Nuclear Luminosity Research Articles

Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries

The energy transfer of W UMa contact binaries and its effects on the secondary in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) and the relative energy transfer rates, i.e. U1, the ratio of the transferred luminosity to the surface luminosity of the primary and U2, the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U1 vs q and U2 vs q) are derived. Although these curves can reflect the distribution of U1 vs q and U2 vs q, some observational systems are significantly deviated from these curves. It is mainly resulted from the difference in the effective temperatures of the components in W UMa systems.The radius and the density of the secondary are related to the relative energy tran-sfer rate U2: the higher is U2, the greater is the expansion and the lower is the density of the secondaries in W UMa systems. The temperature difference of W UMa binary components is correlated with the relative energy transfer rate U1 and decreases with increasing U1. This might suggest that there is a thermal coupling between two components in W UMa contact binaries, and that the classif-ication of W UMa contact binaries into A- or W-types depends on the energy tran-sfer from the primary to the secondary. The temperature difference of W UMa bin-ary components is poorly correlated with the mass of the primary. This suggests that the properties of the common envelope of W UMa contact binaries might not have a significant effect on the energy transfer between two components.

A CENSUS OF X-RAY NUCLEAR ACTIVITY IN NEARBY GALAXIES

We have studied the X-ray nuclear activity of 187 nearby (distance < 15 Mpc) galaxies observed with Chandra/ACIS. We found that 86 of them have a point-like X-ray core, consistent with an accreting black hole (BH). We argue that the majority of them are nuclear BHs, rather than X-ray binaries. The fraction of galaxies with an X-ray detected nuclear BH is higher (~60 per cent) for ellipticals and early-type spirals (E to Sb), and lower (~30 per cent) for late-type spirals (Sc to Sm). There is no preferential association of X-ray cores with a large-scale bar; in fact, strongly barred galaxies appear to have slightly lower detection fraction and luminosity for their nuclear X-ray sources, compared with non-barred or weakly barred galaxies of similar Hubble types. The cumulative luminosity distribution of the nuclear sources in the 0.3-8 keV band is a power-law with slope ~-0.5, from ~2 x 10^{38} erg/s to ~10^{42} erg/s. The Eddington ratio is lower for ellipticals (L_{X}/L_{Edd} ~ 10^{-8}) and higher for late-type spirals (up to L_{X}/L_{Edd} ~ 10^{-4}), but in all cases, the accretion rate is low enough to be in the radiatively-inefficient regime. The intrinsic NH is generally low, especially for the less luminous sources: there appear to be no Type-2 nuclear BHs at luminosities <~ 10^{39} erg/s. The lack of a dusty torus or of other sources of intrinsic absorption (e.g., an optically-thick disk wind) may be directly related to the lack of a standard accretion disk around those faint nuclear BHs. The fraction of obscured sources increases with the nuclear BH luminosity: 2/3 of the sources with L_{X} > 10^{40} erg/s have a fitted NH > 10^{22} cm^{-2}. This is contrary to the declining trend of the obscured fraction with increasing luminosities, observed in more luminous AGN and quasars.

Chandra observations of the H2O megamaser galaxy Mrk1210

We present the first Chandra X-ray observations of the H2O megamaser galaxy Mrk1210 (UGC4203), a Seyfert 2 galaxy at an approximate distance of D ∼ 57.6 Mpc. The Chandra X-ray image, with by far the highest angular resolution (∼1″), displays an unresolved compact core toward the nuclear region of Mrk1210. Comparisons with the previous X-ray observations in the nuclear emission and the spectral shape indicate a fairly stable phase between 2001 (BeppoSAX and XMM-Newton) and 2004 (Chandra) after a dramatic variation since 1995 (ASCA). The best-fit model of Chandra X-ray spectrum consists of two components. The soft scattered component can be best fitted by a moderately absorbed power-law model adding a spectral line at ∼0.9 keV (possibly a Ne-Kα fluorescent line), while the hard nuclear component can be well reproduced by a heavily absorbed power-law model (N H ∼ 2×1023 cm−2) with an additional line at ∼6.19 keV (close to the Fe-Kα fluorescent line). The derived absorption-corrected X-ray luminosity implies that the dramatic variation of spectral properties is caused by significant changes of the absorbing column density along the line-of-sight, while the intrinsic nuclear X-ray luminosity remains stable. In this case, the absorbers should be anisotropic and its size can be constrained to be less than 0.0013 pc. In addition, we also estimate the mass of central engine, the disk radius and the accretion rate of the accretion disk to be 107.12±0.31 M ⊙, ∼1 pc and 0.006, respectively.

