Research
As a student of astronomy and physics I am invested in a variety of topics, however as a researcher I primarily use infrared and sub-millimeter wavelengths of light to study massive star formation, in particular in the extreme environment of the Central Molecular Zone (CMZ), the central few hundred parsecs of the Milky Way. For my research, I use a variety of ground- and space-based telescopes, such as the James Webb Space Telescope (JWST), Hubble Space Telescope (HST), Large Binocular Telescope (LBT), Gemini North Telescope, Spitzer Space Telescope, Statospheric Observatory for Infrared Astronomy (SOFIA; R.I.P.), Herschel Space Telescope, Atacama Large Millimeter Array (ALMA), and MeerKAT radio telescope.
Some key questions that interest me are: how do massive stars form, and how does this process vary by environment? How do massive protostars affect low-mass protostars during their formation, and vice versa? How can we observationally distinguish between massive star formation theories? Does star formation occur differently in the CMZ compared to other regions? If so, why? What novel physical processes occur outside the Galactic Disk, in extreme regions like the CMZ? How is the distribution and morphology of ionized gas in the CMZ shaped by e.g. strong magnetic fields?
See my ADS record here!
Current Research Projects
Pictured: Diagram of Sgr C with JWST-NIRCam
Credit: Crowe et al. (under review)
Peering into the Heart of a CMZ Massive Protocluster with JWST (Began September 2023)
How does the extreme environment of the Central Molecular Zone (CMZ) affect the process of massive star formation? I am the PI of a Cycle 2 JWST Program (data was taken in September 2023) that uses imaging data from the NIRCam and NIRISS instruments to peer into the massive star-forming CMZ molecular cloud Sagittarius C (Sgr C; see left).
Paper I (Crowe+, accepted to ApJ) focuses on star formation in the main Sgr C cloud, with particular emphasis on two massive protostars forming in its central protocluster (labeled left as 'G359.44-0.102'). We identify extensive shocked molecular hydrogen emission from these protostars with JWST, claiming the first unambiguous infrared detection of outflows from individual protstars in the CMZ. We have also discovered a new star-forming region (labeled left as 'G359.42-0.104'), tentatively placed within the CMZ, containing at least two protostars powering bright outflows. With this paper, we usher CMZ star formation into the era of JWST, with promising ramifications for future observations!
Paper II (Bally & Crowe+, submitted to ApJ; under referee review) focuses on the Sgr C HII region, in which NIRCam has revealed a strikingly filamentary morphology (labeled left as 'HII Region', and seen in 'green' Brackett-alpha emission from atomic hydrogen), unlike any HII region in the Galactic Disk. We claim this as evidence that the Sgr C HII region is evolving under magnetically-dominated conditions, in which strong magnetic fields confine the thermal plasma to long, straight filaments of ionized gas. We find spectral indices across the HII region using MeerKAT that indicate a strong non-thermal (i.e. synchrotron) component to the emission, corroborating the claim. We conclude by developing a simple model for filament formation under magnetically dominated conditions, with ramifications for all mature HII regions in the CMZ, and even in the centers of other galaxies!
Paper(s) III+ (in prep.) will focus on topics like the stellar populations in Sgr C, developing tools to be used for future JWST observations across the CMZ, extinction-mapping of infrared-dark clouds in Sgr C, follow-up on G359.42-0.104 with precise distance measurements, outflow association between JWST and ALMA, etc.
My advisors and I also collaborated with NASA/STScI to produce a press release on the JWST images of Sgr C (read it here!), which received international media attention. See the 'Outreach' tab for more!
Deciphering Massive Star Formation and Outflows in AFGL 5180 (Began June 2023)
Paper I (Crowe et al. 2024) When stars form via accretion, they channel enormous amounts of material along magnetic field lines, producing incredibly bright and large-scale protostellar outflows that can be studied with high levels of detail. In this paper, we use near-infrared (LBT) and sub-millimeter (ALMA) data from the to characterize the outflows from individual low- and high-mass protostars in the massive-star forming region AFGL 5180, located about 2 kilo-parsecs from the sun (near the Galactic anticenter, in the constellation Gemini). We find highly chaotic outflows indicative of clustered star formation, corroborated by the detection of tightly grouped protostellar cores with ALMA. We pioneer a method for comparing stellar surface densities between observations and simulations, allowing for direct constraints to be placed on massive star formation theories.
