Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

The 2dF QSO survey is a spectroscopic survey of 48,000 point-sources selected by colour with magnitudes in the range 18.35 < B < 20.95. Amongst QSOs, white dwarfs, narrow-line galaxies and other objects are some cataclysmic variables (CVs). This survey should be sensitive to intrinsically faint CVs. In the standard picture of CV evolution, these form the majority of the CV population. We present the spectra of 6 CVs from this survey. Four have the spectra of dwarf novae and two are magnetic CVs. We present evidence that suggests that the dwarf novae have period P < 2 h and are indeed intrinsically less luminous than average. However, it is not clear yet whether these systems are present in the large numbers predicted.

Abstract:

We examine the highest S/N spectra from the 2QZ 10k release and identify over 100 new low-ionisation heavy element absorbers; DLA candidates suitable for higher resolution follow-up observations. These absorption systems map the spatial distribution of high-z metals in exactly the same volumes that the foreground 2QZ QSOs themselves sample and hence the 2QZ gives us the unique opportunity to directly compare the two tracers of large scale structure. We examine the cross-correlation of the two populations to see how they are relatively clustered, and, by considering the colour of the QSOs, detect a small amount of dust in these metal systems.

Abstract:

We explore the relative importance of the stellar mass density as compared to the inner dark halo, using the observed gas kinematics throughout the disk of the spiral galaxy NGC 4254 (Messier 99). We perform hydrodynamical simulations of the gas flow for a sequence of gravitational potentials in which we vary the stellar disk contribution to the total potential. This stellar portion of the potential was derived empirically from color corrected K-band photometry reflecting the spiral arms in the stellar mass, while the halo was modelled as an isothermal sphere. The simulated gas density and the gas velocity field are then compared to the observed stellar spiral arm morphology and to the H-alpha gas kinematics. We find that this method is a powerful tool to determine the corotation radius of the spiral pattern and that it can be used to place an upper limit on the mass of the stellar disk. For the case of the galaxy NGC 4254 we find R_cr = 7.5 +/- 1.1 kpc, or R_cr = 2.1 R_exp(K'). We also demonstrate that for a maximal disk the prominent spiral arms of the stellar component over-predict the non-circular gas motions unless an axisymmetric dark halo component contributes significantly (>~ 1/3) to the total potential inside 2.2 K-band exponential disk scale lengths.

Abstract:

When the 2dF QSO Redshift Survey (2QZ) is complete, a powerful geometric test for the cosmological constant will be available. By comparing the clustering along and across the line of sight and modelling the effects of peculiar velocities and bulk motions in redshift space, geometric distortions, which occur if the wrong cosmology is assumed, can be detected. In this paper we investigate the effect of geometric and redshift-space distortions in the power spectrum parallel and perpendicular to the observer's line of sight. Ballinger et al. developed a model to estimate the cosmological constant, $\Lambda$, and the important parameter $\beta \approx \Omega_m^{0.6}/b$ from these distortions. We apply this model to a detailed simulation of the final 25k 2QZ, produced using the Virgo Consortium's huge {\it Hubble Volume} N-body $\Lambda$-CDM light cone simulation. We confirm the conclusions of Ballinger et al.; the shape of the redshift-space and geometric distortions are very similar. When all the uncertainties are taken into account we find that only a joint $\Lambda - \beta$ constraint is possible. By combining this result with a second constraint based on mass clustering evolution, however, we can make significant progress. We predict that this method should allow us to constrain $\beta$ to approximately $\pm0.1$, and $\Omega_{m}$ to $\pm0.25$ using the final catalogue. We apply the method to the 2QZ catalogue of 10000 QSOs and find that this incomplete catalogue marginally favours a $\Lambda$ cosmology.