1. The Chemo-Dynamical Structure of Galaxies: intermediate resolution spectroscopy of resolved stellar populations out to Virgo Giuseppina Battaglia ESO Simulations as part of the Design Reference Mission for E-ELT

2. Motivation: insights on galaxy formation and evolution Low mass stars can have lifetimes comparable to the age of the Universe -> record of changing galaxy properties By deriving ages, chemistry and kinematics of LARGE samples of individual stars we can gain insights on how galaxy properties were built up in time These observations are needed for a variety of galaxy types (e.g. dwarfs, spirals, ellipticals) and in a variety of environments (e.g. groups, clusters)=> beyond the Local Group

3. The NIR CaII triplet (CaT) Well tested method for obtaining large numbers of metallicities and l.o.s. velocities of individual stars (currently used in studies of Local Group dwarf galaxies, M31, RAVE, GAIA in the future…) Red Giant Branch stars as targets (usually): -> bright in the NIR -> cover wide age range (> 1 Gyr old) The CaT is a strong feature in the NIR spectra of late-type stars -> need only moderate resolution (R  6000) to obtain accurate l.o.s. vel and EW For individual RGB stars an empirical relation holds between [Fe/H] and CaT EW -> extensive literature for stellar clusters -> in composite stellar population tested in range -2.5 < [Fe/H] < -0.5 CaII triplet at  8600 Å ESO/WFI Colour-Magnitude Diagram of the Fornax dSph (Battaglia et al. 2006) Battaglia et al. 2008, MNRAS, 383, 183 [Fe/H]HR from about 60 Fe lines [Fe/H] from CaT EW Sculptor dSph: 93 stars * Fornax dSph: 36 stars

4. Example from VLT/FLAMES intermediate resolution (R=6500) studies of dSphs from DART team coverage of Sculptor with VLT/FLAMES GIRAFFE With 1h exposure time per pointing S/N=10/Å @ V=19.5. At this S/N: -> l.o.s. velocities accurate ± 5 km/s -> [Fe/H] accurate to ± 0.25 dex 20 pointings -> 670 individual members The Sculptor dSph (distance = 80 kpc)

5. Looking farther out Main points to address: Larger distances Crowding: effect of stellar background in the spatial resolution element (spaxel) on the properties of target RGB star -> to which extent will the CaT [Fe/H] and velocity derived from the integrated spectrum resemble the ones of the target RGB star? => Can we derive accurate [Fe/H] and line-of-sight velocities from the CaT lines for large numbers of individual RGB stars in a “reasonable” observing time? Can we perform similar studies out to the distance of the Virgo cluster with the E-ELT?

6. Setting up the simulations

7. Simulations: creating the stellar catalogue 1Re 2Re 5Re Stellar population code developed by J.Liske & E.Tolstoy Stellar population: constant SF (14-12 Gyr ago); [Fe/H] = -1.8 (MP) or -1 (MR); solar [alpha/Fe] Target: RGB stars of different magnitude Stellar background: - fix the distance and the surface brightness of the object to observe - explore different projected radii (different crowding) - at each radius, simulate a stellar catalogue over a large area (5” x 5”) - include PSF effects (we use LTAO) - find which stars contribute to the light in a 50mas spaxel, where the RGB star target is The stellar catalogue contains all the stars that contribute a fraction of their light to the spaxel (target + stellar background)

8. For each star in the catalogue find the appropriate synthetic spectrum (log g, Teff, [M/H], [alpha/Fe]) in the Munari et al. (2005) library at R=20˙000 Rescale each spectrum according to the light contributed by the star to the spaxel Redshift individual spectra according to stellar velocities (we assume a Gaussian velocity distribution) Produce the integrated spectrum (R=20000) in the spaxel take into account effect of atmosphere, telescope, instrument, site, mirror coating Convolve to desired resolution (R=6000) and add noise Measure the line-of-sight velocity and CaT EWs from the integrated spectrum & compare to the ones of the target RGB star Creating the simulated spectrum

9. Figures of merit (accuracies) We consider that the simulations produce accurate enough velocities and ∑W if they agree with the input values within - 0.7 Å -> 0.3 dex (  [Fe/H] = 0.44 x  ∑W ) - 30 km/s (CenA & M87); 5 km/s (NGC205) (this is similar to accuracies of current studies) We perform 300 random realizations to account for varying stellar background and noise We derive the distribution of (V_los_simulated - V_los_input) and (∑W_simulated - ∑W_input) where ∑W = EW 2 + EW 3 -> the systematics are quantified by the mean of the distributions -> the errors are quantified by the scatter of the distributions

10. SCIENTIFIC: STELLAR POPULATION: constant SFH (14-12 Gyr ago), [alpha/Fe]=0, [Fe/H] = -1.8 (“metal poor”) and [Fe/H]= -1.0 (“metal rich”) DISTANCES: Local Group (800 kpc), Centaurus A (4 Mpc), Virgo (17 Mpc) GALAXIES: NGC205 (dwarf, internal dispersion used = 35 km/s), CenA, M87 (internal dispersion used = 100 km/s). Surface brightness profiles from Mateo 1998, van den Bergh 1976, goldmine web database, respectively RADII: 1, 2, 3.5, 5 Re (depending on the galaxy) Explored parameters

