Active galactic nuclei （AGNs） in low surface brightness galaxies （LSBGs） have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. （1996） APM ...Active galactic nuclei （AGNs） in low surface brightness galaxies （LSBGs） have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. （1996） APM LSBG sample which has been observed spectroscopically by the Sloan Digital Sky Survey Data Release 5 （SDSS DR5）. Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear processes in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% of LSBGs. We find that, contrary to some previous claims, the fraction of galaxies that contain AGNs is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. This result holds true even within each morphological type from Sa to Sc. LSBGs that have larger central stellar velocity dispersions or larger physical sizes tend to have a higher chance of harboring an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-σ. relation established for normal galaxies and AGNs.展开更多
In an examination of the relationship between the black hole mass MBH and stellar velocity dispersion σ＊ in radio-loud active galactic nuclei （AGNs）, we studied two effects which may cause uncertainties in the bla...In an examination of the relationship between the black hole mass MBH and stellar velocity dispersion σ＊ in radio-loud active galactic nuclei （AGNs）, we studied two effects which may cause uncertainties in the black hole mass estimates of radio-loud AGNs： the relativistic beaming effect on the observed optical continuum radiation and the orientation effect on the broad emission line width. After correcting these two effects, we re-examined the MBH- σ[OIII] relation for a sample of radio-loud and radio-quiet AGNs, and found the relation for radio-loud AGNs still deviated from that for nearby normal galaxies and radio-quiet AGNs. We also found there is no significant correlation between radio jet power and narrow [OIII] line width, indicating absence of strong interaction between radio jet and narrow line region. It may be that the deviation of the MBH-σ＊ relation of radio-loud AGNs is intrinsic, or that the [OIII] line width is not a good indicator of σ＊ for radio-loud AGNs.展开更多
It is well accepted that feedback from active galactic nuclei （AGNs） plays an important role in the coevolution of the supermassive black hole （SMBH） and its host galaxy, but the concrete mechanism of feedback rem...It is well accepted that feedback from active galactic nuclei （AGNs） plays an important role in the coevolution of the supermassive black hole （SMBH） and its host galaxy, but the concrete mechanism of feedback remains unclear. A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy. We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties. Although there are some uncertainties, our data still imply the deviation from the star formation law （Kennicutt-Schmidt law）. Further, they indicate that： （1） Feedback correlates with the Eddington ratio, rather than with the mass of SMBH, as a result of decreasing star formation efficiency. （2） The SMBH and the torus are probably undergoing coevolution. Conclusions presented here can be refined through future high resolution CO or HCN observations.展开更多
Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGN...Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGNs）. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 〈 z 〈 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.展开更多
We have analyzed the frequency and properties of the nuclear activity in a sample of galaxies with circumnuclear rings and spirals (CNRs), compiled from published data. From the properties of this sample a typical cir...We have analyzed the frequency and properties of the nuclear activity in a sample of galaxies with circumnuclear rings and spirals (CNRs), compiled from published data. From the properties of this sample a typical circumnuclear ring can be characterized as having a median radius of 0.7 kpc (mean 0.8 kpc, rms 0.4 kpc), located at a spiral Sa/Sb galaxy (75% of the hosts), with a bar (44% weak, 37% strong bars). The sample includes 73 emission line rings, 12 dust rings and 9 stellar rings. The sample was compared with a carefully matched control sample of galaxies with very similar global properties but without detected circumnuclear rings. We discuss the relevance of the results in regard to the AGN feeding processes and present the following results: 1) bright companion galaxies seem not to be important for the appearance of CNRs, which appear to be more related to intrinsic properties of the host galaxies or to minor merger processes;2) the proportion of weak bars in galaxies with a CNR is higher than expected;3) the incidence of Seyfert (Sy) activity coeval with CNRs is significantly larger than the rate expected from the morphological distribution of the host galaxies;4) the rate of Sy 2 to Sy 1 type galaxies with CNRs is about three times larger than the expected ratio for galaxies without CNRs and is opposite to that predicted by the geometric paradigm of the classical unified model for AGNs, although it does support the hypothesis that Sy 2 activity is linked to circumnuclear star formation. The possible selection effects of the sample are discussed, and we conclude that the detected trends are strong enough to justify high quality observations of as large as possible set of galaxies with circumnuclear rings and their matched control samples.展开更多
