looking into the stars by just counting them · offner et al., 2014, ppvi the imf appears largely...
TRANSCRIPT
Pavel Kroupa: University of Bonn / Charles University
ING-Mercator Seminar ING-Mercator Mayantigo building Santa Cruz de La Palma
10th September 2019
The systematically varying stellar IMF and
some implications thereof
1
Pavel Kroupa Helmholtz-Institute for Radiation und Nuclear Physics (HISKP)
University of Bonn
Astronomical Institute, Charles University in Prague
c/o Argelander-Institut für Astronomie University of Bonn
Pavel Kroupa: University of Bonn / Charles University 2
Looking into
the stars by
just counting them
follows Ψ(MV) = −
dm
dMV
ξ(m)
We have = # of stars with MV ∈ [MV, MV + dMV]
dN = ξ(m) dm = # of stars with m ∈ [m, m + dm]
dN
dMV
= −
dm
dMV
dN
dmsince
dN = Ψ(MV) dMV
the observablethe obstacle
the target
Pavel Kroupa: University of Bonn / Charles University 3
Strong sharp maximum
near MV ⇡ 11.5
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MI ⇡ 8.5<latexit sha1_base64="ha1CMxoJRh1pB0udKAz7AITFlVs=">AAAB/nicdVBNS8NAEN3Ur1q/ouLJy2IRPIWkVlNvRS96ECrYWmhC2Gy37dLNJuxuxBIK/hUvHhTx6u/w5r9x20ZQ0QcDj/dmmJkXJoxKZdsfRmFufmFxqbhcWlldW98wN7daMk4FJk0cs1i0QyQJo5w0FVWMtBNBUBQychMOzyb+zS0Rksb8Wo0S4keoz2mPYqS0FJg7l0HmiQhejKGHkkTEd7BmHQVm2bZOase260DbsqfQxHFct1qBTq6UQY5GYL573RinEeEKMyRlx7ET5WdIKIoZGZe8VJIE4SHqk46mHEVE+tn0/DHc10oX9mKhiys4Vb9PZCiSchSFujNCaiB/exPxL6+Tql7NzyhPUkU4ni3qpQyqGE6ygF0qCFZspAnCgupbIR4ggbDSiZV0CF+fwv9Jq2I5h1blqlqun+ZxFMEu2AMHwAEuqINz0ABNgEEGHsATeDbujUfjxXidtRaMfGYb/IDx9gnofJTP</latexit>
Kroupa, Tout & Gilmore 1990
Kroupa, Tout & Gilmore 1990; Kroupa, 2002, Science
The mass-luminosity relation of low-mass stars
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 4
Kroupa, Tout & Gilmore 1990; Kroupa, 2002, Science
The mass-luminosity relation of low-mass stars
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 5
Kroupa, Tout & Gilmore 1990;
Kroupa, 2002, Science
The mass-luminosity relation of low-mass stars
1. position 2. width 3. amplitudeall agree !
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 6
The mass-luminosity relation of low-mass stars
1. position 2. width 3. amplitudeall agree !
Ψ(MV) = −
dm
dMV
ξ(m)
fully convective
radiative interrior,
convective shell
Pavel Kroupa: University of Bonn / Charles University
Kroupa, Tout & Gilmore 1990;
Kroupa, 2002, Science
7
Pavel Kroupa: University of Bonn / Charles University 8
The Galactic-field IMF
There are two luminosity functions for the solar neighbourhood
I. Count stars nearby to Sun
Obtain and from trigonometric parallaxMV d
−→ Well observed individual stars but small numbers at faint end ( )
II. Deep (100 - 300 pc) pencil-beam photographic/CCD surveys
Formidable data reduction Obtain and from photometric parallaxMV d
−→
(105 images −→ ≈ 100 stars)
Large # of stars but poor resolution (2”-3”) and Malmquist bias ( )Ψphot
Ψnear
Pavel Kroupa: University of Bonn / Charles University 9
The possibility of dark matter in the Galactic disk(Bahcall 1984)
−→ Many surveys of type II (pencil-beams) to constrain the LF :
ground
Reid & Gilmore 1982
Gilmore, Reid & Hewett 1985
Hawkins & Bessell 1988
Leggett & Hawkins 1988
Stobie, Ishida & Peacock 1989
Tinney, Reid & Mould 1993
Kirkpatrick et al. 1994
HSTGould, Bahcall & Flynn 1997
Zheng, Flynn, Gould et al. 2001
Pavel Kroupa: University of Bonn / Charles University 10
Ψ(MV) = −
dm
dMV
ξ(m)
see also Bochanski et al.
