UV/optical properties of z~2.5 RG

Bob Fosbury ST-ECF; Leiden Nov. 2002

UV/optical properties of z~2.5 RG

Massive galaxy formation during the “Quasar Epoch”

Bob Fosbury (ST-ECF)Joël Vernet, Sperello di Serego Alighieri (Arcetri)

Marshall Cohen (Caltech), Laura Pentericci (MPIfA)Montse Villar-Martín, Andrew Humphrey (U

Hertfordshire)

Based on: Keck LRISp and VLT ISAAC observations


Radio quasars and radio galaxies

have different

orientations

The galaxies exhibit a ‘natural

coronograph’

QuickTime™ and aGIF decompressor

are needed to see this picture.

Why radio galaxies?


Why redshift ~ 2.5?High star formation

ratePeak of quasar

activityEpoch of elliptical

assemblyRapid chemical

evolutionGroundbased

access to UV and optical restframe

spectrum Courtesy Blain, Cambridge


Earth form

s

3C radio galaxies

z2p5 radio

galaxies

Most distant

QSO

reionization

The Quasar epoch

Now


Main resultsThe interstellar medium of the galaxy,

ionized by the quasar, tells the story of early chemical evolution in massive galaxies

Dust absorption, scattering and re-radiation processes are very important for the overall SED — from the restframe UV through the FIR/sub-mm


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)


A note on sample selectionOptical sample:

Radio galaxies from the ultra-steep spectrum selected sample (Röttgering et al. 1995) with z>2 accessible to KeckIR sample:

Overlapping sample but with 2.2 < z < 2.6 to ensure the major emission lines fall in the J, H and K windows.

LRISp;LRISp+ISAAC;ISAAC

Object z4C+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+438 2.4294C-00.54 2.3604C+48.48 2.343TXS0211-122 2.340MRC0349-211 2.3294C+40.36 2.265MRC1138-262 2.156


K-band Hubble diagram (PMC)


The Keck II LRISp data3,900–9,000Å, R~400 dual beam

polarimeterOne cycle -> 4 x 30min at standard HWP

anglesReduced to I, Q and U Stokes spectra

-> unbiassed estimates of P and Error estimates from Monte-Carlo

simulationsSlit aligned with radio axisFluxes scaled to HST magnitudesCorrected for Galactic extinction



4C+48.48This is the RG

with SCUBA sub-mm measurements — used later for scaling the dust scattering/emission model


Scattering modelA 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 ~ 1Frg ~ Fqso scat exp(–ext)


QuickTime™ and aGIF decompressorare needed to see this picture.


ISAAC K-band spectra


TXS0211-122 z = 2.340



Results: the UV-optical continuumDominated in the UV by scattered light from the hidden quasar. The evidence is:

The polarizationThe continuum shape and intensity

The presence of (polarized) broad lines with ~the expected EWThe nebular continuum (computed from the recombination lines) is a minor contributorIn low P objects there is some evidence for starburst light — population is constrained by the continuum colourIn the optical, the continuum can comprise 3 components: evolved stars, scattered quasar, direct (reddened) quasar


Results: The FIR continuumThe dust scattering model can be used

to calculate the FIR emission from the quasar-heated dust within the ionization cones

This does not include the AGN torus emission (from hot dust in the MIR), nor does it include any contribution from dusty star-formation

Figure based on 4C+48.48



Ly/CIV & NV/CIV vs P(%) correlations

blue: sources with similar data from literature


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

Quasar BLR


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


Spectral sequence

From low-polarization, metal-poor radio galaxiestoHigh-polarization, metal-rich ULIRG


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

absorption line spectra

…there are interesting correlations between the behaviour of the low ionization interstellar lines and the continuum polarization…


SiII SiII+OI CII

0


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

Re-radiaton in the FIR accounts for only a small fraction of the observed sub-mm flux (=> dusty SF?)

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


ConclusionsQuasar-ionized ISM reveals a phase of

rapid chemical evolution during the assembly of massive galaxies

Can construct a consistent model for the transfer of quasar radiation in a dusty galaxy which accounts for both the UV/optical and a fraction of the FIR continuum


Documents

UV/optical properties of z~2.5 RG