Hintze Centre for Astrophysical Surveys

Abstract:

We present a kinematic analysis of the main-sequence galaxy HZ4 at z = 5.5. Our study is based on deep, spatially resolved observations of the [C II] 158 μm transition obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA). From the combined analysis of the disk morphology, the 2D velocity structure, and forward modeling of the 1D velocity and velocity dispersion profiles, we conclude that HZ4 has a regular rotating disk in place. The intrinsic velocity dispersion in HZ4 is high (σ0 = 65.8−3.3+2.9 km s−1), and the ratio between the rotational velocity and the intrinsic velocity dispersion is Vrot/σ0 = 2.2. These values are consistent with the expectations from the trends of increasing σ0 and decreasing Vrot/σ0 as a function of the redshift observed in main-sequence galaxies up to z ≈ 4. Galaxy evolution models suggest that the high level of turbulence observed in HZ4 can only be achieved if, in addition to stellar feedback, there is radial transport of gas within the disk. Finally, we find that HZ4 is baryon-dominated on galactic scales (≲2 × Re), with a dark-matter fraction at one effective radius of fDM(Re) = 0.41−0.22+0.25. This value is comparable to the dark-matter fractions found in lower redshift galaxies that could be the descendants of HZ4: massive (M⋆ ≈ 1011 M⊙), star-forming galaxies at z ∼ 2, and passive, early-type galaxies at z ≈ 0.

Abstract:

Inertial Confinement Fusion involves the implosion of a spherical capsule containing thermonuclear fuel. The implosion is driven by irradiating the outside of the capsule by X-rays or by optical laser irradiation, where in each case the highest uniformity of irradiation is sought. In this paper we consider the theoretical problem of irradiation of a capsule by point sources of X-rays, and configurations which maximize uniformity are sought. By studying the root-mean-square deviation in terms of different order harmonic modes, we rationalise the dependence of uniformity on distance d of the point sources from the centre of a capsule. After investigating simple configurations based on the Platonic solids, we use a global optimisation algorithm (basin-hopping) to seek better arrangements. The optimum configurations are found to depend strongly on d; at certain values which minimise nonuniformity, these involve grouping of sources on the vertices of octahedra or icosahedra, which we explain using a modal decomposition. The effect of uncertainties in both position and intensity is studied, and lastly we investigate the illumination of a capsule whose radius is changing with time.