Cloud structure and young star distribution in the Dragonfish complex

Abstract: One way to shed some light on the star formation process this process is to analyse the relationship 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 applied to the same star-forming region. Here, we use 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. We used different emission maps of the Dragonfish Nebula and photometric information from the AllWISE catalogue to select a total of 1082 YSOs in the region, for some of which we derived physical properties from their spectral energy distributions (SEDs). For both datasets (cloud images and YSOs), the three-dimensional fractal dimension (Df) was calculated using previously developed and calibrated algorithms. The fractal dimension of the Dragonfish Nebula (Df = 2.6-2.7) agrees very well with values previously obtained for the Orion, Ophiuchus, and Perseus clouds. On the other hand, YSOs exhibit on average a significantly smaller value (Df = 1.9-2.0) that indicates a much more clumpy structure than the material from which they formed. This is a 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, but the physical mechanism behind this behaviour is still not clear. Additionally, younger Class I and Class II sources have smaller values (Df = 1.7 +/- 0.1) than more evolved Transition Disk objects (Df = 2.2 +/- 0.1), evidencing a certain evolutionary effect where an initially clumpy structure tends to gradually disappear over time.