Ngc4157

[Ken Crawford]

Hello,

We have had very poor imaging weather this spring in northern CA but I finally managed to get some data on a rarely imaged galaxy. The slight warp - elongation made it a target for our star stream survey but it failed to reveal any stream structures.

It was however good practice in digging out the tiny details of the core and dust lanes. You can zoom in and look around. It is framed by an 8th mag class F5 star that nicely points they way.

AAIC is fast approching and I hope to see many of you very soon.

http://www.imagingdeepsky.com/Galaxies/NGC4157/NGC4157.htm

Kindest Regards,

[renormalised]

Another great shot, Ken. Well done:)

[Fabiomax]

Amazing image. Interesting details and nice colors. In fact there are not many pictures of this galaxy. I saw that you did 460 minutes of L.
Do you think that increasing the exposure time is possible that there could be surprises (stream) or eventually stream is deep enough to exclude that it can be taken with amateur equipment?
Cheers,
Fabiomax

[peter_4059]

Beautiful image Ken. How many nights did it take to aquire all the data?

[Saturn%5]

Very nice shot.

[gregbradley]

Another super hi resolution image from you Ken. Fabulous.

Greg.

[allan gould]

Its amazing what you are doing Ken. Really superb work - keep them coming

[marc4darkskies]

Great shot as always Ken!

Look forward to meeting you at AIC!

Cheers, Marcus

[Ken Crawford]

The reason I took at least 7 hours of luminance is because this target was on my list for the Star Stream Survey that I am part of. So far, this target did not show the debris from a merger but that is also interesting to the PI that we do work for.

Ken

[Ken Crawford]

Thanks for the kind comments, I look forward to meeting you also!

[RobF]

Just wonderful. Soft smooth colours but still with great detail to absorb.
I particularly like your presentation too Ken - the map of "where the heck is this?" in the top right and the option to zoom right in with Zoomify. Groundbreaking stuff as usual.

[astroron]

Nice image as usual Ken.
Cheers:thumbsup:

[Hagar]

Very nice Ken. Obviously very small given the size of the surrounding stars. Detail is great for something so small.

[TrevorW]

Ken

what can one say

top notch as usual

[John Hothersall]

Ursa Major is full of these strange galaxies, love the fuzzies group on the right, detail right in to the core with that acute angle is quite an achievement. Presentation very user friendly.

John.

[Gem]

Wow! I don't know whether to be inspired to follow or just realise I am sssooo far behind others! :lol:
Great site too.

[Leonardo70]

Congratulations Ken,

amazing photo, fullres is very detailed. Interesting subject, thanks for sharing.

Ciao,
Leo

[Ken Crawford]

Thanks so much for the kind comments. My first impression of this galaxy was it was a bit boring until I started digging. The hairy looking outflows are very small and it does look like the galaxy is distorted a bit.

Again, thanks for the encouragement . . .

[cybereye]

Ken,

As I have just started imaging galaxies I find this image quite enthralling and inspiring!

I look forward to meeting you at the AAIC,

Cheers,
Mario

[madbadgalaxyman]

Ken,

The anomalous blue extension on one side is very interesting.

I suppose that it could just be an outer spiral arm, seen almost in our line-of-sight. Very tricky to find out what is really going on here, as everything is foreshortened.
When we look at spiral galaxies in a face-on orientation, a single outer spiral arm is not that unusual......
a "one-armed mode", in the opaque jargon of professional astronomy, refers to a galaxy which is one-armed at a specific range of galactocentric radii....it is not uncommon to find that even famous galaxies that we believe that we know well, actually have only a single spiral arm at some radius.
(Nearly all barred spirals have a trace of one-armed structure; with one weak arm and one strong arm. Perturbations by bars and/or by external galaxies can cause a one-armed look.)

Just by looking at your very fine "two-dimensional" image (obviously, no physical depth is available in a galaxy image), one cannot tell whether the anomalous "arm" is close to the galaxy or far from it. But the velocities of the stars or gas (via spectroscopy) can sometimes give us the true "3D" picture of how a galaxy is actually structured in real space.

Given the outer asymmetry of the image of this galaxy, it does seem possible that this galaxy has undergone some kind of mild perturbation. Mind you, all galaxies are actually perturbed, to some extent!

A candidate perturbing object is UGC 7176 to the south of NGC 4157.
See the attached DSS image taken from server1.wikisky.org :

94991

This little dwarf galaxy is probably significantly bent and warped, that is, it is probably non-planar. Furthermore, its redshift is close enough to that of NGC 4157 to indicate that it may well be in physical proximity. These two facts would support its identity as the perturbing object.
Another possible perturber is the very unusual spiral
NGC 4088, which is probably a member of the same group of galaxies.

I have seen a lot of these types of galaxy pairs before, and I think there is a good chance that there has been an interaction.

Another common cause of asymmetry and non-planarity in a galaxy image that we see edge-on is the existence of a "warp", which implies that a spiral or S0 galaxy is not coplanar....in other words, there is a genuine bend, twist, or even a bifurcation into two different planes.
As I do have a personal "rogues gallery" of ~500 different galaxies with warps.......to me, the hypothesis of a warp or bend in the disk of N4157 seems less likely. (However, I think that there is some literature evidence for the existence of a warp)

If I ever get "A Round Tuit", I will track down some HI data, to see if the gas layer is disturbed in N4157.


cheers,
madbadgalaxyman

[madbadgalaxyman]

Here is the GALEX ultraviolet image of NGC 4157 :

95000

The asymmetric pattern of current star formation ,as traced by FUV light (coded blue), may well be a very significant peculiarity.

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I have found a version of the composite g+r+i image data for NGC 4157 from the Sloan Digital Sky survey..... that gives quite a different slant on the morphology and nature of this galaxy:

95001

I always find that these g+r+i composites from the SDSS tend to over-emphasize blue colours.....but this is no bad thing if we want to find out where current star formation occurs in a galaxy.

__________________________

[Ken Crawford]

Wow Robert - that is all great and interesting information. Thanks for posting it - I learned allot!