The Search for Forming Galaxies: The Search for Forming Galaxies Chris O’Dea Space Telescope Science Institute Acknowledgements: Mauro Giavalisco Harry Ferguson


Outline: Outline Hierarchical Galaxy Formation Star Formation andamp; 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: Hierarchical Galaxy Formation (Virgo consortium)


Hierarchical Galaxy Formation: The Paradigm: Hierarchical Galaxy Formation: The Paradigm At recombination (z~1160), the universe is very homogeneous andamp; 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


Slide5: 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.


Slide6: 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 Evolution: Star Formation andamp; Stellar Evolution


Star Formation: 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: 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: SED of Instantaneous Burst Broadband spectrum of instantaneous burst reddens and dims are the population evolves (massive hot stars die first). Devriendt etal. 1999, Aandamp;A, 350, 381


Star Formation in a Merger: Star 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 andamp; Shioya 2001, ApJS, 134, 241). N-Body simulation of evolution of galaxies with dusty starbursts showing old stellar population.


Star Formation in a Merger: Star 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 andamp; Shioya 2001, ApJS, 134, 241). N-Body simulation of evolution of galaxies with dusty starbursts showing gas and new stars.


Star Formation in a Merger: Star Formation in a Merger Time evolution of star formation rate in solar masses/yr in the merger. (Bekki andamp; 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.


Star Formation in a Merger: Star 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 andamp; 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.


Star Formation in a Merger: Star 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 andamp; 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 Galaxies: Integrated 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 Type: SRF 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 andamp; Spinrad, 1999, PASP, 111, 1475) This implies that the galaxies are obscured by dust.


Extended Lyα Emission: 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 cooling-flows. (Steidel etal, 2000, ApJ, 532, 170)


High z GPS Quasars: High z GPS Quasars A significant fraction of radio-loud quasars at high z (andgt;2) tend to be GPS. GPS quasars tend to be at high z (andgt;2) Possibly, the high z quasars are GPS because the radio sources are confined to small scales (andlt;100 pc) due to dense gas in the host circumnuclear region. The presence of the dense gas necessary to confine a powerful quasar (andgt; 1010 M⊙), suggests that the host is a proto galaxy. (O’Dea 1998, PASP,110, 493)


Radio Galaxies: Radio 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 Fields: The Hubble Deep Fields


Slide24:


HDF Census : 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 andgt; 2 andlt;20 Main-sequence stars to I = 26.3 ~2 Supernovae 0-2 Strong gravitational lenses 6 X-ray sources Ferguson, Dickinson andamp; Williams 2000, ARAA, 38, 667


Advantages and disadvantages of a pencil-beam survey: 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 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: WFPC2 andamp; 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: Galaxy Morphologies Higher fraction of irregular andamp; 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 andamp; Babul 1998…


Galaxy Sizes at z~3: Galaxy Sizes at z~3 The galaxies at z~3 are small but luminous, with half-light radii 1.8 andlt;r1/2andlt; 6.5 h kpc and absolute magnitudes -21.5 andgt; M(B) andgt; -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: F814W


F606W: F606W


F450W: F450W


F300W: F300W


STIS 2300Ǻ: STIS 2300Ǻ


STIS 1600Å: STIS 1600Å


Lyman Break Galaxies: Lyman Break Galaxies


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: Spectral Features due to Hydrogen (Valenti 2001)


Slide40: Lyman-Break selection (Giavalisco 2001)


Lyman-Break selection: Lyman-Break selection (Giavalisco 2001)


Slide42: Steidel etal 1999, ApJ, 519, 1 Expected colors of high z Lyman break galaxies are well defined, and not sensitive to reddening.


Slide43: Steidel etal 1999, ApJ, 519, 1


Slide44: 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 3.7andlt;zandlt;4.8. And yellow objects are interlopers.


Lyman-Break Technique: Lyman-Break Technique NOT photometric redshift Just effective set of selection criteria Requires follow-up spectroscopic identification to be useful


Slide46: Keck-LRIS spectra Rsandlt;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


Slide47: Keck-LRIS spectra Rsandlt;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: Large 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.


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?


