Daily Image

15-08-2014
PreviousNext
Click here or on the picture for a full size image.

An unknown hydrogen cloud near spiral galaxy NGC 2403

Submitter: Erwin de Blok
Description: One of the unanswered questions about galaxies is where they get their gas from. When galaxies form stars, they consume their gas. Measurements show they do not contain enough gas to sustain their star formation for a long time. ASTRON astronomer Erwin de Blok is part of an international team (led by D.J. Pisano from West Virginia University (US)) that uses the Green Bank Telescope (GBT) to search for very faint gas around nearby galaxies to see if they are acquiring gas from their environment.

One of the galaxies studied is NGC 2403. With the GBT the faint signal of an hitherto unknown neutral hydrogen (HI) cloud was discovered outside the main gas disk of NGC 2403. Comparison with deep HI data obtained a number of years ago with the VLA showed that the cloud is most likely associated with a filament of gas in the inner disk that shows peculiar velocities. The cloud and filament probably form one single complex.

There are several possible explanations for this cloud/filament complex. The most likely two are that we are seeing gas being accreted by the galaxy, or that we are looking at gas expelled from the disk due to the passage of smaller galaxy. A study of the rest of the survey should show how frequent these events are, and help explain them.

The picture shows an optical image of NGC 2403 from the SDSS in the background, overlaid in blue with a VLA HI map. The newly discovered cloud is visible as the diffuse emission shown in red in the top-right corner. The filament is shown superimposed on the main disk in white/red colours.
The paper describing this result is available at http://arxiv.org/abs/1407.3648 . It has also been accepted for publication in Astronomy & Astrophysics.
Copyright: Erwin de Blok
 
  Follow us on Twitter
Please feel free to submit an image using the Submit page.