Excess Luminosity Research Articles

Results from the B factories

The Babar and Belle experiments at the PEP-II and KEKB B Factories have successfully established CP violation (CPV) in the B sector, proving the validity of the CKM mechanism. An overall integrated luminosity in excess of 1.2 ab−1, corresponding to more than 1.2 billion BB pairs from Υ(4S) decays, is now driving the physics program at the B Factories towards the search of new physics by detecting deviations from the Standard Model (SM) in processes where virtual particles are involved. This approach to new physics searches is in contrast with, and complementary to, searches to be performed at the LHC, where real particles will be hopefully directly detected. Moreover, the B Factories are an abundant source of charmed particles, allowing for the search of neutral meson mixing in the charm sector, as well as of new states which are difficult to explain in terms of quark-antiquark pairs (quarkonia), and which are an ideal and unique laboratory to probe both the high and low energy regimes of QCD. This review shows recent results from Babar and Belle. Section 2 presents the status and prospects of measurements related to the angles and sides of the CKM Unitarity Triangle. Section 3 presents recent evidence of oscillations of neutral D mesons. The current experimental evidences of new states that might be aggregations of more than just a quark-antiquark pair is shown in section 4. Summary and outlook are given in Section 5.

Analysis of fundamental parameters for V477 Lyr

We analyze the photometric and spectroscopic observations of the young pre-cataclysmic variable (pre-CV) V477 Lyr. The masses of both binary components have been corrected by analyzing their radial velocity curves. We show that agreement between the theoretical and observed light curves of the object is possible for several sets of its physical parameters corresponding to the chosen temperature of the primary component. The final parameters of V477 Lyr have been established by comparing observational data with evolutionary tracks for planetary nebula nuclei. The derived effective temperature of the O subdwarf is higher than that estimated by analyzing the object’s ultraviolet spectra by more than 10000 K. This is in agreement with the analogous results obtained previously for the young pre-CVs V664 Cas and UU Sge. The secondary component of V477 Lyr has been proven to have a more than 25-fold luminosity excess compared to main-sequence stars of similar mass. Comparison of the physical parameters for the cool stars in young pre-CVs indicates that their luminosities do not correlate with the masses of the objects. The observed luminosity excesses in such stars show a close correlation with the post-common-envelope lifetime of the systems and should be investigated within the framework of the theory of their relaxation to the state of main-sequence stars.

Dynamics of Rotating Accretion Flows Irradiated by a Quasar

We study the axisymmetric, time-dependent hydrodynamics of rotating flows that are under the influence of supermassive black hole gravity and radiation from an accretion disk surrounding the black hole. This work is an extension of the earlier work presented by Proga, where nonrotating flows were studied. Here, we consider effects of rotation, a position-dependent radiation temperature, density at large radii, and uniform X-ray background radiation. As in the non-rotating case, the rotating flow settles into a configuration with two components (1) an equatorial inflow and (2) a bipolar inflow/outflow with the outflow leaving the system along the pole. However, with rotation the flow does not always reach a steady state. In addition, rotation reduces the outflow collimation and the outward flux of mass and kinetic energy. Moreover rotation increases the outward flux of the thermal energy and can lead to fragmentation and time-variability of the outflow. We also show that a position-dependent radiation temperature can significantly change the flow solution. In particular, the inflow in the equatorial region can be replaced by a thermally driven outflow. Generally, as it have been discussed and shown in the past, we find that self-consistently determined preheating/cooling from the quasar radiation can significantly reduce the rate at which the central BH is fed with matter. However, our results emphasize also a little appreciated feature. Namely, quasar radiation drives a non-spherical, multi-temperature and very dynamic flow. These effects become dominant for luminosities in excess of 0.01 of the Eddington luminosity.

