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1.
本文讨论了类星体各光谱特征对其色指数的影响以及色指数随红移的变化．随着红移的增加，位于Ｌｙα发射线短波方向的各种吸收特征进入了可见光区，内禀的幂律谱和发射线强度的分布对类星体色指数及其弥散的影响将是次要的，各种吸收系统的作用将改变类星体色指数随红移变化的趋势，其中，Ｌｙｍａｎ系限吸收系统的影响最大。利用ＩＵＥ观测的类星体光谱求得色指数随红移的变化，对上述结果进行了验证。  相似文献   

2.
The near-infrared data of the quasar 3C273 are collected from available literature and are used to analyze its variability properties. The largest amplitudes of variations are ΔJ = 1.0, ΔH = 0.9, and ΔK = 0.86. The color indices are J − H = 0.82, J − K = 1.96, and H − K = 1.13. Analysis with the discrete correlation function (DCF) method indicates that the variability between any two infrared bands is correlated without any time lag. The relation between the color index and brightness is also investigated and the result indicates that the spectrum steepens when the source first dims, while it flattens after the source has dimmed to a some extent, suggesting that the emission of 3C 273 at near-IR consists of at least two components. Some discussions are presented.  相似文献   

3.
Powerful radio galaxies often display enhanced optical/ultraviolet emission regions, elongated and aligned with the radio jet axis. The aim of this series of papers is to investigate separately the effects of radio power and redshift on the alignment effect, together with other radio galaxy properties. In this second paper, we present a deeper analysis of the morphological properties of these systems, including both the host galaxies and their surrounding aligned emission.
The host galaxies of our 6C subsample are well described as de Vaucouleurs ellipticals, with typical scale sizes of  ∼10 kpc  . This is comparable to the host galaxies of low- z radio sources of similar powers, and also the more powerful 3CR sources at the same redshift. The contribution of nuclear point source emission is also comparable, regardless of radio power.
The 6C alignment effect is remarkably similar to that seen around more powerful 3CR sources at the same redshift in terms of extent and degree of alignment with the radio source axis, although it is generally less luminous. The bright, knotty features observed in the case of the z ∼ 1 3CR sources are far less frequent in our 6C subsample; neither do we observe such strong evidence for evolution in the strength of the alignment effect with radio source size/age. However, we do find a very strong link between the most extreme alignment effects and emission-line region properties indicative of shocks, regardless of source size/age or power. In general, the 6C alignment effect is still considerably stronger than that seen around lower redshift galaxies of similar radio powers. Cosmic epoch is clearly just as important a factor as radio power: although aligned emission is observed on smaller scales at lower redshifts, the processes which produce the most extreme features simply no longer occur, suggesting considerable evolution in the properties of the extended haloes surrounding the radio source.  相似文献   

4.
《New Astronomy Reviews》2002,46(2-7):121-134
X-ray emission traces the gaseous environments of radio sources. The medium must be present for jet confinement, but what are its influence on jet fueling, dynamics, propagation, and disruption? The observational situation is both complicated and enriched by radio sources being multi-component X-ray emitters, with several possible regions of non-thermal emission. Recent work, primarily based on sensitive ROSAT pointings, is used to contrast the X-ray emission and environments of radio sources with: (a) low power, (b) high power at high redshift, (c) high power at lower redshift, and (d) GHz peaked spectrum emission. The trends in external gas density and pressure near extended radio structures are reviewed. Imminently-available X-ray measurements with vastly improved resolution and sensitivity have great potential for resolving many open issues.  相似文献   

5.
In this Letter we report the findings of a statistically significant relation between the continuum color indices and redshift of optically violent variable QSOs. No such correlation is found to exist for non-variable and moderately variable QSOs.  相似文献   

6.
Strong emission lines may change the brightness of QSOs and hence their observed magnitudes. Since different lines will affect the magnitudes by entering a particular filter at different redshifts, this effect may alter the number of QSOs at a particular redshift and hence the redshift distribution. The present analysis shows that the influence of the emission lines on the U and B magnitudes are significantly correlated to the redshift distribution. It is concluded that the changes in observed magnitudes of QSOs caused by the emission lines have significant effects on the present redshift distribution.  相似文献   

