Arp Galaxies (and some others)

[London_David]

I have been intending to spend time exploring the Arp catalogue for a while - particularly since I picked up the excellent Kanipe and Webb book. Finally we had a good streak of weather and I was able to get out the scope.

The following are all from my usual location in Zone 2 London with the associated light pollution. I'm using a ASI290MM for mono and ASI294Pro for colour with a 6” SW PDS150 on an iOptron CEM60. The mount is overkill for the scope, but it has virtually no backlash and is great to use because it just works. I might also get a bigger scope one day…

Unfortunately, my usual process of SharpCap observing, then re-examination in Jocular has been impossible since upgrading to macOS Catalina. This seems to have broken the Python installs on my laptop, so everything is SharpCap.

Generally, I do 10 minutes per object. Some objects I let things run longer. In addition, if the weather is good enough I will leave the scope running on the last object of the night and retire to bed.

One interest of mine is to see what I can get in my backyard in 10 minutes or so with 21st century amateur equipment relative to Arp's original images with state of the art 1960s tech at Mt Wilson and Palomar -- including on the 200 inch Hale telescope. As noted I have only 150mm of aperture, though I do have a much better sensor than film.

Over three nights I managed to cover Arp 23, 29, 36/183, 40, 83, 84, 104, 105, 106, 193, 205, 214, 224, 232/137, 242, 269, 281, 299, 320, 337. I'm posting the more interesting ones below. If anyone is particularly curious about any others I'm happy to upload the images - but they're not too exciting.

In terms of image processing, unless otherwise noted, all that’s been done is stretching, levels, curves and crops. Do note that these are all screenshots - and not even at full resolution either, they're over Remote Desktop with low compression. I have the original data and do sometimes re-process if there is something interesting. I usually use Jocular for that, at the moment I'm using AstroPixelProcessor. However, none of the images below are from APP, they're all screenshots.

Where possible I've not cropped the SharpCap screen grab so you can see settings - though I sometimes reduce resolution of the screen grab to fit the post. Where objects are too small and I don't want to reduce resolution I've cropped in.

Overall, I found that most of these were largely disappointing observations - particularly when I was using the ASI294Pro. The post may be more interesting as a real world example of how the cameras perform, over astronomical observational interest. However, this isn't a camera test, it's an observing session report. That said, one key observation is that over the three nights I made these observations, the ASI294Pro just can't get the details that the ASI290MM can. What you get in colour, you give up in detail. It's not a surprise, but I thought there would be more detail in the colour images.

If you're interested in seeing these objects I strongly recommend Rick Johnson's website: https://images.mantrapskies.com/search where you can see spectacular images of all of these objects and more.  He also provides excellent notes, some of which form the basis of information in this post.

Arp 104

The system is at about 140-150 million light years distance, and the separation between the two galaxies is about 22,000 light years (https://en.wikipedia.org/wiki/Arp_104). A bridge of stars spans between them and spotting that was the excitement here - which didn't work, it’s too faint. I may return to this with the ASI290MM, since it has better resolution and more sensitivity, or I may reprocess the FITS files to see if I can see anything.

The original arp image is here: 

http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp104.jpeg

 

Arp 269

This is another galaxy pair with a bridge. It's not as spectacular as Arp 104 however you can see some of the knotty texture across the system.

The interacting pair is about 25 million light years distance. The level of star formation is similar to larger spiral galaxies - this is presumably triggered by the interaction and also, I presume is why the galaxy shows blue, here and in other images. The matter in the intergalactic bridge originates from the disc areas, and it is roughly between 4 and 17 million years old which is when the interaction occured (https://academic.oup.com/mnras/article/459/1/683/2608786). 

The original Arp image is here:

http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp269.jpeg

 

Arp 281

Arp281 is about 30 million light years distant and NGC4631, the large edge on barred spiral galaxy, about 140,000 light years across. The smaller galaxy is estimated between 500,000 and 1 million light years distance from the larger galaxy.

10m52s @15s exposure

 

Arp 320

10m 5s @ 15.9s exposure.

This is also known as Hickson 57 and Coplands Septet. The group is about 400-450 million light years distant.

Again, a disappointing level of detail here. There's just not enough resolution in the system to see a lot.  There may be more information in the data, but that would require reprocessing.

The original Arp image is here:

http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp320.jpeg

And for a proper view of this cluster Rick Johnson's image is great:

https://images.mantrapskies.com/catalog/ARP-GALAXIES/ARP320-NGC3746-NGC3745-NGC3748-NGC3750-NGC3751-NGC3753-NGC3754-PGC036010/NGC3753L4X10RGB2X10X3R2-ID.JPG

 

NGC4244

Not an Arp but in the vicinity of some, so I thought I'd take a look while I was in the neighbourhood. This is the Silver Needle Galaxy, again, colour is nice, but for me it doesn't make up for the lack of detail. Part of that is the light pollution, no doubt. However, the ASI290MM would definitely be getting more detail in this.

The galaxy is 65,000 light-years across and lies roughly 14 million light years distant. 

As ever, Rick Johnson has a great write up and set of images: https://images.mantrapskies.com/catalog/NGC/NGC4244/index.htm

 

Arp 84

I was much happier with the outcome on this one. There isn't a huge amount of detail but you can see some of the interaction and the colour adds to the reading of the spiral, which I take to indicate a redder older core and bluer younger spiral arms. The galaxies are about 330 million light years distant.

