We present a clustering analysis of luminous red galaxies (LRGs) using nearly 9000 objects from the final, three-year catalogue of the 2dF-SDSS LRG and QSO (2SLAQ) Survey. We measure the ...redshift-space two-point correlation function, ξ(s) and find that, at the mean LRG redshift of shows the characteristic downturn at small scales (≲1 h−1 Mpc) expected from line-of-sight velocity dispersion. We fit a double power law to ξ(s) and measure an amplitude and slope of s0= 17.3+2.5−2.0 h−1 Mpc, γ= 1.03 ± 0.07 at small scales (s < 4.5 h−1 Mpc) and s0= 9.40 ± 0.19 h−1 Mpc, γ= 2.02 ± 0.07 at large scales (s > 4.5 h−1 Mpc). In the semiprojected correlation function, wp(σ), we find a simple power law with γ= 1.83 ± 0.05 and r0= 7.30 ± 0.34 h−1 Mpc fits the data in the range 0.4 < σ < 50 h−1 Mpc, although there is evidence of a steeper power law at smaller scales. A single power law also fits the deprojected correlation function ξ(r), with a correlation length of r0= 7.45 ± 0.35 h−1 Mpc and a power-law slope of γ= 1.72 ± 0.06 in the 0.4 < r < 50 h−1 Mpc range. But it is in the LRG angular correlation function that the strongest evidence for non-power-law features is found where a slope of γ=−2.17 ± 0.07 is seen at 1 < r < 10 h−1 Mpc with a flatter γ=−1.67 ± 0.07 slope apparent at r≲ 1 h−1 Mpc scales. We use the simple power-law fit to the galaxy ξ(r), under the assumption of linear bias, to model the redshift-space distortions in the 2D redshift-space correlation function, ξ(σ, π). We fit for the LRG velocity dispersion, wz, the density parameter, Ωm and β(z), where β(z) =Ω0.6m/b and b is the linear bias parameter. We find values of wz= 330 km s−1, Ωm= 0.10+0.35−0.10 and β= 0.40 ± 0.05. The low values for wz and β reflect the high bias of the LRG sample. These high-redshift results, which incorporate the Alcock–Paczynski effect and the effects of dynamical infall, start to break the degeneracy between Ωm and β found in low-redshift galaxy surveys such as 2dFGRS. This degeneracy is further broken by introducing an additional external constraint, which is the value β(z= 0.1) = 0.45 from 2dFGRS, and then considering the evolution of clustering from z∼ 0 to zLRG∼ 0.55. With these combined methods we find Ωm(z= 0) = 0.30 ± 0.15 and β(z= 0.55) = 0.45 ± 0.05. Assuming these values, we find a value for b(z= 0.55) = 1.66 ± 0.35. We show that this is consistent with a simple ‘high-peak’ bias prescription which assumes that LRGs have a constant comoving density and their clustering evolves purely under gravity.
The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this ...hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter beta = Omega0.6/b = 0.43 +/- 0.07, where Omega is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with Omega approximately 0.3.
We have combined optical data from the 2dF-SDSS (Sloan Digital Sky Survey) LRG (Luminous Red Galaxy) and QSO (quasi-stellar object) (2SLAQ) redshift survey with radio measurements from the 1.4 GHz ...VLA (Very Large Array) FIRST (Faint Images of the Radio Sky at Twenty-cm) and NVSS (NRAO VLA Sky Survey) surveys to identify a volume-limited sample of 391 radio galaxies at redshift 0.4 < z < 0.7. By determining an accurate radio luminosity function for luminous early-type galaxies in this redshift range, we can investigate the cosmic evolution of the radio-galaxy population over a wide range in radio luminosity.
The low-power radio galaxies in our LRG sample (those with 1.4 GHz radio luminosities in the range 1024 to 1025 W Hz−1, corresponding to Fanaroff-Riley I (FR I) radio galaxies in the local Universe) undergo significant cosmic evolution over the redshift range 0 < z < 0.7, consistent with pure luminosity evolution of the form (1 +z)
k
, where k= 2.0 ± 0.3. Our results appear to rule out (at the 6-7σ level) models in which low-power radio galaxies undergo no cosmic evolution. The most powerful radio galaxies in our sample (with radio luminosities above 1026 W Hz−1) may undergo more rapid evolution over the same redshift range.
The evolution seen in the low-power radio-galaxy population implies that the total energy input into massive early-type galaxies from active galactic nucleus (AGN) heating increases with redshift, and was at least 50 per cent higher at z∼ 0.55 (the median redshift of the 2SLAQ LRG sample) than in the local universe.
