hydrodynamics

First author: Euclid Collaboration The photometric catalogue of galaxy clusters extracted from ESA Euclid data is expected to be very competitive for cosmological studies. Using state-of-the-art hydrodynamical simulations, we present systematic analyses simulating the expected weak lensing profiles from clusters in a variety of dynamic states and at wide range of redshifts. In order to derive cluster masses, we use a model consistent with the implementation within the Euclid Consortium of the dedicated processing function and find that, when jointly modelling mass and the concentration parameter of the Navarro-Frenk-White halo profile, the weak lensing masses tend to be, on average, biased low with respect to the true mass.

First author: Sukanya Mallik We study the statistical properties of O VI, C IV, and Ne VIII absorbers at low-$z$ (i.e., $z<0.5$) using Sherwood simulations with “WIND” only and “WIND+AGN” feedback and Massive black simulation that incorporates both “WIND” and AGN feedbacks. For each simulation, by considering a wide range of metagalactic ionizing UV background (UVB), we show the statistical properties such as distribution functions of column density ($N$), $b$-paramerer and velocity spread ($\Delta V_{90}$), the relationship between $N$ and $b$-parameter and the fraction of Lya absorbers showing detectable metal lines as a function of $N$(H I) are influenced by the UVB used.

First author: E. P. Tito The recent image of our galaxy’s supermassive black hole Sgr A* derived from the 7 April 2017 data of the Event Horizon Telescope Collaboration shows multiple hot spots in its accretion disk. Using the analytical framework, we demonstrate that the observed hot spots may not be disjoint elements but causally linked components (“petals”) of one rotating quasi-stationary macro-structure formed in the thermo-vorticial field within the accretion disk.

First author: I. Baraffe We perform two-dimensional numerical simulations of core convection for zero-age-main-sequence stars covering a mass range from 3 $M_\odot$ to 20 $M_\odot$. The simulations are performed with the fully compressible time-implicit code MUSIC. We study the efficiency of overshooting, which describes the ballistic process of convective flows crossing a convective boundary, as a function of stellar mass and luminosity. We also study the impact of artificially increasing the stellar luminosity for 3 $M_\odot$ models.

First author: Alexandros Ziampras The vertical shear instability (VSI) is a source of hydrodynamic turbulence that can drive vigorous vertical mixing and moderate levels of accretion in protoplanetary disks, and it could be observable in the near future. With high-resolution three-dimensional numerical hydrodynamics simulations, we modeled the behavior of the VSI in protoplanetary disks with and without embedded planets. We then measured its accretion and mixing capabilities by comparing the full Reynolds stress, which includes the contribution of nonaxisymmetric features, such as spiral arms and vortices, to the Reynolds stress due to the azimuthally averaged velocity field, which can be attributed to good approximation to the VSI.

First author: Hai-Yang Wang Hydrodynamical interaction in circumbinary discs (CBDs) plays a crucial role in various astrophysical systems, ranging from young stellar binaries to supermassive black hole binaries in galactic centers. Most previous simulations of binary-disc systems have adopted locally isothermal equation of state. In this study, we use the grid-based code $\texttt{Athena++}$ to conduct a suite of two-dimensional viscous hydrodynamical simulations of circumbinary accretion on a cartesian grid, resolving the central cavity of the binary.

First author: R. N. Markwick Supersonic interacting flows occurring in phenomena such as protostellar jets give rise to strong shocks, and have been demonstrated in several laboratory experiments. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in three dimensions. We introduce variations in the flow parameters of density, velocity, and cross sectional radius of the colliding flows %radius in order to study the propagation and conical shape of the bow shock formed by collisions between two, not necessarily symmetric, hypersonic flows.

First author: Sung Hak Lim Cosmological N-body simulations of galaxies operate at the level of “star particles” with a mass resolution on the scale of thousands of solar masses. Turning these simulations into stellar mock catalogs requires “upsampling” the star particles into individual stars following the same phase-space density. In this paper, we demonstrate that normalizing flows provide a viable upsampling method that greatly improves on conventionally-used kernel smoothing algorithms such as EnBiD.

First author: Shaobo Zhang The youngest Galactic supernova remnant G1.9+0.3 shows a discrete feature between its radio and X-ray morphologies. The observed radio morphology features a single maximum in the north, while the X-ray observation shows two opposite ’ears’ on the east and west sides. Using 3D magneto hydrodynamical simulations, we investigate the formation of the discrete feature of the remnant. We have tested different parameters for better simulation and reproduced similar discrete features under an environment with density gradient and an environment with clump, which provides a possible explanation of the observation.

First author: Mike Y. M. Lau Transit and radial-velocity surveys over the past two decades have uncovered a significant population of short-period exoplanets. Among them are hot Jupiters, which are gas giant planets with orbital periods of a few days and found in 0.1-1% of Sun-like stars. Hot Jupiters are expected to be engulfed during their host star’s radial expansion on the red giant branch. Planetary engulfment has been studied extensively as it may account for observed rapidly rotating and chemically enriched giant stars.