Arp's original's image is here: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp84.jpeg

I returned to this with the ASI290MM and found much more detail.

This was a longer integration at 76m 28s. That was 347x13.2s exposure. I know those numbers don't quite add up but I left this running when I went to bed and that's what SharpCap told me the stack was.

There is also some stacking artefacts on the ASI290MM image, the repeated pattern of dots leading off the spiral arm - this isn't an object. You can see the repeated pattern in the lower right of the frame, as well as to the upper left. I'm not sure where they come from. I presume it to be some sort of dust on the sensor or scope. If anyone has any ideas - it would be good to hear.

I'm sure there is more information in the ASI290MM data than you can see here, however it will need re-processing in APP.

Using just the screenshots I combined the colour and mono images to get:

 

Arp 224

NGC 3921, the larger galaxy is about 59 million light years away and is the result of a merger about 700 million years ago. I was hoping to see the loop structure here more clearly. It is barely visible, as you can see more clearly on the inverted image.

 

Arp's original's image is here: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp224.jpeg

 

Arp 193

I spent a lot longer on this than I would normally - 268x8s for a total of 35m 44s. This was for two reasons, first the Hubble images of this are quite spectacular and I wanted to see if I could push for more detail (https://en.wikipedia.org/wiki/IC_883). The internal dust lanes are stretched like candy and there is an interesting stream of stars extending for some distance away from the central galaxy. The second was that I made myself some tea, then got distracted looking at something else. When I returned some time had passed...

The galaxy is about 320 million light years distant. It's about 65,000 light years thick and 131,000 light years long.

The stream is not barely visible on the standard view. Inverted it is easier to see.

Arp's original's image is here: http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp193.jpeg

Edited April 10, 2020 by London_David

[Mike JW]

Hi David, Enjoyed your post and it is of value as you indicate to show others what can and cannot be achieved. 

Just a thought - noting how Martin has set up a thread for all future Arp-Madore postings. Would it be worth making this thread one for all future Arp Postings thus keeping all Arp reports in one place rather than them getting lost amongst the many posts. If you thought this is a good idea (or anyone else reading this), if you have a suitable data table, (list Arps, ID, RA/Dec, details) to add into your current post that folk could download that would be good. I have a basic one I made up in excel but needs some refinements. The "mantrapskies" link is first class and I use it all the time. I have various Arps that I had not got around to posting. I shall wait but if you like the idea of a single Arp thread I could add them to this one.

Noting Martin's thread I had been wondering whether to set going a Hickson thread - what do you think (or anyone else reading this).

Thanks again.

Mike

[London_David]

I think single Arp and Hickson threads could be a good idea. I certainly enjoy seeing different observations of the same objects from everyone. However, I suppose it depends on how much other people would want to post and it. I'd be happy posting to a single thread, but I don't get a huge amount of clear nights to get the scope out.

If so, I would be inclined to start an Arp thread fresh rather than use this one. An Arp thread probably doesn't need my long intro at the top... and the Silver Needle shouldn't be in there. Happy to repost some of these though. 

I don't have a data table. Though I'll take a look at creating one. I use an observing list set up in SkySafariPro 6 (I use SS6 to control the mount). It's relatively rough and ready. It was quickly put together using the SS6 search function and probably has duplicates. I know that can be exported. I'll have to see if I can export it as an excel file or a CSV which could then be tidied up. I'll see what I can do.

If I can do a useful observing list from my SS6 list,  I'll start an arp thread. Otherwise -- you can start it and post your images first!

[Martin Meredith]

I haven't had time yet to pay these great images all the attention they deserve -- later! But just to say it would be great to have an Arp thread (same goes for Hicksons too). I have a data table for the Arps that I'm happy to share too in such a thread (might take me until later tomorrow to bash it into shape).

David, I'm planning to upgrade my Mac soon so I'd be interested to know what problems you're having with Jocular/Catalina at some point as I may run into them too! You might have noticed I posted a simpler installation procedure in case you decide to reinstall from scratch. In fact, I did a complete reinstall of Python myself this week and it turned out be quite painless using the miniconda approach that I'm now recommending.

Martin

[Mike JW]

Hi Martin and David, that makes three of us who like the idea of a single thread. Anyone else out there who thinks the same? Mike

PS. Just checked what data sheets I have. I could post basic Arp and Hickson lists in excel. I am happy to initiate these two threads but I will wait to see if there is more feedback and thoughts from others.

Edited April 10, 2020 by Mike JW
added some more information

[roelb]

Hi all.

I'm also interested in separate object type threads.

For Arp's I like this: Arp.Catalogue.xls

 

[Mike JW]

Hi Roelb, Thanks for your support and catalogue.

I will go ahead and initiate a thread, hopefully Monday. Mike

[Martin Meredith]

Great collection of Arps there, many of them new to me. I have one of Arp 84 (looks like a stork or flamingo when oriented vertically). Arp 104 is another favourite and a real challenge to get the stellar bridge. Once we have the Arp thread I'll post an image but I recall it took a long sequence to get any sign of it, and it needs a horrendous dust-shadow inducing stretch. I'd be very impressed if you can get it from London!

Talking of dust, those artefacts look like hot pixels to me, but hot pixels that have been image processed somehow. Were you using some kind of noise reduction in Sharpcap or other similar process? One might get those shapes by processing pixels with some kind of weird convolution. It would be interesting to find out. Are they point-like on the individual fits files?

Martin