J/ApJ/812/39    Fluxes of NGG7793 & NGC4945 with GMOS-S    (Stanghellini+, 2015)
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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    (SIMBAD/NED BibCode)
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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+/-0.112dexR_25_^-1^ (or -0.054+/-0.019dex/kpc) in the
    galactocentric range 0.17<R_G_/R_25_<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+/-0.149dexR_25_^-1^ (or
    -0.019+/-0.011dex/kpc) for 0.04<R_G_/R_25_<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. H{alpha} 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]5007{AA}
    continuum-subtracted images of both galaxies as part of the original
    program, aimed at both planetary nebula (PN) and HII region
    spectroscopy.

Objects:
    ---------------------------------------------------
         RA   (ICRS)   DE        Designation(s)
    ---------------------------------------------------
     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
    ---------------------------------------------------

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 H{beta} flux of
                              HII regions in NGC 7793
table4.dat     84       33   Positions and distances and H{beta} 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 c{beta}
  60- 64  F5.3  ---     e_cbeta     ? cbeta uncertainty
  66- 74  E9.4 10-3W/m2   FHb       ? H{beta} integrated flux (erg/cm^2^/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
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       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 H{beta} (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 H{beta} (1)
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Note (1): Where the extinction constant c{beta} (i.e. the logarithmic
          extinction at H{beta}) and its error, plus the H{beta} integrated
          flux and its error (erg/cm^2^/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

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(End)                 Prepared by [AAS], Emmanuelle Perret [CDS]    01-Feb-2016