J/ApJ/812/39 Fluxes of NGG7793 & NGC4945 with GMOS-S (Stanghellini+, 2015)
Gas-phase oxygen abundances and radial metallicity gradients in the two nearby
spiral galaxies NGC 7793 and NGC 4945.
Stanghellini L., Magrini L., Casasola V.
<Astrophys. J., 812, 39 (2015)>
=2015ApJ...812...39S 2015ApJ...812...39S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Spectra, red ; H II regions
Keywords: galaxies: abundances; galaxies: individual: (NGC 7793, NGC 4945);
H II regions
Abstract:
Gas-phase abundances in HII regions of two spiral galaxies, NGC7793
and NGC4945, have been studied to determine their radial metallicity
gradients. We used the strong-line method to derive oxygen abundances
from spectra acquired with GMOS-S, the multi-object spectrograph on
the 8m Gemini South telescope. We found that NGC7793 has a
well-defined gas-phase radial oxygen gradient of
-0.321±0.112dexR25-1 (or -0.054±0.019dex/kpc) in the
galactocentric range 0.17<RG/R25<0.82, not dissimilar from
gradients calculated with direct abundance methods in galaxies of
similar mass and morphology. We also determined a shallow radial
oxygen gradient in NGC 4945, -0.253±0.149dexR25-1 (or
-0.019±0.011dex/kpc) for 0.04<RG/R25<0.51, where the larger
relative uncertainty derives mostly from the larger inclination of
this galaxy. NGC 7793 and NGC 4945 have been selected for this study
because they are similar, in mass and morphology, to M33 and the Milky
Way, respectively. Since at zeroth order we expect the radial
metallicity gradients to depend on mass and galaxy type, we compared
our galaxies in the framework of radial metallicity models best suited
for M33 and the Galaxy. We found a good agreement between M33 and
NGC7793, pointing toward similar evolution for the two galaxies. We
notice instead differences between NGC 4945 and the radial metallicity
gradient model that best fits the Milky Way. We found that these
differences are likely related to the presence of an active galactic
nucleus combined with a bar in the central regions of NGC 4945, and to
its interacting environment.
Description:
The NGC 7793 images were acquired with GMOS-S in 2012 September and
October, while spectroscopic observations of this galaxy have been
acquired in 2013 July and August. Hα images of NGC 4945 have
been acquired in 2013 March, while spectroscopy was obtained in June
and July of the same year. We have also acquired [OIII]5007Å
continuum-subtracted images of both galaxies as part of the original
program, aimed at both planetary nebula (PN) and HII region
spectroscopy.
Objects:
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RA (ICRS) DE Designation(s)
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23 57 49.83 -32 35 27.7 NGC 7793 = ESO 349-12
13 05 27.28 -49 28 04.4 NGC 4945 = ESO 219-24
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 84 27 Positions and distances and Hβ flux of
HII regions in NGC 7793
table4.dat 84 33 Positions and distances and Hβ flux of
HII regions in NGC 4945
table5.dat 36 216 NGC 7793 fluxes
table6.dat 36 224 NGC 4945 fluxes
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See also:
J/A+A/567/A88 : Abundances in HII regions of M81 (Stanghellini+, 2014)
J/AJ/147/131 : Abundances of nearby late-type galaxies. I. (Pilyugin+, 2014)
J/A+A/559/A114 : Updated O3N2 and N2 abundance indicators (Marino+, 2013)
J/ApJS/190/233 : Spectroscopy & abundances of SINGS galaxies (Moustakas+, 2010)
J/A+A/512/A63 : Abundances of M33 HII regions (Magrini+, 2010)
J/ApJ/706/553 : Fluxes in nearby star-forming galaxies (Boquien+, 2009)
J/AJ/138/1037 : Star formation in Centaurus A Group dwarfs (Cote+ 2009)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/A+A/440/783 : OB associations in NGC 7793 (Pietrzynski+, 2005)
J/A+A/422/941 : Gas content in 1038 interacting galaxies (Casasola+, 2004)
Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
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1 I1 --- Field [1/2]? Field number (only for table 4)
3- 4 I2 --- Reg [1/28] Region number
6 A1 --- f_Reg Flag on Reg (1)
8- 9 I2 h RAh Hour of right ascension (J2000)
11- 12 I2 min RAm Minute of right ascension (J2000)
14- 18 F5.2 s RAs Second of right ascension (J2000)
20 A1 --- DE- Sign of declination (J2000)
21- 22 I2 deg DEd Degree of declination (J2000)
24- 25 I2 arcmin DEm Arcminute of declination (J2000)
27- 31 F5.2 arcsec DEs Arcsecond of declination (J2000)
33- 36 F4.2 --- Rg/R25 [0.04/1] Isophotal radius
38- 42 F5.3 --- e_Rg/R25 [0/0.07] Rg/R25 uncertainty
44- 47 F4.2 kpc Rg [0.4/7.7] Galactocentric distance
49- 52 F4.2 kpc e_Rg [0/1] Rg uncertainty
54- 58 F5.3 --- cbeta [0.09/3.5]? Extinction constant cβ
60- 64 F5.3 --- e_cbeta ? cbeta uncertainty
66- 74 E9.4 10-3W/m2 FHb ? Hβ integrated flux (erg/cm2/s)
76- 84 E9.3 10-3W/m2 e_FHb ? FHb uncertainty
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Note (1): Flag as follows:
a = Very poor spectrum, not used for abundance analysis.
b = Poor spectrum, low S/N, not included in gradients.
c = HII region nature possible, but it could also be a PN. On BPT boundary.
Not included in gradients.
d = HII nature very probable. On BPT boundary. Not included in gradients.
e = HII region nature possible, but it could also be a PN. BPT outlier.
Not included in gradients.
f = HII nature very probable. BPT outlier. Not included in gradients.
g = Low S/N spectrum, not included in gradients.
h = [SII] emission lines have 2.5<S/N<3.
i = Probably not a HII region. BPT outlier. Not included in gradients.
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Byte-by-byte Description of file: table[56].dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- Field [1/2]? Field identifier (only for table 6)
3- 4 I2 --- Reg [1/28] Region identifier (1)
6- 11 A6 --- Ion Ion designation
13- 16 I4 0.1nm lambda [4861/6731] Wavelength in Angstroms
18- 23 F6.1 --- Flux [4/3451]? Observed flux relative to Hβ (1)
25- 30 F6.2 --- e_Flux [0.02/130]? Error in Flux (1)
32- 36 F5.1 --- I [4/920]? Observed intensity relative
to Hβ (1)
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Note (1): Where the extinction constant cβ (i.e. the logarithmic
extinction at Hβ) and its error, plus the Hβ integrated
flux and its error (erg/cm2/s) for each Region is given in
table 3 (for NGC 7793) and table 4 (for NGG 4945).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Feb-2016