We compile a sample of spectral energy distributions （SEDs） of 12 GeV radio galaxies （RGs）, including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significa...We compile a sample of spectral energy distributions （SEDs） of 12 GeV radio galaxies （RGs）, including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR I RGs and BL Lacertae objects （BL Lacs） and between FR II RGs and flat spectrum radio quasars （FSRQs）. However, on average FR I RGs have a larger ＇Tb （break Lorentz factor of electrons） and lower B （magnetic field strength） than FR II RGs, analogous to the differences be- tween BL Lacs and FSRQs. The derived Doppler factors （~） of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent pop- ulations of blazars with smaller tS. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carded by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the ＂sequence＂ behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.展开更多
New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5 - 10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines （PBLs...New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5 - 10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines （PBLs） are absorbed by NH 〈 1024 cm^-2, while two of three Seyfert 2 galaxies without PBLs show evidence of Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs, Adding the measured obscuration indicators （NH, T ratio, and Fe Kα line EW） of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for NH, 99.1% to 99.4% for T ratio, and 95.3% to 97.4% for Fe Kα line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angles of the line of sight to the putative dusty toms, which leads to the obscuration of the broad-line scattering screen, as expected in the unification model.展开更多
Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank （RGB） catalog are presented （Brinkmann et al. 1997） which have been spectroscopically observed in the Sloan ...Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank （RGB） catalog are presented （Brinkmann et al. 1997） which have been spectroscopically observed in the Sloan Digital Sky Survey （SDSS） DR5. The SDSS spectra of the optical counterparts are modeled in a careful and selfconsistent way by incorporating the host galaxy＇s starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4- 5 GHz spectral indices estimated using （non-simultaneous） archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei （AGNs）, particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies （NLRGs）, as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs （low-ionization nuclear emission regions）, based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to ＇weak line radio galaxies＇, are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 10623 - 10^26 W Hz^- 1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies （NLS 1 s）, a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs （HBLs）, as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.展开更多
We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have b...We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have been interpreted as relativistically broad Fe Lc~ lines. Such features are not clearly observed in other active galactic nuclei despite sometimes having high iron abundance required by the best fitted blurred reflection models. Given the importance of these lines, we explore whether the rapid variability of spectral parameters may introduce broad bumps/dips artificially in the time averaged spectrum, which may then be mistaken as broadened lines. We tested this hypothesis by performing time resolved spectroscopy using long （〉 100 ks） XMM-Newton observations and by dividing them into segments with typical exposures of a few ks. We extracted spectra from each such segment and modeled them using a two component phenomenological model consisting of a power law to represent the hard component and a black body to represent the soft emission. As expected, both the sources showed variations in the spectral parameters. Using these variation trends, we simulated model spectra for each segment and then co-added to get a combined simulated spectrum. In the simulated spectra, we found no broad features below 1 keV and in particular no deviation near 0.9 keV as seen in the real averaged spectra. This implies that the broad Fe Lα line that is seen in the spectra of these sources is not an artifact of the variation of spectral components and, hence, provides evidence that the line is indeed genuine.展开更多
We use a sample of type 2 active galactic nuclei （AGNs） from SDSS DR7 in which the [O Ⅲ] ）λ5007 emission line can be modeled by two Gaussian components, a broad wing plus a narrow core, to investigate the origin ...We use a sample of type 2 active galactic nuclei （AGNs） from SDSS DR7 in which the [O Ⅲ] ）λ5007 emission line can be modeled by two Gaussian components, a broad wing plus a narrow core, to investigate the origin of the broad wing and the connection between the velocity shift of the broad wing and the physical parameters of AGNs, as well as their host galaxies. We find that the flux of the wing components is statistically roughly equal to that of the core components. However, the velocity shift of the wing component has only weak, if any, correlations with the physical properties of AGNs and the host galaxies, such as bolometric luminosity, the Eddington ratio, the mass of supermassive black holes, D4000, H3A or stellar mass. Comparing the velocity shift from our type 2 AGN sample to that from the type 1 sample in Zhang et al., we suggest that the [O Ⅲ]] broad wing originates from outflow.展开更多
Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. I...Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST,—a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurate; a proof is given that the solution of the pre-calibration method is the same as the least squares solution.展开更多
We have collected an up-to-date sample of 123 superluminal sources （84 quasars, 27 BL Lac objects and 12 galaxies） and calculated the apparent velocities （βapp） for 224 components in the sources with the A-CDM mo...We have collected an up-to-date sample of 123 superluminal sources （84 quasars, 27 BL Lac objects and 12 galaxies） and calculated the apparent velocities （βapp） for 224 components in the sources with the A-CDM model. We checked the relationships between their proper motions, redshifts,βapp and 5 GHz flux densities. Our analysis shows that the radio emission is strongly boosted by the Doppler effect. The superluminal motion and the relativistic beaming boosting effect are, to some extent, the same in active galactic nuclei.展开更多
Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with ...Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.展开更多
We present simultaneous observations of three recurring jets in EUV and soft X-ray （SXR）, which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic characteristics in these tw...We present simultaneous observations of three recurring jets in EUV and soft X-ray （SXR）, which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic characteristics in these two different wavelengths, we found that EUV and SXR jets had similar locations, directions, sizes and velocities. We also analyzed their spectral properties by using six spectral lines from the EUV Imaging Spectrometer （EIS） onboard Hinode and found that these jets had temperatures from 0.05 to 2.0MK and maximum electron densities from 6.6× 10^9 to 3.4× 10^10cm^-3. For each jet, an elongated blue-shifted component and a red- shifted component at the jet base were simultaneously observed in the Fe XII A195 and the He II A256 lines. The three jets had maximum Doppler velocities from 25 to 121 km s-1 in the FexII A195 line and from 115 to 232 km s -1 in the HeII A256 line. They had maximum non-thermal velocities from 98 to 181 km s-1 in the Fe xII A195 line and from 196 to 399 km s-1 in the He II A256 line. We also examined the relationship between averaged Doppler velocities and maximum ionization temperatures of these three jets and found that averaged Doppler velocities decreased with the increase of maximum ionization temperatures. In the photosphere, magnetic flux emergences and cancelations continuously took place at the jet base. These observa- tional results were consistent with the magnetic reconnection jet model, implying that magnetic reconnection between emerging magnetic flux and ambient magnetic field occurred in the lower atmosphere.展开更多
By modeling the broadband spectral energy distributions （SEDs） of a typical flat spectrum radio quasar （FSRQ, 3C 279） and two GeV narrow-line Seyfert 1 galaxies （NLSls, PMN J0948＋0022 and 1H 0323＋342） in diffe...By modeling the broadband spectral energy distributions （SEDs） of a typical flat spectrum radio quasar （FSRQ, 3C 279） and two GeV narrow-line Seyfert 1 galaxies （NLSls, PMN J0948＋0022 and 1H 0323＋342） in different flux stages with one-zone leptonic models, we find a universal correlation between their Doppler factors （δ） and peak luminosities （Lc） of external Compton scattering bumps. Compiling a combined sample of FSRQs and GeV NLSls, it is found that both FSRQs and GeV NLSls in different stages and in different sources follow the same δ-Lc correlation well. This indicates that the variations of observed luminosities may be essentially due to the Doppler boosting effect. The universal δ-Lo relation between FSRQs and GeV NLS 1 s in different stages may be further evidence that the particle acceleration and radiation mechanisms for the two kinds of sources are similar. In addition, by replacing Lc with the observed luminosity in the Fermi/LAT band （LLAT）, this correlation holds and it may serve as an empirical indicator of δ. We estimate the δ values with LLAT for 484 FSRQs in the Fermi/LAT Catalog and they range from 3 to 41, with a median of 16, which are statistically consistent with the values derived by other methods.展开更多
