All Arps so far
In this topic I am leaving the traditional “eyepiece view” and provide a crop of the original Arp sketches that I have done so far. Therefore, more attention to detail can be achieved. Additionally there is an “inverted color” and enhanced inset with remarks about the Arp details seen (or missed).
All sketches have been corrected to show North ↑ up and West → right.
I will try to sketch every Arp peculiar galaxy with my 16″ from the darkest location possible, preferably from a site with a minimum SQM reading of 21.4. But on occasion I’ll settle for as low as 21.1 (near my home) or go as high as 21.8 (La Palma).
A 16 inch telescope may seem quite large for general amateur astronomy. However, for observing the peculiar features of the Arp galaxies it is rather small and it is therefore that many of the features will not be seen. But that’s OK… with this portfolio of sketches I will still try to provide a guide of what can be achieved with a “mere” 16 inch mirror.
More info about Halton Arp can be found on Wikipedia. Additionally, more info about observing the Arp galaxies can be found on Astroleague and Steve Gottlieb’s website. The complete Arp catalog can be reviewed and downloaded to Excel or Skysafari from Deepskylog, the tool that I use to prepare and log most of my observations.
Last but not least I have to mention one book that I used extensively in my search and analysis of all the Arps; it’s “The Arp Atlas Of Peculiar Galaxies” by Jeff Knipe and Dennis Webb, which contains a wealth of information and which I used as the main data source for my sketches below. It’s a great read and I can recommend it to anyone who is planning to observe the full catalog of 338 objects.
Good luck and above all: have fun!
Arp 13 – NGC 7448
mag 11.6, size 2.7′ x 1.2′
Challenge: Fading texture to the N and SE of nucleus
This is a clear, bean-shaped galaxy with an obvious brightening towards the core. On the S tip very feebly appears one of the detached segments. NW of the galaxy a tripple star can be seen.
Arp 28 – NGC 7678
mag 11.8, size 2.4′ x 1.7′
Challenge: Three arms, one of which is heavy
Very soft and almost round galaxy (face-on) with a compact and somewhat brighter core area, nestled between three brighter stars (and one dimmer). With AV the thicker arm on the S can be seen, mainly because of the darker notch between the arm and the core.
Arp 29 – NGC 6946
mag 8.8, size 11.6′ x 9.9′
Challenge: Five arms
Nicknamed “The Fireworks Galaxy” because of the many supernovae occuring. This is a large face-on with three obvious spiral arms varying in brightness and thickness. The core is small and only a tad brighter than the surrounding (dim) glow. Many foreground stars are visible, embellishing the already splendid view. Two H II knots can be recognized. The fourth arm (detached from the third) and fifth arm were not seen.
Arp 37 – M77 (NGC 1068)
mag 8.9, size 7.1′ x 6.1′
Challenge: The highly textured arms and the knots on the ENE and SW arms. The faint amorphous outer arms
Beautiful face-on galaxy. Extremely bright with stellar nucleus and oval shaped core around it. The outer envelope spans up till halfway a bright star. On the SE side a definite flattening can be seen, here the glow fades more abruptly into the sky background. Two dark lanes can be seen on the SE and NW side, close to the core zone. They give away two spiral arms which can be seen too (with effort), the SE one being the easiest. The start of both arms moving out from the core is a bit brighter. By observing this galaxy at length, you can just “taste” the spiral structure getting through. Fascinating object.
Arp 38 – NGC 6412
mag 11.7, size 2.5′ x 2.2′
Challenge: Northern component
Face-on which appears perfectly round. The glow is very dim and soft. The stellar nucleus is only a bit brighter. A fairly bright star is seen on the S-side of the field. Northern component not visible.
Arp 46 – UGC 12665
mag 15, size 1.2′ x 0.9′
Challenge: Asymmetry and companion to NE and subtle line to the SE
The Arp feature refers to the least brightest galaxy in this field: UGC 12665, but the companion can’t be seen. Instead, a mag 15.8 star can just be glimpsed in the same area. The galaxy itself is very dim and can only be seen with AV as a slightly elongated smudge. The other galaxy, UGC 12667, is brighter and can be seen with direct vision. It is elongated too and bends toward a nearby star.
