Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
OVERVIEWI IntroductionII. Observational constraints based on H II Regions and Planetary NebulaeIII.Big-Bang Nucleosynthesis and the Primordial Helium AbundanceIV.Pagel´s method to derive the O/H ratio in galaxiesV.Chemical Evolution of the Galaxy: C,O, and N Gradients
M. PeimbertInstituto de Astronomía, UNAM
Tonantzintla, August 2005
III. Big bang nucleosynthesisand the primordial helium
abundance
Antonio Peimbert (IA-UNAM, México)Valentina Luridiana (IA de Andalucía)Ma. Teresa Ruiz (Universidad de Chile)
Fernando Fabian Rosales Ortega Elena Terlevich
Roberto Terlevich
Y
106O/H
0.00
0.20
0.40
0.60
0.80
1.00
0 100 200 300
Steigman 2002
Primordial Helium Production
S. Weinberg, The first threeminutes
If the barionic density increases theexpansion velocity increases > theUniverse gets colder earlier > nucleosynthesis starts earlier > a largerfraction of neutrons is available > and a larger fraction of helium atoms isproduced
Primordial Nucleosynthesis
The results depend onthe baryonic mass
of the Universe
Peimbert, Peimbert, & Luridiana 2002
Big BangNucleosynthesisandBaryonicContent of theUniverse
Steigman 2002
Neutrino families vs. DP and YP
Outline
1. Underlying Absorption2. Ionization Structure3. Temperature Structure4. Density Structure5. Collisional Excitation6. Optical Depth of the He I triplet lines7. ∆ Y / ∆ O
Underlying Absorption in H ILines
Peimbert, Peimbert, & Ruiz 2000
Region of NGC 346 (H II Region in the SMC)
Fraction Avoidingthe O & B Stars
WholeSlit
Ionization Structure
1) Density Bounded
He He0+He++He++
H H0+H+
H+, He+
=
He He++He++
H H+=
H+, He+
H+, He+
H+, He0
H0, He+
He He0+He+
H H+
2a) T* ≲ 40 000 K
2b) T* ≳ 40 000 K
2) Ionization Bounded
He He++He++
H H0+H+
=
=
Y underestimated
Y overestimated
Temperature Structure
Te(4363/5007) = T0 [1 + (90800/T0 -3) t 2/2]
Te(Bac/Hβ) = T0 (1 – 1.70 t 2)
Te(4649/5007) = f1 (T0 , t 2)
T0 =
t 2 =
∫ Te Ne Ni dV∫ Ne Ni dV
∫ (Te - T0)2 Ne Ni dVT0
2 ∫ Ne Ni dV
Peimbert 2003
30 Dor
Balmer Continuum in EmissionT(Bac) < T([O III])
Peimbert, Peimbert, & Luridiana 2002
Effect of the Temperature Structureon the T(He II) / T(O III) value
Primordial Helium
Peimbert, Peimbert, & Luridiana, 2002
Density Structure
Density Diagnostic[S II]
[Fe III][Cl III][Ar IV]
f i (He+/H+, T0 , t 2, τ3889)
Volume Fraction~ 5%~ 15%~ 85%~ 5%~ 98%
Collisional Excitation of the He Ilines
He+ I(6678)H+ I(Hβ)
= 2.58 t 0.249 – 2.0 10�� n
He+ I(4471)H+ I(Hβ)
= 2.01 t 0.127 – 4.1 10�� n
He+ I(5876)H+ I(Hβ)
= 0.735 t 0.230 – 6.3 10�� n
t =10-4 Te K; n = electron density
Benjamin, Skillman, & Smits 1999
Collisional Excitation of the H I lines
Davidson & Kinman (1985).Stasinska & Izotov (2001).Peimbert, Peimbert, & Luridiana (2003).
•This is the least studied problem related to the YP determination.•It requires tailor-made models for each object.•Notice that simple photoionization models predictelectron temperatures smaller than observed.•It is extremely sensitive to temperature.•It is very important for objects with Te > 16000K.•It is negligible for objects with Te < 12000K.
