STEP Survey- the SMC in Time: Evolution of a Prototype interacting dwarf galaxy

1. STEP Survey- the SMC in Time: Evolution of a Prototype interacting dwarf galaxy V. Ripepi INAF-OsservatorioAstronomicodiCapodimonte, Napoli Co-I: M. Marconi, I. Musella, M. Dall’Ora,M. Capaccioli (INAF-OAC) G. Clementini, M. Tosi, D. Romano, M. Cignoni (INAF-OABo) M.R. Cioni (Univ. Hertfordshire) E. Cappellaro (INAF-OAPD) E. Brocato, G. Raimondo, M. Cantiello (INAF-OATeramo) A. Nota, M. Sirianni (STSCI) J.S. Gallagher (Univ. Wisconsin) E. Grebel (Max-Planck Institute)

2. The Magellanic System The Magellanic system is composed by LMC and SMC plus the Magellanic Bridge and Stream.

3. Why the SMC? • Dwarf Galaxies (DGs): dominant present-day population of groups and clusters • In hierarchical  CDM models DGs are possible “building blocks” of larger galaxies (including the MW)  understanding DG star formation and chemical enrichment histories is fundamental to constrain models of Galaxy formation. • Local Group DGs are ideal laboratories for understanding DG properties: we can explore in detail ages, metallicities and spatial distributions of their stellar populations. • Among Local Group DGs, the Small Magellanic Cloud (SMC) is the closest late-type dwarf (60 Kpc). • The SMC is a metal poor galaxy (Z  0.004) best local analog of the large majority of DGs and blue compact galaxies. • Tidally interacting with its neighbours: Wing and Bridge towards the LMC  probe galaxy interaction models.

4. Why the VST? • Large field of view • High photometric accuracy • Good spatial resolution • Survey limiting magnitudes fully within the reach of VST capabilities

5. OGLE III STEP Main Aims of the Survey • 1. (Core Survey) To study in a homogeneous waythe SFH of the SMC and of its stellar cluster component through deep (1-2 mag fainter than the TO of the oldest population) CMD over the whole SMC body. • Trends of SFH with position • Compare Field and Cluster SFH • Cluster and Field Age-Metallicity relations (VLT follow-up) • Low Metallicity massive Stellar Cluster with ages 2-9 Gyrs: evolution properties of stars in the mass range 1-2 M • Cluster SBF: age-metallicity degeneracy.

6. 2. (Core Survey) To study for the first time systematically the Wing and Bridge stellar populations: • Inventory of variable stars in the Bridge. • SFH of intra-cloud population by using both CMDs and variable stars (e.g. Cepheids, RR Lyrae, Scuti etc.) as population tracers. • Solve the problem of the formation and evolution of the stellar components in the Bridge (VLT follow-up): tidally stripped or locally formed (Bekki & Chiba 2007, Harris, 2007)? • 3.(Core + Hα-r’ Survey) To study the young (PMS) stellar component: • Help to detect intermediate- and low-mass PMS stars (HerbigAe/Be, T Tauri + PNs, CVs, Be etc.) • Study of IMF at low metallicity

7. Survey description • DEEP SURVEY (Core-first 2 years): • Imaging of 35 sq. deg at B~25, V~24.5, i’~23.8 with S/N=10 ( ~ 30 on the body, 3 on the Bridge, 2 in the directions of the Magellanic Stream) • Seeing < 1.0” and grey time (Moon < 7 days) required ~81 h • SHALLOW SURVEY (Core-first 2 years): • Time series photometry (30 phase points in V, 10 in B and i’) on 30 sq. deg properly placed along the wing and the bridge: B~20, V~19.5, i’ 18.5 (expected magnitude of RR Lyrae) with S/N=100. • Summing up the exposures  same limiting magnitudes as above but with S/N=5. • Seeing <1.2” and bright time (Moon < 10 days) required ~89 h • Hα-r’ SURVEY (third year): • Imaging of 65 sq. deg. at r’~21.5 with S/N~30 (S/N~10 in Hα). • Seeing < 1.0”-1.2” and bright time (no Moon restrictions) required ~ 25 h

8. Survey description

9. Survey description

10. HST/VLT Fields Complementary surveys • HST photometry on selected fields, old and young clusters (P.I. J. Gallagher/A. Nota).Glatt et al. 2008a, 2008b, 2009, Sabbi et al. 2009 • VLT spectroscopy (CaII triplet) on several SMC fields (P.I. E. Grebel). Data analysis on-going.

11. VMC@VISTA Survey • VMC@VISTA ESO Public survey (P.I: M.R. Cioni): YHKs photometry of the Magellanic System (LMC, SMC, Bridge, Stream): 184 sq. deg. at Ks=20.3 mag in five years. • V. Ripepi, G. Clementini, and M. Marconi are Co-I of VMC@VISTA Complementary surveys

12. Survey Data Plans: Data Reduction • Data reduction: • data flow ~ 1 TByte/year • pre-reduction/astrometry: Astrowise/VSTube • image subtraction analysis: VODIA • PSF photometry:Allstar/Allframe • light curve analysis: custom programs

13. STEP • Year1: Obs./data red. • Year2: Obs/data red./expl. • Year3:Obs/data red./expl. • Year4: data red./expl. Survey summary and management plan • Core Survey Summary: • 65 Squared degrees imaged in BVi at V24.5 mag with S/N > 5 • 170 h VST time over the 1st and 2nd years. Core obs: first 2 years! FTEtot = 5 • Hα-r’ Survey Summary: • 65 Squared degrees imaged in Hα-r’ at r’21.5 mag with S/N > 10 • 25 h VST time over the 3rd year.

14. Conclusions • STEP is a project perfectly suited for the VST characteristics and without extreme requirements: grey/bright time, medium seeing. • STEP is a forefront scientific project which will provide a quantum leap in our understanding of galaxy evolution. • Synergies/complementarities with important international projects: a number of HST/VLT investigations and the approved public survey VMC@VISTA. • Observing and data reductions strategies are already planned. • The data we shall release will be used for several stellar and galactic studies for many years to come.