The distances to molecular clouds in the fourth Galactic quadrant

Chen, Bingqiu; Wang, Shu; Hou, Ligang; Yang, Ya‐Bin; Li, Zhiwen; Zhao, H.; Jiang, Biwei

doi:10.1093/mnras/staa1827

Cited by 6 publications

(2 citation statements)

References 42 publications

(39 reference statements)

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“…As a standard candle (Paczyński & Stanek 1998), RC stars are widely used to trace interstellar extinction (Indebetouw et al 2005;Gao et al 2009;Wang & Chen 2019) and nebular distance (Güver et al 2010;Shan et al 2018;Wang et al 2020;Chen et al 2020). RC candidates are usually selected from (J − K S , K S ) CMD with empirical borders defined by naked eyes (e.g., Wang et al 2020;Chen et al 2020). To exclude the contamination of other types of stars, peak colors are determined in different K S bins to form the track of RC toward a given line of sight.…”

Section: Appendix A: Correction For Individual Fieldsmentioning

confidence: 99%

The diffuse interstellar band around 8620 Å

Zhao

Schultheis

Recio–Blanco

et al. 2020

A&A

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Context. Diffuse interstellar bands (DIBs) are interstellar absorption features that widely exist in the optical and near-infrared wavelength range. DIBs play an important role in the lifecycle of the interstellar medium and can also be used to trace the Galactic structure. Aims. We developed a set of procedures to automatically detect and measure the DIB around 8620 Å (the Gaia DIB) for a wide range of temperatures. The method was tested on ∼5000 spectra from the Giraffe Inner Bulge Survey (GIBS) that has a spectral window similar to that of the Gaia-RVS spectra. Based on this sample, we studied the correlation between the equivalent width (EW) of the Gaia DIB and the interstellar reddening E(J − K S) toward the inner Galaxy, as well as the DIB intrinsic properties. Methods. Our procedure automatically checks and eliminates invalid cases, and then applies a specific local normalization. The DIB profile is fit with a Gaussian function. Specifically, the DIB feature is extracted from the spectra of late-type stars by subtracting the corresponding synthetic spectra. For early-type stars we applied a specific model based on the Gaussian process that needs no prior knowledge of the stellar parameters. In addition, we provide the errors contributed by the synthetic spectra and from the random noise. Results. After validation, we obtained 4194 reasonable fitting results from the GIBS database. An EW versus E(J − K S) relation is derived as E(J − K S) = 1.875 (± 0.152) × EW − 0.011 (± 0.048), according to E(B − V)/EW = 2.721, which is highly consistent with previous results toward similar sightlines. After a correction based on the Vista Variables in the Via Lactea (VVV) database for both EW and reddening, the coefficient derived from individual GIBS fields, E(J − K S)/EW = 1.884 ± 0.225, is also in perfect agreement with literature values. Based on a subsample of 1015 stars toward the Galactic center within −3 • < b < 3 • and −6 • < l < 3 • , we determined a rest-frame wavelength of the Gaia DIB as 8620.55 Å. Conclusions. The procedures for automatic detection and measurement of the Gaia DIB are successfully developed and have been applied to the GIBS spectra. A Gaussian profile is proved to be a proper and stable assumption for the Gaia DIB as no intrinsic asymmetry is found. A tight linearity of its correlation with the reddening is derived toward the inner Milky Way, which is consistent with previous results.

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Section: Appendix A: Correction For Individual Fieldsmentioning

confidence: 99%

The diffuse interstellar band around 8620 Å

Zhao

Schultheis

Recio–Blanco

et al. 2020

A&A

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“…One approach involves modeling the dust extinction profiles along different LOS, where the measured cloud is searched for dust clouds from 3D dust structures (Chen et al 2020b;Guo et al 2022). Another approach involves searching for the location of the extinction break point that is caused by molecular clouds (Yan et al 2019;Zucker et al 2019Zucker et al , 2020Chen et al 2020a;Sun et al 2021b). It can also be applied to supernova remnants (Shan et al 2019;Wang et al 2020;Zhao et al 2020;Leike et al 2021).…”

Section: Introductionmentioning

confidence: 99%

New method for estimating molecular cloud distances based on Gaia, 2MASS, and the TRILEGAL galaxy model

Mei,

Chen,

Jiang

et al. 2024

A&A

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We propose a new method for estimating the distances of molecular clouds traced by CO line emission. Stars from 2MASS and Gaia EDR3 are selected as on-cloud stars when they are projected on a cloud. The background on-cloud stars have redder colors on average than the foreground stars. Instead of searching for stars projected away from the cloud, we employed the TRILEGA galaxy model to mimic the stellar population without cloud extinction along the sightline toward the cloud. Our method does not require an exact boundary of a cloud. The boundaries are highly variable and depend on the sensitivity of the molecular line data. For each cloud, we compared the distributions of on-cloud stars to the TRILEGAL stellar populations in the diagram of $J-K_s$ color versus distance. The intrinsic $J-K_s$ colors of main-sequence and evolved stars from TRILEGAL were considered separately, and they were used as the baseline for subtracting the observed $J-K_s$ colors. The baseline-corrected $J-K_s$ color was deployed with the Bayesian analysis and Markov chain Monte Carlo sampling to determine the distance at which the $J-K_s$ color jump is largest. This method was successfully applied to measure the distances of 27 molecular clouds, which were selected from previously published cloud samples. By replacing TRILEGAL with the GALAXIA galaxy model, we were able to measure the distances for 21 of the 27 clouds. The distances of the 21 clouds based on the GALAXIA model agree well with those based on the TRILEGAL model. The distances of the 27 clouds estimated by this method are consistent with previous estimates. We will apply this new method to a larger region of the gaseous galactic plane, in particular, for the inner galactic region, where a region free of CO emission is hard to separate from the crowded field of clouds.

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Distances to molecular clouds in the second Galactic quadrant

Yan

Yang

Sun

et al. 2021

A&A

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We present distances to 76 medium-sized molecular clouds and an extra large-scale molecular cloud in the second Galactic quadrant (104. °75 < l < 150. °25 and |b| < 5. °25), 73 of which are accurately measured for the first time. Molecular cloud samples are drawn from l-b-V space (− 95 < VLSR < 25 km s−1) with the density-based spatial clustering of applications with noise algorithm, and distances are measured with the background-eliminated extinction-parallax method using extinctions and Gaia DR2 parallaxes. The range of the measured distances to the 76 molecular clouds is from 211 to 2631 pc, and the extra large-scale molecular cloud appears to be a coherent structure at about 1 kpc, across about 40° (~700 pc) in the Galactic longitude.

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The distances to molecular clouds in the fourth Galactic quadrant

Cited by 6 publications

References 42 publications

The diffuse interstellar band around 8620 Å

The diffuse interstellar band around 8620 Å

New method for estimating molecular cloud distances based on Gaia, 2MASS, and the TRILEGAL galaxy model

Distances to molecular clouds in the second Galactic quadrant

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