(2010, AJ)
Ψphot
- independent of direction
- maximum (peak) at MV ≈ 12{
peak = turnover in the MF ?
Pavel Kroupa: University of Bonn / Charles University 11
Two solar-neighbourhood samples:
I. nearby
II. deep
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 12
?Stellar
samples should be
well-mixed:σ ≈ 25 km/s = 250 pc/10Myr
BUT: two solar-neighbourhood samples:
I. nearby
II. deep
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 13
Problem :
The nearby and deep LFs are not equal.
Which LF do we use to calculate the MF ?
ξ(m) = −
!
dm
dMV
"
−1
Ψ(MV )
Pavel Kroupa: University of Bonn / Charles University 14
Two solar-neighbourhood samples:
I. nearby
II. deep
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 15
Kroupa et al. 2013
unresolved multiples
Kroupa, Tout & Gilmore
1991
Pavel Kroupa: University of Bonn / Charles University 16
The IMF in star clusters
Ψ(MV) = −
dm
dMV
ξ(m)
Kroupa 2002 Science
Pavel Kroupa: University of Bonn / Charles University 17
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 18
Kroupa 2002 Science
Ψ(MV) = −
dm
dMV
ξ(m)
Pavel Kroupa: University of Bonn / Charles University 19
Kroupa 2002 Science
t = 0 t = 0.3 Tdiss t = 0.6 Tdiss t = 0.9 Tdiss
N = 1.28 × 105
4 × (N = 8000)
(Baumgardt & Makino 2003)f = 0
low-masshigh-mass
P. Kroupa: University of Bonn / Charles University
MF(t) due to cluster evolution
standard
stella
r IMF
dynamical age
20
t = 0 t = 0.3 Tdiss t = 0.6 Tdiss t = 0.9 Tdiss
N = 1.28 × 105
4 × (N = 8000)
(Baumgardt & Makino 2003)f = 0
low-masshigh-mass
P. Kroupa: University of Bonn / Charles University
MF(t) due to cluster evolution
standard
stella
r IMF
dynamical age
21
P. Kroupa: University of Bonn / Charles University
N-body Models of Binary-Rich Clusters
(Kroupa 1995)
20 × (N = 400 stars)f = 1
ξobs(m) ̸= ξtrue(m)
(- 2.5 log L)
#The stellar
luminosity function
22
Massive stars in very young clusters
Pavel Kroupa: AIfA, University of Bonn 23
OB stars in clusters / HII regionsTwo competing processes:
Mass segregation
tmsgr ≈ 2
!
mav
mmassive
"
trelax
for pre-exposed ONCe.g. trelax ≈ 0.6 Myr
tmsgr ≈ 0.12 Myr ≪ age of ONCtrelax =
21
ln(0.4N)
!
Mecl
100 M⊙
"1
2!
1 M⊙
mav
" !
R0.5
1 pc
"3
2
Core decay e.g.tdecay ≈ Nm × tcore,cross
Rcore ≈ 0.02 pc, Mcore ≈ 150 M⊙
tcore
cross ≈ 1.2 × 104 yr
tdecay ≈ 104− 105 yr ≪ age of ONC
tcore
cross ≈ 5
!
M core
100 M⊙
"− 1
2!
Rcore0.5
1 pc
"3
2
(Pflamm-Altenburg & Kroupa 2006)Pavel Kroupa: University of Bonn / Charles University 24
Pavel Kroupa: University of Bonn / Charles University
3000 stars, r0.5=0.5pc, mass segr., f=1, uniform q-distr., Sana P-distr.
