Download Major Themes of “ The First Stars ”

First Light from the Fossil Record:
(1)
A New Synthesis
A Review of Major Themes in the Study of “First Stars”
Jason Tumlinson
(2)
A New
Approach
to Constraints
on the
Yale
Center
for Astronomy
and Astrophysics
IMF of Primordial (“First”) Stars
(3)
The IMF of the “Second” Stars
(4)
Predictions and Future Tests
A slice of the Milky Way at z = 6
The Big ??: When, What, and Where was “First Light”?
Major Themes of “The First Stars”
Physical Models of Star Formation at Zero and Very Low Metallicity
Stellar Evolution and Nucleosynthesis of the First Stars
Chemical Abundance Studies of Metal-Poor Pop II (“Galactic Archaeology”)
Simple recipe for first stars:
• LCDM
• Dark matter “minihalos” of
MDM ~ 106-7 M at z = 20 - 40.
• primordial composition (H,He,H2)
• the absence of other (in)famously
complicating factors (dust, B)
GM J2 MkT

R
mH
1
3
n

 2 T  2
M J M  3 3  nd


cm “2  10Stars”
K
 10 the
Metallicity” and
Key Concept #2: “The Critical
At Zcrit ~ 10-5.5 to 10-3.5 Z‫סּ‬, efficient metal-line cooling may allow
Key
Concept #1:
Heavier
fragmentation
to “Warmer
low-mass(Primordial)
stars (BrommGas
& LoebForms
2003; Santoro
& ShullStars”
2006).
H
primordial
gasmay
to Talso
200
K, for
MJ ~ 100
- 1000the
M‫סּ‬
But
by this
time there
dust,
ionizing
radiation,
2 cools
min ~be
(Bromm,
Coppi,
Larson 1999;
2002,
Bryan,simulation
& Norman 2002) is too hard.
CMB, cosmic
rays,
B &fields.
. so
abAbel,
initio
30 – 300
Kelvin-Helmholz
time (O’Shea & Norman 2007).
ToMcut
the knotinofatheory,
we need observations!
‫ סּ‬accretes
Major Themes of “The First Stars”
Physical Models of Star Formation at Zero and Very Low Metallicity:
Approach: Hydrosims of gas physics in early cosmological halos
Key Results: High mass range (~30 - 300) for limiting Z = 0 case.
Formation of first low-mass stars depends on prior ionization
and/or metal enrichment metals, dust, CMB, other factors (?)
How did the first and second stars form, and what was their IMF?
Stellar Evolution and Nucleosynthesis of the First Stars:
Approach: numerical stellar evolution and supernova models (1-D)
Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”)
Number per Mass Bin
M
Key Idea: The chemical signatures of stars vary with initial
mass and metallicity in complex but calculable fashion.
Our strategy is to use robust and distinct signatures of stellar
mass to diagnose IMF.
Major Themes of “The First Stars”
Physical Models of Star Formation at Zero and Very Low Metallicity:
Approach: Hydrosims of gas physics in early cosmological halos
Key Results: High mass range (~30 - 300) for limiting Z = 0 case.
Formation of first low-mass stars depends on prior ionization
and/or metal enrichment metals, dust, CMB, other factors (?)
How did the first and second stars form, and what was their IMF?
Stellar Evolution and Nucleosynthesis of the First Stars:
Approach: numerical stellar evolution and supernova models (1-D)
Key Results: “Pair Instability SNe” and “Hypernovae” may arise from
the first stars and give distinctive yield patterns.
Big question now is how much rotation alters mass loss and yields.
Given a particular IMF, what are the observational signatures (both
radiation and chemical yields)?
Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”):
10000 from RAVE
(AAO – now)
The Future of “Galactic Archaeology”
>100000 from SDSS/SEGUE for halo,
