cara battersby

Submillimeter Array Postdoctoral Fellow
Harvard-Smithsonian Center for Astrophysics

Forming Star Cluster

The Milky Way Laboratory


THE MILKY WAY LABORATORY

Battersby Shadow Selife at the SMA


Our home Galaxy, the Milky Way, is our closest laboratory for understanding physical processes
throughout the Universe. Submillimeter observations of the cool, dense gas and dust in our Milky
Way provide insights on universal processes including how stars form in both 'regular' and 'extreme'environments and how gas is organized on galactic scales. There are many opportunities for students to become involved with this research, as is evidenced by my work with five undergraduate students and one graduate student while at the Center for Astrophysics.

Currently, as a postdoctoral fellow at the Submillimeter Array at the Harvard-Smithsonian Center for Astrophysics, I am: 1) leading a large survey of star formation in the center of our Galaxy, as a window to understand star formation in the distant Universe, 2) studying gas accretion in massive star-forming clusters, and 3) mapping the structure of the Galaxy using long, skinny, very dense clouds, known as the "Bones of the Milky Way."


Testing Universal Star Formation in our Extreme Galactic Center

Our Galactic Center has extreme properties, more similar to high-redshift galaxies
than our solar neighborhood. I am leading a large survey, the first of its kind, to capitalize on the
close proximity of our Galactic Center to better understand star formation in the early Universe. 

The SMA Legacy Survey of the Central Molecular ZoneThe SMA Legacy Survey of the Central Molecular ZoneThe SMA Legacy Survey of the Central Molecular Zone
Above: The Central Molecular Zone (CMZ, inner 500 pc of the Milky Way): our closest laboratory for understanding star formation in an extreme environment. Shown in red is the column density of molecular gas from Battersby et al. (in prep.), based on Battersby et al. (2011), while green and blue show infrared emission (at 70 and 8 micron, respectively). The white contours throughout show the coverage area of the SMA Legacy Survey (Battersby et al., in prep.). The zoom-box shows results from the SMA Legacy Survey -- 1.3 mm dust continuum emission contours (> 5 sigma) hilighting the present and future sites of star formation.

Cosmic star formation peaked at a redshift of 2, in conditions vastly different from those we observe in the solar neighborhood. Yet our understanding of this fundamental physical process, the conversion of gas into stars, is rooted in detailed observations of our solar neighborhood. The inner few hundred parsecs of the Milky Way, known as the Central Molecular Zone, is our closest laboratory for understanding star formation in the extreme environments that once dominated the Universe.  As the initial phase in using our CMZ as a window into the distant Universe, I am leading the first wide-field, high-resolution (0.2 pc) survey of the CMZ at submm wavelengths, making a comprehensive study of star formation in the CMZ tenable for the first time: the Submillimeter Array (SMA) Legacy Survey of the CMZ.


The Bones of the Milky Way

The basic anatomy of the Milky Way is still poorly understood. Long, skinny clouds tracing spiral arms may help us to fix this. We have several candidate "Bones of the Milky Way" and are working to assemble the full "Skeleton."

The Bones of the Milky Way

Above: Our candidate "Bones of the Milky Way" (labeled by number, black dots show specific measurements of the dense gas) on a Galactic longitude-velocity CO map of the Galaxy (Dame et al. 2001). Various spiral arm models are overlaid to show their disagreement and how the identification of even a handful of \Bones" can improve global log-spiral fits to Milky Way structure. (Figure from Zucker, Battersby, & Goodman 2015.)

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” (figure above and Zucker, Battersby, & Goodman, 2015) and are working to assemble a full "Skeleton."



Gas Accretion onto Forming Star Clusters 

We have identified the most complete sample of starless proto-clusters in the Galaxy, and it has taught us that star clusters continue to accrete gas as they form. This has a big impact - I want to measure the accretion and how it varies.

Gas accretion onto a forming star cluster
Above: The proto-cluster, G32.02+0.05 (Battersby et al. 2014a, 2014b), shows large-scale gas accretion.  The background is a three-color IR image (70, 24, and 8 micron).  Confimed by radiative transfer models (black line on spectra), the blue-shifted self-absorption profie of HCO+ clearly indicates infall of molecular material.  Given the size, densities, and velocities involved, we estimate that this cluster-forming region can roughly double its mass in a Myr. (Figure from Battersby et al., in prep.)