AN ENERGETIC AGN OUTBURST POWERED BY A RAPIDLY SPINNING SUPERMASSIVE BLACK HOLE OR AN ACCRETING ULTRAMASSIVE BLACK HOLE

Powering the 10^62 erg nuclear outburst in the MS0735.6+7421 cluster central galaxy by accretion implies that its supermassive black hole (SMBH) grew by ~6x10^8 solar masses over the past 100 Myr. We place upper limits on the amount of cold gas and star formation near the nucleus of <10^9 solar masses and <2 solar masses per year, respectively. These limits imply that an implausibly large fraction of the preexisting cold gas in the bulge must have been consumed by its SMBH at the rate of ~3-5 solar masses per year while leaving no trace of star formation. Such a high accretion rate would be difficult to maintain by stellar accretion or the Bondi mechanism, unless the black hole mass approaches 10^11 solar masses. Its feeble nuclear luminosities in the UV, I, and X-ray bands compared to its enormous mechanical power are inconsistent with rapid accretion onto a ~5x10^9 solar mass black hole. We suggest instead that the AGN outburst is powered by a rapidly-spinning black hole. A maximally-spinning, 10^9 solar mass black hole contains enough rotational energy, ~10^62 erg, to quench a cooling flow over its lifetime and to contribute significantly to the excess entropy found in the hot atmospheres of groups and clusters. Two modes of AGN feedback may be quenching star formation in elliptical galaxies centered in cooling halos at late times. An accretion mode that operates in gas-rich systems, and a spin mode operating at modest accretion rates. The spin conjecture may be avoided in MS0735 by appealing to Bondi accretion onto a central black hole whose mass greatly exceeds 10^10 solar mass. The host galaxy's unusually large, 3.8 kpc stellar core radius (light deficit) may witness the presence of an ultramassive black hole.

Downsizing of supermassive black holes from the SDSS quasar survey

Starting from the ~50000 quasars of the Sloan Digital Sky Survey for which MgII line width and 3000 A monochromatic flux are available, we aim to study the dependence of the mass of active black holes on redshift. We focus on the observed distribution in the FWHM - nuclear luminosity plane, which can be reproduced at all redshifts assuming a limiting BH mass, a maximum Eddington ratio and a minimum luminosity (due to the survey flux limit). We study the z-dependence of the best fit parameters of assumed distributions at increasing redshift and find that the maximum mass of the quasar population evolves as log[M_BH(max)/M_Sun]~0.3z+9, while the maximum Eddington ratio (~0.45) is practically independent of cosmic time. These results are unaffected by the Malmquist bias.

Clues on black hole feedback from simulated and observed X-ray properties of elliptical galaxies

The centers of elliptical galaxies host supermassive black holes that significantly affect the surrounding interstellar medium through feedback resulting from the accretion process. The evolution of this gas and of the nuclear emission during the galaxies’ lifetime has been studied recently with high-resolution hydrodynamical simulations. These included gas cooling and heating specific for an average AGN spectral energy distribution, a radiative efficiency declining at low mass accretion rates, and mechanical coupling between the hot gas and AGN winds. Here, we present a short summary of the observational properties resulting from the simulations, focussing on (1) the nuclear luminosity; (2) the global luminosity and temperature of the hot gas; (3) its temperature profile and X-ray brightness profile. These properties are compared with those of galaxies of the local universe, pointing out the successes of the adopted feedback and the needs for new input in the simulations.

Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

Context. Supermassive black holes with masses of 10 5 − 10 9 M⊙ are believed to inhabit most, if not all, nuclear regions of g alaxies, and both observational evidence and theoretical models suggest a scenario where galaxy and black hole evolution are tightly related. Luminous AGNs are usually selected by their non-stellar colours or their X-ray emission. Colour selection cannot be used to select low-luminosity AGNs, since their emission is dominated by the host galaxy. Objects with low X-ray to optical ratio escape even the deepest X-ray surveys performed so far. In a previous study we presented a sample of candidates selected through optical variability in the Chandra Deep Field South, where repeated optical observations were performed in the framework of the STRESS supernova survey. Aims. The analysis is devoted to breaking down the sample in AGNs, starburst galaxies, and low-ionisation narrow-emission li ne objects, to providing new information about the possible dependence of the emission mechanisms on nuclear luminosity and blackhole mass, and eventually studying the evolution in cosmic time of the different populations. Methods. We obtained new optical spectroscopy for a sample of variability selected candidates with the ESO NTT telescope. We analysed the new spectra, together with those existing in the literature and studied the distribution of the objects in U− B and B− V colours, optical and X-ray luminosity, and variability amplitude. Results. A large fraction (17/27) of the observed candidates are broad-line luminous AGNs, confirming the e ffi ciency of variability in detecting quasars. We detect : i) extended objects which would have escaped the colour selection and ii) objects of very low X-ray to optical ratio, in a few cases without any X-ray detection at all. Several objects resulted to be narrow-emission line g alaxies where variability indicates nuclear activity, while no emission lines were detected in others. Some of these galaxies have variability and X-ray to optical ratio close to active galactic nuclei, whil e others have much lower variability and X-ray to optical ratio. This result can be explained by the dilution of the nuclear light due to the host galaxy. Conclusions. Our results demonstrate the effectiveness of supernova search programmes to detect large samples of low-luminosity AGNs. A sizable fraction of the AGN in our variability sample had escaped X-ray detection (5/47) and/or colour selection (9/48). Spectroscopic follow-up to fainter flux limits is strongly e ncouraged.

The X-ray variability and the near-IR to X-ray spectral energy distribution of four low luminosity Seyfert 1 galaxies

Context. We present the results from a study of the X-ray variability and the near-IR to X-ray spectral energy distribution of four low-luminosity, Seyfert 1 galaxies. Aims. We compared their variability amplitude and broad band spectrum with those of more luminous AGN in order to investigate whether accretion in low-luminosity AGN operates as in their luminous counterparts. Methods. We used archival XMM-Newton and, in two cases, ASCA data to estimate their X-ray variability amplitude and determine their X-ray spectral shape and luminosity. We also used archival HST data to measure their optical nuclear luminosity, and near-IR measurements from the literature, in order to construct their near-IR to X-ray spectra. Results. The X-ray variability amplitude of the four Seyferts is what one would expect, given their black hole masses. Their near-IR to X-ray spectrum has the same shape as the spectrum of quasars that are 10 2 –10 5 times more luminous. Conclusions. The objects in our sample are optically classified as Seyfert 1–1.5. This implies that they host a relatively unobscured AGN-like nucleus. They are also of low luminosity and accrete at a low rate. They are therefore good candidates to detect radiation from an inefficient accretion process. However, our results suggest that they are similar to AGN that are 10 2 –10 5 times more luminous. The combination of a “radiative efficient accretion disc plus an X-ray producing hot corona” may persist at low accretion rates as well.