Slide50: HST morphology Observed mostly only faint LBGs (mandgt;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: Radial Profile: WFPC2 andamp; NICMOS


Slide52: The HDF-N HST + WFPC2 andamp; NICMOS-3


Slide53: The HDF-N HST + WFPC2 andamp; NICMOS-3


Results From Morphology: 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 (mandgt;m*) LBGs


Observing the Rest-Frame Optical SED: 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 andamp; HDF… …and two methods: Keck near-IR spectroscopy and HST multi-band photometry


Keck + NIRSPEC K-band spectra of LBGs: Keck + 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 LBGs: ISAAC K-band spectra of LBGs Wavelength (μm)


NIRSPEC H-band spectra of LBGs: NIRSPEC H-band spectra of LBGs


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


The metallicity of LBGs: 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


Slide61:


The Metallicity of LBGs vs Normal Galaxies: The Metallicity of LBGs vs Normal Galaxies Metallicity-luminosity for local galaxies from Kobulnicky andamp; 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: The Metallicity of LBGs 0.1andlt;~[O/H]/[O/H]⊙andlt;~ 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: Dynamics from the nebular lines Idea is to use velocity width of nebular lines as dynamical indicator It is found: 50andlt;σandlt;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?: 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: Spatially resolved velocity profiles - 1


HST image, F702W: HST image, F702W


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


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


Gas outflows: Gas outflows Vout ~ 200 - 400 km/s


Results from the near-IR spectroscopy: Results from the near-IR spectroscopy Estimate of metallicity: 0.1andlt;[O/H] andlt;~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: The rest-frame B-band LF Dickinson, Papovich andamp; Ferguson 2001


Fitting age and stellar mass: Fitting age and stellar mass Papovich, Dickinson andamp; Ferguson 2001


Fitting SED with Broad-band photometry: Fitting SED with Broad-band photometry Papovich, Dickinson andamp; Ferguson 2001


Stellar Mass and Burst Age: Stellar Mass and Burst Age Papovich, Dickinson andamp; Ferguson 2001


Stuffing in old stars: Stuffing in old stars Papovich, Dickinson andamp; Ferguson 2001


Stuffing In Old Stars: Stuffing In Old Stars


LBGs at z~3 and z>4: LBGs at z~3 and zandgt;4 The z~3 galaxies do not seem to be the same ones seen at zandgt;4


LBGs at z~3 and z>4: LBGs at z~3 and zandgt;4 Aging zandgt;4 ex- LBG should be visible in the HDF images as red sources. There are no such galaxies. But we do see zandgt;4 LBGs. Where are they at Z~3? Recurrent SF? Just bad luck in The HDF?


Conclusions from SED Fitting: 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: 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: 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: Clustering in the redshift space The Westphal Field


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


UV luminosity and star-formation rates: 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 LUV(1500 Å) (Kennicutt 1998)


UV luminosity and star-formation rates: 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: High-z Galaxy Stellar Populations and Extinction E(B-V)=0.4 0.2 0.0 Ferguson etal 2000, ARAA, 38,667


Slide88: Evidence of dust reddening


Slide89: The star-formation rates


Luminosity Function of LBGs : Luminosity Function of LBGs Luminosity function of LBGs at z=3andamp;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 LBGs : Rest-Frame Luminosity Function of LBGs Luminosity function of LBGs at z=3andamp;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 Universe: Star Formation History of the Universe UV luminosity density as a function of z. (Steidel et al. 1999, ApJ, 519, 1) Extinction corrected emissivity of star formation is ~constant for zandgt;1 Onset of substantial star formation occurs at zandgt; 4.5 ? Star formation does not show strong peak at z~2 as for quasar activity ?


Radio and Sub-mm Searches: Radio and Sub-mm Searches


Radio to IR Spectrum of Luminous IR Galaxies : Radio to IR Spectrum of Luminous IR Galaxies Carilli andamp; Yun 2000, ApJ, 530, 618 'K-correction' increases flux density for high-z objects.


SED of Instantaneous Burst: 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, Aandamp;A, 350, 381


Obscured high-redshift galaxies in the HDF: 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: Conclusions


The End: The End