1. Stellar Populations at intermediate redshift Survey with WEAVE
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. Gonzales-Delgado, 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
I will present this survey – StePS to be performed with WEAVE – a survey were a large fraction of scientists involved are from INAF

2. 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.

3. 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
description of any statistical distribution of physical properties beyond the average
quantifying the amount of stochasticity involved in galaxy evolution processes
understand the time-scales of transitional phases.
Citro, Pozzetti et al. 2016

4. 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

5. WEAVE can do it thanks to: Good resolution (R~5800)
over a wide wavelength range ( Å)
Large FoV
Excellent multiplexing

6. 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
Tracing the evolution with redshift of galaxy stellar population properties in relation to galaxy mass and star formation activity and environment can enable to put additional constraints on the mechanisms leading to the suppression of star formation and the ensuing buildup of the present-day quiescent massive galaxy population.

7. 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 : 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= z= z=
Notice all this should be done on single galaxies: to resolve the dispersion in galaxy properties and gain insight on the individual galaxy evolution as opposed to the overall galaxy population evolution. Good qualityindividual spectra are crucial to obtain a description of any statistical distribution of physical properties that goes beyond the mere average.

8. 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.
Notice all this should be done on single galaxies: to resolve the dispersion in galaxy properties and gain insight on the individual galaxy evolution as opposed to the overall galaxy population evolution. Good qualityindividual spectra are crucial to obtain a description of any statistical distribution of physical properties that goes beyond the mere average.
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%

9. 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 ✖
Notice all this should be done on single galaxies: to resolve the dispersion in galaxy properties and gain insight on the individual galaxy evolution as opposed to the overall galaxy population evolution. Good qualityindividual spectra are crucial to obtain a description of any statistical distribution of physical properties that goes beyond the mere average. ✖ ✖ ✖

10. 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
Notice all this should be done on single galaxies: to resolve the dispersion in galaxy properties and gain insight on the individual galaxy evolution as opposed to the overall galaxy population evolution. Good qualityindividual spectra are crucial to obtain a description of any statistical distribution of physical properties that goes beyond the mere average.

11. 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
Notice all this should be done on single galaxies: to resolve the dispersion in galaxy properties and gain insight on the individual galaxy evolution as opposed to the overall galaxy population evolution. Good qualityindividual spectra are crucial to obtain a description of any statistical distribution of physical properties that goes beyond the mere average.

12. StePS UNIQUENESS StePS will be the first survey to provide:
the necessary spectral quality
for a large sample of galaxies at z=
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.

13. OPENING POST-DOC POSITION
IN ITALY FOR STEPS

14. THANKS!!