Roaming the Deep Sky #12
Hickson Compact Group 44
By Don Clouse
Hickson Compact Group 44 (HCG44) wound up on my observing itinerary because two of its members are on the Hershel 400 Observing List. (See the Astronomical League’s web-page http://www.astroleague.org/al/obsclubs/obsclub.html for details on the Herschel 400.) This close group, spanning about 20’, is composed of four galaxies, NGC’s 3185, 3187, 3190, and 3193. The two brightest members of the group, NGC3190 and NGC3193, are the ones on the Herschel 400 list. This group is located along the eastern side of the Sickle asterism in Leo. As can be seen on the first chart, the group – represented here by NGC3190 – is on the line between Zeta Leonis, or Adhafera, and Gamma Leonis, Algeiba, being somewhat closer to the former. (Any star chart will show the locations of Zeta and Gamma Leonis, Algeiba.) I highly recommend using Algeiba as your jumping off point for locating HCG44. This beautiful double consists of a pair of giants, of spectral classes K1 and G7, 126 light years away. They are separated by only 4.4 arcseconds. At 100x, I was able to cleanly split the two. Their brightness, closeness, and colors are quite striking.
HCG44 is also known as the NGC3190 galaxy group. This group is believed to lie in the vicinity of 60 million light years away (mly). NGC3190, the dominant member of the group, is a spiral galaxy of type Sa-pec. Sa indicates a spiral with a prominent core and tightly wound arms. The "peculiar" designation is due to the apparent distortion of a spiral arm. Photographs show a dust lane that appears to rise well above the plane of the galaxy’s disk. Since we view this galaxy nearly edge-on, the curving dust lane is seen silhouetted against the glow of the disk and hub. Evidently this distortion of the spiral arm is due to interaction with a neighboring galaxy. At 135x, NGC3190 (magnitude 11.2) appeared to me to be about 3’x1.5' in size (which is within the range of sizes listed in various sources) elongated in a WNW-ESE direction. With averted vision, the core appeared compact, but non-stellar. A quote from my log entry reads, "Surrounding haze extends mostly (1’) SSW of core. NNE edge appears sharper than opposite, larger side." At the time I wrote that, I had not seen a photo of NGC3190. Skies at Curby (LAS’s dark site in southern Indiana) that night (3/24/01) were not particularly outstanding. There was a bit of haze. Even so, it seems that I was picking up hints of the dust lane ("NNE edge appears sharper ...") in an 8" telescope! (I love my Celestar 8.)
NGC3190 is evidently interacting with the nearby galaxy, NGC3187. It is assigned a type of SBc-pec meaning that it is a barred spiral galaxy with a small core and loosely wound spiral arms. NGC3187 lies just northwest of NGC3190 with only 5’ separating their centers. However, one source (Nearby Galaxies Catalog, R. Brent Tully, Cambridge University Press, 1988) places these galaxies at the very different distances of 85 mly for NGC3187 and 73 mly for NGC3190. Photographs also show that the major axis of the galaxies are parallel. Note that the depiction of NGC3187 on the second, close-up, chart is incorrect. Mentally rotate its long axis 90 degrees for the correct orientation. (The circle on the second chart represents a 50’ field of view.) Though I tried for sometime to pick-up this magnitude 13.4 galaxy, I was unable to detect it. Even on a very good night, at least 10" of aperture may be required to see this small barred spiral galaxy.
Only slightly "further" from NGC3190, NGC3193 lies 6’ to the northeast. This galaxy is a type E0, nearly "circular", elliptical galaxy. Tully places this galaxy at 75 mly. At 135x, I saw a small, faint, diffuse core surrounded by a 2’ circular haze. This galaxy’s listed magnitude is 10.9.
NGC3185 is somewhat removed from the other three galaxies. It lies about 10.5’ southwest of NGC3190. NGC3185 (magnitude 12.1) is a type SBa galaxy – a barred spiral with tightly wound arms and a prominent core. Again, at 135x, this galaxy appeared relatively large and roughly circular at about 3’x3’. This is about twice the size listed in several sources. (Averted imagination is a wonderful thing.) I glimpsed a dim core with averted vision. Descriptions in the Night Sky Observer’s Guide (by Kepple and Sanner, Willmann-Bell, Inc., 1998) refer to a nucleus that appears stellar, or point-like – contrary to my perception. At 69 mly, according to Tully, this galaxy is somewhat closer to us than the other members of HCG44.
A second source, Sky Atlas 2000.0 Companion 2nd Edition (Strong and Sinnott, Sky Publishing Corporation and Cambridge University Press, 2000), places these galaxies about 20 mly closer than Tully puts them (50 mly for NGC3185, 53 mly for NGC3190, and 56 mly for NGC3193). This closer distance would make these galaxies significantly larger than Tully’s sizes of 39,000 ly, 69,000 ly, 75,000 ly, and 60,000 ly for NGC’s 3185, 3187, 3190, and 3193 respectively.
Regardless of how far away and big they are, this group makes a very interesting and lovely field of view. A telescope of 8 inches or more in aperture will pick-up the three brighter galaxies (all but NGC3187) fairly easily. A 6" scope may also show them since the three are all 11th or 12th magnitude. A 10" may be able to pick-up NGC3187. Individually, these galaxies are best seen at 100x or more. However, as a group, I found a low power, generous, field of view to provide the most pleasing panorama. While they all fit into the 135x, 30’ field, the sense of a group was lost. A 50’, 58x field (illustrated by the circle on the second chart) shows a slightly curving row of three softly glowing, yet distinctly different appearing, galaxies set within a field sprinkled with stars. Let's just say that if you enjoy multiple galaxy fields, then you’re sure to appreciate Hickson Compact Group 44.
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