Object of the Week February 19, 2017 - NGC 3344 Not Just Another Gorgeous Spiral Galaxy

Object of the Week February 19, 2017 - NGC 3344 Not Just Another Gorgeous Spiral Galaxy
Title respectively derived from a Bad Astronomy Blog by Phil Plait "Ho-Hum: Just Another Gorgeous Spiral Galaxy”

NGC 3344, PGC 31968, UGC 5840
Type: face-on ringed barred spiral galaxy
Classification: (R)SAB(r)bc
Constellation: Leo Minor
RA: 10h 43m 31.2s
Dec: 24° 55’ 20”
Magnitude: 9.9v, 10.5B
Mean Surface Brightness:
Size: 6.7’ x 6.3’
Surface Brightness: 13.8

NGC 3344 was discovered by William Herschel in 1785 with his 18.7-inch speculum mirror. Logged as H I-81 on April 6 of that year, he described it as “Considerably bright, considerably large, milky, just preceding 2 stars.” NGC 3344 is the largest and brightest galaxy in the constellation of Leo Minor at magnitude 9.9v. Extending to approximately 6.7’ x 6.3’, its surface brightness measures only 13.8. Still it should be readily visible in apertures of 6” or greater under dark, transparent skies.

Without a doubt NGC 3344 is a gorgeous galaxy; its stunning beauty is nicely captured in this photo taken with a 32-inch Ritchey-Chrétien telescope by Adam Block on Mount Lemmon in Arizona. Take a moment and enjoy the photo.

Attachment 2476
Credit/©Adam Block/Mount Lemmon SkyCenter/University of Arizona

There are two peculiarities to NGC 3344 that are not readily apparent. Peculiarity #1 is that the galaxy’s distance from us is 20 million light years. What is unusual about this? Phil Plait of Bad Astronomy explains it best.

“Our galaxy is in a small collection of 50 or so galaxies called the Local Group, and it’s a few million light years across (the Andromeda Galaxy is the only other big galaxy in the group, and it’s less than three million light years distant). The M81 Group is another small clot of galaxies about 10 million light years away, for example. The nearest actual cluster to us is the Virgo Cluster, about 50 million light years away, and it has well over 1000 galaxies in it.”

“So the distance to NGC 3344 is a bit weird; it’s neither here nor there. It’s apparently part of a small spur off the big Virgo Supercluster, a huge collection of clusters themselves, which contains the Virgo cluster, the Local Group, the M81 Group, and many more. Still, this means NGC 3344 is relatively isolated, off more-or-less by itself.”

Without a doubt NGC 3344 is a spiral galaxy, but does it have a bar? In 1976 in the RC2 catalog it was classified as non-barred. Later study of the galaxy in concluded that it did have a bar, albeit a weak (small) one with semi-axies of 12” x 10”. As a result, in 1991 in the RC3 catalog it was reclassified as (R)SAB(r)bc. This was certainly not a type of galaxy that existed in Edwin Hubble’s 1925 classification schema of galaxy evolution. What does this classification mean? SAB indicates the galaxy is an intermediate-barred spiral galaxy; right in the middle between non-barred and barred. The bc is an indication of the degree of openness and resolution of the spiral arms and also an indication of the relative prominence of a bulge or central concentration. NGC 4303, aka M61, is an example of a SABbc galaxy.

Peculiarity #2 comes into play from the two Rs in the classification - NGC 3344 is a ringed galaxy. In fact, it shows two rings, an inner ring (r) and an outer ring (R). The inner ring, with a diameter of ~ 54”x51”, defines the beginning of the spiral structure. The outer ring measures 360”x360” in size. Both the inner and outer rings present similar colors indicating that they contain active star forming regions. The outer ring is not located symmetrically with respect to the center of the galaxy, its center is shift by ~18”.

Take another moment and examine Adam Block’s photo of NGC 3344. Look closely and you should see some segments of the outer ring. Now examine the following Hubble Space Telescope of photo of the galaxy. Both the weak central bar and the inner ring are visible. Several DSS images follow clearly showing the entire outer ring.

Attachment 2477
Credit: ESA/Hubble & NASA

Attachment 2479 Attachment 2480 Attachment 2478

A mystery emerges when the two peculiarities are examined in context of each other. A detailed study of the ring galaxy NGC 3344 published in 2000 by L. Verdes-Montenegro, A. Bosma, and E. Athanassoula reached this fascinating conclusion.

“We embarked on this study of the galaxy NGC 3344 to seek the explanation for the presence of the inner and outer ring, hoping to link them together as resonance features set up by an underlying structural pattern. This has not proven possible due to the complexity of the galaxy. The inner parts are dominated by a small bulge, a small bar, and an inner ring surrounding it, at whose radius starts a prominent spiral structure. In the outer parts, where the main spiral structure stops, there is an outer pseudo-ring, which is not centered on the nucleus, and beyond this the HI layer shows a strong and asymmetric warp. All these complexities, and in particular the asymmetries, prevent us from deriving correctly the axisymmetric quantities we need to know in order to explore the geometric positions of the resonances. The relative isolation of the galaxy (no bright nearby companion) poses a further problem: are all the remarkable features in this galaxy formed intrinsically and long lived? Instead of relying on intrinsic mechanisms to explain all these phenomena, we can envisage that this galaxy underwent a recent accretion event which modified its morphology. Its basic structure is more like that of a giant Sc galaxy, but with morphological details which are a bit unusual (presence of an outer ring, presence of a small bar of limited radial extent, a yet to be confirmed hint in our data that the bulge does not rotate the same way as the disk). It could be that at least the outer ring is a transient structure set up by this event, thereby explaining the relative rarity of such a feature in average late type spirals.”

To summarize their conclusion: the high density of stars in NGC 3344’s central regions provides enough gravitational influence to affect the movement of other stars in the galaxy. However, NGC 3344’s outer stars are moving in an unusual manner, although the presence of the bar cannot entirely account for this, leaving astronomers puzzled. It is possible that in its past NGC 3344 passed close by another galaxy and accreted stars from it.

Observing NGC 3344 should not be too difficult –under a dark sky the galaxy is obvious. Low and moderate powers frame the galaxy well and provide a sense of its beauty. However, it requires high powers to really explore its structure and features.

Give it a go and let us know!