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HALOGAS - NGC 5023: galactic tomography

Submitter: Gyula I. G. Jozsa

In the HALOGAS project we have observed 22 spiral galaxies with the WSRT, each galaxy for 120 hours. The goal is to characterise the faint, neutral gas component. It is thought that a lot more infalling gas than is observed in spiral galaxies is required to maintain star formation at the observed rates. It is therefore important to know whether the visible gas (neutral hydrogen) shows any signs of infall, and whether this correlates with other characteristics of the galaxies.

Getting a good overview means including galaxies in the sample that at a first glance seem to not be exceedingly exciting. NGC 5023 does not form many stars, and it is not interacting. However, careful kinematical modeling showed that the galaxy appears rather asymmetric. Assuming a symmetric disk, we would deduce a rather strong decline of the rotation velocity with height above the disk - a parameter that is thought to provide information about the connection between the galaxy and its atmosphere. But introducing spiral arms in our models (a possibility in the modelling software TiRiFiC), we achieve a brilliant fit, and the decline in the rotation velocity becomes much more modest.

The little animation shows first the stellar component of the galaxy, to blend with our deep WSRT observation of the neutral hydrogen. Then the modeled neutral-hydrogen component is shown (notice the good match!). We then sharpen our view to finally make the galaxy artificially opaque and to turn it around. We can visualise the (typical) spiral pattern that we believe is present in the galaxy, despite the fact that it is not immediately evident in the observed edge-on view. We are hence using the velocity information in our very deep observation to conduct a galaxy tomography.

The results are described in a paper by Peter Kamphuis et al., soon to appear in the Monthly Notices of the Royal Astronomical Society (MNRAS).
Copyright: Image credits: Gyula I. G. Jozsa, Peter Kamphuis, Rich Rand, George Heald and the HALOGAS consortium.
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