Hubble Fellows Symposium Day 2- Noon Session @stsciresearch6722

STScI Research | Hubble Fellows Symposium Day 2- Noon Session @stsciresearch6722 | Uploaded 2 years ago | Updated 4 hours ago

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$STScI Discovery Seminar Series - Dries Van De Putte (STScI) and Xinfeng Xu (JHU) This Discovery Seminar features talks by Dries Van De Putte (STScI) on the Far-UV Dust Extinction and Molecular Hydrogen in the Diffuse Milky Way Interstellar Medium and Xinfeng Xu (JHU) on the Properties of Starburst-Driven Warm Ionized Outflows from CLASSY Project. March 15, 2022. Speaker: Dries Van De Putte Title: Far-UV Dust Extinction and Molecular Hydrogen in the diffuse Milky Way Interstellar Medium Abstract: We characterize how the amount of far-UV extinction (900-1200A), and variations in the extinction curve shape over the full UV range (900-3000 A), relate to the gas-to-dust ratio and the H2 content of gas along Milky Way sightlines. We combine an existing sample of 75 extinction curves, with estimates for the HI and H2 gas columns. We use H2 column densities based on the absorption line models that were used to correct the extinction curves. For 23 stars, HI column densities were derived by modeling the Lyman alpha absorption line, using archived IUE and HST STIS data. For the other stars, literature values were sufficiently accurate. The H2 column shows a linear relationship with the extinction at wavelengths near 1000 A, A(1000), which is in the dissociation band of H2. There is no relationship between the atomic column and A(1000). The total H column has more scatter as a function of A(1000), while it scales well with the optical extinction A(V) or E(B−V). Small dust grains that absorb most efficiently in the far-UV therefore coincide with molecular gas, indicating that the formation and survival of these grains and H2 are related. The H2 fraction correlates positively with the strength of the far-UV rise, and the width of the 2175 A bump, but not with the gas-to-extinction ratio N(H)/A(V). Finally, we find that UV-to-optical extinction ratios, such as A(1000)/A(V) and A(2175)/A(V) show a positive correlation with N(H)/A(V). This trend can explain several lower-than-average N(H)/A(V) ratios. Therefore, there are dust evolution processes in the diffuse ISM that increase the dust mass relative to the gas, and also decrease the ratio of small to large grains. Speaker: Xinfeng Xu Title: The Properties of Starburst-Driven Warm Ionized Outflows from CLASSY Project Abstract: We live in a time of challenges and opportunities to understand the evolution of galaxies. In the current picture, baryons flow with dark matter on large scales, and some are incorporated into the halos. Unlike dark matter, baryons sink deeper into the potential well of galaxies given the loss of energy by radiation, but this inflow of baryons is halted by the feedback effects cause by stars and/or AGN in one galaxy. Both the inflow and feedback accompany the growth of galaxies over billions of years. I will report our recent analyses of stellar feedback traced by galactic outflows in a sample of 45 low-redshift starburst galaxies. These galaxies are included in the COS Legacy Archive Spectroscopic Survey (CLASSY). The outflows are detected by blueshifted absorption-lines of metals spanning a wide range in ionization potential. We further determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow’s mean velocity and velocity width, and find that both correlate in a highly significant way with the star-formation rate, galaxy mass, and circular velocity over ranges of up to four orders-of-magnitude. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. The outflows’ mass-loading factor increases steeply and inversely with both circular and outflow velocity (log-log slope ~ -1.4). We find that the outflows typically carry about 10 - 100% of the momentum injected by massive stars and about 1 - 20% of the kinetic energy. I will show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.$

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