A UNIVERSAL STELLAR IMF? A CRITAL LOOK AT VARIATIONS:
EXTREME ENVIRONMENTS
Nate Bastian (Exeter) Kevin Covey (Cornell), Michael Meyer (ETH Zurich)
Annual Reviews of Astronomy & Astrophysics (2010, volume 48, arXiv:1001.2965)
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Kroupa 2001
log m [Msol]
log
N
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Kroupa 2001
log m [Msol]
log
N
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Kroupa 2001
log m [Msol]
log
N
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Kroupa 2001
log m [Msol]
log
N
van Dokkum 2008
zSFR
dens
ity [M
sol/y
r/M
pc3 ]
standard
evolving IMF
Tuesday, 27 April 2010
THE IMPORTANCE OF THE IMFAlmost every observable property of a galaxy or stellar population depends on the IMF
SFR indicators only senstive to small range (high masses) - extrapolate down the MF
Observationally, does the IMF vary significantly and systematically?
Problem: difficult to observe due to degenerecy with SFH, extinction, & metallicity
Tuesday, 27 April 2010
EXTREME STAR FORMATION IN THE GALAXY
Tuesday, 27 April 2010
EXTREME STAR FORMATION IN THE GALAXY
Figer et al.
Tuesday, 27 April 2010
EXTREME STAR FORMATION IN THE GALAXY
Figer et al.
Stolte et al. 2005
turn-over at 6-7 Msol
Tuesday, 27 April 2010
EXTREME STAR FORMATION IN THE GALAXY
Figer et al.
Stolte et al. 2005
turn-over at 6-7 Msol
Kim et al. 2006
Tuesday, 27 April 2010
EXTREME STAR FORMATION IN THE GALAXY
Arches, NGC 3603, Westerlund 1 and the ONC are consistent with having the same global IMF through resolved star counts
All show some sign of mass-segregation
Not necessarily primordial - as mass segregation can happen < 1 Myr and may be a product of cluster formation
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS
Larsen & Ritchler 2004
M83
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS
Larsen & Ritchler 2004
5 * 105 Msol
4 * 105 MsolM83
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS
Larsen & Ritchler 2004
J. Hibbard
Maraston et al. 2004Bastian et al. 2006
5 * 105 Msol
4 * 105 Msol
8 * 107 Msol
1.6 * 107 Msol
M83
NGC 7252Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS (>20 MYR)
bottom heavy
top heavy
Maraston 2005 SSP models
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS (>20 MYR)
M82-F
Bastian et al. 2007
bottom heavy
Maraston 2005 SSP models
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS
Tuesday, 27 April 2010
YOUNG MASSIVE CLUSTERS
IMF in these ‘extreme’ environments appears to be the same as seen locally
(<1) < ρ [Msol pc-3] < (>105)
SFR surface densities > 5 x 104 Msol kpc-2 yr-1
Orders of magnitude above even the most extreme galactic starbursts in the nearby or distant universe
Tuesday, 27 April 2010
COSMOLOGICAL VARIATIONS Many claims that the IMF was ‘top-heavy’ at high-z
Based on comparing obs and models
Based on scaling relations of galaxies
Based on integrated properties of the universe
Baugh et al. 2005,
van Dokkum 2008
High mass end has Salpeter index - found through rest- frame UV spectroscopy Pettini et al. 2000; Steidel et al. 2004; Quider et al. 2009
Wilkins et al. 2008
Davé 2008
Tuesday, 27 April 2010
COSMOLOGICAL VARIATIONS Many claims that the IMF was ‘top-heavy’ at high-z
Based on comparing obs and models
Based on scaling relations of galaxies
Based on integrated properties of the universe
Baugh et al. 2005,
van Dokkum 2008
Mc ~ (1+z)2z = 0 1 2 3
Mc= 0.2 2 4.5 8
√
√Wilkins et al. 2008
Davé 2008
Tuesday, 27 April 2010
NEAR FIELD COSMOLOGY
We have direct access to systems that formed at high-z (z > 2)
Globular clusters - Mc ~ 0.3-0.4
Dwarf spheroidal galaxies - Mc ~ 0.2-0.3
de Marchi et al. 2005; 2010
Wyse et al. 2002
Tuesday, 27 April 2010
NEAR FIELD COSMOLOGY
We have direct access to systems that formed at high-z (z > 2)
Globular clusters - Mc ~ 0.3-0.4
Dwarf spheroidal galaxies - Mc ~ 0.2-0.3
de Marchi et al. 2005; 2010
Wyse et al. 2002
“All problems in extragalactic astrophysics can be solved by a suitable choice of the IMF” - Romeel Davé
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
The sum of the IMF of all the star-forming regions in a galaxy may differ from the IMF of a single massive region
Expected *if* the most massive star in a cluster is limited by the cluster mass
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
stochastic samplingusually occasionally
100 clusters with masses of 1000 Msun = 1 cluster with a mass of 1e5 Msol
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
stochastic samplingusually occasionally
100 clusters with masses of 1000 Msun = 1 cluster with a mass of 1e5 Msol
sorted sampling: galaxies that only produce low mass clusters *never* can produce a high mass star
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
Lee et al. 2009, Meurer et al. 2009
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
Lee et al. 2009, Meurer et al. 2009
> 3 Msol
> 15 Msol
Tuesday, 27 April 2010
INTEGRATED GALACTIC INITIAL MASS FUNCTION (IGIMF)
Lee et al. 2009, Meurer et al. 2009
Stromgren sphere around a single O-star is larger than the galaxy -
Melena et al. 2009Hunter et al. 2009
> 3 Msol
> 15 Msol
Tuesday, 27 April 2010
BRIEF SUMMARY Resolved star counts in low mass/low density and ‘starburst’ clusters in the galaxy appear to have the same IMF
Extragalactic young massive clusters also appear to be consistent witha Kroupa/Chabrier type IMF
In terms of SFR density and density, these clusters sample more extreme environments than any starburst galaxy
Near-field cosmology (globular clusters/dwarfs) suggests the IMF at redshifts > 3 was the same as locally
The IGIMF may differ from the IMF, however alternative explanations exist
Tuesday, 27 April 2010