The Moth: An Unusual Circumstellar Structure Associated with HD 61005

We present the discovery of an unusual spatially resolved circumstellar structure associated with the ≈90 Myr, nearby, G dwarf star HD 61005. Observations from the FEPS Spitzer Legacy Science survey reveal thermal emission in excess of expected stellar photospheric levels. Follow-up 0.1 resolution HST NICMOS coronagraphic images reveal scattered starlight ≤7 (~240 AU) from the occulted star (1.1 μm flux density =18 ± 3.3 mJy; and 0.77% ± 0.16% of the starlight). The extremely high near-IR scattering fraction and IR excess luminosity f = L_(IR)/L_* ≈2 × 10^(−3) suggests scattering particle sizes of order a ~<1.1 μm/2π ~ 0.2 μm , comparable to the blowout size (a ≈ 0.3 μm) due to radiation pressure from the star. Dust-scattered starlight is traced inward to an instrumental limit of ~10 AU. The structure exhibits a strong asymmetry about its morphological major axis but is mirror-symmetric about its minor axis.

Vertex detector concept for a SuperB factory

The two existing asymmetric operating B-factories, PEP-II and KEKB, have achieved very high luminosities at the level of 10 34 cm - 2 s - 1 producing impressive physics results. A SuperB factory capable of producing luminosities in excess of 10 36 cm - 2 s - 1 , will permit a program of precision measurements sensitive to New Physics (NP) beyond the Standard Model (SM), complementarily to the LHC experiments. Here we present the conceptual design of the vertex detector, focusing on the physics requirements for time-dependent analysis, according to different configurations for the energy asymmetry of the beams and of the radius of the innermost vertex detector layer. The possibility to reduce the radial dimension of the beam-pipe, down to ≃ 1 cm , allows to measure the first hit of the tracks very close to the interaction point, by adding a layer-0 to the present BABAR five-layer vertex detector configuration. Vertexing requirements for physics will be discussed, considering different technology solutions for the layer-0 sensors, such as striplet, MAPS and hybrid pixel detectors.

Charm Production Studies at CDF

The upgraded Collider Detector at Fermilab (CDF II) has a high bandwidth available for track based triggers. This capability, in conjunction with an integrated luminosity in excess of 1 fb −1 , enables detailed studies of charm hadron production. CDF is now releasing first measurements of the prompt charm meson pair cross-sections, which give access to QCD mechanisms by which charm quarks are produced in proton anti-proton collisions. Recent results on the spin alignment of J / ψ and ψ ( 2 S ) as well as on the relative production of the χ c 1 ( P 1 ) and χ c 2 ( 1 P ) challenge our understanding of the fragmentation of charm quarks into charmonium states.

The luminosity excess of OB stars in quasi-stationary X-ray binaries

We have found a mass—luminosity relation for the OB components of massive X-ray binaries that is a good estimator of the masses of these evolutionarily important binaries. Analysis of this relation showed a systematic luminosity excess of ≈1m for the OB components in these systems. No such excess was discovered for the evolutionarily related WR + O binaries, which also undergo mass exchange between their components and are the immediate precursors of X-ray binaries. A study of possible origins of the luminosity excess suggests that the most likely explanation is an X-ray luminosity related selection effect for massive X-ray binaries. Estimates show that the probability of detecting X-ray binary increases due to the enhancement of the stellar wind, which increases the efficiency of accretion by the relativistic companion while the optical component evolves along the main sequence. This can explain the magnitude of the observed luminosity excess and the position of the optical components of X-ray binaries in the luminosity—radius plane.

Angular momentum transport and disc morphology in smoothed particle hydrodynamics simulations of galaxy formation

