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:mswarren@lanl.gov

Bob Fosbury ST-ECF

Why radio galaxies?

Radio quasars and radio galaxies

have different

orientations

The galaxies exhibit a ‘natural

coronograph’

QuickTime™ and aGIF decompressor

are needed to see this picture.

Bob Fosbury ST-ECF

Why redshift ~ 2.5?

High star formation ratePeak of quasar activityEpoch 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 linesamplified (lensed) background sources

Bob Fosbury ST-ECF

StrategyHi-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)

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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

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The complete spectral range

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H-band spectrum of source with weak continuum

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.

Object z

4C+03.24 3.570MRC0943-242 2.922MRC2025-218 2.63MRC0529-549 2.575USS0828+193 2.5724C-00.62 2.5274C+23.56 2.479MRC0406-244 2.44B30731+4382.4294C-00.54 2.3604C+48.48 2.343TXS0211-1222.340MRC0349-211 2.3294C+40.36 2.265MRC1138-262 2.156

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Example of 2D spectra

HST F439WLyNVCIV

<- M star

Bob Fosbury ST-ECF

Bob Fosbury ST-ECF

Results: the continuumDominated in the UV by scattered light

from the hidden quasar. The evidence is:The polarizationThe continuum shape and intensityThe presence of (polarized) broad lines with

~the expected EWThe 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

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Bob Fosbury ST-ECF

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Results: the emission linesTwo main contributors to the emission

linesScattered 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

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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

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Illustrative enrichment model from Hamann & Ferland (1999). The gE exhausts its gas after ~ 1Gyr followed by passive evolution.

O/H

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Spectral sequenceTop: transparent/metal poorBottom: obscured/metal rich

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Comparison with Ly-break galaxyPettini et al. 2000Note dramatic difference in interstellar

absorption line spectra

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SiII SiII+OI

CII

0

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SummaryRadio sources mark the sites of massive

galaxy and cluster formationRadio galaxies have a built-in coronographUV 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