APOD: NGC 3370: A Sharper View (2013 Aug 08)

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APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by APOD Robot » Thu Aug 08, 2013 4:07 am

Image NGC 3370: A Sharper View

Explanation: Similar in size and grand design to our own Milky Way, spiral galaxy NGC 3370 lies about 100 million light-years away toward the constellation Leo. Recorded here in exquisite detail by the Hubble Space Telescope's Advanced Camera for Surveys, the big, beautiful face-on spiral does steal the show, but the sharp image also reveals an impressive array of background galaxies in the field, strewn across the more distant Universe. Looking within NGC 3370, the image data has proved sharp enough to study individual pulsating stars known as Cepheids that can be used to accurately determine this galaxy's distance. NGC 3370 was chosen for this study because in 1994 the spiral galaxy was also home to a well studied stellar explosion -- a type Ia supernova. Combining the known distance to this standard candle supernova, based on the Cepheid measurements, with observations of supernovae at even greater distances, can reveal the size and expansion rate of the Universe itself.

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by BDanielMayfield » Thu Aug 08, 2013 4:19 am

WOW! There are red shifted galaxies all around NGC 3370. Some can even be discerned shining though its spiral arms.
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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Ann » Thu Aug 08, 2013 5:55 am

This is an old Hubble Heritage image. I remember it well. As far as I can see from the caption of today's APOD, nothing much has changed about the image since it was first published.

However, I have the greatest respect for Adam Riess, who is specializing on the evolution and expansion of the Universe. For him, cosmic distance indicators are absolutely crucial. The fact that there has been a supernova in this galaxy, coupled with the detection of Cepheids here, makes NGC 3370 enormlously interesting to astronomers like Adam Riess.

To me the color of the galaxy is confusing. Apart from the small lens around the nucleus, the galaxy appears to be a uniform cyan color. Yet the B-V index of this galaxy is relatively red, 0.900, which is considerably yellower than the color of the Sun.

But I realize that NGC 3370 wasn't imaged by the Hubble Telescope in order to get the opportunity to flaunt its pretty colors.

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by TheSoftman » Thu Aug 08, 2013 8:10 am

I also noticed that exactly the same image was presented in an older APOD http://apod.nasa.gov/apod/ap111029.html with just a slightly different text.

Anyway it's still a picture of great interest, with Cepheids, a Ia Supernova and all these red shifted galaxies.
About it, in early October 2011 Adam Riess was awarded the 2011 Nobel Prize in Physics http://www.nobelprize.org/nobel_prizes/ ... index.html for his contributions to the discovery of the acceleration of the expansion of the universe, so I imagine the last time it was a kind of tribute.

I have a great respect for his work, but this time it's not even his birthday https://en.wikipedia.org/wiki/Adam_Riess :P

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Boomer12k » Thu Aug 08, 2013 9:20 am

An impressively important galaxy, and a beautiful one at that....Amazing!!!

The galaxy in the upper right is interesting too....

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by owlice » Thu Aug 08, 2013 10:34 am

That's probably why Hubble Heritage is listed in the credits... :-D
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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Peter Smith » Thu Aug 08, 2013 10:56 am

Is the galaxy really "face on"? I would have assumed that it was a roughly circular disc angled at about 60 degrees away from us so as to appear twice as long as it is wide. How can we tell the difference between these two scenarios?

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Lordcat Darkstar » Thu Aug 08, 2013 12:10 pm

Id assume its angled a bit. The way we could tell would be by checking to see if one side is blue shifted and the other side is red shifted. This would tell us that one side is moving towards us and the other side is moving away therfore it wouldn't be face on.

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by neufer » Thu Aug 08, 2013 1:02 pm

Art Neuendorffer

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Beyond » Thu Aug 08, 2013 1:08 pm

Objects may also be smaller than they appear in APOD.
Such as Tardigrades.
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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by stephen63 » Thu Aug 08, 2013 3:03 pm

If you take a close look, you'll see what appear to be H II regions throughout the galaxy that are colored green. I went to the Hubble Legacy Archive and the combined color image has the same green regions. It can't be ionized hydrogen, but what would cause the green structures? I cropped one of the regions to give a visual.
ngc3370_hst_6031 copy.jpg
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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Chris Peterson » Thu Aug 08, 2013 3:27 pm

stephen63 wrote:If you take a close look, you'll see what appear to be H II regions throughout the galaxy that are colored green. I went to the Hubble Legacy Archive and the combined color image has the same green regions. It can't be ionized hydrogen, but what would cause the green structures? I cropped one of the regions to give a visual.
The processing details don't describe how the color image was composited. However, given the approximate natural color, I'd assume that the photometric filters were mapped B (F435W) to blue, V (F555W) to green, and I (F814W) to red. The dominant H-II line is H-alpha, at 656 nm, which falls between the bandpasses of the V and I filters. In other words, we are not seeing any H-alpha emissions in this galaxy, so any H-II regions could only be observed in other, much weaker emission lines, if they are seen at all.

