ASTRO: Arp 38

Arp 38 is a face on spiral in Draco about about 60 million light-years
distant. Arp put it in his class for spirals with low surface
brightness companions on the arm. One major problem here. The
companion probably doesn't exist. NED shows no other galaxy in the
area. It appears the "companion" is most likely just star knots to the
northern side of the galaxy. Arp's comment reads: "Small ring in arm on
north side, part of large ring on following side shows in H-alpha only."
This would be the position of the star knots. Kanipe and Webb make no
mention of the companion in their book. They just repeat Arp's comment.

The only other mention of a companion that I found is in a paper by B.
A. Vorontsov-Velyaminov from 1975 titled "Atlas of Interacting Galaxies,
Part II and the Concept of Fragmentation of Galaxies. This is the VV
catalog in which Arp 38 is entry 444. There they say: "One of the rare
cases where the companion at the end of a spiral arm is also a spiral.
Here, a chain of H II regions encircles the massive condensation thus
forming a small spiral ripening at the periphery of the larger one and
liable to gemmate." Again this reads more like a feature of the galaxy
rather than a separate one except for the part where they state it
really is a spiral. But do they mean a spiral form rather than a galaxy?

Arp 38 does have some plumes to the north that likely indicate some
interaction in the past. I suppose the bright knot to the north could
be mistaken for a galaxy. While I found no released image of this one
by the HST it has imaged it. A very basic combine of a couple filters
is seen at: http://cseligman.com/text/atlas/ngc6412hst.jpg There the
"companion" appears to be just a very large HII region and star cluster.
I suppose if it ate a dwarf galaxy with lots of HII regions this might
be the some of the remains. This could explain the plumes as well.

There seems some disagreement about how to classify this spiral. NED
says SA(s)c while the NGC project says SBc making it a barred spiral.
It sort of looks barred in my image at first glance. But looking closer
in the enlarged image what appears to be a bar to the north is really
star knots at the start of a spiral arm that comes out of a circular
core region. There is no sign of a bar like structure to the south.
This is even more evident (of course) in the Hubble Space Telescope
image above.

The image is out of the area of the Sloan survey so there is little data
on the field. While NED lists a couple dozen galaxies in the field none
have much data and nothing about distance. No annotated image was
prepared due to this lack of data.

14" LX200R @ f/10, L=4x10" RGB=2x10', STL-11000XM, Paramount ME

Rick
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