57 research outputs found
Environments of strong/ultrastrong, ultraviolet Fe II emitting quasars
We have investigated the strength of ultraviolet (UV) Fe ii emission from quasars within the environments of large quasar groups (LQGs) in comparison with quasars elsewhere, for 1.1 ≤ z̅LQG ≤ 1.7, using the DR7QSO catalogue of the Sloan Digital Sky Survey. We use the Weymann et al. W2400 equivalent width, defined between the rest-frame continuum windows 2240–2255 and 2665–2695 Å, as the measure of the UV Fe ii emission. We find a significant shift of the W2400 distribution to higher values for quasars within LQGs, predominantly for those LQGs with 1.1 ≤ z̅LQG ≤ 1.5. There is a tentative indication that the shift to higher values increases with the quasar i magnitude. We find evidence that within LQGs the ultrastrong emitters with W2400 ≥ 45 Å (more precisely, ultrastrong plus with W2400 ≥ 44 Å) have preferred nearest-neighbour separations of ∼30–50 Mpc to the adjacent quasar of any W2400 strength. No such effect is seen for the ultrastrong emitters that are not in LQGs. The possibilities for increasing the strength of the Fe ii emission appear to be iron abundance, Lyα fluorescence and microturbulence, and probably all of these operate. The dense environment of the LQGs may have led to an increased rate of star formation and an enhanced abundance of iron in the nuclei of galaxies. Similarly, the dense environment may have led to more active blackholes and increased Lyα fluorescence. The preferred nearest-neighbour separation for the stronger emitters would appear to suggest a dynamical component, such as microturbulence. In one particular LQG, the Huge-LQG (the largest structure known in the early Universe), six of the seven strongest emitters very obviously form three pairings within the total of 73 members
Objective-prism spectrophotometry of quasars
A procedure is derived for obtaining low -resolution
spectrophotometry of quasars directly from the objective -prism plates
on which they were discovered. Measurements with a PDS
microdensitometer of - 130 quasar candidates in approximately the
central 19 square degrees of the UK Schmidt prism plate UJ3682P were
used in the application of the procedure (practical details of the
searches for quasars and of the objective -prism spectrophotometry are
given). The success of the objective -prism spectrophotometry is
demonstrated in a comparison with 12 slit spectra. Redshífts and
equivalent widths can be determined with typical discrepancies of 1%
and 40% respectively.This work on objective -prism spectrophotometry leads to a quantification
of the selection effects that operate in the searches for
emission-line objects on objective -prism plates. The quantification
successfully explains an apparent discrepancy in the detection
efficiencies of the CTIO-4m and Curtis Schmidt surveys for quasars.Spectra of quasars that were observed with the Image Photon
Counting System on the Anglo- Australian Telescope are presented. The
observations of quasars with broad absorption troughs indicate the
ejection of matter with velocities up to ~ 22O00kms⁻¹ and with
velocity dispersions up to -
~ 11000kms⁻¹.Data on the wavelength dependences of the contrast y and the
grain response function g of the Kodak emulsion IIIaJ are presented
Accidental deep field bias in CMB T and SNe z correlation
Evidence presented by Yershov, Orlov and Raikov apparently showed that the WMAP/Planck cosmic microwave background (CMB) pixel-temperatures (T) at supernovae (SNe) locations tend to increase with increasing redshift (z). They suggest this correlation could be caused by the Integrated Sachs-Wolfe effect and/or by some unrelated foreground emission. Here, we assess this correlation independently using Planck 2015 SMICA R2.01 data and, following Yershov et al., a sample of 2783 SNe from the Sternberg Astronomical Institute. Our analysis supports the prima facie existence of the correlation but attributes it to a composite selection bias (high CMB T × high SNe z) caused by the accidental alignment of seven deep survey fields with CMB hotspots. These seven fields contain 9.2 per cent of the SNe sample (256 SNe). Spearman’s rank-order correlation coefficient indicates the correlation present in the whole sample (ρs = 0.5, p-value =6.7 × 10−9) is insignificant for a sub-sample of the seven fields together (ρs = 0.2, p-value =0.2) and entirely absent for the remainder of the SNe (ρs = 0.1, p-value =0.6). We demonstrate the temperature and redshift biases of these seven deep fields, and estimate the likelihood of their falling on CMB hotspots by chance is at least ∼ 6.8 per cent (approximately 1 in 15). We show that a sample of 7880 SNe from the Open Supernova Catalogue exhibits the same effect and we conclude that the correlation is an accidental but not unlikely selection bias
A structure in the early Universe at z 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology
A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within ~ 2 deg (~ 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle
Compatibility of the large quasar groups with the concordance cosmological model
