arXiv subjects

R. J. Wilman

Publications and source records attributed to R. J. Wilman.

At least 37 records · Page 2Linked to original sources

arXiv2006

The association between gas and galaxies II: The 2-point correlation function

We measure the 2-point correlation function, xi(AG), between galaxies and quasar absorption line systems at z<1, using the dataset of Morris & Jannuzi (2006; paper I) on 16 lines of sight (LOS) with UV spectroscopy and galaxy multi-object spectroscopy. The measurements are made in 2-D redshift space out to pi=20/h Mpc (comoving) along the LOS and out to 2/h Mpc projected; as a function of HI column density in the range N(HI) = 1E13-1E19 cm^-2, for CIV systems and as a function of galaxy spectral type. This extends the absorber-galaxy pair count analysis of paper I. We find that the peak amplitude of xi(AG) at the smallest separations increases slowly as the lower limit on N(HI) is increased from 1E13 to 1E16 cm^-2, and then jumps sharply (albeit with substantial uncertainty) at N(HI)>1E17 cm^-2. For CIV absorbers, the peak strength of xi(AG) is comparable to that of HI absorbers with N(HI)>1E16.5 cm^-2. We do not reproduce the differences reported by Chen et al. between 1-D xi(AG) measurements using galaxy sub-samples of different spectral types, but the full impact of systematic differences in our samples is hard to quantify. We compare the observations with smoothed particle hydrodynamical (SPH) simulations and discover that in the observations xi(AG) is more concentrated to the smallest separations than in the simulations. The latter also display a `finger of god' elongation of xi(AG) along the LOS in redshift space, which is absent from our data, but similar to that found by Ryan-Weber for the cross-correlation of quasar absorbers and HI-emission-selected galaxies. The physical origin of these `fingers of god' is unclear and we highlight several possible areas for further investigation.

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arXiv2006

Ionization of large-scale absorbing haloes and feedback events from high-redshift radio galaxies

We present photoionization calculations for the spatially-extended absorbers observed towards the extended emission line spectrum of two high-redshift radio galaxies: 0943-242 (z=2.922) and 0200+015 (z=2.230), with the aim of reproducing the absorber column ratio, N(CIV)/N(HI). We explore the effects of using different UV continua in the photoionization calculations. A comparison is drawn between the absorber in 0200+015 and the two absorbers in the lensed Lynx Arc Nebula at z=3.36, which present similar N(CIV)/N(HI) ratios. We find that hot stars from a powerful starburst, or a metagalactic background radiation (MBR) in which stars dominate over quasars, are equally successful in producing the observed N(CIV)/N(HI), assuming subsolar absorber metallicities. These softer SEDs eliminate the factor 1000 difference in metallicity between the two absorbers encountered in earlier work assuming a powerlaw SED. The detected level of continuum flux in 0943-242 is consistent with stellar ionization. If the MBR is responsible for the ionization of the radio galaxy absorbing shells, their radii (if spherical) would be large (> 100 kpc) and their mass would be huge (>1E12 M_Sun), implying that a feedback event within the radiogalaxy has expelled more baryonic material than left within it. If, as we believe more likely, stellar sources within the radiogalaxy are responsible for the absorber's ionization, smaller radii of ~25 kpc and much smaller masses (~1E8-1E10 M_Sun) are inferred. This radius is consistent with the observed transition in radio source size between smaller sources where strong HI absorption is almost ubiquitous, and the larger sources where it is mostly lacking. Finally, we outline additional absorption line diagnostics which could further constrain the properties of the haloes and their ionization sources.

