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1.
Low-ionization nuclear emission regions (LINERs) are present in a large fraction of local galaxies, while their connection to the more luminous active galactic nuclei (AGN) remains elusive. We analyze the narrow band images obtained by the Hubble Space Telescope (HST) in Hα [NⅡ] and/or [OⅢ] band for 23 LINERs and low luminosity Seyfert galaxies in the sample of the Palomar Optical Spectroscopic Survey of nearby galaxies in an attempt to resolve the structure of Narrow Emission Line Regions (NLRs) of these objects. In all cases, NLRs are well resolved and their morphology differs from object to object. Clumps, linear structure, spiral arms or a ring are detected in a large fraction of the objects, while there is no significant difference between Seyfert galaxies and LINERs. We find that the NLR size and the narrow line luminosity are strongly correlated for both LINERs and low luminosity Seyfert galaxies, and that the size of Hα [NⅡ] emission line region scales with Hα luminosity as RNLR∞L0.4±0.06Hα, consistent with an extension of the NLR size-luminosity relation defined for luminous Seyfert galaxies and quasars, to two orders of magnitude lower in luminosity and to lower activity levels. Our results suggest that NLRs in LINERs are similar to those of Seyfert galaxies, and they are powered by the central active galactic nucleus.  相似文献   

2.
By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for 468 "normal" galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the "normal" galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 "normal" galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α(25μm,60μm). These galaxies may be classified as "AGN-powered". For "normal" galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.  相似文献   

3.
We present estimated ratios of the central black hole mass to the bulge mass (Mbh/Mbulge) for 15 Narrow Line Seyfert 1 galaxies (NLS1s). It is found that NLS1s apparently have lower mass ratios: the average mass ratio is about 1 × 10-4 with a spread of 2, which is one order of magnitude lower than for Broad Line AGNs and quiescent galaxies. This lower value, as compared to that established essentially for all other types of galaxies, can be accounted for by an underestimation of the black hole masses and an overestimation of the bulge masses in the NLS1s.  相似文献   

4.
We used the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) to study the morphological properties of 1137 nearby infrared (IR) galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite (IRAS) point source catalog redshift survey with DR5 at z(≤)0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 109.5L⊙ to 1012L⊙. By deriving the IR luminosity functions (LF) for different morphological types, we found that normal spiral galaxies are the dominant population below LIR～ 8 × 1010 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR(≈) 5×1010L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.  相似文献   

5.
We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273. The presence of high-order Balmer absorption lines (H8, H9, H10) and weak equivalent widths of Call K A3933, CN A4200, G-band A4300 and MgIb 5173 clearly indicate recent star-forming activity in the nuclear region. Using a simple stellar population synthesis model, we find that for the best fit, the contributions of a power-law featureless continuum, an intermediate-age (~ 108 yr) and an old (> 109yr) stellar population to the total light at the reference normalization wavelength are 10.0%, 33.4% and 56.6%, respectively. The existence of recent starburst activity is also consistent with its high far-infrared luminosity (log LFIR/L = 9.9), its infrared color indexes [a(25,60) = -1.81 and a(60,100) = -0.79, typical values for Seyfert galaxies with circumnuclear starburst], and its q-value (2.23, ratio of infrared to radio flux, very similar to that of normal spirals and starburst galaxies). Byrd et al. have suggested that NGC 2273 mig  相似文献   

6.
We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.  相似文献   

7.
We compare the ionized gas velocity dispersion σgas with the stellar velocity dispersion σ＊ in star-forming galaxies, composite galaxies, Low Ionization Nuclear Emissionline Regions （LINERs） and Seyfert 2s, compiled from a cross-identification of Sloan Digital Sky Survey Fourth Data Release （SDSS DR4） and Point Source Catalogue Redshift Survey （PSCz）. We measure σgas from the FWHMs of emission lines （Hα, [NⅡ]λλ6548, 6583 and [SⅡ]λλ6716, 6731）. A significant correlation between the gas and stellar velocity dispersion exists, despite substantial scatter. The mean value of the gas to stellar velocity dispersion ratio is close to unity. This suggests that gas velocity dispersion can substitute for the stellar velocity dispersion as a tracer of the gravitational potential well for all the four types of galaxies, but the involved uncertainties are different from type to type. We also studied -↑σgas, as a function of the redshift and the axial ratio to test the effects of aperture and galaxy inclination, and found that both effects are weak. Finally we checked the trend of -↑σgas/σ＊ with the infrared luminosity and found no significant correlation.  相似文献   

8.
High energy photon radiations of gamma-ray bursts(GRBs) and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s) follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ_0) of GRBs.It is shown that the AGN sample does not agree with the L_p-E_(p,z)-Γ_0 relation of GRBs.In addition,we obtain a tight relation of ■ for FSRQs and NLS1 galaxies,where L_(syn) is the luminosity at peak photon energy E_(syn,p) of the synchrotron radiations.This relation is different from the L_p-E_(p,z)-Γ_0 relation of GRB s.The dependence of L_(syn) to δ is consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue that Γ_0 may be a representative of the kinetic power of the radiating region and the tight L_p-E_(p,z)-Γ_0 relation is shaped by the radiation physics and the jet power together.  相似文献   

9.
The sizes of the Broad Line Region (BLR) of some Seyfert 1 galax-ies and nearby quasars can be determined by the reverberation mapping method.Combining with the observed FWHM of Hβ emission line and assuming that themotion of BLR clouds is virialized, the black hole masses of these objects have beenestimated. However, this method strongly depends on the poorly-understood geom-etry and inclination of the BLR. On the other hand, a tight correlation between theblack hole mass and the bulge velocity dispersion was recently found for both activeand nearby inactive galaxies. This may provide another method, independent of theBLR geometry, for estimating the black hole mass. Using this method for estimatingthe black hole mass and combining with the measured BLR size and FWHM of Hβemission line, we derived the BLR inclination angles for 20 Seyfert I galaxies underthe assumption that the BLR is disk-like. The derived inclination angles agree wellwith those derived previously by fitting the UV continuum and Hβ emission lineprofiles. Adopting a relation between the FWHMs of [OⅢ]λ5007 forbidden line andthe stellar velocity dispersion, we also estimated the BLR inclinations for 50 nar-row line Seyfert 1 galaxies (NLSls). We found that the inclinations of broad LineSeyfert 1 galaxies (BLS1s) are systematically greater than those of NLS1s, whichseldom exceed 30. This may be an important factor that leads to the differencesbetween NLS1s and BLS1s if the BLR of NLS1s is really disk-like.  相似文献   

10.
Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2 ≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 25 per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2 - 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2 and 2% at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed from theoretical models may n  相似文献   

11.
We present the results of a deep K -band imaging study which reveals the host galaxies around a sample of luminous radio-quiet quasars. The K -band images, obtained at UKIRT, are of sufficient quality to allow accurate modelling of the underlying host galaxy. Initially, the basic structure of the hosts is revealed using a modified clean deconvolution routine optimized for this analysis. Two of the 14 quasars are shown to have host galaxies with violently disturbed morphologies which cannot be modelled by smooth elliptical profiles. For the remainder of our sample, 2D models of the host and nuclear component are fitted to the images using the χ 2 statistic to determine goodness of fit. Host galaxies are detected around all of the quasars. The reliability of the modelling is extensively tested, and we find the host luminosity to be well constrained for nine quasars. The derived average K -band absolute K -corrected host galaxy magnitude for these luminous radio-quiet quasars is 〈 M K 〉=25.15±0.04, slightly more luminous than an L * galaxy. The spread of derived host galaxy luminosities is small, although the spread of nuclear-to-host ratios is not. These host luminosities are shown to be comparable to those derived from samples of quasars of lower total luminosity, and we conclude that there is no correlation between host and nuclear luminosity for these quasars. Nuclear-to-host ratios break the lower limit previously suggested from studies of lower nuclear luminosity quasars and Seyfert galaxies. Morphologies are less certain but, on the scales probed by these images, some hosts appear to be dominated by spheroids while others appear to have disc-dominated profiles.  相似文献   

