Discovery of ammonia (9,6) masers in two high-mass star-forming regions

TL;DR

This study reports the discovery of new ammonia (9,6) masers in two high-mass star-forming regions, enhancing understanding of their occurrence and relation to outflows, with implications for star formation studies.

Contribution

It provides the first detections of NH₃ (9,6) masers in Cepheus A and G34.26+0.15, expanding the known sample and offering insights into their spatial distribution and variability.

Findings

New NH₃ (9,6) masers discovered in Cepheus A and G34.26+0.15.

Masers are associated with outflows in star-forming regions.

Masers originate from compact, unresolved emission regions.

Abstract

Molecular maser lines are signposts of high-mass star formation, probing excitation and kinematics of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax measurements. Only a few NH$_{3}$ (9,6) masers were known so far, and their origin is still poorly understood. Here we aim to find new NH$_{3}$ (9,6) masers to provide a better observational basis to study their role in high-mass star-forming regions. We carried out NH$_{3}$ (9,6) observations toward Cepheus A and G34.26$+$0.15 with the Effelsberg-100 m telescope and the Karl G. Janksy Very Large Array. We discovered new NH$_{3}$ (9,6) masers in Cep A and G34.26$+$0.15, which increases the number of high-mass star-forming regions hosting NH$_{3}$ (9,6) masers from five to seven. Long term monitoring (20 months) at Effelsberg shows that the intensity of the (9,6) maser in G34.26$+$0.15 is decreasing, while the Cep A maser remains stable. Compared to the Effelsberg data and assuming linear variations between the epochs of observation, the JVLA data indicate no missing flux. This suggests that the NH$_3$ (9,6) emission arises from single compact emission regions that are not resolved by the interferometric measurements. As JVLA imaging shows, the NH$_{3}$ (9,6) emission in Cep A originates from a sub-arcsecond sized region, slightly to the west of the peak position of the 1.36\,cm continuum object, HW2. In G34.26$+$0.15, three NH$_{3}$ (9,6) maser spots are observed: one is close to the head of the cometary ultracompact \h2 region C and the other two are emitted from a compact region to the west of the hypercompact \h2 region A. The newly found (9,6) masers appear to be related to outflows. Higher angular resolution of JVLA and VLBI observations are needed to provide more accurate positions and constraints for pumping scenarios.