TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES M. Peimbert  C.R. O’Dell  A. Peimbert  V. Luridiana  C. Esteban  J. García-Rojas  L. Carigi  F. Bresolin  M.T. Ruiz  A.R. López-Sánchez Lake Geneva, Wisconsin, April 2007Microstructures in the ISM: Bob O’Dell 70th birthday

OUTLINE Why is this problem important? Definitions T [O III ], T (Balmer),T (O II ), T (C II ) Which is the cause of temperature variations The Orion nebula and microstructures The Orion nebula and the solar abundances Calibration of the R 23 method The primordial helium abundance Conclusions

Why is the problem of temperature variations important? Physical conditions of gaseous nebulae Abundances in H II regions and PNe Solar abundances Galactic chemical evolution Primordial helium abundance, Y P Metal content and chemical evolution of the universe

Temperature Structure T e ( 4363/5007 ) = T 0 [ 1 + ( 90800/T 0 -3 ) t 2 /2 ] T e ( Bac/H  ) = T 0 ( 1 – 1.70 t 2 ) T e ( 4649/5007 ) = f 1 ( T 0, t 2 ) T 0 = t 2 =  T e N e N i dV  N e N i dV  ( T e - T 0 ) 2 N e N i dV T 0 2  N e N i dV T e ( He lines ) = T 0 ( 1 – k t 2 ) k~1.8 T e (4267/1909) = f 2 (T 0, t 2 )

Ups and downs of t 2 March 2007

How Important Are Temperature Variations? Photoionization homogeneous models predict values of t 2 in the to 0.03 range, with typical values around 0.01 Observational values of t 2 are in the 0.00 to 0.09 range with typical values around 0.03 Typical ratios between the abundances derived from permitted lines and forbidden lines are in the 2 to 3 range (O, C, N, Ne), the so called abundance difference factor, ADF By adopting t 2 values different from 0.00 it is possible to reconcile the abundances derived from forbidden lines with those derived from permitted lines

Presence of Temperature Variations There are temperature variations that can not be explained by chemically homogeneous photoionization models The sources of these variations can be many and a specific model has to be made for each nebula The abundances derived from recombination lines are almost unaffected by temperature variations The abundances derived from collisionally excited lines, under the assumption of constant temperature, typically underestimate the abundances relative to hydrogen by a factor of 2 to 3

Liu & Danziger 1993 Balmer vs. [O III ] Temperatures

N(C ++ ) from Recombination Lines vs. N(C ++ ) from Forbidden Lines Peimbert, Luridiana, & Torres-Peimbert 1995

Recombination to Forbidden O ++ ratios (log ADF) vs. [O III ] – Balmer Temperatures Liu et al. 2001

What causes Temperature Variations? Deposition of mechanical energy Chemical inhomogeneities Presence of WR Stars Dust heating Time dependent ionization Density variations Deposition of magnetic energy Shadowed regions

Microstructures and t 2 in the Orion Nebula O´Dell et al [O III] 5007 image

Based on HST data O´Dell et al We derived 1,500,000 T C [ 4363 / 5007 ] columnar values

Noise vs. True Temperature Variations O´Dell et al The face of the nebula is mottled with small scale variations in T C with angular dimensions of about 10” (~0.02 pc) and amplitudes of 400 K

Histogram of T C [ 4363 / 5007 ] O´Dell et al We obtained a t 2 A (O ++ )=0.008 across the face of the nebula values

Small Scale Ionization Structure O´Dell et al [ N II ] / H I [ O III ] / H I

t 2 in the Orion Nebula From HST narrow filter images: –t 2 A (O ++ )=0.008 From a very small region of Orion Esteban et al. (2004) estimated: –t 2 sr (O ++ )=0.020±0.002 from O II and [O III ] –t 2 sr (H + )=0.022±0.002 from T(He I ) vs. T([O II ]+[O III ]) O´Dell et al. estimated: t 2 Whole Object ( H + ) =0.028±0.006

