Dust and cold gas in high redshift radio galaxies
Because radio emission is not affected by dust, radio galaxies are unbiased tracers of the dust emission in massive galaxies. I shall review two large SCUBA surveys of z>1 radio galaxies, showing a clear increase in the submm detection rate beyond z=3. Assuming standard dust emission parameters, this implies an increase in the far-IR luminosity at z>3. There is mounting evidence that this cool dust emission is powered by starbursts rather than the AGNs, suggesting a higher star-formation rate at z>3. I will present preliminary results of Spitzer/MIPS photometry on 4C23.56 showing evidence for a two-temperature component dust emission, consistent with the hotter (250 K) dust heated by the AGN and the colder dust by star formation. Such high star-formation rates need to be fed by massive gas reservoirs, which can be revealed by their CO emission. There are now 7 z>2 radio galaxies with CO detections, mostly in the higher order lines (J=4-3). However, a at least two sources have also been detected in CO(1-0), including TN J0924-2201 at z=5.2. This source was not detected at 850 microns, suggesting a higher gas/dust ratio compared to most CO detections to date, which have all been pre-selected by their bright dust emission.
I will describe results from a programme of VLT-UVES echelle spectroscopy focussed on the HI Ly-alpha absorption in high-redshift radio galaxies. I will discuss the nature and incidence of this absorption, scenarios for its origin, and its relation to the IGM Ly-alpha forest. For comparison, I will also present integral field spectroscopy of the 100 kpc-scale Ly-alpha haloes around the so-called `Steidel Blobs' in the SSA22 protocluster at z=3.09.
Star formation in high redshift radio galaxies
The study of the host galaxies of type I AGNs is difficulted by the presence of the central point-like source. Different attempts to obtain the spectrum of the host galaxy using classical slit spectroscopy has produced different results, mostly due to not a complete cleaning of the contamination of the AGN. We present a new technique, applicable to IFS, to perform a clean decoupling of the host and nucleus spectra. As an example, we present the analysis of the host spectrum of 3C 120.
Ionized gas in high redshift radio galaxies
There is increasing speculation that quasar and associated jet activity have a major impact on the evolution of the host galaxies. I will review the observational evidence for AGN-induced outflows in the bulges of powerful radio galaxies, and discuss the timing of the AGN activity relative to the major episodes of star formation associated with the triggering merger events. The results will be placed in the context of evolutionary scenarios for the co-evolution of the AGN and the host early-type galaxies.
High redshift radio galaxies are associated with ionized haloes that can extend for more than 100 kpc. Apparently similar nebulae have been found associated with other radio quiet high redshift objects and it has been proposed that such structures might be the gas from which the galaxy is condensing. We have started a program of 3D spectroscopy to map the morphological, ionization and kinematic properties of the giant nebulae associated with high redshift radio galaxies. I will describe this program and present some preliminary results on the radio galaxy MRC2104-242 (z=2.42) based on intregral field spectroscopic data obtained with VIMOS on VLT.
The environment of high redshift radio galaxies
We present deep 350micron maps of five high-z radio galaxies (HzRGs) and their immediate environment obtained with the SHARC-II camera on the CSO. We have compared our maps with SCUBA observations at 850microns in order to confirm the overdensity of SCUBA sources seen in these fields, which are believed to be caused by the infall of dusty starburst/AGN systems into the central regions of a hierarchicarlly forming proto-cluster centered on the HzRG. At the mean redshift of our sample (z~3.7) observations at 350um are probing rest-frame wavelengths shortward of the dust-peak, and could therefore (in concert with 850micron fluxes) provide significant constraints on the dust temperatures, and thus dust masses of HzRGs.
It is now established that the formation and evolution of massive early-type galaxies and their central supermassive black holes are intimately related processes. In order to determine the nature and origins of this relationship, it is now an important observational challenge to investigate the evolution of the spheroid:black-hole mass ratio with redshift. This talk describes the initial results of a study designed to exploit powerful radio-loud AGN to trace the evolution of the spheroid:black-hole mass relation in the most massive galaxies from z=2 to the present day.
