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Martin Meredith

The Leo Hicksons

5 posts in this topic

Of the 100 compact galaxy groupings identified by Paul Hickson, 11 are to be found in the constellation of Leo. They are perfectly placed for viewing in spring, and all 11 can be 'had' in a single relaxed EAA session, given a fair wind. Actually, gustiness was the main adversary last night, and it shows in the resulting observations. Still, I managed to take a long look at them all along with a few Arps on the side in a 2 hour session, with longer-than-usual stacks of up 8 minutes and a little longer in some cases. When you think about it, 8 minutes is still a very short time to be watching the details of these beauties emerge.

The Leo Hicksons are numbered 38, 44, 46, 47, 51, 52, 53, 54, 57, 58, and 59. Actually, 53 and 54 are in the same (narrow) field of view, so the task is a bit easier. Here's some of my favourites. 


Hickson 46 LEO 10h 22 1.8 +17° 48 53.6
Smallish linear group in the centre of the shot; surprisingly bright. All four are either mag 16.4 or 16.5, hence one of the most uniform of all groups, adding to its appeal. The middle pair are so close they appear to be interacting. Three of the 4 are classified as active galactic nuclei. The group is flanked at each extreme by a pair of mag 19.8 (B) quasars (marked) with redshifts of 1.97 and 1.48. 

HCG.46_annot.png.a4e6dbb2b7fc12d7f08615871ffdc08f.png

 

Hickson 51 LEO 11h 22 20.9 +24° 17 35.5 = VV 1435
Quite a dense group of 7, split into two subgroups. Brightest is the elliptical NGC 3651 at the centre, with a pair of galaxies very close in. The bright spiral at the base is NGC 3653, and the other spiral in the separate group of two at the top is IC2759. High redshift (z=3.3) quasar at mag 20.9 (B) close to upper group, visible only with imagination (but definitely doable on a less windy night).

HCG.51_2017.3.16_21_10_10.png.51b7956310ae322daba9c7a77b95a128.png

 

Hickson 44 LEO 10h 18 0.5 +21° 48 44.3 = Arp 316 = VV 307
Although I've observed this group before, I was struck by just what a fantastic patch of the sky this is: is there a better one for a small sensor? Various galaxy types are on display, from the elliptical NGC 3193 to the distorted SB spiral NGC 3187, and two SA spirals, NGC 3190 at the centre, and the Seyfert NGC 3185 at the right, showing an interesting ring-like structure. This is the most distributed of all the Hickson groups, being spread across nearly 17'. There's a fascinating paper about the discovery of a giant HI tail in Hickson 44:  https://arxiv.org/pdf/1209.4107.pdf, possibly due to an earlier interaction with NGC 3162 which is now at some distance from this group.

HCG.44_2017.3.16_20_57_52.png.f2984e67d25023d12f678937d718cc66.png

 

Hickson 53 LEO 11h 28 58.3 +20° 46 34.7 = VV 1441
Hickson 54 LEO 11h 29 15.3 +20° 34 42.6 = VV 498

These two groups are visible in the same field. Unfortunately, the wind got up at this point and it shows. The larger group is Hickson 53, consisting of the elliptical NGC 3697 and 3 much smaller members, the faintest of which is just to the upper left of the star near the base. There is another uncertain galaxy near the galaxy pair looking like a speck of dust. This is just 0.1mag fainter than the faintest Hickson member so didn't make the cut.

Hickson 54 is the most compact of the entire catalogue, occupying just 0.73', less than 20th of Hickson 44. Believe it or not, there are 4 components here. Zooming in, 3 separate bulges can be made out. This is a real tough one but likely to be resolvable with the right conditions. 