We use a sample of 111 radio galaxies with redshift z 〈 0.3 to investigate their nuclear properties. The black hole masses of the sources in this sample are estimated with the velocity dispersion/luminosity of the ga...We use a sample of 111 radio galaxies with redshift z 〈 0.3 to investigate their nuclear properties. The black hole masses of the sources in this sample are estimated with the velocity dispersion/luminosity of the galaxies, or the width of the broad-lines. We find that the excitation index, the relative intensity of low and high excitation lines, is correlated with the Eddington ratio for this sample. The size of the narrow-line region （NLR） was found to vary with ionizing luminosity as RNLR ∝ Lion^0.25 （Liu et al. 2013）. Using this empirical relation, we find that the correlation between the excitation index and the Eddington ratio can be reproduced by photoionization models. We adopt two sets of spectral energy distributions （SEDs）, with or without a big blue bump in ultraviolet as the ionizing continuum, and infer that the modeled correlation between the excitation index and the Eddington ratio is insensitive to the applied SED. This means that the difference between high excitation galaxies and low excitation galaxies is not caused by the different accretion modes in these sources. Instead, it may be caused by the size of the NLR.展开更多
We investigate the Luminosity Function （LF） of the cluster of galaxies Abell 566. The photometric data of 15 intermediate-bands are obtained from the Beijing-Arizona- Taiwan-Connecticut （BATC） photometric sky surv...We investigate the Luminosity Function （LF） of the cluster of galaxies Abell 566. The photometric data of 15 intermediate-bands are obtained from the Beijing-Arizona- Taiwan-Connecticut （BATC） photometric sky survey. For each of the 15 wavebands, the LF of cluster galaxies is well modelled by the Schechter function, with characteristic luminosities from -18.0 to -21.9 magnitude, from the α- to the p-band. Morphological dependence of the LF is investigated by separating the cluster members into ＇red＇ and ＇blue＇ subsamples. It is clear that late type galaxies have a steeper shape of LF than the early type galaxies. We also divided the sample galaxies by their local environment. It was found that galaxies in the sparser region have steeper shape of LF than galaxies in the denser region. Combining the results of morphological and environmental dependence of LFs, we show that Abell 566 is a well relaxed cluster with positive evidence of galaxy interaction and merger, and excess number of bright early type galaxies located in its denser region.展开更多
The distribution of abundance for iron-peak elements in dwarf spheroidal galaxies （dSphs） is important for galaxy evolution and supernova （SN） nucleosynthesis. Nowadays, manganese （Mn） is one of the most observe...The distribution of abundance for iron-peak elements in dwarf spheroidal galaxies （dSphs） is important for galaxy evolution and supernova （SN） nucleosynthesis. Nowadays, manganese （Mn） is one of the most observed iron-peak elements in local dSphs. Studies of its distributions allow us to derive and understand the evolution history of these dSphs. We improve a phenomenological model by a two-curve model including a new initial condition, that includes detailed calculations of SN explosion rates and yields. We compare the results with the observed Mn distribution data for three dSphs： Fornax, Sculpture and Sextans. We find that the model can describe the observed Fe and Mn distributions well simultaneously for the three dSphs. The results also indicate that the initial conditions should be determined by the low metallicity sam- ples in the beginning time of the galaxies and the previous assumption of metellicity-dependant Mn yield of SNIa is not needed when a wide mass range of core-collapse SNe is included. Our method is applicable to the chemical evolution of other iron-peak elements in dSphs and can be modified to provide more detailed processes for the evolution of dSphs.展开更多
We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey Ⅲ （SDSS DR8） by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing gian...We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey Ⅲ （SDSS DR8） by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are ＂almost certain＂ lensing systems with tangential giant arcs, 22 clusters are ＂probable＂ and 31 clusters are ＂pos- sible＂ lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separations of 2.0jj - 25.7j~ from the bright central galaxies. We note that the rich clusters are more likely to be lensing systems and the separations between the arcs and the central galaxies increase with cluster richness.展开更多
Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic field...Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic fields in the active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans, and null-null lines. For the first time, we have identified a spiral magnetic null in Sun＇s corona. The magnetic lines of force twisted around the spine of the null, forming a ＇magnetic wreath＇ with excess of free magnetic energy and resembling observed brightening structures at extraultraviolet （EUV） wavebands. We found clear evidence of topology eruptions which are referred to as catastrophic changes of topology skeleton associated with a coronal mass ejection （CME） and an explosive X-ray flare. These results shed new lights on the structural complexity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather obscure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.展开更多
基金Supported by the National Natural Science Foundation of China.