Difference in Narrow-Emission-Line Spectra of Seyfert 1 and 2 Galaxies

In the unification scheme of Seyfert galaxies, a dusty torus blocks the continuum source and broad line region in Seyfert 2 galaxies. However it is not clear whether or not and to what extent the torus affects the narrow line spectra. In this paper, we show that Seyfert 1 and Seyfert 2 galaxies have different distributions on the [OIII]/H$\beta $ vs [NII]/H$\alpha$ diagram (BPT diagram) for narrow lines. Seyfert 2 galaxies display a clear left boundary on the BPT diagram and only 7.3% of them lie on the left. By contrast, Seyfert 1 galaxies do not show such a cutoff and 33.0% of them stand on the left side of the boundary. Among Seyfert 1 galaxies, the distribution varies with the extinction to broad lines. As the extinction increases, the distribution on BPT diagram moves to larger [NII]/H$\alpha$ value. We interpret this as an evidence for the obscuration of inner dense narrow line region by the dusty torus. We also demonstrate that the [OIII] and broad line luminosity correlation depends on the extinction of broad lines in the way that high extinction objects have lower uncorrected [OIII] luminosities, suggesting that [OIII] is partially obscured in these objects. Therefore, using [OIII] as an indicator for the nuclear luminosity will systematically under-estimate the nuclear luminosity of Seyfert 2 galaxies.

Correlations of the IR Luminosity and Eddington Ratio with a Hard X-Ray-Selected Sample of Active Galactic Nuclei

We use the Swift Burst Alert Telescope (BAT) sample of hard X-ray-selected active galactic nuclei (AGN) with a median redshift of 0.03 and the 2MASS J- and K-band photometry to examine the correlation of hard X-ray emission to Eddington ratio as well as the relationship of the J- and K-band nuclear luminosity to the hard X-ray luminosity. The BAT sample is almost unbiased by the effects of obscuration and thus offers the first large unbiased sample for the examination of correlations between different wavelength bands. We find that the near-IR nuclear J- and K-band luminosity is related to the BAT (14-195 keV) luminosity over a factor of 103 in luminosity (LIR ≈ L1.25BAT) and thus is unlikely to be due to dust. We also find that the Eddington ratio is proportional to the X-ray luminosity. This new result should be a strong constraint on models of the formation of the broadband continuum.

Measuring the Fraction of Obscured Quasars by the Infrared Luminosity of Unobscured Quasars

Recent work has suggested that the fraction of obscured AGNs declines with increasing luminosity, but it has been difficult to quantify this trend. Here we attempt to measure this fraction as a function of luminosity by studying the ratio of mid-infrared to intrinsic nuclear bolometric luminosity in unobscured AGNs. Because the mid-infrared is created by dust reprocessing of shorter wavelength nuclear light, this ratio is a diagnostic of -->fobsc, the fraction of solid angle around the nucleus covered by obscuring matter. In order to eliminate possible redshift dependences while also achieving a large dynamic range in luminosity, we have collected archival 24 μm MIPS photometry from objects with -->z ~ 1 in the Sloan Digital Sky Survey, the Great Observatories Origins Deep Survey, and the Cosmic Evolution Survey. To measure the bolometric luminosity for each object, we used archival optical data supplemented by GALEX data. We find that the mean ratio of 24 μm to bolometric luminosity decreases by a factor of ~3 in the -->Lbol = 1044–3 × 1047 ergs s -->−1 range, but there is also a large scatter at constant -->Lbol. Using radiation transfer solutions for model geometries, we show how the IR/bolometric ratio relates to -->fobsc and compare these values with those obtained from samples of X-ray-selected AGNs. Although we find approximate agreement, our method indicates somewhat higher values of -->fobsc, particularly in the middle range of luminosities, suggesting that there may be a significant number of heavily obscured AGNs missed by X-ray surveys.