APOGEE for bulge and disk
100000 from LAMOST
(China - 2009)
109 from GAIA (ESA2011)
Dwarf Abundance and Radial
Velocities (DART) @ VLT
106 from WFMOS
@ Subaru (2010?)
Massive spectroscopic
multiplexing enables surveys
of > 106 stars for studies of
MW structure and formation.
Up to >~ 105 of these stars
will have [Fe/H] < -2, so are
plausibly from the first few
generations.
About 1% of the abundance
data that will exist in 2013 is
in hand and analyzed today.
But what information about
the first galaxies might these
stars provide?
“Information Overload” from Chemodynamical Probes of Galactic Evolution
“Primary”
Beers & Christlieb (2005) ARA&A
[X/Fe]
“Explosive”
“neutron capture”
[Fe/H]
Measured proper motion, radial velocity, and position trace
galactic components – disk, bulge, or halo.
Color, luminosity, Teff, and metallicity select old, low-mass stars
with [Fe/H] < -2 that most likely trace the first generations.
Expand this ~30-D “data space” by at least four orders of magnitude and you begin to get the idea.
HERES Survey - Barklem et al. (2005) – 15 elements in 253 stars
“Hydrostatic”
VLT data - Cayrel et al. (2004) and Barklem et al. (2005)
[Ba/Fe]
≥ 82% at [Fe/H] ≤ -2.5 show r-process enrichment
HERES Survey - Barklem et al. (2005)
Carbon-Enhanced Metal-Poor Stars (CEMPs):
after Komiya et al. (2007)
HE1327-2326
HE0107-5240
“HMPs”
“C-normal “ ~ solar
100%100%
CEMP = [C/Fe] > 1
@ [Fe/H] < -2
Beers & Christlieb (2005)
Major Themes of “The First Stars”
Physical Models of Star Formation at Zero and Very Low Metallicity:
Approach: Hydrosims of gas physics in early cosmological halos
Key Results: High mass range (~30 - 300) for limiting Z = 0 case.
Formation of first low-mass stars depends on prior ionization
and/or metal enrichment metals, dust, CMB, other factors (?)
How did the first and second stars form, and what was their IMF?
Stellar Evolution and Nucleosynthesis of the First Stars:
Approach: numerical stellar evolution and supernova models (1-D)
Key Results: “Pair Instability SNe” and “Hypernovae” may arise from
the first stars and give distinctive yield patterns.
Big question now is how much rotation alters mass loss and yields.
Given a particular IMF, what are the observational signatures (both
radiation and chemical yields)?
Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”):
Approach: massive surveys to discover stars at [Fe/H] < -2,
followed by high-res spectra to obtain abundance patterns.
Key results: discovery of HMPs with [Fe/H] <~ -5 and widespread
strong enhancement of Carbon, the CEMPs.
Where are the oldest low-mass stars, and what do they tell us about star
and galaxy formation during the Epoch of First Light?
(1)
A Quick Review of Major Themes in the Study of “First Stars”
First Major Conclusion:
The theory of “First Light” is developed to the
point of having some testable predictions,
which can be addressed in the near term with
rapidly growing data from “Galactic
Archaeology” and in the long term with JWST.
So, how can we use Galactic
Archaeology to study the first stars?
The Challenge to Theory
As the sample sizes and dimensionality of the data explode, the
theoretical challenge is to:
- make sense of all this data
- come to grips with the awesome statistics
- define what “information” is present
- place the observations in the proper context of high redshift
