- ID:
- ivo://CDS.VizieR/J/MNRAS/454/3664
- Title:
- Abundance gradients in low SB spirals
- Short Name:
- J/MNRAS/454/3664
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We acquired spectra of 141 HII regions in 10 late-type low surface brightness galaxies (LSBGs). The analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of LSBGs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. The average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. This result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density-metallicity relation. With a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion is reinforced by our result that LSBGs share the same common abundance gradient with HSBGs, when the slope is expressed in terms of the exponential disc scalelength.
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- ID:
- ivo://CDS.VizieR/J/ApJS/162/346
- Title:
- Abundance gradients in the Galaxy
- Short Name:
- J/ApJS/162/346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Six HII regions at galactocentric distances of R=10-15kpc have been observed in the far-IR emission lines of [OIII] (52{mu}m, 88{mu}m), [NIII] (57{mu}m), and [SIII] (19{mu}m) using the Kuiper Airborne Observatory. These observations have been combined with Very Large Array radio continuum observations of these sources to determine the abundances of O++, N++, and S++ relative to hydrogen. In addition, eight of the most recent sets of measurements of ionic line strengths in HII regions have been reanalyzed in order to attempt to reconcile differences in optical versus far-IR abundance determinations. We have in total 168 sets of observations of 117 HII regions in our analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/662/15
- Title:
- Abundances in extragalactic HII regions
- Short Name:
- J/ApJ/662/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the primordial helium mass fraction Yp using 93 spectra of 86 low-metallicity extragalactic HII regions. This sample constitutes the largest and most homogeneous high-quality data set in existence for the determination of Yp. For comparison, and to improve the statistics in our investigation of systematic effects affecting the Yp determination, we have also considered a sample of 271 low-metallicity HII regions selected from Data Release 5 of the Sloan Digital Sky Survey. Although this larger sample shows more scatter, it gives results that are consistent at the 2{sigma} level with our original sample. We have considered known systematic effects that may affect the ^4^He abundance determination.
- ID:
- ivo://CDS.VizieR/J/MNRAS/424/2316
- Title:
- Abundances in HII regions
- Short Name:
- J/MNRAS/424/2316
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We suggest a new way of determining abundances and electron temperatures in HII regions from strong emission lines. Our approach is based on the standard assumption that HII regions with similar intensities of strong emission lines have similar physical properties and abundances. A 'counterpart' for a studied HII region may be chosen among HII regions with well-measured abundances (reference HII regions) by comparison of carefully chosen combinations of strong-line intensities. Then the abundances in the investigated HII region can be assumed to be the same as those in its counterpart. In other words, we suggest to determine the abundances in HII regions 'by precedent'. To get more reliable abundances for the considered HII region, a number of reference HII regions are selected and then the abundances in the target HII region are estimated through extrapolation/interpolation. We will refer to this method of abundance determination as the counterpart method or, for brevity, the C method. We define a sample of reference HII regions and verify the validity of the C method. We find that this method produces reliable abundances. Finally, the C method is used to obtain the radial abundance distributions in the extended discs of the spiral galaxies M83, NGC 4625 and NGC 628.
- ID:
- ivo://CDS.VizieR/J/A+A/464/885
- Title:
- Abundances in 53 HII regions
- Short Name:
- J/A+A/464/885
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Continuing the systematic determination of the electron temperature of HII regions using the Balmer and/or Paschen discontinuities by Guseva et al. (2006ApJ...644..890G) we focus here on 3.6m ESO telescope observations of a large new sample of 69 HII regions in 45 blue compact dwarf (BCD) galaxies. This data set spans a wide range in metallicity (Z_{sun}_/60<Z<Z_{sun}_/3) and, combined with the sample of 47 HII regions from Guseva et al. (2006ApJ...644..890G), yields the largest spectroscopic data set ever used to derive the electron temperature in the H^+^ zone. In the same way as in Guseva et al. (2006ApJ...644..890G) we have used a Monte Carlo technique to vary free parameters and to calculate a series of model spectral energy distributions (SEDs) for each HII region. The electron temperature in the H^+^ zones was derived from the best fitting synthetic and observed SEDs in the wavelength range ~3200-5100{AA}, which includes the Balmer jump. On the base of the present large spectroscopic sample we find that in hot (Te(H^+^)>11000K) HII regions the temperature of the O^2+^ zone, determined from doubly ionised oxygen forbidden lines, does not differ statistically from the temperature of the H^+^ zone. Thus, we confirm and strengthen the finding by Guseva et al. (2006ApJ...644..890G). We emphasize that due to a number of modelling assumptions and the observational uncertainties for individual objects, only a large, homogeneous sample, as the one used here, can enable a conclusive study of the relation between Te(H^+^) and Te(OIII).
