High-redshift Active Galactic Nuclei Research Articles

The water maser in MG 0414+0534: the influence of gravitational microlensing

Water masers have been observed in several high redshift active galactic nuclei, including the gravitationally lensed quasar MG 0414+0534. This quasar is lensed into four images, and the water maser is detected in two of them. The broadening of the maser emission line and its velocity offset are consistent with a group of masers associated with a quasar jet. If the maser group is microlensed we can probe its structure and size by observing its microlensing behaviour over time. We present results of a high resolution numerical analysis of microlensing of the maser in MG 0414+0534, using several physically motivated maser models covering a range of sizes and emission profiles. Time-varying spectra of the microlensed maser are generated, displayed, and analysed, and the behaviour of the different models compared. The observed maser line in MG 0414+0534 is consistent with maser spots as in other quasar jets, provided substructure is de-magnified or currently lost in noise; otherwise smooth extended maser models are also candidates to generate the observed spectrum. Using measures of spectral variability we find that if the maser has small substructure of ~ 0.002 pc then a variation of 0.12 mag in flux and 2.0 km/s in velocity centroid of the maser line could be observed within 2 decades. For the smallest maser model in this study a magnification of > 35 is possible 22% of the time, which is of significance in the search for other lensed masers.

THE STRUCTURE AND DYNAMICS OF AN ACTIVE GALACTIC NUCLEUS TORUS: CO LINE PREDICTIONS FOR ALMA FROM THREE-DIMENSIONAL HYDRODYNAMICAL SIMULATIONS WITH X-RAY-DRIVEN CHEMISTRY

Many efforts have been made to model the mass distribution and dynamical evolution of the circumnuclear gas in active galactic nuclei (AGNs). However, chemical evolution is not included in detail in three-dimensional (3-D) hydrodynamic simulations. The X-ray radiation from the AGN can drive the gas chemistry and affect the thermodynamics, as well as the excitation of the interstellar medium (ISM). Therefore, we estimate the effects (on chemical abundances and excitation) of X-ray irradiation by the AGN, for atomic and molecular gas in a 3-D hydrodynamic model of an AGN torus. We obtain the abundances of various species from an X-ray chemical model. A 3-D radiative transfer code estimates the level populations, which result in line intensity maps. Predictions for the CO J=1-0 to J=9-8 lines indicate that mid-J CO lines are excellent probes of density and dynamics in the central (<60 pc) region of the AGN, in contrast to the low-J CO lines. Analysis of the X_CO/\alpha conversion factors shows that only the higher-J CO lines can be used for gas mass determination in AGN tori. The [C II] 158 um emission traces mostly the hot (T_k>1000m K) central (<60 pc) region of the AGN torus. The [C II] 158 um line will be useful for ALMA observations of high redshift (z>1) AGNs. The spatial scales (>0.25 pc) probed with our simulations match the size of the structures that ALMA will resolve in nearby (<45 Mpc at 0.01") galaxies.

HARD X-RAY PHOTON INDEX AS AN INDICATOR OF BOLOMETRIC CORRECTION IN ACTIVE GALACTIC NUCLEI

We propose the rest-frame 2–10 keV photon index, Γ2–10 keV, acting as an indicator of the bolometric correction, Lbol/L2–10 keV (where Lbol is the bolometric luminosity and L2–10 keV is the rest-frame 2–10 keV luminosity), in radio-quiet active galactic nuclei (AGNs). Correlations between Γ2–10 keV and both bolometric correction and Eddington ratio are presented, based on simultaneous X-ray, UV, and optical observations of reverberation-mapped AGNs. These correlations can be compared with those for high-redshift AGNs to check for any evolutionary effect. Assuming no evolutionary effect in AGNs' spectral properties, together with the independent estimates of L2–10 keV, the bolometric correction, Eddington ratio, and black hole (BH) mass can all be estimated from these correlations for high-redshift AGNs, with the mean uncertainty of a factor of 2–3. If there are independent estimates of BH masses, Γ2–10 keV for high-redshift AGNs can be used to determine their true Lbol and L2–10 keV, and in conjunction with the redshift can be potentially used to place constraints on cosmology by comparison with the rest-frame 2–10 keV flux. We find that the true L2–10 keV estimated from Γ2–10 keV for the brightest Type I AGNs with z < 1 in the Lockman Hole is generally in agreement with the observed L2–10 keV. However, there are still many uncertainties, such as the accurate determination of the intrinsic Γ2–10 keV for distant AGNs and the large uncertainty in the luminosities obtained, which call for significant further study before "AGN cosmology" can be considered a viable technique.

ON THE RADIATIVE EFFICIENCIES, EDDINGTON RATIOS, AND DUTY CYCLES OF LUMINOUS HIGH-REDSHIFT QUASARS

We investigate the characteristic radiative efficiency \epsilon, Eddington ratio \lambda, and duty cycle P_0 of high-redshift active galactic nuclei (AGN), drawing on measurements of the AGN luminosity function at z=3-6 and, especially, on recent measurements of quasar clustering at z=3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are \epsilon, \lambda, and the normalization, scatter, and redshift evolution of the relation between black hole mass \mbh and halo virial velocity V_vir. We compute the luminosity function from the implied growth of the black hole mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z=3 and, especially, at z=4 implies that massive black holes reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency \epsilon and/or low Eddington ratio \lambda, with a lower limit (based on 2\sigma agreement with the measured z=4 correlation length) \epsilon> 0.7\lambda/(1+0.7\lambda), implying \epsilon > 0.17 for \lambda > 0.25. Successful models predict high duty cycles, P_0~0.2, 0.5, and 0.9 at z=3.1, 4.5 and 6, respectively, and they require that the fraction of halo baryons locked in the central black hole is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z>7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z=3-6 luminosity function would predict. (abridged)

Black Hole Demographics: Statistical Characteristics of Accreting Black Holes

This review summarizes the important properties of active black holes (BHs) up to z ~ 2; their mass, accretion rate, and growth rate. At higher redshifts, such information is only available for small samples that do not represent the entire population of active galactic nuclei (AGNs). Black hole spin is still unknown; it is speculated to change with redshift, but with little experimental evidence. The available data sets also enable a direct comparison of BH accretion rates and host galaxy star-formation rates (SFRs). The ratio of the BH growth rate g(BH) and the bulge growth rate g(bulge), suggests that the two are proportional to each other. The local value of g(bulge)/g(BH) in low-luminosity AGNs is of order 100 and the corresponding ratio in high-luminosity, high-redshift AGNs is of order 10. This has important implications regarding the parallel evolution of active BHs and their hosts.

The X-ray luminosity function of AGN at z ∼ 3

We combine Lyman-break colour selection with ultradeep (≳200 ks) Chandra X-ray imaging over a survey area of ∼0.35 deg2 to select high-redshift active galactic nuclei (AGN). Applying careful corrections for both the optical and X-ray selection functions, the data allow us to make the most accurate determination to date of the faint end of the X-ray luminosity function (XLF) at z∼ 3. Our methodology recovers a number density of X-ray sources at this redshift which is at least as high as previous surveys, demonstrating that it is an effective way of selecting high z AGN. Comparing to results at z= 1, we find no evidence that the faint slope of the XLF flattens at high z, but we do find significant (factor ∼3.6) negative evolution of the space density of low luminosity AGN. Combining with bright end data from very wide surveys we also see marginal evidence for continued positive evolution of the characteristic break luminosity L*. Our data therefore support models of luminosity-dependent density evolution between z= 1 and z= 3. A sharp upturn in the the XLF is seen at the very lowest luminosities (LX≲ 1042.5erg s−1), most likely due to the contribution of pure X-ray starburst galaxies at very faint fluxes.

Discovery of a single faint AGN in a large sample of z &gt; 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 (IAB= 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.

Populations of candidate black holes at redshift 7 or above

AbstractI will describe recent results on constructing samples of candidate active galactic nuclei (AGN) at or beyond redshift 7, probing several orders of magnitude fainter than the top end of the quasar luminosity function at redshift 6. These advances have been made possible by the advent of deep, wide multi-waveband surveys that enable the selection of samples of sources that are detected at radio or X-ray wavelengths but completely undetected at optical wavelengths to very deep limits. A variety of multi-band selection criteria are used to identify the high-redshift candidates and eliminate lower-redshift interlopers by means of extensive spectral energy distribution modelling. The resulting constraints on the numbers of high-redshift AGN at or above redshift 7 are used to examine the evolution of the AGN luminosity function at high redshift, and help understand the properties of the first supermassive black holes in the universe.

