On the Sulphur Abundance of Blue Compact Dwarf Galaxies
Carolina Kehrig
1,2
, José M. Vílchez
1,
Enrique
1
Pérez ,
2
Eduardo Telles & François Cuisinier
3
1 – Instituto de Astrofísica de Andalucía (Granada, Spain), 2 - Observatório Nacional (Rio de Janeiro, Brazil)
3 – Departamento de Astronomia, UFRJ (Rio de Janeiro, Brazil)
Motivation
The sulphur and oxygen abundances give us information about the
evolutionary stage of the starburst region since their evolution tells us what
mass range of stars dominates in the production of these two elements, and
whether that mass range has changed with time. Therefore the analysis of
the strong near–IR [SIII] and [SII] lines (??9069, 9532 Å and ??6717, 6731
Å) is fundamental if we want to study the sulphur in HII regions.
However the number of HII galaxies for which measurements exist of these
lines, together with optical emission lines, is still small. This is mainly
because of the difficulty of observing [SIII] 9069,9532 due to atmospheric
absorption in this range. This implies that published S++ abundances, the
dominant sulphur ion, are mostly based on measures of the weak [SIII]6312.
Given the large uncertainties associated with observing [SIII]6312 and the
importance of S++ in determining the sulphur abundance, it is clear that
more observations of the strong near–IR [SIII] lines are desirable. With this
motivation, we have obtained CCD observations of [SIII] in a number of HII
galaxies. Another important point is regarding to sulphur abundance
parameter S23 (Vílchez & Esteban 1996) defined as:
S23 = ( [SII]??6717,6731 + [SIII]??9069,9532 ) / Hß
A calibration of S23 versus sulphur abundance should enable sulphur
abundance determinations in HII regions where the weak temperature
sensitive line [SIII]6312 is undetectable. In addition, the parameter S23 can
also be used to derive oxygen abundance, and this calibration presents two
important advantages against the R23 : it remains single-valued up to
abundances close to solar and it is almost independent of the degree of
ionization of the nebula.
SUMMARY We have analysed long-slit spectrophotometric observations of a
sample of 35 HII galaxies in the red (6000 Å - 1µm), including the nebular
[SIII] lines ??9069,9532. For 6 of the 35 objects observed it has been possible to
measure the auroral [SIII] line at ?6312. All these galaxies were observed
previously in the blue (Kehrig et al 2004) and it has therefore been possible to
derive directly two line temperatures: t([OIII])obs from the [OIII]4363 line
(Kehrig 2003) and t([SIII])obs from the [SIII]6312 line. In this work we present
the physical conditions and chemical abundances to the 6 galaxies with the
[SIII]6312 Å measured. Despite the observed dispersion in the temperatures the
final result for the abundances is in accordance with the expected values for
HII galaxies.
Pysical Conditions & Abundances
Object
IIZW40
Tol0226-390
ne ([SII])
171±73
233± 116
= 278
=170
= 100*
276±86
te ([SIII])obs
1.11±0.12
1.85± 0.22
1.67±0.19
1.82±0.50
1.36±0.29
1.38±0.39
te ([OIII])expa 1.13±0.14
2.02± 0.26
1.81±0.22
1.99±0.60
1.44±0.35
1.46±0.47
te ([OIII])obs
1.31±0.07
1.16± 0.05
1.32±0.07
1.27±0.06
1.32±0.07
1.21±0.06
te ([SIII])expa 1.26±0.06
1.14± 0.04
1.27±0.06
1.22±0.05
1.27±0.06
1.17±0.05
12 +log(O+/H+) 7.12±0.09
7.82± 0.08
7.31±0.08
…
7.54±0.09
…
12 +log(S+/H+)
5.29±0.04
5.93± 0.03
5.56±0.03
5.79±0.04
5.72±0.03
5.70±0.03
12 +log(S++/H+) 6.48±0.09
5.75± 0.07
6.01±0.07
6.12±0.19
6.07±0.17
6.01±0.25
ICF(S+ + S++)b 1.50± 0.11
1.05± 0.04
1.28±0.08
1.18±0.05
1.10±0.05
1.36±0.07
12 +log(S/H)
6.69±0.09
6.17± 0.04
6.25±0.06
6.36±0.13
6.27±0.12
6.31±0.17
12 +log(N+/H+) 5.95±0.04
6.69± 0.03
6.07±0.04
6.26±0.04
6.18±0.04
6.30±0.04
12 +log(N+/O+) 10.84±0.10
10.87± 0.09
10.76±0.09
…
10.64±0.09
…
5.78±0.11
5.43± 0.08
5.26±0.08
5.67±0.22
5.60±0.19
5.65±0.30
-0.20±0.01
-0.03± 0.05
-0.23±0.01
-0.05±0.01
0.00±0.02
-0.08±0.09
12 +log(Ar++/H+)
log(S23)
Tol1924-416
Tol0538-416
Cam0840+1201
CTS1008
* Tol0226-390 and Tol0538-416 present very
high values for the t([SIII])obs; both galaxies
present a poor measurement of the
[SIII]6312 line . In any case, we have to take
into account that it is difficult to apply
homogenous HII region-model results to
these galaxies. Further observations with
higher spectral resolution and larger
aperture telescopes are needed.