We perform controlled N-body/smoothed particle hydrodynamics simulations of disc galaxy formation by cooling a rotating gaseous mass distribution inside equilibrium cuspy spherical and triaxial dark matter haloes. We systematically study the angular momentum transport and the disc morphology as we increase the number of dark matter and gas particles from 10 4 to 10 6 , and decrease the gravitational softening from 2 kpc to 50 pc. The angular momentum transport, disc morphology and radial profiles depend sensitively on force and mass resolution. At low resolution, similar to that used in most current cosmological simulations, the cold gas component has lost half of its initial angular momentum via different mechanisms. The angular momentum is transferred primarily to the hot halo component, by resolution-dependent hydrodynamical and gravitational torques; the latter arising from asymmetries in the mass distribution. In addition, disc particles can lose angular momentum while they are still in the hot phase by artificial viscosity. In the central disc, particles can transfer away over 99 per cent of their initial angular momentum due to spiral structure and/or the presence of a central bar. The strength of this transport also depends on force and mass resolution - large softening will suppress the bar instability, and low mass resolution enhances the spiral structure. This complex interplay between resolution and angular momentum transfer highlights the complexity of simulations of galaxy formation even in isolated haloes. With 10 6 gas and dark matter particles, disc particles lose only 10-20 per cent of their original angular momentum, yet we are unable to produce pure exponential profiles due to the steep density peak of baryons within the central kpc. We speculate that the central luminosity excess observed in many Sc-Sd galaxies may be due to star formation in gas that has been transported to the central regions by spiral patterns.

Unresolved X-ray background: clues on galactic nuclear activity at z &gt; 6

We study, by means of dedicated simulations of massive black hole build-up, the possibility to constraint the existence and nature of the active galactic nucleus (AGN) population at z ≥ 6 with available and planned X-ray and near-infrared space telescopes. We find that X-ray deep field observations can set important constraints to the faint-end of the AGN luminosity function at very high redshift. Planned X-ray telescopes should be able to detect AGN hosting black holes with masses down to ≥10 5 M ⊙ (i.e. X-ray luminosities in excess of 10 42 erg s -1 ), and can constrain the evolution of the population of massive black hole at early times (6 ≤ z ≤ 10). We find that this population of AGN should contribute substantially (∼25 per cent) to the unresolved fraction of the cosmic X-ray background in the 0.5-10 keV range, and that a significant fraction (∼3-4 per cent) of the total background intensity would remain unaccounted even after future X-ray observations. As byproduct, we compute the expected ultraviolet background from AGN at z ≥ 6, and we discuss the possible role of AGN in the reionization of the Universe at these early epochs, showing that AGN alone can provide enough ionizing photons only in the (improbable) case of an almost completely homogeneous intergalactic medium. Finally, we show that super-Eddington accretion, suggested by the observed quasi-stellar objects at z ≃ 6, must be a very rare event, confined to black holes living in the highest density peaks.

Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association

We present 4.5, 8, and 16um photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB Association. The data are used to investigate the frequency and properties of circumstellar disks around stars with masses between ~ 0.1 and 20 Msun at an age of ~ 5 Myr. We identify 35 stars that have emission at 8um or 16um in excess of the stellar photosphere. The lower mass stars (~ 0.1-1.2 Msun) appear surrounded by primordial optically thick disks based on the excess emission characteristics. Stars more massive than ~ 1.8 Msun have lower fractional excess luminosities suggesting that the inner ~ 10 AU of the disk has been largely depleted of primordial material. None of the G and F stars (~ 1.2-1.8 Msun) in our sample have an infrared excess at wavelengths <= 16um. These results indicate that the mechanisms for dispersing primordial optically thick disks operate less efficiently on average for low mass stars, and that longer time scales are available for the buildup of planetary systems in the terrestrial zone for stars with masses < 1 Msun.

Continuum-driven versus line-driven mass loss and the Eddington limit

AbstractBasic stellar structure dictates that stars of ∼ 100 M⊙ or more will be close to the Eddington limit, with luminosities in excess of 106 L⊙, and radiation pressure contributing prominently to the support against gravity. Although it is formally possible to generate static structure models of even more massive stars, recent studies of dense clusters show there is a sharp cutoff at masses above ∼ 150 M⊙. This talk examines the role of extreme mass loss is limiting the masses of stars, emphasizing in particular that continuum driving, possibly associated with structural instabilities of radiation dominated envelope, can lead to much stronger mass loss than is possible by the usual line-scattering mechanism of steady stellar winds.However, population studies of very young, dense stellar clusters now suggest quite strongly that there is a sharp cutoff at masses above ca. 150 M⊙ (see, e.g., the talk by Sally Oey, in this JD 05, p. 206). This is sometimes attributed to a mass limit on star formation by accretion processes, though there are competing formation scenarios by binary or cluster merging that would seem likely to lead to formation of even higher mass stars (see talks in JD14 and S237).So given the above rough coincidence of the observational upper mass limit with the Eddington-limit domain of radiation-pressure dominance, it seems associated instabilities in stellar structure might actually be a more important factor in this upper mass limit, leading to extreme mass loss in LBV and/or giant eruption events, much as inferred from circumstellar nebulae observed around high mass stars like eta Carinae and the Pistol star.

