Halo Angular Momentum Research Articles

Weak lensing with COMBO-17: estimation and removal of intrinsic alignments

We estimate and remove the contamination of weak gravitational lensing measurements by the intrinsic alignment of close pairs of galaxies. We do this by investigating both the aperture mass B mode statistic, and the shear correlations of close and distant pairs of galaxies. These can be used to quantify non-lensing effects in weak lensing surveys. We reanalyse the {COMBO-17} survey, and study published results from the Red-sequence Cluster Survey and the {VIRMOS-DESCART} survey, concluding that the intrinsic alignment effect is at the lower end of the range of theoretical predictions. We also revisit this theoretical issue, and show that misalignment of baryon and halo angular momenta may be an important effect which can reduce the intrinsic ellipticity correlations estimated from numerical simulations to the level that we and the {SuperCOSMOS} survey observe. We re-examine the cosmological parameter estimation from the {COMBO-17} survey, using the shear correlation function, and now marginalizing over the Hubble constant. Assuming no evolution in galaxy clustering, and marginalizing over the intrinsic alignment signal, we find the mass clustering amplitude is reduced by 0.03 to ??8(??m/0.27)0.6= 0.71 +/- 0.11, where ??m is the matter density parameter. We consider the forthcoming {SuperNova/Acceleration} Probe {(SNAP)} wide weak lensing survey, and the {Canada-France-Hawaii} Telescope Legacy wide synoptic survey; we expect them to be contaminated on scales {\textgreater}1 arcmin by intrinsic alignments at the level of {\textasciitilde}1 and {\textasciitilde}2 per cent, respectively. Division of the {SNAP} survey for lensing tomography significantly increases the contamination in the lowest redshift bin to {\textasciitilde}7 per cent and possibly higher. Removal of the intrinsic alignment effect by the downweighting of nearby galaxy pairs will therefore be vital for {SNAP.}

Constraints from Dynamical Friction on the Dark Matter Content of Barred Galaxies

We show that bars in galaxy models having halos of moderate density and a variety of velocity distributions all experience a strong drag from dynamical friction unless the halo has large angular momentum in the same sense as the disk. The frictional drag decreases the bar pattern speed, driving the corotation point out to distances well in excess of those estimated in barred galaxies. The halo angular momentum required to avoid strong braking is unrealistically large, even when rotation is confined to the inner halo only. We conclude, therefore, that bars are able to maintain their observed high pattern speeds only if the halo has a central density low enough for the disk to provide most of the central attraction in the inner galaxy. We present evidence that this conclusion holds for all bright galaxies.