Arp 56 – UGC 1432
mag 14.6, size 0.9′ x 0.6′
Challenge: Western arm and the knot at its end
Very dim, only seen with AV as a smooth round glow without a pronounced core zone. The spiral arm and the knot at its remained invisible.
Arp 65 – NGC 91 (also NGC 90) and NGC 93
NGC 91: mag 13.6, size 3.0′ x 0.9′
NGC 93: mag 13.3, size 1.5′ x 1.0′
Challenge: All three companions off the ends of the arms
Two galaxies at a large distance from each other. E is NGC 93 and is small, pretty bright, oval and with a distinct core area. The PA can be seen with ease. NGC 91 on the other side is a dim cloud and only seen with AV. No extra details were observed and certainly not the three companions.
Arp 78 – NGC 772, NGC 770 and companions
NGC 770: mag 13.9, size 1.2′ x 0.8′
NGC 772: mag 10.3, size 7.3′ x 4.3′
Challenge: Asymmetric arms and E lobe of 772
Nice and bright couple. NGC 772 is large, oval shaped with a distinct core area. near the edge of the soft glow in the SE a somewhat brighter part of the spiral structure is visible. North of the core is a dark intrusion which gives the impression of a spiral arm moving out. This arm however is not seen. nearby NGC 770 is small, nearly round and has some brightening towards the center. Other companions and the E lobe are not seen.
Arp 81 – NGC 6621 and NGC 6622
NGC 6621: mag 13.6, size 2.1′ x 0.8′
NGC 6622: mag 16.0, size 0.5′ x 0.4′
Challenge: Shape of the NE loop
Compact pair with some nebulosity in between. Brightest and largest is NGC 6621 in the N, it can just be seen with direct vision. NGC 6622 to the S is smaller and quite dim, but it can be seen without much effort. On the SW there appears to be a notch in the nebulosity. The loop was not seen.
Arp 85 – M51 (NGC 5194) / NGC 5195
M51: mag 8.4, size 10.3′ x 8.1′
NGC 5195: mag 10.5, size 5.8′ x 4.6′
Challenge: Spiral arms in 5194; The arm connecting NGC 5194 and NGC 5195; The two fainter wisps running NW and SE of NGC 5195; Absorption structures in each arm of 5194
The “Whirlpool Galaxy“, probably the most famous of all Arps and it provides a fantastic view. The (face-on) spiral structure is seen immediately with ease. The E and brightest inner arm appears “hooked”. The N and S outer arms are dim and only seen with AV. The W inner arm is clearly specked with a multitude of H II knots. A detached section of the core is visible on the NE side.
NGC 5195 shows a brighter core area than that of M51. The companion galaxy is pear-shaped and has a dark intrusion on the W side. Its bar is pointing to the centre of M51. Even though an arm is clearly stretching in the direction of M51’s outer N arm, the famous “bridge” is not seen.
Arp 86 – NGC 7752 and NGC 7753
NGC 7752: mag 14.3, size 0.8′ x 0.5′
NGC 7753: mag 12.0, size 3.3′ x 2.1′
Challenge: Arm between galaxies
Here’s a nice pair. NGC 7753 is the mother galaxy and is (almost) face-on with a bright and soft core and a large surrounding glow. Somewhat further to the SW NGC 7752 can be seen with direct vision. It’s small, compact and equally bright as the core of 7753. It’s not round, but slightly oval shaped. The connection between the two galaxies can’t be seen, but a dark intrusion on the N of 7753’s core betrays a spiral arm departing towards a mag 15.6 star.
Arp 98 – UGC 1095 / MCG+5-4-66
UGC 1095: mag 15.0, size 1.4′ x 0.5′
MCG+5-4-66: mag 16.0, size 0.3′
challenge: The differing arms of MCG+5-4-66
This Arp duo is on the verge of visibility. Both are very small, round and only intermittently seen with AV. MCG+5-4-66 forms a triangle with two mag 14 stars and is just a tad easier to spot than UGC 1095. No details were seen. Very hard observation.