Prevalence of Tidal Interactions among Local Seyfert Galaxies

No mechanisms have hitherto been conclusively demonstrated to be responsible for initiating optically luminous nuclear (Seyfert) activity in local disk galaxies. Only a small minority of such galaxies are visibly disturbed in optical starlight, with the observed disturbances being at best marginally stronger than those found in matched samples of inactive galaxies. Here we report the first systematic study of an optically selected sample of 23 active galaxies in atomic hydrogen (H I) gas, which is the most sensitive and enduring tracer known of tidal interactions. Eighteen of these galaxies are (generally) classified as Seyferts, with over half (and perhaps all) having [O III] luminosities within 2 orders of magnitude of QSOs. Only ~28% of these Seyfert galaxies are visibly disturbed in optical DSS2 images. By contrast, ~94% of the same galaxies are disturbed in H I, in nearly all cases not just spatially but also kinematically on galactic (20 kpc) scales. In at least ~67% and perhaps up to ~94% of cases, the observed H I disturbances can be traced to tidal interactions with neighboring galaxies detected also in H I. The majority of these neighboring galaxies have projected separations of 100 kpc and differ in radial velocities by 100 km s–1 from their respective Seyfert galaxies, and many have optical luminosities ranging from the Small to Large Magellanic Clouds. In a companion paper we show that only ~15% of a matched control sample of inactive galaxies display comparable H I disturbances. Our results suggest that (1) most Seyfert galaxies (with high nuclear luminosities) have experienced tidal interactions in the recent past and (2) in most cases these tidal interactions are responsible for initiating events that lead to their nuclear activity.

The Fundamental Plane of QSOs and the Relationship between Host and Nucleus

We present results from an archival study of 70 medium-redshift QSOs observed with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The QSOs have magnitudes M_V <= -23 (total nuclear plus host light) and redshifts $0.06 <= z <= 0.46$. The aim of the present study is to investigate the connections between the nuclear and host properties of QSOs, using high-resolution images and removing the central point source to reveal the host structure. We confirm that more luminous QSO nuclei are found in more luminous host galaxies. Using central black hole masses from the literature, we find that nuclear luminosity also generally increases with black hole mass, but it is not tightly correlated. Nuclear luminosities range from 2.3% to 200% of the Eddington limit. Those in elliptical hosts cover the range fairly evenly, while those in spirals are clustered near the Eddington limit. Using a principal components analysis, we find a kind of fundamental plane relating the nuclear luminosity to the size and effective surface magnitude of the bulge. Using optical nuclear luminosity, this relationship explains 96.1% of the variance in the overall sample, while another version of the relationship uses x-ray nuclear luminosity and explains 95.2% of the variance. The form of this QSO fundamental plane shows similarities to the well-studied fundamental plane of elliptical galaxies, and we examine the possible relationship between them as well as the difficulties involved in establishing this connection.

Nuclear/Circumnuclear Starbursts and Active Galactic Nucleus Mass Accretion in Seyfert Galaxies

We investigated the correlation between nuclear/circumnuclear starbursts around active galactic nuclei (AGNs) and the AGN activities for 43 Seyfert galaxies in the CfA and 12 μm samples. We found that the circumnuclear starburst luminosity, as well as the nuclear starburst luminosity, is positively correlated with the AGN luminosity. Moreover, the nuclear starburst luminosity is more strongly correlated with the AGN luminosity normalized with the AGN Eddington luminosity than is the circumnuclear starburst luminosity. This implies that starbursts nearer the AGN could have a greater effect on AGN mass accretion. We also discuss these results from the viewpoint of the radiation effects from starbursts and sequential starbursts.

