Multiple outflows traced by H2O masers around the ultra-compact HII region G 34.26+0.15

Abstract

We present the results of VLBI observations of the H2O masers associated with the massive-star forming region G 34.26+0.15 with the Very Long Baseline Array (VLBA), the Japanese VLBI Network (JVN), and the VLBI Exploration of Radio Astrometry (VERA) to reveal the whole three-dimensional kinematical structure of the H2O maser region (2'' × 5''). From the result of one of the astrometric observations with VERA and the revealed maser distribution, we found that, in G 34.26+0.15, the H2O masers are likely to be associated with four young stellar objects (YSOs), each of which is traced by at least one of millimeter-continuum and molecular-line emission peaks, rather than by centimeter-continuum peaks that may trace HII regions, including the brightest millimeterand centimeter-continuum emission peak. We also measured the relative proper motions of 33 H2O masers in the VLBA observations (1996 December-1997 May) and 104 ones in JVN/VERA (2006 March-2008 June). We found that these maser motions indicate large random motion (40-70km s-1), but in at least one region they exhibit radial expansion motions. This suggests the existence of outflows originating from accompanying YSOs. We discuss not only the intrinsic physical properties ofmultiple YSOs that harborH2O masers within 0.1 pc but also the implications of the existence of these YSOs. The formation history of the cometary HII region in G 34.26+0.15 is also discussed. © 2011. Astronomical Society of Japan.