共查询到20条相似文献，搜索用时 15 毫秒
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R. J. Smith B. J. Boyle S. J. Maddox 《Monthly notices of the Royal Astronomical Society》2000,313(2):252-262
An angular correlation of low significance (2 σ ) is observed between 0.3< z <0.5 QSOs and V 23 galaxies. Overall, the cross-correlation function between 82 intermediate-redshift (0.3< z <0.7) X-ray selected QSOs and V ≲24 galaxies is investigated, but no signal is detected for the z >0.5 QSOs. After converting to an excess of galaxies physically associated with the QSO, this lack of strong correlation is shown to be consistent with the clustering of normal galaxies at the same moderate redshifts. Combined with previous observations, these results imply that the environments of radio-quiet QSOs do not undergo significant evolution with respect to the galaxy population over a wide range of redshifts (0< z <1.5). This is in marked contrast to the rapid increase in the richness of the environments associated with radio-loud QSOs over the same redshift range. 相似文献
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Margrethe Wold Mark Lacy Per B. Lilje Stephen Serjeant 《Monthly notices of the Royal Astronomical Society》2001,323(1):231-247
We quantify the galaxy environments around a sample of 0.5≤ z ≤0.8 radio-quiet quasars using the amplitude of the spatial galaxy–quasar correlation function, B gq . The quasars exist in a wide variety of environments; some sources are located in clusters as rich as Abell class 1–2 clusters, whereas others exist in environments comparable to the field. We find that, on average, the quasars prefer poorer clusters of ≈Abell class 0, which suggests that quasars are biased tracers of mass compared with galaxies. The mean B gq for the sample is found to be indistinguishable from the mean amplitude for a sample of radio-loud quasars matched in redshift and optical luminosity. These observations are consistent with recent studies of the hosts of radio-quiet quasars at low to intermediate redshifts, and suggest that the mechanism for the production of powerful radio jets in radio-loud quasars is controlled by processes deep within the active galactic nucleus itself, and is unrelated to the nature of the hosts or their environments. 相似文献
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P. N. Wilkinson I. W. A. Browne A. R. Patnaik J. M. Wrobel & B. Sorathia 《Monthly notices of the Royal Astronomical Society》1998,300(3):790-816
We present a catalogue of 540 compact radio sources in the declination ranges +20 ≤ δ B1950 ≤ + 35° and +75 ≤ δ B1950 ≤ + 90°, the positions of which have been measured to an rms accuracy of about 55 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for MERLIN. However, they will also be suitable as phase calibrators for the VLA and can be considered as candidate phase calibrators for very long baseline interferometry (VLBI) networks. 相似文献
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Saul J. Adelman 《Monthly notices of the Royal Astronomical Society》1998,296(4):856-862
Elemental abundances of the superficially normal early and middle B starsζ Dra, ε Lyr, 8 Cyg and 22 Cyg are derived, consistent with previous studies in this series, using spectrograms obtained with Reticon and CCD detectors. Almost all of the derived metal abundances are found to be solar within the errors of the analysis. However, the He/H ratios are slightly greater than solar. 相似文献
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S. Andreon 《Monthly notices of the Royal Astronomical Society》2008,386(2):1045-1052
We measure the relative evolution of the number of bright and faint (as faint as 0.05 L *) red galaxies in a sample of 28 clusters, out of which 16 are at 0.50 ≤ z ≤ 1.27 , all observed through a pair of filters bracketing the 4000-Å break rest frame. The abundance of red galaxies, relative to bright ones, is constant over all the studied redshift range, 0 < z < 1.3 , and rules out a differential evolution between bright and faint red galaxies as large as claimed in some past works. Faint red galaxies are largely assembled and in place at z = 1.3 and their abundance does not depend on cluster mass, parametrized by velocity dispersion or X-ray luminosity. Our analysis, with respect to the previous one, samples a wider redshift range, minimizes systematics and put a more attention to statistical issues, keeping at the same time a large number of clusters. 相似文献
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D. C. Gabuzda T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,319(4):1056-1066
Global VLBI images in intensity and linear polarization at of the BL Lacertae objects 0235+164, 0300+470, 0735+178, 0954+658, 1803+784, 1823+568, and BL Lac and OVV quasar 3C 279 are presented and analysed. These are the highest resolution polarization images currently available for several of these sources. On the whole, the tendencies observed at longer centimetre wavelengths are also exhibited in these 1.3-cm images. When core polarization is detected, the corresponding polarization angles χ tend to lie either parallel or perpendicular to the direction of the inner jet. The core degrees of polarization are usually comparable to those typical at 6 cm, but somewhat lower in several cases, suggesting that the higher resolution data are better separating the contributions of intrinsically weakly polarized cores and highly polarized emerging knots. The observed χ vectors in the jets of 0735+178, 0954+658, 1823+568, BL Lac and 3C 279 are aligned with the jet, implying the presence of transverse magnetic fields. In 0300+470 and BL Lac, there are regions where the direction of χ seems to be neither parallel nor perpendicular to the jet; it is not clear whether this is due to genuine obliquity of the magnetic field structure or to inadequate knowledge of the local flow direction. 相似文献
