A PPMAP analysis of the filamentary structures in Ophiuchus L1688 and L1689

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).

Filaments in the OMC-3 cloud and uncertainties in estimates of filament profiles

“…In all the above studies, the column densities were based on the modelling of dust emission with a single-component MBB. Howard et al (2019) and Howard et al (2021) used the PPMAP method (Marsh et al 2015) to analyse Herschel and SCUBA-2 observations of filaments in the Taurus and Ophiuchus clouds. They noted that the use of the PPMAP method, which takes temperature variations into account, resulted in a reduction in the estimated filament widths.…”

“…The measurements have been used to estimate the typical column-density and massper-length values of star-forming filaments, the width of filaments, and parametric representations for the filament profiles. The questions of the universality of filament widths and the reliability of filament-property estimates are still topical (Howard et al 2021;Panopoulou et al 2022). In Herschel studies, for clouds within distances of 0.5 kpc, the typical filament full-width at half maximum (FWHM) widths are of the order of 0.1 pc, which could point to a common formation mechanism, either through a single event or as a more dynamical accretion process (Arzoumanian et al 2019;Hacar et al 2022).…”