1906.09277
The dust-to-gas and dust-to-metals ratio in galaxies from z=0-6
Li, et al
We present predictions for the evolution of the galaxy dust-to-gas (DGR) and dust-to-metal (DTM) ratios from z=0 to 6, using a model for the production, growth, and destruction of dust grains implemented into the \simba\ cosmological hydrodynamic galaxy formation simulation. In our model, dust forms in stellar ejecta, grows by the accretion of metals, and is destroyed by thermal sputtering and supernovae. Our simulation reproduces the observed dust mass function at z=0, but modestly under-predicts the mass function by ~x3 at z ~ 1-2. The z=0 DGR vs metallicity relationship shows a tight positive correlation for star-forming galaxies, while it is uncorrelated for quenched systems. There is little evolution in the DGR-metallicity relationship between z=0-6. We use machine learning techniques to search for the galaxy physical properties that best correlate with the DGR and DTM. We find that the DGR is primarily correlated with the gas-phase metallicity, though correlations with the depletion timescale, stellar mass and gas fraction are non-negligible. We provide a crude fitting relationship for DGR and DTM vs. the gas-phase metallicity, along with a public code package that estimates the DGR and DTM given a set of galaxy physical properties.
The dust-to-gas and dust-to-metals ratio in galaxies from z=0-6
Li, et al
We present predictions for the evolution of the galaxy dust-to-gas (DGR) and dust-to-metal (DTM) ratios from z=0 to 6, using a model for the production, growth, and destruction of dust grains implemented into the \simba\ cosmological hydrodynamic galaxy formation simulation. In our model, dust forms in stellar ejecta, grows by the accretion of metals, and is destroyed by thermal sputtering and supernovae. Our simulation reproduces the observed dust mass function at z=0, but modestly under-predicts the mass function by ~x3 at z ~ 1-2. The z=0 DGR vs metallicity relationship shows a tight positive correlation for star-forming galaxies, while it is uncorrelated for quenched systems. There is little evolution in the DGR-metallicity relationship between z=0-6. We use machine learning techniques to search for the galaxy physical properties that best correlate with the DGR and DTM. We find that the DGR is primarily correlated with the gas-phase metallicity, though correlations with the depletion timescale, stellar mass and gas fraction are non-negligible. We provide a crude fitting relationship for DGR and DTM vs. the gas-phase metallicity, along with a public code package that estimates the DGR and DTM given a set of galaxy physical properties.
1906.09797
Origin of the chromospheric three-minute oscillations in sunspot umbrae
Felipe
Sunspot umbrae show a change in the dominant period of their oscillations from five minutes in the photosphere to three minutes in the chromosphere. In this paper, we explore the two most popular models proposed to explain the three-minute oscillations: the chromospheric acoustic resonator and the propagation of waves with frequency above the cutoff value directly from lower layers. We employ numerical simulations of wave propagation from the solar interior to the corona. Waves are driven by a piston at the bottom boundary. We have performed a parametric study of the measured chromospheric power spectra in a large number of numerical simulations with differences in the driving method, the height of the transition region (or absence of transition region), the strength of the vertical magnetic field, and the value of the radiative cooling time. We find that both mechanisms require the presence of waves with period in the three-minute band at the photosphere. These waves propagate upward and their amplitude increases due to the drop of the density. Their amplification is stronger than that of evanescent low-frequency waves. This effect is enough to explain the dominant period observed in chromospheric spectral lines. However, waves are partially trapped between the photosphere and the transition region, forming an acoustic resonator. This chromospheric resonant cavity strongly enhances the power in the three-minute band. The chromospheric acoustic resonator model and the propagation of waves in the three-minute band directly from the photosphere can explain the observed chromospheric three-minute oscillations. They are both important in different scenarios. Resonances are produced by waves trapped between the temperature minimum and the transition region. Strong magnetic fields and radiative losses remove energy from the waves inside the cavity, resulting in weaker amplitude resonances.
No comments:
Post a Comment