Our collaborative NSF proposal (led by Prof. Betsy Mills at KU and co-PIed with Adam Ginsburg at UF, Qizhou Zhang at SAO, and John Bally at Colorado) to fund research studying gas flows in our Galaxy’s Center using the ACES survey (more below!) has been awarded! 🥳🥰
With the ALMA CMZ Exploration Survey, an approved ALMA large program to survey the entire Milky Way Central Molecular Zone, we are poised to make the first comprehensive model of mass flows in a galaxy nucleus. We will conduct a complete census of the mass in molecular gas and protostars spanning four orders of magnitude in size scale and characterize the associated gas kinematics with more than a dozen molecular tracers. This project will lead to advances in our understanding of the physics that drives mass flows and will produce the definitive measurements of the rates of inflow, outflow, star formation, and accretion toward the central supermassive black hole. This team comprises the North American Co-PIs of the ACES collaboration, with expertise on multiwavelength observations and simulations of galaxy centers, as well as gas kinematics, star formation, gas chemistry, and fragmentation.
While pursuing her research project to map out and analyze the minimum spanning trees (MSTs) of clouds in the Galactic Center using CMZoom Data, MW Lab undergraduate student Stefania Schuler, supervised by Jen Wallace, made an intriguing discovery. G0.316-0.201 is the designation of an isolated high-mass star-forming region in the CMZoom survey and it is comprised of 12 cores in the robust CMZoom Catalog (Hatchfield et al. 2020), but was found to likely be a foreground object not in the CMZ by Battersby et al. (2020). However, the particular shape of the Minimum Spanning Tree produced for this clump (reminiscent of a charging centaur) has caused G0.316-0.201 to be affectionately nick-named ‘Jeff’ and declared the Milky Way Lab’s unofficial (but much beloved) mascot.
For the minimum spanning tree in this case, a sparse matrix (mostly comprised of zeros) is first built using the (non-redundant) distances between each core in degrees. The sparse matrix is then reduced with a minimum spanning tree algorithm in python into another matrix which represents the minimum possible ‘path’ (in degrees) between all the cores. This ‘path’ can be represented graphically, which is how Jeff came to be. Jeff has been found to have a core spatial distribution ratio of 0.0697, which indicates a fractal substructure. A preliminary (currently lacking standard deviation) mass-segregation ratio of 0.2778 for Jeff suggests that he is inversely mass-segregated; he is mass-integrated, if you will. The data used have been pulled from the CMZoom Robust Catalog.
Dr. Cara Battersby has been awarded an NSF early CAREER grant 🥳 🥳 🥳 ! This award (for nearly $700k) is entitled “CAREER: Shining STARs Amidst the Turbulence” and will be used to study star formation in our Galaxy’s extreme center, by comparing large observational surveys with custom numerical simulations. As part of this program, Dr. Battersby is also founding a new outreach program, named UConn STARs (Science, Technology, and Astronomy Recruits) to recruit, retain, and support physics undergraduate students from historically excluded groups.
Dr. Battersby and her team at the Milky Way Laboratory will perform the first-ever systematic study of the role of turbulence on the Core Mass Function (CMF, the precursor of the stellar initial mass function) in the extreme environment of our Galaxy’s Central Molecular Zone (CMZ, the inner 500 pc of the Milky Way). We will leverage statistical comparisons between cutting-edge numerical simulations and unprecedented large observing programs, spearheaded by the PI, to disentangle the physical origin of CMZ turbulence and measure its properties (the Mach number, virial parameter, and solenoidal fraction).
By taking advantage of pioneering new Atacama Large Millimeter/Submillimeter Array (ALMA) data, we will measure the CMF across the CMZ for the first time and perform a systematic comparison with the CMF in the Galactic disk. We will test for variation in the shape of the CMF as a function of turbulent environment. Since the extreme conditions present in the CMZ are thought to be commonplace at high redshift, the results of the proposed study will provide insight into the role of turbulence in the stellar initial mass function across a range of galaxy types and redshifts.
The results from this research will be brought into under-resourced K-12 classrooms through lesson plans jointly developed by K-12 teachers and undergraduate students from traditionally under-represented groups. We aim to recruit and retain students from under-represented groups in STEM through a new mentorship program UConn-STARs.
H Perry Hatchfield’s stunning paper (Hatchfield et al. 2021) reporting on the current best estimate of the Galactic Center Inflow rate and the origin of molecular clouds in the Central Molecular Zone is now published in ApJ!!! Congratulations Perry!
Here is the abstract:
“The Galactic bar plays a critical role in the evolution of the Milky Way’s Central Molecular Zone (CMZ), driving gas toward the Galactic Center via gas flows known as dust lanes. To explore the interaction between the CMZ and the dust lanes, we run hydrodynamic simulations in AREPO, modeling the potential of the Milky Way’s bar in the absence of gas self-gravity and star formation physics, and we study the flows of mass using Monte Carlo tracer particles. We estimate the efficiency of the inflow via the dust lanes, finding that only about a third (30% ± 12%) of the dust lanes’ mass initially accretes onto the CMZ, while the rest overshoots and accretes later. Given observational estimates of the amount of gas within the Milky Way’s dust lanes, this suggests that the true total inflow rate onto the CMZ is 0.8 ± 0.6 M ⊙ yr-1. Clouds in this simulated CMZ have sudden peaks in their average density near the apocenter, where they undergo violent collisions with inflowing material. While these clouds tend to counter-rotate due to shear, co-rotating clouds occasionally occur due to the injection of momentum from collisions with inflowing material (~52% are strongly counter-rotating, and ~7% are strongly co-rotating of the 44 cloud sample). We investigate the formation and evolution of these clouds, finding that they are fed by many discrete inflow events, providing a consistent source of gas to CMZ clouds even as they collapse and form stars.”
