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Register a new userThe IC133 Water Vapor Maser in the Galaxy M33: A Geometric Distance
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Authors
A. L. Argon
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We report on the results of a 14 year long VLBI study of proper motions in the IC133 H2O maser source in the galaxy M33. The method of Ordered Motion Parallax was used to model the 3-dimensional structure and dynamics of IC133 and obtain a distance estimate, 800 +/- 180 kpc. Our technique for determining the distance to M33 is independent of calibrations common to other distance indicators, such as Cepheid Period-Luminosity relations, and therefore provides an important check for previous distance determinations.
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We report phase-referencing VLBA observations of H2O masers near the star-forming region W3(OH) to measure their parallax and absolute proper motions. The measured annual parallax is 0.489 +/- 0.017 milli-arcseconds (2.04 +/- 0.07 kpc), where the error is dominated by a systematic atmospheric contribution. This distance is consistent with photometric distances from previous observations and with the distance determined from CH3OH maser astrometry presented in a related paper. We also find that the source driving the H2O outflow, the ``TW-object, moves with a 3-dimensional velocity of > 7 km/s relative to the ultracompact HII region W3(OH).
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We report the detection of a 22GHz water maser line in the nearest (D~3.8Mpc) radio galaxy Centaurus A using the Australia Telescope Compact Array (ATCA). The line is centered at a velocity of ~960kms-1, which is redshifted by about 400kms-1 from the systemic velocity. Such an offset, as well as the width of ~120kms-1, could be consistent with either a nuclear maser arising from an accretion disk of the central supermassive black hole, or for a jet maser that is emitted from the material that is shocked near the base of the jet in Centaurus,A. The best spatial resolution of our ATCA data constrains the origin of the maser feature within <3pc from the supermassive black hole. The maser exhibits a luminosity of ~1Lo, which classifies it as a kilomaser, and appears to be variable on timescales of months. A kilomaser can also be emitted by shocked gas in star forming regions. Given the small projected distance from the core, the large offset from systemic velocity, as well as the smoothness of the line feature, we conclude that a jet maser line emitted by shocked gas around the base of the AGN is the most likely explanation. For this scenario we can infer a minimum density of the radio jet of ~>10cm-3, which indicates substantial mass entrainment of surrounding gas into the propagating jet material.
Ice-water, water-vapor interfaces and ice surface are studied by molecular dynamics simulations with the SPC/E model of water molecules having the purpose to estimate the profiles of electrostatic potential across the interfaces. We have proposed a methodology for calculating the profiles of electrostatic potential based on a trial particle, which showed good agreement for the case of electrostatic potential profile of the water-vapor interface of TIP4P model calculated in another way. The measured profile of electrostatic potential for the pure ice-water interface decreases towards the liquid bulk region, which is in agreement with simulations of preferential direction of motion of Li$^{+}$ and F$^{-}$ solute ions at the liquid side of the ice-water interface. These results are discussed in connection with the Workman-Reynolds effect.
We present the detection and modeling of more than 70 far-IR pure rotational lines of water vapor, including the 18O and 17O isotopologues, towards Orion KL. Observations were performed with the Long Wavelength Spectrometer Fabry-Perot (LWS/FP; R~6800-9700) on board the Infrared Space Observatory (ISO) between ~43 and ~197 um. The water line profiles evolve from P-Cygni type profiles (even for the H2O18 lines) to pure emission at wavelengths above ~100 um. We find that most of the water emission/absorption arises from an extended flow of gas expanding at 25+-5 kms^-1. Non-local radiative transfer models show that much of the water excitation and line profile formation is driven by the dust continuum emission. The derived beam averaged water abundance is 2-3x10^-5. The inferred gas temperature Tk=80-100 K suggests that: (i) water could have been formed in the plateau by gas phase neutral-neutral reactions with activation barriers if the gas was previously heated (e.g. by shocks) to >500 K and/or (ii) H2O formation in the outflow is dominated by in-situ evaporation of grain water-ice mantles and/or (iii) H2O was formed in the innermost and warmer regions (e.g. the hot core) and was swept up in ~1000 yr, the dynamical timescale of the outflow.
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