Bob Fosbury ST-ECF 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 Why radio sources? The distant extragalactic radio sources signpost the mass concentrations where clusters and massive galaxies are forming Courtesy:

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

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

Bob Fosbury ST-ECF 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 Expectation Evidence for the hidden quasar Actually hard to see anything else! An ISM excited by the AGN Chemical composition Kinematics Starlight Red/blue ratio and 4000Å break => evolutionary state of stellar population Absorption lines Stellar and interstellar

Bob Fosbury ST-ECF Strategy Hi-res images in optical and NIR with HST (WFPC2 & NICMOS) Optical spectropolarimetry of the restframe UV from Ly  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 H  -> K (constrains z-range) -> forbidden lines and evolved stellar ctm. Understand the K Hubble diagram (K–z)

Bob Fosbury ST-ECF 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 Ly  to H 

Bob Fosbury ST-ECF The complete spectral range

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

Bob Fosbury ST-ECF MRC — ISAAC

Bob Fosbury ST-ECF A note on sample selection 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. Objectz 4C MRC MRC MRC USS C C MRC B C C TXS MRC C MRC

Bob Fosbury ST-ECF 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  Error estimates from Monte-Carlo simulations Slit aligned with radio axis Fluxes scaled to HST magnitudes Corrected for Galactic extinction

Bob Fosbury ST-ECF Example of 2D spectra HST F439W Ly  NV CIV <- M star

Bob Fosbury ST-ECF

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 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 Ly  to H  ) but with dust signatures A ‘luminosity weighting’ process ensures that most of the light we see comes from  ~ 1 F rg ~ F qso  scat exp(–  ext )

Bob Fosbury ST-ECF

K-band Hubble diagram (PMC)

Bob Fosbury ST-ECF 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 (H  ) as well

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

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

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

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

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

Bob Fosbury ST-ECF SiII +OI CI I 0

Bob Fosbury ST-ECF 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