APOD: The Leo Triplet Galaxies from VST (2011 Aug 03)

[islader2]

ATTN neufer jerrythebiker took you for a ride to Mar 6, 09 APOD. I hope he was sober.

[nobby]

NGC 3628 seems to be about twice as big as the other two, which to a novice like me would mean that it was either twice as big or much closer. Can someone please explain why they are judged to be in the same physical area?

[Ann]

NGC 3628 seems to be about twice as big as the other two, which to a novice like me would mean that it was either twice as big or much closer. Can someone please explain why they are judged to be in the same physical area?

We can be sure that three galaxies are in the same physical area, because they show quite similar redshifts, generally between 700 and 800 kilometers per second. That is to say, all three galaxies are moving away from us at a velocity of between 700 and 800 kilometers per second. Because space is expanding and carrying its galaxies with it, and because expansion-induced velocities of galaxies correspond to given distances from us (more or less), we can be quite confident that the Leo Triplet galaxies are at similar distances from us. They are about 30 million light-years away, as the caption of today's APOD pointed out.

Click to view full size image

Photo: Steve Mandel

But the galaxies also show physical signs of interaction. Look at this image of the Leo Triplet, which you could see if you followed one of the links of today's APOD:

A tidal tail like the one belonging to NGC 3628 is an almost sure sign of interaction. So NGC 3628 is interacting with one or more other galaxies, but which one or which ones? Well, take a look at the neighbourhood of NGC 3628. What other galaxies can you see nearby? That's right, you can see M66 and M65. M65, admittedly, looks quiet and undisturbed, but M66 looks rather warped. There can be no doubt that M66 is interacting with NGC 3628, and there can't be much doubt that M65 is part of the action, too.

Click to view full size image

nobby, you pointed out that NGC 3628 looks much bigger than M65 and M66. Assuming that it really is bigger, would that be surprising or unnatural? Is there, in other words, a "standard size" for galaxies? No, absolutely not. Space is full of large galaxies and small galaxies, and sometimes the small and the large ones interact with one another. Take a look at interacting galaxies NGC5394 and NGC5395, one big and one small:

The picture is by Alex Cherney, amateur astrophotographer, and Noel Carboni, astroimage processing expert from ProDigital Software. Surely Noel Carboni must be "our" Noel C? Congratulations, Noel, on helping Alex Cherney produce such a fine picture of interacting galaxies!








But to summarize: The galaxies of the Leo Triplet are at a similar "depth" from us, are close together in the two other spatial dimensions, too ("up" and "down" and "right" and "left"), and show morphological signs of interaction. They are most certainly a physical group in the same physical area.

Ann

[bystander]

Look at this image of the Leo Triplet, which you could see if you followed one of the links of today's APOD

APOD: The Tidal Tail of NGC 3628 (2007 Jul 27)
http://asterisk.apod.com/viewtopic.php?f=9&t=12659

A tidal tail like the one belonging to NGC 3628 is an almost sure sign of interaction. So NGC 3628 is interacting with one or more other galaxies

APOD: Sideways Galaxy NGC 3628 (2008 May 15)
http://asterisk.apod.com/viewtopic.php?f=9&t=13701

Take a look at interacting galaxies NGC5394 and NGC5395, one big and one small:

The picture is by Alex Cherney, amateur astrophotographer, and Noel Carboni, astroimage processing expert from ProDigital Software. Surely Noel Carboni must be "our" Noel C? Congratulations, Noel, on helping Alex Cherney produce such a fine picture of interacting galaxies!

http://asterisk.apod.com/viewtopic.php?f=31&t=24664

[pgp566]

Well, OK but you don't need a multi-million dollar facility in the Atacama desert - a humble amateur can do this with just as much quality and better colour rendition from his back garden - though this example is downscaled - I will dig out the master image...
http://www.astrocruise.com/galaxies/LeoTrio_07.htm

In the meantime here is a precursor showing the 'duo' part of it:
http://www.astrocruise.com/galaxies/M65-M66_110402.htm
--

[bystander]

Well, OK but you don't need a multi-million dollar facility in the Atacama desert - a humble amateur can do this with just as much quality and better colour rendition from his back garden - though this example is downscaled - I will dig out the master image...
http://www.astrocruise.com/galaxies/LeoTrio_07.htm

In the meantime here is a precursor showing the 'duo' part of it:
http://www.astrocruise.com/galaxies/M65-M66_110402.htm

I will assume, from your tag, you are Philip Perkins from Astro Cruise.

