Day 1772

Monday.

2010.11965

Runaway stars masquerading as star formation in galactic outskirts

Andersson, et al

In the outskirts of nearby spiral galaxies, star formation is observed in extremely low gas surface densities. Star formation in these regions, where the interstellar medium is dominated by diffuse atomic hydrogen, is difficult to explain with classic star formation theories. In this work, we introduce runaway stars as an explanation to this observation. Runaway stars, produced by collisional dynamics in young stellar clusters, can travel kilo-parsecs during their main sequence life time. Using galactic-scale hydrodynamic simulations including a treatment of individual stars, we demonstrate that this mechanism enables the ejection of young massive stars into environments where the gas is not dense enough to trigger star formation. This results in the appearance of star formation in regions where it ought to be impossible. We conclude that runaway stars are a contributing, if not dominant, factor to the observations of star formation in the outskirts of spiral galaxies.

2010.12228

Current and next generation survey filter conversions with ProSpect

Robotham

In this work we compute a reasonably comprehensive set of tables for current and next generation survey facility filter conversions. Almost all useful transforms are included with the ProSpect software package described in Robotham et al (2020). Users are free to provide their own filters and compute their own transforms, where the included package examples outline the approach. This arXiv document will be relatively frequently updated, so people are encouraged to get in touch with their suggestions for additional utility (i.e. new filter sets).

2010.12432

Combined magnetic and gravity measurements probe the deep zonal flows of the gas giants

Galanti, Kaspi

During the past few years, both the Cassini mission at Saturn and the Juno mission at Jupiter, provided measurements with unprecedented accuracy of the gravity and magnetic fields of the two gas giants. Using the gravity measurements, it was found that the strong zonal flows observed at the cloud-level of the gas giants are likely to extend thousands of kilometers deep into the planetary interior. However, the gravity measurements alone, which are by definition an integrative measure of mass, cannot constrain with high certainty the exact vertical structure of the flow. Taking into account the recent Cassini magnetic field measurements of Saturn, and past secular variations of Jupiter's magnetic field, we obtain an additional physical constraint on the vertical decay profile of the observed zonal flows on these planets. Our combined gravity-magnetic analysis reveals that the cloud-level winds on Saturn (Jupiter) extend with very little decay, i.e., barotropically, down to a depth of around 7,000~km (2,000~km) and then decay rapidly in the semiconducting region, so that within the next 1,000 km (600~km) their value reduces to about 1\% of that at the cloud-level. These results indicate that there is no significant mechanism acting to decay the flow in the outer neutral region, and that the interaction with the magnetic field in the semiconducting region might play a central role in the decay of the flows.