Physics of jets and the interaction with the ambient medium
Alan Marscher
(Univ. of Boston, USA)
X-ray and radio emission in radio galaxies and the disk-jet connection
We can most easily study jets that are relativistically beamed toward us, and the central engines in AGNs that do not contain beamed jets. There are some objects, however, that are dominated by beamed emission in the radio and unbeamed radiation from the central engine at X-ray and probably optical frequencies. Two such objects are the radio galaxies 3C 120 and 3C 111, and a third is the quasrar 3C 273. A substantial fraction of the X-ray emission from these objects is from the accretion disk region. I will present evidence that in the radio galaxies there is a connection between the two: as in microquasars, X-ray dips preceded ejections of bright superluminal radio knots. I will also discuss an attempt to separate the jet and disk emission in the X-ray light curve of 3C 273; if the separation works, I will determine whether it follows the same pattern as the radio galaxies. Finally, I will discuss theoretical proposals for describing the disk/jet connection.
Geoff Bicknell1, Ralph Sutherland,1 Vicky Safouris1 & Ravi Subrahmanyan 2
(1Research School of Astronomy & Astrophysics, Australian National University
2Australia Telescope National Facility)
Three-dimensional simulations of jets passing through a cloudy medium embedded in a realistic potential reveal an evolutionary sequence of radio source morphology, which at various stages reproduces that of many well-known FR2 radio galaxies. The propagation of the jet and associated bow-shock through the clumpy interstellar medium reveal both hard and soft X-ray morphology that resembles the most recent Chandra images of the classic FR2 radio galaxy, Cygnus A. We note in particular the persistence of soft X-ray emission from dense clouds in the nuclear regions well after the passage of the bow shock. This is a result of the persistence of the high-pressured bubble inside the bow shock and the inhomogeneity of the interstellar medium. Many of these features should be present in high redshift radio galaxies. Simulations of restarting jets in Mpc scale radio galaxies show that jets can have high Lorentz factors ~ 20 on scales of 100's of kpc.
Svetlana Jorstad
(U. Boston / U. St. Petersburg)
I will present the X-ray (0.2-8 keV) and radio (15 and 5 GHz) images of quasars obtained with Chandra and Very Large Array and analyze properties of the X-ray/radio jets. I will discuss possible mechanisms of the X-ray production on kpc-scales using the prominent X-ray jet detected in the gamma-ray blazar 0827+243 as an example of the highly relativistic kiloparsec-scale jet.
Jose Luis Gómez
(IAA-CSIC)
Polarimetric multi-epoch multi-frequency VLBI observations of the jet in the radio galaxy 3C120 are analyzed, providing detailed information on the jet dynamics, structure of the magnetic field, and interaction with the external medium at the inner parsec scales.
Patrick Ogle
Spitzer Science Center, Caltech
Results from surveys
Matt Jarvis
Univ. of Oxford - Astrophysics, UK
Type-2 QSOs at z > 2
I will focus on what we have learnt from the radio survyes that have been undertaken in the past 20years before moving on to how we are now able to combine these with the large surveys being conducted at other wavelengths, such as the SDSS. I will then highlight what the future surveys may have in stall in terms of AGN and star-formation at high redshift.
For a long time, a population of obscured (Type-2) radio-quiet QSOs has been postulated. This population was expected to outnumber the unobscured (Type-1) QSOs by a ratio close to 3:1 to explain the hard X-Ray background. Using the Spitzer Space Telescope First Look Survey (FLS) IRAC, MIPS and NRAO VLA data we selected a sample of candidate (radio quiet) Type-2 QSOs at z > 2 at the ``break'' in the QSO luminosity function at z = 2. Optical spectroscopy with the William Herschel Telescope at La Palma confirmed this to be the long sought after population of Type-2 QSOs. In this talk I will explain the selection criteria used to find this population and the consequences for the accretion history of the Universe.
The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4GHz survey complete to 7.2mJy. Follow up observations in the I and K bands have identified essentially all the host galaxies and the the sample is 60% spectroscopically complete so far. CENSORS was developed with the primary scientific goal of investigating the evolution of the radio luminosity function. The modelling process that allows us to do this will be presented, including some preliminary results.
Radio sources with ultra steep spectra (USS) are the best indicators of high redshift radio galaxies: powerful, obscured AGN hosted by the most massive elliptical galaxies. Most USS samples to date have relatively high flux limits, S(1.4GHz)>10mJy. Using observations from the Indian GMRT and the VLA we have created a well defined sample with a flux limit 100x lower than previous samples. Our sub-mJy USS sample will detect lower luminosity radio galaxies, thereby enabling us to define better the radio luminosity function at high redshift and will probably also find radio galaxies at higher redshifts than in previous samples, enabling us to detect massive galaxies and black-holes in the very earliest stages of formation. From deep, 200ks XMM/Chandra observations 25% of our sources have X-ray counterparts.