Surveying the Extremities of the Magellanic Clouds A work in progress A. Saha Collaborators: Ed Olszewski Chris Smith Knut Olsen Jason Harris Armin Rest Pat Knezek Brian Brondel Pat Seitzer Nick Suntzeff A Subramaniam Kem Cook Dante Minniti (Andrew Dolphin)

The Survey Imaging with MOSAIC on Blanco 4m of ~40 fields ( plus ~20 control fields) between 7 and 15 degrees from LMC and/or SMC, and along Magellanic stream (both, trailing and leading arms) Imaging with MOSAIC on Blanco 4m of ~40 fields ( plus ~20 control fields) between 7 and 15 degrees from LMC and/or SMC, and along Magellanic stream (both, trailing and leading arms) 5 bands: C, R, I, M, DDO51 5 bands: C, R, I, M, DDO51 Gets to R ~24, C~25, I~23.5, well past oldest possible TO. Shallower in M and DDO51 Gets to R ~24, C~25, I~23.5, well past oldest possible TO. Shallower in M and DDO51 Study distribution of stars + abundances + ages as data allow Study distribution of stars + abundances + ages as data allow Identify giants at LMC/SMC like distances and in Galactic halo for follow up kinematic studies and spectroscopic abundances Identify giants at LMC/SMC like distances and in Galactic halo for follow up kinematic studies and spectroscopic abundances

Why study extremities? In our Galaxy the most metal poor (and oldest?) stars are distributed in a spheroidal halo extending beyond 25 kpc. In our Galaxy the most metal poor (and oldest?) stars are distributed in a spheroidal halo extending beyond 25 kpc. Their spatial distribution, chemical composition, and kinematics provide clues regarding the Galaxy’s early history, as well as its continued interaction with neighboring galaxies - - e.g. what is the distribution of the oldest stars along the line between the LMC and SMC, and what does that tell us about the history of interaction between these objects? Their spatial distribution, chemical composition, and kinematics provide clues regarding the Galaxy’s early history, as well as its continued interaction with neighboring galaxies - - e.g. what is the distribution of the oldest stars along the line between the LMC and SMC, and what does that tell us about the history of interaction between these objects? An extended stellar structure provides dynamical clues about a Dark Matter halo An extended stellar structure provides dynamical clues about a Dark Matter halo Ignorance of the extended stellar structure (or lack thereof) in our nearest neighbor is an embarassment! Ignorance of the extended stellar structure (or lack thereof) in our nearest neighbor is an embarassment!

The nature of stellar halos Characterized by extended spatial distribution, high velocity dispersion, and low chemical enrichment Characterized by extended spatial distribution, high velocity dispersion, and low chemical enrichment ---- but until now all 3 only measured in the Galaxy ---- but until now all 3 only measured in the Galaxy What makes a stellar halo? What makes a stellar halo? -- original component ? -- original component ? -- mainly accreted? -- mainly accreted? -- mixture of both? -- mixture of both? Studies within the Galaxy are inconclusive HST studies in M31 still argue about what the real halo is HST studies in M31 still argue about what the real halo is What relationship is there between a stellar halo and a DM halo? What relationship is there between a stellar halo and a DM halo?

L/SMC specific issues How old are stars in the extremities of the Clouds, and what are their chemical properties? How old are stars in the extremities of the Clouds, and what are their chemical properties? How are stars in the L/SMC extremities distributed? --- How are stars in the L/SMC extremities distributed? Disk-like (exponential)? --- Disk-like (exponential)? --- Halo-like (DeVaucouleurs or power law?) --- Halo-like (DeVaucouleurs or power law?) --- How far do they extend? --- How far do they extend? --- Continuity between LMC and SMC? --- Continuity between LMC and SMC? --- Interaction with Galaxy halo? --- Interaction with Galaxy halo? Interaction if any between stars in Galaxy halo with stars in outlying LMC/SMC regions -- kinematic signatures? Interaction if any between stars in Galaxy halo with stars in outlying LMC/SMC regions -- kinematic signatures? Evidence of tidal stripping of stars from the L/SMC by Galaxy Evidence of tidal stripping of stars from the L/SMC by Galaxy

Structure of the LMC disk 2MASS and DENIS 2MASS and DENIS -- shows elongation of the LMC disk and its tilt (van der Marel 2001, AJ 122, 1827) -- shows elongation of the LMC disk and its tilt (van der Marel 2001, AJ 122, 1827) -- yields disk scale length -- yields disk scale length -- not useful beyond ~8 degrees from LMC center -- not much information on metallicities -- not much information on metallicities

Star count densities de-projected to the plane of the LMC Note intrinsic elongation Disk scale length = kpc

