Live captures in Cetus

[Martin Meredith]

Although it never gets really high even at my moderately southern latitude (42 N), Cetus is jam-packed with galaxies, and December seems to be a good time to make the most of them at sociable hours. I spent a fair amount of time looking at Arps and galaxy groups, plus a local group dwarf galaxy, which I'll post later in this thread. But the configuration I most enjoyed seeing was the group of stars in the same field as the NGC 349 group, which due to the orientation of my sensor appears like a celestial question mark, or maybe an ampersand. The NGC galaxies range from mag 14 to 16 but there are several equally-bright galaxies in the field which, surprisingly, don't make it into the NGC or IC catalogues e.g. the one just above the bright star, or to the south NGC 347 (which looks to be as bright as NGC 347), or the one to the right of NGC 350. These all have PGC designations. The group is more extensive than I was able to fit in the Lodestar FOV. Nearby is NGC 356 which is also known as VV 846. Just to the south are a pair of interesting-yet-contrasting spirals, NGC 337 and 337A which I'll also post later.

As an aside I've been experimenting with live LRGB. The idea is to get the best resolution/depth from the luminosity (the above image) and add in some colour. This is the result of adding some RGB into the image (4x30s of each) to bring out the bright yellow star (HD 6031, which has a B-V value of 1.6). So far I'm finding that the L is dominant and I have to push the saturation quite a way up to achieve sufficient colour. There are almost certainly better ways to combine luminance and chrominance (live!)...

Martin

[Martin Meredith]

I started out the session with IC 1613, a dwarf galaxy which is a member of the Local Group at just over 2 million light years distance. This was a tough one to pull out from the gradients arising from local streetlights and the moon, but still the typical sparse structure of a dwarf is seen. 

I was going to write something about this galaxy but I found an authoritative source of information at ESO which, amongst other things, explains how this galaxy helped in working out cosmic distance scales due to the presence of Cepheid and RR Lyrae pulsating variables.

Martin

 

[Martin Meredith]

If you look at one of the wider field photos in the ESO web page I mentioned in the last post, you can spot a slither of light below and left of IC 1613. This is known as FGC 124 from the Flat Galaxy Catalogue. This catalogue was compiled in 1993 and contains 4455 galaxies whose major axes are at least 7 times larger than their minor axes. There is also a revised FGC and only this year a sample of 817 ultra-flats (axis ratio > 10) has been selected from the RFGC.... so plenty to go looking for.

I've also marked what I think is a mag 18.3 (v) quasar whose light has taken around 10 billion years to reach us. It is in the correct position but seems a little on the bright side, though I find no evidence of a star in that position.

Just to the north (and to the east of the dwarf IC 1613) is Abell galaxy cluster 147 which has the mag 6.4 star 29 Cet at its southern edge (just visible at the top of this capture). These galaxies are all fainter than mag 15. At the lower edge, left of centre, is another flat galaxy that is poking out from what looks to be a star. This one is from the 2Mass Flat Galaxy Catalogue.

Martin 

[Martin Meredith]

Less than a degree to the south of the NGC 349 group at the head of this thread are a pair of galaxies that appear quite similar on charts, but which demonstrate that you never know what you are going to get until you look. NGC 337, on the left of this composite shot, is a mag 12 spiral with a surface brightness of 21.5 (quite bright). NGC 337A, which is immediately E of NGC 337 is another spiral, listed as magnitude 12.9. However, its SB is 24.3, nearly 3 full magnitudes fainter than NGC 337. And it shows. 

NGC 337 isn't listed as a peculiar galaxy yet I've seen peculiars which look more normal. It is hard to count the number of arms in this image; some of the bright patches could be star-forming regions I suppose. 

I'd be interested in finding out why one is 337 and the other 337A.

Martin

[Martin Meredith]

Here's one of the two Arps I looked at last night during my Cetus session. Arp 140 is one of the clearest examples I've seen of an interacting spiral-elliptical pair. According to this 2007 paper, there is a C-shaped 'tail' of gas extending some distance from the pair -- but it is so faint as not to be visible here. The length of the tail suggests that we are observing the interaction at an advanced stage. 

The structure of the rightmost member of the pair (NGC 275) is fascinating, with 4 clear dense areas and a number of fainter densifications visible on the upper edge. This galaxy is so bright that the DSS image is burnt out. The elliptical is NGC 274, and also in shot is the mag 13.9 spiral NGC 273.

Arp 140 is sandwiched between Abell 108 about 0.5 degree to the north and Shakhbazian 309 about 20' to the south. Here's a shot of the latter:

Believe it or not, with 14 listed members in the range 17.5 to 19.8, SHK 309 is quite bright as Shakhbazians go! In fact, there are other galaxies in the field too. The only distance estimate I have is 1.28 billion light years for the brightest member. The 'bright' mag 16.2 spiral to the south is 4 times closer.

