4 calculate the average number of galaxies per eld as

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Unformatted text preview: a given area is N , the typical variation from √ ¯ field to field should be N . Lab tasks. 3. Count the number of galaxies brighter than mr = 21 (the galaxies marked by circles) and record the number for each field. 4. Calculate the average number of galaxies per field as well as the average number of galaxies per arcminute squared using counts from all ten fields. You can choose more fields of your own within the areas covered by the SDSS survey, just make sure that they are all 5 arcminutes on a side. 5. Compare counts in each field to the average and expected variation from field to field. Does it look like the distribution of galaxy counts in these fields is close to the Poisson distribution (i.e., is the distribution of galaxies on the sky uniform)? Note: In a couple weeks, you will need the results from the above tasks in another PHSC 12000 lab, so please be sure to keep a separate copy of your results in addition to the lab write up that you turn in. Galaxy Spectra In Google Sky activate the SDSS Galaxy Spectroscopic Layer, make sure the SDSS Galaxy Photometric Layer is turned off. On the lowest zoom, find the strips of sky that were observed by the SDSS. Now zoom in and look for some nearby (i.e., large and bright) galaxies that have spectra available (circled in brown). Remember, circles are only placed around the brightest galaxies in your field of view, so if you’d like to check whether SDSS has a dim galaxy’s spectrum, just zoom in on that galaxy until it is alone or is one of the brightest galaxies. Find a few disk/spiral galaxies, and a few elliptical galaxies. You can mark galaxies and go back to them later with the placemark tool (thumbtack in the top toolbar). To view their spectra click on the desired circled galaxies, and follow the link at the bottom of the popup bubble. Lab tasks. 6. Review the spectra of six elliptical and six spiral galaxies, observe the general pattern and similarities in the spectra of galaxies of either class. PHSC12000 V1.0 5 7. What is the relationship between the morphological class of a galaxy and its spectrum? Sketch a typical spectrum characteristic for elliptical and spiral galaxies. 8. Discuss the main differences in the spectra of elliptical and spiral galaxies and give your explanation for the origin of these differences....
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