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Title: Molecular Clouds in the Extreme Outer Galaxy between l  = 34.°75 to 45.°25

Abstract

We present the results of an unbiased CO survey in the Galactic range of 34.°75 ≤  l  ≤ 45.°25 and −5.°25 ≤  b  ≤ 5.°25, and the velocity range beyond the Outer arm. A total of 168 molecular clouds (MCs) are identified within the Extreme Outer Galaxy (EOG) region, and 31 of these MCs are associated with {sup 13}CO  emission. However, none of them show significant C{sup 18}O  emission under the current detection limit. The typical size and mass of these MCs are 5 pc and 3 × 10{sup 3} M {sub ⊙}, implying a lack of large and massive MCs in the EOG region. Similar to MCs in the outer Galaxy, the velocity dispersions of EOG clouds are also correlated with their sizes; however, they are well displaced below the scaling relationship defined by the inner Galaxy MCs. These MCs with a median Galactocentric radius of 12.6 kpc show very different distributions from those of the MCs in the Outer arm published in our previous paper, while roughly following the Outer Scutum–Centaurus arm defined by Dame and Thaddeus. This result may provide robust evidence for the existence of the Outer Scutum–Centaurus arm. The lower limit of the total mass of this segment is about 2.7 × 10{sup 5} Mmore » {sub ⊙}, which is about one magnitude lower than that of the Outer arm. The mean thickness of the gaseous disk is about 1.°45 or 450 pc, and the scale height is about 1.°27, or 400 pc above the b  = 0° plane. The warp traced by CO emission is very obvious in the EOG region and its amplitude is consistent with the predictions by other warp models using different tracers, such as dust, H i, and stellar components of our Galaxy.« less

Authors:
; ; ; ; ; ; ;  [1]
  1. Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008 (China)
Publication Date:
OSTI Identifier:
22661121
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 230; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON 13; CARBON MONOXIDE; CLOUDS; COSMIC DUST; EMISSION; MASS; MILKY WAY; MOLECULES; SCALE HEIGHT; SENSITIVITY; STARS; VELOCITY

