High redshift radio galaxies

1
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)

2
Why radio sources?

• The distant extragalactic radio sources signpost
  the mass concentrations where clusters and
  massive galaxies are formingCourtesymswarren
  _at_lanl.gov

3
Why radio galaxies?

• Radio quasars and radio galaxies have different
  orientations
• The galaxies exhibit a natural coronograph

4
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)

5
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

6
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
• gt evolutionary state of stellar population
• Absorption lines
• Stellar and interstellar

7
Strategy

• Hi-res images in optical and NIR with HST (WFPC2
  NICMOS)
• Optical spectropolarimetry of the restframe UV
  from Lya to 2500Å
• -gt resonance emission and absorption lines, dust
  signatures, continua from young stars and from
  the scattered (hidden) AGN
• -gt separate the stellar from the AGN-related
  processes
• IR spectroscopy of the restframe optical OII
  -gt J OIII -gt H Ha -gt K
• (constrains z-range)
• -gt forbidden lines and evolved stellar ctm.
• Understand the K Hubble diagram (Kz)

8
What is unique to this study?

• 3 to 8 hrs of Keck LRISp integration for each of
  12 objects gt 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

9
The complete spectral range
10

• H-band spectrum of source with weak continuum

11
MRC1138-262 ISAAC
12
A note on sample selection

• Object z
• 4C03.24 3.570
• MRC0943-242 2.922
• MRC2025-218 2.63
• MRC0529-549 2.575
• USS0828193 2.572
• 4C-00.62 2.527
• 4C23.56 2.479
• MRC0406-244 2.44
• B30731438 2.429
• 4C-00.54 2.360
• 4C48.48 2.343
• TXS0211-122 2.340
• MRC0349-211 2.329
• 4C40.36 2.265
• MRC1138-262 2.156

• Optical sample
• Radio galaxies from the ultra-steep spectrum
  selected sample (Röttgering et al. 1995) with zgt2
  accessible to Keck
• IR sample
• Overlapping sample but with 2.2 lt z lt 2.6 to
  ensure the major emission lines fall in the J, H
  and K windows.

13
The Keck II LRISp data

• 3,9009,000Å, R400 dual beam polarimeter
• One cycle -gt 4 x 30min at standard HWP angles
• Reduced to I, Q and U Stokes spectra
• -gt 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

14

• Example of 2D spectra
• HST F439W
• Lya
• NV
• CIV
• lt- M star

15
(No Transcript)
16
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

17
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 Fqso t scat exp(text)

18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
K-band Hubble diagram (PMC)
23
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

24
Lya/CIV NV/CIV vs P correlations

• Red sources with similar data from literature

25
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 gt 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

26
Quasar BLR

• Comparison of the kpc-scale ISM data from the RG
  with the BLR data discussed by Hamann Ferland

27

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

O/H
28
Spectral sequence

• Top transparent/metal poor
• Bottom obscured/metal rich

29
Comparison with Ly-break galaxy

• Pettini et al. 2000
• Note dramatic difference in interstellar
  absorption line spectra

30
0
SiII
CII
SiII OI
31
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 -gt stellar population and more
  detailed picture of chemical composition

32
(No Transcript)