7.
We present the rest‐frame UV to optical spectrum of the gravitationally lensed galaxy, the “8 o'clock arc” at z = 2.735, obtained with the X‐shooter spectrograph. This is one of the rare comprehensive study of a high‐redshift star‐forming galaxy, usually not feasible due to the faintness of these objects. The spectrum of the 8 o'clock arc is rich in stellar and interstellar absorption features and in nebular emission features. Their analysis allowed us to derive most of the physical properties characterizing the galaxy. From HST images, we reconstruct the morphology of the arc in the source plane and confirm that we resolve a clump in rotation around the main core of galaxy in our X‐shooter spectrum (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
Absorption features shown by QSOs may be identified and measured as reported absorption redshift systems, or may remain unidentified and not measured. The features are believed to be observed in objects with high emission redshifts (z em), although no quantitative analysis exists to examine any such preferential trend, except that by Basu (1982). However, redshift data have since increased enormously both in range of the redshift spectrum and in number. Furthermore, the earlier analysis was based on only the reported absorption redshifts while unidentified absorption features were not dealt with. The present paper analyses the updated data, both identified and unidentified features. It is found that absorption features may be expressed as exponential function ofz em, and upper limits are set for the percentage of QSOs showing absorption features. Finally, an entirely new method of analysis confirms the earlier conclusion of Basu (1982) that the appearance of absorbing clouds is closely associated with the creation of the QSOs, the two may be having a common cause. It is suggested that absorption QSOs may be a separate class of QSOs whose birth is accompanied with creation of absorbing clouds.  相似文献   

9.
We study and quantify gravitational redshift by means of relativistic ray tracing simulations of emission lines. The emitter model is based on thin, Keplerian rotating rings in the equatorial plane of a rotating black hole. Emission lines are characterised by a generalized fully relativistic Doppler factor or redshift associated with the line core. Two modes of gravitational redshift, shift and distortion, become stronger with the emitting region closer to the Kerr black hole. Shifts of the line cores reveal an effect at levels of 0.0015 to 60% at gravitational radii ranging from 105 to 2. The corresponding Doppler factors range from 0.999985 to 0.4048. Line shape distortion by strong gravity, i.e. very skewed and asymmetric lines occur at radii smaller than roughly ten gravitational radii. Gravitational redshift decreases with distance to the black hole but remains finite due to the asymptotical flatness of black hole space–time. The onset of gravitational redshift can be tested observationally with sufficient spectral resolution. Assuming a resolving power of ∼100000, yielding a resolution of ≈0.1 Å for optical and near‐infrared broad emission lines, the gravitational redshift can be probed out to approximately 75000 gravitational radii. In general, gravitational redshift is an indicator of black hole mass and spin as well as for the inclination angle of the emitter, e.g. an accretion disk. We suggest to do multi‐wavelength observations because all redshifted features should point towards the same central mass. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
We study the power spectrum of galaxies in redshift space, with third-order perturbation theory to include corrections that are absent in linear theory. We assume a local bias for the galaxies: i.e., the galaxy density is sampled from some local function of the underlying mass distribution. We find that the effect of the non-linear bias in real space is to introduce two new features: first, there is a contribution to the power which is constant with wavenumber, whose nature we reveal as essentially a shot-noise term. In principle this contribution can mask the primordial power spectrum, and could limit the accuracy with which the latter might be measured on very large scales. Secondly, the effect of second- and third-order bias is to modify the effective bias (defined as the square root of the ratio of galaxy power spectrum to matter power spectrum). The effective bias is almost scale-independent over a wide range of scales. These general conclusions also hold in redshift space. In addition, we have investigated the distortion of the power spectrum by peculiar velocities, which may be used to constrain the density of the Universe. We look at the quadrupole-to-monopole ratio, and find that higher order terms can mimic linear theory bias, but the bias implied is neither the linear bias, nor the effective bias referred to above. We test the theory with biased N -body simulations, and find excellent agreement in both real and redshift space, providing the local biasing is applied on a scale whose fractional rms density fluctuations are < 0.5.  相似文献   

11.
Diffuse γ-rays probe the highest-energy processes at the largest scales. Here we derive model-independent constraints on the hadronic contribution to the Galactic and extragalactic γ-ray spectra at in the energy range 50 MeVEγ10 GeV. The hadronic component is dominated by emission from neutral pions, with a characteristic spectrum symmetric about mπ0/2. We exploit the well-defined properties of the pion decay spectrum to quantify the maximum pionic fraction of the observed γ-ray intensity. We find that the Galactic spectrum above 30 MeV can be atmost about 50% pionic. The maximum pionic contribution to the extragalactic spectrum is energy dependent; it also depends on the redshift range over which the sources are distributed, ranging from as low as about 20% for pions generated very recently, to as much as 90% if the pions are generated around redshift 10. The implications of these constraints for models of γ-ray and neutrino emission are briefly discussed.  相似文献   

