bob fosbury st-ecf high redshift radio galaxies massive galaxy formation during the “epoch of the...
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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:[email protected]
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
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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
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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
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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