The FRACTAL DIMENSION OF THE Ρ OPHIUCUS MOLECULAR CLOUD COMPLEX

Lee, Yongung; Li, Di; Kim, Y. S.; Jung, Jae Hoon; Kang, Hyung Seok; Lee, C. H.; Yim, In-Sung; Kim, H. G.

doi:10.5303/jkas.2016.49.6.255

Journal of The Korean Astronomical Society

2016

DOI: 10.5303/jkas.2016.49.6.255

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The FRACTAL DIMENSION OF THE Ρ OPHIUCUS MOLECULAR CLOUD COMPLEX

Yongung Lee¹,

Di Li²,

Y. S. Kim³

et al.

Abstract: We estimate the fractal dimension of the ρ Ophiuchus Molecular Cloud Complex, associated with star forming regions. We selected a cube (v, l, b) database, obtained with J = 1 − 0 transition lines of 12 CO and 13 CO at a resolution of 22 ′′ using a multibeam receiver system on the 14-m telescope of the Five College Radio Astronomy Observatory. Using a code developed within IRAF, we identified slice-clouds with two threshold temperatures to estimate the fractal dimension. With threshold temperatures of 2.25 K (3… Show more

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Cited by 5 publications

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Cloud structure and young star distribution in the Dragonfish complex

Sanchez,

Nespoli,

Gonzalez

et al. 2024

A&A

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Star formation is a complex process involving several physical mechanisms that interact with each other at different spatial scales. One way to shed some light on this process is to analyse the relation between the spatial distributions of gas and newly formed stars. In order to obtain robust results, it is necessary for this comparison to be made using quantitative and consistent descriptors that are applied to the same star-forming region. We used fractal analysis to characterise and compare in a self-consistent way the structure of the cloud and the distribution of young stellar objects (YSO) in the Dragonfish star-forming complex. Different emission maps of the Dragonfish nebula were retrieved from the NASA/IPAC Infrared Science and the Planck Legacy archives. Moreover, we used photometric information from the AllWISE catalogue to select a total of 1082 YSOs in the region. We derived the physical properties for some of these from their spectral energy distributions (SEDs). For the cloud images and YSOs, the three-dimensional fractal dimension ($D_f$) was calculated using previously developed and calibrated algorithms. The fractal dimension of the Dragonfish nebula ($D_f = 2.6-2.7$) agrees very well with values previously obtained for the Orion, Ophiuchus, and Perseus clouds. On the other hand, YSOs exhibit a significantly lower value on average ($D_f = 1.9-2.0$), which indicates that their structure is far more clumpy than the material from which they formed. Younger Class I and Class II sources have lower values ($D_f = 1.7 0.1$) than more evolved transition disk objects ($D_f = 2.2 0.1$), which shows a certain evolutionary effect according to which an initially clumpy structure tends to gradually disappear over time. The structure of the Dragonfish complex is similar to that of other molecular clouds in the Galaxy. However, we found clear and direct evidence that the clustering degree of the newly born stars is significantly higher than that of the parent cloud from which they formed. The physical mechanism behind this behaviour is still not clear.

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Cloud structure and young star distribution in the Dragonfish complex

Sanchez,

Nespoli,

Gonzalez

et al. 2024

A&A

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show abstract

Identification of molecular clouds in emission maps: a comparison between methods in the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey

Rani

Moore

Eden

et al. 2023

Monthly Notices of the Royal Astronomical Society

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The growing range of automated algorithms for the identification of molecular clouds and clumps in large observational datasets has prompted the need for the direct comparison of these procedures. However, these methods are complex and testing for biases is often problematic: only a few of them have been applied to the same data set or calibrated against a common standard. We compare the Fellwalker method, a widely used watershed algorithm, to the more recent Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES). SCIMES overcomes sensitivity and resolution biases that plague many friends-of-friends algorithms by recasting cloud segmentation as a clustering problem. Considering the 13CO/C18O (J = 3 − 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) and the CO High-Resolution Survey (COHRS), we investigate how these two different approaches influence the final cloud decomposition. Although the two methods produce largely similar statistical results over the CHIMPS dataset, FW appears prone to over-segmentation, especially in crowded fields where gas envelopes around dense cores are identified as adjacent, distinct objects. FW catalogue also includes a number of fragmented clouds that appear as different objects in a line-of-sight projection. In addition, cross-correlating the physical properties of individual sources between catalogues is complicated by different definitions, numerical implementations, and design choices within each method, which make it very difficult to establish a one-to-one correspondence between the sources.

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Analytical Core Mass Function (CMF) from Filaments: Under Which Circumstances Can Filament Fragmentation Reproduce the CMF?

Lee

Hennebelle

Chabrier

2017

ApJ

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Observations suggest that star formation in filamentary molecular clouds occurs in a two-step process, with the formation of filaments preceding that of prestellar cores and stars. Here, we apply the gravo-turbulent fragmentation theory of Hennebelle & Chabrier (2008, 2009, 2013 to a filamentary environment, taking into account magnetic support. We discuss the induced geometrical effect on the cores, with a transition from 3D geometry at small scales to 1D at large ones. The model predicts the fragmentation behavior of a filament for a given mass per unit length (MpL) and level of magnetization. This CMF for individual filaments is then convolved with the distribution of filaments to obtain the final system CMF. The model yields two major results: (i) the filamentary geometry naturally induces a hierarchical fragmentation process, first into groups of cores, separated by a length equal to a few filament Jeans lengths, i.e. a few times the filament width. These groups then fragment into individual cores. (ii) Non-magnetized filaments with high MpL are found to fragment excessively, at odd with observations. This is resolved by taking into account the magnetic field treated simply as additional pressure support). The present theory suggests two complementary modes of star formation: while small (spherical or filamentary) structures will collapse directly into prestellar cores, according to the standard Hennebelle-Chabrier theory, the large (filamentary) ones, the dominant population according to observations, will follow the afore-described two-step process.

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The FRACTAL DIMENSION OF THE Ρ OPHIUCUS MOLECULAR CLOUD COMPLEX

Cited by 5 publications

References 14 publications

Cloud structure and young star distribution in the Dragonfish complex

Cloud structure and young star distribution in the Dragonfish complex

Identification of molecular clouds in emission maps: a comparison between methods in the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey

Analytical Core Mass Function (CMF) from Filaments: Under Which Circumstances Can Filament Fragmentation Reproduce the CMF?

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