Object of the Week, April 14, 2024 - NGC 3445 = Arp 24 in Ursa Major

[Paul Alsing]

Object of the Week, April 14, 2024 - NGC 3445 = Arp 24 = UGC 6021 = PGC 32772

R.A.: 10 54 35 Dec.: +56 59 16
Size: 1.6 'x 1.4', Magnitude: 12.9

NGC 3445 is a one-armed spiral galaxy located in Ursa Major. It is also known as Arp 24 in Halton Arp’s Catalog Of Peculiar Galaxies, which has 338 entries in a variety of categories. Dr. Arp compiled his atlas from photographs he took between 1961 and 1966 using the 200” and the 48” Schmidt telescopes located on Mt. Palomar. His Atlas was published in November of 1966.

As an aside, I was very fortunate to meet Dr. Arp (call me Chip) at a meet-and-greet at UCSD in the mid-1960s after attending a lecture presented by Geoff and Margaret Burbidge… and much of that lecture went right over my head! I attended several Burbidge lectures over the years.

In the eyepiece of my 25” f/5 obsession NGC 3445 was easy enough to pick up and was nearly round. It has a fairly even brightness across its breadth but with a brighter core. I did not know beforehand that this spiral only had one arm, but I did notice a dark skinny “dust lane”, and after staring at it for a while it became clear that there was a fat arm on the south side of the galaxy! Emanating from this arm, almost like an extension (but clearly detached), is a very faint streak of nebulosity, and Sky Tools told me that this is an interacting galaxy, MCG 10-16-24, long and thin (15” X 45”). But wait, there’s more! Approximately 2 arcseconds NE of each of these galaxies is a 10th magnitude star, and within this triangle is yet another galaxy, LEDA 2554198, a tiny mag 17 guy that I did not see, but wasn’t looking for! The interference from the star was substantial. Maybe next time…

HUBBLE NGC 3445.jpg

I can tell you that there are a couple of other “bonus” galaxies in the area. About 10 arcminutes NW of NGC 3445 is NGC 3440, a mag 14 edge-on spiral, 2.6’ X .7’ and about 14 arcminutes to the NE is NGC 3458, a mag 12.9 lenticular galaxy, 1.4’ X .7’. All 3 of these main galaxies fit easily into a FOV of about 20 arcseconds and can be viewed at the same time in a suitable eyepiece. This graphic is showing a 30’circle…

URSA MAJOR - ARP 24.jpg

As always, give it a go and let us know.

Addendum: I wrote this OOTW before I left for the eclipse. On April 4th Deb & I were visiting Jimi & Connie Lowrey in Fort Davis, Texas, on our way to the eclipse, and we had the opportunity to view NGC 3445 in Barbarella, Jimi’s 48” dob. Although the seeing was soft it was still a splendid view. Nevertheless, my old eyes could not detect LEDA 2554198, but Jimi says it popped for him a couple of times. What a treat for me to use such a wonderful telescope! Thanks, Jimi.

[Steve Gottlieb]

There's an interesting tidbit regarding MCG +10-16-024. It was missed by William and John Herschel (not surprising), but it was discovered visually in March 1856 with Lord Rosse's 72-inch Leviathan. While observing NGC 3445, the assistant R.J. Mitchell remarked that "the nebulosity outside this dark curve runs up perhaps to a streak [MCG +10-16-024] south-following [SE] which is very faint, but of the existence of which I have no doubt."

Mitchell returned to the galaxy in early April 1858 and confirmed "a very faint, small patch of nebulosity south-following [of NGC 3445]." The 1856 observation was included in Lord Rosse's 1861 observations of nebulae and clusters, but for some reason John Herschel decided to ignore it when he compiled his General Catalogue (GC) in 1864. Why wasn't it included? I'm guessing because Mitchell gave no offsets (other than southeast) for the companion 'nebula', Herschel didn't even have a rough position to go by.

The bottom line is that Dreyer skipped MCG +10-16-024 when he put together the NGC in the late 1880s, although the galaxy actually deserves a NGC designation!

[Steve Gottlieb]

I also have an observation of NGC 3445 using Jimi's 48" dob back in May 2012, along with Paul! This was on the last of 5 nights we were observing together (Jim Chandler had cleaned the mirror during the daytime with that spray-on film).

NGC 3445 is bright, moderately large, very irregular shape, roughly 1.2' diameter. The brightest portion of the galaxy is on the north and east side where it appeared very mottled with slightly brighter knots (a couple are on the east end). A spiral arm is attached on the west side and spreads further towards the south, appearing more like a wide, diffuse extension. The "arm" fades out on the southeast side of the galaxy and just beyond is MCG +10-16-24, 1.2' SE of center.

MCG +10-16-24, an interacting companion, appeared faint to fairly faint, elongated 5:2 E-W, 20"x8". A second companion, LEDA 2233323, lies 1.5' ENE, between the main galaxy and a mag 10.3 star just 2.2' NE of NGC 3445. It was faint, very small, round, 12" diameter. The bright star detracted somewhat from viewing the fainter companions.

[Uwe Glahn]

Nice gem Paul,

Frank and I were at the observatory when you visited NGC 3445.

I also found an observation and sketch with my 27". For the PGC I took a look at my notes and find: "stellarlike, faint and small but steadily visible with averted vision". I guess the wind and the bad seeing made it difficult to see it through the 48".

sketch: 27", 419x, NELM 6m5+, Seeing III
NGC3445.jpg
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