I(Hβ)2-6%1-3%
0.5-1%
Te18 000 K15 000 K12 000 K
Optical Depth of the He I triplet lines
2 3S
2 3P
3 3D
3 3S
4 3S4 3D
λ10830
λ7065
λ4713
λ3889
λ4471λ3188
λ5876
•Singlets are not affected
•Triplets have 3 times more photons
•Taken together there are 4 times the photons + twice the number ofindependent measurements
•Computations for spherical geometry were carried out by Benjamin, Skillman, & Smits (2002).
•Real objects are not spherically symmetric; for largeτ3889 there can be large discrepancies.
•These authors recommend not to use theircomputations for τ3889 > 2.
•For objects with large optical depth the τ3889 derived from 7065/6678 is more representative for 4471 and 5876 than the τ3889 derived from 3889/6678.
∆ Y / ∆ O
3.5±0.63.5±1.0Peimbert (2002). . .2.7±1.2Izotov & Thuan (1998). . .4.5±1.0Carigi et al. (1995)
The GalaxyIrregularsObservations
2.9 - 4.6. . .Carigi (2000). . .4.2Carigi et al. (1999)3.15. . .Chiappini et al. (1997). . .2.95Carigi et al. (1995)
The GalaxyIrregularsTheory
∆Y/∆O = 3.5 ± 0.9YP = Y - O(∆Y/∆O)
Irregulars: closed box models and outflow models of well mixedmaterial. For O-rich outflows the models enter in contradiction withobserved C/O values.
Galaxy: two infall models with an inside-out formation scenario
∆ Y / ∆ O
. . .5.7 ± 1.8Izotov & Thuan (2004)
3.57 ± 0.67 2.93 ± 0.85Peimbert (2003)
. . .4.3 ± 0.7Izotov & Thuan (2004)
The GalaxyIrregularsObservations
Peimbert 2003
30 Doradus
O II Recombination LinesN(O++, t2>0)FL = N(O++)RL > N(O++, t2=0)FL
Steigman: from Peimbert 2003
SMC, LMC & M17
NOAO
M17
Summary
1. Underlying Absorption in H I Lines2. Underlying Absorption in He I Lines3. He I and H I Line Intensities4. Ionization Structure5. Temperature Structure6. Density Structure7. Collisional Excitation of the He I lines8. Collisional Excitation of the H I lines9. Optical Depth of the He I triplet lines10. He I and H I Atomic Parameters11. ∆ Y / ∆ O
Error Budget*
1. Underlying Absorption in H I Lines2. Underlying Absorption in He I Lines3. He I and H I Line Intensities4. Ionization Structure5. Temperature Structure6. Density Structure7. Collisional Excitation of the He I Lines8. Collisional Excitation of the H I Lines9. Optical Depth of the He I Triplet Lines10. He I and H I Atomic Parameters11. ∆ Y / ∆ O
5725
1510 7
203
1510
-50+70
212
-6045
-90+50
10 3015
* In 1/10,000 of mass fraction
StatisticalIgnoringthis effect
Primordial Value
YP = 0.2452 ± 0.0015 ± 0.0070 (1999) IzotovYP = 0.2391 ± 0.0020 ± 0.0045? (2003) Luridiana
YP = 0.2421 ± 0.0021 ± 0.0045? (2004) Izotov
YP = 0.249 ± 0.009 ± 0.0045? (2004) Olive & Skillman
YP = 0.243 ± 0.004 ± 0.0045? (2004) Rosales
WMAP, YP = 0.2484 ±0.0005 (2003)
SuggestionsBright ObjectsLow Stellar ContinuumHigh Degree of IonizationLow Optical DepthLow Density16000 KTailor-made Models For Each ObjectSimple Photoionization Models DO NOT reproduce the Observed Temperatures
Summary III
For O poor H II regions the models by CLOUDY predict 4363/5007 temperatures smaller thanobserved, this indicates the presence ofadditional heating sources not considered by CLOUDY.
The presence of a typical t2 value reduces Yp by about 0.007. For example from 0.250 to 0.243.
Primordial Value
YP = 0.2452 ± 0.0015 ± 0.0070 (1999)
YP = 0.2391 ± 0.0020 ± 0.0045? (2003)
YP = 0.2??? ± 0.0020 ± 0.0010 (2006?)
The end