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arXiv2006

Integral field spectroscopy of H-alpha emission in cooling flow cluster cores: disturbing the molecular gas reservoir

We present optical integral field spectroscopy of the H-alpha-luminous (>1E42 erg/s) central cluster galaxies in the cores of the cooling flows A1664, A1835, A2204 and Zw8193. From the [NII]+H-alpha complex we derive 2-D views of the distribution and kinematics of the emission line gas, and further diagnostics from the [SII] and [OI] lines. The H-alpha emission shows a variety of disturbed morphologies with velocity gradients and splittings of several hundred km/s on scales of 20 kpc or more. Despite the small sample size, there are some generic features. The most disturbed H-alpha emission appears to be associated with secondary galaxies within 10-20 kpc (projected) of the central galaxy and close in velocity to the H-alpha. The global H-alpha kinematics match those of CO(1-0) emission in single-dish data. The [NII]/H-alpha, [SII]/H-alpha and [OI]/H-alpha ratios vary little with position, local H-alpha surface brightness or between clusters. We propose that the H-alpha and CO emission arise in molecular clouds heated by a starburst which has been triggered by interaction with a secondary galaxy. Such CO emission is known to trace massive (>1E10 M_sun) compact (<20 kpc) reservoirs of cool molecular gas, which an infalling galaxy may disturb, distorting the H-alpha morphology and initiating widespread star formation. We suggest that cloud-cloud collisions in the undisturbed molecular gas reservoir might be an important excitation source for the emission line gas in the cores of lower H-alpha luminosity cluster cores with less intense star formation (abridged).

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arXiv2006

Cold molecular gas in the Perseus cluster core - Association with X-ray cavity, Halpha filaments and cooling flow -

Cold molecular gas has been recently detected in several cooling flow clusters of galaxies where huge optical nebulosities often stand. These optical filaments are tightly linked to the cooling flow and to the related phenomena, like the rising bubbles of relativistic plasma, fed by the radio jets. We present here a map in the CO(2-1) rotational line of the cold molecular gas associated with some Halpha filaments surrounding the central galaxy of the Perseus cluster: NGC 1275. The map, extending to about 50 kpc (135 arcsec) from the center of the galaxy, has been made with the 18-receiver array HERA, at the focus of the IRAM 30m telescope. Although most of the cold gas is concentrated to the center of the galaxy, the CO emission is also clearly associated to the extended filaments conspicuous in ionised gas and could trace a possible reservoir fueling the star formation there. Some of the CO emission is also found where the X-ray gas could cool down more efficiently: at the rims of the central X-ray cavity (where the hot gas is thought to have been pushed out and compressed by the central AGN expanding radio lobes). The CO global kinematics does not show any rotation in NGC 1275. The cold gas is probably a mixture of gas falling down on the central galaxy and of uplifted gas dragged out by a rising bubble in the intracluster medium. As recenlty suggested in other cluster cores, the cold gas peculiar morphology and kinematics argue for the picture of an intermittent cooling flow scenario where the central AGN plays an important role.

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arXiv2005

The discovery of a galaxy-wide superwind from a young massive galaxy at redshift z~3

High-velocity galactic outflows, driven by intense bursts of star formation and black hole accretion, are invoked by current theories of galaxy formation to terminate star formation in the most massive galaxies and to deposit heavy elements in the intergalactic medium. From existing observational evidence on high-redshift galaxies, it is unclear whether such outflows are localized to regions of intense star formation just a few kiloparsecs in extent, or whether they instead have a significant impact on the entire galaxy and its surroundings. Here we present two-dimensional spectroscopy of a star-forming galaxy at redshift z=3.09 (seen 11.5 Gyr ago, when the Universe was 20 per cent of its current age): its spatially extended Ly-alpha emission appears to be absorbed by HI in a foreground screen covering the entire galaxy, with a lateral extent of at least 100 kpc and remarkable velocity coherence. It was plausibly ejected from the galaxy during a starburst several 1E8 yr earlier and has subsequently swept up gas from the surrounding intergalactic medium and cooled. This demonstrates the galaxy-wide impact of high-redshift superwinds.

