Typical Quasars Research Articles

Rapid growth of black holes in massive star-forming galaxies

The tight relationship between the masses of black holes and galaxy spheroids in nearby galaxies implies a causal connection between the growth of these two components. Optically luminous quasars host the most prodigious accreting black holes in the Universe, and can account for greater than or approximately equal to 30 per cent of the total cosmological black-hole growth. As typical quasars are not, however, undergoing intense star formation and already host massive black holes (> 10(8)M(o), where M(o) is the solar mass), there must have been an earlier pre-quasar phase when these black holes grew (mass range approximately (10(6)-10(8))M(o)). The likely signature of this earlier stage is simultaneous black-hole growth and star formation in distant (redshift z > 1; >8 billion light years away) luminous galaxies. Here we report ultra-deep X-ray observations of distant star-forming galaxies that are bright at submillimetre wavelengths. We find that the black holes in these galaxies are growing almost continuously throughout periods of intense star formation. This activity appears to be more tightly associated with these galaxies than any other coeval galaxy populations. We show that the black-hole growth from these galaxies is consistent with that expected for the pre-quasar phase.

Radiative feedback from quasars and the growth of massive black holes in stellar spheroids

We discuss the importance of feedback via photoionization and Compton heating on the co-evolution of massive black holes (MBHs) at the center of spheroidal galaxies and their stellar and gaseous components. We first assess the energetics of the radiative feedback from a typical quasar on the ambient interstellar medium. We then demonstrate that the observed Mbh-sigma relation could be established following the conversion of most of the gas of an elliptical progenitor into stars, specifically when the gas-to-stars mass ratio in the central regions has dropped to a low level ~0.01 or less, so that gas cooling is no longer able to keep up with the radiative heating by the growing central MBH. A considerable amount of the remaining gas will be expelled and both MBH accretion and star formation will proceed at significantly reduced rates thereafter, in agreement with observations of present day ellipticals. We find further support for this scenario by evolving over an equivalent Hubble time a simple, physically based toy model that additionally takes into account the mass and energy return for the spheroid evolving stellar population, a physical ingredient often neglected in similar approaches.

Submillimetre photometry of typical high-redshift radio quasars

We present Submillimetre Common-User Bolometer Array (SCUBA) photometry of a sample of eight high-redshift (2.5 ≤ z < 3.5) radio quasars from two redshift surveys: the TexOx-1000 (or TOOT) Survey and the 7C Redshift Survey (7CRS). Unlike the powerful high-redshift radio sources observed previously in the submillimetre, these radio sources are typical of those dominating the radio luminosity density of the population. We detect just two of the TOOT/7CRS targets at 850 μm, and one of these detections is probably due to synchrotron emission rather than dust. The population represented by the other six objects is detected in a statistical sense with their average 850-μm flux density implying that they are similar to low-redshift, far-infrared luminous quasars undergoing at most moderate (≤200 M ○. yr -1 ) starbursts. By considering all the SCUBA data available for radio sources, we conclude that positive correlations between rest-frame far-infrared luminosity L FIR , 151-MHz luminosity L 151 and redshift z, although likely to be present, are hard to interpret because of subtle selection and classification biases, small number statistics and uncertainties concerning synchrotron contamination and k-correction. We argue that there is not yet any compelling evidence for significant differences in the submillimetre properties of radio-loud and radio-quiet quasars at high redshift.

Iron Emission in the z = 6.4 Quasar SDSS J114816.64+525150.3

We present near-infrared J- and K-band spectra of the z = 6.4 quasar SDSS J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck II telescope, covering the rest-frame spectral regions surrounding the C IV λ1549 and Mg II λ2800 emission lines. The iron emission blend at rest wavelength 2900-3000 A is clearly detected, and its strength appears nearly indistinguishable from that of typical quasars at lower redshifts. The Fe II/Mg II ratio is also similar to values found for lower redshift quasars, demonstrating that there is no strong evolution in Fe/α broad-line emission ratios even out to z = 6.4. In the context of current models for iron enrichment from Type Ia supernovae (SNe Ia), this implies that the SN Ia progenitor stars formed at z 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to estimate the black hole mass from the widths of the C IV and Mg II emission lines and the ultraviolet continuum luminosity. The derived mass is in the range (2-6) × 109 M☉, with an additional uncertainty of a factor of 3 due to the intrinsic scatter in the scaling relations. This result is in agreement with the previous mass estimate of 3 × 109 M☉ by Willott, McLure, & Jarvis and supports their conclusion that the quasar is radiating close to its Eddington luminosity.

