High redshift radio galaxies

1. High redshift radio galaxies Massive galaxy formation during the “Epoch of the Quasars” Bob Fosbury (ST-ECF) Marshall Cohen (Caltech), Bob Goodrich (Keck) Joël Vernet, Ilse van Bemmel (ESO) Montse Villar-Martín (U Hertfordshire) Sperello di Serego Alighieri, Andrea Cimatti (Arcetri) Pat McCarthy (OCIW) Bob Fosbury ST-ECF

2. Why radio sources? • The distant extragalactic radio sources signpost the mass concentrations where clusters and massive galaxies are formingCourtesy:mswarren@lanl.gov Bob Fosbury ST-ECF

3. Why radio galaxies? • Radio quasars and radio galaxies have different orientations • The galaxies exhibit a ‘natural coronograph’ Bob Fosbury ST-ECF

4. High star formation rate Peak of quasar activity Epoch of elliptical assembly? Groundbased access to UV and optical restframe spectrum Courtesy Blain, Cambridge) Why redshift ~ 2.5? Bob Fosbury ST-ECF

5. Main result • The interstellar medium of the galaxy, ionized by the quasar, tells the story of early chemical evolution in massive galaxies • One of the few ways to study detailed properties of the gas phase at high redshift: • cf. quasar absorption lines • amplified (lensed) background sources Bob Fosbury ST-ECF

6. Strategy • Hi-res images in optical and NIR with HST (WFPC2 & NICMOS) • Optical spectropolarimetry of the restframe UV from Lya to ~2500Å • -> resonance emission and absorption lines, dust signatures, continua from young stars and from the scattered (hidden) AGN • -> separate the stellar from the AGN-related processes • IR spectroscopy of the restframe optical: [OII] -> J [OIII] -> H Ha -> K • (constrains z-range) • -> forbidden lines and evolved stellar ctm. • Understand the K Hubble diagram (K–z) Bob Fosbury ST-ECF

7. What is unique to this study? • 3 to 8 hrs of Keck LRISp integration for each of 12 objects => P(continuum) to ±1 or 2 % and high s/n spectrophotometry • Use of the first publicly available 8m IR spectrograph (ISAAC) to see the restframe optical continuum • The Keck and VLT samples partially overlap which gives us ~continuous spectral coverage from Lya to Ha Bob Fosbury ST-ECF

8. The complete spectral range Bob Fosbury ST-ECF

9. H-band spectrum of source with weak continuum Bob Fosbury ST-ECF

10. Optical sample: Radio galaxies from the ultra-steep spectrum selected sample (Röttgering et al. 1995) with z>2 accessible to Keck IR sample: Overlapping sample but with 2.2 < z < 2.6 to ensure the major emission lines fall in the J, H and K windows. Object z 4C+03.24 3.570 MRC0943-242 2.922 MRC2025-218 2.63 MRC0529-549 2.575 USS0828+193 2.572 4C-00.62 2.527 4C+23.56 2.479 MRC0406-244 2.44 B30731+438 2.429 4C-00.54 2.360 4C+48.48 2.343 TXS0211-122 2.340 MRC0349-211 2.329 4C+40.36 2.265 MRC1138-262 2.156 A note on sample selection Bob Fosbury ST-ECF

11. Example of 2D spectra HST F439W Lya NV CIV <- M star Bob Fosbury ST-ECF

12. Bob Fosbury ST-ECF

13. Results: the continuum • Dominated in the UV by scattered light from the hidden quasar. The evidence is: • The polarization • The continuum shape and intensity • The presence of (polarized) broad lines with ~the expected EW • The nebular continuum (computed from the recombination lines) is a minor contributor • In low P objects there is some evidence for starburst light, constrained by the continuum colour • In the optical, the continuum can comprise 3 components: evolved stars, scattered quasar, direct (reddened) quasar Bob Fosbury ST-ECF

14. Bob Fosbury ST-ECF

15. Bob Fosbury ST-ECF

16. Results: the emission lines • Two main contributors to the emission lines • Scattered light from the quasar — characterised by polarization; both broad and (weak) narrow components • Fluorescent emission from the ISM which is ionized predominantly by the AGN — seen directly and thus unpolarized • BOTH of these components are spatially extended • In some objects, we do see direct (reddened) quasar light at longer wavelengths (Ha) as well Bob Fosbury ST-ECF

17. Red: sources with similar data from literature Lya/CIV & NV/CIV vs P correlations Bob Fosbury ST-ECF

18. What does NV/CIV vs. P imply? • Using the modelling, we can rule out ionization, density or depletion explanations • The simplest explanation is a variation of metallicity with nitrogen changing quadratically wrt C/H or O/H => secondary nitrogen production • As the enrichment proceeds, dust is produced and dispersed — leading to increasing obscuration and scattering. AGN-powered ULIRG are the end-point of this process Bob Fosbury ST-ECF

19. Quasar BLR • Comparison of the kpc-scale ISM data from the RG with the BLR data discussed by Hamann & Ferland Bob Fosbury ST-ECF

20. Illustrative enrichment model from Hamann & Ferland (1999). The gE exhausts its gas after ~ 1Gyr followed by passive evolution. O/H Bob Fosbury ST-ECF

21. Top: transparent/metal poor Bottom: obscured/metal rich Spectral sequence Bob Fosbury ST-ECF

22. Comparison with Ly-break galaxy • Pettini et al. 2000 • Note dramatic difference in interstellar absorption line spectra Bob Fosbury ST-ECF

23. 0 SiII CII SiII +OI Bob Fosbury ST-ECF

24. Summary • Radio sources mark the sites of massive galaxy and cluster formation • Radio galaxies have a built-in coronograph • UV spectra are dominated by AGN-related processes: dust scattering and line fluorescence • Emission lines measure the physical and chemical and kinematic properties of the ISM • Evidence for chemical evolution in the host galaxies during the “epoch of the quasars” • Optical spectra -> stellar population and more detailed picture of chemical composition Bob Fosbury ST-ECF