Arp 99 – NGC 7550 group, Hickson 93
NGC 7547: mag 14.7, size 1.1′ x 0.5′
NGC 7549: mag 13.7, size 2.8′ x 0.7′
NGC 7550: mag 12.2, size 1.4′ x 1.2′
Challenge: Connection not seen, but note difference in arm toward and away from E galaxy. Note also material between W spiral and E galaxy.
Arp 99 is a part of Hickson 93 but counts only three galaxies. NGC 7550 is the brightest member of the group and also the largest. Appears perfectly round with a bit brighter core area. NGC 7549 is a pretty large and dim stain and is slightly oval. It points just past NGC 7550. NGC 7547 is the smallest and dimmest one. It’s clearly stretched (2:1) and it too points just past NGC 7550. The light is evenly distributed on the surface. The three galaxies form a nice view and are easy to see. Hickson members NGC 7553 and NGC 7558 were not observed during this session.
Arp 112 – NGC 7805 and NGC 7806
NGC 7805: mag 13.3, size 1.2′ x 0.9′
NGC 7806: mag 14.3, size 1.1′ x 0.8′
MGC+5-1-26: mag 16.5, size 0.6′ x 0.2′
Challenge: N arm of NGC 7806 and asymmetry of MCG+5-1-26
NGC 7805 and NGC 7806 can readily be seen with direct vision. Both are rather small and appear round, although on close inspection NGC 7806 seems a bit stretched. Surprisingly, the neighbour galaxy MCG+05-1-26 can be glimpsed too with much effort. It’s extremely faint and the light of the small streak of light pulsates in and out with AV.
Arp 113 – NGC 67 – 72
NGC 67: mag 15.2, size 1.0′ x 0.7′
NGC 68: mag 14.5, size 1.2 x 1.1′
NGC 69: mag 15.8, size 0.9′ x 0.8′
NGC 70: mag 14.5, size 2.0′ x 1.6′
NGC 71: mag 14.8, size 1.5′ x 1.2′
NGC 72: mag 13.4, size 1.1′ x 1.0′
Challenge: Spiral structure in NGC 70 and NGC 72
A small area rich with galaxies. At low power a combined smudge of light can be seen, but at high power all galaxies can be separated. The brightest three are in the center and form a triangle between three stars. NGC 68, NGC 70 and NGC 71 are well visible with AV and appear similar in size, shape and brightness. At the SE of this group is a dimmer galaxy with a large surrounding glow. This is NGC 72 and is still pretty obvious with AV. E of it is NGC 72A, this one is stellar and can sometimes be seen with AV. W of it is another dim specimen; NGC 69. This one time can only be seen half of the time with AV. Lastly, there are two more difficult galaxies in line with NGC 70 and NGC 68. These are NGC 67 and NGC 67A. These are almost stellar and could only be discovered by use of a detailed chart. No additional details were seen in these eight galaxies in a single field.
Arp 116 – M60 (NGC 4649) / NGC 4647
M60: mag 9.8, size 7.4′ x 6.0′
NGC 4647: mag 11.9, size 2.9′ x 2.3′
challenge: Absorption band on NGC 4647 away from M60
M60 is large, bright and almost perfectly round. There appears to be no visible interaction with the companion galaxy NGC 4647 although they are very close to each other (not in contact). NGC 4647 is softer than M60 and has a smaller core area.
Arp 134 – M49 (NGC 4472)
M49: mag 9.3, size 10.2′ x 8.3′
UGC 7636: mag 14.8, size 1.1′ x 0.9′
challenge: Detect the dwarf irregular galaxy UGC 7636 companion and detect any structure in it
Messier 49 is a large and almost round elliptical, gradually brightening towards the blazing core. In the same field NGC 4467 is visible with AV, but not the fragment UGC 7636. A mag 9 star is close to M49, just touching the edge of it.
