Ngc 3184

NGC 3184 as a classic face on spiral galaxy in southern Ursa Major near one of the bears back feet. It made my list as it is on of the original Herschel 400 objects that I'm slowly working on. Also it is a neat spiral that is overlooked by most imagers. William Herschel discovered it on the night of March 18, 1787. My visual notes with my 10" f/5 scope on May 4, 1884 at 10:15 CDT reads: Beautiful face on spiral, round with much arm detail. How did Messier miss this one? Nucleus is ill-defined. Hard to understand how this was a difficult object in an 8" scope." This refers apparently to the preliminary text I had of the list in which the person making the comments used an 8" scope and found this a difficult object. I no longer have that text. I went on to add: "Was he viewing from Central Park in NYC?."

The part about my finding the core ill defined certainly isn't true for my digital image. Though I had to watch the stretch of the core to preserve the spiral structure in to the very core. Most on line images show it pretty well burned in with a lot of the spiral structure lost. Both the redshift and Tully Fisher distance estimates are in close agreement. It is about 38 million light-years distant. Assuming that is correct I get a size of about 95,000 light-years though see faint hints of it extending another 15 million light-years to the south. I'd need more exposure time to verify that.

NED classifies it as SAB(rs)cd with HII. Radio shows a very strong bar CO. While the bright arms do come from an area away from the core as if there were a bar I see none at visual wavelengths and the faint arm structure continues to spiral in to within a few seconds of arc of the core. The NGC Project goes with the visual and says Sc (no bar). I am picking up a few hints of pink HII regions but most are below my resolution even though this was a better night than average for seeing. Transparency was poor due to a haze however. The haze likely stabilized the seeing however.

This active-galaxy has had two or three super nova in the last 100 years. SN 1937F, SN 2010d and SN 1999gi. SN 2010d might have been an outburst of a Luminous Blue Variable rather than a SN. I don't know why they can't tell for sure which it was. LBV stars are interesting. For those wishing to read up on them this paper might help: http://adsabs.harvard.edu/abs/1994PASP..106.1025H Or just think Eta_Carinae. It's likely the most famous LBV.

The galaxy is also home of two other NGC objects. NGC 3181 is certainly a bright HII region I've pointed to in the annotated image. NGC 3180 is harder to pin down. The NGC Project says: "NGC 3180 is a star cloud or HII region in NGC 3184's northwestern arm. The position in NGC (by Dreyer from LdR's observations) fits the star cloud better, but the HII region is brighter, though smaller. The number may well apply to both objects or simply the general area of the arm where they are found." I've pointed to both in the annotated image. I can't see either as an obvious candidate however.

To the southeast of NGC 3184 is a galaxy that depending on which catalog you consult is either just a galaxy, Or a quasar or a galaxy with an AGN1 core or one with a Seyfert 1 core. Take your pick. It is known only by coordinates in each of these catalogs so I've only listed it as G/Q/AGN1/SY1. To the north near the top edge a bit left of center is ASK 314681.0 which had two separate entries in NED. One as and AGN1 using only coordinates for a label and then as the ASK object as well as others again only by coordinates as a BLAGN candidate. That stands for Broad Line Active Galactic Nucleus. The core is burned in in my image so is very bright compared to the star disk around it. To the south of NGC 3184 is ASK 314329.0. It is listed as an AGN1 and appears starlike in my image but in the Sloan image it has a faint bit of fuzz around it. Another galaxy with a super bright core.

14" LX200R @ f/15, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Rick