Gas metallicity in the narrow-line regions of high-redshift active galactic nuclei

We analyze optical (UV rest-frame) spectra of X-ray selected narrow-line QSOs at redshift 1.5 ≤ z ≤ 3.7 found in the Chandra Deep Field South and of narrow-line radio galaxies at redshift 1.2 ≤ z ≤ 3.8 to investigate the gas metallicity of the narrow-line regions and their evolution in this redshift range. Such spectra are also compared with UV spectra of local Seyfert 2 galaxies. The observational data are inconsistent with the predictions of shock models, suggesting that the narrow-line regions are mainly photoionized. The photoionization models with dust grains predict line flux ratios which are also in disagreement with most of the observed values, suggesting that the high-ionization part of the narrow-line regions (which is sampled by the available spectra) is dust-free. The photoionization dust-free models provide two possible scenarios which are consistent with the observed data: low-density gas clouds (n H ≤ 10 3 cm -3 ) with a sub-solar metallicity (0.2 ≤ Z gas /Z ○. ≤ 1.0), or high-density gas clouds (n H ∼ 10 5 cm -3 ) with a wide range of gas metallicity (0.2 ≤ Z gas /Z ○. ≤ 5.0). Regardless of the specific interpretation, the observational data do not show any evidence for a significant evolution of the gas metallicity in the narrow-line regions within the redshift range 1.2 ≤ z ≤ 3.8. Instead, we find a trend for more luminous active galactic nuclei to have more metal-rich gas clouds (luminosity-metallicity relation), which is in agreement with the same finding in the studies of the broad-line regions. The lack of evolution for the gas metallicity of the narrow-line regions implies that the major epoch of star formation in the host galaxies of these active galactic nuclei is at z ≥ 4.

Deep Extragalactic X-Ray Surveys

▪ Abstract Deep surveys of the cosmic X-ray background are reviewed in the context of observational progress enabled by the Chandra X-Ray Observatory and the X-Ray Multi-Mirror Mission-Newton. The sources found by deep surveys are described along with their redshift and luminosity distributions, and the effectiveness of such surveys at selecting active galactic nuclei (AGN) is assessed. Some key results from deep surveys are highlighted, including (a) measurements of AGN evolution and the growth of supermassive black holes, (b) constraints on the demography and physics of high-redshift AGN, (c) the X-ray AGN content of infrared and submillimeter galaxies, and (d) X-ray emission from distant starburst and normal galaxies. We also describe some outstanding problems and future prospects for deep extragalactic X-ray surveys.

Host Galaxies of High‐Redshift Active Galactic Nuclei in the Great Observatories Origins Deep Surveys Fields

The star formation rates and the stellar masses of the host galaxies of active galactic nuclei (AGNs) at high redshifts are key to understanding the evolution of the relation between the mass of the spheroidal component of a galaxy and the mass of its central black hole (Mbulge-M• relation). We investigate the host galaxies of 31 AGNs with spectroscopic redshifts between 2 and 4 found in the deep Chandra surveys of the Great Observatories Origins Deep Surveys (GOODS) fields. We use the F606W, F775W, and F850LP band images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope (HST). The sample can be divided into 17 extended AGNs and 14 compact AGNs based on the concentration parameter defined as the difference between the aperture magnitudes with 007 and 025 diameter. We derive the upper limits of the UV luminosities of the host galaxies of the compact AGN sample and the upper and lower limits of the UV luminosities of the host galaxies of the extended AGN sample. These limits are consistent with the knee of the luminosity function of the Lyman break galaxies at z ~ 3, suggesting moderate star formation rates, <40 M☉ yr-1, in the host galaxies of the AGNs at 2 < zsp < 4 without correcting the dust extinction. By combining the limits of the UV luminosities with the observed K-band magnitudes for the extended AGNs, we derive the upper and lower limits of the stellar masses of their host galaxies. The derived upper limits on the stellar masses range from 1010 to 1012 M☉. The upper limits imply that the Mbulge-M• relation of the high-redshift AGNs is different from that of the galaxies in the nearby universe, or the average Eddington ratio of the high-redshift AGNs is higher than that of low-redshift AGNs with lower luminosity.

