A structure in the early Universe at z ∼ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology.
Monthly Notices of the Royal Astronomical Society (2013), 429, 2910.
The Largest Structure in the Universe
Roger G. Clowes1, Kathryn A. Harris1,2, Srinivasan Raghunathan1,3, Luis E. Campusano3, Ilona K. Söchting4, Matthew J. Graham5
1 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
2 Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
3 Observatorio Astronómico Cerro Calán, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
4 Astrophysics, Denys Wilkinson Building, Keble Road, University of Oxford, Oxford OX1 3RH, UK
5 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
The Huge-LQG (Clowes et al. 2013) at <z> = 1.27 is a Large Quasar Group (LQG) of characteristic size (volume1/3) ∼ 500 Mpc (present epoch) that exceeds the Yadav et al. (2010) scale of homogeneity of 370 Mpc. Its “CHMS-significance” (Clowes et al. 2012, 2013) of 3.81σ expresses the departure of its volume from that expected from a large control sample for the same number N=73 of quasars. The principal axes of the Huge-LQG are 1240, 640, 370 Mpc, so its longest dimension is 1240 Mpc, compared with the characteristic 500 Mpc. MgII absorbers (strong absorbers!) offer some independent evidence of a mass enhancement. The Huge-LQG is one of six that exceed the Yadav et al. scale at ≥ 2.95σ. It is only the third most CHMS-significant of these six, but it has the highest membership and is the largest. The Huge-LQG is ∼ 8.8º N (∼ 615 Mpc) of the older Clowes & Campusano (1991) LQG (CCLQG) at the same <z> = 1.28; their boundaries approach to ∼ 2º (∼140 Mpc). Work is in progress using the Horizon Run simulations (Kim et al. 2012) to establish whether these very large overdensities are compatible with the concordance cosmological model.
Figure 1. Sky distribution of the 73 quasars of the Huge-LQG (<z> = 1.27, circles) is shown, together with that of the 34 quasars of the older CCLQG (<z> = 1.28, crosses). The members of each LQG are connected at the linkage scale of 100 Mpc. The area shown is approximately 29.5º×24.0º. The SDSS DR7QSO quasars are limited to i ≤ 19.1. Superimposed on these distributions is a kernel-smoothed intensity map (isotropic Gaussian kernel, σ = 0.4º), plotted with logarithmic palette levels (≤ 0.460, 0.460-0.651, 0.651-0.920, 0.920-1.301, 1.301-1.840, 1.840-2.602, 2.602-3.680, ≥ 3.680 deg−2), for all of the quasars in the joint redshift range of the Huge-LQG and the CCLQG (z: 1.1742 → 1.4232).
Figure 2. Snapshot from a visualisation of both the Huge-LQG and the older CCLQG. The scales shown on the cuboid are proper sizes (Mpc) at the present epoch. The tick marks represent intervals of 200 Mpc. The Huge-LQG appears as the upper LQG. For comparison, the members of both are shown as spheres of radius 33.0 Mpc (half of the mean linkage for the Huge-LQG; the value for the CCLQG is 38.8 Mpc). For the Huge-LQG, note the dense, clumpy part followed by a change in orientation and a more filamentary part. There is no difference in linkage properties that might suggest two LQGs. The Huge-LQG and the CCLQG appear to be distinct entities.
Figure 3. Same as Figure 1, but superimposed on these distributions is a kernel-smoothed intensity map (isotropic Gaussian kernel, σ = 0.4º), plotted with logarithmic palette levels (≤ 0.460, 0.460-0.651, 0.651-0.920, 0.920-1.301, 1.301-1.840, 1.840-2.602, 2.602-3.680, ≥ 3.680 deg−2), for all of the MgII λλ2796, 2803 absorbers in the joint redshift range of the Huge-LQG and the CCLQG (z: 1.1742 → 1.4232) that have been found in the SDSS DR7QSO background quasars (z > 1.4232, non-BAL, and restricted to i ≤ 19.1) using the MgII absorber catalogue of Raghunathan et al. (in preparation). The MgII systems used here have rest-frame equivalent widths for the λ2796 component of 0.65 ≤ Wr,2796 ≤ 4.0 Å. Apparent MgII systems occurring shortwards of the Lyα emission in the background quasars are assumed to be spurious and have been excluded.
This work has used the SDSS DR7QSO catalogue (Schneider et al. 2010) and the SDSS spectra.
A new development. Hutsemékers et al. (2014) have shown that the polarisation vectors of member quasars are correlated with the direction of the Huge-LQG and with each other over scales in excess of 500 Mpc.
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