A spectroscopic study of IRAS F10214 + 4724

The z  = 2.286  IRAS galaxy F10214 + 4724 remains one of the most luminous galaxies in the Universe, despite its gravitational lens magnification. We present optical and near-infrared spectra of F10214 + 4724, with clear evidence for three distinct components: lines of width ∼ 1000 km s⁻¹ from a Seyfert 2 nucleus; ≲ 200 km s⁻¹ lines which are likely to be associated with star formation; and a broad (∼ 4000 km s⁻¹) C  III ] 1909-Å emission line which is blueshifted by ∼ 1000 km s⁻¹ with respect to the Seyfert 2 lines. Our study of the Seyfert 2 component leads to several new results. (i) From the double-peaked structure in the Lyα line, and the lack of Lyβ, we argue that the Lyα photons have emerged through a neutral column of N _H ∼ 2.5 × 10²⁵ m⁻², possibly located within the AGN narrow-line region, as proposed for several high-redshift radio galaxies. (ii) The resonant O  VI 1032, 1036-Å doublet (previously identified as Lyβ) is in an optically thick (1:1) ratio. At face value this implies an extreme density ( n _e ∼ 10¹⁷ m⁻³) more typical of broad-line region clouds. However, we attribute this instead to the damping wings of Lyβ from the resonant absorption. (iii) A tentative detection of He  II 1086 suggests little extinction in the rest frame ultraviolet.     

ZEN2: a narrow J-band search for z∼ 9 Lyα emitting galaxies directed towards three lensing clusters

We present the results of a continuing survey to detect Lyα emitting galaxies at redshifts   z ∼ 9  : the ' z equals nine' (ZEN) survey. We have obtained deep VLT Infrared Spectrometer and Array Camera observations in the narrow J -band filter NB119 directed towards three massive lensing clusters: Abell clusters 1689, 1835 and 114. The foreground clusters provide a magnified view of the distant Universe and permit a sensitive test for the presence of very high redshift galaxies. We search for   z ∼ 9 Lyα  emitting galaxies displaying a significant narrow-band excess relative to accompanying J -band observations that remain undetected in Hubble Space Telescope ( HST )/Advanced Camera for Surveys (ACS) optical images of each field. No sources consistent with this criterion are detected above the unlensed 90 per cent point-source flux limit of the narrow-band image,   F _NB= 3.7 × 10⁻¹⁸ erg s⁻¹ cm⁻²  . To date, the total coverage of the ZEN survey has sampled a volume at   z ∼ 9  of approximately 1700 comoving Mpc³ to a Lyα emission luminosity of  10⁴³ erg s⁻¹  . We conclude by considering the prospects for detecting   z ∼ 9 Lyα  emitting galaxies in light of both observed galaxy properties at   z < 7  and simulated populations at   z > 7  .     

The polarization of scattered Lyα radiation around high-redshift galaxies

The high-redshift Universe contains luminous Lyα emitting sources such as galaxies and quasars. The emitted Lyα radiation is often scattered by surrounding neutral hydrogen atoms. We show that the scattered Lyα radiation obtains a high level of polarization for a wide range of likely environments of high-redshift galaxies. For example, the backscattered Lyα flux observed from galaxies surrounded by a superwind-driven outflow may reach a fractional polarization as high as ∼40 per cent. Equal levels of polarization may be observed from neutral collapsing protogalaxies. Resonant scattering in the diffuse intergalactic medium typically results in a lower polarization amplitude (≲7 per cent), which depends on the flux of the ionizing background. Spectral polarimetry can differentiate between Lyα scattering off infalling gas and outflowing gas; for an outflow, the polarization should increase towards longer wavelengths while for infall the opposite is true. Our numerical results suggest that Lyα polarimetry is feasible with existing instruments, and may provide a new diagnostic of the distribution and kinematics of neutral hydrogen around high-redshift galaxies. Moreover, polarimetry may help suppress infrared lines originating in the Earth's atmosphere, and thus improve the sensitivity of ground-based observations to high-redshift Lyα emitting galaxies outside the currently available redshift windows.     

An 80-kpc Lyα halo around a high-redshift type-2 quasi-stellar object

We announce the discovery of an extended emission-line region associated with a high-redshift type-2 quasi-stellar object (QSO). The halo, which was discovered in our new wide-field narrow-band survey, resides at   z = 2.85  in the Spitzer First Look Survey region and is extended over ∼80 kpc. Deep very long baseline interferometry (VLBI) observations imply that approximately 50 per cent of the radio emission is extended on scales >200 pc. The inferred active galactic nuclei (AGN) luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyα halo is as luminous as those found around high-redshift radio galaxies; however, the active nucleus is several orders of magnitude less luminous at radio wavelengths than those Fanarof–Riley type II (FRIIs) more commonly associated with extended emission-line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated, but which also exhibits extended Fanarof–Riley type I (FRI)-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyα emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared spectral energy distribution is well described by a combination of an obscured QSO  ( L _bol∼ 3.4 ± 0.2 × 10¹³ L_⊙)  and a 1.4 Gyr old simple stellar population with mass  ∼3.9 ± 0.3 × 10¹¹ M_⊙  .     

