line emission by the first star formation hiromi mizusawa(niigata university) collaborators ryoichi...
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line emissionby the first star formation
Hiromi Mizusawa(Niigata University)Collaborators
Ryoichi Nishi (Niigata University)Kazuyuki Omukai (NAOJ)
2H
Formation of the First Generation of Galaxies December 2-5, 2003, Niigata University, Japan
Outline
PurposeModel : the method of calculation
Results : the evolution of T, y( ), luminosity
Detectability of the first stars by SPICA
Summary & Discussion
2H
PurposeWe estimate the luminosities of lines, which can be characteristics of the first star formation process, and evaluate the detectability of lines.
The luminosities of lines for the runaway collapse phase Ripamonti et al (2002) and Kamaya & Silk (2002)
However the luminosities of lines for the main accretion phase haven’t been estimated.
protostellar cloud protostarmain sequence star
main accretion phase
we calculate them for both phase .
2H
2H
2H
2H
runaway collapse phase
1
Model
The Larson-Penston-type similarity solution, γ = 1.09 (dotted line), reproduces Omukai&Nishi’ result (solid line) well. a good approximation to the actual collapse dynamics.
center ---- flat density distribution, runaway collapseenvelope ---- leaving the outer part practically unchanged
The thermal and chemical evolution of gravitationally collapsing protostellar clouds is i
nvestigated by hydrodynamical calculations for spherically symmetric clouds. (Omukai&Nishi 1998)
The evolutionary sequences
yr104.1:76
yr102.4:65
0.32yr:54
12yr:43
yr102.8:32
yr108.7 :21
yr
2-
2-
2
3
5107.5:10
The time interval
2
)g/cm( 3
)cm(r
2.2 r
J~
①
②
③time
Contracting region and mass
become more and more small.
Free-fall determined by
the local density
31. Dynamics・ The runaway collapse phase
The central evolution the free-fall relation modified by pressure gradient
G
ttdt
d
32
3, ff
ff
β
the flat core size ;Jα
the collapse time scale ; fftβ
For the Larson-Penston-type similarity solution for γ=1.09,
13.2,33.1
,1
1,1
,78.0gravity
pressure
)g/cm( 3
)cm(r
2/3 r
①
②
③
Inner mass shells fall faster than outer mass shells.
Free-fall determined by the gravitational force of th
e protostar
4・ The main accretion phase
2/3
2
,
,)(
r
vdt
drr
rGM
dt
dv
r
r
: the density of free-falling mass shell
rv : the velocity of free- falling mass shell
r: the distance from mass shell to the center
Approximation,
each mass shell free-fall
2. Energy equation
HH m
kTp
m
kTe
Ldt
dp
dt
de net
,1
1
1 )(
3. Cooling/Heating processes
: the energy per unit mass , : the pressure , : the temperature ,: the adiabatic exponent , : the mean molecular weight , : the mass of the hydrogen nucleus
e p T
Hm
: the cooling rate by line emission ,
: the net cooling rate by continuum emission,
: the net cooling rate by chemical reactionscontLlineL
chemL
chemcontline
net LLLL )(
5
2H
--- the population density of in level i
--- the spontaneous transition probability
--- the energy difference between levels I and j
--- the collisional transition rate from level I to level j
ijA ijCijC
i
j
),H( 2 in
ijA
ij
ijh
ijC
ij --- the optical depth averaged over the line
--- the escape probability
・ line cooling
2H
ij
ij
ije
1
6
)(
)(
),H(),H(
),H(1
22
2H2
jiC
jiCAR
RjnRin
hAinL
ij
ijijij
ij
ji
n
ij
n
ijij
ijijji
ij
eHHH
HeH
2
)cm10(~ 38
Hn
4. Chemical reactions ( formation processes)
( process)
( three-body reactions )22
2
2HH2H
HH3H
)cm10~cm10( 31438H
n
H
2H
・ continuum cooling/heating
bound-free absorption of ,
-H
2H collision induced absorption
Protostar ~ the black body of 6000 K (Omukai & Pala 2003) free-free absorption of ,-H
7
In our calculation, these continuum processes are hardly effective.