- properly translate physical theory into the data space.
. . . In short, to create a “Virtual Galaxy” that will
synthesize all this data, in the high redshift context.
Star Formation Theory
Nucleosynthesis
+
Structure Formation
+
Observations!
=
A New Synthesis of Chemical Evolution & Structure Formation
25
Pop III Halos
20
HIERARCHICAL: Halo merger trees allow
for chemical evolution calculations much
faster than full hydro simulations, much
more realistic than “classical” GCE.
STOCHASTIC: Within each node, gas
budget is tracked and new star formation
samples the IMF “one-star-at-a-time”. New
star formation is assigned a metallicity
based on random sampling of “enrichment
zones” from prior generations.
15
z
10
UNIFIED: Best of all, these “nodes” can be
modeled as individual galaxies for direct
comparisons to data at high redshift – this
is also the core of a galaxy formation code.
5
0
“Milky Way”
Tumlinson 2006, ApJ 641, 1
“Salpeter”
Number per Mass Bin
Z ≥ Zcr
“Log-normal”
Z < Zcr
mc
“Very Massive Stars”
s
Discrete, Stochastic Chemical Evolution, “One Star at a Time”
Tumlinson 2006
Zcrit = 10-4
Fo ≤ 1/N(<2.5)
≤ 0.0019
Pure Z = 0
progenitors!
“Pop II” [Fe/H]
“Pop II” [Fe/H]
Tumlinson, Venkatesan, & Shull (2004)
Yields: Heger+Woosley - Data: McWilliam95, Carretta02, Cayrel04
PISNe yields are characterized by big “Odd Even Effect” and no
neutron capture nucleosynthesis.
Observed Fe-peak, eg. [Zn/Fe], require ≤ ½ of Fe from PISNe.
PISNe have no r-process, so cannot give 82% of EMPs with Ba.
Constraints on the Primordial IMF
Too many “True” Pop III stars.
Tumlinson (2006)
Too much Fe from PISNe
A
C
B
Too little r-process
Convergence on the First Stars IMF?
Number per Mass Bin
Tumlinson 2006a, ApJ, 641, 1
“Data”
B
“Theory”
C
A
Theory is still missing feedback of young star on final mass?
(2)
A New Approach to Constraints on the
IMF of Primordial (“First”) Stars
Second Major Conclusion:
Using a new synthesis of theory that tracks
stochastic early chemical evolution in the
proper high-z, hierarchical context, we can
show that the first stars were predominantly
massive stars, but find hints that additional
feedback might be needed in simulations to
resolve remaining discrepancy.
Q: How can we study the IMF at
Z > 0, i.e. for most stars during the
Epoch of “First Light”?
A: The CEMPs!
HE1327-2326
HE0107-5240
100%
40%
20%
after Komiya et al. (2007)
CEMP = [C/Fe] > 1
@ [Fe/H] < -2
Beers & Christlieb (2005)
10%
The Answer: CEMP stars are born as low-mass partner in a binary system.
80% are CEMP-s that are rich in s-process elements (indicating AGB).
CEMP-s consistent with 100% binarity (Lucatello et al. ’05).
From CEMPs to the IMF
Primary
1.5 -0.8
8M
+‫סּ‬0.8
binaries are
favored.
CEMP
“Low fCEMP”
M ~ 0.8 M‫סּ‬
LMS
0.8 + IMS
binaries are
favored.
High fCEMP.
IMS
IMS
LMS
0.5
1.5
8
40
0.5
1.5
8
40
The ratio of C-rich to C-normal stars in a population measures the
ratio of intermediate to low-mass stars in the IMF!
Estimate from early CEMP studies: Mc > 0.8 M‫( סּ‬Lucatello+05).
There are no C-normal stars at [Fe/H] = -5.5, so Mc = 1.5 - 6 M‫( סּ‬Tumlinson07).
Komiya+2007 find mc ~ 10 M‫ סּ‬to match s-element patterns of CEMPs.
Tumlinson (2007a)
Zcrit
C-rich Pop II stars
“CEMP”
MW
Why would the IMF form more IMS, if Z ~ 10-3Z‫ סּ‬is high
enough to cool efficiently (Bromm+Loeb03, Schneider+02)?
Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars”
GM J2 MkT

