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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’
Bob Fosbury ST-ECF
QuickTime™ and a
GIF decompressor
are needed to see this picture.
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
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
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
The complete spectral range
Bob Fosbury ST-ECF
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.
Bob Fosbury ST-ECF
Object
z
4C+03.24
MRC0943-242
MRC2025-218
MRC0529-549
USS0828+193
4C-00.62
4C+23.56
MRC0406-244
B30731+438
4C-00.54
4C+48.48
TXS0211-122
2.340
MRC0349-211
4C+40.36
MRC1138-262
3.570
2.922
2.63
2.575
2.572
2.527
2.479
2.44
2.429
2.360
2.343
2.329
2.265
2.156
Example of 2D
spectra
HST F439W
Lya
NV
CIV
<- M star
Bob Fosbury ST-ECF
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
QuickTime™ and a
Video decompressor
are needed to see this picture.
Bob Fosbury ST-ECF
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 (Ha) as
well
Bob Fosbury ST-ECF
Lya/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
Quasar BLR
Comparison of the kpcscale ISM data from
the RG with the BLR
data discussed by
Hamann & Ferland
Bob Fosbury ST-ECF
Illustrative
enrichment
model from
Hamann &
Ferland (1999).
The gE exhausts
its gas after ~
1Gyr followed by
passive
evolution.
Bob Fosbury ST-ECF
O/H
Spectral sequence
Top: transparent/metal poor
Bottom: obscured/metal rich
Bob Fosbury ST-ECF
Comparison with Ly-break galaxy
Pettini et al. 2000
Note dramatic difference in interstellar
absorption line spectra
Bob Fosbury ST-ECF
0
SiII SiII
+OI
Bob Fosbury ST-ECF
CI
I
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