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wimvb

Dwarf galaxies

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It's always interesting to find out how deep we can actually go with modest equipment (in this case a SW MN190 telescope on a AZ-EQ6 mount, and a ZWO ASI174MM-Cool camera).

Yesterday I posted my image of galaxy ngc 2683 in Lynx.

Since it's clouded over now, I decided to investigate some of the background galaxies in this image. I started with the image solver in PixInsight to list the most common (PGC) galaxies

ngc2683_HSV_RGB_Annotated.thumb.jpg.c007f6d86835b9c841167238e0746680.jpg

But this left some unanswered questions. The obvious one that image solver missed is the small galaxy right next and below of ngc2683. Then there are several other faint fuzzies that the image solver missed. I did an on line search and found an image on a Germain website that gave more information.

http://www.astro-photos.net/CCD/NGC2683_cctv.html

Among others, it showed a very weak dwarf galaxy that should be in my fov.

A further reference to this dwarf galaxy is in a paper on arxiv.org

https://arxiv.org/abs/1511.00955v1

To see if I captured this object, I superstretched the luminance data. I moved in the black point and white point so far that the main galaxy is completely burnt out, and anything faint in the background will show up. Next I inverted the image, so that it will be easier to see dim objects. I then annotated some of the objects. One of two dwarf galaxies from the German site and the cited paper is indeed visible in the lower left part of my image. What is also interesting is the cluster of objects in the upper right corner around PGC3452022. This will need some further investigation.

ngc2683_172_dcv_L_annotated.thumb.jpg.8def26748cb199294b66031cef5feb31.jpg

(click on the image to enlarge it)

Edit (27 jan): New information further down this thread.

Edited by wimvb
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Great post, I never fail to be impressed  by the capabilities of modern imaging technology compared to the emulsion film era.

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On 26/01/2020 at 15:45, wimvb said:

What is also interesting is the cluster of objects in the upper right corner around PGC3452022. This will need some further investigation.

I posted my ngc 2683 on the Swedish astroforum, and got some interesting feedback regarding the objects near PGC3452022 in the upper right corner of my image.

It turns out that this is in fact a galaxy cluster that extends beyond the fuzzy area indicated by the ellipse my image. The cluster name is ZwCl 0848.5+3341 and it has a redshift of 0.38 (NED says 0.37), which puts it at a distance of a whopping 5600 Mly, if I do the calculations right. The galaxies are also giants; the one indicated by the number "8" has a magnitude of 20.8 and a size of 450 000 ly. In comparison, our own Milky Way is "only" 100 000 ly in diameter, and ngc 2683 a mere 78 000 ly. Cool stuff!! I haven't checked these facts (magnitude and size), so I rely on the feedback I got. According to SIMBAD, there are 98 galaxies in this cluster.

Btw, the cluster may extend to the small galaxies indicated by 1 and 5, between the main cluster and ngc 2683. But when I enter their data in Vizier/NED, I get much smaller redshifts. These galaxies should be much nearer.

ngc2683_172_dcv_L_inv_annot.thumb.png.d5e446e3f79c594a13231350721af244.png

Edited by wimvb
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The fact that one has captured light that has traveled more than 5 billion years, is unfathomable, despite the evidence.  

Very interesting, to say the least, Wim!

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It's fascinating how deep you can go with modest equipment. Your MN190/ASI174MM combo seems to perform really well. The 174MM has a higher read noise compared to newer CMOS sensors, which is of disadvantage when you are interested in faint fuzzies. Still you do well! What gain do you use? Do you live in reasonable dark settings?

/Thommy  

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23 hours ago, Thommy said:

It's fascinating how deep you can go with modest equipment. Your MN190/ASI174MM combo seems to perform really well. The 174MM has a higher read noise compared to newer CMOS sensors, which is of disadvantage when you are interested in faint fuzzies. Still you do well! What gain do you use? Do you live in reasonable dark settings?

/Thommy  

Thanks.

Yes, the 174MM-Cool is one of the noisier ASI models. 😋 But it also has larger pixels and gathers more photons/pixel. As long as the exposure time is long enough to drown the read signal, it really doesn't matter that much. I use the camera at low gain (20) where the dynamic range is largest, and use 120 s exposure time with the L filter (240 s for RGB). This gives me good signal but not too many stars overexposed.

My sky darkness is about 20.6 M/arcsecs2, the Milky Way is just visible. There is some glow from Stockholm to the South, but not too bad.

Edited by wimvb
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