Transcript Steps

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
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well sampled spectroscopic
data to characterize
environment
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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!!