TY - JOUR

T1 - Time-variable Radio Recombination Line Emission in W49A

AU - De Pree, C. G.

AU - Wilner, D. J.

AU - Kristensen, L. E.

AU - Galvan-Madrid, R.

AU - Goss, W. M.

AU - Klessen, R. S.

AU - Mac Low, M-M

AU - Peters, T.

AU - Robinson, A.

AU - Sloman, S.

AU - Rao, M.

PY - 2020

Y1 - 2020

N2 - We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6 cm and at 7 mm at resolutions of 015 (1650 au) and 004 (440 au), respectively. The 3.6 cm data reveal new morphological detail in the ultracompact H ii region population, as well as several previously unknown and unresolved sources. In particular, source A shows elongated, edge-brightened bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components. We also present VLA observations of radio recombination lines at 3.6 cm and 7 mm, and IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2 mm. Three of the smallest ultracompact H ii regions (sources A, B2, and G2) all show broad kinematic linewidths, with Delta V-FWHM greater than or similar to 40 km s(-1). A multi-line analysis indicates that broad linewidths remain after correcting for pressure broadening effects, suggesting the presence of supersonic flows. Substantial changes in linewidth over the 21 yr time baseline at both 3.6 cm and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from 31.7 1.8 km s(-1) to 55.6 2.7 km s(-1), an increase of +23.9 3.4 km s(-1). The G2 source was previously reported to have shown a 3.6 cm continuum flux density decrease of 40% between 1994 and 2015. This source sits near the center of a very young bipolar outflow whose variability may have produced these changes.

AB - We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6 cm and at 7 mm at resolutions of 015 (1650 au) and 004 (440 au), respectively. The 3.6 cm data reveal new morphological detail in the ultracompact H ii region population, as well as several previously unknown and unresolved sources. In particular, source A shows elongated, edge-brightened bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components. We also present VLA observations of radio recombination lines at 3.6 cm and 7 mm, and IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2 mm. Three of the smallest ultracompact H ii regions (sources A, B2, and G2) all show broad kinematic linewidths, with Delta V-FWHM greater than or similar to 40 km s(-1). A multi-line analysis indicates that broad linewidths remain after correcting for pressure broadening effects, suggesting the presence of supersonic flows. Substantial changes in linewidth over the 21 yr time baseline at both 3.6 cm and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from 31.7 1.8 km s(-1) to 55.6 2.7 km s(-1), an increase of +23.9 3.4 km s(-1). The G2 source was previously reported to have shown a 3.6 cm continuum flux density decrease of 40% between 1994 and 2015. This source sits near the center of a very young bipolar outflow whose variability may have produced these changes.

KW - Compact H II region

KW - Galactic radio sources

KW - H II REGIONS

KW - ULTRACOMPACT

KW - MORPHOLOGIES

KW - DISTANCE

KW - MASERS

U2 - 10.3847/1538-3881/abba27

DO - 10.3847/1538-3881/abba27

M3 - Journal article

VL - 160

SP - 1

EP - 13

JO - The Astronomical Journal

JF - The Astronomical Journal

SN - 0004-6256

IS - 5

M1 - 234

ER -