Just how far away are faint fuzzies?

[661-pete]

Yes, I know this is a bit of a 'how long is a piece of string?' question!

Arising out of a light-hearted discussion I had yesterday (off forum), with someone who had done a presentation about how far back in time we can 'see' - I started thinking about the hordes of faint background galaxies, down to about mag. 17-18. The ones that you can see in just about any galaxy deep-sky image, posted on this forum or others.

I said, judging by their size and brightness, a lot of these fuzzy blobs must be a good 500-600 million light years away, and hence offer a sizeable slice back in time through the age of the Universe. He said, no, they're not as far away as that.

Cartes du Ciel, with the PGC catalogue installed, isn't much help: it doesn't even show redshifts for most of its entries.

Who's right?

[damnut]

Hmm, not as far away as 600 million light years. Guesstimates on the age of the universe is c14 BILLION years. From memory furthest galaxy and faintest is a galaxy viewed by Hunbble at 13.2 Billion light years away.

Good thread!

[ncjunk]

Well. Looking up stephan's quintet 1 is 37 million light years and the others 200 to 300 so i would side with you!

I'd think some of these faint fuzzies in photos would be further away than that.

[ncjunk]

Ic4617 is next to m13 and is mag15 ish and 490million ly away.

So i wonder how far some of these other background faint fuzzies we image are?

[umadog]

Things such as nebulae and planetary nebulae are hundreds to thousands of light years away, since they're within our galaxy.

The furthest known milky way globular is around 250,000 light years away.

The Andromeda galaxy is about 2.2 million light years.

M81 and M82, which are pretty bright, are 11 million light years away.

The galaxies in Markarian's Chain (Virgo cluster) are 50 to 60 million light years away.

All of the above are easy telescope and binocular targets.

Stephan's quintet is covered in a previous post. The Perseus A cluster is a comparable distance (240 mly) and, like the Quintet, also visible in a larger scope and/or from dark skies. Those are pretty faint, though.

So most things we see visually are within 300 mly. However, there are quasars... The brightest is 3C 273 in Virgo, that's 2.5 billion light years away. It's mag 13, so is easily visible with a small scope. With a really big scope from dark skies, the Einstein Cross is reputed to be visible and the shape discernible if seeing is good. That's 8 billion light years away.

[mdstuart]

Thats my understanding umadog on the visual stuff. I suspect the background galaxies in the images are 300mly to 1,000 mly but the best plan would be to look up the redshift on the NEDS databse to be sure...

Mark

Of course that is if all the science on RV is right. After all some galaxies have a negative RV!

[swamp thing]

That begs the question is a Quasar a faint fuzzy?

Or one bright mother?

Regards Steve

[Andymac79]

Could 3C 273 in Virgo be imaged with any of the kit people have on here?

Andy

[cantab]

That begs the question is a Quasar a faint fuzzy?

Or one bright mother?

Regards Steve

Well, it's apparently faint (even though the absmag is huge). But it sure ain't fuzzy ("quasi stellar object").

[661-pete]

Could 3C 273 in Virgo be imaged with any of the kit people have on here?

Certainly, but for most people it would only appear as a 'star'. As an example, with my imaging setup (sig.line) I can reach down to magnitude 18 on a good night, whereas 3C273 is magnitude 13. I believe images of it have been posted on SGL.

[dph1nm]

Actually 17-18 is quite bright for galaxies - they are still outnumbered by stars in our galaxy at that magnitude. Even so, the average distance at that magnitude is probably around 200-300 Mpc (maybe a little higher), so about ~1000 million light years.

NigelM

[Syntarsus]

There are surely two distances to consider when it comes to far off objects.

One is the distance to object when the light you see left the object. But because the universe is expanding that object will now be much further away. If the light left a galaxy a billion years ago that galaxy has had a billion years to move that much further away; presumably a pretty long way.

[661-pete]

Seems most people back my idea that the faint fuzzies on a lot of our deep sky images are several hundred MLY away.

I thought of looking into supernovae, since SN type Ia's are regarded as a reasonably reliable 'standard candle' all with an absolute magnitude of about -19.3.

Excluding SN2011fe which is rather a 'special case', there seem to have been a whole load of type Ia's in recent years which peaked at around mag. 16.5. If I remember the formula right:

D = 10 ^ ((m-M)/5 + 1) parsecs

that gives a distance of about 145 million pc, or about 470 million LY. So I would imagine, a lot of these SN's are in the very same 'faint fuzzies' that I'm talking about.

Of course this calculation takes no account of redshift, or (as syntarsus points out) of the expanding universe...

[ncjunk]

There are surely two distances to consider when it comes to far off objects.

One is the distance to object when the light you see left the object. But because the universe is expanding that object will now be much further away. If the light left a galaxy a billion years ago that galaxy has had a billion years to move that much further away; presumably a pretty long way.

But in the context of the original discussion it was the distance based on the light seen and that this gives a decent view into the past. The difference between actual and perceived distance probably is not too important for a friendly argument....and if its down the pub facts get very sparse after the third pint!

[acey]

S@N offered this distance viewing challenge:

1,500 lightyears - The Orion Nebula

7,000 lightyears - The Double Cluster

21,000 lightyears - The Great Cluster

40,000 lightyears - M2

2.4 million lightyears - The Andromeda Galaxy

72 million lightyears - M49

300 million lightyears - The Coma Cluster

500 million lightyears - Hercules Galaxy Cluster

1 billion lightyears - Corona Borealis Cluster

2 billion lightyears - 3C 273

Source: How far can you see?

I've viewed the brightest members of the Hercules Cluster, Abell 2151 (mag 13.5) with a 12". The Corona Borealis cluster has brightest member mag 16.5 and is a challenge for large aperture scopes. 3C 273 is visible in a small scope (I believe some have managed it with a 4") and is star-like, not fuzzy. I've never tried.

Galaxies at mag 17-18 could be a couple of billion light years distant, or else closer dwarfs. The star-like components of the Einstein Cross (8 billion light years) are mag 17-18 and rate as an "ultimate challenge" for big scopes and dark skies.

http://astronomy-mall.com/Adventures.In.Deep.Space/ultimate.htm

[Uranium235]

Thanks for that, Ive often wondered just how deep I could go with my gear. My limit so far is the Coma cluster, so it would be nice to try and push a little further out