Part of disk field 4

1

ABUNDANCE MEASURMENTS IN METAL-RICH H II
REGIONS
Part of disk field 4 4 disk scale lengths from
nucleus region shown is 60 arcsec (200
pc) across


Don Garnett Steward Observatory
2
Methods for deriving abundances

Direct methods -- measure electron
temperatures -- IR fine-structure lines vs.
thermal continuum (radio) -- recombination
lines Indirect methods -- tailored
photoionization models -- bright-line
calibrations (R23, S23, etc.)
3
Direct Abundance Measurements from Electron
Temperatures
Abundances from forbidden lines depend on
electron temperature Te -- lower O/H --gt higher T
(cooling by fine-structure lines) Te diagnostic
line ratio O III ?4363/??4959,5007 --
relatively easy to measure when O/H lt 0.5 solar,
but impossible for high O/H - both 4363
and 5007 too weak Other diagnostic ratios useful
for high abundance regime N II
?5755/??6583 S III ?6312/??9069,9532
O II ??7320-7330/?3727 -- not as good
(reddening, telluric
absorption, density,
recombination) -- still difficult to measure,
but now can be done with 6-10m telescopes
4
First T(N II), T(S III) measurements for presumed
metal-rich H II regions Kinkel Rosa (1994)
- M101-Searle 5 Castellanos, Diaz, Terlevich
(2002) - NGC 1232 Kennicutt, Bresolin Garnett
(2003) - M101 Garnett, Bresolin Kennicutt
(2004), Bresolin, Garnett Kennicutt (2004) -
M51 Derived O/H values as high as solar now
obtained
N II 5755 in two M51 H II Regions
5
H II regions with solar abundance or higher
(12log O/H gt 8.6) Kinkel Rosa (1994) AA -
M101-Searle 5 12log O/H 8.8 Castellanos,
Diaz, Terlevich (2002) MNRAS - NGC 1232-CDT
1 8.95 /- 0.20 Kennicutt, Bresolin
Garnett (2003) ApJ - M101 H1013 8.71
/- 0.05 Searle 5 8.6 /-
0.2 Garnett, Bresolin Kennicutt (2004)
ApJL, Bresolin, Garnett Kennicutt (2004) ApJ
- M51 CCM53 8.66 /- 0.09
CCM55 8.60 /- 0.08 CCM72
8.71 /- 0.10 P203
8.84 /- 0.16
6
Comparison of Measured Temperatures
Relations between TO III, TN II, and TS III
in excellent agreement with relationship
predicted from photoionization models (dashed
lines)
7
Temperatures and abundances from optical lines
are potentially biased in metal-rich H II regions
Stasinska 1978 H II regions with high O/H have
temperature gradients because of strong cooling
in interior by fine-structure lines Optical
forbidden line emissivity weighted toward high-T
regions How bad could it be?
O/H 2X solar O/H solar
8
Stasinska 2005 AA Explored effects of cooling
on measured T, abundances --gt TO III derived
from emission lines can be higher than
average T(O) --gt derived abundances lower
than true for O/H gt 8.6 However, we dont
measure TO III in these objects

O/H derived from TO III
9
We actually measure TN II TN II can be a
good proxy for the actual T(N) under a variety
of conditions Still a potential for biased
abundances, but not as strong a case - depends on
physical properties of real H II
regions Direct comparison of IR emission
lines with visible counterparts should
help resolve this problem
O/H based on TN II
10
Mathis Wood 2005 MNRAS
Explored sensitivity of H II region models to
clumping of gas Monte Carlo treatment of
radiation field, hierarchical distribution of
clumps (15 - 2700 cm-3), Paris H II region
abundances
Uniform density models
11
Both uniform and clumped models show some
temperature bias at solar O/H estimated O/H
about 30 too low Interestingly, models with
clumps show smaller bias!
Clumped models
12
Comparison with O/H from calibration of strong
lines
Abundances we derive based on direct measurement
of T are lower than those derived from a
variety of popular calibrations of R23 (O
II O III)/H?
13
M101 and M51 Abundances vs. Empirical Bright-Line
Relations


O/H vs. N II/H-alpha (Denicolo et al.
2002) O/H vs. O III/N II
(revised) (Pettini Pagel 2004)

14
M101 and M51 Abundances vs. Pilyugins P-method




Pilyugins method has problems at O/H as high as
8.5
15
Optical-IR comparisons


Numerous IR studies for Galactic H II regions,
but few optical-IR comparisons A little better
for extragalactic H II regions - Nollenberg et
al. (2002) ISO spectra of sulfur lines in NGC
6822 and I Zw 36 good agreement with S
abundances from optical spectra - Garnett et al.
(2004) compared ISO spectra of O III 88 µm
with O III ?5007 -- 88 µm/5007 ratio
implies O/H lower by 0.4 dex than previous
estimates (Diaz et al. 1991) --
found significant differences between results of
Cloudy models between v. 74 and v. 94

16

Willner Nelson-Patel 2002 ISO spectra of Ne
II 12.5 µm and Ne III 15.6 µm in M33 H II
regions plus 20 cm continuum --gt Ne/H gradient
-0.034 dex/kpc shallower than O/H gradient
-0.1 dex/kpc from optical
measurements Crockett, Garnett, Massey,
Jacoby, in prep. new opt. Spectra with Te for
6 H II regions with data from Vilchez et al.
1988, new O/H and Ne/H gradients -0.02 dex/kpc


However, still a 0.2 dex offset between optical
and IR neon abundances
17
Recombination Lines


Recombination lines from heavy elements, ratioed
to H lines, give abundances essentially
independent of T. Various studies show that
recombination lines give higher abundances than
optical forbidden lines In planetary nebulae,
RLs can give abundances as much as 10-20X
higher, but this is not seen in comparing optical
and IR forbidden lines (Liu, Barlow et al. 1995,
et seq. ) The discrepancy between RL and FL
abundances not fully understood possible
explanations include metal-rich clumps,
dielectronic recombination Element ratios from
RLs (C/O, N/O etc.) generally agree with FL
results


18
Summary

Direct abundance measurements have been extended
to include H II regions with O/H as much as 0.2
dex higher than solar Potential biases in direct
abundances exist, but their magnitude have not
been characterized Needs for improved abundance
results - More direct comparison of IR and
optical forbidden lines - More temperature
measurements for low-excitation H II regions
look for evidence of biases in measurements and
in analysis - Better understanding of
discrepancy between recombination lines and
forbidden lines - Better understanding of
discrepancies between ionization models and
observed spectra