Page last updated Feb 12, 2013|
PGC 4578 (= NGC 446 = IC 89)
A 12th-magnitude lenticular galaxy (type SB0?) in Pisces (RA 01 16 03.7, Dec +04 17 40)
PGC 4606 (= IC 90)
A 14th-magnitude elliptical galaxy (type cD/E3) in Cetus (RA 01 16 30.3, Dec -07 58 36)
PGC 4724 (= IC 93 = IC 1671 = PGC 889345)
A 13th-magnitude spiral galaxy (type Sb pec) in Cetus (RA 01 19 02.2, Dec -17 03 40)
PGC 4728 (= Arp 88)
A 17th-magnitude spiral galaxy (type Sb? pec) in Pisces (RA 01 19 05.3, Dec +12 28 24)
Apparent size 0.5 by 0.2 arcmin. Nothing else available.
Above, a 2.4 arcmin wide closeup of PGC 4728
Below, a 12 arcmin wide region centered on the galaxy, also showing PGC 4748 and 4750
PGC 4748 (with PGC 4750 = Arp 119)
A 15th-magnitude elliptical galaxy (type E3?) in Pisces (RA 01 19 24.6, Dec +12 27 43)
PGC 4748 and 4750, collectively known as Arp 119, are a pair of galaxies that underwent a galactic collision around 70 million years before the time at which we see them. They must be at essentially the same distance from us, especially in comparison to their relatively small separation. To determine that distance, we can use their recessional velocities (14655 km/sec for PGC 4748 and a little less for PGC 4750, which see) and the Hubble Law of Universal expansion. Depending upon the value used for the recessional velocity of PGC 4750, a straightforward calculation indicates that the pair are about 670 to 680 million light years away. However, for objects at such distances we should take into account the Universal expansion during the time it took their light to reach us. Doing that shows that they were between 635 and 645 million light years away when the light by which we see them was emitted, 650 to 660 million years ago (the difference between the numbers for light years and years being due to the expansion of the intervening space during the light-travel time). Given that and its apparent size of 0.9 by 0.6 arcmin, PGC 4748 is about 170 thousand light years across, 1.0 by 0.55 arcmin wide PGC 4750 is about 190 thousand light years across, and at the time represented by our present view the centers of the galaxies were about 200 thousand light years apart (of course, since that was over half a billion years ago, they are now much further apart).
A theoretical study of the system convincingly argues that the now northern elliptical galaxy approached the now southern spiral at a relatively high rate of speed (probably in excess of 1000 km/sec) from 'below', passed through the disc of the spiral nearly perpendicularly a little to the west ('right') side as seen by us, and is now moving 'up' and away from it at a similar but slightly slower velocity. The arc of stars extending northward from the spiral represents the gravitational momentum and tug of the elliptical during and after the collision, while the waves of star formation throughout the gas-rich spiral, now greatly distorted by the collision, represent the outward moving gravitational shock of the galaxies' interaction. Very few if any of the stars in either galaxy would have collided directly with stars in the other, but their motions would have been greatly disturbed, and as the shockwave spread through clouds of gas and dust in the gas-rich spiral, several waves of star formation resulted. In the gas-poor elliptical, such star formation is not possible, especially since roughly a billion solar masses of high-velocity gas in the spiral galaxy can be best explained by its having been stripped from the elliptical as it passed through, and its appearance probably remains much the same as before the collision despite the altered motions of its individual stars.
Above, a 2.4 arcmin wide closeup of PGC 4748 and 4750
Below, a 12 arcmin wide region centered on the pair, also showing PGC 4728
PGC 4750 (with PGC 4748 = Arp 119)
A 14th-magnitude spiral galaxy (type SBdm? pec) in Pisces (RA 01 19 24.2, Dec +12 26 49)
NED lists two recessional velocities for PGC 4750. The first is 14265 km/sec, and the second is 14530 km/sec. Either is close enough to that for PGC 4748 (which see for images and most of the discussion of the pair and its history) that even without their obvious interaction (apparently the result of a galactic collision about 70 million years before the time at which we see them) it would be clear that they are at the same distance (as discussed at PGC 4748's entry, around 640 million light years, give or take several million light years). Given that and its apparent size of 1.0 by 0.55 arcmin, PGC 4750 is about 190 thousand light years across.
PGC 4780 (= NGC 468 = IC 92)
A 14th-magnitude lenticular galaxy (type S0/a?) in Pisces (RA 01 19 48.4, Dec +32 46 02)
PGC 4789 (with "a low surface-brightness companion" = Arp 48)
A 15th-magnitude spiral galaxy (type SBab pec) in Pisces (RA 01 20 00.4, Dec +12 20 54)
Arp 48 is supposed to be an example of a spiral galaxy with a low surface brightness companion. However, as in the case of several other Arp objects, it also has nearby brighter companions which are typically (and probably erroneously) presumed to be part of the original Arp listing. Referring to Arp's original atlas (there is a reference image below), it seems clear that Arp 48 was supposed to be PGC 4789 and its faint companion is the small condensation just to its west (at about RA 01 19 59.5, Dec +12 20 52); but most catalogs list the brighter galaxy still further to the west -- listed as Arp 48 NED01 in the NED, as an example) is the supposedly fainter companion. As a result, this entry discusses both the "standard" and more probable definitions of Arp 48.