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arXiv2005

X-rays from the Type II quasar in the hyperluminous infrared galaxy IRAS F15307+3252

We report the detection of X-ray emission from the hyperluminous infrared galaxy IRAS F15307+3252 at z=0.93 and its properties obtained from XMM-Newton observations. Although the X-ray emission is very faint and the data are noisy, a prominent line-like feature in the observed 3-4 keV range is inferred from both photometric and spectroscopic techniques. It indicates an X-ray spectrum dominated by 6.4 keV Fe K emission and the presence of a Compton-thick AGN. Our estimate of the luminosity of the illuminating source (L(2-10keV)>=1e45 erg/s), required to produce the observed Fe K emission in reflection from cold matter, means that the hidden quasar nucleus accounts for a significant fraction of the large bolometric luminosity. The soft X-ray emission below 2 keV is found to be spatially extended and probably of a separate origin. The temperature and bolometric luminosity (kT=2 keV and L(bol,CL)=1e44 erg/s) obtained from a thermal spectrum place this X-ray source on the L-Tx relation of galaxy clusters. The possible association with a galaxy cluster can be added to the list of remarkable similarities between IRAS F15307+3252 and another hyperluminous infrared galaxy IRAS 09104+4109 (z=0.44), both of which have bolometric luminosities dominated by hidden quasar nuclei. Our result on IRAS F15307+3252 illustrates how difficult it is to detect Compton thick Type II quasars at z>=1, particularly if their bolometric outputs do not rival the hyperluminous population.

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arXiv2005

The nature of the molecular gas system in the core of NGC 1275

We present near-infrared integral field spectroscopy of the central kiloparsec of NGC 1275 at the heart of the Perseus cluster of galaxies, obtained with the UIST IFU on UKIRT. The nuclear ro-vibrational H_2 emission is spatially resolved and is likely to originate approximately 50 pc from the active nucleus. The Pa-alpha emission is, by contrast, spatially unresolved. The requirements for thermal excitation of the H_2 by nuclear X-radiation, its kinematics on sub-arcsec scales, and its stability against self-gravity, together suggest that the observed H_2 is part of a clumpy disk rotating about the radio-jet axis. The sharp jump in H_2 velocity across the nucleus implies a black hole mass of 3.4E8 M(Solar), with a systematic error of 0.18 dex due to the uncertainty in the radio jet inclination. This agrees well with the value implied by the empirical correlation between black hole mass and stellar velocity dispersion for nearby elliptical galaxies, and is ~100 times the stellar mass in this region.

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arXiv2004

The discovery of a type-II quasar at z = 1.65 with integral-field spectroscopy

In this letter we report the serendipitous discovery of a genuine type-II quasar at z = 1.65 using integral-field data from VIMOS on the VLT. This is the first discovery of a type-II quasar at z > 1 from optical data alone. J094531-242831, hereafter J0945-2428, exhibits strong narrow (v < 1500km/s) emission lines, has a resolved host galaxy, and is undetected to a radio flux-density limit of S_{5GHz} = 0.15 mJy (3 sigma). All of these lead us to believe that J0945-2428 is a bona fide type-II quasar. The luminosity of the narrow-emission lines in this object suggest that the intrinsic power of the central engine is similar to that found in powerful radio galaxies, indicative of similarly large supermassive black hole of ~3 x 10^8 M_solar (assuming that it is accreting at its Eddington limit). However, from near-infrared imaging observations we find that the old stellar population in the host galaxy has a luminosity of ~0.2 L*, mildly inconsistent with the correlation between black-hole mass and bulge luminosity found locally, although the uncertainty in the black-hole mass estimate is large. This discovery highlights the power that integral-field units have in discovering hidden populations of objects, particularly the sought after type-II quasars which are invoked to explain the hard X-ray background. As such, future large integral-field surveys could open up a new window on the obscured accretion activity in the Universe.