Arp 135 – NGC 1023 / NGC 1023A
NGC 1023: mag 9.3, size 8.8′ x 3.0′
NGC 1023A: mag 13.0, size 1.6′ x 1.4′
challenge: NGC 1023A
The “Perseus Lenticular Galaxy“. Large and cigar-shaped with a bright and diffuse core. With effort the galaxy NGC 1023A can be seen by AV on the SE tip as a tine smudge just a tad brighter than the sky background. But one has to know where to look.
Arp 158 – NGC 523
mag 13.5, size 2.5′ x 0.7′
Challenge: Faint ESE extension
Strange object. Hard to see with direct vision as a (slightly bend) stretched galaxy with some central brightening. At both “tips” a knot can be seen. The W knot is brightest and stellar (like a dim star), while the E knot is larger, softer and can only be glimpsed with AV.
Arp 166 – NGC 750 and NGC 751
NGC 750: mag 12.9, size 1.7′ x 1.3′
NGC 751: mag 13.5, size 1.4′
Challenge: Three faint radial companions
Two galaxies are visible in this Arp. Both can be seen and separated easily. The surrounding nebulosity has a droplet shape because there’s a small notch on the E side. On the N side the nebulosity is a bit broader. NGC 750 is the largest and brightest of the two, the core is round. NGC 751 is smaller and oval shaped, the PA can be followed. The companions were not seen.
Arp 168 – M32 (NGC 221)
mag 9.0, size 8.8′ x 6.5′
challenge: The plume
Often overlooked while observing the great M31 nearby. No special detail can be seen. M32 is moderately large and slightly oval shaped. At high magnification the difference in brightness within the galaxies is notable and not equally decreasing towards the outer section; the core is almost stellar and the brightness remains high until 50% outwards, after which it drops significantly. The plume was not seen.
Arp 170 – NGC 7578 group, Hickson 94
NGC 7578A: mag 14.4, size 1.4′ x 1.4′
NGC 7578B: mag 15.0, size 1.0′ x 1.0′
PGC 70936: mag 16.3, size 0.3′ x 0.2′
Challenge: Faint members of Hickson group, and counter-tail
This is a very compact group of many galaxies, of which two are quite easily seen (with AV). NGC 7578A is in the center as a small and round glow, just a bit brighter than NGC 7578B SW of it, which shows a similar size and shape. In the extension of these two a mag 14 star is seen. Very close to this star PGC 70936 seems to blink now and then in and out of view as a very dim star, but it’s a doubtful observation. I did not observe any other members of the Hickson group, while 94C just a bit further away should not be a very big problem to see.
Arp 182 – NGC 7674 Group, Hickson 96
NGC 7674: mag 13.9, size 1.1′ x 1.0′
NGC 7675: mag 14.8, size 0.6′ x 0.5′
MCG+1-59-81: mag 16.1, size 0.4′ x 0.3′
PGC 71507: mag 17.1, size 0.2′ x 0.1′
Challenge: Long straight, very faint filament like bow wave from companion
Compact group of four galaxies, of which three are visible. Also known as Hickson 96.
NGC 7674 is the largest and brightest member, brightening towards the core en with a large surrounding glow. No spiral structure is visible. A very small and dim galaxy is just next to it: MGC+1-59-81. This one is only seen with AV, but still set loose from its neighbour. NGC 7675 can just be seen with direct vision as a small oval, the PA can be seen. There is no brightening towards the core. PGC 71507 is out of reach for now, but should be possible from an even darker location.
Arp 185 – NGC 6217
mag 11.2, size 3.0′ x 2.5′
Challenge: outer filaments
Bright galaxy with stellar nucleus. The start of the N arm can be seen with AV, curling to the E. The S arm is more difficult. Only the start can be seen with AV, but the curl is dimmer and shorter than the N arm. The filaments are invisible.
Arp 212 – NGC 7625
mag 12.1, size 1.6′ x 1.5′
Challenge: Detect the absorption tubes
Compact and bright galaxy, easily seen. The core is not stellair but gets brighter towards the center. A mag 6 star is just outside the field. The edge is soft, but appears flattened in the SE, this gives the galaxy a triangular shape. The absorption tubes were not seen.