XMM-Newton observation of the Be/neutron star system RX J0146.9+6121: a soft X-ray excess in a low luminosity accreting pulsar

We report on the XMM-Newton observation of the Be/neutron star X-ray binary system RX J0146.9+6121, a long period (∼23 m) pulsar in the NGC 663 open cluster. The X-ray luminosity decreased by a factor of two compared to the last observation carried out in 1998, reaching a level of ∼1 × 10 34 erg s −1 , the lowest ever observed in this source. The spectral analysis reveals the presence of a significant excess at low energies over the main power-law spectral component. The soft excess can be described by a black-body spectrum with a temperature of about 1 keV and an emitting region with a radius of ∼140 m. Although the current data do not permit us to ascertain whether the soft excess is pulsed or not, its properties are consistent with emission from the neutron star polar cap. This is the third detection of a soft excess in a low luminosity (∼1 × 10 34 erg s −1 ) pulsar, the others being X Per and 3A 0535+262, suggesting that such a spectral component, observed to date in higher luminosity systems, is a common feature of accreting X-ray pulsars. The results of these three sources indicate that, in low luminosity systems, the soft excess tends to have a higher temperature and a smaller surface area than in the high luminosity ones.

The ACS Virgo Cluster Survey. VIII. The Nuclei of Early‐Type Galaxies

The ACS Virgo Cluster Survey is a Hubble Space Telescope program to obtain high-resolution imaging in widely separated bandpasses (F475W ≈ g and F850LP ≈ z) for 100 early-type members of the Virgo Cluster, spanning a range of 460 in blue luminosity. We use this large, homogenous data set to examine the innermost structure of these galaxies and to characterize the properties of their compact nuclei. We present a sharp upward revision in the frequency of nucleation in early-type galaxies brighter than M_B ≈ -15 (66% ≾ f_n ≾ 82%) and show that ground-based surveys underestimated the number of due to surface brightness selection effects, limited sensitivity and poor spatial resolution. We speculate that previously reported claims that nucleated dwarfs are more concentrated toward the center of Virgo than their nonnucleated counterparts may be an artifact of these selection effects. There is no clear evidence from the properties of the nuclei, or from the overall incidence of nucleation, for a change at M_B ~ -17.6, the traditional dividing point between dwarf and giant galaxies. There does, however, appear to be a fundamental transition at M_B ~ -20.5, in the sense that the brighter, core-Sersic galaxies lack resolved (stellar) nuclei. A search for that may be offset from the photocenters of their host galaxies reveals only five candidates with displacements of more than 05, all of which are in dwarf galaxies. In each case, however, the evidence suggests that these nuclei are, in fact, globular projected close to the galaxy photocenter. Working from a sample of 51 galaxies with prominent nuclei, we find a median half-light radius of (r_h) = 4.2 pc, with the sizes of individual ranging from 62 pc down to ≤2 pc (i.e., unresolved in our images) in about a half-dozen cases. Excluding these unresolved objects, the sizes are found to depend on luminosity according to the relation r_h α L ^(0.50±0.03). Because the large majority of are resolved, we can rule out low-level AGNs as an explanation for the luminosity excess in almost all cases. On average, the are ≈3.5 mag brighter than a typical globular cluster. Based on their broadband colors, the appear to have old to intermediate age stellar populations. The colors of the in galaxies fainter than M_B ≈ -17.6 are tightly correlated with their luminosities, and less so with the luminosities of their host galaxies, suggesting that their chemical enrichment histories were governed by local or internal factors. Comparing the to the nuclear clusters found in late-type spiral galaxies reveals a close match in terms of size, luminosity, and overall frequency. A formation mechanism that is rather insensitive to the detailed properties of the host galaxy properties is required to explain this ubiquity and homogeneity. The mean of the frequency function for the nucleus-to-galaxy luminosity ratio in our nucleated galaxies, (log η) = -2.49 ± 0.09 dex (σ = 0.59 ± 0.10), is indistinguishable from that of the SBH-to-bulge mass ratio, log(M/M_(gal) = -2.61 ± 0.07 dex (σ = 0.45 ± 0.09), calculated in 23 early-type galaxies with detected supermassive black holes (SBHs). We argue that the compact stellar found in many of our program galaxies are the low-mass counterparts of the SBHs detected in the bright galaxies. If this interpretation is correct, then one should think in terms of central massive objects—either SBHs or compact stellar nuclei—that accompany the formation of almost all early-type galaxies and contain a mean fraction ≈0.3% of the total bulge mass. In this view, SBHs would be the dominant formation mode above M_B ≈ -20.5.

