We measure the large-scale intrinsic alignments of galaxy clusters in the Sloan Digital Sky Survey (SDSS) using subsets of two cluster catalogues: 6625 clusters with 0.1<z<0.3 from the maxBCG cluster catalogue (Koester et al. 2007, 7500 sq. deg.), an
d 8081 clusters with 0.08<z<0.44 from the Adaptive Matched Filter catalogue (Dong et al. 2008, 6500 sq. deg.). We search for two types of cluster alignments using pairs of clusters: the alignment between the projected major axes of the clusters (`correlation alignment), and the alignment between one cluster major axis and the line connecting it to the other cluster in the pair (`pointing alignment). In each case, we use the cluster member galaxy distribution as a tracer of the cluster shape. All measurements are carried out with each catalogue separately, to check for dependence on cluster selection procedure. We find a strong detection of the pointing alignment on scales up to 100 Mpc/h, at the 6 or 10-sigma level depending on the cluster selection algorithm used. The correlation alignment is only marginally detected up to ~20 Mpc/h, at the 2 or 2.5-sigma level. These results support our current theoretical understanding of galaxy cluster intrinsic alignments in the LCDM paradigm, although further work will be needed to understand the impact of cluster selection effects and observational measurement errors on the amplitude of the detection.
In this paper, we derive scaling relations between photometric observable quantities and disk galaxy rotation velocity V_rot, or Tully-Fisher relations (TFRs). Our methodology is dictated by our purpose of obtaining purely photometric, minimal-scatte
r estimators of V_rot applicable to large galaxy samples from imaging surveys. To achieve this goal, we have constructed a sample of 189 disk galaxies at redshifts z<0.1 with long-slit H-alpha spectroscopy from Pizagno et al. (2007) and new observations. By construction, this sample is a fair subsample of a large, well-defined parent disk sample of ~170 000 galaxies selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). The optimal photometric estimator of V_rot we find is stellar mass M_* from Bell et al. (2003), based on the linear combination of a luminosity and a colour. Assuming a Kroupa IMF, we find: log [V_{80}/(km s^-1)] = (2.142 +/- 0.004)+(0.278 +/- 0.010)[log (M_*/M_sun)-10.10], where V_{80} is the rotation velocity measured at the radius R_{80} containing 80 per cent of the i-band galaxy light. This relation has an intrinsic Gaussian scatter of 0.036 +/- 0.005 dex and a measured scatter of 0.056 dex in log V_{80}. For a fixed IMF, we find that the dynamical-to-stellar mass ratios within R_{80}, (M_dyn/M_*)(R_{80}), decrease from approximately 10 to 3, as stellar mass increases from M_* ~ 10^9 to 10^{11} M_sun. At a fixed stellar mass, (M_dyn/M_*)(R_{80}) increases with disk size, so that it correlates more tightly with stellar surface density than with stellar mass or disk size alone. In future work, we will use these results to study disk galaxy formation and evolution, and perform a fair, statistical analysis of the dynamics and masses of a photometrically-selected sample of disk galaxies. [Abridged]
Correlations between the intrinsic shapes of galaxies and the large-scale galaxy density field provide an important tool to investigate galaxy intrinsic alignments, which constitute a major astrophysical systematic in cosmological weak lensing (cosmi
c shear) surveys, but also yield insight into the formation and evolution of galaxies. We measure galaxy position-shape correlations in the MegaZ-LRG sample for more than 800,000 luminous red galaxies, making the first such measurement with a photometric redshift sample. In combination with a re-analysis of several spectroscopic SDSS samples, we constrain an intrinsic alignment model for early-type galaxies over long baselines in redshift (z ~ 0.7) and luminosity (4mag). We develop and test the formalism to incorporate photometric redshift scatter in the modelling. For r_p > 6 Mpc/h, the fits to galaxy position-shape correlation functions are consistent with the scaling with r_p and redshift of a revised, nonlinear version of the linear alignment model for all samples. An extra redshift dependence proportional to (1+z)^n is constrained to n=-0.3+/-0.8 (1sigma). To obtain consistent amplitudes for all data, an additional dependence on galaxy luminosity proportional to L^b with b=1.1+0.3-0.2 is required. The normalisation of the intrinsic alignment power spectrum is found to be (0.077 +/- 0.008)/rho_{cr} for galaxies at redshift 0.3 and r band magnitude of -22 (k- and evolution-corrected to z=0). Assuming zero intrinsic alignments for blue galaxies, we assess the bias on cosmological parameters for a tomographic CFHTLS-like lensing survey. Both the resulting mean bias and its uncertainty are smaller than the 1sigma statistical errors when using the constraints from all samples combined. The addition of MegaZ-LRG data reduces the uncertainty in intrinsic alignment bias on cosmological parameters by factors of three to seven. (abridged)
