APOD: The Leo Trio (2019 Apr 18)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4439
Joined: Fri Dec 04, 2009 3:27 am

APOD: The Leo Trio (2019 Apr 18)

Post by APOD Robot » Thu Apr 18, 2019 4:06 am

Image The Leo Trio

Explanation: This group is popular in the northern spring. Famous as the Leo Triplet, the three magnificent galaxies gather in one field of view. Crowd pleasers when imaged with even modest telescopes, they can be introduced individually as NGC 3628 (left), M66 (bottom right), and M65 (top). All three are large spiral galaxies but they tend to look dissimilar because their galactic disks are tilted at different angles to our line of sight. NGC 3628, also known as the Hamburger Galaxy, is temptingly seen edge-on, with obscuring dust lanes cutting across its puffy galactic plane. The disks of M66 and M65 are both inclined enough to show off their spiral structure. Gravitational interactions between galaxies in the group have left telltale signs, including the tidal tails and warped, inflated disk of NGC 3628 and the drawn out spiral arms of M66. This gorgeous view of the region spans almost two degrees (four full moons) on the sky. The field covers about a million light-years at the trio's estimated distance of 30 million light-years. Of course the spiky foreground stars lie within our own Milky Way.

<< Previous APOD This Day in APOD Next APOD >>

shaileshs
Ensign
Posts: 50
Joined: Mon Mar 13, 2017 8:14 pm

Re: APOD: The Leo Trio (2019 Apr 18)

Post by shaileshs » Thu Apr 18, 2019 4:23 am

Hello,

I wonder -

1. why tidal tail of left galaxy and drawn out spiral of right bottom galaxy are not towards eachother ? Their direction gives no clue if there was any interaction between them..

2. Stars with spikes visible are in our own milky way but -
a. the objects without spikes - are they stars or galaxies ?
b. If galaxies, are they nearer (but faint) than these 3 shown or way far out ?
Without doing scientific observations and knowing, just by looking at such image, is there anyway we can guess/tell ?

Thanks in advance for all comments/answers/clarifications.

User avatar
Ann
4725 Å
Posts: 11567
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Ann » Thu Apr 18, 2019 5:49 am

shaileshs wrote:
Thu Apr 18, 2019 4:23 am
Hello,

I wonder -

1. why tidal tail of left galaxy and drawn out spiral of right bottom galaxy are not towards eachother ? Their direction gives no clue if there was any interaction between them..

2. Stars with spikes visible are in our own milky way but -
a. the objects without spikes - are they stars or galaxies ?
b. If galaxies, are they nearer (but faint) than these 3 shown or way far out ?
Without doing scientific observations and knowing, just by looking at such image, is there anyway we can guess/tell ?

Thanks in advance for all comments/answers/clarifications.
Here are my attempts at answering you.

1) To my knowledge, the direction of the tidal tail of NGC 3628 is totally dependent on the exact "mechanics" of the interactions between M65, M66 and NGC 3628. I don't think we know enough of the past interactions of these galaxies to say exactly why the tail of NGC 3628 looks the way it does.

This video of galaxy interactions may be of some interest to you.

2 a) If you enlarge today's APOD, you will see that many of the fainter stars do have faint spikes. I believe that all point sources have spikes, but if the point source is too faint, the spikes will not be resolved. In the case of this APOD, you can clearly see a number of elongated galaxies, which are easily visible because of their shapes. You can also see a group of distant galaxies near a yellow star right below the galaxy M66. We can see that these are distant galaxies because they are tiny, faint, reddish and close together. In other cases, you can see a faint halo around a star-like object. The halo means that the star-like object is a galaxy with a disk surrounding a bright bulge.

I'd say that most at least moderately bright objects in today's APOD are stars, but a number of sources are clearly galaxies.

Stephan's Quintet.
Hubble Legacy Archive, ESA, NASA; Processing: Al Kelly.
























2 b) Of the galaxies that can be seen in today's APOD, M65, M66 and NGC 3628 are by far the most nearby ones. All other galaxies in the APOD are much, much farther away. How can we know?

We can know it because moderately nearby dwarf galaxies tend to have lower surface brightnesses than large galaxies. Look at the picture above. This group of galaxies is called Stephan's Quintet. Can you see that one of the galaxies has a much fainter bulge than the other four? Four of the galaxies have bright yellow bulges, which glow almost white in the center. But one galaxy has a faint bulge, with a tiny little bright object at the center. The galaxy with the faint bulge looks larger than the others, however. Why is that?

The answer is that the large galaxy with the faint bulge is a foreground object. That galaxy, NGC 7320, is located some 40 million light-years away, but the other four ones are almost 300 light-years away.

Not only is NGC 7320 a foreground object, but it is also an intrinsically small galaxy. The faint small bulge and the tiny nucleus of the galaxy shows that it is a small galaxy.