R
mH
MJ
n


M  3 3 
 10 cm 
1
2
 T 


 10K 
3
2
H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 M‫סּ‬
Coppi, & Larson
1999; 2002,
Abel, Bryan,
& Norman
2002)
Studies of local(Bromm,
star formation
(Larson
‘98,’05;
Jappsen
et al.
’05) suggest that
the characteristic mass of stars responds to the minimum T at which gas
30
– 300 optically
M‫ סּ‬accretes
a Kelvin-Helmholz
time (O’Shea
& Norman
2007).
becomes
thick toincooling
radiation and thermally
coupled
to dust.
At low redshift, Z = Zmin = 10 K is set by metal and dust cooling.
But at high z, the CMB at T = 2.73(1+z) K sets the minimum gas temperature!
Thus stars formed early in MW history, at z > 5, should be affected!
MC ≈ 0.9 M‫[ סּ‬TCMB/10K]1.70-3.35
z = 5, 10, 20
TCMB = 16, 30, 57 K
MC = 2, 6, 17 M‫סּ‬
(3)
CEMPs and the IMF of the “Second” Stars
Third Major Conclusion:
IMF diagnostics in the most metal-poor stars,
Q: How
can webytest
the
CMB-IMF
hypothesis?
interpreted
a new
hierarchical,
stochastic
theoretical framework, show evidence for a
top-heavy IMF at high redshift that may be
A: Look
for
agreement
between
what
we
see
physically independent of metallicity.
as old in the nearby Universe and what we see
as young in the distant Universe.
Low-z Test #1: Variation of CEMP Fraction with Metallicity
(Tumlinson 2007b, ApJL, 664, L63)
Tumlinson (2006)
stochastic MW
Stochastic, local phenomenon
of chemical evolution implies
that, on average, more metalpoor stars form earlier, so
fCEMP should increase with
declining [Fe/H].
HMPs
With a CMB-IMF, fCEMP is
high at low [Fe/H], and
declines with increasing
[Fe/H] as the typical
formation redshift at a given
metallicity declines.
Key Idea for Prediction 2: The Halo is Built from the Inside Out. . .
Inside-out construction the halo causes extended epoch of star
formation at fixed [Fe/H], so
fCEMP should increase in “older” regions of the Galaxy and decrease
in “younger” regions, at fixed metallicity.
Low-z Prediction #2: Variation of CEMPs with Galactic Location
UPDATE
NCEMP
NCEMP+NC-normal
Also:
The CMB-dominated mass scale at ~ 10 kpc is 2 -10 M‫סּ‬.
Faint end of WD luminosity function? (JWST)
At a given metallicity, stars in the inner halo are older, and this
fgradient
dwarf
spheroidals
(GSMT)?
gives
a gradient
of C-rich/C-normal
fraction.
CEMP in
>100000 from SDSS/SEGUE for halo,
APOGEE for bulge and disk
SDSS-III =
SEGUE-II (2008)
+ APOGEE (2011)
SEGUE2: 105 more halo and thick disk stars w/ current SDSS spectrograph.
APOGEE: H-band spectroscopic survey of 105 giants in inner disk and bulge.
with the ARCHES spectrograph (PI Majewski at UVa).
“Virtual Galaxy” will be important to comparing the results of the two surveys
for chemical and kinematic substructure in the ancient MW.
High-z Test: Mass-to-light ratios in High-z Galaxies
van Dokkum (2008)
technique from Tinsley (1980)
When estimates of dynamical mass / light ratios of “firstlight” galaxies become possible with JWST and GSMTs,
expect to see M/L decline with redshift, 2 - 5 times lower
than for a normal IMF.
The Morals of the Story
1. Because many of the first galaxies are still with us, “Galactic
Archaeology” with growing stellar surveys can uncover unique insights
into the history of star and galaxy formation during First Light.
2. With this rich dataset and a new synthesis of theory, we can directly
address some of the most pressing questions about the galaxies of
“First Light” – such as how metallicity, redshift, and environment
interact in shaping the IMF.
3. Early indications are that the Pop III and early Pop II IMFs during the
epoch of reionization preferred intermediate and massive stars, with
major implications for observable features of galaxies by JWST.
4. A new synthesis of theory is being developed to take advantage of this
wealth of data, and connect it explicitly to high-z, as a perfect partner
and complement to JWST. In the JWST era, we can test and extend
these models to uncover a deep, unified view of First Light.
A Three-fold Vision for the Future
Theoretical: Complete the N-body theoretical framework,
including many MW realizations, sharpened predictions for
tests of the CMB-IMF hypothesis, and a systematic study of
dSph abundances. Begin building framework for high-z.
Observational: Collaborate (join?) with observers to test
predictions and develop new ideas.
Sloan SEGUE (current) > 20000 @ [Fe/H] < -2
Radial Velocity Experiment (RAVE, current), 10000+
SDSS3 = SEGUE2 (Halo) + APOGEE (Bulge) 2008 – probably most critical
WFMOS: Wide Field Multi-Object Spectrograph (?) and others later
The challenge: to integrate the results and make optimal use of all information.
Unification: The goal is a full realization (gas included) that
follows both a high-resolution MW to z=0 and a
cosmological volume at high redshift. This model will allow
us to test the same galaxy formation physics with both
JWST and Galactic Archaeology data.
•Extra slides follow
Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars”
GM J2 MkT