New γ Cassiopeiae-like objects: X-ray and optical observations of SAO 49725 and HD 161103

A growing number of early Be stars exhibit X-ray luminosities that are intermediate between those typical of early type stars and those emitted by most Be/X-ray binaries in quiescence. We report on XMM-Newton observations of two such Be stars, SAO 49725 and HD 161103, which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity excess (LX ~ 1032-33 erg s-1) and the hardness of their X-ray spectra, which are both unusual for normal early type stars. An iron Kα complex is clearly detected in HD 161103 in which the H-like, He-like, and fluorescent components are resolved, while strong evidences also exist for the presence of similar features in SAO 49725. X-ray spectra can be equally well-fitted by a thermal plasma (mekal) with T ~ 108 K and solar abundances or by a power law + iron line model with photon index ~1.5–1.8, both with a soft thermal component with T ~ 107 K. The intensity of the fluorescence 6.4 keV line reflects the presence of large amounts of cold material close to the X-ray sources and strongly argues against accretion onto a companion neutron star in a large orbit. On the other hand, the probable thermal origin of the X-ray emission, as supported by the ionised iron lines, disagrees with those observed in all known Be/X-ray binaries, in which a non-thermal component is always required. Remarkably, the X-ray features are similar to those of white dwarves in several cataclysmic variables. There is no evidence of high frequency pulsations in neither of the two systems. However, a large oscillation in the light curve of HD 161103 with P ~ 3200 s is readily detected. The X-ray light curve of SAO 49725 exhibits clear variability by ~80% on time scales as short as ~1000 s. New optical observations provide updated spectral types (B0.5 III-Ve) and disclose a dense, large, and apparently stable circumstellar disc for both stars. The nature of the excess X-ray emission is discussed in light of the models proposed for γ Cas, magnetic disc-star interaction, or accretion onto a compact companion object – whether neutron star or white dwarf. These two new objects, added to similar cases discovered in XMM-Newton surveys, point to the emergence of a new class of γ Cas analogs.

Venus phase function and forward scattering from H 2SO 4

Ground-based and spacecraft photometry covering phase angles from 2° to 179° has been acquired in wavelength bands from blue to near infrared. An unexpected brightness surge is seen in the B and V bands when the disk of Venus is less than 2% illuminated. This excess luminosity appears to be the result of forward scattering from droplets of H 2SO 4 (sulfuric acid) in the high atmosphere of Venus. The fully sunlit brightness of Venus, adjusted to a distance of one AU from the Sun and observer, was found to be V = − 4.38 , and the corresponding geometric albedo is 67%. The phase integral is 1.35 and the resulting spherical albedo is 90%. Comparison between our data and photometry obtained over the past 50 years indicates a bias in the older photoelectric results, however atmospheric abundance variations suggest that brightness changes may have occurred too.

