15715110
Suppressed star formation in circumnuclear regions in seyfert galaxies
Feedback from black hole activity is widely believed to play a key role in regulating star formation and black hole growth. A long-standing issue is the relation between star formation and the fueling of the supermassive black holes in active galactic nuclei (AGNs). We compile a sample of 57 Seyfert galaxies to tackle this issue. We estimate the surface densities of gas and star formation rates in circumnuclear regions (CNRs). Comparing them with the well-known Kennicutt-Schmidt (K-S) law, we find that the star formation rates (SFRs) in the CNRs of most Seyfert galaxies are suppressed in this sample. Feedback is suggested to explain the suppressed SFRs.
16064481
The central engines of radio-loud quasars
We have assembled a sample of 37 radio-loud quasars that have been imaged with the Hubble Space Telescopein order to investigate their black hole masses, accretion rates, and the structure of their accretion disks. The black hole masses were estimated from the luminosities of the host galaxies, and the accretion powers were extrapolated from the emission-line luminosities. The majority of the quasars have masses in the range MBH 10 8 10 9 M. Their accretion rates, ˙ M 0:01 1 times the Eddington rate, suggest that most of the objects possess standard optically thick, geometrically thin accretion disks, in some cases perhaps accompanied by an optically thin advection-dominated component. The coexistence of strong radio emission and a standard disk conflicts with recent models for jet formation. We discuss modifications of the standard model that can resolve this discrepancy. We find there is a strong correlation between the accretion rate and the extended radio luminosity. This lends support to the idea that the extended radio emission is somehow linked to the accretion disk. Lastly, we combine the present sample of radio-loud quasars with the sample of BL Lac objects studied by Wang et al. (2002) to reevaluate the unification picture for radio-loud active galactic nuclei. Consistent with current ideas for the unification of radio-loud sources, we find that flat-spectrum radio quasars and FR II radio galaxies indeed seem to belong to the same population, as do BL Lac objects and FR I radio galaxies on the opposite end of the luminosity spectrum. However, some members of the low frequency- peaked BL Lac objects may be more closely associated with FR II rather than FR I radio galaxies. We describe how the various subclasses of radio-loud sources can be viewed as a continuous sequence of varying accretion rate.
17722290
Active galactic nuclei with double-peaked balmer lines: I. Black hole masses and eddington ratios
Using stellar population synthesis, we model the stellar contribution for a sample of 110 double- peaked broad- line active galactic nuclei ( AGNs) from the Sloan Digital Sky Survey ( SDSS). The stellar velocity dispersions (sigma(*)) are obtained for 52 double- peaked AGNs with obvious stellar absorption features, ranging from 106 to 284 km s(-1). We also use multicomponent profiles to fit O III lambda lambda 4959, 5007 and H beta emission lines. Using the well- established M-bh-sigma(*) relation, the black hole masses are calculated to range from 1.0 x 10(7) to 5.5 x 10(8) M circle dot, and the Eddington ratio from similar to 0.01 to similar to 1. Comparing these with the known R-BLR-L relation, we can find the factor f, which indicates the BLRs' geometry, inclination, and kinematics. We find that f deviates greatly from 0.75, suggesting the nonvirial dynamics of broad- line regions. The peak separation is mildly correlated with the Eddington ratio and SMBH mass with almost the same correlation coefficients. This implies that it will be difficult to detect obvious double- peaked AGNs with higher Eddington ratios. Using the monochromatic luminosity at 5100 8 to trace the bolometric luminosity, we find that external illumination of the accretion disk is needed to produce the observed strength of the H similar to emission line.