Detection of type 2 quasars in the radio galaxies B3 0731+438 and 3C 257

We present XMM-Newton observations and spectral fitting of two highly redshift, [OIII]-luminous, narrow-line radio galaxies, B3 0731+438 and 3C 257. Their X-ray continua are well fitted by a partial covering model with intrinsically unabsorbed and absorbed powerlaw components. The spectral models indicate that both objects harbour highly obscured nuclei, with N_H ~ 0.5 - 2 x 10^23 cm^-2. Correcting for this absorption we find large intrinsic luminosities in the range L_X ~ 0.2 - 1 x 10^45 erg/s. Thus, both sources are type-2 quasars.

X-ray Astronomy from the Solar System to the High Redshift Universe

F01 XMM-Newton: Mission Status and Science Archive F02 Introduction to the Chandra X-ray Observatory F03 Discovery of X-rays from Mars with Chandra F04 Investigation of Stellar Coronae with Chandra and XMM-Newton F05 High-resolution X-ray Spectra of Young Stars F06 Chandra Spectroscopy of an Extremely Hot Bare Stellar C/O Core F07 Blobby Accretion in the Polar V1309 Ori F08 The Cyclotron Line in GX301–2 F09 Do we live in a Local Chimney? F10 The Bright Halo of GX13+1 Observed by XMM F11 The XMM-NEWTON View of the LMC Superbubble N51D F12 X-ray SNRs in Nearby Galaxies and CR Source Distribution F13 The Hamburg/RASS Catalogue of Optical Identifications of ROSAT BSC X-ray Sources F14 X-ray Variability in the ROSAT All-Sky Survey F15 NGC 6240, Local Key Representative and Pathfinder to the High-redshift Universe of ULIRGs: the Chandra High-resolution View F16 Wide-Angle X-ray Cluster Surveys and their Impact on Cosmology F17 XMM-Newton Discovery of an Ionized Fe-K Edge in the z = 3.91 BAL Quasar APM08279+5255 F18 The Population of High-redshift Type-2 Quasars Found in Deep Chandra and XMM-Newton Surveys

Observational Constraints on the Internal Velocity Field of Quasar Emission‐Line Clouds

This paper addresses the question, what does the spectrum of a typical quasar reveal about the velocity structure within its broad emission line region clouds? Turbulent (i.e., nonthermal) broadening of spectral lines can be due to macroturbulence or microturbulence. Microturbulence affects line formation and the emitted spectrum and may be required to account for the observed smoothness of the line profiles. The velocity field is crucial since it addresses the fundamental nature of the individual clouds and the global structure of the active galactic nuclei (AGNs) environment. For example, stellar winds or magnetically confined blobs might be highly microturbulent, requiring only a few internally broadened clouds to account for the observed smooth line profiles in AGNs. On the other hand, clouds in pressure confinement would have only thermal line widths, requiring many clouds moving in a large-scale velocity field to achieve the same effect. There are almost no previous studies of the effects of microturbulence, even though the observation that AGN lines are very smooth seems to require additional line broadening mechanisms. We present a broad range of photoionization calculations in which the microturbulence is varied between 0 km s-1 (thermal broadening only) and 104 km s-1, an upper limit set by the observed line width. In general, the line spectrum grows stronger relative to the continuum as turbulence increases. This is because lines more easily escape due to diminished line optical depth and permitted lines are selectively strengthened by continuum pumping. Comparisons with observations reveal two cases. The predicted relative intensities of the majority of the strong lines in typical objects do not depend strongly on the microturbulent field. A turbulence of ~103 km s-1 does not violate observations, but is not required either. However, in the sharp-lined quasars, some lines require a turbulence of the same order as the observed line width to reproduce the spectrum.