I will agree that 'you don't need a multi-million dollar facility in the Atacama desert" just to take pretty pictures (and you do have some), but can you do important science from your back garden?

[NoelC]

The picture is by Alex Cherney, amateur astrophotographer, and Noel Carboni, astroimage processing expert from ProDigital Software. Surely Noel Carboni must be "our" Noel C? Congratulations, Noel, on helping Alex Cherney produce such a fine picture of interacting galaxies!

Yes, that's me - thanks! That image is the clearest ever taken of those two galaxies. Not surprising, given it was captured through the world's largest telescope! What a thrill to have the opportunity to work with that data.

I knew the press release was going out, but I hadn't run across it online yet myself before today... I wonder if Alex has submitted that image for APOD consideration.

-Noel

[ozalba@aapt.net.au]

Does anyone know what the interloper is to the left of the lower right galaxy (M66)? There is a small red streak followed by a purple streak.

It's one of several pairs of astoid trails: the red/magenta pairing shows that these were consecutive exposures. Elsewhere in the image there are isolated green trails, these coming from an image exposed at another time. I thought the magenta colour was just my work monitor, which has a distinct warm bias, but now I see it is just the strange palette that ESO have used.

[ozalba@aapt.net.au]

It's one of several pairs of astoid trails...

That should, of course, be asteroid...

[DavidLeodis]

It is interesting to read in the full ESO release eso1126 that "Very much closer to home, this image also contains the tracks of several asteroids within the Solar System that have moved across the images during the exposures. These show up as short coloured lines and at least ten can be seen in this picture. As Leo is a zodiacal constellation, lying in the plane of the Solar System, the number of asteroids is particularly high".

[pgp566]

I will assume, from your tag, you are Philip Perkins from Astro Cruise.

Guilty as charged!

I will agree that 'you don't need a multi-million dollar facility in the Atacama desert" just to take pretty pictures (and you do have some), but can you do important science from your back garden?

Agreed, but there wasn't much science in that particular image from the Atacama desert was there? Wasn't it just as much a 'pretty picture' as most amateur images, taken with a few million dollars less outlay, and with rather better colour balance? Gravitational interactions are mentioned of course, but they are referenced just as much, and are more clearly visible, in many amateur images. As you've probably deduced, there are two latent thoughts in this:
1. A rather mediocre illustration of gravitational interaction considering this absolutely HUGE professional facility, in a prime location, provided at considerable taxpayer expense.
2. A preference for using 'professional' images over amateur images even though many of the latter provide _much_ better illustrations of gravitational interaction.
Wasn't producing this kind of result something of waste of taxpayer money when much better can be produced by amateurs at NO cost to the taxpayer at all?

[owlice]

2. A preference for using 'professional' images over amateur images even though many of the latter provide _much_ better illustrations of gravitational interaction.

Preference? What are you talking about? Whose preference? "Using" for what?

[owlice]

I like this part of the field in particular:

Screen shot 2011-08-04 at 10.40.02 PM.png (210.33 KiB) Viewed 1301 times

Isn't that nice?

[bystander]

Agreed, but there wasn't much science in that particular image from the Atacama desert was there? Wasn't it just as much a 'pretty picture' as most amateur images, taken with a few million dollars less outlay, and with rather better colour balance? Gravitational interactions are mentioned of course, but they are referenced just as much, and are more clearly visible, in many amateur images. ...

Wasn't producing this kind of result something of waste of taxpayer money when much better can be produced by amateurs at NO cost to the taxpayer at all?

The science performed at 'professional' observatories is their primary mission. The 'pretty pictures' are just an added bonus.

A waste? Not in my opinion! I'm sensing your real objection is they didn't use your images.

[Psnarf]

n8zrj » Wed Aug 03, 2011 7:44 am
Does anyone know what the interloper is to the left of the lower right galaxy (M66)? There is a small red streak followed by a purple streak.

Thanks, Ann!

Very much closer to home, this image also contains the tracks of several asteroids within the Solar System that have moved across the images during the exposures. These show up as short coloured lines* and at least ten can be seen in this picture. As Leo is a zodiacal constellation, lying in the plane of the Solar System, the number of asteroids is particularly high.

This image is a composite created by combining exposures taken through three different filters. Light that passed through a near-infrared filter was coloured red, light in the red part of the spectrum is coloured green, and green light is coloured magenta.

These are either green or pairs of magenta/red trails. This is because the exposures used to make the green channel of the final colour image were taken on a different night to those used for the red and magenta, which were taken in sequence on the same night.