* Despite the observed dispersion in the
temperatures the final result for the
abundances is in accordance with the
expected values for HII galaxies.
* - low density limit ; a – assuming that t(S2+)=0.83t(O2+)+0.17(Garnett 1992); b- Barker(1980) and French(1981)
Line Intensities
Line
i(?)a
IIZW40
[OI]6300 … 5.8±0.7
[SIII]6312 … 3.6±0.8
[OI]6364 …
…
[NII]6548 …
…
Ha
103 103±16.0
[NII]6584 … 26.0±4.0
HeI 6678 … 11.1±3.0
[SII]6717 … 25.1±0.3
[SII]6731 … 20.0±1.0
HeI 7065 … 16.1±0.4
[ArIII]7136 … 28.7±0.6
[OII]7320 … 3.8±0.2
[OII]7330 … 3.4±0.2
Pa14
2.3 2.3±0.2
Pa13
2.9 2.8±0.1
Pa12
3.9 4.8±0.9
Pa11
4.8 5.3±0.6
Pa10
6.4 6.8±0.6
[SIII]9069 … 50.8±0.3
Pa9
8.8 9.4±1.6
[SIII]9532 … 74.3±1.5*
Pa8
12.8 13.8±3.0c
Tol0226-390 Tol1924-416 Tol0538-416 Cam0840+1201 CTS1008
25.8±0.7
7.7±0.4
12.0±1.3
50.0±10.0
103 ±30.0
116.0±8.0
15.0±3.0
88.0±4.0
73.0±3.0
16.0±0.1
33.0±2.0
10.0±0.4
11.5±0.9
…
…
…
…
…
43.6±0.9*
7.7±0.8
117.9±11.4
13:b
18.3±0.5
4.7±0.7
3.4±0.5
14.0±7.0
103 ±20.0
35.0±3.0
14.0±2.0
51.0±3.0
39.0±3.0
11.0±0.6
18.7±0.2
7.7±0.1
6.0±0.3
1.4±0.2
3.0±0.9
…
5.6±2.0
6.1±0.2
33.5±0.3
…
72.3±0.9*
16:b
14.2±1.4
7.7±2.6
4.9±2.4
17.5±2.5
103±14.5
50.1±3.5
12.9±1.3
82.5±2.7
60.6±4.4
10.8±1.5
55.3±1.7
…
…
…
…
…
…
…
48.9±0.8*
…
73.4±2.5*
13:b
19.9±2.0
6.4±2.1
…
20.0±3.0
103±50.0
45.0±2.0
…
78.0±1.0
54.0±0.7
11.4±0.4
29.0±1.0
10.0±0.5
8.9±0.6
…
…
…
…
…
34.1±0.9*
…
154.4±3.8*
21:b
13.7±1.5
5.8±1.9
…
22.0±6.0
103 ±190.0
50.0±10.0
13.0±1.0
54.0±2.0
46.0±1.0
13.0±1.0
33.0±1.0
…
…
…
…
…
…
…
36.0±1.0*
14.0±3.0
137.1±17.8*
13:b
A comparison between the measured line
temperatures of [OIII] and [SIII]. The dark dotdashed line is the model-deduced relation for the
same ion-weighted temperatures from Garnett
(1992).
.
a) i(?)=jP(?)/jHa adopting case B recombination ratios (Osterbrock 1989)
b) severe blending with [SIII]9532; c) blended with [SIII]9532
*) measured [SIII] fluxes more affected by atmospheric absorption
Note – Intensities relative to Ha = 1000.0; : indicates uncertain value
The parameter S23 plotted against the oxygen and
sulphur abundances of the galaxies.
Our measurements agree with the observed
global relation in Pérez-Montero & Díaz (2003).
But there are non-negligible deviations between
the fit and the observed points which might affect
the calculation of sulphur abundances in the
regime of high excitation. The validity of this
relation should be further explored, including
third parameter dependence.
HII Galaxies
Red Spectra
References
Bresolin, F. , Garnett, D. R. & Kennicutt R.C. , astro-ph/0407065
Acknowledgements
Conselho Nacional de Desenvolvimento Científico e Tecnológico in Brazil (CNPq)
Instituto de Astrofísica de Andalucía
Royal Astronomical Society
We have added our observed HII galaxies data points to the
empirical calibration of the metallicity parameter, S23 =
([SII]+[SIII])/Hß (Pérez-Montero & Díaz 2003). This
calibration presents two important advantages over the
commonly used one based on the optical oxygen lines: it
remains single-valued up to abundances close to solar and is
almost independent of the ionization parameter of the
nebula. The sulphur abdundance is also included (with a
1dex bias.)
Garnett, D. R., 1992, AJ, 103, 1330
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Kehrig C., Telles E. & Cuisinier F., 2004, accepted
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