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