Ann
Color Commentator

madtom1999
Ensign
Posts: 71
Joined: Mon Jan 12, 2009 11:21 am

Re: APOD: The Leo Trio (2019 Apr 18)

Post by madtom1999 » Thu Apr 18, 2019 8:01 am

NGC 3628 just needs putting on its side to stop all the stars leaking out.

Starholio

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Starholio » Thu Apr 18, 2019 11:33 am

What happened to “pixels in space”??? :(

User avatar
orin stepanek
Plutopian
Posts: 6881
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: The Leo Trio (2019 Apr 18)

Post by orin stepanek » Thu Apr 18, 2019 12:13 pm

Beautiful Trio of galaxies with a beautiful bright star within the Milky Way to Accent them! Love this group! The top: M 65 is a perfectly shaped galaxy! 8-) M 66 looks like it may actually be two galaxies merging. :?
Orin

Smile today; tomorrow's another day!

User avatar
Chris Peterson
Abominable Snowman
Posts: 16174
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Chris Peterson » Thu Apr 18, 2019 1:27 pm

Ann wrote:
Thu Apr 18, 2019 5:49 am
2 a) If you enlarge today's APOD, you will see that many of the fainter stars do have faint spikes. I believe that all point sources have spikes, but if the point source is too faint, the spikes will not be resolved. In the case of this APOD, you can clearly see a number of elongated galaxies, which are easily visible because of their shapes.
If the source is too faint, the spikes won't rise above the noise floor and be visible. It isn't related to resolution. Also, all extended sources have spikes, including galaxies. Again, though, there's not usually enough signal in them to be visible. The diffraction artifacts around stars and extended sources are often detectable in the original data, which is usually higher dynamic range than the 8-bit JPEG processed images that get published.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Guest

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Guest » Thu Apr 18, 2019 2:50 pm

Starholio wrote:
Thu Apr 18, 2019 11:33 am
What happened to “pixels in space”??? :(
Patience, my friend. It’s not “tomorrow” yet!

User avatar
bystander
Apathetic Retiree
Posts: 20782
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Re: APOD: The Leo Trio (2019 Apr 18)

Post by bystander » Thu Apr 18, 2019 4:53 pm

Starholio wrote:
Thu Apr 18, 2019 11:33 am
What happened to “pixels in space”??? :(

Did you not enjoy today's image?

astrophotography ≈ “pixels in space”
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

shaileshs
Ensign
Posts: 50
Joined: Mon Mar 13, 2017 8:14 pm

Re: APOD: The Leo Trio (2019 Apr 18)

Post by shaileshs » Thu Apr 18, 2019 6:43 pm

Ann wrote:
Thu Apr 18, 2019 5:49 am
shaileshs wrote:
Thu Apr 18, 2019 4:23 am
Hello,

I wonder -

1. why tidal tail of left galaxy and drawn out spiral of right bottom galaxy are not towards eachother ? Their direction gives no clue if there was any interaction between them..

2. Stars with spikes visible are in our own milky way but -
a. the objects without spikes - are they stars or galaxies ?
b. If galaxies, are they nearer (but faint) than these 3 shown or way far out ?
Without doing scientific observations and knowing, just by looking at such image, is there anyway we can guess/tell ?

Thanks in advance for all comments/answers/clarifications.
Here are my attempts at answering you.

1) To my knowledge, the direction of the tidal tail of NGC 3628 is totally dependent on the exact "mechanics" of the interactions between M65, M66 and NGC 3628. I don't think we know enough of the past interactions of these galaxies to say exactly why the tail of NGC 3628 looks the way it does.

This video of galaxy interactions may be of some interest to you.

2 a) If you enlarge today's APOD, you will see that many of the fainter stars do have faint spikes. I believe that all point sources have spikes, but if the point source is too faint, the spikes will not be resolved. In the case of this APOD, you can clearly see a number of elongated galaxies, which are easily visible because of their shapes. You can also see a group of distant galaxies near a yellow star right below the galaxy M66. We can see that these are distant galaxies because they are tiny, faint, reddish and close together. In other cases, you can see a faint halo around a star-like object. The halo means that the star-like object is a galaxy with a disk surrounding a bright bulge.

I'd say that most at least moderately bright objects in today's APOD are stars, but a number of sources are clearly galaxies.

Stephan's Quintet.
Hubble Legacy Archive, ESA, NASA; Processing: Al Kelly.
























2 b) Of the galaxies that can be seen in today's APOD, M65, M66 and NGC 3628 are by far the most nearby ones. All other galaxies in the APOD are much, much farther away. How can we know?

We can know it because moderately nearby dwarf galaxies tend to have lower surface brightnesses than large galaxies. Look at the picture above. This group of galaxies is called Stephan's Quintet. Can you see that one of the galaxies has a much fainter bulge than the other four? Four of the galaxies have bright yellow bulges, which glow almost white in the center. But one galaxy has a faint bulge, with a tiny little bright object at the center. The galaxy with the faint bulge looks larger than the others, however. Why is that?