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N. A. Hatch R. A. Overzier J. D. Kurk G. K. Miley H. J. A. Röttgering A. W. Zirm 《Monthly notices of the Royal Astronomical Society》2009,395(1):114-125
We study the stellar mass assembly of the Spiderweb galaxy (MRC 1138−262) , a massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z = 0 , increasing its stellar mass by up to a factor of ≃2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores. 相似文献
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TomasDahlén ClaesFransson MagnusNäslund 《Monthly notices of the Royal Astronomical Society》2002,330(1):167-183
Photometric redshifts are used to determine the rest-frame luminosity function (LF) of both early- and late-type galaxies to MB ∼−17.6 for the cluster Cl 1601+42 at z=0.54 . The total LF shows a steep faint-end slope α ∼−1.4 , indicating the existence of a population of numerous dwarf galaxies. Luminous galaxies, with MB ≲−19.5 are mostly red, early-type galaxies, with a LF best described by a Gaussian. Faint galaxies are predominantly blue, late-type galaxies, well fitted by a Schechter function with α ∼−1.7 . Compared with clusters at lower redshift, the steepening of the faint end starts at brighter magnitudes for Cl 1601+42, which may indicate a brightening of the present-day dwarf population relative to the giant population with increasing redshift. Early-type galaxies are centrally concentrated, and dominate the core region, implying that the radial gradient of early-type galaxies seen in local clusters is already established at z∼0.5 . Bright, late-type galaxies are rare, consistent with a decrease in star formation in field galaxies as they are accreted on to the cluster, while faint, blue galaxies are evenly distributed across the cluster, except for a depletion in the core region. The blue fraction is fB ∼0.15 , which is somewhat lower than the Butcher–Oemler average at z∼0.5 . The value of f B is found to increase with limiting magnitude and with radius from the centre. 相似文献
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C. Koen Jerome A. Orosz & Richard A. Wade 《Monthly notices of the Royal Astronomical Society》1998,300(3):695-704
The subdwarf B (sdB) star KPD 0422 + 5421 was discovered to be a single-lined spectroscopic binary with a period of P = 0.090 1795 ± (3 × 10−7 ) d (2 h 10 min). The U B light curves display an ellipsoidal modulation with amplitudes of ≈ 0.02 mag. The sdB star contributes nearly all of the observed flux. This and the absence of any reflection effect suggest that the unseen companion star is small (i.e. R comp ≈ 0.01 R⊙ ) and therefore degenerate. We modelled the U B light curves and derived i = 78.05° ± 0.50° and a mass ratio of q = M comp / M sdB = 0.87 ± 0.15. The sdB star fills 69 per cent of its Roche lobe. These quantities may be combined with the mass function of the companion [ f ( M ) = 0.126 ± 0.028 M⊙ ] to derive M sdB = 0.72 ± 0.26 M⊙ and M comp = 0.62 ± 0.18 M⊙ . We used model spectra to derive the effective temperature, surface gravity and helium abundance of the sdB star. We found T eff = 25 000 ± 1500 K, log g = 5.4 ± 0.1 and [He/H] = −1.0. With a period of 2 h 10 min, KPD 0422 + 5421 has one of the shortest known orbital periods of a detached binary. This system is also one of only a few known binaries that contain a subdwarf B star and a white dwarf. Thus KPD 0422 + 5421 represents a relatively unobserved, and short-lived, stage of binary star evolution. 相似文献
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Michael C. Cooper Jeffrey A. Newman † Alison L. Coil † Darren J. Croton Brian F. Gerke Renbin Yan Marc Davis S. M. Faber Puragra Guhathakurta David C. Koo Benjamin J. Weiner Christopher N. A. Willmer ‡ 《Monthly notices of the Royal Astronomical Society》2007,376(4):1445-1459
Using a sample of 19 464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy colour and environment at 0.4 < z < 1.35 . We find that the fraction of galaxies on the red sequence depends strongly on local environment out to z > 1 , being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at z > 1 detected at a greater than 5σ level. Over the entire redshift regime studied, we find that the colour–density relation evolves continuously, with red galaxies more strongly favouring overdense regions at low z relative to their red-sequence counterparts at high redshift. At z ≳ 1.3 , the red fraction only weakly correlates with overdensity, implying that any colour dependence to the clustering of ∼ L * galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e. galaxy groups) at z ≲ 1.5 . Furthermore, we identify the epoch ( z ∼ 2) at which typical ∼ L * galaxies began quenching and moved on to the red sequence in significant number. The strength of the observed evolutionary trends at 0 < z < 1.35 suggests that the correlations observed locally, such as the morphology–density and colour–density relations, are the result of environment-driven mechanisms (i.e. 'nurture') and do not appear to have been imprinted (by 'nature') upon the galaxy population during their epoch of formation. 相似文献
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