Evolution of chemical abundances in Seyfert galaxies

Aims. To compute the chemical evolution of spiral bulges hosting Seyfert nuclei, based on updated chemical and spectro-photometrical evolution models for the bulge of our Galaxy, to make predictions about other quantities measured in Seyferts, and to model the photometric features of local bulges. The chemical evolution model contains updated and detailed calculations of the Galactic potential and of the feedback from the central supermassive black hole, and the spectro-photometric model covers a wide range of stellar ages and metallicities. Methods. We computed the evolution of bulges in the mass range 2× 10 9 − 10 11 M⊙ by scaling the effi ciency of star formation and the bulge scalelength as in the inverse-wind scenario for el liptical galaxies, and considering an Eddington limited accretion onto the central supermassive black hole. Results. We successfully reproduced the observed relation between the mass of the black hole and that of the host bulge. The observed nuclear bolometric luminosity emitted by the supermassive black hole is reproduced only at high redshift or for the most massive bulges; in the other cases, at z≃ 0 a rejuvenation mechanism is necessary. The energy provided by the black hole is in most cases not significant in the triggering of the galactic wind. The observed high star formation rates and metal overabundances are easily achieved, as well as the constancy of chemical abundances with the redshift and the bulge present-day colours. Those results are not affected if we vary the index of the stellar IMF from x = 0.95 to x = 1.35; a steeper IMF is instead required in order to reproduce the colour-magnitude relation and the present K-band luminosity of the bulge. Conclusions. We show that the chemical evolution of the host bulge, with a short formation timescale of∼ 0.1 Gyr, a rather high effi ciency of star formation ranging from 11 to 50 Gyr −1 according to the bulge mass and an IMF flatter with respect to t he solar neighbourhood, combined with the accretion onto the black hole is suffi cient to explain the main observed features of Seyfert galaxies.

IC 5063: AGN driven outflow of warm and cold gas

We present new ATCA 17- and 24- GHz radio images and ESO- NTT optical spectra of the radio- loud Seyfert galaxy IC 5063, the first galaxy in which a fast (similar to 600 km s(-1)) outflow of neutral hydrogen was discovered. The new radio data confirm the triple radio structure with a central, unresolved flat- spectrum core and two resolved radio lobes with steep spectral index. This implies that the previously detected fast outflow of neutral gas is occurring off- nucleus, near a radio lobe about 0.5 kpc from the core. The ionised gas shows highly complex kinematics in the region co- spatial with the radio emission. Broad and blueshifted (similar to 500 km s(-1)) emission is observed in the region of the radio lobe, at the same location as the blueshifted Hi absorption. The velocity of the ionised outflow is similar to the one found in Hi. The first order correspondence between the radio and optical properties suggests that the outflow is driven by the interaction between the radio jet and the ISM. However, despite the high outflow velocities, no evidence is found for the ionisation of the gas being due to fast shocks in the region of the outflow, indicating that photoionisation from the AGN is likely to be the dominant ionisation mechanism. The outflow rate of the warm ( ionised) gas is small compared to that of the cold gas, similar to what is found in other radio galaxies. The mass outflow rate associated with the Hi is in the same range as for mild starburst- driven superwinds in ULIRGs. However, in IC 5063, the AGN- driven outflow appears to be limited to the inner kpc region of the galaxy. The kinetic power associated with the Hi outflow is a small fraction (a few x 10(-4)) of the Eddington luminosity of the galaxy but is a significant fraction (similar to 0.1) of the nuclear bolometric luminosity. In IC 5063, the observed outflows may have sufficient kinetic power to have a significant impact on the evolution of the ISM in the host galaxy.

Cosmic Evolution of Black Holes and Spheroids. II. Scaling Relations atz = 0.36

We use high-resolution images obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope to determine morphology, nuclear luminosity, and structural parameters of the spheroidal component for a sample of 20 Seyfert galaxies atz = 0.36. We combine these measurements with spectroscopic information from the Keck Telescope to determine the black hole mass-spheroid luminosity relation (MBH-LB), the fundamental plane (FP) of the host galaxies, and the black hole mass-spheroid velocity dispersion relation (MBH-σ). The FP is consistent with that of inactive spheroids at comparable redshifts. Assuming pure luminosity evolution, we find that the host spheroids had smaller luminosity and stellar velocity dispersion than today for a fixed MBH. The offsets correspond to Δ log LB,0 = 0.40 ± 0.11 ± 0.15 (Δlog MBH= 0.51 ± 0.14 ± 0.19) and Δloge σ = 0.13 ± 0.03 ± 0.05 (Δlog MBH = 0.54 ± 0.12 ± 0.21), respectively, for the MBH-L and M BH-σ relations (the double error bars indicate random and ystematic uncertainties, respectively). A detailed analysis of known systematic errors and selection effects shows that they cannot account for the observed offset. We conclude that the data are inconsistent with pure luminosity evolution and the existence of universal and tight scaling relations. In order to obey the three local scaling relations by z = 0, assuming no significant black hole growth, the distant spheroids have to grow their stellar mass by approximately 60% (Δ log Msph = 0.20 ± 0.14) in the next 4 billion years, while preserving their size and holding their stellar mass-to-light ratio approximately constant. The measured evolution can be expressed as MBH/Msph ∝ (1 + z) 1.5±1.0, consistent with black holes of a few × 10 8 M⊙ completing their growth before their host galaxies. Based on the disturbed morphologies of a fraction of the sample (6/20), we suggest collisional mergers with disk-dominated systems as the physical mechanism driving the evolution. © 2007. The American Astronomical Society. All rights reserved.