PGC 4789, the certain main component of Arp 48, has a recessional velocity of 14485 km/sec. Based on that, a straightforward calculation indicates that it is about 675 million light years away. However, for such distances we should take into account the expansion of the Universe during the time it took its light to reach us. Doing that shows that it was about 640 million light years away at the time the light by which we see it was emitted, about 660 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and its apparent size of about 0.7 by 0.4 arcmin, PGC 4789 is about 130 thousand light years across.
The "standard" fainter member of Arp 48, the brighter galaxy to the west, is 2MASX J01200039+122053 (based on its position of RA 01 20 00.4, Dec +12 20 53). Its recessional velocity is unknown, as is whether it has any physical relationship to PGC 4789; so all that can really be said about it is that its apparent size is about 0.25 by 0.2 arcmin, and that although normally considered part of Arp 48, it probably should not.
The galaxy to the east of PGC 4789 is not generally considered to be part of the system, but since it is shown even in the close-up image, it seems appropriate to remark that it is 2MASX J01200182+1220497 (based on its position of RA 01 20 00.2, Dec +12 20 50), and its apparent size is about 0.2 by 0.15 arcmin.
The most likely "low surface-brightness companion" of PGC 2789 that would make up the rest of Arp 48 is the bright knot on its western side, pointed out by an arrow in the image below. It has no designation, being considered part of PGC 4789 itself.
Above, a 2.4 arcmin wide closeup of PGC 4789 and the other objects discussed above
Below, an image from Halton Arp's Atlas for reference in the argument above
Below, a 12 arcmin wide region centered on PGC 4789
PGC 4796 (= NGC 475 = IC 97)
A 15th-magnitude elliptical galaxy (type E0?) in Pisces (RA 01 20 01.9, Dec +14 51 42)
PGC 4840 (probably not IC 96)
A 14th-magnitude spiral galaxy (type Sbc?) in Pisces (RA 01 20 33.0, Dec +29 36 57)
Usually (but probably incorrectly) listed as IC 96, which as discussed at that entry is more likely to be PGC 4848. For that reason, PGC 4840 is discussed there.
PGC 4848 (= IC 1672; probably also = IC 96)
A 13th-magnitude spiral galaxy (type Sb?) in Pisces (RA 01 20 38, Dec +29 41 56)
PGC 4869 (= IC 98)
A 15th-magnitude elliptical galaxy (type E0?) in Cetus (RA 01 20 54.8, Dec -12 36 15)
PGC 4906 (with 2MASXi J0121174-003312 = Arp 67)
A 14th-magnitude spiral galaxy (type SB(r)ab) in Cetus (RA 01 21 16.6, Dec -00 32 40)
Based on a recessional velocity of 5230 k/sec, PGC 4906 is about 245 million light years away. Given that and its apparent size of 1.3 by 1.2 arcmin, it is about 90 thousand light years across. It is apparently accompanied by two faint companions on its southeastern side, the brighter of which, 2MASXi J0121174-003312 (shortened to J012117.4-003312 in the closeup image), is presumably the reason it was listed as Arp 67. Information about it and the fainter one (shortened to B011845.7-004852) can be found at their entries, immediately below.
Above, a 2.4 arcmin wide closeup of PGC 4906 and its fainter companions
Below, a 12 arcmin wide region centered on the galaxy
2MASXi J0121174-003312 (with PGC 4906 = Arp 67)
Not a PGC object, but listed here since its association with PGC 4906 is probably the basis for Arp 67
An 18th-magnitude lenticular galaxy (type S0?) in Cetus (RA 01 21 17.4, Dec -00 33 12)
The brighter companion of PGC 4906 (which see for images), and as a result, probably the object that helps form Arp 67. As it happens, it is only an optical double with the brighter galaxy, because its recessional velocity of 16495 km/sec is far greater than that of PGC 4906. Using its velocity to calculate a Hubble expansion distance, a straightforward calculation indicates that J0121174-003312 is about 770 million light years away. However, for objects at such distances we should take into account the Universal expansion during the time it took their light to reach us. Doing that shows that the galaxy was about 720 million light years away (nearly 500 million light years more distant than PGC 4906) at the time the light by which we see it was emitted, about 740 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and the galaxy's apparent size of 0.35 by 0.2 arcmin, it is about 75 thousand light years across.
Not a PGC object, but listed here because of its proximity to PGC 4906
A 19th-magnitude lenticular galaxy (type S0+/a?) in Cetus (RA 01 21 19.1, Dec -00 33 10)
Apparent size 0.3 by 0.1 arcmin; nothing else available. (See PGC 4906 for images.)
PGC 4992 (= NGC 497 = Arp 8)
PGC 4997 (= IC 99)
A 15th-magnitude barred spiral galaxy (type SB?) in Cetus (RA 01 22 27.3, Dec -12 57 09)