J/A+A/643/A80 sample of HeII-emitters abundances (Perez-Montero+, 2020)
Photon leaking or very hard ionizing radiation?
Unveiling the nature of HeII-emitters using the softness diagram.
Perez-Montero E., Kehrig C., Vilchez J.M., Garcia-Benito R.,
Duarte Puertas S., Iglesias-Paramo J.
<Astron. Astrophys. 643, A80 (2020)>
=2020A&A...643A..80P 2020A&A...643A..80P (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, spectra ; Abundances
Keywords: stars: Wolf-Rayet - galaxies: abundances - galaxies: stellar content -
galaxies: star formation
Abstract:
Star-forming galaxies with nebular HeII emission contain very
energetic ionizing sources of radiation, which can be considered as
analogs to the major contributors of the reionization of the Universe
in early epochs. It is therefore of great importance to provide a
reliable absolute scale for the equivalent effective temperature (T*)
for these sources.
We study a sample of local (z<0.2) star-forming galaxies showing
optical nebular HeII emission using the so-called softness
diagrams, involving emission lines of two elements in two consecutive
stages of ionization (e.g., [SII]/[SIII] vs. [OII]/[OIII]). We use for
the first time the HeI/HeII ratio in these diagrams in order to
explore the higher range of T* expected in these objects, and to
investigate the role of possible mechanisms driving the distribution
of galaxy points in these diagrams. We build grids of photoionization
models covering different black-body temperatures, model cluster
atmospheres, and density-bounded geometries to explain the conditions
observed in the sample.
We verified that the use of the softness diagrams including the
emission-line ratio HeI/HeII combined with black-body photoionization
models can provide an absolute scale of T* for these objects. The
application of a Bayesian-like code indicates T* in the range 50-80kK
for the sample of galaxies, with a mean value higher than 60kK. The
average of these high temperature values can only be reproduced using
cluster model populations with nearly metal-free stars, although such
ionizing sources cannot explain either the highest T* values, beyond
1σ, or the dispersion observed in the softness diagrams.
According to our photoionization models, most sample galaxies could be
affected to some extent by ionizing photon leaking, presenting a mean
photon absorption fraction of 26% or higher depending on the
metallicity assumed for the ionizing cluster. The entire range of
HeI/HeII, [SII]/[SIII], and [OII]/[OIII] ratios for these
HeII-emitting galaxies is reproduced with our models, combining nearly
metal-free ionizing clusters and photon leaking under different
density-bounded conditions.
Description:
We present a study of 186 SF galaxies with prominent nebular
HeII 4686Å taken from SDSS-DR7, a sample previously studied by
Shirazi & Brinchmann (2012MNRAS.421.1043S 2012MNRAS.421.1043S, Cat. J/MNRAS/421/1043). We
investigated their behavior in the so-called softness diagram, which
is useful to derive the scale of equivalent effective temperature in
combination with the ionization parameter. The inclusion of the
emission-line ratio HeI/HeII in this diagram allows us to more
accurately explore the hard ionizing sources in HeII emitters as it
better traces the high-energy range in their SEDs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 171 186 Measured reddening corrected relative to Hβ
emission line and derived properties for the
sample of HeII-emitters
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See also:
J/MNRAS/421/1043 : Emission-line galaxies from SDSS DR7 (Shirazi+, 2012)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 4 I4 -- Plate SDSS plate
6- 10 I5 -- MJD SDSS mjd
12- 14 I3 -- Fiber SDSS fiberid
16- 19 F4.2 -- z Redshift
21 I1 -- WRclass [0/1] WR class (1)
23- 27 F5.3 -- I([OII]3727) I([OII] 3727)/I(Hbeta)
reddening corrected
29- 33 F5.3 -- e_I([OII]3727) Error for I([OII] 3727)/I(Hbeta)
35- 39 F5.3 -- I([OIII]4363) I([OIII] 4363)/I(Hbeta)
reddening corrected
41- 45 F5.3 -- e_I([OIII]4363) Error for I([OIII] 4363)/I(Hbeta)
47- 51 F5.3 -- I(HeII3727) I(HeII 3727)/I(Hbeta)
reddening corrected
53- 57 F5.3 -- e_I(HeII3727) Error for I(HeII 3727)/I(Hbeta)
59- 63 F5.3 -- I([OIII]5007) I([OIII] 5007)/I(Hbeta)
reddening corrected
65- 69 F5.3 -- e_I([OIII]5007) Error for I([OIII] 5007)/I(Hbeta)
71- 75 F5.3 -- I(HeI5876) I(HeI 5876)/I(Hbeta)
reddening corrected
77- 81 F5.3 -- e_I(HeI5876) Error for I(HeI 5876)/I(Hbeta)
83- 87 F5.3 -- I([NII]6583) I([NII] 6583)/I(Hbeta)
reddening corrected
89- 93 F5.3 -- e_I([NII]6583) Error for I([NII] 6583)/I(Hbeta)
95- 99 F5.3 -- I([SII]6717+6731) I([SII] 6717+6731)/I(Hbeta)
reddening corrected
101-105 F5.3 -- e_I([SII]6717+6731) Error for I([SII] 6717+6731)/I(Hbeta)
107-111 F5.3 -- I([SIII]9069) I([SIII] 9069)/I(Hbeta)
reddening corrected
113-117 F5.3 -- e_I([SIII]9069) Error for I([SIII] 9069)/I(Hbeta)
119-122 F4.2 -- 12+log(O/H) 12+log(O/H) as derived from HCm
124-127 F4.2 -- e_12+log(O/H) Error for 12+log(O/H)
129-133 I5 K Teff Effective temperature in K
135-139 I5 K e_Teff Error for effective temperature in K
141-145 F5.2 [-] logUbb log of the ionization parameter as
derived from black-body grids
147-150 F4.2 [-] e_logUbb Error for the ionization parameter as
derived from bb models
152-155 F4.2 -- fabs Absorption fraction of ionizing
photons as derived from
BPASS v.2.1 (2)
157-160 F4.2 -- e_fabs Error for fabs
162-166 F5.2 [-] logUBPASS log of the ionization parameter as
derived from BPASS models
168-171 F4.2 [-] e_logUBPASS Error for log U as derived from
BPASS models
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Note (1): WR class according to Shirzia & Brinchmann (2012MNRAS.421.1043S 2012MNRAS.421.1043S,
Cat, J/MNRAS/421/1043) as follows:
0 = no WR bump
1 = WR bump
Note (2): Absorption fraction of ionizing photons as derived from BPASS v.2.1,
a(IMF)=-1.35, Mup=300M☉, age=4Myr.
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Acknowledgements:
Enrique Perez Montero, epm(at)iaa.es
(End) Patricia Vannier [CDS] 16-Sep-2020