We study the compatibility of large quasar groups with the concordance cosmological model. Large quasar groups are very large spatial associations of quasars in the cosmic web, with sizes of 50–250 h−1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ∼860 h−1 Mpc, larger than the scale of homogeneity (∼260 Mpc), which has been noted as a possible violation of the cosmological principle. Using mock catalogues
constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 ± 1 times larger than the one currently studied
The FSVS Cluster Catalogue: Galaxy Clusters and Groups in the Faint Sky Variability Survey
We describe a large sample of 598 galaxy clusters and rich groups discovered
in the data of the Faint Sky Variability Survey. The clusters have been
identified using a fully automated, semi-parametric technique based on a
maximum likelihood approach applied to Voronoi tessellation, and enhanced by
colour discrimination. The sample covers a wide range of richness, has a
density of ~28 clusters per sqdeg, and spans a range of estimated redshifts of
0.05 = 0.345. Assuming the presence of a cluster red
sequence, the uncertainty of the estimated cluster redshifts is assessed to be
\~0.03. Containing over 100 clusters with z > 0.6, the catalogue contributes
substantially to the current total of optically-selected, intermediate-redshift
clusters, and complements the existing, usually X-ray selected, samples. The
FSVS fields are accessible for observation throughout the whole year, making
them particularly suited for large follow-up programmes. The construction of
this FSVS Cluster Catalogue completes a fundamental component of our continuing
programmes to investigate the environments of quasars and the chemical
evolution of galaxies. We publish here the list of all clusters with their
basic parameters, and discuss some illustrative examples in more detail. The
full FSVS Cluster Catalogue, together with images and lists of member galaxies
etc., will be issued as part of the ``NOAO data products'', and accessible at
http://www.noao.edu/dpp/. We describe the format of these data and access to
them.Comment: 19 pages and 17 figures, MNRAS accepte
Correlated orientations of the axes of large quasar groups on Gpc scales
Abstract Correlated orientations of quasar optical and radio polarisation, and of radio jets, have been reported on Gpc scales, possibly arising from intrinsic alignment of spin axes. Optical quasar polarisation appears to be preferentially either aligned or orthogonal to the host large-scale structure, specifically large quasar groups (LQGs). Using a sample of 71 LQGs at redshifts 1.0 ≤ z ≤ 1.8, we investigate whether LQGs themselves exhibit correlated orientation. We find that LQG position angles (PAs) are unlikely to be drawn from a uniform distribution (p-values 0.008 ≲ p ≲ 0.07). The LQG PA distribution is bimodal, with median modes at , remarkably close to the mean angles of quasar radio polarisation reported in two regions coincident with our LQG sample. We quantify the degree of alignment in the PA data, and find that LQGs are aligned and orthogonal across very large scales. The maximum significance is (2.4σ) at typical angular (proper) separations of ∼30○ (1.6 Gpc). If the LQG orientation correlation is real, it represents large-scale structure alignment over scales larger than those predicted by cosmological simulations and at least an order of magnitude larger than any so far observed, with the exception of quasar-polarisation / radio-jet alignment. We conclude that LQG alignment helps explain quasar-polarisation / radio-jet alignment, but raises challenging questions about the origin of the LQG correlation and the assumptions of the concordance cosmological model
Two close large quasar groups of size ∼ 350 Mpc at
The Clowes & Campusano large quasar group (LQG) at inline image has been re-examined using the quasar data from the DR7QSO catalogue of the Sloan Digital Sky Survey. In the 1991 discovery, the LQG impinged on the northern, southern and eastern limits of the survey. In the DR7QSO data, the western, northern and southern boundaries of the LQG remain essentially the same, but an extension eastwards of ∼2° is indicated. In the DR7QSO data, the LQG has 34 members, with inline image. A new group of 38 members is indicated at inline image and within ∼2bsl000640 of the Clowes & Campusano LQG. The characteristic sizes of these two LQGs, ∼350–400 Mpc, appear to be only marginally consistent with the scale of homogeneity in the concordance cosmology. In addition to their intrinsic interest, these two LQGs provide locations in which to investigate early large-scale structure in galaxies and to identify high-z clusters. A method is presented for assessing the statistical significance and overdensity of groups found by linkage of points
A structure in the early Universe at z 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology
A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within ~ 2 deg (~ 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle
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