Submillimetre observations of luminous z &gt; 4 radio-quiet quasars and the contribution of AGN to the submm source population

We present sensitive 850µm SCUBA photometry of a statistically-complete sample of six of the most luminous (MB 10 13 L⊙), z > 4 radio-quiet quasars, reaching noise levels (1� � 1.5mJy) comparable with the deep blank sky surveys. These observations probe the rest frame far infrared region (�150µm), at luminosity levels for thermal sources comparable with those that IRAS permitted for low redshift quasars. One quasar (BR2237 0607; z = 4.55) is detected at 850µm with a flux of 5.0±1.1mJy (4.5�), whilst a second (BR0019 1522; z=4.52) has a detection at the 2� level. When combined with our previous millimetre measurements of z>4 quasars, we find that there is a large range (5–10) in far infrared (FIR) luminosity (LFIR) at fixed UV luminosity, and that the typical quasar has a LFIR and mass of cool (50K) dust similar to that of the archetyepal low redshift (z=0.018) ultraluminous IRAS galaxy(ULIRG) Arp220 (LFIR � 5 × 10 12 L⊙; Md(cool) � 10 8 M⊙). If one assumes a fiducial FIR luminosity of 5 × 10 12 L⊙ for for all quasars with MB 15 per cent of the sources in the SCUBA deep surveys could be classical broad-lined radio-quiet AGN. Thus if one considers the observed ratio of Seyfert II to Seyfert I galaxies at low redshift and any contribution from totally optically obscured AGN, a significant fraction of the SCUBA source population will harbour AGN and hence the inferred star formation rates from submm fluxes may be overestimated if the active nuclei are bolometrically dominant or the IMF is top heavy.

Thermal-infrared imaging of 3C radio galaxies at z 1

We present the results of a programme of thermal-infrared imaging of 19 z∼ 1 radio galaxies from the 3CR and 3CRR (LRL) samples. We detect emission at L′ (3.8 μm) from four objects; in each case the emission is unresolved at 1-arcsec resolution. 15 radio galaxies remain undetected to sensitive limits of L′≈ 15.5. Using these data in tandem with archived HST data and near-infrared spectroscopy, we show that three of the detected ‘radio galaxies’ (3C 22, 3C 41 and 3C 65) harbour quasars reddened by AV≲ 5 mag. Correcting for this reddening, 3C 22 and 3C 41 are very similar to coeval 3C quasars, whilst 3C 65 seems unusually underluminous. The fourth radio galaxy detection (3C 265) is a more highly obscured (AV∼ 15) but otherwise typical quasar, which previously has been evident only in scattered light. We determine the fraction of dust-reddened quasars at z∼ 1 to be 28−13+25 per cent at 90 per cent confidence. On the assumption that the undetected radio galaxies harbour quasars similar to those in 3C 22, 3C 41 and 3C 265 (as seems reasonable, given their similar narrow emission line luminosities) we deduce extinctions of AV≳: 15 towards their nuclei. The contributions of reddened quasar nuclei to the total K-band light range from ∼0 per cent for the non-detections, through ∼10 per cent for 3C 265 to ∼80 per cent for 3C 22 and 3C 41. Correcting for these effects does not remove the previously reported differences between the K magnitudes of 3C and 6C radio galaxies, so contamination by reddened quasar nuclei is not a serious problem for drawing cosmological conclusions from the K–z relation for radio galaxies. We discuss these results in the context of the ‘receding torus’ model which predicts a small fraction of lightly reddened quasars in samples of high-radio-luminosity sources. We also examine the likely future importance of thermal-infrared imaging in the study of distant powerful radio sources.

ASCA Observations of the Type-2 Quasar RXJ13434+0001 at z = 2.35

RXJ 13434+0001 is a rare example of radio-quiet type-2 quasars at high redshift. It was discovered through deep ROSAT observations and identified with a galaxy with a strong but narrow Lyα emission line at z = 2.35. In order to constrain the hard-X-ray properties we observed RXJ 13434+0001 with ASCA. The main purpose is to study the origin of the X-ray emission observed with ROSAT. If it is a scattered component from a strongly absorbed AGN, we could see it much brighter in the hard X-ray band.

Faraday Rotation Measure Observations on the Pc-Scale: Probing the AGN Environment

AbstractWe present multi-frequency VLBA polarimetric observations of a small sample of quasars revealing their Faraday rotation measure (RM) structure at ~ 1 mas resolution. Two of the sources (OQ 172 and 3C 216) were chosen on the basis of high RMs seen by the VLA and single dish telescopes. A few more typical quasars (3C 273, 3C 279, 3C 345 and 3C 380) were also included in the study. In OQ 172, 3C 273, 3C 279 and 3C 380 we find high RMs (&gt;3000 rad m−2) associated with the nuclear region. Only 1-10 mas from the nucleus the jet |RM|s in all 4 of these sources fall to less than 100 rad m−2. This RM structure may be produced by strong magnetic fields in the the narrow line region of the quasar.