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arXiv2004

HI in the proto-cluster environment at z>2: absorbing haloes and the Lyman alpha forest

We present VLT-UVES echelle spectra of the Lyman alpha emission and absorption in five radio galaxies at redshifts z=2.55-4.1. Together with data from our pilot study, we have a sample of 7 such systems with radio source sizes ~ 1-90 kpc with which to address the origin of the absorbing gas. Echelle resolution again reveals that some systems with N_HI>1E18 cm^-2 in lower resolution data in fact consist of several weaker absorbers with N_HI<1E15 cm^-2. We identify two groups of HI absorbers: strong absorbers with N_HI=1E18-1E20 cm^-2 and weaker systems with N_HI=1E13-1E15 cm^-2. There are none at intermediate N_HI. The strong absorbers may be a by-product of massive galaxy formation or could instead represent material cooling behind the expanding bow-shock of the radio jet, as simulated by Krause. New observations are required to discriminate between these possibilities. We argue that the weaker absorbers with N_HI=1E13-1E15 cm^-2 are part of the Lyman alpha forest, as their rate of incidence is within a factor of 2-4 of that in the IGM at large. Such column densities are consistent with models of a multi-phase proto-intracluster medium at z>2.

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arXiv2004

Deep SAURON Spectral-Imaging of the diffuse Lyman-alpha halo LAB1 in SSA22

We have used the SAURON panoramic integral field spectrograph to study the structure of the Ly-alpha emission-line halo, LAB1, surrounding the sub-millimeter galaxy SMM J221726+0013. This emission-line halo was discovered during a narrow-band imaging survey of the z=3.1 large-scale structure in the SSA22 region. Our observations trace the emission halo out to almost 100 kpc from the sub-millimeter source and identify two distinct Ly-alpha `mini-haloes' around the nearby Lyman-break galaxies. The main emission region has a broad line profile, with variations in the line profile seeming chaotic and lacking evidence for a coherent velocity structure. The data also suggests that Ly-alpha emission is suppressed around the sub-mm source. Interpretation of the line structure needs care because Ly-alpha may be resonantly scattered, leading to complex radiative transfer effects, and we suggest that the suppression in this region arises because of such effects. We compare the structure of the central emission-line halo with local counter-parts, and find that the emission line halo around NGC 1275 in the Perseus cluster may be a good local analogue, although the high redshift halo is factor of ~100 more luminous and appears to have higher velocity broadening. Around the Lyman-break galaxy C15, the emission line is narrower, and a clear shear in the emission wavelength is seen. A plausible explanation for the line profile is that the emission gas is expelled from C15 in a bipolar outflow, similar to that seen in M82.

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arXiv2003

The spatial clustering of radio sources in NVSS and FIRST; implications for galaxy clustering evolution

We have measured the angular correlation function of radio sources in the 1.4 GHz NVSS and FIRST surveys. Below ~6 arcminutes w(theta) is dominated by the size distribution of radio galaxies. A model of the size distribution of radio galaxies can account for this excess signal in w(theta). The amplitude of the cosmological clustering of radio sources is roughly constant at A~0.001 from 3 to 40 mJy, but has increased to A~0.007 at 200 mJy. This can be explained if powerful (FRII) radio galaxies probe more massive structures at z~1 compared to average power radio galaxies, consistent with powerful high-z radio galaxies generally having massive (forming) elliptical hosts in rich cluster environments. For FRIIs we derive a spatial (comoving) correlation length of r_0=14\pm3 h^{-1} Mpc. This is close to that measured for extremely red objects (EROs) associated with a population of old elliptical galaxies at z~1 by Daddi et al. (2001). Based on their similar clustering properties, we propose that EROs and powerful radio galaxies may be the same systems seen at different evolutionary stages. Their r_0 is ~2 times higher than that of QSOs at a similar redshift, and comparable to that of bright ellipticals locally. This suggests that r_0 (comoving) of these galaxies has changed little from z~1 to z=0, in agreement with current LCDM hierarchical models for clustering evolution of massive early-type galaxies. Alternatively, the clustering of radio galaxies can be explained by the galaxy conservation model. This then implies that radio galaxies of average power are the progenitors of the local early-type field population, while the most powerful radio galaxies will evolve into a present-day population with r_0 similar to that of local rich clusters.