Paper II (in prep.) will provide a spectroscopic follow-up on the deep imaging survey of paper I, using long-slit spectra from LBT, as well as integral field unit (IFU) spectra from the Very Large Telescope (VLT), to obtain kinematics of the outflows in AFGL 5180, including the identification of red- and blue-shifted outflow lobes, derivation of outflow knot temperatures and densities, construction of excitation and extinction maps, and other pieces of analysis.
Pictured: AFGL 5180 with HST-WFC3
Credit: ESA/Hubble & NASA, J. C. Tan, R. Fedriani, J. Schmidt
Digging for Embedded Clusters in Nearby Star-forming Galaxies (Began May 2024)
In summer 2024, as part of a Research Experiences for Undergraduates (REU) program at the University of Wyoming, I joined the PHANGS collaboration and began work with the other REU students developing a sample of embedded clusters—forming stellar clusters still embedded in their natal gas and dust—in nearby star-forming galaxies with JWST and HST. We surveyed over 10 galaxies covered by the PHANGS survey, found over 200 embedded clusters (the largest survey of embedded clusters to date!), and used our by-eye identifications to train machine learning models (using both the ResNet and VGG-19 neural networks) that can identify embedded clusters with ~80% accuracy! Our team is currently preparing a paper for publication on this work.
Pictured: Mosaic of 19 JWST images of PHANGS galaxies
Credit: NASA, ESA, CSA, STScI, Janice Lee (STScI), Thomas Williams (Oxford), PHANGS Team, Elizabeth Wheatley (STScI)
Characterizing a High-Mass, Low-Metallicity Protostellar Outflow with Gemini & JWST (Began December 2023)
We have obtained 2 sets of Gemini North long-slit spectroscopy (GN-2023B-FT-208, PI S. Crowe; GN-2024A-FT-103, PI Y. Cheng) on the large-scale outflow (discovered by JWST-NIRCam) in the low-metallicity, massive star-forming region Sh-284, at a distance of around 4 kilo-parsecs from the sun. We aim to use this data set to pioneer a method for obtaining the physical characteristics of outflow knots using NIRCam imaging data alone. This has the potential to dramatically increase the science output of all NIRCam imaging of protostellar outflows, past and future!
Pictured: The Sh-284 outflow with JWST-NIRCam
Credit: R. Fedriani, Y. Cheng
Pictured: Fitted SED for a massive protostar in Sgr C.
Credit: Crowe et al. (under review)
A Global Sample of CMZ Massive Protostars (Began February 2022)
Can we identify individual massive protostars in the CMZ? Can we characterize them? In this project, I have been developing a global survey of massive protostars in the CMZ to sample their emission across a spectrum of near-, mid- and far-infrared wavelengths. This is used to construct their spectral energy distributions (SEDs; e.g. left) and fit them to theoretical models of massive star formation to place constraints on their physical characteristics. This rich data set can be used to derive estimates of the initial mass function (IMF), star formation rate (SFR), and star formation efficiency (SFE) in the CMZ, which are crucial parameters for our understanding of CMZ star formation.
MHD Simulations of Magnetized HII Region Evolution (Began September 2024)
What are the effects of strong magnetic fields on the evolution of HII regions: the zones of hot, ionized plasma surrounding massive stars? For my undergraduate senior thesis, under the supervision of UVa Professor Zhi-Yun Li, I am currently attempting to answer this question using state-of-the-art magnetohydrodynamic (MHD) simulations of HII region expansion and evolution with the Athena++ code. Ultimately, we would like to replicate and understand the conditions for forming bright filaments of ionized plasma in HII regions, as we have observed in the Sgr C HII region in the Central Molecular Zone (see above).
Other Research Participation
I am also interested and participate in other astronomy-related research, primarily through student groups at the University of Virginia.
UVa Pulsar Club
Credit: Chris Butler / Science Photo Library
Since Fall 2021 I have been an active member in the UVa Pulsar Club, which is a club dedicated to providing training in scientific computing and research methods, in particular with respect to pulsar research, to underclassmen interested in astronomy. Past activities have included beta-testing NASA's Radio JOVE telescope kit and developing an observing program at the Long Wavelength Array (Socorro, NM) to update timing models for outdated pulsars.
UVa Occultation Group
Pictured: Training night in Boulder, Colorado for the PO20230204 campaign.
Since early 2023 I have been an active participant in the UVa Occultation Group, which regularly observes occultations: events in which a target asteroid passes in front of a star. I have participated in several campaigns with the group, including with ~10 other club members in the PO20230204 campaign with NASA and the Southwest Research Institute (SWRI) to observe the occultation of the asteroid Polymele and its satellite Shaun, a target of NASA's Lucy mission, in Colorado and Kansas.