Interestingly, despite the fact that it is almost starless, the column density peaks 1 in the Pipe appear to show a clear imprint of clustering, as well as segregation by density and mass (e.g. Many of these works have the common goal of determining how GMCs are organized in the stages that precede their collapse and the consequent conversion of gas into stars. 2007 Alves, Franco & Girart 2008 Lada et al. Alves, Lombardi & Lada 2007 Muench et al. 2009, 2010) has played a workhorse role in a number of previous studies (e.g. The Pipe Nebula, a nearby ( d = 130 pc) GMC with a total mass of 7.9 × 10 3 M ⊙ (Lada, Lombardi & Alves 2010) and very little star formation activity (Brooke et al. In this sense, determining the early stages of cluster formation in GMCs may be key to understanding many distinct and complex processes involved in such a phenomenon. An additional complication is that once stars are born, they destroy most of the evidence relating to the initial stages of their formation. However, clusters and their families can be quite diverse, and there is no consensus yet on a general model for cluster formation. In the currently accepted model of star formation, most stars form in families of star clusters within giant molecular clouds (GMCs). Stars: formation, ISM: clouds, ISM: structure, infrared: ISM 1 INTRODUCTION Our work strongly supports the idea that the formation of clusters in GMC could be the result of the primordial organization of pre-stellar material. Despite the clearly distinct evolutive stage of the clouds, there are very important similarities in the physical and spatial distribution properties of the column density peaks, pointing to a scenario where they form as a result of uniform fragmentation of filamentary structures across the various scales of the cloud, with density being the parameter leading the fragmentation, and with clustering being a direct result of thermal fragmentation at different spatial scales. The peak mass distributions for Orion A, the Tail, and the convolved Pipe have similar ranges, sharing a maximum near 5 M ⊙ and a similar power-law drop above 10 M ⊙. We compare the distribution functions for dust temperature, mass, equivalent radius, and mean volume density of peaks in both clouds, and made a more fair comparison by isolating the less active Tail region in Orion A and by convolving the Pipe Nebula map to simulate placing it at a distance similar to that of the Orion Complex. The density peaks were extracted from dust extinction maps constructed from Herschel/SPIRE far-infrared images. We present a comparative study of the physical properties and the spatial distribution of column density peaks in two giant molecular clouds (GMCs), the Pipe Nebula and Orion A, which exemplify opposite cases of star cluster formation stages.
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