I've been working on this one for a little while now, since May in fact. It's

maybe time to draw a line under it and share what I've found.

NGC 4151 is actually not one of Arp's galaxies, for some reason it does not

appear in his atlas of peculiar galaxies. However, he showed great interest in

it and it was one of the centrepieces in his arguements against distant related

redshifts.

In 1966 Arp obtained a fabulous 3 hour exposure of this galaxy through the 200".

By examining his image very closely he was drawn to the conclusion that each of

the 2 spiral arms of ngc 4151 terminated in a connected galaxy.

He obtained spectra from each galaxy and, of course, found the connected

galaxies to have much higher redshifts than ngc 4151. So his arguement was that

the low redshift galaxy was physically connected to the 2 high redshift

galaxies. Furthermore, he claimed that the Southerly spiral arm was partly made

up from very faint galaxies. Examining modern databases does indeed confirm a

great many very faint spiral galaxies visible, either within or through the

spiral arm. By examining his original plate I cannot, in all honesty, say that I

can see the connection to the 2 smaller galaxies that Halton Arp claimed to see;

in fact I`m not even sure which galaxy he is referring to in the Southern arm.

I imaged the system in May of this year and examining my image did not throw

much light on the subject. The spiral arms are extremely faint and could or

could not be connected to the small galaxies. I decided that I could add nothing

to the debate and shelved the project for a couple of months.

Halton Arp's arguements usually revolve around ejected quasars, which he again

claims are associated with relatively nearby galaxies. For whatever reasons Arp

makes no reference to any quasars near to NGC 4151. Possibly he had no spectra

from all nearby objects and was unable to identify possible quasars.

Fortunately, we have access to superb extra-galactic databases these days and I

decided to do my own search. I found at least 10 nearby quasars within a 1000

arcsec radius from ngc 4151 and they mostly all fall on a circle of about 20 arc

min radius. The 2 nearest of them to ngc 4151 are recorded on my image. Whether

they have any cosmological significance I cannot say but I list below some

relevant redshift data for the included galaxies and quasars:

Object : Type : Magnitude : redshift, z

ngc 4151 : Seyfert Galaxy : 11.9 : 0.003262

ngc 4156 : Spiral Galaxy : 14.3 : 0.022569

B1207+39 : Quasar : 20.8 : 0.615

182.507190+39.364131 : Quasar : 21.9 : 2.96182

I think the interesting feature is the way the Aladin skyplot shows how the quasars

appear to fall on a circle, just as though they have been ejected from ngc 4151 and

are travelling away from the parent galaxy.

Of course I could just be biased!

My image : 50 x 2min exposures sigma combined in AstroArt, processed in AA and

Pixinsight.

10" Newtonian / H9C ccd camera. PHD guidance using a KWIQ Guider.

Database info from Simbad and Aladin.