NGC 55 and its interstellar medium

NGC 55 is a galaxy that has been traditionally linked to the Sculptor Group, and it still is considered so in most web sites that you can browse currently. This group is close to our Local Group and has several large and well known galaxies, like NGC 253, the Silver Dollar Galaxy. But in 2003, Karachentsev et al. determined the distance to be too short for NGC 55 to belong to this group. This was confirmed in 2006, by van de Steene et al. by measuring the luminosity of planetary nebulae within it. Now, it is considered that it forms a gravitational pair with its close neighbor, NGC 300, and that they are located between the Sculptor and the Local Group. Their recession speed (around 130 km/s) also advocated for these galaxies not belonging the Sculptor group. NGC 55 is considered to be an SBm galaxy, a medium- to low sized barred Magellanic spiral galaxy.

There is still something that makes NGC 55 quite peculiar: NGC 55’s interstellar medium is very rich in dust and gas.

To confirm this, far-infrared and radio continuum studies showed large-scale outflows and diffuse emission, suggesting that stellar feedback from massive stars drives galactic winds perpendicular to the disk (Otte & Dettmar 1999). This makes NGC 55 a useful analogue for understanding starburst-driven outflows in irregular galaxies. X-ray observations with XMM-Newton have revealed a population of X-ray binaries and supernova remnants, further underscoring its active evolutionary state (Stobbart, Roberts & Warwick 2006).

This fact is what triggered our interest in the potentially conspicuous rich field of nebulae inside this galaxy. In order to capture these nebulosities, deep exposures with Luminosity, Halpha and OIII filters were taken with a 24 inch telescope, and we also used the RGB images taken nine years before, with a 20 inch telescope, that were blended in this final image. The combined exposure time was 52 hours. This is another result of the collaboration with Christian Sasse.