15522277
Blob Ejection from Advection-dominated Accretion Flow. II. The Multiwavelength Properties of Light Curves
It has been argued that blobs ejected from advection-dominated accretion flow through the accretion-ejection instability undergo expansion because of their high internal energy density. The expanding blobs interact with their surroundings and form a strong shock, which accelerates a group of electrons to be relativistic. Then flares are formed. This model has advances in two aspects: shock acceleration and self-consistent injection. We derive an analytical formula of the injection function of relativistic electrons based on Sedov's law. We calculate the time-dependent spectrum of relativistic electrons in such an expanding blob. The light-travel effect, the evolution of the electron spectrum due to energy loss, and the escape of relativistic electrons from the radiating region are considered, as well as the expansion (at subrelativistic speed) of the coasting blob. A large number of light curves spanning a wide range of parameters have been given in this paper. Regarding the symmetry, relative amplitude, duration of a flare, and the time lag between peak fluxes, we find four basic kinds of light curves for the nonexpanding blob and seven basic kinds of light curves for the expanding blob. The expansion weakens the magnetic field as well as enlarging the size of the blob. The predicted light curves thus show very complicated properties that are composed of the basic light curves, because the physical conditions are changing in the expanding blob. For the rapid decays of magnetic field (for example, B proportional to r(-n)), we find that the falling profile is a power law of time as nuF(nu) proportional to t((1-alpha)n/5), where alpha is the power-law index of injected electrons. This decline is controlled by the decay of magnetic field rather than the energy losses of relativistic electrons. We also calculate the evolution of the photon spectrum from both nonexpanding and expanding blobs, Different shapes in the phase of decreasing luminosity are then obtained for different parameter values. The photon index alpha(ph) stays constant for nonexpanding blobs when luminosity decreases, whereas alpha(ph) continues to decrease after the luminosity reaches its maximum for expanding blobs. It is expected that we can extract the information on ejected blobs from the observed light curves based on the present model.
15881761
The Unified Model of Active Galactic Nuclei. II. Evolutionary Connection
We assemble a sample composed of 243 nearby Seyfert galaxies with redshifts z ≤ 0.05 to test the unification scheme. The sample contains 94 broad emission line Seyfert 1 galaxies (BLS1s), 44 narrow emission line Seyfert 1s (NLS1s), 36 X-ray-absorbed hidden broad line region Seyfert 2s (HBLR S2s), 42 X-ray-absorbed non-HBLR S2s, and 27 X-ray-unabsorbed Seyfert 2s (unabsorbed non-HBLR S2s and HBLR S2s). We find that (1) NLS1s have less massive black hole masses than BLS1s, (2) HBLR S2s have the same mass distribution of black holes as BLS1s, (3) absorbed non-HBLR S2s have less massive black holes than HBLR S2s, and (4) unabsorbed non-HBLR S2s have the most massive black holes. We thus have a queue of black hole masses from small to large: narrow- to broad-line Seyfert galaxies, providing new evidence for the evolutionary sequence. We find that the opening angles of the torus in NLS1s and absorbed non-HBLR S2s are significantly smaller than those in BLS1s and HBLR S2s. We also find that the unabsorbed Seyfert 2 galaxies could be caused by low gas-to-dust ratios in the present sample. This indicates that the star formation histories could be different in the unabsorbed and absorbed Seyfert 2 galaxies, showing evidence for suppressed star formation by black hole activities. We outline a new unification scheme based on the orientation hypothesis: Seyfert galaxies can be unified by including the growth of black holes, Eddington ratios, changing opening angles of tori, and gas-to-dust ratios in tori. Seyfert galaxies tend to finally evolve to unabsorbed non-HBLR Seyfert 2 galaxies, in which the black holes accrete with low accretion rates and both the broad-line region and dusty torus disappear.
16148475
Cosmological Evolution of the Duty Cycle of Quasars
Quasars are powered by accretion onto supermassive black holes, but the problem of the duty cycle related to the episodic activity of the black holes remains one of the major questions of the cosmological evolution of quasars. In this Letter, we obtain quasar duty cycles based on analyses of a large sample composed of 10,979 quasars with redshifts z ≤ 2.1 from the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3). We estimate the masses of the quasar black holes and obtain their mass function (MF) in the present sample. We then get the duty cycle (z) = 10-3 ~ 1 based on Soltan's argument, implying that black holes are undergoing multiple episodic activity. We find that the duty cycle has a strong evolution. By comparison, we show that the evolution of the duty cycle follows the history of the cosmic star formation rate (SFR) density in the universe, providing intriguing evidence of a natural connection between star formation and the triggering of black hole activity. Feedback on star formation from black hole activity is briefly discussed.
8085635
Beam test results of the BTeV silicon pixel detector
We report the main results of the BTeV silicon pixel detector beam test carried out at Fermilab during the fixed target run 1999-2000. The tests were performed using a 227 GeV/c pion beam incident on a 6 plane silicon microstrip telescope. Several single-chip silicon pixel planes were placed in the middle of the apparatus. The pixel detector spatial resolution has been studied as a function of track inclination and the number of ADC bits. The effect of an applied external magnetic field was also studied.
