Your Catalogs

Below are some HI catalogs created by students like you!

Julie M. and Claire R.

New York, NY


Research was conducted using the outline written by Sloan Digital Sky Survey, SDSS. Using the program Photo, created by SDSS, HII regions that were previously misclassified were searched for. Background information was gathered from various research articles and websites. For information on how to distinguish HII regions from galaxies, the SDSS website was used. The SDSS website and the x-ray ROSAT survey were the only two data sources investigated in this experiment.

These regions were searched for within all of the images taken by SDSS. To narrow the investigation down, a search query was written. However, before a query was created, several regions were searched for manually to find similarities. The regions were searched for manually to create a list of several regions for research and to determine what traits they shared. The similar characteristics found in the regions were recorded so they could be included into the query. With these characteristics in the query, it was ensured that the results would return other HII regions because they have the same characteristics.

The GALAXY table was searched, since all of the misclassified regions were recorded as galaxies. The GALAXY table is a table in the SDSS database consisting of all their recorded galaxies. Within this table, the columns ra, dec, u, g, r, i, and z were investigated. The section of the query written to determine where to search varied as different areas were examined for HII regions. The query was established based on the similar traits of HII regions. The ra section of the query was included to ensure that the computer return a specific area for investigation. The five magnitudes, u, g, r, i and z were included because they were alike in HII regions that were previously found. The computer retuned the results of the query.

Once the query was written and the ra and dec of possible HII regions were noted, the SDSS Navigation Tool was used to determine if the candidate regions were actually HII regions. This tool displayed a picture of the candidate region. This picture contained information used to distinguish between HII region and galaxies, such as the color.

The pictures were printed and studied. Then, using the SDSS Object Explorer, the spectral line graphs of the possible regions were investigated to see if the possible regions contained hydrogen emission lines that HII regions contain. The spectral chart for an HII region contains a spike at the wavelength of approximately 6500. Also, for some possible regions, the x-ray ROSAT survey was investigated. The ROSAT survey is similar to SDSS’s database, except the survey only gives objects emitting x-rays. This survey was only investigated if SDSS did not give enough information to identify a region. If the possible region was included in the ROSAT survey, then it was not an HII region since HII regions do not emit x-rays. Below is our search query.

select ra, dec, u, g, r, i, z
where ra BETWEEN 195 and 196 AND
u BETWEEN 16 and 18.5 AND
g BETWEEN 16 and 18.5 AND
r BETWEEN 16 and 18 AND
i BETWEEN 17 and 19 AND
z BETWEEN 17 and 19

Download catalog as Excel spreadsheet (.xls file, 57 KB)