Co- funded by the European Union PASTIS: Probing Abundances and Star formation Timescales with Integral field Spectroscopy Anna Gallazzi INAF - Osservatorio Astrofisico di Arcetri Stefano Zibetti, Filippo Mannucci (INAF-OAA), Eric Bell (Michigan), Jarle Brinchmann (Leiden), Sune Toft, Andrew Zirm (DARK), Anna Pasquali (ARI-Heidelberg), Jakob Walcher (AIP), Paula Coelho (Sao Paulo), Stephane Charlot (IAP) CALIFA collaboration LVII Congresso SAIt, 9/5/2013
THE IDEA BEHIND PASTIS Age and chemical composition of stars and ISM main epoch of SF, its duration and efficiency Dynamical mass and structure SF and assembly histories Linking age and chemical properties with galaxy mass and structure can provide important clues to how SF and mass assembly relate to each other Different measures of chemical enrichment in relation to age, star formation and structural properties both on local and global scales Constraining typical timescales of star formation and chemical enrichment in relation to galaxy structure and environment Archaeological versus direct approach: Is the inferred timescale consistent with observed evolution of galaxy scaling relations?
HOW CAN WE STUDY THEM? OBSERVATIONAL CONSTRAINTS Physical parameters of unresolved stellar populations are encoded in integrated galaxy spectra Individual absorption features are almost insensitive to dust attenuation and help in breaking age-metallicity degeneracy [Lick system; e.g. Worthey+94, Trager+2000, Sanchez-Balzquez +06..G05] full spectrum fitting [MOPED, VESPA, Starlight, STECKMAP, PCA analysis Ferreras+06, see Walcher +10 review] H Balmer absorption [Z/H] H Balmer absorption Older Bursts of [Mg2Fe] ~ metallicity 4000A -break
A BAYESIAN APPROACH MONTE CARLO LIBRARY OF COMPLEX SFH AND METALLICITIES: exponential SFH + random burst; metallicity fixed for each model (i.e. no chemical evolution) - based on BC03 convolve models to galaxy velocity dispersion and measure absorption index strengths as in observed spectra build full probability density function of STELLAR MASS, LUMINOSITY- AND MASS-WEIGHTED AGE, STELLAR METALLICITY Optimal set of absorption features: D4000, Hβ, Hγ+Hδ, [Mg 2 Fe], [MgFe] Age Metallicity
GALAXY SCALING RELATIONS Chemical enrichment Stellar Age [ /Fe] abundance ratio M * ~ 3x10 10 Stellar mass Gallazzi et al 2005 THOMAS ET AL 2010 Gas metallicity Mannucci et al 2010 Large spectroscopic surveys have provided a quantitative description of present-day galaxy populations Mass is the primary parameter in determining the age and metallicity of present-day galaxies Scatter depends on galaxy morphology and on star formation activity Analogy between metallicity of stars and metallicity of gas in star-forming galaxies
THE REDSHIFT EVOLUTION OF STELLAR POPULATIONS Still limited knowledge about the evolution with redshift of the stellar populations in galaxies Deep multi-object spectroscopy with IMACS on Magellan for a sample of 80 galaxies selected at 0.65<z<0.75 Well-defined red-sequence of quiescent galaxies at z=0.7 with similar metallicities as present-day galaxies and ages consistent with oldest present-day galaxies, under passive evolution Population of intermediate-mass star-forming galaxies at z=0.7 could contribute to the younger and more metal-rich fraction of local massive galaxies Residuals in age and metallicity correlate with specific SFR NIR multi-object spectrographs will allow to extend evolutionary studies out to z 2 (only a handful of objects so far) Gallazzi et al, 2013, to be subm.
IMPROVING THE FOSSIL RECORD Robust estimates of α/fe for galaxies with different star formation activity Updated Coelho et al 2007 and Walcher et al 2009 differential SPS models with variable α/fe and Fe/H at high spectral resolution and down to few-tens-myr populations Most spectra of low-redshift galaxies lack spatially resolved information: prevent studying correlated spatial variations in stellar populations, gas and kinematic properties, which are the record of galaxy assembly history incomplete and unresolved coverage can translate into severe biases in derived physical properties: affect comparison with galaxy formation models and assessment of redshift evolution CALIFA: the Calar Alto Legacy Integral Field Area survey (PI: S.Sanchez)
Courtesy Sebastian Sanchez Sanchez et al 2012 Husemann et al 2013 Color CALIFA survey at the 3.5m CAHA telescope with PMAS/PPAK IFU 600 diameter-selected low-redshift (z<0.03) galaxies spanning the whole color magnitude space Magnitude high and low spectral resolution set-up covering the whole optical range ( 3700-7000A ) ideal for emission line and absorption/stellar continuum studies DR1 of 100 objects: http://www.caha.es/califa/public_html/
gas velocity field emission lines THE MICE major merger of two massive gas-rich galaxies after first passage star formation stellar populations Wild et al 2013, submitted
NGC6515 1.1e11M NGC0776 5e10M NGC0001 4e10M
NGC6515 1.1e11M NGC0776 5e10M NGC0001 4e10M
WORK IN PROGRESS... Stellar population gradients as a function of mass and morphology derive un-biased galaxy scaling relations stellar metallicity Stellar and gas-phase metallicities trace different phases of chemical evolution. How do they correlated on local scales? How is the scatter correlated with age and α/fe (SF timescale)? Gain insight into the synchronization of the enrichment of the two phases and the occurrence of inflows/outflows at certain stages of galaxy evolution Stellar mass Gallazzi et al 2005 gas-phase metallicity Dynamical (total) versus stellar mass: link between SF and assembly processes Confirm and better quantify the age dependence of the DM fraction and explore any correlation of SF timescale Gallazzi et al 2006 Dynamical (total) mass