12.
This paper is the second one of a series of papers on the redshift distribution of QSOs. In this paper, we shall study the influence of the selection effect in the identification of emission lines on the redshift distribution of QSOs more thoroughly than the previous paper (Zhouet al., 1983). If we assume that the QSO's redshift is cosmological, adopt the standard model, and consider the selection effect due to the redshift identification, the limiting apparent magnitude in the observation and the evolutionary effect of QSOs, we can compute the emission line redshift distribution for the so-called optically selected QSOs discovered by objective prism, grating prism technique alone, the QSOs discovered by positional methods or by colour technique and for whole QSOs, respectively (see Figures 6, 11, 12). The results of computation agree with the observations very well, especially for optically selected QSOs; the computational distribution has almost the same shape with the observational one. For this kind of the QSOs the computational distribution may give the positions and heights of all these observed peaks. The correlation coefficient between the calculated and observed distributions is larger than 0.95. It shows that (a) the peaks and dips in the redshift distribution of QSOs are mainly caused by the selection effect in the redshift identification, and (b) the redshift of QSOs is cosmological.  相似文献   

13.
Two-color diagrams including magnitudes from several photometric systems are investigated with respect to the possibility of determining from the integrated photometry the galaxy type and its redshift. The color indices of galaxies are calculated using the energy distribution curves of Colemanet al. (1980). It is shown that redshift determination at low values ofz requires an ultraviolet magnitude with λ0 shorter than 300 nm. At redshiftsz>0.6, the infrared magnitude photometry becomes important. Different sources of errors and uncertainties are discussed.  相似文献   

14.
We present spectroscopic observations of a sample of faint gigahertz peaked‐spectrum (GPS) radio sources drawn from the Westerbork Northern Sky Survey (WENSS). Redshifts have been determined for 19 (40 per cent) of the objects. The optical spectra of the GPS sources identified with low‐redshift galaxies show deep stellar absorption features. This confirms previous suggestions that their optical light is not significantly contaminated by active galactic nucleus-related emission, but is dominated by a population of old (>9 Gyr) and metal-rich (>0.2 [Fe/H]) stars, justifying the use of these (probably) young radio sources as probes of galaxy evolution. The optical spectra of GPS sources identified with quasars are indistinguishable from those of flat-spectrum quasars, and clearly different from the spectra of compact steep‐spectrum (CSS) quasars. The redshift distribution of the GPS quasars in our radio-faint sample is comparable to that of the bright samples presented in the literature, peaking at z ∼2–3. It is unlikely that a significant population of low-redshift GPS quasars is missed as a result of selection effects in our sample. We therefore claim that there is a genuine difference between the redshift distributions of GPS galaxies and quasars, which, because it is present in both the radio-faint and bright samples, cannot be caused by a redshift–luminosity degeneracy. It is therefore unlikely that the GPS quasars and galaxies are unified by orientation, unless the quasar opening angle is a strong function of redshift. We suggest that the GPS quasars and galaxies are unrelated populations and just happen to have identical observed radio spectral properties, and hypothesize that GPS quasars are a subclass of flat-spectrum quasars.  相似文献   

15.
Optical variability of extragalactic objects, viz., QSOs, BL Lacs and Seyfert galaxies has been monitored systematically over an appreciable period of time and a large amount of data have accumulated. The present work reports results of investigations involving statistical analysis of updated data on relationships between variability and various observed properties of the objects, viz., redshift, color indices, radio spectral index and absorption lines. It is found that at high frequencies (rest frame) radio spectral index does not change significantly with the degree of variability. However, the degree of variability depends on redshifts. On the other hand, presence or absence of absorption lines is significantly associated with variability for QSOs with larger redshifts (z > 1.0), while no such relationship exists for QSOs at smaller redshifts (z < 1.0) or other objects. Correlation between color indices and redshifts depends on the degree of variability and the sample chosen for the color index.  相似文献   

16.
For the GMRT, we calculate the expected signal from red-shifted HI emission at two frequency bands centered at 610 and 325 MHz. The study focuses on the visibility-visibility cross-correlations, proposed earlier as the optimal statistical estimator for detecting and analyzing this signal. These correlations directly probe the power spectrum of density fluctuations at the redshift where the radiation originated, and thereby provide a method for studying the large scale structures at large redshifts. We present detailed estimates of the correlations expected between the visibilities measured at different baselines and frequencies. Analytic fitting formulas representing the salient features of the expected signal are also provided. These will be useful in planning observations and deciding an optimal strategy for detecting this signal.  相似文献   