Relative Positions of LMC - SMC- Galaxy …van der Marel(2001) AJ, 122, 1827

Indirect Evidence for LMC halo (an incomplete discussion) Feast (1964, 68) - PN velocity dispersion ~22 km/s in LMC exceeds that of H II regions (~10 km/s)  a less flattened system Feast (1964, 68) - PN velocity dispersion ~22 km/s in LMC exceeds that of H II regions (~10 km/s)  a less flattened system Schommer et al. (1992) - used kinematics of old clusters (instead of PN) to show the same. But also argued that an ~30 km/s dispersion is insufficient for an isothermal halo Schommer et al. (1992) - used kinematics of old clusters (instead of PN) to show the same. But also argued that an ~30 km/s dispersion is insufficient for an isothermal halo Hughes et al (1991) - Short period (~180 days) Miras in the LMC have velocity dispersion ~ 33 km/s. But Hartwick & Cowley (1989, 91) -- CH stars have dispersion of only ~24 km/s Hughes et al (1991) - Short period (~180 days) Miras in the LMC have velocity dispersion ~ 33 km/s. But Hartwick & Cowley (1989, 91) -- CH stars have dispersion of only ~24 km/s Kinman (1992) -- RR Lyraes as far out as 15 degrees have mags and velocities consistent with LMC membership. Observed distribution fits a King model with central density of 22 RRLs/sq degree. Suntzeff (1992) and Alves (2004) argue show they are also consistent with an extended disk model, a possibility also discussed by Kinman. Kinman (1992) -- RR Lyraes as far out as 15 degrees have mags and velocities consistent with LMC membership. Observed distribution fits a King model with central density of 22 RRLs/sq degree. Suntzeff (1992) and Alves (2004) argue show they are also consistent with an extended disk model, a possibility also discussed by Kinman. Minniti et al (2003) - Velocity dispersion of RRLs over the LMC bar of 53  10 km/s Minniti et al (2003) - Velocity dispersion of RRLs over the LMC bar of 53  10 km/s

Direct detection of extended structure Irwin (1991) -- star counts from UKSTU Irwin (1991) -- star counts from UKSTU Stryker (1984) -- photometry from 4m PF plates of sky around NGC 2257 Stryker (1984) -- photometry from 4m PF plates of sky around NGC 2257 Gallart et al (2004) -- Deep CMD 8 degrees from the LMC Gallart et al (2004) -- Deep CMD 8 degrees from the LMC

Designing a new Survey What we want to map: What we want to map: 1. Spatial Distribution of star densities at very low levels - - needs separation from Galactic fore-ground stars solution: use MS stars: has stars of all ages and abundances -- UNBIASED !! 2. Metallicities and ages of component populations 3. Kinematics of representative stars - requires identification of individual stars as members of LMC/SMC/Galaxy-halo 4. Distinction from background galaxies

Survey requirements Need at least 4 bands to separate temperature, metallicity, age, reddening Need at least 4 bands to separate temperature, metallicity, age, reddening Giant vs dwarf separation Giant vs dwarf separation Mitigate age-metallicity degeneracy Mitigate age-metallicity degeneracy

Need to control systematic errors, especially in R and I !!

Preliminary Results

7 degrees North of LMC

9 degrees North

11 degrees North

12.5 degrees North

Control Field : l = 225, b = -75

Preliminary Conclusions CRI photomtery (2 hrs per pointing) very cleanly identifies the MS stars in LMC and SMC. CRI photomtery (2 hrs per pointing) very cleanly identifies the MS stars in LMC and SMC. Provides a handle to study differences in metallicities and ages Provides a handle to study differences in metallicities and ages At first sight, the age of the extended structure is metal poor and old, but not “ancient” At first sight, the age of the extended structure is metal poor and old, but not “ancient” Can be counted -- after corrections for FG and BG pollution -- and used as probes of stellar density …. Expected to work past 15 kpc Can be counted -- after corrections for FG and BG pollution -- and used as probes of stellar density …. Expected to work past 15 kpc Could be used to search for stars formed in the wake of the Magellanic stream Could be used to search for stars formed in the wake of the Magellanic stream

Survey Practicalities Need R ~24 & I ~23.5 w S/N ~ 20; C ~25 w S/N ~5 ==> 4m class telescope. T/his also provides S/N > 50 at R~21 in all above bands Need R ~24 & I ~23.5 w S/N ~ 20; C ~25 w S/N ~5 ==> 4m class telescope. T/his also provides S/N > 50 at R~21 in all above bands M and S/N ~ 50 at R ~21 M and S/N ~ 50 at R ~21 Need large areas ==> MOSAIC on Blanco 4m is the best available Need large areas ==> MOSAIC on Blanco 4m is the best available Observing times ~ 4hrs per field Observing times ~ 4hrs per field Area per field = 36x36 arc-min square = 0.36 sq degrees Area per field = 36x36 arc-min square = 0.36 sq degrees “Reasonable” time request: 30 nights ==> ~ 60 fields “Reasonable” time request: 30 nights ==> ~ 60 fields Need control fields: wide range of Galactic latitudes Need control fields: wide range of Galactic latitudes

An Early Result Counting stars in the MS in the 4 LMC outskirt fields shown: Counting stars in the MS in the 4 LMC outskirt fields shown:

Another Early Result…

Status Feasibility for attaining science goals demonstrated Feasibility for attaining science goals demonstrated Data collection in progress in earnest -- approx half way through Data collection in progress in earnest -- approx half way through Processing and photometry to requisite precision proved feasible Processing and photometry to requisite precision proved feasible Production processing to begin soon Production processing to begin soon

Early Results Extended structure to 10 disk scale lengths appears disk-like Extended structure to 10 disk scale lengths appears disk-like Dominant age in LMC periphery (albeit limited sample) is ~8 Gyrs: significantly younger than oldest clusters Dominant age in LMC periphery (albeit limited sample) is ~8 Gyrs: significantly younger than oldest clusters Early hints that Magellanic Stream has stars after all Early hints that Magellanic Stream has stars after all

Complete Coverage? Depending on what complexities this survey reveals, there will likely be a strong case for doing a “filled” survey over ~1000 square degrees. Depending on what complexities this survey reveals, there will likely be a strong case for doing a “filled” survey over ~1000 square degrees. Ideal case for LSST !!! Ideal case for LSST !!!

27 degrees West