N4727/4724.....that's an interesting close pair of galaxies, Mr PGC Hunter! (do you like PGC galaxies?!?)
It is very poorly studied by professional astronomers, judging from the very few papers mentioning it in the last 30 years.
(see: //adsabs.harvard.edu , the astronomy and astrophysics abstracts service)
When I looked in the public Hubble Space Telescope archive at //hla.stsci.edu, again, there was no imagery available....so, this is a
mysterious pair!! Furthermore, it is outside of the SDSS footprint, and there is little about this galaxy pair in the data archives.
Here is the DSS image (a composite of ER + J images), which I downloaded from the (usually) excellent online version of DSS known as Aladin(//aladin.u-strasbg.fr). Normally, these images are quite good (about equivalent to a modestly good amateur CCD image), yet this particular scan of the Schmidt plates is particularly poor.
An image search at the comprehensive NED extragalactic database (//nedwww.ipac.caltech.edu) also comes up nearly empty handed;
but - lucky for us - the available Near infrared image (J+H+K composite) from the 2MASS survey is good enough to give us a reasonable idea of what kind of galaxies these are:
We are lucky here, because the best of the 2MASS infrared images are of decent angular resolution. The larger of the two galaxies is obviously a spiral. The smaller of the two galaxies is probably an S0 galaxy (strongly dominant bulge with a small disk/planar component) though the existence of spiral arms cannot be ruled out due to the modest morphological resolution that is available.
The case for these assigned galaxy types is strengthened by the GALEX satellite far-ultraviolet and near-ultraviolet images of this pair, as the spiral produces significant extended FUV emission (presumably from hot young stars in its arms and/or in its inner ring), yet the smaller of the two galaxies has little or no FUV flux which indicates that it is a quiescent disk+bulge system having little or no star formation....in other words, the lack of star formation in the smaller galaxy is strongly consistent with the idea of it being an S0 galaxy.
The prominent central bulge (or the pseudo-bulge, if it is not a spheroidal structure) that is seen in the infrared image of the spiral need not be so prominent at visual wavelengths, as the near-infrared regime can reduce the obscuring effect of the dust within a galaxy by 10 or more times. Another interesting aspect of the spiral is that it appears to have a strong pseudo-ring structure made of two tightly-wound inner arms (in the terminology of the CSRG), with a probable bar structure existing inside the ring.
An existing expert Hubble classification (on the DDO system) for the the spiral NGC 4727 by Sidney van den Bergh, is
S(B)b II with an uncertainty flag, indicating that this is likely to be a barred spiral, perhaps weakly barred, but with a significant degree of uncertainty attached to the assigned Hubble type. I think that NGC 4727 is undoubtedly a barred spiral, from consideration of the several low resolution images that can be found on the internet, and that it does have an inner ring structure that surrounds its bar.
The LEDA database also claims that this galaxy does have a bar structure and a ring structure.
The asymmetry visible in the DSS image of the spiral, with one prominent spiral arm in its outer regions that does not have a corresponding prominent arm on the other side, could be a sign of a mild galaxy interaction or of a past interaction between the two galaxies. However, there is a large difference in recession velocity between the two galaxies, which would indicate a greater
probability that this is a non-interacting galaxy alignment in the same-line-sight........ that is, IF my available optical redshifts are correct!! (it is surprising how often redshifts that are made from optical spectra turn out to be incorrect.....HI line data (21cm line) are far more reliable)
A possibility that something more interesting is going on than the line-of-sight alignment of two galaxies that are actually far apart, is indicated by the DSS image found at //wikisky.org
[ The wikisky server does not display the sharpest available Digitized Sky Survey images, but it does display DSS images at high contrast; which is useful for looking for faint outer features in galaxies ]
There does appear to be some unusual and anomalous outer material (or objects) outside of the optical body of NGC 4727, but this would have to be crosschecked with other deeper and sharper imagery.
Of course, if there has been some kind of interaction between NGC 4727 and another galaxy, the perturbing object need not be the most obvious smaller companion that is very easy to see (NGC 4724). Indeed, there seem to be one or two very small galaxies near to NGC4727 that are candidate perturbers.
cheers,
the mad galaxy man