Cluster-formation in the Rosette molecular cloud at the junctions of filaments

Abstract

Aims. For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. Instead, gravitational collapse of filaments and/or merging of filamentary structures can lead to building up dense high-mass star-forming clumps. However, the overall density structure of the cloud has a large influence on this process, and requires a better understanding. Methods. The Rosette molecular cloud, irradiated by the NGC 2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. Results. The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peaked PDF we interprete as caused by shock compression, while the PDFs of the center and other cloud parts are more complex, partly with a power-law tail. A deviation of the log-normal PDF form occurs at A V ≈ 9 m for the center, and around 4 m for the other regions. Only the part of the cloud farthest from the Rosette nebula shows a log-normal PDF. Conclusions. The deviations of the PDF from the log-normal shape typically associated with low-and high-mass star-forming regions at A V ≈ 3-4 m and 8-10 m , respectively, are found here within the very same cloud. This shows that there is no fundamental difference in the density structure of low-and high-mass star-forming regions. We conclude that star-formation in Rosette -and probably in high-mass star-forming clouds in general -is not globally triggered by the impact of UV-radiation. Moreover, star formation takes place in filaments that arose from the primordial turbulent structure built up during the formation of the cloud. Clusters form at filament mergers, but star formation can be locally induced in the direct interaction zone between an expanding H II-region and the molecular cloud.

The Link Between Turbulence, Magnetic Fields, Filaments, and Star Formation in the Central Molecular Zone Cloud G0.253+0.016

“…Indeed, star-forming cores in nearby spiral-arm clouds are often located along dense filaments (Polychroni et al 2013;Könyves et al 2015) and young star clusters tend to form at their intersections (Myers 2011;Schneider et al 2012). Recent observations and simulations of spiral-arm clouds show that filaments have coherent velocities (Hacar et al 2013Moeckel & Burkert 2015;Smith et al 2016) and orientations preferentially (but not always) perpendicular to the magnetic field (Gaensler et al 2011;Sugitani et al 2011;Hennebelle 2013;Palmeirim et al 2013;Planck Collaboration et al 2016a, 2016b, 2016cTomisaka 2014;Zhang et al 2014;Pillai et al 2015;Seifried & Walch 2015).…”

“…We do not have direct access to the 3D (volume) density from observations-only to the 2D (column) density distribution (Berkhuijsen & Fletcher 2008;Kainulainen et al 2009;Lombardi et al 2011;Schneider et al 2012Schneider et al , 2013Hughes et al 2013;Kainulainen & Tan 2013;Berkhuijsen & Fletcher 2015;Schneider et al 2015). However, one can estimate the 3D density dispersion and the 3D density PDF by extrapolating the 2D density information given in the plane of the sky to the third dimension (along the line of sight), assuming isotropy of the clouds (Brunt et al 2010a(Brunt et al , 2010bKainulainen et al 2014).…”

“…Star formation often seems to be associated with such dense filaments and, in particular, their intersections (Schneider et al 2012). Here we find that G0.253 +0.016 in the CMZ has similar filament properties as seen in spiral-arm clouds, e.g., that over-dense regions are located along filaments (see Figure 1).…”

Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

“…Federrath et al 2010), while gravity (Klessen 2000) and non-isothermality (Passot & Vázquez-Semadeni 1998) provoke power-law tails at higher densities. Observationally, powerlaw tails seen in PDFs that are obtained from column density maps of visual extinction or Herschel imaging were attributed to self-gravity for low-mass star-forming regions (e.g., Kainulainen et al 2009;Schneider et al 2013) and high-mass star-forming regions (e.g., Hill et al 2011;Schneider et al 2012;Russeil et al 2013). Recently, it was shown (Schneider et al 2012, Tremblin et al, in prep.…”

The impact of turbulence and magnetic field orientation on star-forming filaments

“…More recently, the advent of the Herschel satellite has uncovered the filamentary structure in molecular clouds and infrared dark clouds in great detail (e.g. André et al 2010;Könyves et al 2010;Arzoumanian et al 2011Arzoumanian et al , 2013Peretto et al 2012;Schneider et al 2012;Palmeirim et al 2013, but see also the review of André et al 2014).…”