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arXiv2002

XMM-Newton observations of two hyperluminous IRAS galaxies: Compton-thick quasars with obscuring starbursts

We present XMM-Newton observations of two hyperluminous IRAS galaxies (L_Bol>1E13 L_sun), neither of which was previously detected by ROSAT. Published models of the infrared SEDs imply that a starburst and obscured quasar contribute equally to the power of each source. IRAS F12514+1027 (z=0.30) is detected in 18.6 ks with 130 EPIC-pn counts over 0.2-12 keV. The soft X-ray spectrum exhibits thermal emission from the starburst, with T=0.3 keV and L(0.5-2.0keV)=2.1E42 erg/s. With its Fe K-edge, the flat continuum above 2 keV is interpreted as cold reflection from a hidden AGN with an intrinsic L(2-10keV) of at least 1.8E44 erg/s. Comparison with the infrared power requires that the X-ray reflector subtend ~2pi/5 sr at the central engine. IRAS F00235+1024 (z=0.575) is not detected by the EPIC-pn in 15.9 ks; the limits imply that the starburst is X-ray weak, and (for the AGN) that any hard X-ray reflector subtend <2pi/5 sr. The direct lines of sight to the AGN in both objects are Compton-thick, and the presence of a reflection component in F12514+1027, but not in F00235+1024, suggests that the AGN in the latter object is more completely obscured. This is consistent with their Seyfert-2 and starburst optical spectra, respectively.

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arXiv2002

The clustering of sub-mJy radio sources in The Bootes Deep Field

We measure the angular clustering of ~2000 radio sources in The Bootes Deep Field, covering 5.3 deg^2 down to S(1.4 GHz)=0.2 mJy. With reference to work by Blake & Wall, we show that the size distribution of multi-component radio galaxies dominates the overall clustering signal, and that its amplitude extrapolates smoothly from their measurements above 5 mJy. The upper limits on any true galaxy-galaxy clustering are consistent with the clustering of the sub-mJy radio-loud AGN being effectively diluted by the more weakly-clustered IRAS-type starburst galaxies. Source count models imply that the survey contains around 400 of the latter galaxies above 0.2 mJy out to z ~ 1 to 2. Measurement of their clustering must await their identification via the optical and infrared data due on this field.

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arXiv2002

Probing the absorbing haloes around two high-redshift radio galaxies with VLT-UVES

We present VLT-UVES echelle spectroscopy of the HI and CIV absorption in the spatially-extended Lyman-alpha emission around two high-redshift radio galaxies 0200+015 (z=2.23) and 0943-242 (z=2.92). The absorbers in 0943-242 exhibit little additional structure compared with previous low-resolution spectroscopy and the main absorber is still consistent with HI column density of ~10^19 cm^-2. This is consistent with a picture in which the absorbing gas has low density and low metallicity and is distributed in a smooth absorbing shell located beyond the emission-line gas. However, the main absorbers in 0200+015 are very different. The previous single absorber fit of HI column density \~10^19 cm^-2, now splits into two ~4 x 10^14 cm^-2 absorbers which extend more than 15kpc to obscure additional Ly-alpha emission coincident with a radio lobe in these high-resolution observations. Although consistent with the shell-like distribution for the absorption systems, 0200+015 requires a much higher metal enrichment than 0943-242. The metallicity, inferred from the CIV absorption, is considerably lower in 0943-242 than in 0200+015. We explain these differences with an evolutionary scenario based on the size of the radio source. In both sources the HI absorption gas originates from either a gas-rich merger or pristine cluster gas which cools and collapses towards the centre of the dark matter halo. The higher metallicity in the larger radio source (0200+015) may be a result of a starburst driven superwind (concurrent with the triggering of the radio emission) which has engulfed the outer halo in this older source.

