J/ApJ/510/104 Ionizing Stars of Extragalactic H II Regions (Bresolin+ 1999)
The Ionizing Stars of Extragalactic H II Regions
Bresolin F., Kennicutt R. C., Garnett D. R.
<Astrophys. J. 510, 104 (1999)>
=1999ApJ...510..104B 1999ApJ...510..104B
ADC_Keywords: Galaxies, optical; H II regions; Spectroscopy
Keywords: galaxies: ISM - galaxies: spiral
Abstract:
Medium-resolution spectra from 3650 to 10000 Å are presented for 96
giant H II regions distributed in 20 spiral galaxies. In order to
interpret the data, we have calculated two separate grids of
photoionization models, adopting single-star atmospheres (Kurucz) and
star clusters synthesized with different initial mass functions (IMFs)
as ionizing sources. Additional models were computed with more recent
non-LTE stellar atmospheres, in order to check the effects of
different stellar ionizing fluxes. We use the radiation softness
parameter η'=([O II]/[O III])/([S II]/[S III]) of Vilchez & Pagel
(1988MNRAS.231..257V 1988MNRAS.231..257V) to test for a metallicity dependence of the
effective temperatures of the ionizing stars. Our results are
consistent with a significant decrease in mean stellar temperatures of
the ionizing stars with increasing metallicity. The magnitude of the
effect, combined with the behavior of the He I λ5876/Hβ
ratio, suggest a smaller upper mass limit for star formation at
abundances higher than solar, even when considering the effects of
metallicity on stellar evolution and atmospheric line blanketing.
However, the exact magnitudes of the stellar temperature and IMF
variations are dependent on the choice of stellar atmosphere and
evolution models used, as well as on uncertainties in the nebular
abundance scale at high metallicities. Our results also constrain the
systematic behavior of the ionization parameter and the N/O ratio in
extragalactic H II regions. The observed spectral sequences are
inconsistent with current stellar evolution models, which predict a
luminous, hot W-R stellar population in evolved H II regions older
than 2-3 Myr. This suggests either that the hardness of the emitted
Lyman continuum spectrum has been overestimated in the models or that
some mechanism disrupts the H II regions before the W-R phases become
important.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 102 96 Reddening-corrected line fluxes of HII regions
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See also:
J/A+AS/112/35 : Emission lines from giant HII regions (Garcia Vargas+, 1995)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Galaxy name
13- 14 I2 --- Seq Galaxy sequence number
17- 21 I5 arcsec RAoff Right ascension offset from the galaxy nucleus
25- 29 I5 arcsec DEoff Declination offset from the galaxy nucleus
32- 35 I4 --- OII OII (3727Å) flux (1)
39- 40 I2 --- e_OII Uncertainty in OII
43- 46 I4 --- OIII OIII (5007+4959Å) flux (1)
49- 50 I2 --- e_OIII Uncertainty in OIII
53- 55 I3 --- HeI HeI (5876Å) flux (1)
59- 60 I2 --- e_HeI Uncertainty in HeI
63- 66 I4 --- NII NII (6548+6583Å) flux (1)
69- 70 I2 --- e_NII Uncertainty in NII
73- 75 I3 --- SII SII (6716+6731Å) flux (1)
79- 80 I2 --- e_SII Uncertainty in SII
85- 88 I4 --- SIII (9069+9532Å) flux (1)
91- 92 I2 --- e_SIII Uncertainty in SIII
94-108 A15 --- HIIName HII region names (2)
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Note (1): Line fluxes given in units of Hβ = 100
Note (2): Names use the abbreviations:
HK = Hodge & Kennicutt 1983, An Atlas of H II Regions in 125
Galaxies (PAPS Document ANJOA88-296-300) (New York: AIP
Auxiliary Publication Service)
H = Hodge 1976 (1976ApJ...205..728H 1976ApJ...205..728H)
P = Pellet+ 1978 (1978A&AS...31..439P 1978A&AS...31..439P)
CC = Carranza+ 1969 (1969A&A.....1..479C 1969A&A.....1..479C)
GS = Garnett & Shields 1987 (1987ApJ...317...82G 1987ApJ...317...82G)
D = Dufour+ 1980 (1980ApJ...236..119D 1980ApJ...236..119D)
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History:
* 07-Feb-2000: From ApJ electronic edition.
* 15-Nov-2005: HII regions in NGC 3521 were erroneously attached
to NGC 3368
References:
McCall+ 1985 (1985ApJS...57....1M 1985ApJS...57....1M)
Oey & Kennicutt 1993 (1993ApJ...411..137O 1993ApJ...411..137O)
Zaritsky+ 1994 (1994ApJ...420...87Z 1994ApJ...420...87Z)
(End) Greg Schwarz (AAS) 07-Feb-2000