Oh & Kroupa 2015, 2016
P. Kroupa: University of Bonn / Charles University
Sverre Aarseth Nbody6 code
25
Pavel Kroupa: University of Bonn / Charles University
30000 stars, r0.5=0.5pc, mass segr., f=1, uniform q-distr., Sana P-distr.
P. Kroupa: University of Bonn / Charles University
Oh & Kroupa 2015, 2016 Sverre Aarseth Nbody6 code
26
Pavel Kroupa: University of Bonn / Charles University
Clusters depopulate themselves off low-mass stars and high mass stars.
loss
stellar mass
0.1Msun 150Msun
time-dependent
27
Thus, stellar-dynamical processes are
extremely important when determining the IMF shape!!
Pavel Kroupa: University of Bonn / Charles University 28
Pavel Kroupa: University of Bonn / Charles University 29
Bastian, Covey, Meyer,
2010, ARAA
Offner et al., 2014, PPVI
The IMF appears largely
invariant (in MW CSFEs /
embedded clusters)
Kroupa et al., 2013
Kroupa 2001, 2002
Bastian et al. 2010
Pavel Kroupa: University of Bonn / Charles University 30
The invariant canonical IMF
the canonical IMF :
discontinuity: Thies & Kroupa (2007, 2008), Parker & Goodwin (2010)
log(m)
ξ(m) ∝ m−αi
O starsG starsM stars
α2 = 2.3
α1 = 1.3
α3,Massey = 2.3
0
logdN/dlog(m)
α0 ≈ 0.3
BDs
�0 � 0.3
solivagent Jupiters
1.9 times more
frequent than stars
31 Pavel Kroupa: University of Bonn / Charles University
discontinuity: Thies & Kroupa (2007, 2008), Parker & Goodwin (2010)
log(m)
ξ(m) ∝ m−αi
O starsG starsM stars
α2 = 2.3
α1 = 1.3
α3,Massey = 2.3
0
logdN/dlog(m)
α0 ≈ 0.3
BDs
�0 � 0.3
solivagent Jupiters
1.9 times more
frequent than stars
32 Pavel Kroupa: University of Bonn / Charles University
the canonical IMF :
Rederived later by Chabrier ---
essentially identical result to the
canonical IMF fig.4-24 in Kroupa et al. 2013
Pavel Kroupa: University of Bonn / Charles University 33
Hints towards a variable IMF
Pavel Kroupa: University of Bonn / Charles University 34
Correct star-counts in R136 for ejected starsStar-counts:
Some subtle hints for a systematically varying IMF are available at high masses
R136
35 P. Kroupa: University of Bonn / Charles University
2 Myr old
Pavel Kroupa: University of Bonn / Charles University 36
Correct star-counts in R136 for ejected stars
Excess of massive stars in whole 30Dor region(Schneider et al. 2018)
IMF in R136 top-heavy (Banerjee & Kroupa 2012)
Top-heavy IMF in Magellanic Bridge cluster NGC796(Kalari et al. 2018)
Star-counts:
Some subtle hints for a systematically varying IMF are available at high masses
GCs in M31: more top-heavy IMF at lower metallicity(Zonoozi et sl. 2016; Haghi et al. 2017)
What we know from observation :
Pavel Kroupa: University of Bonn / Charles University 37
Globular clusters : deficit of low-mass stars increases with decreasing concentrationdisagrees with dynamical evolution (Marks et al. 2012)
GCs (extreme star burst "clusters")
Pavel Kroupa: University of Bonn / Charles University 38
gas expulsion +
mass segregation !
