By Ramsey Sahli and Brandy Stewart ASTR 498 Dr. Hayes-Gehrke December 17, 2008Sahli and Stewart 2I. Introduction The Sloan Digital Sky Survey (SDSS) is mapping out the entire sky through the use of a 2.5m telescope at Apache Point Observatory, New Mexico. This particular telescope has been specially fitted with a 120 mega pixel camera, which can image 1.15 square degrees of the sky at a time (roughly equivalent to 8 times the area of the full moon), allowing for large amounts of data to be collected in a single image. It also has been fitted with a pair of spectrographs to accurately measure the spectra of up to 600 stellar objects in a single observation. Currently, the SDSS has mapped a total of roughly a quarter of the entire sky and has been in operation since 2000. Our research focused on finding and cataloging HII regions by creating data filters to sort through the data collected thus far by the SDSS. HII regions, also known as emission nebula, are clouds of hydrogen gas and plasma that can reach sizes of several hundred light years across. As phenomena such as stellar winds, interactions between clouds and magnetic interactions ripple through these regions, stars begin to form. Molecular clouds, or huge clouds of molecular hydrogen form HII regions. As these clouds condense due to gravity, supernovas and other shocks, UV light from high-mass stars ionize the hydrogen atoms, which is where HII regions derive their name. As these hydrogen atoms ionize, it causes them to emit a reddish light when they recombine, which gives them their characteristic reddish hue. HII regions are normally located within spiral galaxies, specifically within the spiral arms. Spiral arms form as a result of what is known as spiral density waves, which collect gas and stars within the spiral arms. This dense region allows the gas to compress enough for star birth to take place. Other galaxies are normally less likely to contain HII regions due to their age and lack of free gas to begin star formation (such as elliptical galaxies). Cataloging the HII regions and describing how we located them is important for a number of reasons. The most important reason is for research purposes relating to HII regions. First and foremost is the SDSS own challenges section, which lists HII region identification as one major issue they are currently experiencing. The program used by the SDSS to identify different stellar objects has had trouble identifying HII regions in large galaxies, often misidentifying them for standalone galaxies or quasars. By finding a new method to filter and classify HII regions, astronomers will have access to more accurate lists of HII regions on the SDSS as well as a simpler method to search for HII regions on the SDSS.Sahli and Stewart 3Studying HII regions is considered to be an important part of the SDSS due to the difficulty in examining them as well as controversies surrounding certain aspects of HII regions. One major mystery concerning HII regions is the early stages of stellar formation within them: since newborn stars are still wrapped in "cocoons" of interstellar dust, actual observation has proven difficult. Since no light can physically be seen, visible light observations are not possible. Furthermore, these young stars cannot be studied very well through the use of infrared observations because they are still too young to emit much light at these wavelengths. By cataloging these HII regions, astronomers can attempt to find other ways to analyze these younger stars to better understand the early stages of star formation. II. Data Navigating through the data was our initial challenge. We started looking through the pictures that were in the “Famous Places” section on the SDSS site, but after determining the archetype HII region, we then had to search for our own. When we started searching for data, we used the search form to start our quest for specific data. On the SDSS SkyServer Search Form, there were several boxes chosen to bring back the specific data we were looking for. First, we specified in the “show me” section, that has a scroll down menu to choose stars, galaxies or quasars; for our data purposes, we chose galaxies. We never specified a region because we wanted all of the data that fit our criteria returned to us. The query also searches by magnitude and/or colors. Under the colors and magnitudes section, there was an option that allowed us to return only images with spectra, since this is the primary means to determine whether or not said object was an HII region. Pressing “generate query” yields a list of objects with their object IDs and the RA (Right Ascension) and Dec (Declination). Once the query is returned, it can be submitted to an image list generator at the bottom of the form. This returns a thumbnail list of images to go through. Once a thumbnail image is explored, there is a list of drawing options on the lower left side of the page: grid, label, photometric objects, objects with spectra, invert image, and other actions. For our research purposes, we only checked the box labeled “objects with spectra” to single out the objects in the picture that hadSahli and Stewart 4 spectra associated with it. When this option was selected, it would highlight all objects with spectra inside red boxes. Once the cursor was centered on the red box and clicked, an option is then made available to explore it by clicking “explore” on the bottom left of the page. This opens up another very detailed page with the spectrum of the object as well as a chart that lists the magnitudes, color, redshift, and other data. This page gave as the majority of the decision making data required to determine whether we would classify the object as an HII region or not. This page contained all of the necessary information we needed on the object. We used this box to explore the spectrum of the object and make a decision.We would find the redshift here. Ra, Dec, and ObjIDU, G, R, I, Z magnitudes for the object. The option we chose to single out the object. Takes you to the next pageSahli and Stewart 5The first thing we had to note was that there are 5 images taken of each object, each one through a different filter: u (UV), g (green), r (red), i (short IR), and z (long IR). The red hydrogen-emission line is at about 6500 Å and the purple hydrogen emission line is at about 4800 Å. The HII