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arXiv2002

A survey of molecular hydrogen in the central galaxies of cooling flows

We present a large sample of H- and K-band spectra of 32 optically line luminous central cluster galaxies. We find significant rovibrational H_2 emission in 23 of these galaxies as well as H recombination and/or [FeII] emission in another 5. This represents a fourfold increase in the number of molecular line detections known. A number of the detections are of extended emission (5-20 kpc). In several objects we find significant [SiVI] emission that appears to correlate with the strength of high ionization lines in the optical (e.g. [OIII]). This comprehensive sample builds on previous work and confirms that warm (1000-2500K) molecular hydrogen is present wherever there is ionized material in the cores of cooling flows and in most cases it also coincides with CO molecular line emission.

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arXiv2002

Exciting molecular hydrogen in the central galaxies of cooling flows

The origin of rovibrational H_2 emission in the central galaxies of cooling flow clusters is poorly understood. Here we address this issue using data from our near-infrared spectroscopic survey of 32 of the most line luminous such systems, presented in the companion paper by Edge et al. (2002). We consider excitation by X-rays from the surrounding intracluster medium, UV radiation from young stars, and shocks. The v=1-0 K-band lines with upper levels within 10^4 K of the ground state appear to be mostly thermalised (implying gas densities above ~10^5 cm^-3), with excitation temperatures typically exceeding 2000K, as found earlier by Jaffe, Bremer and van der Werf (2001). Together with the lack of strong v=2-0 lines in the H-band, this rules out UV fluorescence. Using the CLOUDY photoionisation code, we deduce that the H_2 lines can originate in a population of dense clouds, exposed to the same hot (T~50000K) stellar continuum as the lower density gas which produces the bulk of the forbidden optical line emission in the H-alpha luminous systems. This dense gas may be in the form of self-gravitating clouds deposited directly by the cooling flow, or may instead be produced in the high-pressure zones behind strong shocks. Furthermore, the shocked gas is likely to be gravitationally unstable, so collisions between the larger clouds may lead to the formation of globular clusters.

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arXiv2001

On the detectability of distant Compton-thick obscured quasars

Chandra and XMM-Newton have resolved the 2-8 keV X-ray Background (XRB) into point sources. Many of the fainter sources are obscured active galactic nuclei (AGN) with column densities in the range of 10^22-10^23 pcmsq, some of which have quasar-like luminosities. According to obscuration models, the XRB above 8 keV is dominated by emission from Compton-thick AGN, with column densities exceeding 1.5 times 10^24 pcmsq. Here, we consider whether Compton-thick quasars are detectable by Chandra and XMM-Newton by their direct (i.e. not scattered) X-ray emission. Detectability is optimized if the objects individually have a high luminosity and high redshift, so that the direct emission has a significant flux in the observed band. Using a simple galaxy formation model incorporating accreting black holes, in which quasars build most of their mass in a Compton-thick manner before expelling the obscuring matter, we predict that moderately deep 100 ks Chandra and XMM-Newton exposures may contain a handful of detectable Compton-thick quasars. Deep Ms or more Chandra images should contain 50-100 distant, optically-faint, Compton-thick sources. In passing we show that radiation pressure can be as effective in expelling the obscuring gas as quasars winds, and yields a black hole mass proportional to the velocity dispersion of the host bulge to the fourth power.

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arXiv2001

Multi-wavelength observations of serendipitous Chandra sources

We describe progress in a programme to study a sample of sources typical of those which contribute a large fraction of the hard X-ray background. The sources are selected from the fields of approximately 10 ks Chandra cluster observations with follow-up in the near-infrared and optical. The X-ray data indicate that many of these are powerful, obscured sources. Two hard objects which are lensed by the cluster are good candidates for X-ray type-2 quasars, with luminosities of the order 10^{44}-10^{45} erg s^{-1} and obscuring column densities of the order 10^{23} cm^{-2}. We find that the sources are bright in the infra-red (K typically 17-18). From Keck optical spectra and photometric redshifts, we find that the host galaxies are consistent with being early-type, massive hosts at redshifts ranging from 0.2 to 3, with median redshift approximately 1.5. The two obscured quasars also have mid-infrared detections and 850-micron upper-limits implying that the surrounding dust is at warm-to-hot temperatures (T of the order of 1000 K).

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