11. TECHNICAL: TELESCOPE DIAMETER = 42 m SPAXEL SIZE= 50mas PSF: LTAO in I band (to minimize the loss of flux from the spaxel) AIRMASS = 1.0 & SEEING = 0.8” INSTRUMENT EFFICIENCY: 0.28 WAVELENGTH RANGE: 8000-9000 Å RESOLVING POWER: R  6000 (3 pixels per resolution element) MIRRORS COATING: bare Al; Ag/Al SITE: Paranal-like; High&Dry EXPOSURE TIME: from 20min to 50h, depending on the object Explored parameters

12. Results

13. Results for the Local Group: NGC205 Down to 1 mag below the tip (I  21.4) Exp. times: 20m, 30m, 1h, 2h Stars resolved with a 50 mas spaxel at every radius 20min, Paranal-like site, bare Al coating 20m exposure time x pointing => accuracy: ± 2 km/s accuracy: ± 0.2 dex Velocity EW Tip of the RGB 1 mag below the tip Velocity * MP MR

14. Centaurus A: example of spectra Targets: MR and MP RGB at the tip and 0.5 mag below tip (MR: I= 23.9, 24.4; MP: I= 23.7, 24.2) R/Re = 1, 2, 3.5, 5 -> R  6, 12, 22, 31 kpc (crowding is not a problem at these radii, for the considered spaxel size) Exp. time: 1h, 2h, 5h MR, Paranal, Ag/Al, 5h, tip of the RGB Tip of the RGB 0.5 mag below the tip Tip of the RGB 0.5 mag below the tip Example of different crowding

15. Centaurus A: velocity (0.5 mag below the tip) 5h 2h 1h High&Dry+ Ag/Al Paranal-like + Ag/Al Paranal-like + Bare Al

16. Centaurus A: EW (0.5 mag below the tip) 5h 2h 1h High&Dry+ Ag/Al Paranal-like + Ag/Al Paranal-like + Bare Al

17. Results for M87 (Virgo): R= 2Re Targets: MR and MP RGB at the tip ( I = 27.2, I = 27.0) R/Re = 2 (a lot of crowding), 5 (not so much crowding) -> R  18, 45 kpc Exp. time: 20h, 50h Integration on: 1 spaxel, 9 spaxels, 25 spaxels Paranal, Ag/Al, 50h, tip of the RGB MR VRGB= -79km/s MP VRGB= +312 km/s -integrated spectrum on 25 spaxels - integrated spectrum on 1 spaxel - rescaled spectrum of the target RGB star Integrated spectrum on 25 spaxels dominated by stellar background

18. Results for M87 (Virgo): R= 5Re Targets: MR and MP RGB at the tip ( I = 27.2, I = 27.0) R/Re = 2 (a lot of crowding), 5 (not so much crowding) -> R  18, 45 kpc Exp. time: 20h, 50h Integration on: 1 spaxel, 9 spaxels, 25 spaxels Paranal, Ag/Al, 50h, tip of the RGB MR VRGB= -79km/s MP VRGB= +312 km/s -integrated spectrum on 25 spaxels - integrated spectrum on 1 spaxel - rescaled spectrum of the target RGB star Integrated spectrum on 25 spaxels considerable improvement

19. Results for M87 (Virgo): summary Integrated spectrum on 1 spaxel has too low a s/n both at 2Re and 5Re, in all of the explored cases => too much flux is lost because of small spaxel size + PSF effect At 2Re, integrated spectrum on 25 spaxels is dominated by stellar background => at this and smallest projected radii there is too much crowding At 5Re: - metallicities are usually underestimated of about 1 dex - the Paranal-like + bare Al case yields very discrepant velocities - velocities can be measured within the desired accuracy for very bright targets (at the tip of the RGB, MP) with 20h exposure time when integrating on 25 spaxels (50h for 9 spaxels).

20. Observing time to collect samples of 1000 targets M87 (10” = 0.8 kpc): At the tip of the RGB, in the outer parts (around 5 Re), about 6 pointings would be needed: -20h exp. time per pointing -> 120h on source -50h exp. time per pointing -> 300h on source ASSUMPTION: single IFU with 10”x10” field-of-view (spaxel size= 50mas) NGC205 (10” = 40pc): Down to 1 mag below the tip, with 20m exp. time per pointing => 25 pointings (within 2Re), I.e. 8h exposure time on source Centaurus A (10” = 180pc): Down to 0.5 mag below the tip: -5h exp. time per pointing (Paranal-like, bare Al), 25 pointings within 5Re => 130h on source -2h exp. time per pointing (Paranal-like, Ag/Al), 25 pointings within 5Re => 50h on source ±

21. Sensitivity to input parameters INSTRUMENT EFFICIENCY: M87 case appears to be “border-line” -> important to have values as realistic as possible SITE: negligible influence MIRRORS COATING: Appears to be important for -CenA => reduced exp. time per pointing from 5h to 2h -M87 => when considering 20h exp. time, velocities are not recovered with a bare Al coating FIELD-OF-VIEW: A 10”x10” field-of-view is sufficient in most cases. Given the goal of acquiring large number of targets over large areas, a larger field-of-view (or multi-IFUs) would allow shorter exposure times