The Low Te Regions behind Clumps within the Ionized Gas Proplyds  Shadows, as long as 0.2 pc, covering 0.5% of the field of view contribute with to t 2 (O + ) Neutral High Density Clumps  Shadows, as long as pc, covering about 1/250 of the volume contribute with < t 2 (O + ) <

Neutral High Density Clumps O´Dell et al. 2003

Different Components of t 2 The total value of t 2 (H + ) has to consider both the O + and the O ++ regions

Chemically inhomogeneous H II regions: Pros + In favor is the study of the N excess in NGC 5253 studied by Angel Sanchez-Lopez et al.(2007). who found from the O II and C II recombination lines t 2 values of and 0.072, and that the excess N is due to pollution by massive WR stars + Also in favor is the study by Tsamis and Pequignot (2005) that produced a chemically inhomogeneous model of 30 Doradus that also reproduces the observed line intensities of the forbidden and permitted O, C, and N lines

Chemically inhomogeneous H II regions : Objections – One of the problems with the model of TP is that the excess abundance of O in the clumps is of a factor of 8, and that it requires an excess of 14 for C. Models of chemical evolution of irregular galaxies by Carigi, Colin, and Peimbert predict that 64% of the C is due to IMS and 36% to massive stars. Therefore for an excess of a factor of 8 in O the TP model should predict an excess of only a factor of 3 for C – An even larger discrepancy between the model by TP is present in the case of N for which ~80% is due to IMS – The small dispersion in abundances of H II regions in irregular galaxies and in the abundance gradient in our galaxy are against this idea

Chemically inhomogeneous H II regions: Implications The two phases chemically inhomogeneous model by Tsamis and Pequignot and the observations of 30 Doradus of A. Peimbert give: 12 + log O/H = 8.45, while the chemically homogeneous model gives 8.33 for t 2 = and 8.54 for t 2 = Therefore the TP model is closer to the abundances given by the O II lines than to those given by the [O III ] lines and the T[O III ] temperature

Orion and the Galactic gradient vs. the Solar abundances Galactic abundances from collisionally excited lines (assuming t 2 =0.00) are almost a factor of 2 lower than those we found from solar studies and Galactic chemical evolution models –Pilyugin et. al (2003, A&A, 401, 557) find O/H = 8.52 dex in the solar vicinity –Deharveng et. al (2000, MNRAS, 311, 329) find O/H = 8.53 dex in the solar vicinity

Galactic Abundance Gradients Esteban et al.ApJ, 2005

Determinations from Recombination Lines (Equivalent to t 2 ≠0.00 ) We have found the O/H abundance as a function of Galactocentric distance. From observations of H II Regions we found a solar vicinity abundance of 8.79 dex with a gradient of dex kpc -1 (Esteban et. al, 2005, ApJ, 618, 95) –The slope of this gradient is similar to those derived from [O III ] and t 2 =0.00 This value is consistent with the O/H = 8.66 dex Solar value derived by Asplund et al. (2005), and with Galactic chemical evolution models that estimate that, in the 4.6 Gy since the Sun was formed, there has been an 0.13 dex increase in oxygen abundance of the ISM (Carigi et al. 2005, ApJ, 623, 213)

Additional Support for a Higher O/H Initial Solar Value There are two results that indicate that the initial solar abundance was higher than the one adopted by Carigi et al., and that correspondingly the ISM t 2 values are even higher than those derived by Esteban et al )Estimates of the gravitational settling indicate that the original oxygen solar abundance was higher by about 0.05 dex than the present photospheric one, e. g. Piersanti et al. (2007), Bahcall et al. (2006), Basu & Antia (2004)… 2)There is a strong discrepancy between the Asplund et al photospheric abundances and the solar interior ones determined from helioseismic measurements that amounts to ~ 0.1 dex

Determination of O/H abundances in distant extragalactic H II regions: Calibration of the O 23 method 1)Calibration with observed T e [O III ] values 2)Calibration with models 3)Calibration with O II recombination lines

