122 research outputs found
Mystery of the Lyα Blobs
We present Spitzer Space Telescope observations of the extended Lyman α blobs associated with the z=2.38 over-density J2143-4423, the largest known structure (110 Mpc) above z=2. We detect all 4 of the Lyα blobs in all four IRAC channels and we also detect 3 out of 4 of the blobs with MIPS 24μm. Conversion from rest-wavelength 7μm to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs or even Hyper-LIRGs. We find a weak correlation between Lyα and mid-infrared emission for the Lyα blobs (L_(Lyα)/L_(bol) = 0.05-0.2%). Nearly all Lyα blobs show some evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lyα cloud. This suggests that interaction or even mergers may be related to the production of Lyα blobs. Optical through infrared SEDs of the Lyα blobs do not show a clear 1.6μm bump, but rather are indicative of a composite of star formation and AGN energy sources
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
A Study of the Reionization History of Intergalactic Helium with FUSE and VLT
We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to
study the properties of the intergalactic medium between redshifts z=2.0-2.9.
The high-quality optical spectrum allows us to identify approximately 850 HeII
absorption components with column densities between N~5X10^11 and $ 10^18
cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the
HeII absorption down to an observed wavelength of 920 A. Approximately 1400
HeII absorption components are identified, including 917 HeII Ly-alpha systems
and some of their HeII Ly-beta, Ly-gamma, and Ly-delta counterparts. The
ionization structure of HeII is complex, with approximately 90 components that
are not detected in the hydrogen spectrum. These components may represent the
effect of soft ionizing sources. The ratio Eta=N(HeII)/N(HI) varies
approximately from unity to more than a thousand, with a median value of 62 and
a distribution consistent with the intrinsic spectral indices of quasars. This
suggests that the dominant ionizing field is from the accumulated quasar
radiation, with contributions from other soft sources such as star-forming
regions and obscured AGN, which do not ionize helium. We find an evolution in
Eta toward smaller values at lower redshift, with the gradual disappearance of
soft components. At redshifts z>2.7, the large but finite increase in the HeII
opacity, Tau=5+/-1, suggests that we are viewing the end stages of a
reionization process that began at an earlier epoch. Fits of the absorption
profiles of unblended lines indicate comparable velocities between hydrogen and
He^+ ions. At hydrogen column densities N<3X10^12 cm^-2 the number of forest
lines shows a significant deficit relative to a power law, and becomes
negligible below N=10^11 cm^-2.Comment: 40 pages, 10 Postscript figures, uses Aastex.sty The Astrophysical
Journal, in pres
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
Large-scale structure in the Lyman-alpha forest II: analysis of a group of ten QSOs
The spatial distribution of Ly-alpha forest absorption systems towards ten
QSOs has been analysed to search for large-scale structure over the redshift
range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are
concentrated within a 1 deg^2 field. We have employed a technique based on the
first and second moments of the transmission probability density function which
is capable of identifying and assessing the significance of regions of over- or
underdense Ly-alpha absorption. We find evidence for large-scale structure in
the distribution of Ly-alpha forest absorption at the > 99 per cent confidence
level. In individual spectra we find overdense Ly-alpha absorption on scales of
up to 1200 km s^-1. There is also strong evidence for correlated absorption
across line of sight pairs separated by < 3 h^-1 proper Mpc (q_0 = 0.5). For
larger separations the cross-correlation signal becomes progressively less
significant.Comment: 15 pages, LaTeX, 6 Postscript figures, accepted for publication in
MNRA
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