Distances to ~60 star-forming regions in Reipurth (2008, Star Formation Handbook, vols I and II) have been computed using stellar photometry and Gaia DR2 parallax measurements. Usually, several distance estimates are taken across each cloud.
For each sightline, the median distance (d50) is provided, plus the 16th and 84th percentiles on the distance probability distribution function. There is an additional systematic uncertainty, which is unknown but estimated to be ~5% in distance for clouds <1.5kpc, ~10% in distance for clouds >1.5kpc, and ~7% in distance for the southern clouds Lupus, Chamaeleon, and Corona Australis. These should be added in quadrature with the statistical uncertainties reported in the table. In addition to the distances, ancillary model parameters used in our fit are also included (e.g. the amount of foreground extinction "f"). See Section 3.2.1 and Section 3.2.2 in Zucker et al. (2019ApJ...879..125Z) for a complete description of model parameters.
WorldWide Telescope (WWT) is a powerful visualization program that allows users to connect Earth-based and space-based views of the Sun- Earth-Moon system. By blending hands-on physical activities with WWT's virtual models, students can visualize spatially complex concepts like seasons, Moon phases, and eclipses. In this workshop, we will demonstrate how WWT and the physical models are used together in our WWT ThinkSpace curriculum, developed with funding from the National Science Foundation. We will also present student learning outcomes based on written assessments and student interviews.
We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of spectral line observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterized HOG using synthetic observations of HI and 13CO (J = 1 → 0) emission from numerical simulations of magnetohydrodynamic (MHD) turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We found a significant spatial correlation between the two tracers in velocity channels where vHI ≈ v13CO, almost independent of the orientation of the collision with respect to the line of sight. Subsequently, we used HOG to investigate the spatial correlation of the HI, from The HI/OH/recombination line survey of the inner Milky Way (THOR), and the 13CO (J = 1 → 0) emission from the Galactic Ring Survey (GRS), toward the portion of the Galactic plane 33°.75 ≤l ≤ 35°.25 and |b| ≤ 1°.25. We found a significant spatial correlation between the two tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption (HISA) features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results derived for the observational data indicate significant differences between individual regions: some show spatial correlation in channels around vHI ≈ v13CO while others present spatial correlations in velocity channels separated by a few kilometers per second. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.
Over the past century, major advances in astronomy and astrophysics have been driven by improvements in instrumentation. With the amassing of high quality data from new telescopes it is becoming clear that research in astrostatistics and astroinformatics will be necessary to develop new methodology needed in astronomy.
We compare the magnetic field orientation for the young giant molecular cloud Vela C inferred from 500 μm polarization maps made with the BLASTPol balloon-borne polarimeter to the orientation of structures in the integrated line emission maps from Mopra observations. Averaging over the entire cloud we find that elongated structures in integrated line-intensity or zeroth-moment maps, for low-density tracers such as 12CO and 13CO J → 1 - 0, are statistically more likely to align parallel to the magnetic field, while intermediate- or high-density tracers show (on average) a tendency for alignment perpendicular to the magnetic field. This observation agrees with previous studies of the change in relative orientation with column density in Vela C, and supports a model where the magnetic field is strong enough to have influenced the formation of dense gas structures within Vela C. The transition from parallel to no preferred/perpendicular orientation appears to occur between the densities traced by 13CO and by C18O J → 1 - 0. Using RADEX radiative transfer models to estimate the characteristic number density traced by each molecular line, we find that the transition occurs at a molecular hydrogen number density of approximately 103 cm-3. We also see that the Centre Ridge (the highest column density and most active star-forming region within Vela C) appears to have a transition at a lower number density, suggesting that this may depend on the evolutionary state of the cloud.