R
mH
MJ
n


M  3 3 
 10 cm 
1
2
 T 


 10K 
3
2
H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 M‫סּ‬
(Bromm, Coppi, & Larson 1999; 2002, Abel, Bryan, & Norman 2002)
30 – 300 M‫ סּ‬accretes in a Kelvin-Helmholz time (O’Shea & Norman 2007).
ORIGINAL
Key Concept #2: “The Critical Metallicity” and the “2nd Stars”
At Zcrit ~ 10-5.5 to 10-3.5 Z‫סּ‬, efficient metal-line cooling may allow
fragmentation to low-mass stars (Bromm & Loeb 2003; Santoro & Shull 2006).
But by this time there may also be dust, ionizing radiation, the
CMB, cosmic rays, B fields. . so ab initio simulation is too hard.
To cut the knot of theory, we need observations!
Paths to Star Formation during “First Light”
To understand the stars in “First Light” galaxies, we can apply some
canonical diagnostic tests in the high-redshift Universe:
- blue colors and unusual emission lines (He II) with JWST and 30-m
- color and luminosity evolution in evolved populations
- GP effect and other tracers of reionization (CMB, 21 cm, LAEs)
However. . .
. . . these tests require facilities that are some years away (2013+), and
. . . they detect direct/reprocessed emission of massive stars, so
are insensitive to the bulk of the stellar mass (in a normal IMF), and
provide poor tests of star formation physics at very low metallicity.
Both of these problems can be avoided if we
look instead in the low-redshift Universe!
First Stars: The Hows and Whys
Simple recipe for first stars:
• LCDM
• Dark matter “minihalos” of
MDM ~ 106-7 M at z = 20 - 40.
• primordial composition (H,He,H2)
• the absence of other (in)famously
complicating factors (dust, B)
GM J2 MkT

R
mH
ORIGINAL
1
Key Concept #2: “The Critical
10-5.5
Red = Bound at z = 10
3
 T  2
n

 2nd
M J Mand

Metallicity”
 3 the
3 “2  Stars”
 10 cm   10K 
At Zcrit ~
to 10-3.5 Z‫סּ‬, efficient metal-line cooling may allow
Key
Concept #1:
Heavier
fragmentation
to “Warmer
low-mass(Primordial)
stars (BrommGas
& LoebForms
2003; Santoro
& ShullStars”
2006).
H
primordial
gasmay
to Talso
200
K, for
MJ ~ 100
- 1000the
M‫סּ‬
But
by this
time there
dust,
ionizing
radiation,
2 cools
min ~be
(Bromm,
Coppi,
Larson 1999;
2002,
Bryan,simulation
& Norman 2002) is too hard.
CMB, cosmic
rays,
B &fields.
. so
abAbel,
initio
30 – 300
Kelvin-Helmholz
time (O’Shea & Norman 2007).
‫ סּ‬accretes
ToMcut
the knotinofatheory,
we need observations!
Major Themes of “The First Stars”
Physics of Star Formation at Zero and Very Low Metallicity:
Approach: Hydrosims of gas physics in early cosmological halos
Key Results: High mass range (~30 - 300) for limiting Z = 0 case.
Formation of first low-mass stars depends on prior ionization
and/or metal enrichment metals, dust, CMB, other factors (?)
How did the first and second stars form, and what was their IMF?
Stellar Evolution and Nucleosynthesis of the First Stars:
Approach: numerical stellar evolution and supernova models (1-D)
Key Results: “Pair Instability SNe” and “Hypernovae” may arise from
the first stars and give distinctive yield patterns.
Big question now is how much rotation alters mass loss and yields.
Given a particular IMF, what are the observational signatures (both
radiation and chemical yields)?
ORIGINAL
Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”):
Approach: massive surveys to discover stars at [Fe/H] < -2,
followed by high-res spectra to obtain abundance patterns.
Key results: discovery of HMPs with [Fe/H] <~ -5 and widespread
strong enhancement of Carbon, the CEMPs.
Where are the oldest low-mass stars, and what do they tell us about star
and galaxy formation during the Epoch of First Light?
“Low-z” Predictions of the CMB-IMF Hypothesis
(Tumlinson 2007a, ApJL, 664, 63)
(1)
Stochastic, local phenomenon of chemical evolution
implies that, on average, more metal-poor stars form
earlier, so fCEMP should increase with declining [Fe/H].
ORIGINAL
(2)
Inside-out construction the halo causes extended
epoch of star formation at fixed [Fe/H], so
fCEMP should increase in “older” regions of the Galaxy
and decrease in “younger” regions, at fixed metallicity.
Discrete, Stochastic Chemical Evolution, “One Star at a Time”
Tumlinson 2006
Zcrit = 10-4
Fo ≤ 1/N(<2.5)
≤ 0.0019
ORIGINAL
Pure Z = 0
progenitors!
“Pop II” [Fe/H]
“Pop II” [Fe/H]
Theme 1: Theory of Star Formation in Early Universe
Kinetic Feedback
Metal enrichment
Reionization
IMF
Spectral Features
Colors
Compact Objects
Theme 1: Theory of Star Formation in Early Universe
Structure Formation
Cooling (Metals)
Heating (adiabatic,CMB)
IMF
Feedback
Turbulence
Magnetic Fields