Dr Harley Katz

Abstract:

We study the baryonic Tully–Fisher relation (BTFR) at z ≃ 0 using 153 galaxies from the Spitzer Photometry and Accurate Rotation Curve sample. We consider different definitions of the characteristic velocity from H I and H α rotation curves, as well as H I line-widths from single-dish observations. We reach the following results: (1) The tightest BTFR is given by the mean velocity along the flat part of the rotation curve. The orthogonal intrinsic scatter is extremely small (⁠∼6 per cent⁠) and the best-fitting slope is 3.85 ± 0.09, but systematic uncertainties may drive the slope from 3.5 to 4.0. Other velocity definitions lead to BTFRs with systematically higher scatters and shallower slopes. (2) We provide statistical relations to infer the flat rotation velocity from H I line-widths or less extended rotation curves (like H α and CO data). These can be useful to study the BTFR from large H I surveys or the BTFR at high redshifts. (3) The BTFR is more fundamental than the relation between angular momentum and galaxy mass (the Fall relation). The Fall relation has about seven times more scatter than the BTFR, which is merely driven by the scatter in the mass-size relation of galaxies. The BTFR is already the ‘Fundamental Plane’ of galaxy discs: no value is added with a radial variable as a third parameter.

Abstract:

We use the photon flux and absorption tracer algorithm presented in Katz et al. 2018, to characterise the contribution of haloes of different mass and stars of different age and metallicity to the reionization of the Universe. We employ a suite of cosmological multifrequency radiation hydrodynamics AMR simulations that are carefully calibrated to reproduce a realistic reionization history and galaxy properties at z ≥ 6. In our simulations, haloes with mass 109M⊙h−1 < M < 1010M⊙h−1, stars with metallicity 10−3Z⊙ < Z < 10−1.5Z⊙, and stars with age 3 Myr < t < 10 Myr dominate reionization by both mass and volume. We show that the sources that reionize most of the volume of the Universe by z = 6 are not necessarily the same sources that dominate the meta-galactic UV background at the same redshift. We further show that in our simulations, the contribution of each type of source to reionization is not uniform across different gas phases. The IGM, CGM, filaments, ISM, and rarefied supernova heated gas have all been photoionized by different classes of sources. Collisional ionisation contributes at both the lowest and highest densities. In the early stages of the formation of individual HII bubbles, reionization proceeds with the formation of concentric shells of gas ionised by different classes of sources, leading to large temperature variations as a function of galacto-centric radius. The temperature structure of individual HII bubbles may thus give insight into the star formation history of the galaxies acting as the first ionising sources. Our explorative simulations highlight how the complex nature of reionization can be better understood by using our photon tracer algorithm.