APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Comments and questions about the APOD on the main view screen.
JohnM

Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by JohnM » Wed Aug 04, 2021 11:47 am

Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

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John

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by johnnydeep » Wed Aug 04, 2021 1:54 pm

JohnM wrote: Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John
You seem to be correct, at least with regard to the image. This "UDF" APOD pic matches the image of the XDF at https://www.nasa.gov/mission_pages/hubb ... e/xdf.html
Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full moon.

The Hubble Ultra Deep Field is an image of a small area of space in the constellation Fornax, created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over many hours of observation, it revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time.

The new full-color XDF image is even more sensitive, and contains about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see.
Comparing the image at the NASA XDF link with the image at this NASA UDF link (https://svs.gsfc.nasa.gov/309460) show that the XDF is a (slightly - appears to be about half the area) smaller field of view of the UDF field of view:

XDF versus UDF.JPG

But, I'm wrong [ EDIT: actually, mostly right] about the FOV comparison. From https://en.wikipedia.org/wiki/Hubble_Ul ... Deep_Field
The Hubble eXtreme Deep Field (HXDF), released on September 25, 2012, is an image of a portion of space in the center of the Hubble Ultra Deep Field image. Representing a total of two million seconds (approximately 23 days) of exposure time collected over 10 years, the image covers an area of 2.3 arcminutes by 2 arcminutes,[15] or approximately 80% of the area of the HUDF. This represents approximately one thirty-two millionth of the sky.

The HXDF contains approximately 5,500 galaxies, the oldest of which are seen as they were 13.2 billion years ago.
EDIT: and I found this nice comparison that shows the overlapping FOVs of the XDF and UDF quite well:
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Last edited by johnnydeep on Wed Aug 04, 2021 2:46 pm, edited 1 time in total.
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by bystander » Wed Aug 04, 2021 2:23 pm

JohnM wrote: Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John
Hubble Ultra Deep Field 2014
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by johnnydeep » Wed Aug 04, 2021 2:49 pm

bystander wrote: Wed Aug 04, 2021 2:23 pm
JohnM wrote: Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John
Hubble Ultra Deep Field 2014
As I tried to show above, this APOD seems to show the XDF not the UDF, though the XDF is nevertheless just an 80% sub-FOV of the UDF.
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by bystander » Wed Aug 04, 2021 4:18 pm

johnnydeep wrote: Wed Aug 04, 2021 2:49 pm
bystander wrote: Wed Aug 04, 2021 2:23 pm
JohnM wrote: Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John
Hubble Ultra Deep Field 2014
As I tried to show above, this APOD seems to show the XDF not the UDF, though the XDF is nevertheless just an 80% sub-FOV of the UDF.
This is not just the XDF. It's the XDF plus UV.
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by johnnydeep » Wed Aug 04, 2021 6:24 pm

bystander wrote: Wed Aug 04, 2021 4:18 pm
johnnydeep wrote: Wed Aug 04, 2021 2:49 pm
bystander wrote: Wed Aug 04, 2021 2:23 pm

Hubble Ultra Deep Field 2014
As I tried to show above, this APOD seems to show the XDF not the UDF, though the XDF is nevertheless just an 80% sub-FOV of the UDF.
This is not just the XDF. It's the XDF plus UV.
I'm only trying to say that the area of the APOD image shown matches that of the smaller XDF, not the larger UDF. Why call it the UDF? Is it supposed to be XDF image (and data) plus UV from from the UDF?
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by beryllium732 » Thu Aug 05, 2021 12:31 am

I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Another example in the picture is two galaxies one more blueish the other more reddish which looks to be neightbours but the reddish one is nine billion light years away and still the one farthest away is still as big as the much nearer galaxy. Is there a lens effect in play here?

Can someone explain?

I did find several very distant ones 13.1BY away and some ranging from 12.6 to 12.9BY distant.

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by neufer » Thu Aug 05, 2021 1:25 pm

beryllium732 wrote: Thu Aug 05, 2021 12:31 am
I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Another example in the picture is two galaxies one more blueish the other more reddish which looks to be neightbours but the reddish one is nine billion light years away and still the one farthest away is still as big as the much nearer galaxy. Is there a lens effect in play here?

Can someone explain?
The rainbow HUDF "colors" are NOT true colors
in the narrow "octave": Violet (380 nm) to Red (740 nm)
but represent a broader (~435 to ~1600 nm) spectrum
in which broad Black Body radiation often
appear as narrow pure primary pseudo-colors:

Code: Select all

Camera 	Filter 	Wavelength 	Exposure time
----------------------------------------------
ACS 	F435W 	 435 nm 	56 orbits
ACS 	F606W 	 606 nm 	56 orbits
ACS 	F775W 	 775 nm 	144 orbits
ACS 	F850LP 	 850 nm 	144 orbits
WFC3 	F105W 	1050 nm 	14 orbits
WFC3 	F125W 	1250 nm 	16 orbits
WFC3 	F160W 	1600 nm 	28 orbits
...................................................
		Spitzer? 
Art Neuendorffer

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by Arne » Thu Aug 05, 2021 6:14 pm

I found one! This is a really cool tool. Someone opined that a lot of effort and time went into producing this and they deserve kudos. Thx!

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by beryllium732 » Fri Aug 06, 2021 5:09 pm

neufer wrote: Thu Aug 05, 2021 1:25 pm
beryllium732 wrote: Thu Aug 05, 2021 12:31 am
I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Another example in the picture is two galaxies one more blueish the other more reddish which looks to be neightbours but the reddish one is nine billion light years away and still the one farthest away is still as big as the much nearer galaxy. Is there a lens effect in play here?