Arp 229 – NGC 507 and NGC 508
NGC 503: mag 15.1, size 0.3′
NGC 504: mag 14.3, size 1.7′ x 0.4′
NGC 507: mag 12.2, size 3.1′
NGC 508: mag 14.1, size 1.3′
IC1687: mag 13.7, size 0.5′ x 0.3′
CGCG 502-72: mag 14.5, size 0.5′ x 0.4′
Challenge: Faint outer halo of NGC 507 enveloping NGC 508
NGC 507 and NGC 508 are in the center of the group, pretty close to each other. The halo enveloping 508 is not visible. NGC 507 is brightest and largest, it’s round can be seen easily. NGC 508 just N of it is still pretty bright, small and round and with no central brightening. NW is NGC 503 and this one is very small, dim and can only be seen with AV. SW is NGC 504 and this is the second brightest of the group, to be seen with direct vision. The shape is round and compact. The protrusions are not observed. Two more dim galaxies enrich the field; MCG +05-04-048 (also CGCG 502-72) is very small en dim and can only be spotted with difficulty. IC 1687 was observed as a dim star, so it’s very small (only the core to be seen) but not too difficult with AV. This is a nice and rich Arp group.
Arp 242 – NGC 4676A / NGC 4676B
NGC 4676A: mag 14.7, size 2.3′ x 0.7′
NGC 4676B: mag 14.4, size 2.2′ x 0.8′
challenge: Both tails, differing structure in cores
“The Mice“. Very small and dim ovals, hard to locate. At first (direct) sight NGC 4676B appears brightest with a stellar core, but with AV NGC 4676A swells and the extension can be seen as a straight line (with much effort). The second tail remains invisible.
Arp 269 – NGC 4485 / NGC 4490
NGC 4485: mag 12.3, size 2.3′ x 1.6′
NGC 4490: mag 10.2, size 6.3′ x 3.1′
challenge: Knots, asymmetry and the tail E of NGC 4490
The “Cocoon Galaxy“. This famous duo in Canes Venatici is a real treat in the northern sky. It comprises two galaxies that have an obvious influence on each other. A lot of structure and irregularities can be seen; NGC 4490 is oval shaped and the largest and brightest of the two, with a distinct (mottled) core area and two spiral arms showing a long and flattened “S”. NGC 4485 has a curved “droplet” shape with a loose fragment on top.
A – The core of 4490; bright and mottled, shaped like a stretched “D” or “Δ”. On the SE and NW side two spiral arms are reaching outwards.
B – Slightly brighter part of the northern arm.
C – The SE arm, a bit brighter, thicker and shorter than the N one.
D – A brighter “patch” of nebulosity at the end of the N arm.
E – A streak of nebulosity, like an island, set loose from the galaxy and separated by a dark lane.
F – Dustlane? Or just an empty space between NGC 4490 and the “island”.
G – Suspicion of a dim star, or maybe a H II knot?
H – Fragment, set loose from NGC 4485.
I – NGC 4485; a droplet shaped galaxy, arching towards NGC 4490. The core is small and just a tiny bit brighter.
J – A mag 14.7 star, easily seen at the outer SE region of 4490, embedded in a darker notch.
Arp 273 – UGC 1810 and UGC 1813
UGC 1810: mag 13.4, size 2.0′ x 1.3′
UGC 1813: mag 15.1, size 1.5′ x 0.4′
Challenge: Asymmetrical arms in UGC 1810
Extremely hard observation. UGC 1810 is the brightest of the two, but despite that only seen with AV (mainly the core). However, the extension in both directions is suspected as well as the curving arm on the E side. UGC 1813 is only sometimes seen with AV as a small streak of light and is a threshold observation.
Arp 278 – NGC 7253A and NGC 7253B
NGC 7253A: mag 13.6, size 1.7′ x 0.7′
NGC 7253B: mag 14.4, size 1.6′ x 0.5′
Challenge: Asymmetry in the outer areas
Nice but faint duo. NGC 7253A is brightest and is best seen with AV as a stretched galaxy with some central brightening. Almost perpendicular to it is NGC 7253B and is barely seen with AV as a streak of light. The two are “separated” by a dim double star (m15.4) which give this Arp a nice touch. A dark sky is mandatory.