Initial Conditions
The physical condition of fragments (protopstellar clouds)
832
34 10)(,10)(),(200),(10 eHKcmH yyTn
The contraction and fragmentation of primordial, metal-free gas clouds is investigated by some authors .(e.g., Uehara et al. 1996; Nakamura & Umemura 2002 ;Abel et al. 2002; Bromm et al. 2002)
JM : Jeans mass
)H(/)H()H( i nny i : the concentration of the i-th species
: the number density of the hydrogen nucleus
)H(n
We adopt the typical values for the star-formingcores from Bromm et al.(2002).
8
MJ
310~M
Results
time
The runaway collapse phase
9
time
an order
Effective cooling by 2H
The time evolution of the central temperature
three body reactions
process -H
)H(y
)H( 2y
The time evolution of the central abundance of 2HH,
~ ten orders of magnitude
time time
Comparison between runaway collapse phase and main accretion phase
For the accretion phase, the evolutionary trajectories of the mass shells of are shown.
M20M5
M102
The main accretion phase
The runaway collapse phase
)H( 2y
)H(y
100,20,5/)( MrM
10
The evolution of line emission
red : (1,1)→(0,1), green: (1,1)→(0,3), blue : (0,6)→(0,4), purple :(0,5)→(0,3) 2.34μm , 2.69μm , 8.27μm , 10.03μm
Pick upPick up : four of the strongest lines
2H2H
rest frame :
11
rovibrational lines
rotational lines
runaway collapse phase
main accretion phase
Peak luminosityPeak luminosityThe central The central protostarprotostar
M20~
The protostar formation
])(log[
))((
(cm)
(erg/s)ch
rd
rd L
(K)T
600
1000
1400
1800
20013 14 15 16 17 18 19
The sources of radiated energy
Compressional heating
formation heating
Until peak luminosity
At the same radius,)()( rTrT ac
)()( ,, rr achcch LL
Area indicates the chemical energy unit time,
(erg/s))( rch L
)()(
)()(
,,
,,
rr
rr
alinecline
achcch
LL
LL The final stage of collapse phase
Three selected time in accretion phase
M5
M20
M50
M20
M50
M52H
For mid-infrared region ( ), SPICA(ISAS), a large(3.5m),cooled(4.5K) telescope, is the best . (better than JWST and ALMA)
19zD)m/W(10~4
227
2
19
peak
z
peak
D
LF
peakL
μm40~
)μm(34.2:),1,0()1,1( framerest
)(8.46:)201 μm z(redshifted
:The luminosity distance to z=19
:The peak luminosity
The line detection limit of SPICA is about in .
more than sources SPICA can observe.6510
μm40~
13
)(10 21 2W/m
Limited by the high background of the zodiacal light (private communication H.Matsuhara).
Detectability
Summary & Discussion ・ We estimate the line luminosities from the first-generation star formation process. ・ the luminosities of both rovibrational lines and rotational lines become maximum value at the main accretion phase.
・ For the runaway collapse phase, the strongest lines are rotational lines. For the main accretion phase, rovibrational lines overwhelm them.・ For the peak, rovibratinal lines are stronger than rotational lines.
rotational lines ----- low density region such as envelope of the protostellar clouds rovibrational lines ----- high density region such as final stage of star formation processrovibrational lines the strong evidencethe strong evidence of the first-generation star formation
For observation of the first-generation star, rovibrational lines are importanrovibrational lines are importantt..
2H
14
@ high z,detecting line emission by SPICA is highly improbable.
@ low z, such as ,detecting it from Pop III stars by SPICA is maybe possible.
Formation of Galactic scaleGalactic scale with such low metallicitylow metallicity is maybe excluded in the context of standard cosmology (e.g., Scannapieco,Schneider,& Ferrara 2003).
Although, it is necessary to investigate how the mixing of metals occur.
IfIf sources @ , SPICA can observe forming first-generation stars.
6510 19~z
To emit mainly in lines,
the metallicity in the pregalactic clouds (Omukai 2000).
Z410~
2H
2H
3~z
To exist sources is difficult situation at early universe.6510
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