Do the Broad Emission Line Clouds See the Same Continuum That We See?

Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many of them have remarkably soft ionizing continua (f� / � 2 , 13.6 eV – 100 eV). We point out that the number of h� > 54.4 eV photons is insufficient to create the observed strengths of the He ii emission lines. While the numbers of photons which energize C iv �1549 and O vi �1034 are sufficient, even the most efficiently emitting clouds f or these two lines must each cover at least 20% – 40% of the source. If the typical quasar ionizing continuum is indeed this soft, then we must conclude that the broad emission line clouds must see a very different (harder) continuum than we see. The other viable possibility is that the UV – EUV SED is double-peaked, with the second peaking near 54 eV, its Wien tail the observed soft X-ray excess. Subject headings: line: formation — quasars: emission lines and general — ultraviolet

Learning about Active Galactic Nucleus Jets from Spectral Properties of Blazars

We use multiwavelength spectra of core-dominated flat spectrum radio-loud quasars (FSRQs) to study properties of jets in active galactic nuclei. From a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes, we find that these jets must be optically very thin. This eliminates the importance of such processes as Coulomb interactions, pair annihilation, and bremsstrahlung and determines the minimum distance from the black hole where a powerful jet can be fully developed (accelerated, collimated, and mass loaded). In the case of pair dominated jets, this distance is 100GMBH/c2. Further constraints on the parameters of a jet can be derived from luminosities and positions of spectral peaks of low-energy (IR/optical) and high-energy (γ-ray) radiation components, provided that both are produced by the same population of electrons. Whereas there appears to be a consensus about the synchrotron origin of the low-energy component, there is still debate about the mechanism of production of γ-rays. Most likely, they result from Comptonization of a soft radiation field by the same electrons that produce synchrotron radiation. Such a soft radiation field can be provided by the synchrotron process in a jet, by the accretion disk, and by a fraction of the disk radiation that is reprocessed/rescattered by emission line clouds, dust, and intercloud medium. We show that for FSRQs, the production of the high-energy radiation can be dominated by Comptonization of synchrotron radiation only for jets with moderate bulk Lorentz factors Γj (3) or if external radiation fields are much weaker than those observed in typical quasars. Furthermore, in synchrotron self-Compton (SSC) models, the relativistic plasma producing nonthermal radiation is constrained to be very weakly magnetized (B' < 0.01 gauss) and located at very large distances (r ~ 1019 cm). These can impose problems with jet confinement and with short observed timescale of variability. In the external radiation Compton (ERC) models, the magnetic fields are predicted to be much stronger (B' ~ 100 gauss), and nonthermal radiation can be produced very closely to the black hole (r ~ 1016 cm), which alleviates the problems with plasma confinement and short timescale variability. However, because of the close proximity to the black hole, the constraints imposed by the bulk Compton radiation imply that the plasma must be free of e+e- pairs. Finally, we discuss the difficulties that existing models have in explaining the sharp spectral breaks at MeV energies and postulate a hot version of the ERC scenario for the production of MeV peaks. We show that appropriate electron temperatures (kT ~ 100 MeV) to produce the luminosity peak at MeV energies by Comptonization of external UV radiation are achievable at subparsec distances only for proton-electron plasmas.

The role of an extended corona in the formation of emission lines and continuum in active galactic nuclei

We study a model of an accretion disc surrounded by an extended corona of the temperature 10^7 - 10^8 K. This corona modifies the disk spectrum since it redirects a significant fraction of the emission from the central parts towards the more distant parts of the disk. The same corona is indirectly the source of the broad emission lines because we expect the formation of cool clouds at the basis of the corona due to thermal instabilities. We model the number of the clouds and their motion through the corona adopting a few different physically sound assumptions. Comparing the predicted optical/UV continua and emission line ratios and profiles with the observed values we favor a particular model of a typical quasar. It radiates at ~0.5 of the Eddington luminosity, the corona surrounding the disk is additionally heated in excess of the Inverse Compton heating, and the broad line clouds are most probably destroyed when accelerated vertically above the sound speed within the corona.

