The Milky Way Laboratory
Decades of research have uncovered the basic formation mechanisms of stars in our own solar neighborhood, however, most stars in the Universe were formed in `extreme’ environments with conditions vastly different than the relative calm of our local universe. My research capitalizes on the one cosmologically representative region that is close enough to study individual protostellar cores, the Central Molecular Zone (CMZ, the inner 500 pc of the Milky Way). At UConn, I have founded the Milky Way Laboratory, a research group focused on using our Galaxy as a laboratory for understanding star formation throughout the Universe with both observations and simulations.
Star Formation in the Central Molecular Zone
We have performed the first complete, unbiased, high-resolution survey of the dense star-forming gas in the Central Molecular Zone (CMZ: inner 500 pc of the Milky Way), CMZoom (Battersby et al. 2020) on the Submillimeter Array in Hawai’i. We have developed a catalog of sources in the CMZ that is 99% complete (Hatchfield et al. 2020) and are using this as a finder chart for Atacama Large Millimeter/Submillimeter Array (ALMA) follow-up observations (e.g. Lu et al. 2020, Barnes et al. 2019). CMZoom data is publicly available on the Harvard Dataverse. (Figure from Battersby et al. 2020, shows CMZoom in red, Herschel 70 micron in green, and Spitzer 8 micron in blue.)
Galactic Center Simulations
In the Milky Way Laboratory our approach is manifold. The complex interplay of physical processes involved precludes a simple predictive theory for star formation and necessitates direct comparisons between observations and simulations. We have developed a series of arepo simulations of our Galaxy’s Center that accurately reproduce its major kinematic and structural features. These simulations include an accurate gravitational potential and star formation physics, including self-gravity and feedback (Sormani et al. 2020, Tress et al. 2020). We are currently running high-resolution zoom simulations toward clouds in the simulated CMZ, from which we will construct synthetic observations for direct comparison with observational data. (Figure shows total column density of gas from Sormani et al. 2020.)
The CMZ is the only galaxy center we can presently study in exquisite detail, yet the diverse physics in this region connects communities across the electromagnetic spectrum. With its extreme properties, the CMZ bridges the gap from our local, quiescent environment to more distant galaxies. The 3-D CMZ project will produce, for the first time, a comprehensive, self-consistent 3-D picture of the CMZ. This map is relevant for communities across astrophysics, impacting constraints on dark-matter annihilation in the Galactic Center and allowing us to test the universality of a star formation-dense gas relationship. We will create a self-consistent, probabilistic 3-D picture of the Central Molecular Zone, (CMZ: the inner 500 pc of the Milky Way), for the first time, including the best available constraints and uncertainties. This map will be physically motivated and consistent with all observational constraints. Image on the right is an artist’s rendition (credit: Francesca Holland) of a top-down view of the two-spiral arm model of our Galaxy’s CMZ, inspired by Henshaw et al. 2016, based on e.g. Sofue et al. 1995, Sawada et al. 2004).
ALMAGAL is a large program on ALMA (2019.1.00195.L, PIs: Cara Battersby, Paul Ho, Sergio Molinari, Peter Schilke) dedicated to studying the evolution of high-mass protocluster formation in the Galaxy. ALMAGAL will observe at 1mm continuum and lines more than 1000 dense clumps with M>500 M_sun and d < 7.5 kpc with similar linear resolution. The sample covers all evolutionary stages from IRDC to HII regions from the tip of the Bar to the outskirts of the Galaxy. The setup with 0.1 mJy sensitivity will enable a complete study of the clump-to-core fragmentation process down to at least 1000 AU and 0.3 M_sun Galaxy-wide, mapping the temperature and the local/global infall velocity patterns of the cores-hosting clumps. ALMAGAL publicly accessible data cubes and catalogs will be an invaluable legacy of ALMA, that will allow numerous community followup studies. .
