arXiv subjects

Maya A. Petkova

Publications and source records attributed to Maya A. Petkova.

22 records · Page 2Linked to original sources

arXiv2021

Modelling of ionising feedback with Smoothed Particle Hydrodynamics and Monte Carlo Radiative Transfer on a Voronoi grid

The ionising feedback of young massive stars is well known to influence the dynamics of the birth environment and hence plays an important role in regulating the star formation process in molecular clouds. For this reason, modern hydrodynamics codes adopt a variety of techniques accounting for these radiative effects. A key problem hampering these efforts is that the hydrodynamics are often solved using smoothed particle hydrodynamics (SPH), whereas radiative transfer is typically solved on a grid. Here we present a radiation-hydrodynamics (RHD) scheme combining the SPH code Phantom and the Monte Carlo Radiative Transfer (MCRT) code CMacIonize, using the particle distribution to construct a Voronoi grid on which the MCRT is performed. We demonstrate that the scheme successfully reproduces the well-studied problem of D-type H II region expansion in a uniform density medium. Furthermore, we use this simulation setup to study the robustness of the RHD code with varying choice of grid structure, density mapping method, and mass and temporal resolution. To test the scheme under more realistic conditions, we apply it to a simulated star-forming cloud reminiscing those in the Central Molecular Zone of our galaxy, in order to estimate the amount of ionised material that a single source could create. We find that a stellar population of several $10^3~\rm{M_{\odot}}$ is needed to noticeably ionise the cloud. Based on our results, we formulate a set of recommendations to guide the numerical setup of future and more complex simulations of star forming clouds.

astro-ph.GA↗

arXiv2019

Gas flows in galactic centre environments: cloud evolution and star formation in the Central Molecular Zone

The Central Molecular Zone (CMZ) is the most extreme star-forming environment in the Milky Way in terms of gas pressures, densities, temperatures, and dynamics. It acts as a critical test bed for developing star formation theories applicable to the (high-redshift-like) conditions under which most stars in the Universe formed. We present a set of numerical simulations of molecular clouds orbiting on the 100-pc stream that dominates the molecular gas reservoir of the CMZ, with the goal of characterising their morphological and kinematic evolution in response to the external gravitational potential and their eccentric orbital motion. These simulations capture the evolution of single clouds in a strong and plausibly dominant background potential. We find that the evolution of the clouds is closely coupled to the orbital dynamics and their arrival on the 100-pc stream marks a transformative event in their lifecycle. The clouds' sizes, aspect ratios, position angles, filamentary structure, column densities, velocity dispersions, line-of-sight velocity gradients, angular momenta, and overall kinematic complexity are controlled by the background potential and their passage through the orbit's pericentre. We compare these predictions of our simulations to observations of clouds on the Galactic Centre `dust ridge' and find that the inclusion of galactic dynamics naturally reproduces a surprisingly wide variety of key observed morphological and kinematic features. We argue that the accretion of gas clouds onto the central regions of galaxies, where the rotation curve turns over and the tidal field becomes fully compressive, is likely to lead to their collapse and associated star formation. This can generate an evolutionary progression of cloud collapse with a common zero point. Together, these processes may naturally give rise to the synchronised starbursts observed in numerous galactic nuclei.

astro-ph.GA↗

arXiv2017

Fast and accurate Voronoi density gridding from Lagrangian hydrodynamics data

Voronoi grids have been successfully used to represent density structures of gas in astronomical hydrodynamics simulations. While some codes are explicitly built around using a Voronoi grid, others, such as Smoothed Particle Hydrodynamics (SPH), use particle-based representations and can benefit from constructing a Voronoi grid for post-processing their output. So far, calculating the density of each Voronoi cell from SPH data has been done numerically, which is both slow and potentially inaccurate. This paper proposes an alternative analytic method, which is fast and accurate. We derive an expression for the integral of a cubic spline kernel over the volume of a Voronoi cell and link it to the density of the cell. Mass conservation is ensured rigorously by the procedure. The method can be applied more broadly to integrate a spherically symmetric polynomial function over the volume of a random polyhedron.

astro-ph.IM↗

arXiv2016

A Model for (Quasi-)Periodic Multi-wavelength Photometric Variability in Young Stellar Objects

We present radiation transfer models of rotating young stellar objects (YSOs) with hotspots in their atmospheres, inner disk warps and other 3-D effects in the nearby circumstellar environment. Our models are based on the geometry expected from the magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hotspots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project (Morales-Calderon et al. 2014, Cody et al. 2014) to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting "dipper" behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hotspot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that the magneto-accretion theory is consistent with certain aspects of the multi-wavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hotspot and inner disk geometries of particular sources.

astro-ph.SR↗