3D Astrophysics Newsletter

THINGS data cube of NGC 628 visualizaed in FRELLED (Click to open a 18 MB Gif animation)

THINGS data cube of NGC 628 visualizaed in FRELLED (Click to open a 18 MB Gif animation)

3.6 Today´s new entry:

FRELLED : A 3D Visualisation Tool For FITS Files

Rhys Taylor

Abstract: Punzo et al. (2015) recently reported on the state of the art for visualisation of H I data cubes. I here briefly describe another program, FRELLED, specifically designed for dealing with H I data. This is designed primarily as a 3D viewer for astronomical FITS files, with the main motivation being to enable very fast visual source finding capabilities. Data can be shown in 3D with little or no clipping required. FRELLED can handle astronomical world coordinates, easily and interactively mask and label specific volumes within the data, overlay optical data from the SDSS, generate contour plots and renzograms, make basic spectral profile measurements via an interface with MIRIAD, and can switch between viewing the data in 3D and 2D. The code is open source and can potentially be extended to include any astronomical function possible with Python, displaying the result in the interactive 3D environment of Blender.

Journal: (Astro-ph) Comment on ‘The role of 3-D interactive visualization in blind surveys of HI in galaxies’
Comments: 6 pages, 2 figures
URL: http://arxiv.org/abs/1506.04621
Submitted by: Rhys Taylor

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3D Astrophysics Newsletter

Schematic diagram of essential features of K3-50

Schematic diagram of essential features of K3-50

3.5 Today´s new entry

Magnetic Field Structures in Star Forming Regions: Mid-Infrared Imaging Polarimetry of K3-50

Peter Barnes, Dan Li, Charles Telesco, Nahathai Tanakul, Naibi Marinas, Chris Wright, Chris Packham, Eric Pantin, Patrick Roche, James Hough

Abstract: We report new imaging polarimetry observations of the Galactic compact HII region K3-50 using CanariCam at the Gran Telescopio Canarias. We use a standard polarimetric analysis technique, first outlined by Aitken, to decompose the observed polarisation images centred at 8.7, 10.3, and 12.5 μm into the emissive and absorptive components from silicate grains that are aligned with the local magnetic field. These components reveal the spatially-resolved magnetic field structures across the mid-infrared emission area of K3-50. We examine these structures and show that they are consistent with previously observed features and physical models of K3-50, such as the molecular torus and the ionised outflow. We propose a 3D geometry for all the structures seen at different wavelengths. We also compute relevant physical quantities in order to estimate the associated magnetic field strengths that would be implied under various physical assumptions. We compare these results with MHD simulations of protostar formation that predict the magnetic field strength and configuration. We find that the magnetic field may be dynamically important in the innermost 0.2 pc of the molecular torus, but that the torus is more likely to be rotationally-supported against gravity outside this radius. Similarly, magnetic fields are unlikely to dominate the global physics of the ionised outflow, but they may be important in helping confine the flow near the cavity wall in some locations. Ours is the first application of the Aitken technique to spatially-resolved magnetic field structures in multiple layers along the line of sight, effectively a method of “polarisation tomography.”

Journal: Monthly Notices of the Royal Astronomical Society
Comments: Accepted 2015 June 4, 15 pages, 12 figures
URL of preprint: http://arxiv.org/abs/1506.02173
Submitted by: Peter Barnes

Observations vs. 3D visualization for the press

Young Boy on Rope Swing under Pohutukawa Tree at Sunset, Thames, Coromandel, North Island, New Zealand

Young Boy on Rope Swing under Pohutukawa Tree at Sunset, Thames, Coromandel, North Island, New Zealand (Foto: David Wall)

The press loves 3D visualizations. I do, too. They are my bread and butter. However, when I see that the visuals that the press uses in their reports hardly ever include any of the original observed data representations, my feelings become rather mixed. Actually, they go back and forth as if I was sitting on a swing.

On the one hand, it is precisely the job of the 3D visualization to deliver the key insight from the paper in a form that can be grasped within seconds. Why bother the marginally interested reader with noisy contour maps? On the other hand, the public never gets a feel for the incredible skill that the researchers show at interpreting data that usually look very different from the clean 3D visualization. Then again, is it worth the effort to include and explain much more than the actual final scientific insight  that might be well represented by a 3D visualization?

I can´t make up my mind, because too often small-print that says “artist´s rendition” does not get through to the reader or viewer such that she or he ends up thinking that this is the way the object looks like when seen through a giant optical telescope. On the other hand, the term “artist´s rendition” could produce the feeling that it is all rather more artistic than scientific, i.e. subjective rather than objective.

Maybe we need a different word that can replace “artistic rendition” or its similes. Why not use “conceptual visualization” or something similar, close to a scientific terminology. In the end, it is the scientific insight or concept that is being shown. Besides, often enough the person who makes the images is a scientist and not an artist anyway.

Wo.

3D Astrophysics Newsletter

Tilted-ring parameters derived with 3DBarolo using the THINGS data-cube of the warped galaxy NGC 5055.

Tilted-ring parameters derived with 3DBarolo using the THINGS data-cube of the warped galaxy NGC 5055.

3.4 Today´s new entry

3D-Barolo: a new 3D algorithm to derive rotation curves of galaxies

Di Teodoro, E. M., Fraternali, F.

Abstract: We present 3D-Barolo, a new code that derives rotation curves of galaxies from emission-line observations. This software fits 3D tilted-ring models to spectroscopic data-cubes and can be used with a variety of observations: from HI and molecular lines to optical/IR recombination lines. We describe the structure of the main algorithm and show that it performs much better than the standard 2D approach on velocity fields. A number of successful applications, from high to very low spatial resolution data are presented and discussed. 3D-Barolo can recover the true rotation curve and estimate the intrinsic velocity dispersion even in barely resolved galaxies (about 2 resolution elements) provided that the signal to noise of the data is larger that 2-3. It can also be run automatically thanks to its source-detection and first-estimate modules, which make it suitable for the analysis of large 3D datasets. These features make 3D-Barolo a uniquely useful tool to derive reliable kinematics for both local and high-redshift galaxies from a variety of different instruments including the new-generation IFUs, ALMA and the SKA pathfinders.

Journal: Monthly Notices of the Royal Astronomical Society
URL of preprint: http://arxiv.org/abs/1505.07834
Comments: 13 pages, 9 figures
Submitted by: Enrico Di Teodoro