APOD: Breaking Distant Light (2020 Sep 20)

[APOD Robot]

Breaking Distant Light

Explanation: In the distant universe, time appears to run slowly. Since time-dilated light appears shifted toward the red end of the spectrum (redshifted), astronomers are able to use cosmological time-slowing to help measure vast distances in the universe. Featured, the light from distant galaxies has been broken up into its constituent colors (spectra), allowing astronomers to measure the cosmological redshift of known spectral lines. The novelty of the featured image is that the distance to hundreds of galaxies can be measured from a single frame, in this case one taken by the Visible MultiObject Spectrograph (VIMOS) operating at the Very Large Telescope (VLT) array in Chile. Analyzing the space distribution of distant objects will allow insight into when and how stars and galaxies formed, clustered, and evolved in the early universe.

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[DaveDerl]

What are these bright almost completely white spectra below the center? I thought foreground stars but you probably won't bother doing the data analysis for them if it is about galaxy motion?

[heehaw]

What are these bright almost completely white spectra below the center? I thought foreground stars but you probably won't bother doing the data analysis for them if it is about galaxy motion?

Maybe just stars too bright and so overexposed?

[Holger Nielsen]

I also wondered about the allmost white spectra: If they are foreground stars, why include them?
Further questions:
The parallel horizontal arrangement of the spectra suggests that the positions of the spectra in the image are not correlated with the position of the galaxy in the sky, but then why are there variable horizontal shifts of the spectra?
Are there four spectra in each row?
Why does the height of the spectra vary?
What is the wavelength range, can any prominent lines be identified?
What is the origin of the many white lines appearing mostly on the right hand side?
Are colors used just to prevent a black-end-white image?

[neufer]

What are these bright almost completely white spectra below the center? I thought foreground stars but you probably won't bother doing the data analysis for them if it is about galaxy motion?

Maybe just stars too bright and so overexposed?

<<MOS-spectra obtained with two quadrants totaling 221 slits + 6 reference objects (stars placed in square holes to ensure a correct alignment). Exposure time 900 seconds; LR(red) grism. This is the raw (unprocessed) image of the spectra.>>

[Chris Peterson]

I also wondered about the allmost white spectra: If they are foreground stars, why include them?
Further questions:
The parallel horizontal arrangement of the spectra suggests that the positions of the spectra in the image are not correlated with the position of the galaxy in the sky, but then why are there variable horizontal shifts of the spectra?
Are there four spectra in each row?
Why does the height of the spectra vary?
What is the wavelength range, can any prominent lines be identified?
What is the origin of the many white lines appearing mostly on the right hand side?
Are colors used just to prevent a black-end-white image?

The white lines are the slits, each of which is aligned with a galaxy of interest. They appear white because they show the overexposed direct light of the target galaxy. They correspond to the physical location of the galaxy on the image plane. On the vertical axis they are positioned so they don't overlap, in order to keep the spectra separate. There are four spectra in each row because that's what will fit on the sensor given the nature of the grism. There are rows with fewer than four, presumably because there were not four galaxies available. The height varies because the length of the slits is variable, depending on the size of the galaxy and on the constraint of avoiding overlaps. The actual spectral range depends on the grism they've utilized; nominally they can resolve from 360-1000 nm.

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

[Cousin Ricky]

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

I was going to ask about that! Thanks for anticipating my question.

[neufer]

Click to play embedded YouTube video.

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

I was going to ask about that! Thanks for anticipating my question.

Well...one of the colors has relationship to actual color of the object.

• A stopped clock is right twice a day

[orin stepanek]

Looks like the gears in an old clock; and it's about time!

[Ann]

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

Thanks, Chris. I found the colors so confusing that I decided against commenting.

Ann

[BDanielMayfield]

DistantSpectra_ESO_960.jpg

Ah, the awesome splendor of majestic galaxies, reduced to something only a barcode reader can appreciate.

[Holger Nielsen]

The white lines are the slits, each of which is aligned with a galaxy of interest. They appear white because they show the overexposed direct light of the target galaxy. They correspond to the physical location of the galaxy on the image plane. On the vertical axis they are positioned so they don't overlap, in order to keep the spectra separate. There are four spectra in each row because that's what will fit on the sensor given the nature of the grism. There are rows with fewer than four, presumably because there were not four galaxies available. The height varies because the length of the slits is variable, depending on the size of the galaxy and on the constraint of avoiding overlaps. The actual spectral range depends on the grism they've utilized; nominally they can resolve from 360-1000 nm.

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

Thank you for your explanations!

[scr33d]

"astronomers are able to use cosmological time-slowing to help measure vast distances in the universe."

Curiously the link provided in the sentence goes to wiki page that describes special relativistic time dilation, whereas the intention is about cosmological time dilation, a different, but related, thing. CTD is a result of the expansion of space while the photons are en route to us, the duration of any event we witness is dilated by a factor 1/a(t), the inverse of the scale factor, and is equal to the ratio of observed vs emitted photon wavelengths, which of course is the subject of the image.

[TheZuke!]

Looks like the gears in an old clock; and it's about time!

Or stacks of gold coins viewed edge on?

[orin stepanek]

Looks like the gears in an old clock; and it's about time!

Or stacks of gold coins viewed edge on?

Yeah; they do!