Galaxies
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Interacting Galaxies NGC 1549 and NGC 1553 in the Dorado Group
This very deep image shows the two large interacting galaxies NGC 1549 and NGC 1553 in the Dorado Group. Located around 60 million light years away towards the southern constellation Dorado, it is one of the richest galaxy groups of the Southern Hemisphere with 46 members and tens of additional candidate members.
The interaction of NGC 1549 and NGC 1553 appears to be in an early stage, and gravitational disruption in the form of irregular shells and tidal jet/arcs of material is clearly visible in both galaxies.
Between the two large galaxies a small fuzzy blob with a faint spiral structure is visible; perhaps a remnant core from an earlier interaction, similar to the one observed in the shell elliptical galaxy NGC 3923 in Hydra.
The largest of the galaxies is NGC 1549 to the North (top), discovered by John Herschel on 6 December 1835. It contains a supermassive black hole with an estimated mass between 390 and 810 million solar masses.
To the south lies NGC 1553; the second brightest member of the Dorado Group. It is an impressive lenticular galaxy with a prominent soft isophotic ring surrounding another highly structured ring encircling the centre. A further very small spiral structure is visible in the core. In 2000 an inner torus-like dust lane about 3″ across was observed by the Hubble Space Telescope at the galaxy's center. The galaxy is thought to host an obscured central active galactic nucleus (AGN).
In the lower left of the image lies the small edge-on spiral galaxy, IC 2058, featuring a dark dust lane. This galaxy is slightly further away and does not appear involved in the gravitational interaction between the two bright galaxies.
Both large galaxies have populations of globular clusters, with NGC 1549 containing up to 150 globular clusters which is similar to our own Milky Way's globular population size but somewhat low compared with other similar galaxies. NGC 1553 has a larger population with up to 600 globular clusters.
The background in this image is particularly rich and littered with distant galaxies of various sizes and shapes. Some of these are even visible through the diffuse glow from the large galaxies. Many of these background galaxies are so far away that their light is visibly reddened because of the cosmological redshift. Judged by their colour and apparent size the faintest of these remote galaxies lie several billion light-years away.
For some reason, this interesting pair of galaxies is rarely imaged by amateurs. Possibly because just outside the field of view lies the Dorado Group's brightest member, the beautiful grand spiral NGC 1566, also known as the Spanish Dancer.
Image details:
Date: November 2019 to March 2020
Exposure: LRGB: 1695:235:230:220 mins, total 43 hours 28 mins @ -25C
Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand
