3 Attachment(s)
Object of the Week, June 11th, 2017: The elliptical dumbbell NGC 4782/3 (VV 201)
NGC 4782 and NGC 4783 (= VV 201, 3C 278, MCG-02-33-050)
Corvus
RA: 12 54 36
Dec: -12 34 07
Magnitude: 11.6, 11.7
This unusual pair is an example of a dumbbell galaxy pair, defined as a pair of galaxies “in which two separated, approximately equal, nuclei are observed in a common envelope.” (Matthews et. al., 1964). Moreover, the fact that this is a pair of elliptical galaxies makes it even more unique.
Here is an image of the object from the PanSTARRS survey:
Attachment 2583
William Herschel discovered this pair on March 27th, 1786 (Steinicke). There is some confusion regarding the designation of the two galaxies. According to Harold Corwin, William Herschel catalogued both galaxies with a single designation, whereas John Herschel and Dreyer have distinguished the two in the NGC. The modern day designation is consistent with increasing RA, assigning the northern component NGC 4783 and the southern one NGC 4782. However, there is still potential for confusion and exchange of data between the two galaxies.
Research suggests that the pair forms the dominant members of a cluster of about 40 galaxies, presumably lying beyond the Virgo cluster given the higher redshift.
The asymmetry of the light from the galaxies, amongst other things, indicates that the pair is not an overlap, but has suffered some tidal interaction. Simulations suggest that the galaxies have had a recent fly by with one simulation (Madejsky and Bien 1993) estimating that the closest approach happened 13.5 million years before observation and another (Borne et. al., 1988) placing it at about 25 million years. The latter simulation suggests that the encounter caused energy loss from the motion of the galaxies into the motions of individual stars, that turned the hyperbolic orbit of the galaxies into an elliptical orbit -- they predict that the group will fly apart and then merge again after about 800 million light years if undeterred by other interactions.
Below is the path of the galaxies on the sky as inferred by Borne et. al., taken from their 1988 paper:
Attachment 2584
The radio source 3C 278 has been identified with NGC 4782 (Baum et. al. 1988), a peculiar radio jet of which seems to be a subject of controversy (Madejsky 1992).
Observationally speaking, Steve Gottlieb has reports with 8” and 17.5” aperture, and Rich Jakiel lists an observation with a 20” in his book with Steinicke.
Here is a POSS II image of the object:
Attachment 2585
I observed this object with my 18” in April 2016 from central Texas. My notes read: “Bright, nice contact pair. Great views at all powers.” and “It was a very nice pair, bright and easily found.”. The cores did appear disjoint in the eyepiece unlike the overexposed POSS II image. Jimi has observed this with his 48” and says that the cores appeared disjoint as well.
This is an unique, yet bright and easy object and should be fun for all apertures! As always…
Give it a go and let us know!
This is my first OOTW, so Jimi Lowrey helped me with several suggestions, and I want to thank him for them!
(On a side note, the closest morphologically similar object I could find in my internet research for this OOTW was NGC 750/1. This paper tabulates some interacting ellipticals.)
Clear Skies
Akarsh
