Looking for Low Luminosity Galaxies Among the SDSS Sky Fibers

1. Looking for Low Luminosity Galaxies Among the SDSS Sky Fibers Presented by Margaret Shaw, Princeton ’12 Prof. Michael Strauss Valery Rashkov, Princeton ‘08

2. Background  The search for low luminosity galaxies The core of DDO 70 galaxy • Very hard to find—we don’t know very much about them • It would be useful to have a greater population of these to study • Learn about the characteristics and formation • Close by example—stars visible

3. Background  The search for low luminosity galaxies The core of the Draco dwarf galaxy • What we are looking at are fainter and further away • Use the spectroscopic database of the SDSS and search for faint emission • lines from these objects

4. Background  The search for low luminosity galaxies  Sky fibers • SDSS telescope can take spectra instead of images using a fiber plug plate • Individually drilled for each specific field • Fibers plugged in only at the position of an object • Each plate has 640 spectroscopic fibers • About 3,000 plates have been taken • 32/640 saved for empty sky spectra (necessary to later subtract the spectrum of the sky) That’s about 96,000 sky objects in total.

5. Background  The search for low luminosity galaxies  Sky fibers Spectrum of a sky fiber before the sky is subtracted away

6. Background  The search for low luminosity galaxies  Sky fibers • My project: I am examining these sky spectra to look for low luminosity galaxies’ emission lines. These galaxies would logically be detected in low flux regions. • Don’t show up in images

7. Galaxy at Plate 500, Fiber 11 Rest Hβ NII OII OIII Hα Observed Hα Hβ OIII OIII NII NII

9. Low luminosity galaxy at Plate 1871, Fiber 437 OII 3726 Å OIII OIII 4959 Å 5007 Å

11. Sky spectra “Good” emission lines • Signal-to-noise ratio > 2.0 • Difference of maximum 3 Å between λ emittedand λ expected • Lines must be made up of 3+ pixels • Some looked for as pairs: two N lines, two OIII lines. • For a galaxy to be considered real, it would have to have 3 valid emission lines. • z > 0.001 to avoid emission line gas in the milky way

12. Sky spectra Detecting potential galaxies • Several programs are used to analyze the data. • wavesort identifies valid emission lines (written by V. Rashkov) • galaxysearch uses wavesort to pick out objects with 3+ valid emission lines and outputs a list of potential real galaxies. • These must be looked at manually. • Valery Rashkov already found 9 galaxies using these programs. • 96,000  100 objects

13. Results • Added changes to some of the programs to make it more convenient to look through the large data files • Found 3 low luminosity galaxies so far by relaxing the criteria in the programs and producing several different lists of potential real galaxies. • 2 valid emission lines • More error in the difference between λ emitted and λ expected

14. Results  Plate 291, Fiber 092 OII Hβ OIII OII Hβ OIII OIII

15. Results  Plate 2228, Fiber 377 NII Hα Hα NII NII

16. Results  Plate 756, Fiber 371 OII OIII OII OIII This light was emitted 7 billion years ago.

17. Results  Further work • Several programs run very slowly – could use work • Study characteristics of low luminosity galaxies—take images of these to see continuum • Follow up observations

18. Thank you! Professor Michael Strauss Tobias Marriage and Princeton USRP