Citation Formats

Sun, Yan, Su, Yang, Zhang, Shao-Bo, Xu, Ye, Chen, Xue-Peng, Yang, Ji, Jiang, Zhi-Bo, and Fang, Min, E-mail: yansun@pmo.ac.cn. Molecular Clouds in the Extreme Outer Galaxy between l  = 34.°75 to 45.°25. United States: N. p., 2017. Web. doi:10.3847/1538-4365/AA63EA.
Sun, Yan, Su, Yang, Zhang, Shao-Bo, Xu, Ye, Chen, Xue-Peng, Yang, Ji, Jiang, Zhi-Bo, & Fang, Min, E-mail: yansun@pmo.ac.cn. Molecular Clouds in the Extreme Outer Galaxy between l  = 34.°75 to 45.°25. United States. doi:10.3847/1538-4365/AA63EA.
Sun, Yan, Su, Yang, Zhang, Shao-Bo, Xu, Ye, Chen, Xue-Peng, Yang, Ji, Jiang, Zhi-Bo, and Fang, Min, E-mail: yansun@pmo.ac.cn. Thu . "Molecular Clouds in the Extreme Outer Galaxy between l  = 34.°75 to 45.°25". United States. doi:10.3847/1538-4365/AA63EA.
@article{osti_22661121,
title = {Molecular Clouds in the Extreme Outer Galaxy between l  = 34.°75 to 45.°25},
author = {Sun, Yan and Su, Yang and Zhang, Shao-Bo and Xu, Ye and Chen, Xue-Peng and Yang, Ji and Jiang, Zhi-Bo and Fang, Min, E-mail: yansun@pmo.ac.cn},
abstractNote = {We present the results of an unbiased CO survey in the Galactic range of 34.°75 ≤  l  ≤ 45.°25 and −5.°25 ≤  b  ≤ 5.°25, and the velocity range beyond the Outer arm. A total of 168 molecular clouds (MCs) are identified within the Extreme Outer Galaxy (EOG) region, and 31 of these MCs are associated with {sup 13}CO  emission. However, none of them show significant C{sup 18}O  emission under the current detection limit. The typical size and mass of these MCs are 5 pc and 3 × 10{sup 3} M {sub ⊙}, implying a lack of large and massive MCs in the EOG region. Similar to MCs in the outer Galaxy, the velocity dispersions of EOG clouds are also correlated with their sizes; however, they are well displaced below the scaling relationship defined by the inner Galaxy MCs. These MCs with a median Galactocentric radius of 12.6 kpc show very different distributions from those of the MCs in the Outer arm published in our previous paper, while roughly following the Outer Scutum–Centaurus arm defined by Dame and Thaddeus. This result may provide robust evidence for the existence of the Outer Scutum–Centaurus arm. The lower limit of the total mass of this segment is about 2.7 × 10{sup 5} M {sub ⊙}, which is about one magnitude lower than that of the Outer arm. The mean thickness of the gaseous disk is about 1.°45 or 450 pc, and the scale height is about 1.°27, or 400 pc above the b  = 0° plane. The warp traced by CO emission is very obvious in the EOG region and its amplitude is consistent with the predictions by other warp models using different tracers, such as dust, H i, and stellar components of our Galaxy.},
doi = {10.3847/1538-4365/AA63EA},
journal = {Astrophysical Journal, Supplement Series},
number = 2,
volume = 230,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • Using the Purple Mountain Observatory Delingha (PMODLH) 13.7 m telescope, we report a 96 deg{sup 2} {sup 12}CO/{sup 13}CO/C{sup 18}O mapping observation toward the Galactic region of l  = [139.°75,149.°75], b  = [−5.°25, 5.°25]. The molecular structures of the Local Arm and Perseus Arm are presented. Combining H i data and part of the Outer Arm results, we obtain that the warp structure of both atomic and molecular gas is obvious, while the flare structure only exists in atomic gas in this observing region. In addition, five filamentary giant molecular clouds on the Perseus Arm are identified. Among them, four are newlymore » identified. Their relations with the Milky Way large-scale structure are discussed.« less
  • Maps of the CO (J = 1 to 0) line have been obtained in order to explore the physical conditions and star-forming activities in 31 molecular clouds in the outer Galaxy. On a large scale, the clouds are found to follow the H I warp. Antenna temperatures (corrected for atmospheric attenuation, ohmic losses, and rear and forward spillover) are shown to decrease somewhat with distance. The results suggest low kinetic temperatures in the clouds and that the CO line is optically thick. Most of the clouds lie between R = 11.5 kpc and R = 14 kpc, are about 40more » pc in the longest dimension, and have masses in the 10 to the 4th to 10 to the 5th solar mass range. 33 references.« less
  • Giant molecular clouds in the outer arm of the Galaxy comparable in size and mass to the largest clouds in the inner Galaxy between R about 3 kpc and the solar circle have been detected in a new CO survey along the Galactic plane from l = 65 deg to 71 deg centered about b = + 1 deg. These objects at R about 12 kpc are underluminous in CO; the N(H2)/W(CO) ratio determined from either virial masses or the CO luminosity-line width relation is 4 + or - 2 times that in the inner Galaxy. When extrapolated to themore » entire Galaxy beyond R = 11 kpc, the present survey and related data yield a total molecular mass in the range (1-7) x 10 to the 8th solar masses. The outer arm complexes surveyed contain the two most luminous H II regions known beyond R about 10 kpc; one is the distant component of W58, and the other is a previously unidentified distant component of S98. 20 refs.« less
  • Star formation has been studied in 17 outer Galaxy molecular clouds using the VLA to perform 6 and 20 cm continuum observations to search for H II regions as evidence of massive star formation. IRAS data are used to measure the far-IR luminosity as an indicator of the total star formation rate. H II regions are found to be associated with each of the clouds. The number of ionizing photons required by radio luminosity ranges from 6 x 10 to the 45th/s to 5.5 x 10 to the 49th/s. Far-IR emission was detected from each of the clouds with themore » range of luminosities being 500 to one million solar. From the data, it is concluded that there is no strong correlation between star formation activity and cloud mass. 39 refs.« less
  • The study of extragalactic supernova (SNs) suggests that Type II SNs, not Type I, tend to occur near extreme optical Population I objects, but the detection of these objects in the Galaxy is limited by heavy local obscuration. A CO survey has been conducted toward every confirmed outer Galaxy SNR from l = 70 to 210 deg, for a total of 26, and it is found that roughly half of them, within uncertainties of distance estimates, revealed spatial coincidences with large molecular cloud complexes. Most of the cloud complexes in these coincidences probably are the birthplaces of the progenitors ofmore » the corresponding Type II SNRs, because it is statistically improbable that the coincidences result from change superposition. 118 references.« less