Read more in the paper! Figure 5 below shows several time snapshots of the simulation demonstrating the movement of the tracer particles, how it is used to trace the inflow rate, and determine the origin of CMZ clouds.
The Milky way Laboratory was awarded a grant through the NASA Astrophysics Data Analysis Program in Fall 2021 entitled: “3-D MC: Mapping Circumnuclear Molecular Clouds from X-ray to Radio.” This program will combine archival Chandra X-ray data, with Herschel and Spitzer IR data, and ground-based radio/millimeter data to perform the first 3-D mapping of molecular clouds in the center of the Galaxy, while also constraining their distribution and previous flaring activity from SgrA*.
Chandra has detected X-ray reflections in the CMZ caused by previous flaring events of SgrA* propagating outwards and interacting with the surrounding molecular gas. As the X-rays propagate radially outwards, they reflect and illuminate different parts of the cloud, mapping it over time, like an X-ray scan. Different epoch Chandra observations slice through the 3-D structure of the molecular clouds. We combine these multi-epoch Chandra X-ray data with archival Herschel and ground-based radio spectral line data to map the molecular clouds in 3-D.
Our SOFIA Archival Research Program, “IGNITES: Investigating the Galactic Nuclear Infrared Thermal Emission from young Stars” was selected for funding! This program was initiated and led by H Perry Hatchfield. IGNITES will utilize archival FORCAST data (Program ID: 70_0300) to characterize the star-forming properties and thermal evolutionary states of a large sample of dense gas structures identified by the CMZoom survey of compact submillimeter emission. The CMZoom survey is an SMA Large program (~550 hours observing time), which has been used to identify and catalog ~99% of all possible sites of deeply embedded massive SF in the Milky Way’s innermost 500pc. Analysis of this unique catalog with SOFIA will provide the most complete census and characterization to date of deeply embedded massive SF in the cosmologically-representative environment at the center of our Galaxy.
In Summer 2021, the Milky Way Laboratory was awarded an NSF grant entitled: “Uncovering the Seeds of Star Clusters across the Galaxy.” This grant is focused on utilizing the ALMAGAL large survey to address fundamental questions about how stars form across our Galaxy’s disk.
Overview: The majority of stars in the Universe formed in a clustered environment. Large- scale surveys of our Galaxy have revealed dense clumps of molecular gas that are the pre- cursors to these star clusters. However, lack of spatial resolution has limited our ability to observe the deep substructure within these forming star clusters and to measure the individual star-forming cores within them. Understanding the process by which dense proto-cluster clumps fragment into star-forming cores and the role that Galactic environment plays is of utmost importance in developing a predictive theory of star and cluster formation that can be broadly applied throughout the cosmos.
The Atacama Large Millimeter/submillimeter Array (ALMA) is pioneering new territory with its ability to uncover fragmentation on core scales (0.01 pc) across the Galaxy. With the advent of the ALMAGAL large program, we now have access to statistically significant samples of cores as a function of Galactic environment and evolutionary stage for the first time.
As part of this grant, we plan to expand the reach of ALMAGAL, which will openly share all its data products with the astrophysics community, to the broader community by integrating this unprecedented dataset into the WorldWide Telescope (WWT) platform and developing an educational tour entitled: Zooming in on Star Formation across the Galaxy.
The ACES (ALMA Central Molecular Zone Exploration Survey) large collaborative program led in part by members of the Milky Way Laboratory has been accepted with priority grade A in ALMA Cycle 8! This large program will begin observations in the next few months and will provide the most comprehensive image of our Galaxy’s center in submillimeter wavelengths ever, mapping the entire central 100 pc of our Galaxy down to sub-pc size scales.
ACES will derive the gas properties from cloud scales down to the size scale of individual forming stars across the inner 100pc of the Galaxy. This will address fundamental open questions in star formation and galaxy formation/evolution, providing a new benchmark for understanding how the mass flows and energy cycles shape the centers of galaxies, regulate star formation and control the activity of the central supermassive black holes.
We had our final group meeting and presentations of the semester yesterday. This fantastic group has done so much incredible research this semester, all while being a supportive, welcoming, and friendly group – even having fun together at times. Thank you all for being a part of the Milky Way Laboratory! ☺️🤩🥳
Postdoc Daniel Walker in our group has published a paper reporting some of the very first detections of protostellar outflows1 in our Galaxy’s Center! These outflows are found toward “The Brick” cloud (G0.253+0.016), which previously showed tentative signs of active star formation. Using ALMA Band 6 data, Dr. Walker found 18 continuum sources, 9 of which are driving bipolar molecular outflows in SiO (5-4) emission. Somewhat amazingly though, there is NO evidence for high-mass protostars within this field, the observations instead being consistent with a cluster of low- to intermediate-mass protostars. These incredible new data demonstrate that we are likely not missing any high-mass star formation in our estimates (meaning the low star formation rate of the CMZ is probably real!) and also provide some of the first examples of protostellar outflows toward our Galactic Center, for detailed study of the physics of protostellar accretion in this environment. Congrats, Dan!