On the X-ray properties of OH megamaser sources: Chandra snapshot observations

We present Chandra snapshot observations for a sample of 7 sources selected from the Arecibo OH megamaser (OHM) survey at z ≈ 0.13 − 0.22 and with far-infrared luminosities in excess of 10 11 L⊙. In contrast with the known H2O megamasers, which are mostly associated with powerful Active Galactic Nuclei (AGN), the situation is far less clear for OHMs, which have been poorly studied in the X-ray band thus far. All of the observed sources are X-ray weak, with only one OHM, IRAS FSC 03521+0028 (z = 0.15), being detected by Chandra (with 5 counts). The results from this pilot program indicate that the X-ray emission, with luminosities of less than ≈ 10 42 erg s −1 , is consistent with that from star formation (as also suggested in some cases by the optical spectra) and low-luminosity AGN emission. If an AGN is present, its contribution to the broad-band emission of OHM galaxies is likely modest. Under reasonable assumptions about the intrinsic X-ray spectral shape, the observed count distribution from stacking analysis suggests absorption of ≈ 10 22 cm −2 .

Revealing the Supernova Remnant Population of M33 withChandra

We present results of a search for supernova remnants (SNRs) in archival Chandra images of M33. We have identified X-ray SNRs by comparing the list of Chandra X-ray sources in M33 with tabulations of SNR candidates identified from (1) elevated [S II]/Hα ratios in the optical and (2) radio spectral indices. In addition, we have searched for optical counterparts to soft sources in the Chandra images and X-ray SNR candidates identified in the XMM-Newton survey of M33. Of the 98 optically known SNRs in M33, 22 have been detected at >3 σ level in the soft band (0.35–1.1 keV). At least four of these SNR candidates are spatially extended based on a comparison of the data to simulated images of point sources. Aside from the optically matching SNRs, we have found one soft X-ray source in M33 that exhibits no optical emission and is coincident with a known radio source. The radio spectral index of this source is consistent with particle acceleration in shocks, leading us to suggest that it is a nonradiative SNR. We have also found new optical counterparts to two soft X-ray SNRs in M33. These counterparts exhibit enhanced [S II]/Hα ratios characteristic of radiative shocks. Pending confirmation from optical spectroscopy, the identification of these two optical counterparts increases the total number of known optically emitting SNRs in M33 to 100. This brings the total number of identified SNRs with X-ray counterparts, including those exclusively detected by the XMM-Newton survey of M33, to 37 SNRs. We find that while there are a similar number of confirmed X-ray SNRs in M33 and the LMC with X-ray luminosities in excess of 1035 ergs s-1, nearly 40% of the LMC SNRs are brighter than 1036 ergs s-1, while only 13% of the M33 sample exceed this luminosity. Including X-ray SNR candidates from the XMM-Newton survey (objects lacking optical counterparts) increases the fraction of M33 SNRs brighter than 1036 ergs s-1 to 22%, still only half the LMC fraction. The differences in luminosity distributions cannot be fully explained by uncertainty in spectral model parameters and are not fully accounted for by abundance differences between the galaxies.

An XMM-Newton observation of the multiple system HD 167971 (O5-8V + O5-8V + (O8I)) and the young open cluster NGC 6604

