Ngc3621

[markas]

NGC3621 is listed as SA(s)d spiral with loosely wound arms. According to Wikipedia it has an active nucleus exhibiting a Seyfert type2 optical spectrum. There is no evidence of a bulge, and there is a black hole of 'up to 3 million Solar masses'. The galaxy is about 22Mly distant in Hydra, and is about 93kly across.


Whilst it is quite bright - Mag 10 - the arms are very faint, and the tricky processing is complicated somewhat by the bright foreground stars.


This LRGB image was shot over two reasonable nights with average seeing.
Total exposure time 290 minutes - clearly a lot more time would benefit the faint arms.


Mark

[alpal]

Very Nice Mark,
what are the technical details of your equipment?


cheers
Allan

[willik]

Quality image Mark very good detail and colour :thumbsup:
Martin/ Willik

[Startrek]

Beautiful image Mark and so much fine detail in the arms
I’d like to go after this galaxy towards end of May when back from OS
What’s your set up ?
Cheers

[markas]

Allan, Willik, Martin.


Thanks for the comments - glad you liked this one.


The gear is: Officina Stellare RiDK 300 f/8 scope; Moravian G4-9000 camera; Astrodon filters; FLI Atlas focuser; ASA DDM85A mount (unguided). The system resolution is 1"/px.


Mark

[topheart]

Great image....great gear !! :)
Those foreground stars would have been a pain.
Cheers,
Tim

[alpal]

Hi Mark,
no wonder it's so good -
you have all high end equipment.
Unguided is amazing from a DDM85A - how long were the subframes?


cheers
Allan

[Stevec35]

Nice job on one of the most picturesque galaxies out there

Cheers

Steve

[Placidus]

Very nice result.

The histogram shows that the background darks are strongly clipped to black. That will lose a lot of faint stuff. If you can reprocess with the dark point set much further to the left, just left of the "foothill" of the histogram, you should bring out more very faint detail.

We wondered if the core of the galaxy might be a tiny tad on the blue side, but the ESO shot (https://cdn.eso.org/images/screen/potw1148a.jpg) also looks less obviously salmon pink than most galactic cores.

The star colours and the galactic detail look great.

[markas]

Tim, Allan, Steve, M&T


Thanks to all for the comments.


Allan, my standard sub exposure time is 5min R,G,B; 2 - 5min L; 10-15min NB.


M&T, thanks for your suggestions. In this instance, as I had not educated myself about the strong RBI characteristics of the KAF9000 sensor, I unfortunately ran one set of data immediately after shooting a fairly bright asterism. So the background blacks have been clipped to remove the offending smudges, but not in the galaxy area. That was my preferred solution, rather than lose a lot of good data on the galaxy.


I think the only solution for getting better detail on those faint arms is more data.....


Now I am aware of the perils of ignoring RBI on this sensor - much to do with the 12micron pixels - I hope I can avoid the problem in future.


Thanks,



Mark