12.
Narrow Line Seyfert 1 galaxies (NLS1s) are intriguing owing to their continuum as well as emission-line properties. The observed peculiar properties of the NLS1s are believed to be as a result of an accretion rate close to the Eddington limit. As a consequence of this, for a given luminosity, NLS1s have smaller black hole (BH) masses compared with normal Seyfert galaxies. Here we argue that NLS1s might be Seyfert galaxies in their early stage of evolution and as such may be low-redshift, low-luminosity analogues of high-redshift quasars. We propose that NLS1s may reside in rejuvenated, gas-rich galaxies. We also argue in favour of collisional ionization for production of Fe  ii in active galactic nuclei.  相似文献   

13.
During the ROSAT All-Sky Survey (RASS; Voges 1992, 1997) about 80,000 X-ray sourceswith a detection likelihood 2 10 were detected, from which 18,811 sources having a PSPC countrate larger than 0.05 ets s--1 and detection likelihood 3 15 were compiled in the RASS-BSC(VOges et al. 1996a). More than 65% RASS sources remain unidentified (Voges et al. 1996b).The optical spectroscopic study of these RASS sources is essential for understanding them moreclearly.The idelltification of X-…  相似文献   

14.
We combine Chandra and XMM–Newton X-ray data from our previous papers with new X-ray observations and with Spitzer mid-infrared (mid-IR) data in order to study the nature of the nuclei of radio galaxies and radio-loud quasars with   z < 1.0  from the 3CRR sample. The significant increase in sample size over our previous work, the reduction of bias in the sample as a result of new observations and the availability of more mid-IR data allow us to show conclusively that almost all objects classed as low-excitation radio galaxies in optical spectroscopic studies lack a radiatively efficient active nucleus. We show that the distribution of absorbing columns in the narrow-line radio galaxies differs from the population of X-ray-selected radio-quiet type 2 quasars and from that in local Seyfert 2s. We comment on the current evidence for the nature of the soft X-ray component in radio-galaxy nuclear spectra, concluding that a jet origin for this component is very hard to evade. Finally, we discuss the recently discovered 'fundamental plane' of black hole activity, showing that care must be taken when placing radio-loud active galactic nucleus (AGN) on such diagnostic diagrams.  相似文献   

15.
We have observed a sample of 149 Seyfert galaxies and radio-quiet quasars at 13 cm with both a 275-km radio interferometer and the 6-km compact array of the Australia Telescope. The high-resolution observations searched for the presence of compact, high-brightness-temperature radio emission from the active nucleus. The low-resolution observations measured the total radio emission from the galaxy disc and Seyfert core and lobes. From these we draw the following conclusions. (i) Seyfert galaxies that lack compact radio cores display a correlation between radio and far-infrared (FIR) emission similar to the correlation displayed by normal spirals, albeit with greater scatter. The correlation is found to be intrinsic and is not an artefact of the richness effect. (ii) A very different radio–FIR correlation is displayed by those Seyferts that harbour compact radio cores. These tend to be more radio-loud than either normal spirals or the Seyferts that lack compact cores. The compact core emission thus seems to be responsible for the generally poor radio–FIR correlation displayed by Seyfert galaxies. (iii) The radio–FIR correlation is not significantly improved by subtracting off the 0.1-arcsec (20- to 200-pc) compact radio emission from the total radio emission. This suggests that the emission from the active galactic nucleus has significant structure on scales larger than 0.1 arcsec. Perhaps these structures are the 'linear' radio features that have been seen previously in Seyfert nuclei.  相似文献   