We discuss the results of two XMM-Newton observations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5-8V + O5-8V + (O8I)). The soft part of the EPIC spectrum of this system is thermal with typical temperatures of about 2 × 10 6 to 9 × 10 6 K. The nature (thermal vs. non-thermal) of the hard part of the spectrum is not unambiguously revealed by our data. If the emission is thermal, the high temperature of the plasma (∼2.3 × 10 7 to 4.6 × 10 7 K) would be typical of what should be expected from a wind-wind interaction zone within a long period binary system. This emission could arise from an interaction between the combined winds of the O5-8V + O5-8V close binary system and that of the more distant O8I companion. Assuming instead that the hard part of the spectrum is non-thermal, the photon index would be rather steep (∼3). Moreover, a marginal variability between our two XMM-Newton pointings could be attributed to an eclipse of the O5-8V + O5-8V system. The overall X-ray luminosity points to a significant X-ray luminosity excess of about a factor 4 possibly due to colliding winds. Considering HD 167971 along with several recent X-ray and radio observations, we propose that the simultaneous observation of non-thermal radiation in the X-ray (below 10.0 keV) and radio domains appears rather unlikely. Our investigation of our XMM-Newton data of NGC 6604 reveals a rather sparse distribution of X-ray emitters. Including the two bright non-thermal radio emitters HD 168112 and HD 167971, we present a list of 31 X-ray sources along with the results of the cross-correlation with optical and infrared catalogues. A more complete spectral analysis is presented for the brightest X-ray sources. Some of the members of NGC 6604 present some characteristics suggesting they may be pre-main sequence star candidates.

Mixed-Morphology Pairs as a Breeding Ground for Active Nuclei

Mixed-morphology pairs offer a simplification of the interaction equation that involves a gas-rich fast rotator paired with a gas-poor slow rotator. In past low-resolution IRAS studies it was assumed that the bulk of the far-infrared (FIR) emission originated in the spiral component. However, our Infrared Space Observatory studies revealed a surprising number of early-type components with significant IR emission, some of which turned out to show active nuclei. This motivated us to look at the current statistics of active nuclei in mixed pairs using the radio-FIR continuum correlation as a diagnostic. We find a clear excess of early-type components with radio continuum emission and active nuclei. We suggest that they arise more often in mixed pairs via cross-fueling of gas from the spiral companion. This fuel is more efficiently channeled into the nucleus of the slow-rotating receptor. In a sample of 112 mixed-morphology pairs from the Karachentsev catalog, we find that about 25%–30% of detected mixed pairs show a displacement from the radio-FIR relation defined by normal star-forming galaxies. The latter objects show excess radio continuum emission, while others extend the relation to unusually high radio and FIR flux levels. Many of the outliers or extreme emitters involve an early-type component with an active nucleus. The paired E/S0 galaxies in the sample exhibit a significant excess detection fraction and a marginal excess luminosity distribution compared to those of isolated unpaired E/S0 galaxies.

The Origin of the Spatial Distribution of X-Ray-luminous Active Galactic Nuclei in Massive Galaxy Clusters

We study the spatial distribution of a 95% complete sample of 508 X-ray point sources (XPSs) detected in the 0.5-2.0 keV band in Chandra ACIS-I observations of 51 massive galaxy clusters found in the MAssive Cluster Survey (MACS). Covering the redshift range z = 0.3-0.7, our cluster sample is statistically complete and comprises all MACS clusters with X-ray luminosities in excess of 4.5 × 1044 ergs s-1 (0.1-2.4 keV, h0 = 0.7, ΛCDM). Also studied are 20 control fields that do not contain clusters. We find the XPS surface density, computed in the cluster rest frame, to exhibit a pronounced excess within 3.5 Mpc of the cluster centers. The excess, believed to be caused by active galactic nuclei (AGNs) in the cluster, is significant at the 8.0 σ confidence level compared to the XPS density observed at the field edges. No significant central excess is found in the control fields. To investigate the physical origin of the AGN excess, we study the radial AGN density profile for a subset of 24 virialized clusters. We find a pronounced central spike (r < 0.5 Mpc), followed by a depletion region at about 1.5 Mpc, and a broad secondary excess centered at approximately the virial radius of the host clusters (≈2.5 Mpc). We present evidence that the central AGN excess reflects increased nuclear activity triggered by close encounters between infalling galaxies and the giant cD-type elliptical galaxy occupying the very cluster center. By contrast, the secondary excess at the cluster-field interface is likely due to black holes being fueled by galaxy mergers. In-depth spectroscopic and photometric follow-up observations of the optical counterparts of the XPSs in a subset of our sample are being conducted to confirm this picture.