Nickolas Moeckel edited Filament selection and analysis.tex  over 10 years ago

Commit id: dc805aed735022b6e9e053f1e09d454a6b202e12

deletions | additions      

       

At 2.09 Myr we selected three filamentary features. Two are evolved versions of the features at 1.23 Myr (filaments C2 and D2), while filament E formed in the intervening time. At this point there are more sinks scattered through the box, including at least one in each of the filaments. The total sink mass is 92 M$_{\sun}$, i.e. a global integrated sink formation efficiency $\sim1.6\%$\footnote{We note in passing that this efficiency is a factor of 1.8 lower than the most equivalent simulation of \citet{2012ApJ...761..156F}, within the expected scatter resulting from different turbulent seeds, box sizes, and densities.}. We chose to analyse these early times, before the gas has begun converting to sinks in earnest, to approximate the evolutionary state of Hacar et al.'s observations. The masses and dimensions of the sinks are summarized in table \ref{filtable}.  \subsection{Line-of-sight velocity structure}  The rectangles surrounding the selected filaments define a coordinate system with axes aligned along the long axis or length $L$ of the filament, and the width $W$. The depth $D$ is the same axis that the surface density is projected along. We stepped along the $L$ and $W$ coordinates with a stepsize equal to the simulation's base resolution, and calculated at each point the density-weighted line-of-sight velocity integrated along the $D$ axis, using the same density range used to calculate the surface density. These points were then smoothed with a Gaussian with dispersion 0.052 km s$^{-1}$, suitable to the thermal width of  a C$^{18}$O line at 10 K. We binned these spectra into histograms with bin width 0.025 km s$^{-1}$. In figures \ref{filvels1} and \ref{filvels2} we show this data above the blowups of each filament. We summed the histograms along the $W$ dimension, yielding the total velocity distribution along slices perpendicular to the filament's long axis. The character of the velocity distributions are qualitatively similar to the observations of \citet{2013A&A...554A..55H}; overlapping individual features with subsonic widths, combined into features with mildly supersonic dispersions. Note that we plot the raw density weighted velocity structure, rather than the centroids of line fits like Hacar et al present. This accounts for the low intensity background in the velocity plots. Nonetheless, arcs of higher intensity signal are clearly seen in our data.