文摘Active galactic nuclei （AGNs） in low surface brightness galaxies （LSBGs） have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. （1996） APM LSBG sample which has been observed spectroscopically by the Sloan Digital Sky Survey Data Release 5 （SDSS DR5）. Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear processes in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% of LSBGs. We find that, contrary to some previous claims, the fraction of galaxies that contain AGNs is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. This result holds true even within each morphological type from Sa to Sc. LSBGs that have larger central stellar velocity dispersions or larger physical sizes tend to have a higher chance of harboring an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-σ. relation established for normal galaxies and AGNs.
基金Supported by the National Natural Science Foundation of China.
文摘In an examination of the relationship between the black hole mass MBH and stellar velocity dispersion σ＊ in radio-loud active galactic nuclei （AGNs）, we studied two effects which may cause uncertainties in the black hole mass estimates of radio-loud AGNs： the relativistic beaming effect on the observed optical continuum radiation and the orientation effect on the broad emission line width. After correcting these two effects, we re-examined the MBH- σ[OIII] relation for a sample of radio-loud and radio-quiet AGNs, and found the relation for radio-loud AGNs still deviated from that for nearby normal galaxies and radio-quiet AGNs. We also found there is no significant correlation between radio jet power and narrow [OIII] line width, indicating absence of strong interaction between radio jet and narrow line region. It may be that the deviation of the MBH-σ＊ relation of radio-loud AGNs is intrinsic, or that the [OIII] line width is not a good indicator of σ＊ for radio-loud AGNs.
基金the National Natural Science Foundation of China
文摘It is well accepted that feedback from active galactic nuclei （AGNs） plays an important role in the coevolution of the supermassive black hole （SMBH） and its host galaxy, but the concrete mechanism of feedback remains unclear. A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy. We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties. Although there are some uncertainties, our data still imply the deviation from the star formation law （Kennicutt-Schmidt law）. Further, they indicate that： （1） Feedback correlates with the Eddington ratio, rather than with the mass of SMBH, as a result of decreasing star formation efficiency. （2） The SMBH and the torus are probably undergoing coevolution. Conclusions presented here can be refined through future high resolution CO or HCN observations.
基金Supported by the National Natural Science Foundation of China
文摘Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGNs）. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 〈 z 〈 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.
文摘We have analyzed the frequency and properties of the nuclear activity in a sample of galaxies with circumnuclear rings and spirals (CNRs), compiled from published data. From the properties of this sample a typical circumnuclear ring can be characterized as having a median radius of 0.7 kpc (mean 0.8 kpc, rms 0.4 kpc), located at a spiral Sa/Sb galaxy (75% of the hosts), with a bar (44% weak, 37% strong bars). The sample includes 73 emission line rings, 12 dust rings and 9 stellar rings. The sample was compared with a carefully matched control sample of galaxies with very similar global properties but without detected circumnuclear rings. We discuss the relevance of the results in regard to the AGN feeding processes and present the following results: 1) bright companion galaxies seem not to be important for the appearance of CNRs, which appear to be more related to intrinsic properties of the host galaxies or to minor merger processes;2) the proportion of weak bars in galaxies with a CNR is higher than expected;3) the incidence of Seyfert (Sy) activity coeval with CNRs is significantly larger than the rate expected from the morphological distribution of the host galaxies;4) the rate of Sy 2 to Sy 1 type galaxies with CNRs is about three times larger than the expected ratio for galaxies without CNRs and is opposite to that predicted by the geometric paradigm of the classical unified model for AGNs, although it does support the hypothesis that Sy 2 activity is linked to circumnuclear star formation. The possible selection effects of the sample are discussed, and we conclude that the detected trends are strong enough to justify high quality observations of as large as possible set of galaxies with circumnuclear rings and their matched control samples.
