Crescenzo Tortora

Insights on galaxy evolution from the dark matter content of massive early-type galaxies

ITP Zurich

What is fun with dark matter (DM)?

DARK MATTER

DC comics

Futurama

…come back to talk about science!

Cosmology

Flat rotation curves

Clusters

Cosmic structures

• Direct detection of dark matter(CDMS, CRESST, EDELWEISS, EURECA, SIMPLE, PICASSO, ZEPLIN,XENON, DEAP, ArDM, WARP, LUX, DAMA/NaI, DAMA/LIBRA, ……)

• Indirect detection of dark matter(EGRET, MAGIC, PAMELA, AMANDA, IceCube, ANTARES, ……)

Unfortunately, no strong evidencesemerge from these observations

…..but DM remains the best, mosttested and simpler way to reproduceobservations!

Alternatives:

• MOND• Extended theories of gravity (f(R), etc.)•……

Shankar et al. 2006

Dark matter is 10-20 times more than stars

Overall DM content

few hundred kiloparsecs

• DM fraction vs mass and size

• DM density and cuspiness

• DM fraction vs formation epoch

• Insights on galactic ingredients (IMF, halo contraction, star formation efficiency, etc.)

few kiloparsecs

In this talk…

The physics behind

dark matter potential wells

baryons

Mcold

Mstar(SF efficiency)-1 =

Initial mass function (IMF)adiabatic contraction

Why central (<Reff) dark matter fractions?

- Star formation efficiency

- IMF and stellar population parameters

- DM distribution and halo contraction

- Infall processes- (Supernovae or AGN) feedback phenomena

- Shock heating- Merging

Most of the spectro-photometric data are available in the central regions (typically within 1 effective radius, Reff, or few Reff)

More extended data (out to the outskirts ofthe galaxies) available for few galaxies

Data and procedures

Multiband photometryStellar mass and population parameters(age and metallicity)

Spectra (slit, IFU, etc)

Velocity dispesion Total mass

Strong gravitationallensing

Mass model(SIS, constant M/L, NFW+light)

Toy-models from CDM predictions and simulations

We model the total mass profile using a SIS

SIS reproduces quite good the total mass profilein massive ETGs (e.g., Koopmans et al. 2006, Gavazzi et al. 2007)

Dark matter vs mass (size) and Fundamental Plane

Fundamental Plane

Observed Virial

Dressler et al. 1987

Non-homologiesStellar populationsDark matter

Typically, DM fraction is calculated at a homogeneous scale radius, the effective radius (enclosing one-half of the total stellar mass)

Cappellari et al. 2006

Hyde & Bernardi 2009

Taylor et al. 2010

Graves et al. 2010

Auger et al. 2010

Grillo et al. 2010

~ 400 local galaxies from Prugniel & Simien (1996)

Central DM fraction is anincreasing function ofluminosity/mass

Tortora et al. 2009

Bolton et al. 2007, Hyde & Bernardi 2009, La Barbera et al. 2010,…

Similar trends are found if IMF or the galaxy model are changed

Cardone et al. 2009

Cardone & Tortora 2010

Cardone et al. 2011

Phenomenological model with variable M/L

NFW or Burkert for DM profile

Semianalytical model

Napolitano, Romanowsky & Tortora 2010

The effective radius is the primary driver of DM fractions

Tortora et al. 2010

Sample of intermediate-redshift gravitational lenses (SLACS survey)

A definitive analysison dark matter!

SPIDER Spheroids Panchromatic Investigation in Different Environmental Regions

~ 5000 massive ETGs with grizYJHK photometry

La Barbera et al. 2010 (SPIDER I)

• structural parameters in all wavebands (determined using 2DPHOT, La Barbera et al. 2008)

• stellar masses derived from fitting synthetic models (Bruzual & Charlot 2003) to observed colours• recomputed velocity dispersions which allow to probe the total mass• different environments

SDSS + UKIDSS

SIS

Constant M/L profile

Mdyn > Mstar

SIS

Constant M/L

Mass follows light (modelled as a Sérsic profile)

DM plane

Environment

fieldsatellites

centrals

…vs simulations

Ruszkowski & Springel 2009

Non-contracted halo

Contracted halo

High gas conversionefficiencyLow gas conversionefficiency

Onorbe et al. 2007

• NFW for DM profile with a c-Mvir relation

• Sersic law for the light distribution

CDM toy-model predictions

Empirical relations among parameters like stellar mass, size, galaxy age, etc.

SF is a free parameter or fixed using literature trends (e.g. Conroy & Wechsler 2009)

Dynamical mass and DM fraction

Standard profileAdiabatic contraction (AC, Blumenthal et al. 1986, Gnedin et al. 2004)

Dark matter density and cuspiness

Napolitano, Romanowsky & Tortora 2010

LTGs

ETGs

DwEs

Non-contracted NFW

Contracted NFW

Evidence of cuspiness

Sample of intermediate-redshift gravitational lenses (SLACS survey)

SLACS lenses

LTGs

Dark matter vs formation epoch

Sample of intermediate-redshift gravitational lenses (SLACS survey)

Older galaxies are more compact

CDM fDM-age toy-model predictions

SF is left free

We divide the sample in stellar mass bins

Size-age relation in each mass bin

fDM-age predictions

Halo contraction

Standard CDM

Standard CDM

Halo contraction

IMF-AC degeneracy

Kroupa IMF

Salpeter IMF

10-30% 40-60%

Salpeter IMF (many low mass stars) Kroupa or Chabrier IMF (less low mass stars)

Salpeter + NFW Chabrier+ contracted NFW

DMhigh stellar M/L low stellar M/L

0 1 2 3 4 5m

0

0.05

0.1

0.15

0.2

m

Toy-models

What behind this correlation?

Size-age (e.g., Khochfar & Silk 2006)

Size-age (e.g., Khochfar & Silk 2006)

SF variation(e.g., Conroy & Wechsler 2009)

low SF

high SF

Size-age (e.g., Khochfar & Silk 2006)

SF variation(e.g., Conroy & Wechsler 2009)

AC variationyounger systems showing AC

AC

no-AC

Size-age (e.g., Khochfar & Silk 2006)

SF variation(e.g., Conroy & Wechsler 2009)

AC variationyounger systems showing AC

IMF variationbottom-havier (Salpeter-like) IMF for younger systems

Work in progress on the DM-age correlation

• SPIDER • SAURON• ……..

….promising tool to test galaxy evolutionprocesses……

Conclusions• Central DM driven by mass but mainly by the size (DM plane)

• First evidences of cuspiness in ETGs

• IMF – halo contraction degeneracy

• An inverse correlation between DM fraction and formation timehas been found

• It is possibly suggesting variations of star formationefficiency, IMF and halo contraction with age and/or mass

Better data-quality and wider samples of galaxies to checkthe results and improve the physical implications

VST

Grazie