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Register a new userStar formation activity beyond the outer Arm I: WISE-selected candidate star-forming regions
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The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at $R_{rm G}$ $ge$ 13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer (WISE) mid-infrared all-sky survey. From their color distribution, we developed a simple identification criterion of star-forming regions in the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at $R_{rm G}$ $ge$ 13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) $^{12}$CO survey of the outer Galaxy, of which the survey region is 102$^circ$.49 $le$ $l$ $le$ 141$^circ$.54, $-$3$^circ$.03 $le$ $b$ $le$ 5$^circ$.41, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star-formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star-formation properties, including star-formation rate, star-formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.
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We report parallaxes and proper motions of three water maser sources in high-mass star-forming regions in the Outer Spiral Arm of the Milky Way. The observations were conducted with the Very Long Baseline Array as part of Bar and Spiral Structure Legacy Survey and double the number of such measurements in the literature. The Outer Arm has a pitch angle of 14.9 +/- 2.7 deg and a Galactocentric distance of 14.1 +/- 0.6 kpc toward the Galactic anticenter. The average motion of these sources toward the Galactic center is 10.7 +/- 2.1 km/s and we see no sign of a significant fall in the rotation curve out to 15 kpc from the Galactic center. The three-dimensional locations of these star-forming regions are consistent with a Galactic warp of several hundred parsecs from the plane.
The Outer Scutum-Centaurus arm (OSC) is the most distant molecular spiral arm known in the Milky Way. The OSC may be the very distant end of the well-known Scutum-Centaurus arm, which stretches from the end of the Galactic bar to the outer Galaxy. At this distance the OSC is seen in the first Galactic quadrant. The population of star formation tracers in the OSC remains largely uncharacterized. Extragalactic studies show a strong correlation between molecular gas and star formation, and carbon monoxide (CO) emission was recently discovered in the OSC. Here we use the Arizona Radio Observatory (ARO) 12-m telescope to observe the $^{12}$CO J = 1-0 and $^{13}$CO J = 1-0 transitions toward 78 HII region candidates chosen from the WISE Catalog of Galactic HII Regions. These targets are spatially coincident with the Galactic longitude-latitude ($ell, b$) OSC locus as defined by HI emission. We detect CO emission in $sim 80$% of our targets. In total, we detect 117 $^{12}$CO and 40 $^{13}$CO emission lines. About 2/3 of our targets have at least one emission line originating beyond the Solar orbit. Most of the detections beyond the Solar orbit are associated with the Outer Arm, but there are 17 $^{12}$CO emission lines and 8 $^{13}$CO emission lines with LSR velocities that are consistent with the velocities of the OSC. There is no apparent difference between the physical properties (e.g., molecular column density) of these OSC molecular clouds and non--OSC molecular clouds within our sample.
As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high mass star forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well studied regions: 1.9 +0.1/-0.1 kpc for M17, 5.3 +1.3/-0.9 kpc for W51, and 7.9 +0.9/-0.7 kpc for GAL 045.5+00.0. Peculiar motions for all but one source are less than 20 km/s. We fit a log-periodic spiral to the locations and estimate an average pitch angle of 7.2+-1.9 deg. We find that the section of the arm beyond the tangent point in the first quadrant of the Milky Way appears 15 pc below the IAU-defined Galactic plane.
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We report trigonometric parallax and proper motion measurements of 6.7-GHz CH3OH and 22-GHz H2O masers in eight high-mass star-forming regions (HMSFRs) based on VLBA observations as part of the BeSSeL Survey. The distances of these HMSFRs combined with their Galactic coordinates, radial velocities, and proper motions, allow us to assign them to a segment of the Perseus arm with ~< 70 deg. These HMSFRs are clustered in Galactic longitude from ~30 deg to ~50, neighboring a dirth of such sources between longitudes ~50 deg to ~90 deg.
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