Object of the Week, January 21, 2018 - Arp 25 and Arp 114 - NGC 2276 and NGC 2300

[Howard B]

Asymmetrical spiral galaxy (Arp 25) and elliptical galaxy (Arp 114)
Cepheus
RA 07h 27m 17s
DEC +85d 45m 20s
Magnitude 11.8 (V) and 12.1 (B)
Size: 2.8 x 2.6 and 2.0 x 2.0 arc minutes
(magnitude and size data for NGC 2276 are listed first)

Arp25_114_wikisky.JPG

These are two of the most economical Arp galaxies because NGC 2276 (Arp 25) and NGC 2300 (Arp 114) have only five minutes of declination between them so you can see two Arps in one interacting pair of galaxies. All but six other Arp galaxies this close share the same Arp number.

This is a nice bonus, especially if you’re out to observe all the Arp’s, but these two galaxies have an appeal beyond their designations. The slightly oval core of NGC 2300 is brighter and more obvious than the lower surface brightness of NGC 2276’s asymmetrical spiral arms. However, 2276 looks larger than 2300 and has some intriguing details.

Both galaxies are approximately 115 million light years distant, making 2276 about 90,000 light years in diameter. That’s only a little smaller than our Milky Way galaxy, giving a perspective on what our home galaxy might look like from that immense distance.

The asymmetry is a notable feature of 2276, and I was able to detect it with my 28-inch scope, with the small, faint core being noticeably off-center, with the brightest areas between the core and the near edge. I was able to see a linear feature that corresponds to an interior spiral arm, along with the faint arm that’s swings out from the general body of the galaxy. Halton Arp described it as “Tubular arm, straight at first, then bent. Secondary arm from straight portion.”

Unfortunately, I can’t find his comments about 2300.

However, my comments from a 2009 observation with my 28-inch scope read:

“Hey now, this is a dandy Arp galaxy! (this was before I realized each galaxy has its own Arp designation) The face on spiral is NGC 2276 and although a subtle sight it is definitely an asymmetrical face on spiral galaxy. NGC 2300 is the elliptical galaxy at the top (of my sketch) and is brighter than 2276, but the spiral is much more interesting because of its delicate spiral structure. Very nice! 253x, 21.13 SQM.”

By the way, north is on the right side of my sketch and the color DSS image from Wikisky.

Arp25_Arp114_crop.jpg Arp25_Arp114_crop_invert.jpg

Another indication that 2276 is the more visually interesting galaxy strikes me right now – look at all the field stars I included in my sketch around 2276, with none around 2300!

"GIVE IT A GO AND LET US KNOW"

[Ivan Maly]

In 16" (330x, SQM 21.7) I only noticed this in NGC 2276: "Diffuse. Compact core. SW edge closer to it and more definite. Broad enhancement on WNW edge." In 12 (230x, same SQM): "Vague but persistent hints of spiral structure." Glad to see that some of the tendrils actually show in 28.

[lamperti]

With an 18" at 286x back in 1997, NGC-2300 = "With NGC-2276. Easier of the 2 to see. Almost stellar center with oval glow around it." NGC=2276 = "Dimmer of the two. Closer to a field star. Better with averted vision." My notes indicated that there was dew and incoming high clouds at the time.
With a 20" at 313 in 2009, NGC-2300 = "Very easy to see with direct vision and has a brighter center." NGC-2276 = "Direct vision. Hard to see spiral shape. Maybe brighter towards the adjacent star." Seeing and Transparency were both 6/10.
Two-in-a-View with a 22" in 2014 at 177x; Similar skies.

Al

[kisspeter]

I drew this pair in 2003 using my little 4.3" Newtonian (96x, 25' field). "Észak" stands for North.
ngc2276-2300_kisspeter.jpg

Everything was faint in the field except for one star. I was surprised to see slight asymmetry in NGC 2276. Interesting galaxies but they certainly need a much bigger scope.

[Ciel Extreme]

I believe Arp 114 is actually NGC 2276 and NGC 2300 together, as they are under the heading: “Elliptical and Elliptical-like Galaxies close to and perturbing spirals” in Arp’s atlas.

[Howard B]

Hi Mark,

Yes, you're right! Arp 114 is NGC 2276 and NGC 2300 together - thanks for making that clarification!

[Uwe Glahn]

To my surprise the different morphology of both is just visible in the 4-inch binocular telescope.
While NGC 2300 is the smaller and brighter galaxy of the pair, it looks clearly better concentrated to its middle. NGC 2276 (Arp 25) looks more like a fuzzy patch of light with nearly no concentration and around 1/3 larger diameter than NGC 2300.

4" bino, 110x, NELM 6m5+
NGC2276_NGC2300.jpg

[akarsh]

I believe Arp 25 might be one of the few examples of Jellyfish galaxies where we can visually see the effects of ram pressure stripping from the galaxy falling through the intracluster medium in sm. I base this on the following snippet from this paper:

"Rasmussen et al. (2006) and Wolter et al. (2015) conclude that ram pressure (along with viscous effects) is responsible for both the disturbed morphology and high star formation rate (SFR) in NGC 2276"

The paper by Rasmussen et. al. referenced argues that ram-pressure stripping is the more likely explanation for the bow shock of star forming knots seen on the western front of the galaxy:

"The distributions of optical light, H-i gas, and radio continuum emission in this galaxy show a bow-shock-like structure along the western edge, which may suggest a shocked gas component. If so, the galaxy must be moving supersonically through the ambient IGM. Evidence supporting this interpretation is the high star formation rate (SFR) of NGC 2276 (?5-M?-yr?1; Davis et al. 1997), with much of this starburst activity occurring along the western edge, as expected if an interaction with the IGM has triggered some of the star formation via ram-pressure compression of molecular gas."

What I am not sure of, is whether the asymmetric position of the visual nucleus is also a result of ram pressure stripping. In any case, it looks like some of the star formation on the bow shock was picked up by Howard in his 28" sketch.

Motivated by its Jellyfish nature, I looked at Arp 25 during the January new moon:

"NGC 2276 appeared as a very low surface brightness circular glow. A bright star nearby detracts from the view. The asymmetry of the glow (presumably attributed by the paper to ram-pressure stripping) was challenging, but certainly detected to be lopsided in the direction of the star."

and also NGC 2300:

"NGC 2300 nearby appeared as an easy, high surface brightness elliptical glow. The two made for a nice pair in the same FOV."

Clear Skies!