Comoving Space Density of X‐Ray–selected Active Galactic Nuclei

For measurement of the active galactic nucleus (AGN) luminosity function and its evolution, X-ray selection samples all types of AGNs and provides reduced obscuration bias in comparison with UV excess or optical surveys. The apparent decline in optically selected quasars above z ~ 3 may be strongly affected by such a bias. The Chandra Multiwavelength Project (CHAMP) is characterizing serendipitously detected X-ray sources in a large number of fields with archival Chandra imaging. We present a preliminary measure of the comoving space density using a sample of 311 AGNs found in 23 CHAMP fields (~1.8 deg2) supplemented with 57 X-ray-bright AGNs from the Chandra Deep Field-North and Chandra Deep Field-South. Within our X-ray flux (f0.3-8.0 keV > 4 × 10-15 ergs cm-2 s-1) and optical magnitude (r' 3. Using this X-ray-selected sample, we detect a turnover in the comoving space density of luminous type 1 AGNs (log LX > 44.5 ergs s-1, measured in the 0.3-8.0 keV band and corrected for Galactic absorption) at z > 2.5. Our X-ray sample is the first to show a behavior similar to the well-established evolution of the optical quasar luminosity function. A larger sample of high-redshift AGNs and with a greater fraction of identified sources, either spectroscopic or photometric, at faint optical magnitudes (r' > 22.5) are required to remove the remaining uncertainty in our measure of the X-ray luminosity function, particularly given the possibility that AGNs might be more easily obscured optically at high redshift. We confirm that for z < 1, lower luminosity AGNs (log LX < 44.5) are more prevalent by more than an order of magnitude than those with high luminosity. We have combined the Chandra sample with AGNs from the ROSAT surveys to present a measure of the space density of luminous type 1 AGNs in the soft X-ray band (0.5-2.0 keV) that confirms the broadband turnover described above.

Identifying High-Redshift Active Galactic Nuclei Using X-Ray Hardness

The X-ray color (hardness ratio) of optically undetected X-ray sources can be used to distinguish obscured active galactic nuclei (AGNs) at low and intermediate redshift from viable high-redshift (i.e., z > 5) AGN candidates. This will help determine the space density, ionizing photon production, and X-ray background contribution of the earliest detectable AGNs. High-redshift AGNs should appear soft in X-rays, with hardness ratio HR ~ -0.5, even if there is strong absorption by a hydrogen column density NH up to 1023 cm-2, simply because the absorption redshifts out of the soft X-ray band in the observed frame. Here the X-ray hardness ratio is defined as HR = (H - S)/(H + S), where S and H are the soft and hard band net counts detected by Chandra. High-redshift AGNs that are Compton thick (NH 1024 cm-2) could have HR ~ 0.0 at z > 5. However, these should be rare in deep Chandra images, since they have to be 10 times brighter intrinsically, which implies a 100 times drop in their space density. Applying the hardness criterion (HR < 0.0) can filter out about 50% of the candidate high-redshift AGNs selected from deep Chandra images.

An X‐Ray–selected Active Galactic Nucleus atz = 4.6 Discovered by the CYDER Survey

We present the discovery of a high-redshift, X-ray-selected active galactic nucleus (AGN) by the Calan-Yale Deep Extragalactic Research (CYDER) survey: CXOCY J033716.7-050153, located at z = 4.61, the second high-redshift AGN discovered by this survey. Here we present its optical, near-IR, and X-ray properties and compare it with other optical and X-ray-selected high-redshift AGNs. The optical luminosity of this object is significantly lower than most optically selected high-redshift quasars. It also has a lower rest-frame UV to X-ray emission ratio than most known quasars at this redshift. This mild deviation can be explained either by dust obscuring the UV radiation of a normal radio-quiet AGN emitting at 10% of its Eddington luminosity or because this is intrinsically a low-luminosity radio-loud AGN with a supermassive black hole of ~108 M☉ emitting at 1% of its Eddington luminosity. Deep radio observations can discriminate between these two hypotheses.