Black Hole Masses and Eddington Ratios of AGNs atz&lt; 1: Evidence of Retriggering for a Representative Sample of X‐Ray‐selected AGNs

WeestimatedblackholemassesandEddingtonratiosforasampleof X-ray-selectedactivegalacticnuclei(AGNs) inthefieldscoveredbytheGreatObservatoryOriginsDeepSurvey(GOODS).Thespannedrangesinredshift(0:4 < z < 1) and hard X-ray luminosity(10 42 PLX P4 ; 10 43 ergss � 1 )allowus tostudy arepresentative subsampleofthe main contributors to the 2Y10 keV X-ray background. Nuclear and bulge magnitudes in four bands have been measured via a two-dimensional decomposition applied toHSTACS images. Using the black hole versus bulge luminosity relation and the intrinsic nuclear emission, we derived the black hole mass and the AGN bolometric luminosity. Wefindinoursamplethat(1)theX-rayYtoYopticalindicesarelargerthaninopticallyselectedQSOs,asexpecteddue to the X-ray selection); (2) the X-ray bolometric corrections are generally small, suggesting a decrease with the nuclear luminosity; (3) the Eddington ratios are about a factor 10 below the values found at higher redshift and luminosity; (4) the central black holes have rather largemasses; and (5) at least for z P0:8, a scarceness of black holes with

Chemical evolution of Seyfert galaxies

AbstractWe computed the chemical evolution of Seyfert galaxies, residing in spiral bulges, based on an updated model for the Milky Way bulge with updated calculations of the Galactic potential and of the feedback from the central supermassive black hole (BH) in a spherical approximation. We followed the evolution of bulges of masses 2 × 109 − 1011M⊙ by scaling the star-formation efficiency and the bulge scalelenght as in the inverse-wind scenario for ellipticals. We successfully reproduced the observed relation between the BH mass and that of the host bulge, and the observed peak nuclear bolometric luminosity. The observed metal overabundances are easily achieved, as well as the constancy of chemical abundances with the redshift.

The Discovery of an Active Galactic Nucleus in the Late-Type Galaxy NGC 3621: Spitzer Spectroscopic Observations

We report the discovery of an active galactic nucleus (AGN) in the nearby SAd galaxy NGC 3621 using Spitzer high spectral resolution observations. These observations reveal the presence of [Ne V] 14 and 24 μm emission that is centrally concentrated and peaks at the position of the near-infrared nucleus. Using the [Ne V] line luminosity, we estimate that the nuclear bolometric luminosity of the AGN is ~5 × 1041 ergs s-1, which, based on the Eddington limit, corresponds to a lower mass limit of the black hole of ~4 × 103 M☉. Using an order-of-magnitude estimate for the bulge mass based on the Hubble type of the galaxy, we find that this lower mass limit does not put a strain on the well-known relationship between the black hole mass and the host galaxy's stellar velocity dispersion established in predominantly early-type galaxies. Multiwavelength follow-up observations of NGC 3621 are required to obtain more precise estimates of the bulge mass, black hole mass, accretion rate, and nuclear bolometric luminosity. The discovery reported here adds to the growing evidence that a black hole can form and grow in a galaxy with no or minimal bulge.