What am I Imaging?

My current project is to image the galaxy catalogued as NGC 4945

NGC 4945 - This is NOT my image - I'm still working on mine!

NGC 4945 is a barred spiral galaxy in the constellation Centaurus. It is also known as Caldwell 83. The galaxy was discovered by Scottish astronomer James Dunlop in 1826. It is located at a distance of approximately 11.0 million light-years (3.36 Mpc) from the Milky Way. NGC 4945 hosts one of the closest active galactic nuclei to Earth and is classified as a Seyfert 2 galaxy.

NGC 4945 is one of the brightest galaxies of the Centaurus A/M83 Group, a large, nearby group of galaxies. The galaxy is the second brightest galaxy in the subgroup centred on Centaurus A.

How do I image this galaxy?

In order to create a colour image I gather data over many nights through a number of filters, RED, GREEN, BLUE, LUMINANCE(No Filter) and HYDROGEN ALPHA.

I take what are called 'sub-frames' - these are multiple exposures through specific filters and in this case each sub frame (exposure time) is 5 minutes. I judged this to be the right exposure in order to capture the fine filaments yet at the same time not do over-expose the bright galaxy core.

I build up sub frames through each filter until I judge to have enough data. I throw away any sub frames that are imperfect - around 25% (satellite streaks, clouds, poor seeing, software issues etc).

The hydrogen alpha filter captures areas of star formation and I blend this data with the red channel. This accentuates those areas of star formation in the final image.

Once I have the sub frames I go through a laborious 'calibration routine' which removes the artefacts associated with long exposures, such as noise.

Once I have the 'clean' sub frames I will stack them together ending with four files, L,R.G and B which I can then use to process a colour image - that's when more hard begins - to tease out the beauty of this object 11 million light years away!

Examples of single sub frames through various filters

A single 5 minute uncalibrated sub frame (no filter) - Luminance NGC 4945 Galaxy

A single 5 minute uncalibrated sub frame BLUE filter NGC 4945 Galaxy

I'll show you the result when I've finished!