Abstract
ABSTRACT We use the Point Process MAPping (PPMAP) algorithm to reanalyse the Herschel and SCUBA-2 observations of the L1688 and L1689 subregions of the Ophiuchus molecular cloud. PPMAP delivers maps with high resolution (here 14 arcsec, corresponding to ${\sim}0.01\, {\rm pc}$ at ${\sim}140\, {\rm pc}$), by using the observations at their native resolutions. PPMAP also delivers more accurate dust optical depths, by distinguishing dust of different types and at different temperatures. The filaments and pre-stellar cores almost all lie in regions with $N_{\rm H_2}\gtrsim 7\times 10^{21}\, {\rm cm}^{-2}$ (corresponding to AV ≳ 7). The dust temperature, T, tends to be correlated with the dust opacity index, β, with low T and low β concentrated in the interiors of filaments. The one exception to this tendency is a section of filament in L1688 that falls – in projection – between the two B stars: S1 and HD147889; here T and β are relatively high, and there is compelling evidence that feedback from these two stars has heated and compressed the filament. Filament fwhms are typically in the range $0.10$ to $0.15\, {\rm pc}$. Most filaments have line-densities in the range $25$ to $65\, {\rm M_{\odot }\, pc^{-1}}$. If their only support is thermal gas pressure, and the gas is at the canonical temperature of $10\, {\rm K}$, the filaments are highly supercritical. However, there is some evidence from ammonia observations that the gas is significantly warmer than this, and we cannot rule out the possibility of additional support from turbulence and/or magnetic fields. On the basis of their spatial distribution, we argue that most of the starless cores are likely to disperse (rather than evolving to become pre-stellar).
Highlights
In the past decade, far-infrared and submillimetre dust observations have greatly enhanced our understanding of the star formation process within the Milky Way
Extensive surveys conducted with telescopes such as Herschel1 and the James Clerk Maxwell Telescope (JCMT) have helped to disentangle the complicated nature of molecular clouds, revealing widespread networks of dense filaments (Andreet al. 2010; Arzoumanian et al 2011, 2019; Hacar et al 2013; Konyves et al 2015; Ladjelate et al 2020), and linking them to the earliest stages of pre-stellar and protostellar core formation (Andreet al. 2014; Pattle et al 2015; Marsh et al 2016; Ladjelate et al 2020)
Point Process MAPping (PPMAP) returns a 4D data-hypercube giving, for each pixel on the sky, the surface density, as estimated from the opacity of dust of different types and at different temperatures (T). Throughout both subregions, the PPMAP results show a network of filaments with complex temperature-coherent structures, and a systematic change in the dust properties in high-density regions, similar to that observed in the Taurus L1495 filament by Howard et al (2019)
Summary
Far-infrared and submillimetre dust observations have greatly enhanced our understanding of the star formation process within the Milky Way. The Ophiuchus molecular cloud complex is a nearby (∼140 pc, Mamajek 2008), well-studied region of star formation associated with the Gould Belt (Wilking & Lada 1983; Nutter, Ward-Thompson & Andre 2006; Pattle et al 2015; Soler 2019; Ladjelate et al 2020). Despite the early identification of filamentary structures associated with the Ophiuchus complex, most studies have focused on the prestellar and protostellar cores within L1688 and L1689 We reanalyse Herschel and SCUBA-2 observations of the L1688 and L1689 subregions of the Ophiuchus cloud complex, using the Bayesian Point Process MAPping (PPMAP) algorithm (Marsh, Whitworth & Lomax 2015).
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