Can someone explain?
The rainbow HUDF "colors" are NOT true colors
in the narrow "octave": Violet (380 nm) to Red (740 nm)
but represent a broader (~435 to ~1600 nm) spectrum
in which broad Black Body radiation often
appear as narrow pure primary pseudo-colors:

Code: Select all

Camera 	Filter 	Wavelength 	Exposure time
----------------------------------------------
ACS 	F435W 	 435 nm 	56 orbits
ACS 	F606W 	 606 nm 	56 orbits
ACS 	F775W 	 775 nm 	144 orbits
ACS 	F850LP 	 850 nm 	144 orbits
WFC3 	F105W 	1050 nm 	14 orbits
WFC3 	F125W 	1250 nm 	16 orbits
WFC3 	F160W 	1600 nm 	28 orbits
...................................................
		Spitzer? 
Thanks but I didn't understand anything. Isn't the UDF showing the real visible spectrum?

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by neufer » Fri Aug 06, 2021 5:56 pm

beryllium732 wrote: Fri Aug 06, 2021 5:09 pm
Isn't the UDF showing the real visible spectrum?
The UDF is blue-shifting & compressing a broader (~1600 to ~435 nm) spectrum
into a visible ROYGBIV (~740 to ~380 nm) pseudo-color spectrum.
Art Neuendorffer

Shmurk

Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by Shmurk » Thu Mar 17, 2022 7:28 pm

I found this same exact picture march 5th 2018. any reason for repeats in pics and description?

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by bystander » Thu Mar 17, 2022 7:44 pm

Shmurk wrote: Thu Mar 17, 2022 7:28 pm I found this same exact picture march 5th 2018. any reason for repeats in pics and description?
APOD FAQ

Q4: Have some APOD pictures been run more than once?
A4: Yes. Many of our readers have been with us less than a year and are unaware of some really spectacular or important astronomy pictures. New information about old pictures is becoming available over the WWW. The text and links for rerun pictures will make use of this newly available information. So although the picture might be old, some of the text and links of each APOD will be new. Also, more web surfers have larger bandwidth connections, which allows us to post higher-resolution image files that can be transferred conveniently. Software to handle more sophisticated image file formats has also become more common, so the picture's size and/or format might be new. Lastly, rerunning APODs saves us time and helps us update our archive. In general, our rerun policy currently is to only rerun APODs more than one year old to keep the pictures relatively "new" to new APOD viewers. We will almost never rerun more than two pictures in any given week. So when you load the current APOD,it is still, most probably, a new picture.
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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by Ann » Thu Mar 17, 2022 9:31 pm

beryllium732 wrote: Thu Aug 05, 2021 12:31 am I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Take a look at this picture the Hubble Deep Field. There really are a number of small blue galaxies that are a lot more distant than many of the orange galaxies. How can the blue galaxies look blue if they are more redshifted than many of the orange ones?


Answer: Because they are so blue and starforming in themselves. Or rather, they are extremely ultraviolet, pumping out huge amounts of far ultraviolet light from their massive, extremely hot stars. We see these galaxies as they looked at the age of peak star formation in the Universe. More importantly: The far ultraviolet light from these galaxies has been redshifted so that it looks blue.


What about the much larger yellow or orange galaxies? Many of them are elliptical galaxies, devoid of star formation. They lack hot stars altogether. Other orange galaxies do have some star formation, but not a lot of it, and they don't form very hot or massive stars.

The orange galaxies are dominated by yellow-white stars, and because these galaxies are redshifted, they look yellow or orange to us.

The green-looking galaxies aren't green. They are just redshifted galaxies that have been detected by the green filter used for the image, or else they are simply "intermediate" in color and have been mapped as green.

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by beryllium732 » Thu Jun 02, 2022 9:10 am

Ann wrote: Thu Mar 17, 2022 9:31 pm
beryllium732 wrote: Thu Aug 05, 2021 12:31 am I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Take a look at this picture the Hubble Deep Field. There really are a number of small blue galaxies that are a lot more distant than many of the orange galaxies. How can the blue galaxies look blue if they are more redshifted than many of the orange ones?


Answer: Because they are so blue and starforming in themselves. Or rather, they are extremely ultraviolet, pumping out huge amounts of far ultraviolet light from their massive, extremely hot stars. We see these galaxies as they looked at the age of peak star formation in the Universe. More importantly: The far ultraviolet light from these galaxies has been redshifted so that it looks blue.


What about the much larger yellow or orange galaxies? Many of them are elliptical galaxies, devoid of star formation. They lack hot stars altogether. Other orange galaxies do have some star formation, but not a lot of it, and they don't form very hot or massive stars.

The orange galaxies are dominated by yellow-white stars, and because these galaxies are redshifted, they look yellow or orange to us.

The green-looking galaxies aren't green. They are just redshifted galaxies that have been detected by the green filter used for the image, or else they are simply "intermediate" in color and have been mapped as green.

Ann
It's a bit late but thank you! It's amazing! It would be a sight to behold if we could be there at that particular time. The light from them would be blindingly bright at least for the light we would be able to see.

So the redshift shifts the ultraviolet which we can't see with our eyes to the 400-500nm range in the visible spectrum which we can see?

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Re: APOD: The Hubble Ultra Deep Field in Light... (2021 Aug 02)

Post by Ann » Thu Jun 02, 2022 9:28 am

beryllium732 wrote: Thu Jun 02, 2022 9:10 am
It's a bit late but thank you! It's amazing! It would be a sight to behold if we could be there at that particular time. The light from them would be blindingly bright at least for the light we would be able to see.

So the redshift shifts the ultraviolet which we can't see with our eyes to the 400-500nm range in the visible spectrum which we can see?
Yes, that's correct!

Ann
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