HCG_53.54_annot.png.54b6e465badf7b4e51d2c25902025748.png

 

Hickson 57 LEO 11h 37 50.5 +21° 59 6.0 = Arp 320 = VV 282 = Copeland's Septet
This is a well-known group of 7 NGC galaxies, to which Hickson added a mag 17.0 8th member. The warped NGC 3753 appears to be trying to swerve its way past its close attendants. One thing I never noticed until last night is the sparse cluster of galaxies to the right of the Septet. This may be a random collection -- Leo is so dense in mag18+ galaxies hereabouts.

HCG.57_2017.3.16_22_36_22.png.9f51d0d56f15b247e1b844a6e9a3599c.png

 

Hickson 58 LEO 11h 42 11.8 +10° 19 1.2
Although its centre is in Leo, this group pretty much straddles the border with Virgo. Of the 5 NGC galaxies making up the group, the central member, NGC 3817 is itself right on the border, which runs perfectly parallel to the lines of declination as if some colonial ruler had drawn it. 

HCG.58_annot.png.8378d09e56b37ecd9c08b857805a4d9a.png

Although Hickson 58 is a marvellous grouping, especially the spiral NGC 3825 with its prominent pair of arms, I was drawn to the coincidental placing of the distant galaxy cluster Abell 1354. In contrast to Hickson 58, whose members are around 300 MLys distant, the mag 18-20 'fireflies' of the Abell cluster lie at around 2 billion LYs. This conjunction was the find of the night for me. If you look closely, the whole shot is covered with galaxies, with a particularly rich group in the upper left, which is part of another Abell cluster (1356). There are even faint galaxies hiding behind the skirts of NGC 3817. There are 6 Abell clusters within about 1 square degree in this part of Leo. 

What struck me seeing these groups in sequence was the tremendous variety in the Hickson catalogue, from the least compact of all Hicksons to the barely-resolvable most compact group. Lots to come back for on a still night...

Cheers

Martin

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Great post Martin, some really interesting observations. You are right about the variety of Hicksons. Hickson 44 has some interesting galaxies with structure which deserves a closer look. Nicely caught.

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Thanks Rob. I could stare at Hickson 44 all night...

Martin

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Posted (edited)

On 3/17/2017 at 23:25, Martin Meredith said:

Of the 100 compact galaxy groupings identified by Paul Hickson, 11 are to be found in the constellation of Leo. They are perfectly placed for viewing in spring, and all 11 can be 'had' in a single relaxed EAA session, given a fair wind. Actually, gustiness was the main adversary last night, and it shows in the resulting observations. Still, I managed to take a long look at them all along with a few Arps on the side in a 2 hour session, with longer-than-usual stacks of up 8 minutes and a little longer in some cases. When you think about it, 8 minutes is still a very short time to be watching the details of these beauties emerge.

The Leo Hicksons are numbered 38, 44, 46, 47, 51, 52, 53, 54, 57, 58, and 59. Actually, 53 and 54 are in the same (narrow) field of view, so the task is a bit easier. Here's some of my favourites. 


Hickson 46 LEO 10h 22 1.8 +17° 48 53.6
Smallish linear group in the centre of the shot; surprisingly bright. All four are either mag 16.4 or 16.5, hence one of the most uniform of all groups, adding to its appeal. The middle pair are so close they appear to be interacting. Three of the 4 are classified as active galactic nuclei. The group is flanked at each extreme by a pair of mag 19.8 (B) quasars (marked) with redshifts of 1.97 and 1.48. 

HCG.46_annot.png.a4e6dbb2b7fc12d7f08615871ffdc08f.png

 

Hickson 51 LEO 11h 22 20.9 +24° 17 35.5 = VV 1435
Quite a dense group of 7, split into two subgroups. Brightest is the elliptical NGC 3651 at the centre, with a pair of galaxies very close in. The bright spiral at the base is NGC 3653, and the other spiral in the separate group of two at the top is IC2759. High redshift (z=3.3) quasar at mag 20.9 (B) close to upper group, visible only with imagination (but definitely doable on a less windy night).