We have combined optical data from the 2dF-SDSS (Sloan Digital Sky Survey) LRG (Luminous Red Galaxy) and QSO (quasi-stellar object) (2SLAQ) redshift survey with radio measurements from the 1.4 GHz ...VLA (Very Large Array) FIRST (Faint Images of the Radio Sky at Twenty-cm) and NVSS (NRAO VLA Sky Survey) surveys to identify a volume-limited sample of 391 radio galaxies at redshift 0.4 < z < 0.7. By determining an accurate radio luminosity function for luminous early-type galaxies in this redshift range, we can investigate the cosmic evolution of the radio-galaxy population over a wide range in radio luminosity. The low-power radio galaxies in our LRG sample (those with 1.4 GHz radio luminosities in the range 10 super(24) to 10 super(25) W Hz super(-1), corresponding to Fanaroff-Riley I (FR I) radio galaxies in the local Universe) undergo significant cosmic evolution over the redshift range 0 < z < 0.7, consistent with pure luminosity evolution of the form (1 +z) super(k), where k= 2.0 plus or minus 0.3. Our results appear to rule out (at the 6-7 sigma level) models in which low-power radio galaxies undergo no cosmic evolution. The most powerful radio galaxies in our sample (with radio luminosities above 10 super(26) W Hz super(-1)) may undergo more rapid evolution over the same redshift range.The evolution seen in the low-power radio-galaxy population implies that the total energy input into massive early-type galaxies from active galactic nucleus (AGN) heating increases with redshift, and was at least 50 per cent higher at z similar to 0.55 (the median redshift of the 2SLAQ LRG sample) than in the local universe.
Organisational structures in the transport sector are often complex and fragmented, with different authorities responsible for different stages of a traveller’s journey. In such circumstances, ...collaboration across organisationalboundaries is required to facilitate intermodal journeys. This paper aims to provide empirically grounded insights into collaboration in transport planning, extending the literature to include cycling as an access and egress mode. This is done by examining the challenge of improving bicycle parking facilities at railway stations in Copenhagen, Denmark. Interviews with key actors involved in public transport and cycling planning reveal three main inter-organisational barriers to improving station bicycle parking in Copenhagen. First, station bicycle parking falls between the responsibilities of different organisations and levels of governance. Second, the absence of an established funding formula contributes to negotiation-oriented rather than collaborative interactions among the stakeholders. Third, the tension between cyclist satisfaction and rail passenger growth targets hinders collective action. In summary, despite Copenhagen’s strong cycling identity and the prioritisation of this transportation mode in the city’s political decision-making and transport planning, the issue of station bicycle parking highlights the complexity of multi-actor governance of intermodal journeys.
We report on the AAT-AAOmega LRG Pilot observing run to establish the feasibility of a large spectroscopic survey using the new AAOmega instrument. We have selected luminous red galaxies (LRGs) using ...single epoch SDSS riz-photometry to i < 20.5 and z < 20.2. We have observed in three fields including the COSMOS field and the COMBO-17 S11 field, obtaining a sample of ∼600 redshift z≳ 0.5 LRGs. Exposure times varied from 1–4 h to determine the minimum exposure for AAOmega to make an essentially complete LRG redshift survey in average conditions. We show that LRG redshifts to i < 20.5 can be measured in ≈1.5 h exposures and present comparisons with 2SLAQ and COMBO-17 (photo)redshifts. Crucially, the riz selection coupled with the three to four times improved AAOmega throughput is shown to extend the LRG mean redshift from z= 0.55 for 2SLAQ to z= 0.681 ± 0.005 for riz-selected LRGs. This extended range is vital for maximizing the signal-to-noise ratio for the detection of the baryon acoustic oscillations (BAOs). Furthermore, we show that the amplitude of LRG clustering is s0= 9.9 ± 0.7h−1Mpc, as high as that seen in the 2SLAQ LRG Survey. Consistent results for this clustering amplitude are found from the projected and semi-projected correlation functions. This high amplitude is consistent with a long-lived population whose bias evolves as predicted by a simple ‘high-peak’ model. We conclude that a redshift survey of 360 000 LRGs over 3000 deg2, with an effective volume some four times bigger than previously used to detect BAO with LRGs, is possible with AAOmega in 170 nights.
We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325deg2 (about 20 per cent of ...the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications – the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4GHz for both active and star-forming galaxies, and derive a local star formation density of .
Ann Savage 1946–2017 Watson, Fred; Cannon, Russell
Astronomy & geophysics : the journal of the Royal Astronomical Society,
04/2017, Letnik:
58, Številka:
2
Journal Article
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