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  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.

10 6 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.

Time evolution of gas mass accumulated within the central regions.

(Bekki & Shioya 2001, ApJS, 134, 241).

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). 10 4 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. 10 4 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 ~ 10 43 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 Ly α 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 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 (> 10 10 M ⊙ ), suggests that the host is a proto galaxy.

(O’Dea 1998, PASP,110, 493)

(Carilli 2000)

Radio Galaxies

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 ~9 Galaxies at 3.2

m m ~50 Galaxies at 6.7 or 15 m m ~5 Sources at 850 m m 0 Galaxies at K Sources at 450 m m or 2800 m m ~16 Sources at 8.5 GHz ~150 ~30 0-2 Measured redshifts Galaxies with spectroscopic

z

Strong gravitational lenses > 2 <20 Main-sequence stars to I = 26.3

~2 Supernovae 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 no evolution 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 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 2300 Ǻ

STIS 1600 Å

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)

(Giavalisco 2001) Lyman-Break selection

(Giavalisco 2001) Lyman-Break selection

 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

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

 Results of spectroscopic follow up of color selected LBGs.

 The two samples are consistent with having similar colors. Large survey 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: r1/2~1 3 kpc •Dispersion of properties: both disk-like and spheroid-like observed •Rest-UV and rest optical 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: LBGs HST has mostly imaged faint (m>m*)

Observing the Rest-Frame Optical 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 LBGs R~7-14 Å T exp ~5-18 Ksec Wavelength (μm) Pettini et al. 2001

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 :  R 23 =([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 10 10 M ⊙ within r 1/2 ~2-3 kpc

Are the nebular lines good dynamical indicators?

No correlation with with either L UV or M B 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 V out ~ 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

Aging z>4 ex LBG 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?

LBGs at z~3 and z>4

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 10 10 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 star formation rate: SFR (M ⊙ /yr) = 1.4x10

-28 x L UV (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