GeminiFocus July 2018 | Page 9

evolved stars, resulting in cosmic maser emission. Indeed, these emissions (intense laser-like spectral lines at microwave fre- quencies) seem to be found in star-forming regions, close to young-stellar objects such as protostars and compact HII regions. As a number of ULIRGs are also a source of OH- megamaser emissions, observations of them may hold important clues as to the main power source in these galaxies (Lo, 2005). OH megamaser emission lines are commonly associated with ULIRGs with the warmest IR colors. Importantly, the OH luminosity is also observed to increase with the IR luminosity: the emission from these interacting galax- ies is surprisingly brighter than that associ- ated with galactic masers in non-interacting galaxies. The OH megamaser emission can be used to trace high density regions, and separation of the megamaser emission com- ponents could be linked to outflows of less dense ma tter, but at high speed. A general feature of many models is that the masers are pumped radiatively by the absorption of infrared photons. Identifying the source of the maser pump may therefore indicate whether the ultimate energy source is a burst of star formation, or an active nu- cleus (Lo, 2005). Dissecting an OH Megamaser Galaxy Merger We used multiwavelength observations to investigate the origin of the gas emission and kinematics of the inner 6 kiloparsecs (kpc) of the OH megamaser galaxy IRAS F23199+0123. Located at a distance of 558 megaparsecs (Mpc), its OH megamaser was first detected by the Arecibo OH Megama- ser Survey (which observed 52 objects with 0.1< z <0.26). Previous optical spectroscopy of the galaxy suggests that it also harbors a type 2 active galaxy nucleus (AGN). July 2018 The data comprise both optical and radio imaging, as well as spectroscopy obtained with the Gemini Multi-Object Spectrograph (GMOS)/integral field unit (IFU) at the Gemi- ni North telescope, Hubble Space Telescope (HST), and Very Large Array (VLA). We used the HST to make I-band, broad-band, and [NII]+H-alpha narrow-band images. We used the VLA to obtain 1.6- and 8-gigahertz (GHz) continuum images and spectra centered at the OH maser line. And we used Gemini’s GMOS/IFU to conduct H-alpha and [N II; (6583-Ångstrom) observations that would match HST’s. The HST observations revealed that IRAS F23199+0123 is actually an interacting pair with a tidal tail connecting the two galaxies (Figure 1). The VLA observations indicate that both nuclei present extended radio emission at 3 and 20 centimeters (cm), with intensity peaks at each nucleus. The 20-cm radio emis- sion of the eastern nucleus is elongated in the direction of the most extended emission in the HST continuum image (northeast – southwest), while in the western nucleus the 20-cm radio emission is tilted by about 45º (Figure 2). The VLA spectra also reveal two GeminiFocus Figure 2. Top panel: VLA L-band (1.6 GHz) continuum image of IRAS F23199+0123, shown as filled contours. The contours are (black) 0.071 (3 σ), 0.15, (white) 0.32, 0.69, and 1.5 mJy beam-¹. The OH1 and OH2 labels identify the locations where the OH maser sources were detected. Bottom panel: VLA X-band (8 GHz) continuum image of IRAS F23199+0123, shown as filled contours. The contours are (black) 0.0278 (3σ), 0.0647, (white) 0.150, and 0.349 mJy beam-¹. 7