Continuum and line emission in Cygnus A

Continuum and line emission in Cygnus A

Collapse of primordial gas clouds and the formation of quasar black holes

The formation of quasar black holes during the hydrodynamic collapse of protogalactic gas clouds is discussed. The dissipational collapse and long-term dynamical evolution of these systems is analyzed using three-dimensional numerical simulations. The calculations focus on the final collapse stages of the inner baryonic component and therefore ignore the presence of dark matter. Two types of initial conditions are considered: uniformly rotating spherical clouds, and iirotational ellipsoidal clouds. In both cases the clouds are initially cold, homogeneous, and not far from rotational support (T/(absolute value of W) approximately equals 0.1). Although the details of the dynamical evolution depend sensitively on the initial conditions, the qualitative features of the final configurations do not. Most of the gas is found to fragment into small dense clumps, that eventually make up a spheroidal component resembling a galactic bulge. About 5% of the initial mass remains in the form of a smooth disk of gas supported by rotation in the gravitational potential potential well of the outer spheroid. If a central seed black hole of mass approximately greater than 10(exp 6) solar mass forms, it can grow by steady accretion from the disk and reach a typical quasar black hole mass approximately 10(exp 8) solar mass in less than 5 x 10(exp 8) yr. In the absence of a sufficiently massive seed, dynamical instabilities in a strongly self-gravitating inner region of the disk will inhibit steady accretion of gas and may prevent the immediate formation of quasar.

Radio emission from IRAS-selected quasars

All six southern quasars discovered in the IRAS point source catalogue have been detected with the Molonglo Observatory Synthesis Telescope at 843 MHz, with flux densities in the range 10-50 mJy. The corresponding radio luminosities indicate that these are typical radio-quiet quasars. The ratio of radio to far-infrared (FIR) luminosity for the six objects places them on the remarkable correlation between radio and FIR luminosity that exists for low surface brightness and early-type spiral galaxies and for galaxies having high rates of star formation

Radiation Hydrodynamics of the Broad Line Region in Seyfert Galaxies and Quasars

The broad line region in quasars and in the nuclei of active galaxies is the site of remarkable hydrodynamic activity unprecedented elsewhere in the universe. Considerable theoretical effort has been directed to determine how this intense radiation is related to high velocity gas motions in these small regions, which, because of their great distances, cannot be resolved by direct observation. A better theoretical understanding of the nature of the broad line-emitting gas involves many novel aspects of radiation hydrodynamics and may eventually provide insights into the nature of the mysterious quasar phenomenon itself.Continuum and emission line properties of active galaxies and quasars are sufficiently similar that there is little doubt that both can be accounted for by a similar or closely related physical model. The main difference is one of luminosity; typical quasars are considerably brighter than Seyfert galaxies.In the discussion below the relevant observations of quasars and active galaxies are briefly reviewed with an emphasis on the physical properties of the line-emitting gas and its immediate environment. Arguments that support the importance of radiation forces in producing the observed gas velocities are summarized. Finally, the nature of the acceleration process is described with particular attention paid to the various instabilities that may be present and which are generally characteristic of situations in which plasma velocities result directly from the deposition of radiative momentum. In fact, these troublesome instabilities suggest that radiative forces, although very strong, may provide only a partial explanation of the gasdynamical activity observed.

X-ray emission from red quasars

A dozen red quasars were observed with the Einstein Observatory in order to determine their X-ray properties. The observations show that for all these sources, the infrared-optical continuum is so steep that when extrapolated to higher frequencies, it passes orders of magnitude below the measured X-ray flux. The X-ray emission is better correlated with the radio than with the infrared flux, suggesting a connection between the two. By applying the synchrotron-self-Compton model to the data, it is found that the infrared-optical region has a size of 0.01 pc or more and a magnetic field more than 0.1 G, values considerably different than are found in the radio region. Unlike other quasars, the ionizing continuum is dominated by the X-ray emission. The peculiar line ratios seen in these objects can be understood with a photoionization model, provided that the photon to gas density ratio (ionization parameter) is an order of magnitude less than in typical quasars.

Optical characteristics of young quasars as sources of the cosmic X-ray background

The sources which dominate the thermal cosmic X-ray background cannot have X-ray spectra similar to the power laws measured for bright active galactic nuclei. The optical consequences of this disparity are pursued by considering a standard model for the photoexcitation and heating of the line-emitting gas surrounding a central source (e.g., such as a quasar). The optical line emission to be associated with compact young quasar sources having the same X-ray spectrum as the X-ray background is found to be substantially different from that characteristic of typical quasars. Implications on quasar source counts and the identification of such new objects are discussed.