Photoionized Hβ emission in NGC 5548: it breathes!

Emission-line regions in active galactic nuclei (AGNs) and other photoionized nebulae should become larger in size when the ionizing luminosity increases. This 'breathing' effect is observed for the Hβ emission in NGC 5548 by using Hβ and optical continuum light curves from the 13-yr (1989–2001) AGN Watch monitoring campaign. To model the breathing, we use two methods to fit the observed light curves in detail: (i) parametrized models and, (ii) the memecho reverberation-mapping code. Our models assume that optical continuum variations track the ionizing radiation, and that the Hβ variations respond with time-delays τ due to light travel-time. By fitting the data using a delay-map  Ψ(τ, F _c)  that is allowed to change with continuum flux F _c, we find that the strength of the Hβ response decreases and the time-delay increases with ionizing luminosity. The parametrized breathing models allow the time-delay and the Hβ flux to depend on the continuum flux so that,  τ∝ F ^β_c  and   F _Hβ∝ F ^α_c  . Our fits give  0.1 < β < 0.46  and  0.57 < α < 0.66. α  is consistent with previous work by Gilbert and Peterson, and Goad, Korista and Knigge. Although we find β to be flatter than previously determined by Peterson et al. using cross-correlation methods, it is closer to the predicted values from recent theoretical work by Korista and Goad.     

The AGN and gas disc in the low surface brightness galaxy PGC 045080

We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disc and massive H  i gas content. Radio continuum observations of the galaxy were carried out at 320, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disc at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with active galactic nucleus (AGN) activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the Hα flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centres can host significant AGN activity. We also mapped the H  i gas disc and velocity field in PGC 045080. The H  i disc extends well beyond the optical disc and appears warped. In the H  i intensity maps, the disc appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disc but is fairly uniform in the other half. We derived the H  i rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ∼190 km s⁻¹.     

Spectroscopy of the optical Einstein ring 0047 – 2808

We present optical and near-infrared spectroscopic observations of the optical Einstein ring 0047 – 2808. We detect both [O III ] lines λλ4959, 5007 near ∼ 2.3 μm, confirming the redshift of the lensed source as z  = 3.595. The Lyα line is redshifted relative to the [O III ] line by 140 ± 20 km s⁻¹. Similar velocity shifts have been seen in nearby starburst galaxies. The [O III ] line is very narrow, 130 km s⁻¹ FWHM. If the ring is the image of the centre of a galaxy, the one-dimensional stellar velocity dispersion σ = 55 km s⁻¹ is considerably smaller than the value predicted by Baugh et al. for the somewhat brighter Lyman-break galaxies. The Lyα line is significantly broader than the [O III ] line, probably due to resonant scattering. The stellar central velocity dispersion of the early-type deflector galaxy at z  = 0.485 is 250 ± 30 km s⁻¹. This value is in good agreement both with the value predicted from the radius of the Einstein ring (and a singular isothermal sphere model for the deflector), and with the value estimated from the D _n −σ relation.     

Discovery of a single faint AGN in a large sample of z > 5 Lyman break galaxies

As part of a large spectroscopic survey of   z > 5  Lyman break galaxies (LBGs), we have identified a single source which is clearly hosting an active galactic nucleus (AGN). Out of a sample of more than 50 spectroscopically confirmed R -band dropout galaxies at   z ∼ 5  and above, only J104048.6−115550.2 at   z = 5.44  shows evidence for a high ionization potential emission line indicating the presence of a hard ionizing continuum from an AGN. Like most objects in our sample the rest-frame-UV spectrum shows the UV continuum breaking across a Lyα line. Uniquely within this sample of LBGs, emission from N  v is also detected, a clear signature of AGN photoionization. The object is spatially resolved in Hubble Space Telescope ( HST ) imaging. This, and the comparatively high Lyα/N  v flux ratio indicates that the majority of the Lyα (and the UV continuum longward of it) originates from stellar photoionization, a product of the ongoing starburst in the LBG. Even without the AGN emission, this object would have been photometrically selected and spectroscopically confirmed as a Lyman break in our survey. The measured optical flux  ( I _AB= 26.1)  is therefore an upper limit to that from the AGN and is of order 100 times fainter than the majority of known quasars at these redshifts. The detection of a single object in our survey volume is consistent with the best current models of high redshift AGN luminosity function, providing a substantial fraction of such AGN is found within luminous starbursting galaxies. We discuss the cosmological implications of this discovery.     

