1 / 98

The Search for Forming Galaxies

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

shiri
Télécharger la présentation

The Search for Forming Galaxies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. 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

  3. Hierarchical Galaxy Formation (Virgo consortium)

  4. 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

  5. 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

  6. 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

  7. Star Formation & Stellar Evolution

  8. 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).

  9. 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).

  10. 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

  11. 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).

  12. 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).

  13. 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).

  14. 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). 104 Å = 1μ.

  15. 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. 104 Å = 1μ.

  16. 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)

  17. 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).

  18. 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.

  19. 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)

  20. 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 (> 1010 M⊙), suggests that the host is a proto galaxy. (O’Dea 1998, PASP,110, 493)

  21. Radio Galaxies (Carilli 2000)

  22. 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

  23. The Hubble Deep Fields

  24. 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 > 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

  25. 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)

  26. 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

  27. 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

  28. 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…

  29. Galaxy 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)

  30. F814W

  31. F606W

  32. F450W

  33. F300W

  34. STIS 2300Ǻ

  35. STIS 1600Å

  36. Lyman Break Galaxies

  37. 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

  38. Spectral Features due to Hydrogen (Valenti 2001)

  39. Lyman-Break selection (Giavalisco 2001)

  40. Lyman-Break selection (Giavalisco 2001)

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

  42. Steidel etal 1999, ApJ, 519, 1

  43. 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. Steidel etal 1999, ApJ, 519, 1

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

  45. 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

  46. 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

  47. Large survey • Results of spectroscopic follow up of color selected LBGs. • The two samples are consistent with having similar colors. Steidel etal 1999, ApJ, 519, 1

  48. 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?

  49. 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

More Related