基金supported by the National Natural Science Foundation of China(grants 11573034,11533003,11373036 and 11133002)the National Basic Research Program(973 Program)of China(grant 2014CB845800)the Guangxi Science Foundation(2013GXNSFFA019001)
文摘We compile a sample of spectral energy distributions （SEDs） of 12 GeV radio galaxies （RGs）, including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR I RGs and BL Lacertae objects （BL Lacs） and between FR II RGs and flat spectrum radio quasars （FSRQs）. However, on average FR I RGs have a larger ＇Tb （break Lorentz factor of electrons） and lower B （magnetic field strength） than FR II RGs, analogous to the differences be- tween BL Lacs and FSRQs. The derived Doppler factors （~） of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent pop- ulations of blazars with smaller tS. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carded by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the ＂sequence＂ behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.
基金the National Natural Science Foundation of China
文摘New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5 - 10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines （PBLs） are absorbed by NH 〈 1024 cm^-2, while two of three Seyfert 2 galaxies without PBLs show evidence of Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs, Adding the measured obscuration indicators （NH, T ratio, and Fe Kα line EW） of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for NH, 99.1% to 99.4% for T ratio, and 95.3% to 97.4% for Fe Kα line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angles of the line of sight to the putative dusty toms, which leads to the obscuration of the broad-line scattering screen, as expected in the unification model.
基金Supported by the National Natural Science Foundation of China
文摘Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank （RGB） catalog are presented （Brinkmann et al. 1997） which have been spectroscopically observed in the Sloan Digital Sky Survey （SDSS） DR5. The SDSS spectra of the optical counterparts are modeled in a careful and selfconsistent way by incorporating the host galaxy＇s starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4- 5 GHz spectral indices estimated using （non-simultaneous） archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei （AGNs）, particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies （NLRGs）, as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs （low-ionization nuclear emission regions）, based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to ＇weak line radio galaxies＇, are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 10623 - 10^26 W Hz^- 1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies （NLS 1 s）, a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs （HBLs）, as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.
基金financial support from CSIR, New Delhifinancial support from DST, New Delhi through the INSPIRE Scheme
文摘We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have been interpreted as relativistically broad Fe Lc~ lines. Such features are not clearly observed in other active galactic nuclei despite sometimes having high iron abundance required by the best fitted blurred reflection models. Given the importance of these lines, we explore whether the rapid variability of spectral parameters may introduce broad bumps/dips artificially in the time averaged spectrum, which may then be mistaken as broadened lines. We tested this hypothesis by performing time resolved spectroscopy using long （〉 100 ks） XMM-Newton observations and by dividing them into segments with typical exposures of a few ks. We extracted spectra from each such segment and modeled them using a two component phenomenological model consisting of a power law to represent the hard component and a black body to represent the soft emission. As expected, both the sources showed variations in the spectral parameters. Using these variation trends, we simulated model spectra for each segment and then co-added to get a combined simulated spectrum. In the simulated spectra, we found no broad features below 1 keV and in particular no deviation near 0.9 keV as seen in the real averaged spectra. This implies that the broad Fe Lα line that is seen in the spectra of these sources is not an artifact of the variation of spectral components and, hence, provides evidence that the line is indeed genuine.
基金supported by the National Natural Science Foundation of China (Grant Nos.11273015,11133001 and 11003007)the National Basic Research Program of China (973 program,No.2013CB834905)the Specialized Research Fund for the Doctoral Program of Higher Education (20100091110009)
文摘We use a sample of type 2 active galactic nuclei （AGNs） from SDSS DR7 in which the [O Ⅲ] ）λ5007 emission line can be modeled by two Gaussian components, a broad wing plus a narrow core, to investigate the origin of the broad wing and the connection between the velocity shift of the broad wing and the physical parameters of AGNs, as well as their host galaxies. We find that the flux of the wing components is statistically roughly equal to that of the core components. However, the velocity shift of the wing component has only weak, if any, correlations with the physical properties of AGNs and the host galaxies, such as bolometric luminosity, the Eddington ratio, the mass of supermassive black holes, D4000, H3A or stellar mass. Comparing the velocity shift from our type 2 AGN sample to that from the type 1 sample in Zhang et al., we suggest that the [O Ⅲ]] broad wing originates from outflow.
文摘Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST,—a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurate; a proof is given that the solution of the pre-calibration method is the same as the least squares solution.
