TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES

1
TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND
CHEMICAL ABUNDANCES

• M. Peimbert
• C.R. ODell
• A. Peimbert
• V. Luridiana
• C. Esteban
• J. García-Rojas
• L. Carigi
• F. Bresolin
• M.T. Ruiz
• A.R. López-Sánchez

Lake Geneva, Wisconsin, April 2007
Microstructures in the ISM Bob ODell 70th
birthday
2
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 R23 method
• The primordial helium abundance
• Conclusions

3
Why is the problem of temperaturevariations
important?

• Physical conditions of gaseous nebulae
• Abundances in H II regions and PNe
• Solar abundances
• Galactic chemical evolution
• Primordial helium abundance, YP
• Metal content and chemical evolution of the
  universe

4
Temperature Structure
Te(4363/5007) T0 1 (90800/T0 -3) t 2/2
Te(Bac/Hb) T0 (1 1.70 t 2)
Te(He lines) T0 (1 k t 2)
k1.8
Te(4649/5007) f1 (T0 , t 2)
Te(4267/1909) f2(T0 , t2)
5
(No Transcript)
6
Ups and downs of t 2
March 2007
7
How Important Are Temperature Variations?

• Photoionization homogeneous models predict values
  of t 2 in the 0.003 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

8
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

9
Balmer vs. O III Temperatures
Liu Danziger 1993
10
N(C) from Recombination Lines vs. N(C) from
Forbidden Lines
Peimbert, Luridiana, Torres-Peimbert 1995
11
Recombination to Forbidden O ratios (log ADF)
vs. O III Balmer Temperatures
Liu et al. 2001
12
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

13
Microstructures and t 2 in the Orion Nebula
ODell et al. 2003
O III 5007 image
14
Based on HST data
We derived 1,500,000 TC4363/5007 columnar values
ODell et al. 2003
15
Noise vs. True Temperature Variations
The face of the nebula is mottled with small
scale variations in TC with angular dimensions of
about 10 (0.02 pc) and amplitudes of 400 K
ODell et al. 2003
16
Histogram of TC4363/5007
We obtained a t2A(O)0.008 across the face of
the nebula values
ODell et al. 2003
17
Small Scale Ionization Structure
ODell et al. 2003
18
t 2 in the Orion Nebula

• From HST narrow filter images
• t2A (O)0.008
• From a very small region of Orion Esteban et al.
  (2004) estimated
• t2sr(O)0.0200.002 from O II and O III
• t2sr (H)0.0220.002 from T(He I) vs. T(O
  IIO III)
• ODell et al. estimated
  t2Whole
  Object(H)0.0280.006

19
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 0.0093 to
  t2(O)
• Neutral High Density Clumps
• ? Shadows, as long as 0.025 pc, covering about
  1/250 of the volume contribute with 0.0016
  t2(O)

20
Neutral High Density Clumps
ODell et al. 2003
21
Different Components of t2

• The total value of t2(H) has to consider both
  the O and the O regions

22
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 0.052 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

23
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

24
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 t2 0.000 and 8.54 for t2 0.033
• 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 TO III
  temperature

25
Orion and the Galactic gradient vs. the Solar
abundances

• Galactic abundances from collisionally excited
  lines (assuming t 20.00) are almost a factor of
  2 lower than those we found from solar studies
  and Galactic chemical evolution models
• Pilyugin et. al (2003, AA, 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

26
Galactic Abundance Gradients
Esteban et al.ApJ, 2005
27
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 -0.044 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 20.00
• 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)

28
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. 2005
• 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)
• There is a strong discrepancy between the Asplund
  et al. 2005 photospheric abundances and the solar
  interior ones determined from helioseismic
  measurements that amounts to 0.1 dex

29
Determination of O/H abundances in distant
extragalactic H II regions Calibration of the
O23 method

• Calibration with observed Te O III values
• Calibration with models
• Calibration with O II recombination lines

30
Peimbert et al. 2006
31
(No Transcript)
32
Which Calibration for O23 ?

• The best way to calibrate the O23 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

33
Implications of the O23 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

34
Determination of the Primordial Helium Abundance,
YP , with t2 0.000 and t2 ? 0.000
Peimbert et al. 2007
35
The YP DeterminationError Budget
Systematic effects
Peimbert et al. 2007
36
The YP DeterminationYP , DP , and WMAP
Comparison
Cosmological predictions based on SBBN and
observations
Observed values
Peimbert et al. 2007
37
1/5 Oxygen Abundance of 30 Doradus
38
2/5 Oxygen Abundance of Orion Nebula
39
3/5 Oxygen Abundance of Solar Vicinity
40
4/5 Oxygen Abundance of H II Regions
log (O/H) 12 8.2 - 8.9
41
5/5 Primordial Helium Abundance H II Regions
42
The End