Pavel Kroupa: University of Bonn / Charles University 39
Cluster reaction to thermal gas removal :
40Baumgardt & Kroupa 2007
(movie by Baumgardt)
P. Kroupa: University of Bonn / Charles University
Nbody models of binary rich initially mass segregated clusters with redisual gas expulsion after birth
(Marks, Kroupa & Baumgardt 2008)
gas expulsion
stellar loss independent of mass
loose mostly low-mass stars
41 P. Kroupa: University of Bonn / Charles University
What we know from observation :
density
Pavel Kroupa: University of Bonn / Charles University 42
UCDs : higher dynamical M/L ratios (Dabringhausen et al. 2009)
mutual consistency !!
cannot be exotic dark matter
no explanation other than many remnants
Globular clusters : deficit of low-mass stars increases with decreasing concentration
UCDs : larger fraction of X-ray sources than expected (Dabringhausen et al. 2012)
disagrees with dynamical evolution (Marks et al. 2012)
What this implies :
starsBDs
# stars / mass bin
stellar mass
(need gas expulsion from mass-segregated clusters)
Pavel Kroupa: University of Bonn / Charles University 43
IMF = IMF(Z, SFRD) Z=metallicity, SFRD=star-formation rate density
Thus
P. Kroupa: University of Bonn / Charles University
Top-heavy IMF in extreme-density environments :
Marks et al. 2012 Kroupa et al. 2013
44
Z
Pavel Kroupa: University of Bonn / Charles University 45
Top-heavy IMF and
"quasars" a la
Tereza Jerabkova
UCDs ( = Hilker objects) (extremely extreme star burst "clusters")
Pavel Kroupa: University of Bonn / Charles University 46
Properties of ultra compact dwarf galaxies (UCDs)
Image by M. Hilker
UCD
dE
UCDs occur mostly in
galaxy clusters
Pavel Kroupa: University of Bonn / Charles University 47
From close distance, a UCD probably looks similar to this:
Image from ESO
� Cen 48
Would UCDs with a top-heavy IMF survive their early evolution?
Perform N-Body simulations of UCDs with mass-loss through gas expulsion and stellar evolution
UCDs can also form with top-heavy IMFs, but this implies extreme initial conditions for them.
(Dabringhausen, Fellhauer & Kroupa 2010)
Pavel Kroupa: University of Bonn / Charles University 49
(Dabringhausen, Fellhauer & Kroupa 2010)
Mass [10 Solar masses ]
106
1000100
2.31.91.5
2.3
small present-dayUCD
massive present-day UCD
}�3
Initial parameters thereby implied for UCDs
Pavel Kroupa: University of Bonn / Charles University 50
scouting work by Tereza Jerabkova
Pavel Kroupa: University of Bonn / Charles University
Can this IMF variation be confirmed?
---> probe conditions at high redshift
51
ESO student of the year with ESO staff of the year
(Chris Harrison and Michael Hilker) ESO Annual Report 2018
Pavel Kroupa: University of Bonn / Charles University
100 101 102 103 104
time [Myr]
106
107
108
109
1010
1011
1012
1013
Lbol[L§]
MUCD = 108 M§
Lbol ÃMUCD (NOT for MKDP)
10 7M§
10 8M§
10 9M§
[Fe/H]=≠2
[Fe/H]= 0
MKDP IMFCAN IMF
≠27.5
≠25.0
≠22.5
≠20.0
≠17.5
≠15.0
≠12.5
≠10.0
Mbol[m
ag]
UC
DD
ATA
QUASARS
SUPE
RN
OVA
EJerabkova et al. 2017===> Quasar-like objects
The redshift dependent photometric properties are calculated as predictions for James Webb Space Telescope (JWST) observations.
52
Pavel Kroupa: University of Bonn / Charles University
10 20 30 40 50time [Myr]
10≠4
10≠3
10≠2
10≠1
100
SNeI
Irat
e[y
r≠1 ]
MUCD = 109 M§
ÃMUCD (NOT for MKDP)
[Fe/H]=≠2[Fe/H]= 0
107 M§
108 M§
shorter SF historyMKDP IMFCAN IMF
Jerabkova et al. 2017
53
Pavel Kroupa: University of Bonn / Charles University
Conclusions
Significant evidence that the IMF varies with Z and rho.
The galaxy-wide IMF (the gwIMF) changes with SFR, as expected.
Testbed: extremely star-bursting clusters (UCDs) at high-z.
Are some/most quasars at very high z merely young UCDs ?
54
Jerabkova et al. 2017
The IMF is not observable (it is a mathematical "hilfsconstruct")
This hilfsconstruct is not a probability distribution function.