Submillimeter Observations of a Sample of Broad Absorption Line Quasars

The broad absorption line (BAL) features seen in a small fraction of quasar optical/UV spectra are attributed to bulk outflows away from the quasar core. Observations suggest that dust plays a key role in these systems, although whether the inferred dust properties are a signature of orientation effects or whether they are indicative of an evolutionary sequence remains an outstanding issue. Submillimeter detections of BAL quasars (BALQSOs), which would clearly help to resolve this issue, have so far been sparse. This Letter reports on new submillimeter observations of seven BALQSOs. The strongest influence on the observed flux is found to be the redshift, with the two highest redshift sources appearing intrinsically more submillimeter-luminous than the lower redshift ones. Since this trend is also seen in other high-redshift active galactic nuclei (AGNs), including non-BAL quasars, it implies that the dust emission properties of these systems are no different from those of the general AGN population, which is difficult to reconcile with the evolutionary interpretation of the BAL phenomenon.

X-Ray, Optical, and Infrared Imaging and Spectral Properties of the 1 M[CLC]s[/CLC] Chandra Deep Field North Sources

We present the optical, near-infrared, submillimeter, and radio follow-up catalog of the X-ray–selected sources from an ≈1 Ms Chandra observation of the Hubble Deep Field North region. We have B, V, R, I, and z' magnitudes for the 370 X-ray point sources, HK' magnitudes for 276, and spectroscopic redshifts for 182. We present high-quality spectra for 175 of these. The redshift distribution shows indications of structures at z = 0.843 and 1.0175 (also detected in optical surveys), which could account for a part of the field-to-field variation seen in the X-ray number counts; however, these structures do not dominate the number of X-ray sources in the sample and hence should not strongly affect the redshift distribution. All of the X-ray sources with z > 1.6 are either broad-line active galactic nuclei (AGNs) or have narrow Lyα and/or C III] 1909 A emission; none of the known z > 1.6 absorption-line galaxies in the field are detected individually in X-rays. We estimate photometric redshifts for the sources with (B-I) > 1.5 (bluer than this and it is hard to distinguish between low-redshift irregulars and luminous high-redshift AGNs) and find agreement (most are within 25%) with the available spectroscopic redshifts. The majority of the galaxies in both the 2–8 keV (hard) and 0.5–2 keV (soft) samples have absolute magnitudes comparable to or more luminous than M = -22. The flux contributions separated into unit bins of redshift show that the z < 1 spectroscopically identified sources already contribute about one-third of the total flux in both the hard and soft bands. Thus, major accretion onto supermassive black holes has occurred since the universe was half its present age. We find from ratios of the X-ray counts that the X-ray spectra are well described by absorption of an intrinsic Γ = 1.8 power law, with NH values ranging from about 1021 cm-2 to 5 × 1023 cm-2. We find very little evolution in the maximum rest-frame opacity-corrected and K-corrected 2–8 keV X-ray luminosities with decreasing redshift until z 0.5, where the volume becomes too small to probe effectively very high luminosity sources. We estimate that the Chandra sources that produce 87% of the HEAO A X-ray background (XRB) at 3 keV produce 57% at 20 keV, provided that at high energies the spectral shape of the sources continues to be well described by a Γ = 1.8 power law. However, when the Chandra contributions are renormalized to the BeppoSAX XRB at 3 keV, the shape matches fairly well the observed XRB at both energies. Thus, whether a substantial population of as yet undetected Compton-thick sources or some change in the spectral shape of the current sources from the simple power-law dependence is required to completely resolve the XRB above 10 keV depends critically on how the currently discrepant XRB measurements in the 1-10 keV energy range tie together with the higher energy XRB.

Determining Central Black Hole Masses in Distant Active Galaxies

An empirical relationship, of particular interest for studies of high-redshift active galactic nuclei (AGNs) and quasars, between the masses of their central black holes and rest-frame ultraviolet (UV) parameters measured in single-epoch AGN spectra is presented. This relationship is calibrated to recently measured reverberation masses of low-redshift AGNs and quasars. An empirical relationship between single-epoch rest-frame optical spectrophotometric measurements and the central masses is also presented. The UV relationship allows reasonable estimates of the central masses to be made for high-redshift AGNs and quasars for which these masses cannot be directly or easily measured by the techniques applicable to the lower luminosity, nearby AGNs. The central mass obtained by this method can be estimated to within a factor of ~3 for most objects. This is reasonable given the intrinsic uncertainty of a factor of less than 2 in the primary methods used to measure the central masses of nearby inactive and active galaxies, namely, resolved gas and stellar kinematics in the underlying host galaxy and reverberation-mapping techniques. The UV relationship holds good potential for being a powerful tool for studying black hole demographics at high redshift as well as statistically studying the fundamental properties of AGNs. The broad-line region size-luminosity relationship is key to the calibrations presented here. The fact that its intrinsic scatter is also the main source of uncertainty in the calibrations stresses the need for better observational constraints to be placed on this relationship. The empirically calibrated relationships presented here will be applied to quasar samples in forthcoming work.

TheBeppoSAXHigh‐Energy Large‐Area Survey. V. The Nature of the Hard X‐Ray Source Population and Its Evolution

We present optical spectroscopic identifications of hard X-ray (5-10 keV) selected sources belonging to the High-Energy Large-Area Survey sample obtained with BeppoSAX down to a 5-10 keV flux limit of f5-10 keV ~ 3 × 10-14 ergs cm-2 s-1. The sample consists of 118 sources. There are 25 sources that have been identified through correlations with catalogs of known sources. A spectroscopic identification for 49 more has been searched for with the telescope. The results of 13 fields were empty down to R = 21. There were 37 sources identified as type 1 active galactic nuclei (AGNs) and nine as type 2 AGNs. The remaining sources are five narrow emission-line galaxies, six clusters, two BL Lac objects, one radio galaxy, and one star. Combining these objects with other hard X-ray selected AGNs from ASCA and HEAO 1, we find that the local luminosity function of type 1 AGNs (AGN 1s) in the 2-10 keV band is fairly well represented by a double power law function. There is evidence for significant cosmological evolution according to a pure luminosity evolution (PLE) model [LX(z) (1 + z)k], with k = 2.12 and 2.22 (σk 0.14) in a (Ωm, Ωλ) = (1.0, 0.0) and a (Ωm, Ωλ) = (0.3, 0.7) cosmology, respectively. The data show an excess of faint high-redshift type AGN 1s, which is well modeled by a luminosity-dependent density evolution (LDDE), similar to what is observed in soft X-rays. However, in both cosmologies, the statistics are not significant enough to distinguish between the PLE and LDDE models. The fitted models imply a contribution of AGN 1s to the 2-10 keV X-ray background from 35% up to 60%.

Testing the correlation of ultrahigh energy cosmic rays with high redshift sources

We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival direction of cosmic rays above ${10}^{19}$ eV using an updated list of air shower detections. Our Monte Carlo simulations reveal no significant correlations above random results, and some previous positive results appear to be an effect of the small sample size. Consequently, there is no evidence for ultrahigh energy cosmic ray primaries being new particles or particles with new interactions beyond the electroweak scale, produced in high-redshift active galactic nuclei.

Emission-line properties of MG 2016+112: A luminous obscured quasar at high redshift

We present new high signal-to-noise ratio spectra of the components B and C of the gravitational lensing system MG 2016+112. We show that image C displays strong emission lines of Lyα, NV, CIV, HeII, and CIII] redshifted to z = 3.27, similar to images A and B. We examine the emission-line flux ratios in order to put constraints on the lens models as well as to investigate the intrinsic nature of MG 2016+112. The observed line ratios of B and C are consistent with those expected in the simple photo-ionization models for narrow-line region of active galactic nuclei (AGN) except for the enhanced NV lines. The line ratios difference of components B and C can be interpreted as a difference in ionization parameters. This result is consistent with lens model prediction that C is a fold image of a slightly outer part of the nucleus. MG 2016+112 is known to be very unique among the high-redshift AGN; it is neither an ordinary broad-line quasar nor a powerful radio galaxy as indicated by the width and flux ratio of the emission lines. Together with other observed properties discussed in literature, we argue that MG 2016+112 may be an obscured luminous radio-quiet quasar.