Description of NGC 4945

NGC 4945 is a beautiful galaxy located in the constellation Centaurus, approximately 13 million light-years away from Earth. It is classified as a barred spiral galaxy, meaning that it has a central bar-like structure that extends through its disk. The galaxy is about 60,000 light-years in diameter and is known for its bright and active nucleus, which emits large amounts of radiation across the electromagnetic spectrum.

NGC 4945 is particularly noteworthy for its prominent dust lanes, which can be seen in stunning detail in many images of the galaxy. These dark, filamentous structures are thought to be sites of ongoing star formation, as the dust and gas in these regions can clump together to form new stars. In addition to the dust lanes, NGC 4945 also contains many bright and colorful regions of active star formation, particularly in its spiral arms.

Another interesting feature of NGC 4945 is its supermassive black hole, which is estimated to have a mass of around 200 million times that of the Sun. The black hole is located at the center of the galaxy's nucleus and is surrounded by a disk of hot gas that emits X-rays and other high-energy radiation. The presence of such a massive black hole is thought to be responsible for the intense activity seen in NGC 4945, including the production of high-energy particles and the formation of powerful jets that extend far beyond the galaxy's boundaries.

Discovery

NGC 4945 was first discovered by the Scottish astronomer James Dunlop in August 1826, during his observations of the southern sky from the Parramatta Observatory in Australia. Dunlop was a wealthy amateur astronomer who had emigrated to Australia, where he built a private observatory and conducted extensive observations of the southern skies. Dunlop was a prolific observer of the southern hemisphere and is credited with discovering a large number of other notable objects, including:

1. Omega Centauri: A large and bright globular cluster located about 16,000 light-years from Earth in the constellation Centaurus.
2. NGC 104 (47 Tucanae): One of the brightest and most massive globular clusters in the Milky Way, located in the constellation Tucana.
3. NGC 253: A spiral galaxy located about 11 million light-years from Earth in the constellation Sculptor. It is one of the brightest galaxies in the southern sky.
4. NGC 288: A globular cluster located about 28,000 light-years from Earth in the constellation Sculptor.
5. NGC 292: A barred spiral galaxy located about 20 million light-years from Earth in the constellation Sculptor.
6. NGC 300: A spiral galaxy located about 6.1 million light-years from Earth in the constellation Sculptor.
7. NGC 4755 (Jewel Box): An open cluster located about 6,440 light-years from Earth in the constellation Crux.
8. NGC 5128 (Centaurus A): A peculiar galaxy located about 13 million light-years from Earth in the constellation Centaurus. It is one of the closest radio galaxies to Earth and contains a massive active galactic nucleus (AGN).

Comparison with the Milky Way

NGC 4945 is smaller than the Milky Way, both in terms of its mass and its physical size. NGC 4945 has an estimated mass of about 10 billion times that of the sun, which is roughly one-tenth the mass of the Milky Way. In terms of physical size, NGC 4945 has a diameter of around 80,000 light-years, which is about three-quarters the size of the Milky Way, which has a diameter of approximately 100,000 light-years.

NGC 4945 is located in a separate group of galaxies known as the Centaurus A/M83 Group, which is located about 13 million light-years away from the Milky Way in the southern hemisphere of the sky. The Centaurus A/M83 Group contains several other galaxies in addition to NGC 4945, including the famous galaxy Centaurus A (NGC 5128) and the spiral galaxy M83 (NGC 5236). This group is one of the closest galaxy groups to the Milky Way and is often studied by astronomers to gain a better understanding of galaxy evolution and the structure of the universe.

Data collection and processing

I stated collecting data on NGC 4945 in January 2021 and stopped in June 2022 in 21 sessions. The RC10A + ASI294MM collected the luminance and Ha; and the RC8 + ASI1600MM collected the RGB channels.  The RC10A collects 50% more photons than the RC8 and the ASI294MM has roughly 50% more quantum efficiency than the ASI1600MM. 

Also the colors were calibrated with PhotometricColorCalibration and, apart from a saturation boost, un-tweaked. Ha data was added in the usual way to the Red channel. I found it helpful to review the standard method lucidly covered in this YouTube video: Adding Ha to Red or Luminance Data.