RESOLUTION OF THE DISTANCE AMBIGUITY FOR GALACTIC H ii REGIONS

By L. Anderson, T. Bania. 2008

139 citations recorded by the source corpus.

We resolve the kinematic distance ambiguity for 266 inner Galaxy H ii regions out of a sample of 291 using existing H i and 13CO sky surveys. Our sample contains all H ii regions with measured radio recombination line emission over the extent of the 13CO Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (18° < l < 55° and |b| < 1) and contains ultra compact (UC), compact, and diffuse H ii regions. We use two methods for resolving the distance ambiguity for each H ii region: H i emission/absorption (H i E/A) and H i self-absorption (H i SA). We find that the H i E/A and H i SA methods can resolve the distance ambiguity for 72% and 87% of our sample, respectively. When projected onto the Galactic plane, this large sample appears to reveal aspects of Galactic structure, with spiral arm-like features at Galactocentric radii of 4.5 and 6 kpc, and a lack of H ii regions within 3.5 kpc of the Galactic center. Our H ii regions are approximately in the ratio of 2 to 1 for far versus near distances. The ratio of far-to-near distances for UC H ii regions is 2.2 to 1. Compact H ii regions are preferentially at the near distance; their ratio of far-to-near distances is 1.6 to 1. Diffuse H ii regions are preferentially at the far distance; their ratio of far-to-near distances is 3.8 to 1. This implies that the distinction between UC and compact H ii regions is largely due to distance, and that the large angular size of diffuse H ii regions is not solely due to proximity to the Sun.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f793935dfca2be603ed0db9d036931d9371493ca

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Citations in the corpus

ATLASGAL - The APEX telescope large area survey of the galaxy at 870 μm (2009, background): “Finally, results from, both, Sewilo et al. (2004) and Anderson & Bania (2009) generally agree with our conclusions for the objects located in the test field, the+65 km s−1 complex being at the near distance and the+20 km s−1 clump G19.”
The RMS survey : Galactic distribution of massive star formation (2013, background): “Similar features have also been reported in the Galactocentric distribution of methanol masers (Green & McClure-Griffiths 2011), H II regions (Paladini, Davies & De Zotti 2004; Anderson & Bania 2009), thermal dust emission (Dunham et al. 2011) and molecular gas (Rathborne et al. 2009).”
THE GREEN BANK TELESCOPE H ii REGION DISCOVERY SURVEY. II. THE SOURCE CATALOG (2011, background): “This velocity corresponds to a kinematic distance of 5.7 kpc (Anderson & Bania 2009), which places W43 at the end of the Galactic bar (Benjamin et al. 2005).”
THE WISE CATALOG OF GALACTIC H ii REGIONS (2013, methodology): “The utility of this method for H ii region studies relies on the association between the H ii region and molecular gas (see Anderson & Bania 2009).”
The Milky Way Project First Data Release: a bubblier Galactic disc (2012, methodology): “Cross-matching with Anderson & Bania (2009) provides distances to 185 of the larger MWP bubbles (cross-matching as described in Section 4.2).”
A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays - II. Results for the diffusion model combining B/C and radioactive nuclei (2010, background): “The intensity of the latter is well measured 0.018 ± 0.002 cm−3 (Berkhuijsen et al. 2006; Berkhuijsen & Müller 2008), whereas the former depends strongly on the Galactocentric radius r (Anderson & Bania 2009).”
The 6-GHz methanol multibeam maser catalogue – II. Galactic longitudes 6° to 20° (2010, background): “Both Kolpak et al. (2003) and Anderson & Bania (2009) ascribe the associated Hii region to a far kinematic distance based on HI absorption and HI self-absorption, in contrast to Downes et al. (1980), who ascribe it to a near kinematic distance based on the absence of formaldehyde absorption.”
Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, background): “Moreover, the same features of Galactic structure were discovered already by the first H II region radio recombination line survey (Reifenstein et al. 1970) and more recently in Anderson & Bania (2009) in a sample of H II regions over the extent of the GRS (see Fig.”
The spiral structure of our Milky Way Galaxy (2009, methodology): “Kuchar & Bania (1994), Kolpak et al. (2003), Fish et al. (2003), Pandian et al. (2008), Anderson & Bania (2009) used HI absorption to resolve the distance ambiguity for other samples of HII regions.”