Abstract:We use the 13CO (2-1) emission from the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) high-resolution spectral-line survey of the inner Galaxy, to extract the molecular cloud population with a large dynamic range in spatial scales, using the Spectral Clustering for Interstellar Molecular Emission Segmentation (scimes) algorithm. This work compiles a cloud catalogue with a total of 10663 molecular clouds, 10300 of which we were able to assign distances and compute phys… Show more
“…In the Milky Way, GMCs have long been known as good tracers of spiral arms (e.g., Myers et al, 1986;Grabelsky et al, 1988;Hou and Han, 2014). From the wealthy dataset of Galactic CO surveys (see Heyer and Dame, 2015, for a review), a large number of isolated molecular clouds have been identified by different methods (e.g., García et al, 2014;Rice et al, 2016;Miville-Deschênes et al, 2017;Yan et al, 2020;Duarte-Cabral et al, 2021). For the majority of them, only kinematic distances are known, which depend on the adopted Galaxy rotation curve, the solution of the kinematic distance ambiguity, and deviation from the hypothetic circular rotation.…”
Section: Giant Molecular Cloudsmentioning
confidence: 99%
“…For the majority of them, only kinematic distances are known, which depend on the adopted Galaxy rotation curve, the solution of the kinematic distance ambiguity, and deviation from the hypothetic circular rotation. For instance, Duarte-Cabral et al (2021) compiled a large catalogue of 10,663 molecular clouds in the inner Galaxy. They estimated the kinematic distances for 10,300 clouds after solving the distance ambiguities through different methods.…”
The spiral structure in the solar neighborhood is an important issue in astronomy. In the past few years, there has been significant progress in observation. The distances for a large number of good spiral tracers, i.e., giant molecular clouds, high-mass star-formation region masers, HII regions, O-type stars, and young open clusters, have been accurately estimated, making it possible to depict the detailed properties of nearby spiral arms. In this work, we first give an overview about the research status for the Galaxy’s spiral structure based on different types of tracers. Then the objects with distance uncertainties better than 15% and <0.5 kpc are collected and combined together to depict the spiral structure in the solar neighborhood. Five segments related with the Perseus, Local, Sagittarius-Carina, Scutum-Centaurus, and Norma arms are traced. With the large dataset, the parameters of the nearby arm segments are fitted and updated. Besides the dominant spiral arms, some substructures probably related to arm spurs or feathers are also noticed and discussed.
“…In the Milky Way, GMCs have long been known as good tracers of spiral arms (e.g., Myers et al, 1986;Grabelsky et al, 1988;Hou and Han, 2014). From the wealthy dataset of Galactic CO surveys (see Heyer and Dame, 2015, for a review), a large number of isolated molecular clouds have been identified by different methods (e.g., García et al, 2014;Rice et al, 2016;Miville-Deschênes et al, 2017;Yan et al, 2020;Duarte-Cabral et al, 2021). For the majority of them, only kinematic distances are known, which depend on the adopted Galaxy rotation curve, the solution of the kinematic distance ambiguity, and deviation from the hypothetic circular rotation.…”
Section: Giant Molecular Cloudsmentioning
confidence: 99%
“…For the majority of them, only kinematic distances are known, which depend on the adopted Galaxy rotation curve, the solution of the kinematic distance ambiguity, and deviation from the hypothetic circular rotation. For instance, Duarte-Cabral et al (2021) compiled a large catalogue of 10,663 molecular clouds in the inner Galaxy. They estimated the kinematic distances for 10,300 clouds after solving the distance ambiguities through different methods.…”
The spiral structure in the solar neighborhood is an important issue in astronomy. In the past few years, there has been significant progress in observation. The distances for a large number of good spiral tracers, i.e., giant molecular clouds, high-mass star-formation region masers, HII regions, O-type stars, and young open clusters, have been accurately estimated, making it possible to depict the detailed properties of nearby spiral arms. In this work, we first give an overview about the research status for the Galaxy’s spiral structure based on different types of tracers. Then the objects with distance uncertainties better than 15% and <0.5 kpc are collected and combined together to depict the spiral structure in the solar neighborhood. Five segments related with the Perseus, Local, Sagittarius-Carina, Scutum-Centaurus, and Norma arms are traced. With the large dataset, the parameters of the nearby arm segments are fitted and updated. Besides the dominant spiral arms, some substructures probably related to arm spurs or feathers are also noticed and discussed.
“…The validity of these scaling relations has been challenged both in the local environment and in extragalactic targets with different environmental conditions. Most observations do find a correlation between the size and the linewidth, but there seems to be no agreement for the power-law exponent and all observations find large uncertainties in the slope (Duarte-Cabral et al 2020;Imara et al 2020). Moreover, the third Larson relation is likely to be an artefact produced by the limited dynamical range of early observations of column density, and the sample of observed clouds being located in similar environmental conditions.…”
mentioning
confidence: 93%
“…The trends are observed, but the scatter is large, and different surveys reach different conclusions for the exponents. Within the disc, no strong variations of GMC properties in relation to the position in the disc are observed (Duarte-Cabral et al 2020).…”
mentioning
confidence: 95%
“…Moreover, the third Larson relation is likely to be an artefact produced by the limited dynamical range of early observations of column density, and the sample of observed clouds being located in similar environmental conditions. Several studies have indeed confirmed that surface densities of GMCs can span over two orders of magnitude (Heyer et al 2009;Hughes et al 2010Hughes et al , 2013Leroy et al 2015;Duarte-Cabral et al 2020) though other surveys still find confirmation of the third Larson relation (Lombardi, Alves & Lada 2010).…”
To investigate how molecular clouds react to different environmental conditions at a galactic scale, we present a catalogue of giant molecular clouds resolved down to masses of ∼10 M⊙ from a simulation of the entire disc of an interacting M51-like galaxy and a comparable isolated galaxy. Our model includes time-dependent gas chemistry, sink particles for star formation and supernova feedback, meaning we are not reliant on star formation recipes based on threshold densities and can follow the physics of the cold molecular phase. We extract giant molecular clouds from the simulations and analyse their properties. In the disc of our simulated galaxies, spiral arms seem to act merely as snowplows, gathering gas and clouds without dramatically affecting their properties. In the centre of the galaxy, on the other hand, environmental conditions lead to larger, more massive clouds. While the galaxy interaction has little effect on cloud masses and sizes, it does promote the formation of counter-rotating clouds. We find that the identified clouds seem to be largely gravitationally unbound at first glance, but a closer analysis of the hierarchical structure of the molecular interstellar medium shows that there is a large range of virial parameters with a smooth transition from unbound to mostly bound for the densest structures. The common observation that clouds appear to be virialised entities may therefore be due to CO bright emission highlighting a specific level in this hierarchical binding sequence. The small fraction of gravitationally bound structures found suggests that low galactic star formation efficiencies may be set by the process of cloud formation and initial collapse.
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