118415484
UNVEILING THE PHYSICAL PROPERTIES AND KINEMATICS OF MOLECULAR GAS IN THE ANTENNAE GALAXIES (NGC 4038/9) THROUGH HIGH-RESOLUTION CO (J=3-2) OBSERVATIONS
We present a similar to 1 '' (100 pc) resolution (CO)-C-12 (3-2) map of the nearby intermediate-stage interacting galaxy pair NGC 4038/9 (the Antennae galaxies) obtained with the Submillimeter Array. We find that half the CO (3-2) emission originates in the overlap region where most of the tidally induced star formation had been previously found in shorter wavelength images, with the rest being centered on each of the nuclei. The gross distribution is consistent with lower resolution single-dish images, but we show for the first time the detailed distribution of the warm and dense molecular gas across this galaxy pair at resolutions comparable to the size of a typical giant molecular complex. While we find that 58% (33/57) of the spatially resolved Giant Molecular Associations (a few x 100 pc) are located in the overlap region, only <= 30% spatially coincides with the optically detected star clusters, suggesting that the bulk of the CO (3-2) emission traces the regions with very recent or near future star formation activity. The spatial distribution of the CO (3-2)/CO (1-0) integrated brightness temperature ratios mainly ranges between 0.3 and 0.6, which suggests that on average the CO (3-2) line in the Antennae is not completely thermalized and similar to the average values of nearby spirals. A higher ratio is seen in both nuclei and the southern complexes in the overlap region. A higher radiation field associated with intense star formation can account for the nucleus of NGC 4038 and the overlap region, but the nuclear region of NGC 4039 shows relatively little star formation or active galactic nucleus activity and cannot be easily explained. We show kinematical evidence that the high line ratio in NGC 4039 is possibly caused by gas inflow into the counter-rotating central disk.
119236957
Derrick’s theorem beyond a potential
Scalar field theories with derivative interactions are known to possess solitonic excitations, but such solitons are generally unsatisfactory because the effective theory fails precisely where nonlinearities responsible for the solitons are important. A new class of theories possessing (internal) galilean invariance can in principle bypass this difficulty. Here, we show that these galileon theories do not possess stable solitonic solutions. As a by-product, we show that no stable solitons exist for a different class of derivatively coupled theories, describing for instance the infrared dynamics of superfluids, fluids, solids and some k-essence models.
15644301
A CHANDRA ACIS STUDY OF THE YOUNG STAR CLUSTER TRUMPLER 15 IN CARINA AND CORRELATION WITH NEAR-INFRARED SOURCES
Using the highest-resolution X-ray observation of the Trumpler 15 star cluster taken by the Chandra X-ray Observatory, we estimate the total size of its stellar population by comparing the X-ray luminosity function (XLF) of the detected sources to a calibrator cluster and identify for the first time a significant fraction (~14%) of its individual members. The highest-resolution near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the Very Large Telescope) was found to detect most of our X-ray selected sample of cluster members, with a K-excess disk frequency of 3.8% ± 0.7%. The near-IR data, XLF, and published spectral types of the brightest members support a cluster age estimate (5-10 Myr) that is older than those for the nearby Trumpler 14 and Trumpler 16 clusters, and suggest that high-mass members may have already exploded as supernovae. The morphology of the inner ~0.7 pc core of the cluster is found to be spherical. However, the outer regions (beyond ~2 pc) are elongated, forming an "envelope" of stars that, in projection, appears to connect Trumpler 15 to Trumpler 14; this morphology supports the view that these clusters are physically associated. Clear evidence of mass segregation is seen. This study appears in this special issue devoted to the Chandra Carina Complex Project, a 1.42 deg2 Chandra X-ray survey of the Great Nebula in Carina.
119234828
CS 5-4 survey toward nearby IR bright galaxies
With the observations of the CS 5-4 line toward a sample of 24 infrared bright galaxies using HHSMT, we detected CS 5-4 emission in 14 galaxies, including 12 ULIRGs/LIRGs and 2 nearby normal galaxies. As a good dense gas tracer, which has been well used for studying star formation in the Milky Way, CS 5-4 can trace the active star forming gas in galaxies. The correlation between CS 5-4 luminosity, which is estimated with detected CS 5-4 line emission, and infrared luminosity in these 14 galaxies is fitted with correlation coefficient of 0.939 and the slope close to unity. This correlation confirmed that dense gas, which is closely linked to star formation, is very important for understanding star formation in galaxies.