Author Topic: How to find the redshift of the galaxy in the following image?  (Read 1404 times)

Avotus

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Hello, everyone. I'm new here, so I'm not sure if I posted this on the right forum...but anyways, I have a school assignment that requires me to find the redshift of the galaxy in images such as this. http://www.galaxyzoo.org/#/examine/AGZ0002xix.

My teacher said there would be a link under the photo that says "more information about this object"...but as you can see, there's nothing there...It's been really frustrating, please help. Thanks for reading this :)

planetaryscience

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Re: How to find the redshift of the galaxy in the following image?
« Reply #1 on: May 16, 2014, 11:44:04 pm »
Well, from that image, on the right there are 2 links: 'View on Skyserver' and "search NED". The NED link shows you various classifications for different galaxies, such as, in this case, 2MASX J07144497+6515530 from the 2 Micron All Sky Survey (2MASS) catalog. Skyserver, where the images shown in GZ come from, shows you other information on the galaxy, such as magnitude (UGRIZ values), nearby objects (finding chart and navigate), and redshift.

For the redshift, NED will occasionally show redshift (not in this case) where the velocity/redshift description is shown.

For the SDSS redshift, go to the left of the linked page, find the link labeled 'PhotoZ' and go to it; the value you want is 'z', the 2nd from top. Zerr, below it is the upper and lower limits on it (the redshift in this case is 0.10151 +/- 0.025317, or 0.076193 to 0.126827.

important note:
the spectrum of an image is the most reliable redshift value, occasionally shown below galaxies in certain areas like this:

the z value for this sample galaxy has a fairly high certainty.

The 2nd most reliable is NED, and the PhotoZ should only be used if all else fail, as it is based simply off the galaxy's color.
I like to find asteroids and galaxy mergers- but all galaxies are still fine to me.

Rick Nowell

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Re: How to find the redshift of the galaxy in the following image?
« Reply #2 on: May 17, 2014, 08:29:33 am »
the redshift of the galaxy in images such as this.

There are different ways to measure redshift (z=redshift). If we read that the redshift is
z=0.1 from an SDSS spectrum, or most any spectrum, this refers to the Light Travel Time.
LTT is as much a measure of time as of distance and therefore is the most useful. There are
however other ways to measure distance.

As we live in an expanding and thus co-moving Universe, so measuring distance is problematic.
Quoting from an article from this website might help:
http://www.atlasoftheuniverse.com/redshift.html

"This is the problem of defining a distance in an expanding universe: Two galaxies are near to
each other when the universe is only 1 billion years old. The first galaxy emits a pulse of light.
The second galaxy does not receive the pulse until the universe is 14 billion years old. By this
time, the galaxies are separated by about 26 billion light years; the pulse of light has been
travelling for 13 billion years; and the view the people receive in the second galaxy is an image
of the first galaxy when it was only 1 billion years old and when it was only about 2 billion light
years away."