionsConclusions

The EndThe End

the search for forming galaxies

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