Constraining quasar host halo masses with the strength of nearby Lyα forest absorption

Using cosmological hydrodynamic simulations, we measure the mean transmitted flux in the Lyα forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel quasar separation distance can be fitted using a simple power-law form including the usual correlation function parameters r ₀ and γ, so that     . From the simulations, we find the relation between r ₀ and quasar host mass, and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ∼9000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 5, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data). We find that the best-fitting host halo mass for SDSS quasars with mean redshift z = 3 and absolute G -band magnitude −27.5 is  log  M /M_⊙= 12.68^+0.81_−0.67  . We also use the Lyman-Break Galaxy (LBG) and Lyα forest data of Adelberger et al. in a similar fashion to constrain the halo mass of LBGs to be  log₁₀  M /M_⊙= 11.41^+0.54_−0.59  , a factor of ∼20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyα forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar Lyα forest correlation function as a measure of the squashing effect. We find its dependence on halo mass difficult to measure, but find that it may be useful for constraining cosmic geometry.     

The lens and source of the optical Einstein ring gravitational lens ER 0047–2808

We perform a detailed analysis of the optical gravitational lens ER 0047–2808 imaged with the Wide Field Planetary Camera 2 on the Hubble Space Telescope . Using software specifically designed for the analysis of resolved gravitational lens systems, we focus on how the image alone can constrain the mass distribution in the lens galaxy. We find that the data are of sufficient quality to strongly constrain the lens model with no a priori assumptions about the source. Using a variety of mass models, we find statistically acceptable results for elliptical isothermal-like models with an Einstein radius of 1.17 arcsec. An elliptical power-law model  (Σ∝ R ^−β)  for the surface mass density favours a slope slightly steeper than isothermal with  β= 1.08 ± 0.03  . Other models including a constant mass-to-light ratio (M/L), pure Navarro, Frenk & White halo and (surprisingly) an isothermal sphere with external shear are ruled out by the data. We find the galaxy light profile can only be fit with a Sérsic plus point-source model. The resulting total  M/L _B   contained within the images is  4.7  h ₆₅± 0.3  . In addition, we find the luminous matter is aligned with the total mass distribution within a few degrees. This is the first time a resolved optical gravitational lens image has been quantitatively reproduced using a non-parametric source.
The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is ∼0.1 arcsec and its (unlensed) Lyα flux is  3 × 10⁻¹⁷ erg s⁻¹ cm⁻²  .     

The far-infrared–submillimetre spectral energy distribution of high-redshift quasars

We combine photometric observations of high-redshift     quasars, obtained at submillimetre to millimetre wavelengths, to obtain a mean far-infrared (rest-frame) spectral energy distribution (SED) of the thermal emission from dust, parametrized by a single temperature ( T ) and power-law emissivity index ( β ). The best-fitting values are     and     . Our method exploits the redshift spread of this set of quasars, which allows us to sample the SED at a larger number of rest wavelengths than is possible for a single object: the wavelength range extends down to ∼60 μm, and therefore samples the turnover in the greybody curve for these temperatures. This parametrization is of use to any studies that extrapolate from a flux at a single wavelength, for example to infer dust masses and far-infrared luminosities.
We interpret the cool, submillimetre component as arising from dust heated by star formation in the host galaxy of the quasar, although we do not exclude the presence of dust heated directly by the active galactic nucleus (AGN). Applying the mean SED to the data, we derive consistent star formation rates ∼1000 M_⊙ yr⁻¹ and dust masses ∼10⁹ M_⊙, and investigate a simple scheme of AGN and host galaxy co-evolution to account for these quantities. The time-scale for formation of the host galaxy is     , and the luminous quasar phase occurs towards the end of this period, just before the reservoir of cold gas is depleted. Given the youth of the Universe at     (1.6 Gyr), the coexistence of a massive black hole and a luminous starburst at high redshifts is a powerful constraint on models of quasar host galaxy formation.     