Peimbert et al. 2006

Which Calibration for O 23 ? The best way to calibrate the O 23 method is to use O II recombination lines to obtain the O/H values The O II recombination lines provide abundances that are about 0.2 to 0.3 dex higher than those given by the observed T( 4363/5007 ) values The use of the observed T( 4363/5007 ) values provides a lower limit to the O/H values Since nebular lines are less sensitive to temperature variations than auroral lines, model calibrations (that adjust the nebular lines) are closer to our calibration than those derived using the observed T( 4363/5007 ) values

Implications of the O 23 Calibration Our new calibration has implications on the metal production in the Universe and therefore on the star formation rate With this calibration and observations at different z values of strong nebular lines it will be possible to study the chemical evolution of the Universe as a whole

Determination of the Primordial Helium Abundance, Y P, with t 2 = and t 2 ≠ ∆Y (Hc) Y (t 2 = 0.000) Y (t 2 ≠ 0.000) Y P (t 2 ≠ 0.000) NGC ± ± ± ± ± NGC ± ± ± ± ± Haro ± ± ± ± ± SBS ± ± ± ± ± I Zw ± ± ± ± ± Y (sample) ± ± ± ± ± Peimbert et al. 2007

The Y P Determination Error Budget SourceError Collisional Excitation of the H I Lines± Temperature Structure± O (∆Y/∆O) Correction± Recombination Coefficients of the He I Lines± Density Structure± Underlying Absorption in the He I Lines± Reddening correction± Recombination Coefficients of the H I Lines± Underlying Absorption in the H I Lines± Ionization Structure± Collisional Excitation of the He I Lines± Optical Depth of the He I Triplet Lines± He I and H I Line Intensities± Systematic effects Peimbert et al. 2007

The Y P Determination Y P, D P, and WMAP Comparison MethodYPYP D P × 10 5  10 bh2bh2 Y P ± * − ± ± D P ± ± 0.28*5.764 ± ± WMAP ± ± ± ± * *Observed values Cosmological predictions based on SBBN and observations Peimbert et al. 2007

1/5 Oxygen Abundance of: 30 Doradus Observational “Direct Method” ( T ( 4363 / 5007 ); t 2 =0.00 ) A. Peimbert Chemically Inhomogeneous Photoionization Model Tsamis & Pequignot Observational t 2 Method ( Oxygen Recombination Lines ) A. Peimbert

2/5 Oxygen Abundance of: Orion Nebula Observational “Direct Method” ( T ( 4363 / 5007 ); t 2 =0.00 ) Osterbrock et al Pilyugin et al Deharveng et al Chemically Homogeneous Photoionization Models Baldwin et al Rubin et al Observational t 2 Method ( Oxygen Recombination Lines ) Esteban et al

3/5 Oxygen Abundance of: Solar Vicinity Photospheric Solar Value Asplund et al Present Day ISM based on the Solar Value and Galactic Chemical Evolution Models Carigi et al Present Day ISM based on the Solar Value and Young G Dwarf Stars Bensby & Feltzing Present Day ISM based on H II Regions + Dust Content (Mainly Orion) Esteban et al

4/5 Oxygen Abundance of: H II Regions Observational “Direct Method” ( T ( 4363 / 5007 ); t 2 =0.00 ) e.g. Pilyugin & Thuan — Photoionization Models (Fitting Nebular Lines) e.g. Kobulnicky & Kewley 2004 McGaugh — — Observational t 2 Method ( Oxygen Recombination Lines ) e.g. Peimbert et al * log (O/H) + 12 =

5/5 Primordial Helium Abundance: H II Regions Observational “Direct Method” ( T ( 4363 / 5007 ); t 2 =0.0; Incomplete Error Estimate ) Izotov et al ± O bservational “Direct Method” ( T ( 5007 / 4363 ); t 2 =0.0; Full Error Estimate ) Peimbert et al ± Observational t 2 Method ( Balmer continuum and He I lines with MLM ) Peimbert et al ± Primordial Deuterium + SBBN O´Meara et al ± Wilkinson Microwave Anisotropy Probe + SBBN Spergel et al ±

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