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241.
Minfeng Gu Xinwu Cao D. R. Jiang 《Monthly notices of the Royal Astronomical Society》2009,396(2):984-996
Based on the Königl's inhomogeneous jet model, we estimate the jet parameters, such as bulk Lorentz factor Γ, viewing angle θ and electron number density n e from radio very long-baseline interferometry and X-ray data for a sample of active galactic nuclei (AGNs) assuming that the X-rays are from the jet rather than the intracluster gas. The bulk kinetic power of jets is then calculated using the derived jet parameters. We find a strong correlation between the total luminosity of broad emission lines and the bulk kinetic power of the jets. This result supports the scenario that the accretion process is tightly linked with the radio jets, though how the disc and jet are coupled is not revealed by present correlation analysis. Moreover, we find a significant correlation between the bulk kinetic power and radio extended luminosity. This implies that the emission from the radio lobes is closely related with the energy flux transported through jets from the central part of AGNs. 相似文献
242.
Yuping Tang Q.-S. Gu J.-S. Huang Y.-P. Wang 《Monthly notices of the Royal Astronomical Society》2009,397(4):1966-1975
We present the Spitzer Space Telescope Infrared Array Camera observations for a sample of local elliptical galaxies to study later stages of active galactic nucleus (AGN) activity. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in nine of them. There is unambiguous evidence of circumnuclear dust in these nine galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related to nuclear activity. The possible origin of infrared excess emission from hot dust heated by the central AGN is supported by the spectral indices of the infrared excess emission. 相似文献
243.
The formation and evolution of elliptical galaxies (EGs) are still an open question. In particular, recent observations suggest that EGs are not only simple spheroidal systems of old stars. In this paper, we analyse a sample of EGs selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local EGs. Among these 487 ellipticals, we find that 13 EGs show unambiguous evidence of recent star formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices, we derive stellar ages, metallicities and α-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample.
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
244.
245.
We revisit the vertical structure of neutrino-dominated accretion flows (NDAFs) in spherical coordinates with a new boundary
condition based on the mechanical equilibrium. The solutions show that NDAF is significantly thick. The Bernoulli parameter
and neutrino trapping are determined by the mass accretion rate and the viscosity parameter. According to the distribution
of the Bernoulli parameter, the possible outflow may appear in the outer region of the disk. The neutrino trapping can essentially
affect the neutrino radiation luminosity. The vertical structure of NDAF is like a “sandwich”, and the multilayer accretion
may account for the flares in gamma-ray bursts. 相似文献
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249.
M. Guélin N. Brouillet J. Cernicharo F. Combes A. Wooten 《Astrophysics and Space Science》2008,313(1-3):45-51
High angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI),
reveal the presence of several cores of size 103 AU, which have distinct spectral signatures. Complex molecules such as ethanol, vinyl cyanide and dimethyl ether show different
distributions and their relative abundance varies from core to core by orders of magnitude. The molecular column densities
derived in the cores also differ widely from the beam-averaged column densities observed with large single-dish telescopes.
Obviously, the predictions of hot core chemistry models must be checked against high resolution observations. ALMA, which
allies sensitivity and high angular resolution, will be a key instrument for this type of studies.
The PdBI observations were part of a search for interstellar glycine, also carried out with the IRAM 30-m telescope and the
Green Bank Telescope. We derive a 3σ upper limit on the column density of glycine of 1×1015 cm−2 per 2″×3″ beam in the Orion Hot Core and Compact Ridge.
Based on observations made with the IRAM PdB Interferometer, the IRAM 30-m telescope and the NRAO Green-Bank telescope. IRAM
is supported by CNRS, MPG and IGN. 相似文献
250.
We present a study of the nearby Seyfert galaxy NGC 3982 using optical,infrared and X-ray data acquired by SDSS,Spitzer and Chandra.Our main results are as follows:(1) A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions.(2) The Spitzer Infrared Spectrograph (IRS) spectrum of the central region (~3") shows a power-law continuum,a silicate emission feature at 9.7 μm,and significant PAH emission features at 7.7,8.6,11.3 and 12.7/zm,suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982.(3) We estimate the star formation rate (SFR) of the circumnuclear (~5"-20") region from the Ha luminosity to be for the active nucleus of NGC 3982 from radio to X-ray,and obtain a bolometric luminosity of Lbol=4.5×1042 erg s-1,corresponding to an Eddington ratio (Lbol/LEdd) of 0.014.The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear starforming region and the nucleus,which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region. 相似文献