Arp 281 – NGC 4627 / NGC 4631
NGC 4627: mag 13.1, size 2.6′ x 1.8′
NGC 4631: mag 9.8, size 15.5′ x 2.7′
challenge: Plumes N and S of NGC 4627; filamentary absorption structures throughout body of NGC 4631
This is “The Whale” or “Herring” galaxy and the resemblance is striking. The size of NGC 4631 is enormous and fills a great deal of the field. The core is not clearly defined but looks more as if snowballs have been thrown at it. The surface is highly mottled and absorption lanes can be suspected, running vertically through the center. NGC 4627 can just be seen with direct vision as a dim smudge. A bright star is located between it and the core of NGC 4631.
Arp 282 – NGC 169 and IC 1559
NGC 169: mag 12.4, size 2.7′ x 0.7′
IC 1559: mag 14.7, size 0.8′ x 0.4′
Challenge: The spirals in NGC 169
Two galaxies really close to one another, but seen separated. NGC 169 is stretched and dim, best seen with AV. IC 1559 is even dimmer, smaller and round. It’s nearly perpendicular to the NGC galaxy. A very bright mag 6.3 star adorns the field, but it complicates a good observation.
Arp 318 – NGC 833/835/838/839
NGC 833: mag 12.7, size 1.8′ x 0.7′
NGC 835: mag 12.1, size 1.3′ x 1.1′
NGC 838: mag 13.0, size 1.2′ x 0.9′
NGC 839: mag 13.1, size 1.6′ x 0.7′
Challenge: Tail from NGC 835 toward NGC 838
All four components are seen, but not the streamers. NGC 833 shows a bit of an ellipse and is not noticeably brighter in the center. NGC 835 is the most distinct member one of the group, it’s round with a bright core. NGC 838 is smaller en dimmer, but the stellar core is clearly visible. NGC 839 is a small and round glow without any central brightening, with AV it swells a bit more.
Arp 331 – NGC 379 – 388, Pisces Cloud Galaxy chain
NGC 373: mag 16.6, size 0.4′
NGC 375: mag 15.7 size 1.4′
NGC 379: mag 13.9, size 1.4′ x 0.8′
NGC 380: mag 13.6, size 1.4′ x 1.2′
NGC 382: mag 14.2, size 0.7′
NGC 383: mag 13.4, size 1.6′ x 1.4′
NGC 384: mag 14.0, size 1.1′ x 0.9′
NGC 385: mag 13.9, size 1.1′ x 1.0′
NGC 386: mag 15.4, size 0.9′ x 0.8′
NGC 387: mag 17.2, size 0.4′
NGC 388: mag 15.4, size 0.9′ x 0.8′
UGC 679: mag 16.6, size 1.0′ x 0.3′
Challenge: All twelve galaxies in Arp’s field
In total, 11 galaxies were seen in a field of 23 arc minutes. Most prominent is NGC 383 in the center of the chain. It’s the brightest and largest member of the group. Very close to it is NGC 382, somewhat dimmer and smaller. NGC 380 and NGC 379 to the N are about the same in size and brightness. NGC 379 is the only member in the group that does not appear round, but is shaped like an ellips (2:1). On the S side, NGC 384 and NGC 385 mark the end of the chain. These galaxies are dimmer than the ones in the center and to the N. With some effort NGC 386 and NGC 375 are visible too as small and dim specks in the field. Finally, with a lot of effort and AV, NGC 373; NGC 387 and NGC 388 can be glimpsed as well as tiny specks of nebulosity. UGC 679 remains hidden.
Arp 337 – M82 (NGC 3034)
mag 8.4, size 11.4′ x 4.3′
Challenge: The filaments projecting from the center
The “Cigar Galaxy“. Very bright and very large with many immediately visible details. Three dark lanes, of which one is very apparent, are seen perpendicular to the plane. Additionally, there is a dark “notch” just behind a mag 15 star. The core is split by the the thickest dark lane and has a very mottled appearance. Stunning!