HCG.51_2017.3.16_21_10_10.png.51b7956310ae322daba9c7a77b95a128.png

 

Hickson 44 LEO 10h 18 0.5 +21° 48 44.3 = Arp 316 = VV 307
Although I've observed this group before, I was struck by just what a fantastic patch of the sky this is: is there a better one for a small sensor? Various galaxy types are on display, from the elliptical NGC 3193 to the distorted SB spiral NGC 3187, and two SA spirals, NGC 3190 at the centre, and the Seyfert NGC 3185 at the right, showing an interesting ring-like structure. This is the most distributed of all the Hickson groups, being spread across nearly 17'. There's a fascinating paper about the discovery of a giant HI tail in Hickson 44:  https://arxiv.org/pdf/1209.4107.pdf, possibly due to an earlier interaction with NGC 3162 which is now at some distance from this group.

HCG.44_2017.3.16_20_57_52.png.f2984e67d25023d12f678937d718cc66.png

 

Hickson 53 LEO 11h 28 58.3 +20° 46 34.7 = VV 1441
Hickson 54 LEO 11h 29 15.3 +20° 34 42.6 = VV 498

These two groups are visible in the same field. Unfortunately, the wind got up at this point and it shows. The larger group is Hickson 53, consisting of the elliptical NGC 3697 and 3 much smaller members, the faintest of which is just to the upper left of the star near the base. There is another uncertain galaxy near the galaxy pair looking like a speck of dust. This is just 0.1mag fainter than the faintest Hickson member so didn't make the cut.

Hickson 54 is the most compact of the entire catalogue, occupying just 0.73', less than 20th of Hickson 44. Believe it or not, there are 4 components here. Zooming in, 3 separate bulges can be made out. This is a real tough one but likely to be resolvable with the right conditions. 

HCG_53.54_annot.png.54b6e465badf7b4e51d2c25902025748.png

 

Hickson 57 LEO 11h 37 50.5 +21° 59 6.0 = Arp 320 = VV 282 = Copeland's Septet
This is a well-known group of 7 NGC galaxies, to which Hickson added a mag 17.0 8th member. The warped NGC 3753 appears to be trying to swerve its way past its close attendants. One thing I never noticed until last night is the sparse cluster of galaxies to the right of the Septet. This may be a random collection -- Leo is so dense in mag18+ galaxies hereabouts.

HCG.57_2017.3.16_22_36_22.png.9f51d0d56f15b247e1b844a6e9a3599c.png

 

Hickson 58 LEO 11h 42 11.8 +10° 19 1.2
Although its centre is in Leo, this group pretty much straddles the border with Virgo. Of the 5 NGC galaxies making up the group, the central member, NGC 3817 is itself right on the border, which runs perfectly parallel to the lines of declination as if some colonial ruler had drawn it. 

HCG.58_annot.png.8378d09e56b37ecd9c08b857805a4d9a.png

Although Hickson 58 is a marvellous grouping, especially the spiral NGC 3825 with its prominent pair of arms, I was drawn to the coincidental placing of the distant galaxy cluster Abell 1354. In contrast to Hickson 58, whose members are around 300 MLys distant, the mag 18-20 'fireflies' of the Abell cluster lie at around 2 billion LYs. This conjunction was the find of the night for me. If you look closely, the whole shot is covered with galaxies, with a particularly rich group in the upper left, which is part of another Abell cluster (1356). There are even faint galaxies hiding behind the skirts of NGC 3817. There are 6 Abell clusters within about 1 square degree in this part of Leo. 

What struck me seeing these groups in sequence was the tremendous variety in the Hickson catalogue, from the least compact of all Hicksons to the barely-resolvable most compact group. Lots to come back for on a still night...

Cheers

Martin

Really do like these targets, amazing when you think of the  FOV. 

Edited by 2STAR
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Thanks 2star. I find the 1/2 a degree FOV suitable for lots of objects. At times I'd like to go wider for dark nebulae and open clusters in the main but for galaxy lovers it works well.

Martin

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