Getting your feet wet with images at IRSA

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Based on the larger idea of Dustier, Messier Messier Marathon, this more focused activity suggestion works with fewer images to (a) get comfortable with working with images at IRSA and (b) explore differences between optical and IR properties of images of various types of objects.

Go here: and pick your favorite Messier object and/or pick one of each broad type (globular cluster, galaxy, star-forming region, planetary nebula, etc.).

Go to IRSA Finder Chart (for small objects) or IRSA Viewer (for larger objects, or objects where you want to explore images beyond what is available in Finder Chart). You may want to just start in Finder Chart and see what it looks like, then move to IRSA Viewer once you learn a little about the object(s), like size, or how different it looks in visible vs. IR.

Finder Chart has DSS, SDSS (both optical); 2MASS, WISE, Spitzer (cryo only), AKARI, IRAS (all IR). IRSA Viewer has much more data, but of the stuff that covers a large enough fraction of the sky that any given Messier object might be in it, in addition to the stuff also in Finder Chart, try SINGS (for galaxies), GLIMPSE (for galactic plane, e.g., star-forming regions), ZTF/PTF, Herschel (several versions, incl HHLI, *HPDP), MSX (for galactic plane, e.g., star-forming regions).

Skill building: play with the color stretch. Why does this matter? Why would you need to play with the stretch? What details does it bring out in any given image you’ve selected?

Science: does any given object type look the same or different in optical vs. IR? Why? Does it look the same in NIR and FIR? Why? What are the images you have loaded telling you about the spatial resolution across the wavelengths of your target?

Extension: make color images. In Finder Chart, it’s a single click that makes a 3-color image at the end of each row of images, and you don’t get to control which band is which color plane. In IRSA Viewer, you control what image is in each plane. Conventionally, red is the longest wavelength, but do what you wish. Note that IRSA Viewer will downsample images to the red plane, so if you choose an IRAS image to be the red plane, all the images will have the same enormous pixels. What is the 3-color image telling you about the science in your image? What is bright in which wavelength? What is the 3-color image you have created telling you about the spatial resolution across the wavelengths of your target? Can you create a 3-color image where the colors enhance the spatial resolution differences?

Possibly relevant IRSA videos (links may be out of date; if they are, there should be a more recent one with a similar name in the IRSA YouTube feed):