Here's an inverted and auto-white balance shot (not sure why it came out pink -- I thought I was capturing in mono...) oriented with N to the top to compare against a chart showing the 14 members.

Thanks for looking

Martin

 

[RobertI]

A fascinating selection of objects, nicely captured and researched as always. I always learn something new from your posts - thanks for posting.

[stash_old]

I totally agree with RobertI you all ways give us a great deal of info and ,for me anyway, makes me look harder. Keep it up thanks.

 

 

 

[Martin Meredith]

Thanks Rob and Stash. I too learn a lot while checking out what I've been observing! 

A case in point is this shot of NGC 309 that I observed on the same night. I had it on my list as it was right next to an Abell Galaxy Cluster and I thought the conjunction would be interesting. But the more I looked into NGC 309 the more fascinating it appears.

 

This beautiful mag 12.7 face-on galaxy is one of the largest spiral galaxies known. It has bright yet exceedingly thin arms. According to this article, it also has two short 'dumpy' red arms in the central zone corresponding to the older stellar population, and no fewer than six blue arms (in two groups of 3), representing the young stars!

Halton Arp, in his Catalogue of Discordant Redshift Associations (p31) has an image of M81 superimposed on NGC 309, showing how M81 would fit in between a pair of knots in one of the spiral's arms. I've tried to replicate the size difference in this zoomed image.

Arp was arguing that since M81 is itself a large galaxy (and very close at under 12 million LYs), the size of NGC 309 implied by its redshift distance of 269 MLY was not believable, calling into question the whole notion of the reality of the redshift-distance relation. Arp also argued that if it were really that large, it would provide 5 supernovae a year. In fact, it has hosted 3 or 4 in the last 8 years that have been spotted, so is one to keep an eye on.

Another way to judge the size of NGC 309 is to consider that the rather sparse Abell Galaxy Cluster 117 is at a distance of about 800 MLY. This is only 3 times the distance of NGC 309, yet the member galaxies that appear as fuzzy dots are tiny compared to the giant spiral. The size difference is best seen by looking at the mag 18.3 galaxy (PGC 984505) that I've marked (unlabelled) just to the N of NGC 309 (just off the end of the upper arm) which is at around 780 MLY and may be part of the cluster. NGC 309 really is huge!

There is more in this image. There are a couple of recently-discovered compact groups marked that were identified in the Sloan Digital Sky Survey. The one closest to NGC 309 is very faint and only the central member of 4 is (just about) visible in my image. I had more success with the other one marked, which has 5 members all resolved.  Finally, there is a mag 19.3(v) quasar shown in the zoomed image with a redshift of 1.65, equivalent to a distance of 8-10 billion LY. Taking the foreground stars into account, there is real depth of space visible here even in the zoomed image!

Martin

 

[RobertI]

Its hard to grasp the size of a really large galaxy such as that, even when compared to a galaxy we already know and love. If it were as close as M81 it would look spectacular in our skies, although it probably would have eaten the Milky Way long ago!

[2STAR]

On 12/6/2016 at 18:41, Martin Meredith said:

Here's one of the two Arps I looked at last night during my Cetus session. Arp 140 is one of the clearest examples I've seen of an interacting spiral-elliptical pair. According to this 2007 paper, there is a C-shaped 'tail' of gas extending some distance from the pair -- but it is so faint as not to be visible here. The length of the tail suggests that we are observing the interaction at an advanced stage. 

The structure of the rightmost member of the pair (NGC 275) is fascinating, with 4 clear dense areas and a number of fainter densifications visible on the upper edge. This galaxy is so bright that the DSS image is burnt out. The elliptical is NGC 274, and also in shot is the mag 13.9 spiral NGC 273.

Arp 140 is sandwiched between Abell 108 about 0.5 degree to the north and Shakhbazian 309 about 20' to the south. Here's a shot of the latter:

Believe it or not, with 14 listed members in the range 17.5 to 19.8, SHK 309 is quite bright as Shakhbazians go! In fact, there are other galaxies in the field too. The only distance estimate I have is 1.28 billion light years for the brightest member. The 'bright' mag 16.2 spiral to the south is 4 times closer.

Here's an inverted and auto-white balance shot (not sure why it came out pink -- I thought I was capturing in mono...) oriented with N to the top to compare against a chart showing the 14 members.

Thanks for looking

Martin

 

Nice reading & interesting Martin

[Astrojedi]

Thanks Martin. Very well researched and a very interesting read.