An emission region in NGC 4559. Apparent size 0.45 by 0.25 arcmin.

Part of NGC 4559.

Part of NGC 4559.

Per Dreyer, IC 3553 (Wolf list IV #221, 1860 RA 12 28 59, NPD 63 02.0) is "very faint, very small, round, brighter middle". The position precesses to RA 12 35 56.1, Dec +26 11 42, practically on top of the star listed above, so the identification is certain.

Per Dreyer, IC 3554 (Wolf list IV #222, 1860 RA 12 29 00, NPD 61 18.0) is a "nebula involved in I 92 (2 seconds to west, 1.8 arcmin to south)", (WH) I 92 being NGC 4559, on which IC 3554 is superimposed. The position precesses to RA 12 35 56.0, Dec +27 55 42, practically on top of the star listed above, so the identification is certain. Located within an arcmin of IC 3550, which see for images.

Part of NGC 4559.

Per Dreyer, IC 3556 (Wolf list IV #225, 1860 RA 12 29 02, NPD 62 15.7) is "faint, small, round, brighter middle". The position precesses to RA 12 35 58.6, Dec +26 58 00, right on the galaxy, so the identification is certain. However, per Corwin, four modern catalogs have still managed to misidentify the galaxy as NGC 4536, 4558 or 4563, hence the warning in the title for this entry. Based on a recessional velocity of 7395 km/sec, IC 3556 is about 345 million light years away. Given that and its apparent size of 0.75 by 0.45 arcmin, it is about 75 thousand light years across.

Per Dreyer, IC 3557 (Frost #975, 1860 RA 12 29 05, NPD 72 37) has a "brighter middle, magnitude 15.5". The position precesses to RA 12 36 07.2, Dec +16 36 42, just under 2 arcmin south of a small cluster of distant galaxies that appears to be generally accepted as including the IC object. The brightest member of the cluster would be the main contributor to Frost's observation, so its properties and position are the ones adopted for this entry. How many other cluster members should be considered part of the IC object depends upon the resolution of Frost's plate, which I do not know, but plates from that era show less detail than even "amateur" images taken today, and Corwin states that the IC object is "a double (at least) galaxy" within the cluster. Based on a recessional velocity of 23505 km/sec, a straightforward calculation indicates that IC 3557 is about 1095 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 1000 million light years away at the time the light by which we see it was emitted, about 1035 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 0.6 by 0.4 arcmin, the main galaxy is about 175 thousand light years across.

Per Dreyer, IC 3558 (Frost #976, 1860 RA 12 29 05, NPD 77 23) is "double; faint, round, 12 arcsec distance north and south". The position precesses to RA 12 36 09.5, Dec +11 50 42, about 1.6 arcmin east of the galaxy listed above, but the description perfectly fits the galaxy and the star to its north and there is nothing else nearby, so the identification is reasonably certain. (Note that the description of the object as a double nebula indicates that the IC listing should include both the galaxy and the foreground star.) Based on a recessional velocity of 28140 km/sec, a straightforward calculation indicates that IC 3558 is about 1310 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 1175 million light years away at the time the light by which we see it was emitted, about 1230 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 0.4 by 0.2 arcmin, the galaxy is about 140 thousand light years across.

Apparent size 0.5 by 0.15 arcmin.

Apparent size 0.65 by 0.5 arcmin.

Apparent size 0.75 by 0.25 arcmin.

Apparent size 0.7 by 0.25 arcmin. Listed as a member (VCC 1654) of the Virgo Cluster.

Per Corwin, the emission region is blended with IC 3564 and a foreground star to their south on a print of Wolf's plate, but since Wolf listed the two separately, the two emission regions must have appeared as separate objects on the original plate. Part of NGC 4559.

Per Corwin, the emission region is blended with IC 3563 (which see for a closeup image) and a foreground star to their south on a print of Wolf's plate, but since Wolf listed the two separately, the two emission regions must have appeared as separate objects on the original plate. Part of NGC 4559.

