EI2GYB > ASTRO 20.11.25 18:00l 51 Lines 4653 Bytes #200 (0) @ WW
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Subj: Mapping the OH MegaMaser emission in an ultra-luminous infr
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Mapping the OH MegaMaser emission in an ultra-luminous infrared galaxy
Using high-resolution 1665/1667 MHz OH line and continuum spectrum observational data from the European VLBI Network and the Multi-Element Radio Linked Interferometer Network, Antneh Gashaye, a Ph.D. student from the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, has mapped the OH MegaMaser emission in the ultra-luminous infrared galaxy IRAS 15250+3609, and revealed the nature and structure of the OH MegaMaser emission in the galaxy.
The findings are published in the Monthly Notices of the Royal Astronomical Society.
Ultra-luminous infrared galaxies (ULIRGs) are extremely active objects in the universe and are often associated with galaxy mergers, active galactic nuclei (AGN), and intense starbursts.
Recent high-resolution radio observations have shown that OH MegaMaser emission can serve as a probe to reveal the gas dynamics and merging mechanisms in the galaxy's nuclear region. IRAS 15250+3609, a ULIRG located about 241 Mpc away, is considered a post-merger system.
The results show that the nuclear region is a complex starburst zone measuring 130 ž 95 parsecs with an obscured central source. Earlier low-resolution observations only viewed it as a point source, but high-resolution data revealed the extended starburst structure. This structure confirms the presence of the AGN's radio emission and aligns with its optical composite classification with a low ionization nuclear emission line region and a starburst.
The OH MegaMaser emission arises from and remains confined within the nuclear source of the host galaxy, which has an active galactic nucleus and an extended starburst region. The emission covers a velocity range from -250 km s?û to 400 km s?û, with a strong and systematic velocity gradient across the nucleus from west to east.
Analysis shows that the excitation for the OH molecules comes from the far-infrared radiation field from the starburst nucleus of the host galaxy, which allows for maser amplification of the nuclear radio continuum in the background.
The velocity signature and structure of the OH emission indicate that the masering foreground material is part of an ongoing minor merger, with a dwarf galaxy falling nearly radially into the nucleus of IRAS 15250+3609 from the west.
Moreover, three velocity ranges were identified during the merger process: a high velocity for infalling material that is still mostly unperturbed, an intermediate velocity range where material first interacts with the host galaxy, and a negative velocity region where material has already crashed into the host.
This study offers new insights into the dynamics of minor mergers and sheds light on how such events influence the kinematics of a galaxy's nuclear region. It also emphasizes the importance of high-resolution radio observations in understanding the complex interactions that shape the evolution of galaxies like IRAS 15250+3609.
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