The Search for Forming Galaxies Chris ODea 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 Jenkins etal 1998, ApJ, 499, 20 Blow up of dark matter density in the region around a rich cluster in a simulation of a CDM 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 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 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 M burst with solar metals and Salpeter IMF 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 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. 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 & 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 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. 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 & Shioya 2001, ApJS, 134, 241) = 1. 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 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, = 1. Effect of dust is to remove UV light and re-radiate in the IR. Integrated Spectra of Galaxies Fluxes Normalized at 5500 . ( Kennicutt 1992, ApJS, 79, 255 ) Spectra reflect the large difference in SFR as a function of 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 A proto galaxy forming stars at a rate of 100 M /yr should produce a Ly luminosity ~ ergs/s (e.g., Thompson etal, 1995, AJ, 110, 963). Yet, with some exceptions (see next viewgraph) Ly 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 Emission Two large, bright, diffuse Ly 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 ( M ), suggests that the host is a proto galaxy. (ODea 1998, PASP,110, 493) Radio Galaxies (Carilli 2000) 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 HDF Census ~3000 Galaxies at U,B,V,I ~1700 Galaxies at J, H ~300 Galaxies at K ~9 Galaxies at 3.2 m ~50 Galaxies at 6.7 or 15 m ~5 Sources at 850 m 0 Sources at 450 m or 2800 m ~16 Sources at 8.5 GHz ~150 Measured redshifts ~30 Galaxies with spectroscopic z > 2 -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 STIS 1600 Lyman Break Galaxies Lyman-Break Galaxies Color selection of star-forming galaxies from the 912 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) Steidel etal 1999, ApJ, 519, 1 Expected colors of high z Lyman break galaxies are well defined, and not sensitive to reddening. 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