The answer is that the large galaxy with the faint bulge is a foreground object. That galaxy, NGC 7320, is located some 40 million light-years away, but the other four ones are almost 300 light-years away.

Not only is NGC 7320 a foreground object, but it is also an intrinsically small galaxy. The faint small bulge and the tiny nucleus of the galaxy shows that it is a small galaxy.

Ann
Thank you Ann for your detailed response. It helps a lot.

User avatar
Ann
4725 Å
Posts: 11567
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Ann » Fri Apr 19, 2019 6:25 am

shaileshs wrote:
Thu Apr 18, 2019 6:43 pm

Thank you Ann for your detailed response. It helps a lot.
Glad to be of some assistance! :D

I was going to write a private message to you, but that wasn't possible, so I'll write a bit more here about judging the intrinsic properties of a galaxy by simply looking at it.

Wide angle visible light image of the Tadpole galaxy.
Photo: KuriousGeorge.
The Tadpole galaxy and background galaxies.



























The most interesting thing about the Hubble image of the Tadpole galaxy, in my opinion, is the wealth of background galaxies. You can use their appearance to make an educated guess about their intrinsic properties.


Background galaxy Tadpole.png
In the picture at left, you can see the brightest and most obvious of the background galaxies in the Tadpole galaxy picture. It defintely looks like an intrinsically large galaxy to me. Its bulge is large and bright, and its disk is large and well-formed, too. Note the dust lanes and the outer arms.

A fascinating tail seems to emanate from this galaxy. But if you look closely, a tiny object seems to be located right inside this tail. I'd say that this is a tiny satellite galaxy, and a long stream of stars has been pulled out of this galaxy by the mighty gravity of its large bully of a neighbour. And yes, the stellar stream doesn't just extend towards the large spiral galaxy, but it extends in the opposite direction too.

But wait. There is more. The outer end of the tail is curving, as if it has been caught in another gravitational field. What causes it? The two interacting yellow galaxies at left?

I'd say no. The two interacting yellow galaxies are just a shade too yellow to be at the same distance as the large spiral galaxy. I'd say that they are some distance in the background, far enough to be slightly affected by redshift-reddening. The farther away a galaxy is, the more its light will be reddened by the sheer expansion of space, which tugs at the wavelengths of light emitted by the galaxies and makes them appreciably longer by the time the light reaches us.

So the pair of yellow galaxies (which are intrinsically large by the look of their large bright centers) are not responsible for curving the stellar stream from the tiny satellite galaxy caught in the large spiral galaxy's powerful gravity.

But look at the galaxy above left. It is slightly less yellow than the two interacting yellow galaxies. And see how diffuse it is? And it's not very bright in the center.

In fact, this galaxy is much the same color as the large spiral galaxy, and it is certainly much the same color as the stellar stream. Because the colors are virtually identical, I'd say that this galaxy is at the same distance as the edge-on spiral galaxy. But it is clearly much smaller than the spiral galaxy.

So it seems extremely likely that the diffuse galaxy at upper left is another satellite galaxy of the spiral galaxy. Moreover, this diffuse galaxy could very well be the source of gravity that makes the stellar stream from the really tiny little satellite galaxy curve at one end.

We are not done yet. Look at the very red galaxy at the right end of the large spiral galaxy. The very red color of this galaxy suggests to me that it is really quite distant. If so, it must be intrinsically quite bright to look as bright and obvious as it does. It does have a bright center, and it looks like a quite well-formed barred spiral galaxy with sprawling arms. So I'd say that this galaxy is really quite large and bright, a beast from the past!

Ann
You do not have the required permissions to view the files attached to this post.
Last edited by Ann on Fri Apr 19, 2019 2:33 pm, edited 1 time in total.
Color Commentator

sillyworm 2

Re: APOD: The Leo Trio (2019 Apr 18)

Post by sillyworm 2 » Fri Apr 19, 2019 1:51 pm

Thanks,as always Ann,for all the intricate info and analysis you post nearly daily! Just to make sure I have this right...for example...the red barred galaxy mentioned above...we are seeing it as it appeared millions/billions of years ago?

User avatar
Ann
4725 Å
Posts: 11567
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Leo Trio (2019 Apr 18)

Post by Ann » Fri Apr 19, 2019 2:32 pm

sillyworm 2 wrote:
Fri Apr 19, 2019 1:51 pm
Thanks,as always Ann,for all the intricate info and analysis you post nearly daily! Just to make sure I have this right...for example...the red barred galaxy mentioned above...we are seeing it as it appeared millions/billions of years ago?
Exactly. We are seeing that galaxy as it appeared probably at least a billion years ago, and probably more.

The Tadpole galaxy itself is some 400 million light-years away, and the red barred spiral background galaxy is certainly much farther away.

https://en.wikipedia.org/wiki/Tadpole_Galaxy

Thanks for your kind words! I've been free from school for a week now and won't have nearly as much time to post here at Starship Asterisk* for a couple of months now.

Ann
Color Commentator