基金the NSFC(Grants 10573005 and 10633010)the 973 project(2007CB815405)
文摘We have collected an up-to-date sample of 123 superluminal sources （84 quasars, 27 BL Lac objects and 12 galaxies） and calculated the apparent velocities （βapp） for 224 components in the sources with the A-CDM model. We checked the relationships between their proper motions, redshifts,βapp and 5 GHz flux densities. Our analysis shows that the radio emission is strongly boosted by the Doppler effect. The superluminal motion and the relativistic beaming boosting effect are, to some extent, the same in active galactic nuclei.
基金Supported by the National Natural Science Foundation of China
文摘Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10973038 and 40636031)supported by the National Basic Research Program of China (973 Program+1 种基金 Grant No. 2011CB811403)the Scientific Application Foundation of Yunnan Province (Grant Nos. 2007A112M and 2007A115M)
文摘We present simultaneous observations of three recurring jets in EUV and soft X-ray （SXR）, which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic characteristics in these two different wavelengths, we found that EUV and SXR jets had similar locations, directions, sizes and velocities. We also analyzed their spectral properties by using six spectral lines from the EUV Imaging Spectrometer （EIS） onboard Hinode and found that these jets had temperatures from 0.05 to 2.0MK and maximum electron densities from 6.6× 10^9 to 3.4× 10^10cm^-3. For each jet, an elongated blue-shifted component and a red- shifted component at the jet base were simultaneously observed in the Fe XII A195 and the He II A256 lines. The three jets had maximum Doppler velocities from 25 to 121 km s-1 in the FexII A195 line and from 115 to 232 km s -1 in the HeII A256 line. They had maximum non-thermal velocities from 98 to 181 km s-1 in the Fe xII A195 line and from 196 to 399 km s-1 in the He II A256 line. We also examined the relationship between averaged Doppler velocities and maximum ionization temperatures of these three jets and found that averaged Doppler velocities decreased with the increase of maximum ionization temperatures. In the photosphere, magnetic flux emergences and cancelations continuously took place at the jet base. These observa- tional results were consistent with the magnetic reconnection jet model, implying that magnetic reconnection between emerging magnetic flux and ambient magnetic field occurred in the lower atmosphere.
基金supported by the National Basic Research Program of China (973 Program) (grant 2014CB845800)the National Natural Science Foundation of China (grants 11573034, 11533003, 11373036 and 11133002)+1 种基金the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences (grant XDB09000000)the Guangxi Science Foundation (2013GXNSFFA019001)
文摘By modeling the broadband spectral energy distributions （SEDs） of a typical flat spectrum radio quasar （FSRQ, 3C 279） and two GeV narrow-line Seyfert 1 galaxies （NLSls, PMN J0948＋0022 and 1H 0323＋342） in different flux stages with one-zone leptonic models, we find a universal correlation between their Doppler factors （δ） and peak luminosities （Lc） of external Compton scattering bumps. Compiling a combined sample of FSRQs and GeV NLSls, it is found that both FSRQs and GeV NLSls in different stages and in different sources follow the same δ-Lc correlation well. This indicates that the variations of observed luminosities may be essentially due to the Doppler boosting effect. The universal δ-Lo relation between FSRQs and GeV NLS 1 s in different stages may be further evidence that the particle acceleration and radiation mechanisms for the two kinds of sources are similar. In addition, by replacing Lc with the observed luminosity in the Fermi/LAT band （LLAT）, this correlation holds and it may serve as an empirical indicator of δ. We estimate the δ values with LLAT for 484 FSRQs in the Fermi/LAT Catalog and they range from 3 to 41, with a median of 16, which are statistically consistent with the values derived by other methods.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11173043 and 11233006)the Strategic Priority Research Program “the Emergence of Cosmological Structures” of the CAS (Grant No. XDB09000000)the CAS/SAFEA International Partnership Program for Creative Research Teams
文摘We use a sample of 111 radio galaxies with redshift z 〈 0.3 to investigate their nuclear properties. The black hole masses of the sources in this sample are estimated with the velocity dispersion/luminosity of the galaxies, or the width of the broad-lines. We find that the excitation index, the relative intensity of low and high excitation lines, is correlated with the Eddington ratio for this sample. The size of the narrow-line region （NLR） was found to vary with ionizing luminosity as RNLR ∝ Lion^0.25 （Liu et al. 2013）. Using this empirical relation, we find that the correlation between the excitation index and the Eddington ratio can be reproduced by photoionization models. We adopt two sets of spectral energy distributions （SEDs）, with or without a big blue bump in ultraviolet as the ionizing continuum, and infer that the modeled correlation between the excitation index and the Eddington ratio is insensitive to the applied SED. This means that the difference between high excitation galaxies and low excitation galaxies is not caused by the different accretion modes in these sources. Instead, it may be caused by the size of the NLR.
