J/MNRAS/455/2627 Oxygen abundance gradient in M81 (Arellano-Cordova+, 2016)
The oxygen abundance gradient in M81 and the robustness of abundance
determinations in HII regions.
Arellano-Cordova K.Z., Rodriguez M., Mayya Y.D., Rosa-Gonzalez D.
<Mon. Not. R. Astron. Soc., 455, 2627-2643 (2016)>
=2016MNRAS.455.2627A 2016MNRAS.455.2627A (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; H II regions ; Abundances
Keywords: ISM: abundances - HII regions - galaxies: abundances -
galaxies: individual: M81
Abstract:
We study the sensitivity of the methods available for abundance
determinations in HII regions to potential observational problems. We
compare the dispersions they introduce around the oxygen and nitrogen
abundance gradients when applied to five different sets of spectra of
HII regions in the galaxy M81. Our sample contains 116 HII regions
with galactocentric distances of 3 to 33kpc, including 48 regions
observed by us with the OSIRIS long-slit spectrograph at the 10.4-m
Gran Telescopio Canarias telescope. The direct method can be applied
to 31 regions, where we can get estimates of the electron temperature.
The different methods imply oxygen abundance gradients with slopes of
-0.010 to -0.002dex/kpc, and dispersions in the range 0.06-0.25dex.
The direct method produces the shallowest slope and the largest
dispersion, illustrating the difficulty of obtaining good estimates of
the electron temperature. Three of the strong-line methods, C, ONS,
and N2, are remarkably robust, with dispersions of ∼0.06dex, and
slopes in the range -0.008 to -0.006dex/kpc. The robustness of each
method can be directly related to its sensitivity to the line
intensity ratios that are more difficult to measure properly. Since
the results of the N2 method depend strongly on the N/O abundance
ratio and on the ionization parameter, we recommend the use of the C
and ONS methods when no temperature estimates are available or when
they have poor quality, although the behaviour of these methods when
confronted with regions that have different properties and different
values of N/O should be explored.
Description:
We present spectra of 48 HII regions in M81 obtained with the
long-slit spectrograph of the OSIRIS instrument at the 10.4-m GTC
telescope. The observations have total exposure times of 2700 s and
were acquired on 2010 April 5-7. We employed the R1000B grism, which
allowed us to cover the spectral range from 3630 to 7500 Angstroms
with a spectral resolution of ∼7 Angstroms.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 98 48 *Coordinates, sizes, galactocentric distances,
physical conditions and oxygen abundances for
the 48 HII regions in our sample
table2.dat 21 48 The extinction coefficients c(Hbeta) and the
reddening-corrected intensities for Hbeta
table3.dat 29 1008 Observed and reddening-corrected line ratios
normalized to I(Hbeta)=100
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Note on table4.dat: The oxygen abundances have been derived with the direct
method (Te) and five strong-line methods (P, ONS, C, O3N2, and N2).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Region Region sequential number
4- 7 A4 --- Box Box
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 16 I2 s RAs Right ascension (J2000)
18 A1 --- DE- Declination sign (J2000)
19- 20 I2 deg DEd Declination (J2000)
22- 23 I2 arcmin DEm Declination (J2000)
25- 26 I2 arcsec DEs Declination (J2000)
28- 30 F3.1 arcsec Size Angular sizes of the extracted region
32- 34 F3.1 kpc R Galactocentric distance
36- 38 I3 cm-3 ne ?=- Electron density
40- 41 I2 cm-3 e_ne ? rms uncertainty on ne
42 A1 --- u_ne Uncertainty flag on ne
44- 48 I5 K Te([NII]) ?=- Effective temperature from [NII]
50- 53 I4 K E_Te([NII]) ? Error on Te([NII]) (upper value)
55- 58 I4 K e_Te([NII]) ? Error on Te([NII]) (lower value)
60- 63 F4.2 --- 12+log(O/H) ?=- Oxygen abundance derived with the
direct method (Te)
65- 68 F4.2 --- E_12+log(O/H) ? Error on 12+log(O/H) (upper value)
70- 73 F4.2 --- e_12+log(O/H) ? Error on 12+log(O/H) (lower value)
75- 78 F4.2 --- 12+log(O/H)P Oxygen abundance derived with P method
80- 83 F4.2 --- 12+log(O/H)ONS Oxygen abundance derived with ONS method
85- 88 F4.2 --- 12+log(O/H)C Oxygen abundance derived with C method
90- 93 F4.2 --- 12+log(O/H)O3N2 Oxygen abundance derived with O3N2 method
95- 98 F4.2 --- 12+log(O/H)N2 Oxygen abundance derived with N2 method
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Region Region sequential number
4- 7 F4.2 --- c(Hbeta) Hbeta extinction coefficient
9- 12 F4.2 --- e_c(Hbeta) Error in the Hbeta extinction coefficient
14- 21 E8.3 mW/m2 I0(Hbeta) Hbeta extinction-corrected intensity
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Region Region sequential number
4- 7 I4 0.1nm Lambda Wavelength
9- 15 A7 --- Ion Ion
16- 20 F5.1 --- I ? Observed Intensity relative to I(Hbeta)=100
22- 26 F5.1 --- I0 ? Extinction-corrected intensity relative
to I(Hbeta)=100
28- 29 I2 % e_I0 ? Percentage error in the extinction-corrected
intensity
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Acknowledgements:
Karlaz Arellano-Cordova, karlaz(at)inaoep.mx
(End) Patricia Vannier [CDS] 07-Jul-2016