Areas that display as green are bright over most of the visible spectrum, except deep blue and middle to deep red. This could mean regions of ionized oxygen, or certain reflection nebulas.
Chris

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by tkc » Thu Aug 08, 2013 6:23 pm

Boomer12k wrote:An impressively important galaxy, and a beautiful one at that....Amazing!!!

The galaxy in the upper right is interesting too....

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Which one? In one tight area cropped out of the upper right area I count at least four galaxies and one foreground star.

Image

The upper right almost edge on spiral in red.
The upper right face on bar in yellow. (with foreground star)
The lower left brighter face on spiral with a much fainter face on spiral to its lower left.

Then there are various smudges. Are they galaxies too?

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by BDanielMayfield » Fri Aug 09, 2013 12:58 am

tkc wrote:
Boomer12k wrote:The galaxy in the upper right is interesting too....
The upper right almost edge on spiral in red.
The upper right face on bar in yellow. (with foreground star)
The lower left brighter face on spiral with a much fainter face on spiral to its lower left.

Then there are various smudges. Are they galaxies too?
My eyes were drawn to this part of the APOD also. I the yellow/organge open barred sprial is impressive, it's two sweeping arms extending quite beyond the area that tkc has cropped. Yes tkc, many of the "various smudges", especially the redish ones, are galaxies, incredibly distant galaxies.
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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by pimorton » Fri Aug 09, 2013 4:12 am

"NGC 3370 was chosen for this study because in 1994 the spiral galaxy was also home to a well studied stellar explosion -- a type Ia supernova."
Given the galaxy is 100 million light years away, I think NGC 3370 was chosen for this study because in 1994 the spiral galaxy was seen to be the home to a well-studied stellar explosion -- a type Ia supernova.

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Re: APOD: NGC 3370: A Sharper View (2013 Aug 08)

Post by Ann » Fri Aug 09, 2013 5:59 am

tkc wrote:
Boomer12k wrote:An impressively important galaxy, and a beautiful one at that....Amazing!!!

The galaxy in the upper right is interesting too....

:---[===] *
Which one? In one tight area cropped out of the upper right area I count at least four galaxies and one foreground star.

Image

The upper right almost edge on spiral in red.
The upper right face on bar in yellow. (with foreground star)
The lower left brighter face on spiral with a much fainter face on spiral to its lower left.

Then there are various smudges. Are they galaxies too?
Thanks for pointing out these galaxies, tkc! :D

The strongly barred yellow galaxy actually has two long, faint bluish "outer arms" emanating from the ends of their thick inner yellow arms. The part that you cropped from the larger image shows the beginning of the bluish arm emanating from the upper left yellow arm, and the end of the bluish arm emanating from the lower right arm. Both these bluish arms can be seen in the middle of your cropped image. It is true that one or two of the brightenings in the upper arm could be background galaxies seen along the line of sight.

The color of the yellow galaxy seems realistic for a galaxy made up of old stars, encircled by two faint outer arms with star formation. Admittedly the yellow color of the galaxy is sufficiently yellow-orange that it must be affected by redshift reddening. The white galaxy to the left of it is a spiral galaxy with a lot of star formation, since its color is a mixture of an underlying yellowish population and a multitude of young blue stars. The white and the yellow galaxies are probably not as close together as they appear to be here, but they are probably at moderately similar distances from us. Judging by their colors and apparent stellar content, they appear to be equally affected by redshift reddening.

The red galaxy which appears to "sit on" the yellow galaxy is a background object, strongly affected by redshift reddening. But the color of this galaxy is is probably also affected by dust reddening due to dust in the yellow galaxy. The light from the red background galaxy has to pass through this dust, which reddens its light further. There is star formation in the red galaxy, seen as bright patches in its dust lane. The great contrast in color between the yellow and the red galaxy, coupled with a relatively modest contrast in size, suggests that the red galaxy is an intrinsically large and bright object.

Note that there is another strongly yellow galaxy in this picture, an edge-on galaxy at about 5 o'clock. This galaxy is made up of a predominantly old population, although there appear to be patches of younger stars immediately to the left of the dust lane. Fascinatingly, there are faint "extensions" of the dust lane stretching to a considerable distance on both sides of the main luminous body of the galaxy. No star formation can be seen in these extensions.

The yellow color of this edge-on galaxy suggests that it is at a moderately similar distance from us as the yellow galaxy in your cropped image, tkc. Faint bluish galaxies could be very distant, however, and if so they must be strongly dominated by ultraviolet light from star formation.

The interesting and revealing colors of the background galaxies could help explain the strange cyan color of NGC 3370 itself. It could be that the colors of this image have indeed been balanced in such a way that the background galaxies would have colors that help us identify their stellar contents and distances. Or, to put it differently: If NGC 3370 had been more realistically yellow, too many of the background galaxies might have been too uniformly red.

Ann
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