Apparent size 0.3 by 0.2 arcmin.

Per Dreyer, IC 3566 (Frost #980, 1860 RA 12 29 16, NPD 78 04) is "cometic, round with 1 arcmin tail at 110°". The position precesses to RA 12 36 20.8, Dec +11 09 42 (whence the position above), but there is nothing there. Per Corwin, although Frost's description was that of a comet and the object was also identified as cometary by Adelaide Ames in a list of otherwise unidentifiable NGC/IC objects, no effort to associate the observation with any known comet has succeeded; so although this could represent the only observation of an otherwise unknown cometary body, Corwin concludes that the "object" was almost certainly a plate defect, and therefore nonexistent.

Apparent size 0.6 by 0.5 arcmin. Listed as a member (VCC 1660) of the Virgo Cluster.

Historical Identification: Per Dreyer, IC 3568 (Aitken, ([A.N.] 3667), 1860 RA 12 29 18, NPD 06 39.9) is "a planetary or nebulous 9.5 magnitude star; 13th magnitude star 15 arcsec to west". The position precesses to RA 12 33 03.2, Dec +82 33 46, right on the nebula listed above, and the star to the west makes the identification certain.
Physical Information: The distance of IC 3568 is very uncertain (see the following paragraph), with values ranging from about 4500 light years (the most commonly quoted value) to about 9000 light years (the distance stated in the Hubble news release). Given that and its apparent size of about 18 arcsec for the outer fainter region, and about 7.0 by 6.5 arcsec for the brighter central region (from the HLA image below), the newer brighter nebula is about 0.3 to 0.6 light years across, while the older fainter shell is about 0.8 to 1.6 light years across. The inner nebula has a complex structure resembling a sliced lemon (whence its name), but the outer shell is exceptionally smooth. The central star, which is heating up as it shrinks from its former red giant stage to a future white dwarf stage, is about magnitude 12.3, with a temperature between 55 and 60 thousand Kelvin, or 100 to 105 thouand Fahrenheit degrees.
Note About Distance Estimate: The paper published by Ciardullo et al, based on a statistical study of a number of planetary nebulae, concluded that "traditional" distances of planetary nebulae were typically overestimated by a factor of two; but even obtaining that result required eliminating some "discrepant" objects from the study. One of those eliminated was IC 3568, meaning that its distance may be even less certain than the broad range of distances in the paragraph above.

Per Dreyer, IC 3569 (Frost #978, 1860 RA 12 29 18, NPD 69 56) is "considerably small, spiral, 2 brighter resolvable, faint star in middle, faint star involved". The position precesses to RA 12 36 18.7, Dec +19 17 42, about 3 arcmin southeast of NGC 4561 (which see for anything other than historical information). There is nothing else in the area, so either the IC object is NGC 4561 and Frost's position is off (leading to the duplicate entry), or his #978 is a nonexistent object. The entry does appear to match NGC 4561, as the faint star near the northern edge of the galaxy and its bright central region would correspond to the two stars in the IC description, so the identification as NGC 4561 is considered reasonably certain.

Per Dreyer, IC 3570 (Wolf list IV #233, 1860 RA 12 29 20, NPD 65 09.0) is "extremely faint, small, irregular figure, 13th magnitude star to northwest". The position precesses to RA 12 36 18.1, Dec +24 04 42, right on the star listed above, and the brighter (albeit 15th-magnitude) star to the northwest confirms the identity.

Apparent size 0.45 by 0.3 arcmin.

Per Dreyer, IC 3572 (Schwassmann 205, 1860 RA 12 29 23, NPD 77 36.6) is "extremely faint, very small, very questionable". The position precesses to RA 12 36 27.6, Dec +11 37 06, just west of the mid-point of the pair of stars listed above, so the identification is certain.

Apparent size 0.6 by 0.3 arcmin.

Apparent size 0.9 by 0.7 arcmin. Listed as a member (VCC 1665) of the Virgo Cluster.

