The Outer Limits Survey: Stellar Populations at the Extremities of the Magellanic Clouds

1. The Outer Limits Survey: Stellar Populations at the Extremities of the Magellanic Clouds Abi Saha and Edward Olszewski, co-P.I.’s Collaborators: Chris Smith Knut Olsen (Jason Harris) Armin Rest Pat Knezek (Brian Brondel) Pat Seitzer Nick Suntzeff A Subramaniam Kem Cook Dante Minniti (Andrew Dolphin)

2. I. Goals Extent and Structure of LMC and SMC Does the stellar pop finally merge into and become part of an all-encompassing halo? What is this outer population like compared to those of Milky Way and M31? Do we see signs of tidal features? Do we see evidence of star formation in Magellanic Stream and in the path of the newly measured LMC orbit?

3. II. Fields to Study Several pencil beams or crosscuts as seen from Center of LMC/SMC. Guided by Saha’s original test project from 7 to 12.5 degrees N of LMC Center. Studying Populations beyond normal view of extent of each galaxy.

5. III. Imaging Need to observe to well below 15 Gyr MSTO Requires approx 3000 sec in C, 1800 sec in R, and 2200 sec in I Need wide range of color to help separate populations– C and R for instance Need metallicity sensitivity- C and DDO51 Require followup spectroscopy using 4-6.5m telescopes- M and DDO 51 isolate giants (400s in M, 1800s in DDO51)

6. IV. Status of the project ALL DATA ARE REDUCED (how I spent my summer) We are in year 3-- all year-3 observing in late Oct and late December 2008. 10 4m mosaic nights and 3 0.9m calibration nights 4m-- we have had 20 nights to date (about 1/4th with half nights to accommodate Essence) 16 nights clear– 4 cloudy or horrible seeing. We are exactly on track- 38 fields completed out of about 60 planned. We can observe about 2-2.5 fields/night 0.9m– 16 nights to date, 10 photometric 35 of 38 completed fields are calibrated. We can observe about 6 fields per night

7. We are asking for an augmentation of 4 0.9m nights in 2009B. If the 4m weather is problematic we may have to ask for a few more nights, but we won’t know until approx Jan 1. Data remaining to be taken include Magellanic Stream fields, LMC orbit fields, regions between the Clouds, and some last control fields. Because we have reduced all our data to date, we are slightly modifying some field choices to continue to survey farther from LMC and to study the outer falloff in SMC.

8. V. Quick Primer on Data Reduction • We have developed a procedure, after extensive testing, • that is almost a pipeline, but requires a small amount • of human help at each step. • The usual steps through flatfielding (IRAF based). • We have found that dome flats are sufficient. • We put images back on almost same pixel from • night to night or run to run. • 2) We have put L92 and L98 standard fields on all 8 chips • during bad seeing and find that the zeropoints • and color terms are statistically the same chip-to-chip. • 3) Pre-photometry • We use IRAF routines to • Update the World Coordinate System

9. 4. We rectify image and join all 8 chips into one image. We have discovered, by extensive testing and experimentation, how to do photometry on rectified images. This falsifies the Massey NOAO memo that says that excellent stellar phot cannot be done on same. 5. We form deep, medium, shallow images Example C band – 3x1080s, 300s, 30s Deep is weighted sum of all Medium is 300 + 30; Shallow 30 6) Update header for new gain and readnoise, set all saturated pixels to -32000, clean up regions where same number of images not seen. 7) We therefore have 13 images, approx 8.5kx8.5k, on which to do photometry for each field.

10. VI. Photometry We use Saha’s DoPhot, with added routines to deal with PSF variation and focus and CCD tilt across focal plane. We have 13 instrumental magnitude sets per field. Since R band is deepest with usually good seeing, we use R band objects as our fiducial. We match objects from other lists using the RA/Dec and the DoPhot object type.

11. VII. Calibration We take 2 images per 4m field on 0.9m, called N and S, positioned to cover pieces of 4 4m chips per image. We use DoPhot and then do standard photometry reductions. In a perfect world, the N and S are taken on different nights for further tests of photometry. We add the long, medium, short 4m lists together, using overlap to determine the internal transformation. We then use overlap of 4m and 0.9m magnitudes to convert the 0.9m phot to 4m phot using a linear transformation (color terms are in the 0.9m reductions).

12. Observe all fields with 0.9m telescope in photometric conditions Calibrate against standard stars Transfer onto 4m fields allowing zero-point and color adjustments Photometric Calibration

13. VIII. Testing and reductions 1 man year of pipeline and photometry testing Saha and Brian Brondel 0.3 man years of 0.9m reductions and testing of conversion to 4m data– Saha 0.5 man years of 4m reductions- Olszewski and Saha 0.3 man years of creation of combined photometry sets- Saha (and of course observing, about 45 nights in all to date because of 1/2nights shared with Essence)

14. IX. Archive 38 fields x 13 images ready to go into archive now. That’s about 500 gigabytes. Photometry and starlists and coordinates will be placed in archive concurrently with science analysis. (We note that regular NOAO TACs have given time to two projects exceedingly similar to OLS during the past 2 years.)

15. X. Three results. • Fields from 7 to 14 degrees North of LMC • (1 degree is about 0.85 kpc) • Dominant population is about 8 Gyr in the more • outer populations. • LMC continues beyond 14 degrees (tidal radius • is about 13 degrees according to M Weinberg) • Exponential disk continues out beyond 14 degrees.

16. F9N

17. F11N

20. Log Counts Distance from LMC center (degrees)

22. 2) Pencil Beam away from SMC SMC extent seems to be about 1/3rd that of LMC. Roughly in line with masses. SMC outer regions seems to show a slower falloff than expected

24. 3) One set of control fields as f(latitude) This set of control fields looks a bit different from a set on another side. We are starting work on a proper way to statistically subtract control fields and to account for variation in the Milky Way as longitude changes and latitude is held constant.

26. Where do we go from here? • Construct “Hess diagrams” accounting for incompleteness • Construct empirical Galaxy model “Hess diagram” from control fields. • Model multi-component Hess diagrams using stellar evolution models using Bayesian methods and look for depth effects Tolstoy & Saha 1996, ApJ 462, 672 Dolphin 2002, MNRAS, 332, 91 • Identify giants associated with Clouds – follow up spectroscopy for velocities – use brighter MS stars? • Identify objects of extreme color, incl. QSOs, WDs, BDs