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StePS Stellar Populations at intermediate redshift Survey with WEAVE Bianca Poggianti – Angela Iovino (co-Leads) on behalf of the StePS team A. Mercurio, M. Longhetti, L. Morelli, L. Pozzetti, A. Gallazzi, M. Bolzonella, S. Zibetti, C. Haines , S. Trager, M. Balcells, I. Ferreras, J. Gallego, R. Garcia Benito, R. GonzalesDelgado, J. Iglesia, J. Iglesias Paramo, J. Knapen, A. Pizzella, S. McGee, P. Sanchez Blazquez, C. Weidner, P. Merluzzi, G. Busarello, N. Napolitano, F. La Barbera, E. Zucca, S. Bardelli StePS motivation Studies of galaxy evolution based on an “archaelogical” approach (stellar populations of present-day galaxies to infer the galaxy history – e.g. SDSS), or observing galaxies at earlier epochs (mainly snapshots of their evolution, eg. large spectroscopic surveys such as zCOSMOS, VIPERS). Application of archaelogical approach at different epochs a significant step forward. NEED FOR GOOD S/N and resolution Our and others’ simulations show that S/N>15 needed to do detailed stellar population analysis (stellar ages, metallicities, sigma, dust with 10% accuracy or better) Stacking is poor substitute because high quality individual spectra crucial for a) description of any statistical distribution of physical properties beyond the average a) quantifying the amount of stochasticity involved in galaxy evolution processes a) understand the time-scales of transitional phases. Citro, Pozzetti et al. 2016 NEED FOR GOOD S/N and resolution As of today, spectroscopic studies with sufficient S/N and resolution at intermediate redshift have been limited to relatively small samples of galaxies or to co-added spectra. Examples: BOSS typical S/N 3-5 per 69km/s (rebinned) pixel Lega-C (VLT) 2700 galaxies at z=0.6-1 (but StePS >10X number of galaxies, complementary redshift range and possibility to address environmental issues) VIPERS (dashed) vs SDSS (solid coloured) and model (solid black) spectra WEAVE can do it thanks to: Good resolution (R~5800) over a wide wavelength range (3700-9500Å) Large FoV Excellent multiplexing StePS science goal: Tracing back in cosmic time the evolution of galaxy stellar population properties as a function of galaxy stellar mass and environment, to understand the physical mechanisms that regulate galaxy formation and assembly history. StePs will extend the SDSS results to a baseline encompassing the last 7 Gyr of cosmic time StePS in a nutshell I StePS is a spectroscopic survey of ~ 30K galaxies magnitude brighter than IAB =20.5 pre-selected from photometric redshifts to be at z > 0.3 (except in the COSMOS field) – redshift range 0.3-0.7: an epoch when galaxies are quickly evolving and SFR drops by a factor of 2 At least 100 galaxies in: 4 bins of galaxy masses 4 bins of color 5 bins of environment 4 bins of cosmic epochs Log mass limits: z=0.3 10.2 z=0.5 11.0 z=0.7 11.3 StePS in a nutshell II LR mode (R=5000) For each galaxy S/N per resolution element >15 to study: stellar ages, star formation and star formation histories, stellar and gas metallicities, dust attenuation, stellar velocity dispersions and gas kinematics and their relation with the intrinsic (galaxy stellar mass, morphology/color/size) and environmental properties. THIS REQUIRES EXPOSURE TIMES OF 7 HOURS PER GALAXY (14 HOURS FOR THE REDDEST SUBSET, 20% of the targets) – This sets StePS apart from the other WEAVE surveys for the requirement of completion of long exposure on each galaxy Multipass strategy of 5 passes (5passesX7hours/tile) + 10 passes in COSMOS 65% sampling rate, except in COSMOS 80% StePS in a nutshell III On a relatively wide area: 25 deg^2 Why: excellent optical+nearIR data, reliable photo-z ✖ well sampled spectroscopic data to characterize environment ✖ ✖ ✖ extra ancillary data to define environment (eg X-ray), galaxy structure (HST) etc StePS in a nutshell IV StePS will carry out a detailed analysis of: Stellar ages and metallicities Stellar masses Star formation rates and histories Gas metallicities, electron density, ionization parameter Dust attenuation Stellar velocity dispersion Gas kinematics Galaxy dynamical masses Gas outflows … via -- absorption-line spectral indices (optical and UV) -- full spectral fitting -- emission-line measurements StePS in a nutshell V Extra sample in COSMOS with no photo-z preselection yields 2.2k galaxies with z<0.3 to: extend to lower masses tha analysis done by SDSS perform spectral analysis at rest frame lambda > 8000 A for IMF determination in early-type galaxies StePS UNIQUENESS StePS will be the first survey to provide: the necessary spectral quality for a large sample of galaxies at z=0.3-0.7 to obtain an accurate estimate of all main stellar population characteristics, stellar velocity dispersions, gas metallicity and kinematics and their relations with galaxy stellar mass + other intrinsic properties (type, color) and environment over a significant interval of cosmic time. OPENING POST-DOC POSITION IN ITALY FOR STEPS THANKS!!