Apparent size 0.8 by 0.5 arcmin. Listed as a member (VCC 1674) of the Virgo Cluster.

Apparent size 2.2 by 1.8 arcmin. Listed as a member (VCC 1678) of the Virgo Cluster.

Per Dreyer, IC 3577 (Schwassmann 207, 1860 RA 12 29 32, NPD 77 19.9) is "very faint, pretty small, diffuse, 13th magnitude star involved to northeast". The position precesses to 12 36 36.4, Dec +11 53 49 (whence the position above), but there is nothing there save for a faint star just to the northeast. Per Corwin, the IC object must have been a defect on Schwassmann's plate just to the southwest of the star. Some references list the star as the IC object, but the description shows that Schwassmann meant his #207 to refer to the supposed nebulosity, and the star (which per Corwin is #207a in Schwassmann's list) though "involved" with the nonexistent nebula was not considered to be part of it; so the IC object itself does not exist.

Apparent size 1.2 by 0.55 arcmin. Listed as a member (VCC 1684) of the Virgo Cluster.

Per Dreyer, IC 3579 (Wolf list IV #236, 1860 RA 12 29 36, NPD 63 07.5) is "extremely faint, small, irregular figure, others near". The position precesses to RA 12 36 32.9, Dec +26 06 13, right on the star listed above, so the identification is certain. (See the wide-field view of IC 3571 for an image of IC 3579.)

Apparent size 0.7 by 0.6 arcmin.

Apparent size 1.05 by 0.75 arcmin.

Per Dreyer, IC 3582 (Wolf list IV #238, 1860 RA 12 29 40, NPD 62 59.6) is "faint, very small, cometic, brighter middle, others near". The position precesses to RA 12 36 36.8, Dec +26 14 07, right on the galaxy, so the identification is certain. Despite that almost everyone has misidentified PGC 42060 (the brighter galaxy to the southwest) as IC 3582; but (per Corwin) both galaxies appear stellar on a print of Wolf's plate, so there is no reason to believe that Wolf meant to record the other galaxy, let alone made what would have been a very uncharacteristic error in its position. Apparent size 0.2 by 0.2 arcmin.

Apparent size 0.6 by 0.3 arcmin.

Historical Identification: Per Dreyer, IC 3583 (Roberts, Frost, 1860 RA 12 29 40, NPD 75 58.5) is "very much extended, 13th magnitude star attached on southeast, 2 stars of 12th magnitude near".
Physical Information: Listed as a member (VCC 1686) of the Virgo Cluster. Its recessional velocity of 1120 km/sec corresponds to a Hubble distance of about 50 million light years, in good agreement with redshift-independent distance estimates of 25 to 55 million light years, and it probably is an actual member of the Cluster. Whether it is a companion of NGC 4569, with which it comprises Arp 76, is another matter. A study of stripping of gas from NGC 4569 as it moves through the Virgo Cluster states that there is some indication that the two galaxies are interacting, in which case they would be physical as well as apparent companions; but since their recessional velocities differ by nearly 1500 km/sec, they would not remain companions for long even if they are companions now. Assuming a distance of about 50 million light years, IC 3583's apparent size of 2.8 by 1.2 arcmin corresponds to about 40 thousand light years. (Note: The Hubble site page linked below has a caption stating that the galaxy is about 30 million light years away; but unless it is a foreground galaxy and not a member of the Virgo Cluster or a companion of NGC 4569, that can't be correct.) (Magnitude from LEDA)

Per Dreyer, IC 3584 (Schwassmann 208, 1860 RA 12 29 41, NPD 76 59.8) is "very faint, very small, perhaps a 14th magnitude star". The position precesses to RA 12 36 45.2, Dec +12 13 55, right on the star listed above, so the identification is certain.

Apparent size 1.1 by 1.0 arcmin.

