Cosmic Collisions

Frequently Asked Questions

The galaxy that I'm looking at is really low resolution and doesn't look like any of the categories here. How do I classify that?
Objects that are incredibly low resolution (only a few pixels across and generally circular) are point sources, and have their own category. These are objects that are too small to be resolved clearly. Objects that are larger than point sources but still difficult to see clearly require a bit more judgment. You should choose the answer that most closely matches the examples given.

How do I tell the difference between a spheroid and a point source?
A point source will be small, only 2-3 pixels across at it's brightest, with no structure outside of this. In addition, due to the laws of optics, a point source will appear larger in the mid-infrared panels on the bottom of the classification image, so if you're unsure, compare the left and middle image with the image on the right.

Here is an example of a spheroid galaxy, as you would see it when you classify.

And here is a point source. Note that the spheroid galaxy looks smaller in the mid-IR than in the near-IR panels, where the point source looks larger. Also note that the point source is only a few pixels across, no matter what wavelength its shown in, while the spheroid galaxy is well resolved and much larger.

How do I tell the difference between a face-on disk and a spheroid?
A face-on disk will likely have some internal structure, and will appear bright over its entire surface rather than just in the center. A spheroid is brighter in the center and dimmer into the outskirts than a face-on disk, and is more likely to appear internally smooth.

Here is an example of a face-on disk. As you can see, it is circular, which, in the two dimensional projection of the sky, is the same shape as a spheroid galaxy. However, because this object has clear spiral structure we can assert that it is a disk, not a sphere. Compare this with the image of a spheroid galaxy in the previous question.

There are certainly some disks without this telltale internal structure, especially at low resolution, and for those objects, there isn't a good way to distinguish between face-on disks and spheroids, so in those cases, you will just have to use your best judgment.

How do I decide if an irregular galaxy is a merger or not?
In general, try to look for the specific merger signatures outlined in the field guide; multiple nuclei sharing a common envelope, tadpole-like tidal tails extending away from the galaxy, and companions that are visibly interacting and distorting the object. If a galaxy is distorted/irregular but lacks these features, it may just be a galaxy in the early universe that is still in the process of coalescing.

What if I see something that doesn't match any of the examples?
Galaxies are very diverse and come in all shapes. It's possible that you're seeing a galaxy of a type we haven't named yet and didn't consider when we made our categories! In this case, you should choose the answer that most closely matches the examples given, and then tell us about it in the talk page so we can get a look at it ourselves!

Do these images show what the galaxies would actually look like, if we could see them with our eyes?
Probably not, but it's possible in some cases. JWST observes at much redder wavelengths than our eyes can see. Our eyes observe wavelengths of light 0.3 to 0.7 microns; JWST observes from 0.9 to 21 microns, though the PRIMER survey we're using only goes to 18 microns (see the figure below). The color picture in the classification image is a color balanced composite of all the available NIRCam bands, from 0.9 to 4.4 microns, in the near-infrared. For nearby, low-redshifted galaxies, this will not show what the galaxy looks like to our eyes. But for galaxies around redshift of 2, the visible spectrum has moved into the range of NIRCam, and so the composite image does show approximately what the object would look like to the eye - if you were close enough to see it.

This figure shows the various filters and their corresponding wavelengths for the PRIMER survey. The RGB composite image uses all available NIRCam filters shown here except for F410M. The middle image shows the object at 2.77 microns using the F277W filter. The rightmost image shows the object at 7.7 microns using the F770W filter.

What if I classify a galaxy "incorrectly?"
These images will be seen many people, so don't worry if you aren't completely sure about your answers. One uncertain answer won't throw off the overall result, and if everyone is uncertain then that will be displayed in an inconclusive classification result.

Will I get credit for helping out here?
Yes, if you included your real name in your Zooniverse account and helped classify galaxies for us, you'll be included in the acknowledgements section of any paper that gets published using this data.