基金Supported by the National Natural Science Foundation of China.
文摘We investigate the Luminosity Function （LF） of the cluster of galaxies Abell 566. The photometric data of 15 intermediate-bands are obtained from the Beijing-Arizona- Taiwan-Connecticut （BATC） photometric sky survey. For each of the 15 wavebands, the LF of cluster galaxies is well modelled by the Schechter function, with characteristic luminosities from -18.0 to -21.9 magnitude, from the α- to the p-band. Morphological dependence of the LF is investigated by separating the cluster members into ＇red＇ and ＇blue＇ subsamples. It is clear that late type galaxies have a steeper shape of LF than the early type galaxies. We also divided the sample galaxies by their local environment. It was found that galaxies in the sparser region have steeper shape of LF than galaxies in the denser region. Combining the results of morphological and environmental dependence of LFs, we show that Abell 566 is a well relaxed cluster with positive evidence of galaxy interaction and merger, and excess number of bright early type galaxies located in its denser region.
基金partly supported by the National Natural Science Foundation of China (Grant Nos. 11305133, 11273020 and U1331121)China Scholarship (Grant No. 2011851096)
文摘The distribution of abundance for iron-peak elements in dwarf spheroidal galaxies （dSphs） is important for galaxy evolution and supernova （SN） nucleosynthesis. Nowadays, manganese （Mn） is one of the most observed iron-peak elements in local dSphs. Studies of its distributions allow us to derive and understand the evolution history of these dSphs. We improve a phenomenological model by a two-curve model including a new initial condition, that includes detailed calculations of SN explosion rates and yields. We compare the results with the observed Mn distribution data for three dSphs： Fornax, Sculpture and Sextans. We find that the model can describe the observed Fe and Mn distributions well simultaneously for the three dSphs. The results also indicate that the initial conditions should be determined by the low metallicity sam- ples in the beginning time of the galaxies and the previous assumption of metellicity-dependant Mn yield of SNIa is not needed when a wide mass range of core-collapse SNe is included. Our method is applicable to the chemical evolution of other iron-peak elements in dSphs and can be modified to provide more detailed processes for the evolution of dSphs.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10821061, 10833003 and 11103032)Young Researcher Grant of National Astronomical Observatories, Chinese Academy of Sciences and the National Key Basic Research Science Foundation of China (2007CB815403)Funding for SDSS-III has been provided by the Alfred P.Sloan Foundation,the Participating Institutions,the National Science Foundation and the U.S.Department of Energy
文摘We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey Ⅲ （SDSS DR8） by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are ＂almost certain＂ lensing systems with tangential giant arcs, 22 clusters are ＂probable＂ and 31 clusters are ＂pos- sible＂ lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separations of 2.0jj - 25.7j~ from the bright central galaxies. We note that the rich clusters are more likely to be lensing systems and the separations between the arcs and the central galaxies increase with cluster richness.
基金the National Natural Science Foundation of China
文摘Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic fields in the active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans, and null-null lines. For the first time, we have identified a spiral magnetic null in Sun＇s corona. The magnetic lines of force twisted around the spine of the null, forming a ＇magnetic wreath＇ with excess of free magnetic energy and resembling observed brightening structures at extraultraviolet （EUV） wavebands. We found clear evidence of topology eruptions which are referred to as catastrophic changes of topology skeleton associated with a coronal mass ejection （CME） and an explosive X-ray flare. These results shed new lights on the structural complexity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather obscure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.
