Andromeda VII - a dwarf galaxy in Cassiopeia

[wimvb]

Unexpected clear skies and not in the mood for a new long time project, so what do you do? You go for the faint objects. That makes perfect sense, doesn't it.

Yesterday night we had a few hours of clear-ish skies, so I pointed my scope at this faint dwarf galaxy. It is a satellite of the Andromeda galaxy, hence its name: Andromeda VII. This spheroidal galaxy is situated in the constellation Cassiopeia, hence its other name: Cassiopeia dwarf. Scientists refer to it as PGC 2807155.

I could find only three images in a Google search, one from the HST, one from the Keck telescope, and a rather blurry one from an amateur.

This galaxy was discovered in 1998 by Russian and Ukrainian astronomers, and originally named the Cassiopeia Dwarf Spheroidal Galaxy. It is located 1 600 kLy distant, and being behind the Milky Way plane, it is obscured by dust and stars.

Technical data:

Imaged with a SkyWatcher 190MN, and ZWO ASI294MM camera with Optolong LRGB filters

Total exposure time 200 minutes.

Quick process in PixInsight

There is dust from our own galaxy in the image, hence the uneven, mottled background (which actually is the foreground, of course).

 

Edited September 26, 2022 by wimvb

[josefk]

love it 👍

[gorann]

Love it too! And discovered in 1998 by Russian and Ukrainian astronomers. Times are changing.....

[wimvb]

57 minutes ago, josefk said:

love it 👍

 

15 minutes ago, gorann said:

Love it too! And discovered in 1998 by Russian and Ukrainian astronomers. Times are changing.....

Thanks, both

I was a bit careless when collecting data. It seems that Ekos was still set to a gain of 200, from an earlier session. This caused an error in calibration (my darks are at gain 0), and may very well have contributed to the mottled background. Oops. If I decide to collect more data on this object, I will have to be more carefull.

[gorann]

Well, we optimist just call mottled data IFN😄

[symmetal]

Thanks for posting Wim. Impressive. I've imaged a few dwarfs before as they don't get the attention compared to the usual objects, and an image you create can easily be one of the best amateur ones around. 😊

I've been searching for any reference information on dwarf galaxies and there aren't many. Two I've found are

The observed properties of dwarf galaxies in and around the Local Group, McConnachie, A.W. 2012, with an updated 2019 table a bit further down.

Dwarf galaxies of the Local Group, Whiting A. B. 2007

The Whiting paper has two tables, one of Local Group candidates and one of Local Group non-candidates and most of the commonly named ones seem to be in the non-candidates list. I've haven't checked what is meant by non-candidate though.

There doesn't seem to be any 'official' convention in their naming so it's hard to integrate the lists. A nice neat table of various names, RA, Dec, apparent size and apparent brightness would be handy. Maybe I'll try and make one. 😛

The closest Dwarf Galaxy to us is what's left of the Canis Major Dwarf, also called the Canis_Major_Overdensity which is 12 degrees across 😮  and is now located within the Milky Way. It has been torn apart by tidal disruption such that it forms stellar streams which wrap around the Milky Way three times, called the Monocerus Ring. It's hard to see the core of the Dwarf apparently, as it's obscured by dust, and I couldn't find any wide field images of that area that shows it. It's also disputed as to whether the Monocerus Ring is derived from the Canis Major Dwarf though.

Alan

 

Edited September 26, 2022 by symmetal

[Paul M]

I don't think I'd even heard of this object before now. Very interesting. I wonder how it would look without our own galaxy getting in the way? 

Difficult to determine it's extent in your image Wim. I seem to be picking out some structure in the "background" that is concentric with the obvious central structure and out to some distance.

Maybe my eyes playing up.

[wimvb]

1 hour ago, Paul M said:

Difficult to determine it's extent in your image Wim. I seem to be picking out some structure in the "background" that is concentric with the obvious central structure and out to some distance.

It’s just the central gray smudge, the rest is interstellar dust or maybe ifn.

[wimvb]

1 hour ago, symmetal said:

I've been searching for any reference information on dwarf galaxies and there aren't many. Two I've found are

Thanks for those references. I’ll have a look tomorrow.

I’ve imaged a few dwarf galaxies before, among others the Ursa Major dwarf UMa1. Atm, I’m working on an image showing three dwarf galaxies belonging to ngc 7331.

https://www.astrobin.com/0gvm5z/

 

[symmetal]

1 hour ago, wimvb said:

I’ve imaged a few dwarf galaxies before, among others the Ursa Major dwarf UMa1. Atm, I’m working on an image showing three dwarf galaxies belonging to ngc 7331.

Yes, I remember you posting them here. 😀

I've currently done the Ursa Minor Dwarf, Draco Dwarf, Regulus Dwarf and Leo II Dwarf. 🙂

I found this great image on Wikipedia showing the Local Group with all the Dwarf galaxies, and how close The Milky Way and Andromeda are, along with there future collision location. Your Cassiopeia Dwarf location is shown too. Would be nice as a wall poster but would use a lot of ink. 

The Canis Major one I mentioned before is listed here as unidentified. This image and the table on the Wiki page is as good as any to use. 😀

Alan

 

Edited September 27, 2022 by symmetal

[wimvb]

5 hours ago, symmetal said:

I found this great image

Very interesting. I sense that a deep field image of ngc147 is due…

[wimvb]

On 27/09/2022 at 07:29, wimvb said:

Very interesting. I sense that a deep field image of ngc147 is due…

@symmetal, just a quick follow up. The last two nights I've pointed my scope at ngc 147, but unfortunately managed to collect only 8 (!) usable subs due to clouds. I've integrated the subs, and even in an extrene stretch, there is no background structure at all visible in this galaxy's neighbourhood. But the galaxy does extend further than what is normally shown.

I will collect more data, just to make sure, but for now it seems that this spheroidal galaxy is "exceptionally ordinary".

[symmetal]

Hi @wimvb, That's a pity Wim. There are some Hubble Pictures of NGC147, but they only show detail around the core which doesn't help show any debris that is indicated on the Local Group poster. I wonder where they got the information that there is debris as indicated.

This other NASA image  of NGC147 and NGC185, shown below, has far too much jpeg compression with noise reduction to show anything interesting. It seems the Cassiopeia II dwarf is also part of this stable binary galaxy system though. Not sure if that's the one you imaged. 🙂

Alan