16.
We use host galaxy imaging studies of the PG quasar survey to compare the far-infrared (FIR) properties of quasars with disturbed and undisturbed host galaxies. By using survival analysis, we show that the quasars with disturbed host galaxies, with morphologies classified from a homogeneous data set, have a 60-μm luminosity distribution that is different from that of those with undisturbed hosts with >97 per cent confidence. For morphological classifications using an inhomogeneous data set, including HST data for some objects, this confidence rises to >99 per cent confidence. The mean 60-μm luminosity of the disturbed-host quasars is several times greater than that of the undisturbed-host quasars. However, possible biases in the PG survey might affect these conclusions. Our results are interpreted as supporting the idea that quasars are related to at least some ultraluminous infrared galaxies. We discuss the implications of this result for studies of quasar and galaxy evolution.  相似文献   

17.
Black hole mass determination in active galaxies is a key issue in understanding various luminosity states. In the present paper, we try to generalize the mass determination method based on the X-ray excess variance, successfully used for typical broad line Seyfert 1 galaxies (BLS1) to narrow line Seyfert 1 (NLS1) galaxies. NLS1 galaxies differ from BLS1 with respect to several properties. They are generally more variable in 2–10 keV energy band so the natural expectation is the need to use a different scaling coefficient between the mass and the variance in these two types of sources. However, we find that such a simple approach is not enough. Although for majority of the 21 NLS1 galaxies in our sample a single scaling coefficient (larger by a factor 20) provided us with a satisfactory method of mass determination, in a small subset of NLS1 galaxies this approach failed. Variability of those objects appeared to be at the intermediate level between NLS1 and BLS1 galaxies. These exceptional NLS1 galaxies have much harder soft X-ray spectra than majority of NLS1 galaxies. We thus postulate that the division of Seyfert 1 galaxies into BLS1 and NLS1 according to the widths of the  Hβ  line is less generic than according to the soft X-ray slope.  相似文献   

18.
星暴和活动星系核之间的联系是活动星系研究领域最重要、最活跃的研究课题之一。Seyfert星系由于距离较近、数目较多和相对低的核活动,已成为研究星暴和活动星系核之间联系的理想天体。综述了活动星系核中存在星暴的观测证据和Seyflert2型星系核区星暴活动的最新研究结果,着重讨论了存在两类Seyflert2型星系(一类是被遮挡的Seyfert1型星系,另一类是“真正”的Seyfert2型星系即不存在宽线区的Seyfert2型星系)的可能性．通过比较具有和不具有偏振宽线的Seyflert2型星系在红外、射电、光学和X射线光谱性质的差别,发现具有偏振宽线的Seyfert2型星系在本质上和Seyflert1型星系是同一类天体,差别只在于观测者视线方向的不同;而不具有偏振宽线的Seyfert2型星系是一些星系核活动较弱而星暴活动占主导的天体,这些星系从射电、红外、光学到硬X射线,都具有和星暴星系相似的性质。由于这些星系中核的吸积率将比Seyflert1型星系低近两个量级,因而它们很有可能是一些没有宽发射线区的Seyfert2型星系,即所谓的“真正”Seyflert2型星系。  相似文献   

19.
Stellar velocity dispersion in narrow-line Seyfert 1 galaxies   总被引：1，自引：0，他引：1  
Several authors have recently explored, for narrow-line Seyfert 1 galaxies (NLS1s), the relationship between black hole mass ( M BH) and stellar velocity dispersion (σ*). Their results are more or less in agreement and seem to indicate that NLS1s fill the region below the fit obtained by Tremaine et al., showing a range of σ* similar to that of Seyfert 1 galaxies, and a lower M BH. Until now, the [O  iii ] width has been used in place of the stellar velocity dispersion, but some indications have begun to arise against the effectiveness of the gaseous kinematics in representing the bulge potential, at least in NLS1s. Bian & Zhao have stressed the urgency of producing true σ* measurements. Here, we present new stellar velocity dispersions obtained through direct measurements of the Ca  ii absorption triplet (∼8550 Å) in the nuclei of eight NLS1 galaxies. The resulting σ* values and a comparison with σ[O III] confirm our suspicion that [O  iii ] typically overestimates the stellar velocity dispersion. We demonstrate that NLS1s follow the   M BH–σ*  relation as Seyfert 1, quasars and non-active galaxies.  相似文献   

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