This month's observing program changes again, getting away from the two hour RA window and looking at a class of target, like we did last month with planetary nebulae. It is galaxy season, just before the rise of the Sagittarius arm of our galaxy begins to dominate the sky. So, let's look beyond our galaxy, at some of the active star forming regions like we see in our local Orion Nebula or other stellar nurseries, but visible as the faint glow of creation in other galaxies.
Thanks to local deep sky expert Steve Gottlieb for providing a list of the HII regions in external galaxies, noted in his observing logs. All but the first observations are from his notes.
NGC 4631 (RA 12 24 30.7 Dec -18 47 05, m 9.2, Surface Brightness (SB) 13.1, 15.5'x2.7') is in Canes Venatici near the border of Coma Berenices. This galaxy triggered my curiosity about HII regions in other galaxies. It is known as The Slug, which is probably not a name its residents would approve of (unless they are slugs). But a view I had in my 18" Obsession fascinated me - I took the scope up to 294X and confirmed small knots of blue, glowing in the dark lane of this spiral. The thought that I can see star forming regions, similar to the Orion Nebula, in another galaxy 22.5 million light years distant amazes me. It gave the view of this galaxy a distinctly 3-D appearance.
Move to Camelopardalis and check NGC 2366 (RA 07 28 55 Dec +69 12.57, m 11.1, SB 14.5, 8.1'x3.3'). In a 13" scope the galaxy "is fairly faint, very large, elongated 5:2 SW-NE, low almost even surface brightness. An unusually bright HII region is at the SW end of the galaxy (2' from the center) and appears as a "fuzzy" 12th magnitude star. Although very small it seems elongated SW-NE and similar to a poorly resolved double star. Definite contrast gain with OIII filter."
Very nearby is NGC 2403 (RA 07 36 54 Dec +65 35.58, m 8.5, SB 14.4, 21.9'x12.3'). In a 17.5" scope it is "very bright, very large, bright core, elongated 5:2 NW-SE, 15'x6'. Impressive galaxy with spiral structure clearly visible. Two spiral arms are attached at opposite ends of the main body and both wind almost 180ø. The tip of the northern arm ends at the emission nebula N2404. Several stars are superimposed including two mag 11 stars."
Known as Coddington's Nebula, IC 2574 (RA 10 28 43 Dec +68 24.03, m 10.0, SB --, 12.0'x4.0') is "faint, very large, elongated 5:2 SW-NE, 7.0'x2.5', low surface brightness, no concentration. Four faint stars are near the N side. There is a fairly bright nonstellar HII region which is clearly visible at the NE end as a high surface brightness knot. Member of the M81 group."
Spiral galaxy NGC 4395 (RA 12 25 49 Dec +33 32.51, m 10.2, SB 15.4, 13.2'x11.0') in Canes Venatici is challenging. Steve writes "a chaotic galaxy dominated by several bright HII regions. At 100x, the large low surface brightness glow is clearly clumpy with a couple of faint knots evident on the east side of the haze. At 220x, the glow of the galaxy is more difficult to view and several nonstellar knots and a couple of very faint superimposed stars are more prominent."
One of my favorite galaxies is NGC 2903 in Leo (RA 09 32 10 Dec +21 30.02, m 9.0, SB 13.6, 12.6'x6.0') - it is easy to locate and shows nice detail. Its HII region is known as NGC 2905 and "is one of the brightest non-Messier galaxies.ÿ Very bright and large, elongated 5:2 SSW-NNE, 10'x4'.ÿ A very faint knot is involved on the NNE side 1.2' from center = N2905.ÿ An extremely faint knot is also symmetrically placed opposite the core on the SW end 1.2' from center.ÿ The galaxy has a dusty, mottled appearance with knots and arcs easily visible with averted vision."
NGC 3239 (RA 10 25 Dec +17 10, m 11.3, SB 14.2, 5.0'x3.3') is also in Leo. It has a "very unusual appearance as a mag 9 star (BD+17 2217) is superimposed on the south side. An unusually bright knot is following the bright star by 51" on the SE side of the galaxy. This is possibly an offset nucleus or a close double star. The galaxy appears to extend to the west from this knot.ÿ The galaxy exhibits an irregular surface brightness with edges difficult to define as it fades into the background."
In Ursa Major NGC 3319 (RA 10 39 09 Dec +41 41.14, m 11.1, SB 14.2, 6.2'x3.4') is fairly faint in a 17.5" scope. "The brightest portion is a large bar with a knotty extension attached at the SW end and extending on a right angle to the south." Compare notes from North bay observer Robert Leyland - "averted vision shows a couple of knots, one at each end. It is a good galaxy in a larger telescope, but a challenge in an 8 inch."
Moving to Canes Venatici, find NGC 4528 (M106, RA 12 18 57.5 Dec +47 18 15, m 8.4, SB 13.6, 18.6'x7.2'). "13 inch: bright, very large, bright core, substellar nucleus, mottling near core.ÿ A large bright knot is at end of the southern arm."
Also in Canes Venatici is NGC 4449 (RA 12 42 06.5 Dec +32 32 24, m 9.2, SB 13.1, 15.5'x2.7') - a bright elongated galaxy. "Knot is involved at the north end and the galaxy generally appears brighter to the north of the core."
I find it fun to look for what sets objects apart, and the glow of nebulae in distant galaxies is intriguing. You'll need some dark skies to hunt these down. The Shingletown Star Party would be a perfect place - check it out at Shingletown Star Party.
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