The obscured BLR in the radio galaxy 3C 234

We present spectropolarimetric observations of the radio galaxy 3C 234 at optical and, for the first time, near-IR wavelengths. In agreement with previous observations we detect broad Hα in total and polarized flux, consistent with the scenario in which the central active nucleus is hidden from view and observed via scattered radiation.
We model the flux and polarization properties at optical and near-IR wavelengths, which result in a point-source, cone-based scattering geometry in the optical, and an extended source scattering in the near-IR, with a dichroic view to the emission regions, which becomes important only at the longer wavelengths. From this model we calculate an intrinsic Hα luminosity of 4.9×10⁴⁴ erg s⁻¹, and an extinction to the near-IR emission region of 60 mag for A_V . The scattered radiation also undergoes extinction, this time by 1 mag for A_V , assuming a source function of a typical stellar-subtracted Seyfert 1 galaxy. Our modelling does not require the presence of a second featureless continuum (FC2).
Additionally, we require that the scatterers are in bulk radial outflow at approximately 600 km s⁻¹ to explain an observed increase in the intrinsic polarization of the scattered broad Hα line in the red wing, and blueshifted narrow-line components in polarized flux.     

Ly+ and ultraviolet emission from high-redshift gamma-ray burst hosts: to what extent do gamma-ray bursts trace star formation?

We report the result of a search for Lyα emission from the host galaxies of the gamma-ray bursts  (GRBs) 030226 ( z = 1.986), 021004 ( z = 2.335)  and  020124 ( z = 3.198)  . We find that the host galaxy of GRB 021004 is an extended (around 8 kpc) strong Lyα emitter with a rest-frame equivalent width (EW) of 68⁺¹²₋₁₁Å, and a star formation rate of  10.6 ± 2.0 M_⊙ yr⁻¹  . We do not detect the hosts of GRB 030226 and GRB 020124, but the upper limits on their Lyα fluxes do not rule out large rest-frame EWs. In the fields of GRB 021004 and GRB 030226 we find seven and five other galaxies, respectively, with excess emission in the narrow-band filter. These galaxies are candidate Lyα-emitting galaxies in the environment of the host galaxies. We have also compiled a list of all   z ≳ 2  GRB hosts, and demonstrate that a scenario where they trace star formation in an unbiased way is compatible with current observational constraints. Fitting the   z = 3  luminosity function (LF) under this assumption results in a characteristic luminosity of   R *= 24.6  and a faint-end slope of  α=−1.55  , consistent with the LF measured for Lyman-break galaxies.     

An absorption event in the X-ray light curve of NGC 3227

We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer ( RXTE ) since 1999 January. During late 2000 and early 2001 we observed an unusual hardening of the 2–10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 × 10²³ cm⁻² crossing the line of sight to the X-ray source. A spectrum obtained by XMM–Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionized. The XMM–Newton spectrum also shows that ∼10 per cent of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on the cloud ionization parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be   R ∼ 10–100  light-days from the central X-ray source, and its density to be   n _H∼ 10⁸ cm⁻³  , implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud.     

Neutral hydrogen absorption observations of the central region of NGC 5929

We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 10²¹ cm⁻². Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE–SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s⁻¹) and full width at half-maximum (43 ± 6 km s⁻¹) of the absorbing gas with previous [O  III ] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 10²¹ cm⁻²) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.     

ΛCDM predictions for galaxy protoclusters – I. The relation between galaxies, protoclusters and quasars at z∼ 6

Motivated by recent observational studies of the environment of   z ∼ 6  QSOs, we have used the Millennium Run (MR) simulations to construct a very large  (∼4°× 4°)  mock redshift survey of star-forming galaxies at   z ∼ 6  . We use this simulated survey to study the relation between density enhancements in the distribution of i ₇₇₅-dropouts and Lyα emitters, and their relation to the most massive haloes and protocluster regions at   z ∼ 6  . Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1°, much larger than probed by current surveys. Approximately one-third of all   z ∼ 6  haloes hosting i -dropouts brighter than   z = 26.5  mag  (≈ M *_{UV, z =6})  become part of   z = 0  galaxy clusters. i -dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i -dropouts and Lyα emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six   z ∼ 6  QSO fields observed with Hubble Space Telescope show no significant enhancements in their i ₇₇₅-dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at   z ∼ 6  .     

Supermassive Black Holes in Early-Type Galaxies: Relationship with Radio Emission and Constraints on the Black Hole Mass Function

Using recently published estimates — based on high spatial resolution spectroscopy — of the mass M _BH of nuclear black holes for a sample of nearby galaxies, we explore the dependence of galaxy nucleus emissivity at various wavelengths on M _BH. We confirm an almost linear scaling of the black hole mass with the baryonic mass of the host spheroidal galaxy. A remarkably tight relationship is also found with both nuclear and total radio centimetric flux, with a very steep dependence of the radio flux on M _BH ( P  ∝  M ^2.5_BH). The high-frequency radio power is thus a very good tracer of a supermassive black hole, and a good estimator of its mass. This, together with the lack of significant correlations with the low-energy X-ray and far-IR flux, supports the view that advection-dominated accretion is ruling the energy output in the low accretion rate regime. Using the tight dependence of total radio power on M _BH and the rich statistics of radio emission of galaxies, we derive an estimate of the mass function of remnants in the nearby Universe. This is compared with current models of quasar and active galactic nucleus (AGN) activity and of the origin of the hard X-ray background (HXRB). As for the former, continuous long-lived AGN activity is excluded by the present data with high significance, whereas the assumption of a short-lived, possibly recurrent, activity pattern gives remarkable agreement. The presently estimated black hole mass function also implies that the HXRB has been produced by a numerous population (∼ 10⁻² Mpc⁻³) of moderately massive ( M _BH ∼ 10⁷ M⊙) black holes.     

Neutral gas and dust in the central region of the ultraluminous infrared galaxy Mrk 273

We have used MERLIN to observe neutral hydrogen absorption against the central region of the ultraluminous infrared galaxy (ULIRG) galaxy Mrk 273 with an angular resolution of 0.2 arcsec. This represents a factor of 5 increase in resolution compared with previous work. Absorption has been resolved against two of three radio continuum components. A Hubble Space Telescope ( HST ) image reveals a complex central region composed of clumpy emission obscured by dust lanes. We find that the northern and south-eastern radio components are associated with two optical components. The alignment supports the idea that Mrk 273 has a double nucleus due to a recent galactic merger event.
Broad, strong and spatially varying absorption is seen against the northern radio component with a velocity gradient of 1990±50 km s⁻¹ kpc⁻¹. The absorption resolves into six discrete components with an average column density of 1.7×10²² atom cm⁻². We propose that the absorption is due to a clumpy ring or disc of neutral gas of radius ∼250 pc rotating around a central starburst. In addition to the broad component, narrow absorption (<100 km s⁻¹) is detected against the northern and south-eastern components. Absorption is not detected against the weak (2 mJy) south-western component. We propose that the narrow absorption is due to quiescent gas in a large-scale dust lane that coincides with these regions of narrow absorption.     

Chandra measurements of the X-ray core and cluster of 3C 220.1

We report results of an 18-ks exposure with the ACIS instrument on Chandra of the powerful z =0.62 radio galaxy 3C 220.1. The X-ray emission separates into cluster gas of emission-weighted kT ∼5 keV , 0.7–12 keV luminosity (to a radius of 45 arcsec) of 5.6×10⁴⁴ erg s⁻¹ and unresolved emission (coincident with the radio core). While the extended X-ray emission is clearly thermal in nature, a straightforward cooling-flow model, even in conjunction with a point-source component, is a poor fit to the radial profile of the X-ray emission. This is despite the fact that the measured properties of the gas suggest a massive cooling flow of ∼130 M_⊙ yr⁻¹, and the data show weak evidence for a temperature gradient. The central unresolved X-ray emission has a power-law spectral energy index α ∼0.7 and 0.7–12 keV luminosity of 10⁴⁵ erg s⁻¹, and any intrinsic absorption is relatively small. The two-point spectrum of the core emission between radio and X-ray energies has α _rx=0.75 . Since this is a flatter spectrum than seen in other sources where the X-ray emission is presumed to be radio-related, regions close to the active galactic nucleus (AGN) in this source may dominate the central X-ray output, as is believed to be the case for lobe-dominated quasars. Simple unification models would be challenged if this were found to be the case for a large fraction of high-power radio galaxies.     

Submillimetre detection of a high-redshift type 2 QSO

We report on the first SCUBA detection of a type 2 QSO at   z = 3.660  in the Chandra Deep Field South. This source is X-ray-absorbed, shows only narrow emission lines in the optical spectrum and is detected in the submillimetre: it is the ideal candidate in an evolution scheme for active galactic nuclei (AGN) (e.g. Fabian 1999 ; Page et al. 2004 ) of an early phase corresponding to the main growth of the host galaxy and formation of the central black hole. The overall photometry (from the radio to the X-ray energy band) of this source is well reproduced by the spectral energy distribution (SED) of NGC 6240, while it is incompatible with the spectrum of a type 1 QSO (3C 273) or a starburst galaxy (Arp 220). Its submillimetre (850 μm) to X-ray (2 keV) spectral slope  (α_SX)  is close to the predicted value for a Compton-thick AGN in which only 1 per cent of the nuclear emission emerges through scattering. Using the observed flux at 850 μm we have derived a star formation rate of  550–680 M_⊙ yr⁻¹  and an estimate of the dust mass   M _dust= 4.2 × 10⁸ M_⊙  .