PASTIS: Probing Abundances and Star formation Timescales with Integral field

Spectroscopy

Co-‐funded  by  the  European  Union

Anna GallazziINAF - 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

Thursday, May 9, 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?

Thursday, May 9, 2013

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]

Hβ

Bal

mer

abs

orpt

ion

[Mg2Fe] ~ metallicity

[Z/H]

Older

Burs

ts o

f

4000Å-break

Hδ

Bal

mer

abs

orpt

ion

Thursday, May 9, 2013

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, [Mg2Fe], [MgFe]’

Age Metallicity

Thursday, May 9, 2013

GALAXY SCALING RELATIONS

Stellar mass

Chemical enrichment Stellar Age

M* ~ 3x1010 Gallazzi et al 2005 THOMAS ET AL 2010

Mannucci et al 2010Gas metallicity

[α/Fe] abundance ratio

★ 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

Thursday, May 9, 2013

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

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)

Thursday, May 9, 2013

Courtesy Sebastian Sanchez

★ CALIFA survey at the 3.5m CAHA telescope with PMAS/PPAK IFU

★ 600 diameter-selected low-redshift (z

Wild et al 2013, submitted

THE MICE

gas velocity field

stellar populations

star formationemission lines

majo r me rge r of two massive gas-rich galaxies after first passage

Thursday, May 9, 2013

NGC6515 1.1e11M⨀

NGC0776 5e10M⨀

NGC0001 4e10M⨀

Thursday, May 9, 2013

NGC6515 1.1e11M⨀

NGC0776 5e10M⨀

NGC0001 4e10M⨀

Thursday, May 9, 2013

★ Stellar population gradients as a function of mass and morphology ➝ derive un-biased galaxy scaling relations

★ 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

★ Dynamical (total) versus stellar mass: link between SF and assembly processesConfirm and better quantify the age dependence of the DM fraction and explore any correlation of SF timescale

Gallazzi et al 2005

gas-phase metallicity

stel

lar

met

alli

city

Ste

llar

mas

s

Dynamical (total) mass

Gallazzi et al 2006

WORK IN PROGRESS...

Thursday, May 9, 2013