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UV/optical properties of z~2.5 RG

UV/optical properties of z~2.5 RG. Massive galaxy formation during the “Quasar Epoch” Bob Fosbury (ST-ECF) Joël Vernet, Sperello di Serego Alighieri (Arcetri) Marshall Cohen (Caltech), Laura Pentericci (MPIfA) Montse Villar-Martín, Andrew Humphrey (U Hertfordshire)

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UV/optical properties of z~2.5 RG

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  1. UV/optical properties of z~2.5 RG Massive galaxy formation during the “Quasar Epoch” Bob Fosbury (ST-ECF) Joël Vernet, Sperello di Serego Alighieri (Arcetri) Marshall Cohen (Caltech), Laura Pentericci (MPIfA) Montse Villar-Martín, Andrew Humphrey (U Hertfordshire) Based on: Keck LRISp and VLT ISAAC observations Bob Fosbury ST-ECF; Leiden Nov. 2002

  2. Why radio galaxies? • Radio quasars and radio galaxies have different orientations • The galaxies exhibit a ‘natural coronograph’ Bob Fosbury ST-ECF; Leiden Nov. 2002

  3. High star formation rate Peak of quasar activity Epoch of elliptical assembly Rapid chemical evolution Groundbased access to UV and optical restframe spectrum Courtesy Blain, Cambridge Why redshift ~ 2.5? Bob Fosbury ST-ECF; Leiden Nov. 2002

  4. The Quasar epoch z2p5 radio galaxies reionization Most distant QSO Now 3C radio galaxies Earth forms Bob Fosbury ST-ECF; Leiden Nov. 2002

  5. Main results • The interstellar medium of the galaxy, ionized by the quasar, tells the story of early chemical evolution in massive galaxies • Dust absorption, scattering and re-radiation processes are very important for the overall SED — from the restframe UV through the FIR/sub-mm Bob Fosbury ST-ECF; Leiden Nov. 2002

  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; Leiden Nov. 2002

  7. 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. LRISp;LRISp+ISAAC;ISAAC 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; Leiden Nov. 2002

  8. K-band Hubble diagram (PMC) Bob Fosbury ST-ECF; Leiden Nov. 2002

  9. The Keck II LRISp data • 3,900–9,000Å, R~400 dual beam polarimeter • One cycle -> 4 x 30min at standard HWP angles • Reduced to I, Q and U Stokes spectra • -> unbiassed estimates of P and q • Error estimates from Monte-Carlo simulations • Slit aligned with radio axis • Fluxes scaled to HST magnitudes • Corrected for Galactic extinction Bob Fosbury ST-ECF; Leiden Nov. 2002

  10. Bob Fosbury ST-ECF; Leiden Nov. 2002

  11. 4C+48.48 • This is the RG with SCUBA sub-mm measurements — used later for scaling the dust scattering/emission model Bob Fosbury ST-ECF; Leiden Nov. 2002

  12. Scattering model • A simple dust scattering model is borne out by analytical and Monte-Carlo simulations of transfer through a dusty, clumpy medium (eg, Varosi & Dwek, 1999; Witt & Gordon 1999) • The scattering is approximately grey (from Lya to Ha) but with dust signatures • A ‘luminosity weighting’ process ensures that most of the light we see comes from t ~ 1 • Frg ~ Fqsotscat exp(–text) Bob Fosbury ST-ECF; Leiden Nov. 2002

  13. Bob Fosbury ST-ECF; Leiden Nov. 2002

  14. ISAAC K-band spectra Bob Fosbury ST-ECF; Leiden Nov. 2002

  15. TXS0211-122 z = 2.340 Bob Fosbury ST-ECF; Leiden Nov. 2002

  16. Bob Fosbury ST-ECF; Leiden Nov. 2002

  17. Results: the UV-optical 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 — population is 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; Leiden Nov. 2002

  18. Results: The FIR continuum • The dust scattering model can be used to calculate the FIR emission from the quasar-heated dust within the ionization cones • This does not include the AGN torus emission (from hot dust in the MIR), nor does it include any contribution from dusty star-formation • Figure based on 4C+48.48 Bob Fosbury ST-ECF; Leiden Nov. 2002

  19. Bob Fosbury ST-ECF; Leiden Nov. 2002

  20. blue: sources with similar data from literature Lya/CIV & NV/CIV vs P(%) correlations Bob Fosbury ST-ECF; Leiden Nov. 2002

  21. Quasar BLR • Comparison of the kpc-scale ISM data from the RG with the BLR data discussed by Hamann & Ferland Bob Fosbury ST-ECF; Leiden Nov. 2002

  22. Illustrative enrichment model from Hamann & Ferland (1999). The gE exhausts its gas after ~ 1Gyr followed by passive evolution. O/H Bob Fosbury ST-ECF; Leiden Nov. 2002

  23. From low-polarization, metal-poor radio galaxiestoHigh-polarization, metal-rich ULIRG Spectral sequence Bob Fosbury ST-ECF; Leiden Nov. 2002

  24. Comparison with Ly-break galaxy • Pettini et al. 2000 • Note dramatic difference in interstellar absorption line spectra • …there are interesting correlations between the behaviour of the low ionization interstellar lines and the continuum polarization… Bob Fosbury ST-ECF; Leiden Nov. 2002

  25. 0 SiII CII SiII +OI Bob Fosbury ST-ECF; Leiden Nov. 2002

  26. 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 • Re-radiaton in the FIR accounts for only a small fraction of the observed sub-mm flux (=> dusty SF?) • 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; Leiden Nov. 2002

  27. Conclusions • Quasar-ionized ISM reveals a phase of rapid chemical evolution during the assembly of massive galaxies • Can construct a consistent model for the transfer of quasar radiation in a dusty galaxy which accounts for both the UV/optical and a fraction of the FIR continuum Bob Fosbury ST-ECF; Leiden Nov. 2002

  28. Bob Fosbury ST-ECF; Leiden Nov. 2002

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