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We present an analysis of the orientations of 1433 galaxies found in the region 15h 48m ≤α(2000) ≤ 19h 28m , −68°≤δ(2000) ≤−62° . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies ( b / a < 0.5, 0.4 < b / a ≤ 0.5) show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre. 相似文献
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T. J. Waskett S. A. Eales W. K. Gear H. J. McCracken S. Lilly M. Brodwin 《Monthly notices of the Royal Astronomical Society》2005,363(3):801-810
The environmental properties of a sample of 31 hard X-ray selected active galactic nuclei (AGN) are investigated, from scales of 500 kpc down to 30 kpc, and are compared to a control sample of inactive galaxies. All the AGN lie in the redshift range 0.4 < z < 0.6 . The accretion luminosity density of the Universe peaks close to this redshift range, and the AGN in the sample have X-ray luminosities close to the knee in the hard X-ray luminosity function, making them representative of the population that dominated this important phase of energy conversion.
Using both the spatial clustering amplitude and near-neighbour counts, it is found that the AGN have environments that are indistinguishable from normal, inactive galaxies over the same redshift range and with similar optical properties. Typically, the environments are of subcluster richness, in contrast to similar studies of high- z quasars, which are often found in clusters with comparable richness to the Abell R ≥ 0 clusters.
It is suggested that minor mergers with low-mass companions are a likely candidate for the mechanism by which these modest luminosity AGN are fuelled. 相似文献
Using both the spatial clustering amplitude and near-neighbour counts, it is found that the AGN have environments that are indistinguishable from normal, inactive galaxies over the same redshift range and with similar optical properties. Typically, the environments are of subcluster richness, in contrast to similar studies of high- z quasars, which are often found in clusters with comparable richness to the Abell R ≥ 0 clusters.
It is suggested that minor mergers with low-mass companions are a likely candidate for the mechanism by which these modest luminosity AGN are fuelled. 相似文献
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Chris Simpson Martin Ward J. V. Wall 《Monthly notices of the Royal Astronomical Society》2000,319(3):963-976
It has been claimed by Taylor et al. that the low-redshift end of the K – z relation for radio galaxies is too bright by about half a magnitude owing to contributions from the obscured quasar nuclei. Such a result has major implications for the use of the K -band Hubble diagram in understanding the cosmological evolution of radio galaxies. In this paper we present 1–5-μm imaging data of a nearly complete sample of low-redshift radio galaxies; this approach allows us to determine accurately the strengths of any unresolved nuclear components in the galaxies. We detect nuclear sources in five targets, whose broad-band colours are consistent with reddened quasar spectra. In all the five cases the ratio of the inferred intrinsic near-infrared luminosity to the narrow-line luminosity is typical of quasars. We find a correlation between the inferred nuclear extinction and core-to-lobe ratio, which places constraints on the geometry of the torus. We find evidence for a shift of the K – z relation to fainter magnitudes, but by a much smaller amount (∼0.1 mag) than determined by Taylor et al. Under the assumption that the nuclear sources in radio galaxies have the same intrinsic near-infrared spectra as quasars, our multiwavelength images allow us to limit any possible shift to less than 0.3 mag. 相似文献
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Elizabeth R. Stanway † rew J. Bunker Karl Glazebrook Roberto G. Abraham James Rhoads Sangeeta Malhotra David Crampton Matthew Colless Kuenley Chiu 《Monthly notices of the Royal Astronomical Society》2007,376(2):727-738
The galaxy population at z ≈ 6 has been the subject of intense study in recent years, culminating in the Hubble Ultra Deep Field (HUDF) – the deepest imaging survey yet. A large number of high-redshift galaxy candidates have been identified within the HUDF, but until now analysis of their properties has been hampered by the difficulty of obtaining spectroscopic redshifts for these faint galaxies. Our 'Gemini Lyman-Alpha at Reionization Era' (GLARE) project has been designed to undertake spectroscopic follow-up of faint ( z ' < 28.5) i '-drop galaxies at z ≈ 6 in the HUDF. In a previous paper we presented preliminary results from the first 7.5 h of data from GLARE. In this paper we detail the complete survey. We have now obtained 36 h of spectroscopy on a single GMOS slitmask from Gemini-South, with a spectral resolution of λ/ΔλFWHM ≈ 1000 . We identify five strong Lyα emitters at z > 5.5 , and a further nine possible line emitters with detections at lower significance. We also place tight constraints on the equivalent width of Lyα emission for a further ten i '-drop galaxies and examine the equivalent width distribution of this faint spectroscopic sample of z ≈ 6 galaxies. We find that the fraction of galaxies with little or no emission is similar to that at z ≈ 3 , but that the z ≈ 6 population has a tail of sources with high rest-frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass function. 相似文献
