J/A+A/321/363 NGC 4736 H II regions properties (Martin+ 1997)
Nebular gas abundances and mixing processes in the ringed galaxy NGC 4736
Martin P., Belley J.
<Astron. Astrophys. 321, 363 (1997)>
=1997A&A...321..363M 1997A&A...321..363M (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Galaxies, ring
Keywords: galaxies: abundances - galaxies: evolution -
galaxies: individual (NGC 4736) - galaxies: ISM -
galaxies: kinematics and dynamics - galaxies: spirals
Abstract:
Results of imaging spectrophotometry in the nebular lines Hα,
Hβ, [O III]λ5007 and [N II]λ6584 of 65 H II regions
in the early-type ringed galaxy NGC 4736 are presented. The oxygen
abundance is derived using the line ratios [O III]/Hβ and
[N II]/[O III] as calibrated by Edmunds & Pagel (1984MNRAS.211..507E 1984MNRAS.211..507E).
Analysis of the O/H distribution in the bright resonance ring of star
formation in NGC 4736 reveals that the O/H scatter is similar to that
of the ISM of the disc of gas-rich galaxies, despite the very high
star formation rate presently observed in the ring. The magnitude of
azimuthal mixing induced by supernovae explosions and galaxy
differential rotation is estimated in the ring; it is found that both
can explain the small O/H dispersion observed in this structure. The
radial distribution of O/H in the disc of NGC 4736 is also studied.
Although the number of H II regions located outside the ring, and for
which a reliable O/H value was obtained is limited, a slope for the
global gradient is derived and found to be moderate
(~-0.035±0.020dex/kpc). This gradient is shallower than gradients
observed in normal galaxies, and is comparable to the slopes found for
galaxies with bars of medium strength. Two evolutionary scenarios are
proposed to explain this O/H distribution: i) Oval distortions, like
bars, induce large-scale gas flows throughout the disc of NGC 4736,
resulting in radial mixing of the chemical composition on a relatively
short time scale (≤1Gyr); ii) A strong bar was present in the recent
past and has flattened the abundance gradient.
Objects:
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RA (2000) DE Designation(s)
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12 50.9 +41 07 NGC 4736
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 17 65 Sample of HII regions in NGC 4736
table4 43 65 Properties of HII regions in NGC 4736
tables.tex 79 175 LaTeX version of the tables
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 2 I2 --- Region Region number
4- 7 I4 arcsec Xpos X position (1)
9- 11 I3 arcsec Ypos Y position (1)
13 I1 --- AP [1/3] Code for the size of square apertures
used to measure the integrated fluxes (2)
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Note (1): X and Y positions relative to the galaxy center,
north and east are positive
Note (2): 1: 4 arcsec2; 2: 12 arcsec2; 3: 24 arcsec2
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Byte-by-byte Description of file: table4
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Bytes Format Units Label Explanations
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1- 2 I2 --- Region Region number
4- 8 F5.2 --- log([OIII]/Hbeta) De-reddened [OIII]/Hbeta line ratio (1)
10- 13 F4.2 --- e_log([OIII]/Hbeta) rms uncertainty on log([OIII]/Hbeta)
15- 18 F4.2 --- log([NII]/[OIII]) De-reddened [NII]/[OIII] line ratio (2)
20- 23 F4.2 --- e_log([NII]/[OIII]) rms uncertainty on log([NII]/[OIII])
25- 28 F4.2 kpc Dist Galactocentric distance corrected for
galaxy inclination
30- 33 F4.2 ---- log(c(Hbeta)) Logarithmic extinction at Hbeta
35- 38 F4.2 --- (O/H)EP 12 + log(O/H) derived from the
[OIII]/Hbeta ratio calibrated by EP (3)
40- 43 F4.2 --- (O/H)A 12 + log(O/H) derived from the ratio
[NII]/[OIII] calibrated by EP (3) (4)
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Note (1): [OIII]/Hbeta = 1.35I([OIII]lambda5007)/I(Hbeta)
Note (2): [NII]/[OIII] = I([NII]lambda6584)/I([OIII]lambda5007)
Note (3): EP: Edmunds & Pagel (1984MNRAS.211..507E 1984MNRAS.211..507E)
Note (4): Ratio [NII]/[OIII] from Alloin et al. (1979A&A....78..200A 1979A&A....78..200A)
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References:
Alloin D. et al., 1979, A&A 78, 200 =1979A&A....78..200A 1979A&A....78..200A
Edmunds M.G. & Pagel B.E.J. 1984, MNRAS 211, 507 =1984MNRAS.211..507E 1984MNRAS.211..507E
(End) Patricia Bauer [CDS] 03-Sep-1996