I was a member of the NASA’s Science and Technological Definition Team for the Far-IR Surveyor Mission Concept for the 2020 Decadal Survey. Together with a community of scientists and engineers, we developed the scientifically-compelling and technically-feasible mission concept The Origins Space Telescope. Origins offers a factor of 1000 (yep, you read that right!) improvement in sensitivity over previous observations at these wavelengths, and if selected, Origins will open unprecedented discovery space in the infrared, unveiling our cosmic origins.
Origins will address some of our most compelling questions:
- “How did we get here?
- How do the conditions for habitability develop during the process of planet formation”,
- “How does the Universe Work?:
- How do galaxies form stars, make metals, and grow their central supermassive black holes from reionization to today?”, and
- “Are we alone?:
- Do planets orbiting M-dwarf stars support life?”
Milky Way Bones
Despite decades of research, the structure of our Milky Way, such as the number and orientation of spiral arms, remains a topic of much debate. Goodman et al. (2014) argue that very thin, very long Infrared Dark Clouds (IRDCs) may trace out the densest portion of the spiral structure of the Milky Way, a much denser version of the dark dust lanes seen in nearby face-on spiral galaxies. Identifying and characterizing these “Bones of the Milky Way” may ultimately help assemble a global fit to the Galaxy’s spiral arm by piecing together individual skeletal features. We have undertaken a search for more “Bones of the Milky Way” (Zucker, Battersby, & Goodman, 2015 and Zucker, Battersby, & Goodman 2018) and are working to understand their properties. (Figure showing the position-position-velocity structure of Filament 5 in C18O from the IRAM telescope, Battersby et al., in prep.)
High-Mass Star and Cluster Formation
Understanding formation of high-mass stars is complicated by their relative rarity (and therefore higher than average distance), their dusty, highly-extincted birthplaces, and the fact they quickly disrupt their natal environment with their immense feedback. Cara Battersby studied the properties, evolution, and kinematics of high-mass star and cluster formation as part of her PhD thesis (Battersby et al. 2010, 2011, 2014a, 2014b, 2017) and as part of the Bolocam Galactic Plane Survey (Aguirre et al. 2011, Rosolowsky et al. 2010) and Hi-GAL (Molinari et al. 2010, 2011) teams. The Milky Way Laboratory continues to investigate these mysteries, in particular the nature of the most quiescent clumps (Svoboda et al. 2016, 2019), the nature of massive protoclusters (W51, Machado et al., in prep.), and the high-resolution perspective with ALMAGAL. (Figure from Battersby et al. 2010.)
Turbulence in the CMZ and Testing for Environmental Variation in the Core Mass Function
Turbulence is a key physical process that sets the density structure of the interstellar medium (ISM) and ultimately the distribution of stellar masses, the Initial Mass Function (IMF) and its pre-cursor the protostellar Core Mass Function (CMF). The I/CMF underpins many areas of astrophysics from galaxy evolution to the formation of planets. Yet turbulence is poorly understood and most existing turbulence simulations and observations focus on nearby molecular clouds probing a limited range of environments that show a relatively uniform I/CMF.
We hope to overhaul our understanding of how turbulence affects the CMF in different environments by using a combination of cutting-edge large observational programs and custom numerical simulations. The Central Molecular Zone (CMZ, the inner 500 pc of the Milky Way) contains the extreme environmental conditions (hot, dense, turbulent gas) typical of galaxies at the peak of cosmic star formation, shows evidence for a deviant IMF, yet is close enough to observe individual star-forming cores to measure the CMF. The CMZ is the only cosmologically representative environment in which we can study how turbulence affects the CMF on the scale of individual protostellar cores.
With the advent of unprecedented large observational programs and custom numerical simulations spearheaded by our group, it is for the first time possible to study turbulence in a systematic way in the CMZ and evaluate its role in shaping the CMF, thereby bridging our understanding from the solar neighborhood to high-redshift galaxies. PI Battersby is in the unique position to lead this study, having lead the first complete observational survey of the sites of star formation in the CMZ (CMZoom), currently co-leading the large ALMA program investigating the CMF across our Galaxy (ALMAGAL), and having developed state-of-the-art numerical simulations of the CMZ and a computing cluster on which to run them.