17.
We present new calculations of the evolving UV background out to the epoch of cosmological reionization and make predictions for the amount of GeV gamma-ray attenuation by electron–positron pair production. Our results are based on recent semi-analytic models of galaxy formation, which provide predictions of the dust-extinguished UV radiation field due to starlight, and empirical estimates of the contribution due to quasars. We account for the reprocessing of ionizing photons by the intergalactic medium. We test whether our models can reproduce estimates of the ionizing background at high redshift from flux decrement analysis and proximity effect measurements from quasar spectra, and identify a range of models that can satisfy these constraints. Pair production against soft diffuse photons leads to a spectral cut-off feature for gamma rays observed between 10 and 100 GeV. This cut-off varies with redshift and the assumed star formation and quasar evolution models. We find only negligible amounts of absorption for gamma rays observed below 10 GeV for any emission redshift. With observations of high-redshift sources in sufficient numbers by the Fermi Gamma-ray Space Telescope and new ground-based instruments, it should be possible to constrain the extragalactic background light in the UV and optical portion of the spectrum.  相似文献   

18.
We propose a strategy for detecting and analyzing optical afterglows (OAs) of long gamma-ray bursts (GRBs) without the need to obtain their light curves. This approach is useful for the Gaia satellite, which provides sampled optical ultra-low-dispersion spectroscopic observations of the sky. For this purpose, we show that most OAs of long GRBs display specific values of some of their color indices, representing synchrotron emission of the jet. They are stable in time during the event. These indices, which can be determined from the spectra, are very similar for the ensemble of OAs with redshift z < 3.5 and display a strong clustering in some color-color diagrams. These indices also enable to constrain the properties of the local interstellar medium of GRBs. The long-lasting mapping of the sky with the Gaia instruments also gives us a hope to search for the so-called orphan afterglows, which, according to some authors, can be considerably more numerous than OAs of the observed GRBs. We also show how to resolve OAs from other transients in the Gaia data. The color indices and the properties of the quiescent sources (host galaxies of OAs detectable later by the large ground-based telescopes at the co-ordinates of the OA determined by Gaia) would tell us which one, among transients detected by Gaia, is a GRB OA.  相似文献   

19.
We report on the optical color variability of a sample of 24 blazars, consisting of nine flat spectrum radio quasars(FSRQs) and 15 BL Lacertae objects(BL Lacs), on timescales of years using simultaneous V-and R-band observations observed by the Kanata telescope at Higashi-Hiroshima Observatory.The correlations between color indices V-R and magnitudes reveal that 11 BL Lacs and one FSRQ exhibited significant(i.e., r 0.2 and P 0.01) bluer-when-brighter(BWB) trend and two FSRQs followed the redder-when-brighter(RWB) tend, indicating a possibility that the BWB chromatic trend is dominant for BL Lacs and the RWB trend is especially found in FSRQs, which has been presented occasionally in different samples of blazars.The superpositions of the red emission component from the Doppler-boosted relativistic jet and the blue component arising from the accretion disk might be a possible interpretation for the long-term color behaviors.  相似文献   

20.
We studied the scatter across clusters of the color of the red sequence in are presentative and large sample of clusters (more than 200) detected on the Early Data Release of the Sloan Digital Sky Survey (EDR-SDSS) in the redshift range 0.06<z<0.34. We found an extreme degree of homogeneity in the color of the red sequence (the intrinsic scatter is about 0.02 to 0.03 mag)suggesting that either galaxies on the red sequence formed a long time ago (z>2) or else their star formation is universally delayed with preservation of a small spread in age formation. The latter possibility is ruled out by the mere existence of galaxies at high redshift. While the old age of ellipticals was already been claimed for a small heterogeneous collection of clusters, most of which are rich ones, we found that it holds for a ten to one hundred larger sample, representative of all clusters and groups detected on the EDR-SDSS. Hence, we claim the possible universality of the color of the galaxies on the red sequence. Furthermore, the sample includes a large number of very poor clusters (also called groups), not studied in previous works, for which the hierarchical and monolithic scenarios of elliptical formation predict different colors for the brightest ellipticals. The observed red sequence color does not depend on cluster/group richness at a level of 0.02 mag, while a 0.23 mag effect is expected according to the hierarchical prediction. Therefore, the stellar population of red sequence galaxies is similar in clusters and groups, in spite of different halo histories. Finally, since the observed rest-frame color of the red sequence does not depend on environment and redshift, it can be used as a distance indicator, with an error σz=0.018, a few times better than the precision achieved by other photometric redshift estimates and twice better than the precision of the Fundamental Plane for a single galaxy at the median redshift of the EDR-SDSS. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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