Astronomers using NSF’s Karl G. Jansky Very Large Array (VLA) have captured new, high-resolution radio images of a massive star-forming region called W49A.
This overlay shows radio (orange) and infrared images of the giant molecular cloud W49A, where new stars are being formed. Image credit: De Pree et al. / Sophia Dagnello, NRAO / AUI / NSF / Spitzer / NASA.
W49A, also known as GAL 043.169+00.00, lies approximately 36,000 light-years away in the constellation of Aquila.
It harbors a large number of ultra- and hypercompact H II regions highly clustered within a small area on the sky.
“Regions of ionized hydrogen (H II regions) are detected in the vicinity of young, high mass stars,” explained Professor Christopher De Pree from the Department of Physics & Astronomy at Agnes Scott College and his colleagues from the United States, Denmark, Germany, and Mexico.
“Some of the earliest high resolution radio observations of star forming regions found very small H II regions associated with the earliest stages of star formation, with diameters an order of magnitude smaller than the canonical 1 parsec.”
“These ultracompact H II regions have typical diameters of 0.1 parsec, while hypercompact H II regions are even smaller (0.03 parsec in diameter), and have higher density.”
Professor De Pree and co-authors observed the central region of W49A with VLA at different radio wavelengths.
They also used data gathered by the NOrthern Extended Millimeter Array (NOEMA).
High-resolution VLA radio image of the W49A molecular cloud, with close-ups of individual regions where hydrogen gas is ionized by intense ultraviolet radiation from young stars. Image credit: De Pree et al. / Sophia Dagnello, NRAO / AUI / NSF.
The new images revealed some tantalizing changes that have occurred since an earlier set of VLA observations in 1994 and 1995.
These changes include a narrow, fast-moving jet in one hypercompact H II region, supersonic gas motions in three others, and an unexpected reduction in the radio brightness in another.
“The new data reveal new morphological detail in the ultracompact H II region population, as well as several previously unknown and unresolved sources,” the astronomers said.
“In particular, source A shows elongated, edge-brightened, bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components.”
“The three sources detected at the shortest wavelength (A, B2, and G2) all have kinematic linewidths in excess of over 40 km/s, indicating supersonic motions perhaps associated with youth.”
“Source G2, which is the only source in the region to undergo a significant flux density change between 1995 and 2015, also shows a significant increase in linewidth at both 3.6 cm and 7 mm wavelengths over a similar 20 year time span. This may be related to the evolution of the young bipolar outflow traced by the water masers in the region.”
The team plans to continue observing the W49A region regularly to track changes that will reveal new details about the complex processes of star formation and interactions of the outflows from young stars.
The results appear in the Astronomical Journal.
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C.G. De Pree et al. 2021. Time-variable Radio Recombination Line Emission in W49A. AJ 160, 234; doi: 10.3847/1538-3881/abba27