Apparent size of central region 1.3 by 1.0 arcmin; outer regions cover 1.9 by 1.7 arcmin. Listed as a member (VCC 1695) of the Virgo Cluster.

Apparent size 1.6 by 0.25 arcmin.

Per Dreyer, IC 3588 (Schwassmann #293, 1860 RA 12 29 53, NPD 75 00.6) is "considerably faint, pretty large, a little brighter middle". The position precesses to RA 12 36 56.2, Dec +14 13 07, right on the galaxy, so the identification is certain. The NGC position was also good, so there shouldn't have been a duplicate entry, but (per Corwin) Schwassmann misidentified the 15th magnitude star on the western side of the galaxy as NGC 4571 (which see for anything else), and thought his #293 was a new discovery. As a result two essentially identical observations led to a double listing.

Per Dreyer, IC 3589 (Schwassmann 29, 1860 RA 12 29 54, NPD 82 17.5) is "very faint, small, round, stellar". The position precesses to RA 12 37 00.8, Dec +06 56 13, just west of the star listed above, so the identification is certain. There is a galaxy (IC 3591, which see for images) just southeast of the star, but (per Corwin) Schwassmann recorded both objects in the same "zone" and their relative positions are accurate, so there is no doubt that IC 3589 is the star, and not a duplicate listing of IC 3591.

Apparent size 0.9 by 0.2 arcmin.

Apparent size 1.25 by 0.7 arcmin. Listed as a member (VCC 1699) of the Virgo Cluster.

Apparent size 1.05 by 0.45 arcmin. Also pointlessly known as NGC 4559A (pointlessly since it has a perfectly good IC listing, and isn't particularly close to its NGC namesake.)

Apparent size 0.65 by 0.45 arcmin. Also pointlessly known as NGC 4559B (pointlessly since it has a perfectly good IC listing, and isn't particularly close to its NGC namesake.)

Per Dreyer, IC 3594 (Wolf list IV #244, 1860 RA 12 30 00, NPD 63 06.9) is "extremely faint, very small, irregular figure". The position precesses to RA 12 36 56.7, Dec +26 06 49, just south of the star listed above, so the identification would be reasonably certain even without any other information. As it turns out the slight error in position is due to the fact that the "irregular figure" refers to the star and a small plate defect superimposed on the star which (per Corwin) is visible on a print of Wolf's plate. If the plate defect had not been present, perhaps Wolf would not have bothered to record the object; but since the star is not separately listed it is a valid identification of the IC entry, and as entitled to its entry as any of the many other stars in the NGC/IC.

Per Dreyer, IC 3595 (Wolf list IV #245, 1860 RA 12 30 08, NPD 65 26.4) is "extremely faint, small, irregular figure". The position precesses to RA 12 37 06.0, Dec +23 47 20, on the northwestern edge of the northern member of the pair of galaxies listed above, so the identification is certain. (Note: NED lists only the northern galaxy as IC 3595, but such a close pair would appear to be a single object on Wolf's plate, so the IC entry should refer to both of them.) The apparent size of PGC 1693589 is 0.45 by 0.1 arcmin, and of PGC 1693713 is 0.45 by 0.35 arcmin. Nothing else is known, so whether the galaxies have any connection save for their IC listing is also unknown; but since there is no obvious interaction between them they are probably an optical double, and not a physical pair.

Per Dreyer, IC 3596 (Wolf list IV #246, 1860 RA 12 30 23, NPD 62 42.5) is "very faint, small, irregular figure, near double star". The position precesses to RA 12 37 19.3, Dec +26 31 14 (whence the position above), but there is nothing there save for the double star noted in the description. Per Corwin, there is a plate defect visible on a print of Wolf's plate near the double star, so Wolf #246 is the defect and IC 3596 represents a nonexistent object.

Apparent size 0.6 by 0.55 arcmin.

Apparent size 1.4 by 0.45 arcmin.

Apparent size 0.6 by 0.35 arcmin. Listed as a Seyfert galaxy (type S1n).