How is it done?

[rstevenson]

Hello all,

I have a vague idea of how astrophysicists can deduce information about objects like galaxies -- their distance, rate of revolution, types and ages of stars, and so on, from data collected through earth-based and orbital instruments. But I'd like to know more about that process so that I can better understand what I'm seeing and learning here on the Asterisk*.

Attached below, for example, is a detail of an intriguing little scene from the bottom-right corner (in its usual orientation as I find it on-line) of the Hubble Ultra Deep Field. If a person were interested in that central yellowish galaxy and the smaller blueish galaxy at its end, and in the tail that seems to come from one of them, where could one go to look for more information? (And how to find the relevant information, which means how to reference the objects of interest?) Or if one could command other telescopes, what would one ask for to determine, say, how far away each of them is, whether they're near each other or just coincidentally aligned, which one of them that tail is attached to, in what direction and how fast are they each moving, and so on?

Yeah, I know, you have to study astrophysics at a university level for several years to get started, and I am in the process of getting started doing just that. But I'm impatient. Any thoughts you may have on finding out more about this process, that I can follow up on-line, would be greatly appreciated.

Thanks,

Rob

[Chris Peterson]

Attached below, for example, is a detail of an intriguing little scene from the bottom-right corner (in its usual orientation as I find it on-line) of the Hubble Ultra Deep Field. If a person were interested in that central yellowish galaxy and the smaller blueish galaxy at its end, and in the tail that seems to come from one of them, where could one go to look for more information? (And how to find the relevant information, which means how to reference the objects of interest?) Or if one could command other telescopes, what would one ask for to determine, say, how far away each of them is, whether they're near each other or just coincidentally aligned, which one of them that tail is attached to, in what direction and how fast are they each moving, and so on?

Well, to start with you'd want to see if the objects have any sort of formal identification. In the Deep Field, they might not. There are different ways of going about this; what I'd probably do is obtain the FITS files for the image, which contain WCS data in their headers. This would allow me to very accurately determine the coordinates of the objects. (There are other ways of getting the coordinates, using various software tools.) Armed with the coordinates, I'd look for matching objects in Simbad, Vizier, or similar online databases. If I found identifiers, I'd do a literature search and see if anybody has studied these objects.

These objects are very small, so getting any higher resolution images could prove difficult, which could limit structural analysis of something like the tail. Optically, the richest data usually comes from spectroscopic analysis, which would allow you to determine the redshift for each object. If both had the same redshift, you would probably assume they are interacting, otherwise you'd assume they are simply chance, line-of-sight objects. You might be able place the spectroscope slit along the plane of the edge-on galaxy, and derive a rotation curve (from the Doppler shift of sample emission lines). This would provide information that could assist in determining the mass of the galaxy. Knowing the distance (from the redshift) and the measured luminosity will allow you to estimate the absolute luminosity, which is also useful in determining mass. Spectral data can also help determine overall metallicity, which tells something about the age and evolution of the galaxies.

[rstevenson]

Thanks Chris. I did a Google for "Hubble Ultra Deep Field FITS files" which brought up a number of interesting links. That, plus the other things you mentioned, ought to keep me busy for a while.

Rob

[neufer]

Thanks Chris.

I did a Google for "Hubble Ultra Deep Field FITS files" which brought up a number of interesting links.
That, plus the other things you mentioned, ought to keep me busy for a while.

<<Googly eyes are small plastic craft supplies used to imitate eyeballs. Googly eyes traditionally are composed of a clear, hard-plastic shell, with a smaller, black plastic disk trapped within. The plastic shells come in a variety of sizes ranging from 15/16 of an inch to over 3 inches in diameter. The inner black disk is allowed to move freely within the larger clear plastic shell, which makes the eyes appear to move. These disks come in a variety of colors including pink, blue, yellow, and green. Googly eyes are used for a variety of arts and crafts projects including pipe cleaner farm animals, silly sock puppets, and other creations brought forth from the imaginations of children. Googly eyes may also be attached to inanimate objects in order to give the objects a "silly" or "cute" appearance. This use often personifies the objects for a humorous effect.>>

[owlice]

Last year's litter of reindeer

[rstevenson]

Seeing there were more posts to this thread, I eagerly opened it up to reveal ... ... Googley Eyes.

Rob

[owlice]

My apologies, Rob; I thought you were busy with the FITS files and databases....

As you progress with your examination of the data, you might want to look through the Engineering Deck to see what tools there might help you/be fun to play with. A number of them manipulate FITS data in various ways.