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Hardcastle Alexander Pooley & Riley 《Monthly notices of the Royal Astronomical Society》1998,296(2):445-462
In previous papers we have discussed high-resolution observations of a large sample of powerful radio galaxies with z < 0.3. Jets are detected in up to 80 per cent of the sample, and radio cores in nearly all the objects; in addition, we are able to resolve the hotspots in most sources. In this paper we present measurements of the radio properties of these components. The prominences of the jets detected do not appear to be a function of radio luminosity, providing the clearest evidence yet that the reported low detection rate of jets in radio galaxies has been an artefact of low-sensitivity observations. We find a positive correlation between the total source length and core prominence in the narrow-line radio galaxies. We have found evidence for a relationship between hotspot size and total source size, but few other significant relationships between hotspot properties and those of the jets or lobes. We compare our measurements with those of Bridle et al., based on observations of a sample of quasars, and argue that the results are consistent with a modification of the unified model in which the broad-line radio galaxies are the low-luminosity counterparts of quasars, although the situation is complicated by contamination with low-excitation radio galaxies which appear to have radio properties different from the high-excitation objects. We discuss the classes of empirical model that can be fitted to the data set. 相似文献
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Chris Simpson Steve Rawlings 《Monthly notices of the Royal Astronomical Society》2000,317(4):1023-1028
We present JHKL ' photometry of a complete sample of steep-spectrum radio-loud quasars from the revised 3CR catalogue in the redshift range 0.65 z <1.20. After correcting for contributions from emission lines and the host galaxies, we investigate their spectral energy distributions (SEDs) around 1 μm. About 75 per cent of the quasars are tightly grouped in the plane of optical spectral index, α opt , versus near-infrared spectral index, α IR , with the median value of α opt close to the canonical value, and the median α IR slightly flatter. We conclude that the fraction of moderately obscured, red quasars decreases with increasing radio power, in accordance with the 'receding torus' model which can also explain the relatively flat median near-infrared spectra of the 3CR quasars. Two of the red quasars have inverted infrared spectral indices, and we suggest that their unusual SEDs might result from a combination of dust-scattered and transmitted quasar light. 相似文献
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Paul A. Crowther Raman K. Prinja Max Pettini Charles C. Steidel 《Monthly notices of the Royal Astronomical Society》2006,368(2):895-902
We reconsider the use of the equivalent width of C iv λ1549, EW(C iv ), as an indicator of the oxygen abundance in star-forming galaxies, as proposed by Heckman et al. for nearby starbursts. We refine the local calibration of EW(C iv ) versus log (O/H) by using a restricted wavelength window which minimizes blending with interstellar absorption lines. When applied to the stellar component only of the complex C iv λ1549 features in two high-redshift galaxies with good quality spectra, MS 1512−cB58 ( z = 2.7268) and Q1307−BM1163 ( z = 1.4105) , the local calibration gives values of the oxygen abundance which are in good agreement with other metallicity determinations based on nebular emission and interstellar absorption lines. Our main conclusion is that for this method to give reliable results at high redshifts, it should only be used on data of sufficiently high spectral resolution ( R ≳ 1000) for stellar and interstellar C iv components to be clearly separated. Oxygen abundances will be systematically overestimated if the local calibration is applied to spectra of high-redshift galaxies obtained with the low resolving powers ( R ≃ 200–300) of many current wide-field surveys. It will also be necessary to understand better the causes of the scatter in the local relation, before we can be confident of inferences from it at high z . 相似文献
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