Testing the Universality of the Stellar IMF with the E-ELT

Nate Bast ian ( IoA)

Michael Meyer (ETH Zurich)Kev in Covey (Cornell)

Selma De Mink (Utrecht)

Quotes“Resorting to altering the initial mass function

is a sign of moral weakness” Mike Edmunds

“All problems in extragalactic astrophyics can be solved by a suitable choice of the IMF” Romeel Dave

IMF is one of the best hopes to constrain the process of star-formation

Nearly all stellar properties of galaxies and populations are controlled by the IMF at some level.

“... the last refuge for scoundrels” Mike Edmunds

IMF: Resolved Star Approach

ONC - VLT/ISAAC

IMF: Resolved Star Approach

ONC - VLT/ISAAC

Muench et al. 2002

Mtot ~ 103 Msun

IMF: Resolved Star Approach

high mass clusters rare -> far away -> can’t get their low mass stars

due to stochasticity, need IMF in many clusters over the full mass range

ONC - VLT/ISAAC

Muench et al. 2002

Mtot ~ 103 Msun

IMF: Resolved Star Approach

high mass clusters rare -> far away -> can’t get their low mass stars

due to stochasticity, need IMF in many clusters over the full mass range

ONC - VLT/ISAAC

Muench et al. 2002

E-ELT same sensitivity as has been done for the ONC out to ~4kpc - 10-20 MJupiter

Mtot ~ 103 Msun

Need for ever deeper Observations

Arches

Stolte et al. 2008

Need for ever deeper Observations

Arches

Stolte et al. 2008

Kim et al. 2006

cluster distance (kpc) Mass (Msun) lower mass limit

Cygnus OB2 1.7 ~104 < 20 MJupiter

Trumpler 14 2.8 ~ 104 < 20 MJupiter

NGC 3603 6.5 few * 104 < 0.02 Msun

Westerlund 1 5.5 >105 < 0.02 Msun

Arches 8 few * 104 < 0.02 Msun

E-ELT: reaching into the substellar mass regime for all known Galactic young massive clusters

cluster distance (kpc) Mass (Msun) lower mass limit

Cygnus OB2 1.7 ~104 < 20 MJupiter

Trumpler 14 2.8 ~ 104 < 20 MJupiter

NGC 3603 6.5 few * 104 < 0.02 Msun

Westerlund 1 5.5 >105 < 0.02 Msun

Arches 8 few * 104 < 0.02 Msun

E-ELT: reaching into the substellar mass regime for all known Galactic young massive clusters

While crowding will be an issue in the centers of the clusters, limits still possible outside the cluster cores

de Marchi, Paresce, & Portegies Zwart 2009, in prep.

MC

de Marchi, Paresce, & Portegies Zwart 2009, in prep.

MC

de Marchi, Paresce, & Portegies Zwart 2009, in prep.

MC

-The form of the (low mass) IMF doesn’t depend on formation epoch

Wyse et al. 2002

Ursa Minor dSph

M92

-The form of the (low mass) IMF doesn’t depend on densityor dark matter content.

Wyse et al. 2002

Ursa Minor dSph

M92

-The form of the (low mass) IMF doesn’t depend on densityor dark matter content.

It has been claimed that the IMF may be dependent on the SFR density, hence it should vary with redshift.

Local stellar clusters (ONC, Arches, NGC 3603) have SFR densities orders of magnitudes larger than high-z galaxies.

IMF variations in Extreme Environments

Smith et al. 2006

IMF variations in Extreme Environments

Direct detection of low mass starsPoint sources: I=20-23, K=20.5-23.5

Smith et al. 2006

IMF variations in Extreme Environments

Direct detection of low mass starsPoint sources: I=20-23, K=20.5-23.5

need S/N > 100

Meyer & Greissl 2005

Smith et al. 2006

High Redshift Universe

Pettini et al. 2000

UV spectral features (CIV)

sensitive to the shape of the high mass end of the IMF

can compare with UV surveys of local star-forming regions

(e.g. Pellerin 2007)

Quider et al. 2009

Many Indirect Studies Report IMF Variations

Larson 2005

Baugh et al. 2005

Weidner, Kroupa, Pflamm-Altenburg et al. 2006, 2007, 2009

Wang et al. 2006

Fardal et al. 2007

Maness et al. 2007

Mieske & Kroupa 2008

Wilkins et al. 2008a,b

Dave 2008

Hoversten & Glazebrook 2008

van Dokkum 2008

Meurer et al. 2009

Many Indirect Studies Report IMF Variations

Larson 2005

Baugh et al. 2005

Weidner, Kroupa, Pflamm-Altenburg et al. 2006, 2007, 2009

Wang et al. 2006

Fardal et al. 2007

Maness et al. 2007

Mieske & Kroupa 2008

Wilkins et al. 2008a,b

Dave 2008

Hoversten & Glazebrook 2008

van Dokkum 2008

Meurer et al. 2009

Conclusions

❖ Many lines of evidence point to the universality of the stellar IMF.

❖ But absence of evidence is not evidence of absence.

❖ The E-ELT will be able to refine the tests carried out so far, and search for variations in the sub-stellar regime.

Intermediate age clusters in the LMC

Mackey & Brobie Neilson 2007

~1.5 Gyr

V-I

mv

Intermediate age clusters in the LMC

Mackey & Brobie Neilson 2007

~1.5 Gyr

V-I

mv

Intermediate age clusters in the LMC

Mackey & Brobie Neilson 2007

~1.5 Gyr

300 Myr age difference

V-I

mv

V-I

MV

Bastian & de Mink 2009

1.25 Gyr isochrone

1.5 Gyr isochrone

1.2 Msun

V-I

MV

Bastian & de Mink 2009

1.25 Gyr isochrone

1.5 Gyr isochrone

1.2 Msun

V-I

MV

Bastian & de Mink 2009

1.25 Gyr isochrone

1.5 Gyr isochrone

1.2 Msun

V-I

MV

Bastian & de Mink 2009

fast rotators

slow rotators

Outline

❖ Stellar IMF in starbursts and the early universe

❖ Multiple populations within clusters?

❖ Resolved star approach

❖ Universality of the IMF?

Stellar IMF in the Galaxy

Extreme environments