EPoS Contribution
EPoS Contribution
Differential Column Density in Super-Resolution in Taurus

Alexander Howard
U Cardiff, Cardiff, UK
The standard procedure for estimating column density from sub-mm dust continuum observations is to fit an SED to each pixel, assuming a uniform dust temperature and dust opacity index (beta) along each line of sight, and convolving all images to the coarsest resolution. However, these assumptions are unlikely to hold in turbulent filaments, and the convolution results in data loss, producing inaccurate column density estimates. Furthermore, in the standard procedure, beta and temperature are intrinsically anti-correlated, making spatial mapping of both quantities extremely difficult and unreliable.
PPMAP is a Bayesian algorithm that produces differential column density maps as functions of temperature and beta, by utilising multi-wavelength observations at their native resolutions to provide better estimates of column density. This gives the distribution of different dust components along the line of sight within a star forming region, and thereby allows us to constrain the evolution of dust in star formation regions. It also allows us to distinguish sub-structure on a much smaller scale than previously possible. This is done by dropping the assumptions of the standard procedure, and it resolves the temperature/beta degeneracy mentioned above (as evidenced by a positive correlation between temperature and beta in PPMAP results). Thus PPMAP provides a method of examining the internal structure of star forming filaments, which up to now has been impossible with the standard procedure. Here it is applied to the Taurus L1495 cloud, an area of local star formation with a prominent filamentary structure, using observations in all five Herschel bands.
We have used PPMAP to produce super-resolution column density hypercubes, allowing us to examine the characteristics of the L1495 filaments in much greater detail than was previously possible, and thereby constrain the detailed internal structure of the filament. This work is compared earlier work, with our PPMAP image displaying a resolution greater than the standard method by a factor 3.
Caption: PPMAP Differential Column Density plots of the Taurus L1495 filament, displaying 4 contiguous temperature slices out of the 12 produced by the algorithm. The cold dust in the filament spine is clearly visible at 9.6 K, with increasing quantities of warmer dust visible as the temperature rises. At 15.5 K, only dust in the outer shell of the filament is present, indicating external illumination. White circles are masked 70 μm sources.
Collaborators:
K. Marsh, Cardiff, UK
M. Griffin, Cardiff, UK
A. Whitworth, Cardiff, UK
O. Lomax, Cardiff, UK
S. Clarke, Cologne, DE
Key publication

Suggested Session: Filaments