- ID:
- ivo://CDS.VizieR/J/A+A/521/A3
- Title:
- Abundances in HII regions and PNe of M81
- Short Name:
- J/A+A/521/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M81 is an ideal laboratory to investigate the galactic chemical and dynamical evolution through the study of its young and old stellar populations. We analyze the chemical abundances of planetary nebulae and HII regions in the M81 disk for insight on galactic evolution, and compare it with that of other galaxies, including the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A88
- Title:
- Abundances in HII regions of M81
- Short Name:
- J/A+A/567/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new set of weak-line abundances of HII regions in M81, based on Gemini Multi-Object Spectrograph (GMOS) observations. The aim is to derive plasma and abundance analysis for a sizable set of emission-line targets to study the galactic chemical contents in the framework of galactic metallicity gradients. We used the weak-line abundance approach by deriving electron density and temperatures for several HII regions in M81. Gradient analysis is based on oxygen abundances. Together with a set of HII region abundances determined similarly by us with Multi-Mirror Telescope (MMT) spectra, the new data yield to a radial oxygen gradient of -0.088+/-0.013dex/kpc, which is steeper than the metallicity gradient obtained for planetary nebulae (-0.044+/-0.007dex/kpc). This result could be interpreted as gradient evolution with time: Models of galactic evolution with inside-out disk formation associated to pre-enriched gas infall would produce such difference of gradients, although stellar migration effects would also induce a difference in the metallicity gradients between the old and young populations.
- ID:
- ivo://CDS.VizieR/J/ApJ/675/1213
- Title:
- Abundances in M33 HII regions
- Short Name:
- J/ApJ/675/1213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new determination of the metallicity gradient in M33, based on Keck LRIS measurements of oxygen abundances using the temperature-sensitive emission line [OIII] {lambda}4363 in 61 HII regions. These data approximately triple the sample of direct oxygen abundances in M33. We find a central abundance of 12+log(O/H)=8.36+/-0.04 and a slope of -0.027+/-0.012dex/kpc, in agreement with infrared measurements of the neon abundance gradient but much shallower than most previous oxygen gradient measurements. There is substantial intrinsic scatter of 0.11dex in the metallicity at any given radius in M33, which imposes a fundamental limit on the accuracy of gradient measurements that rely on small samples of objects. We also show that the ionization state of neon does not follow the ionization state of oxygen as is commonly assumed, suggesting that neon abundance measurements from optical emission lines require careful treatment of the ionization corrections.
- ID:
- ivo://CDS.VizieR/J/A+A/448/955
- Title:
- Abundances of emission galaxies in SDSS-DR3
- Short Name:
- J/A+A/448/955
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have re-evaluated empirical expressions for the abundance determination of N, O, Ne, S, Cl, Ar and Fe taking into account the latest atomic data and constructing an appropriate grid of photoionization models with state-of-the art model atmospheres. Using these expressions we have derived heavy element abundances in the ~310 emission-line galaxies from the Data Release 3 of the Sloan Digital Sky Survey (SDSS, <III/241>) with an observed Hbeta flux F(Hbeta)>10^-14^erg/s/cm^2^ and for which the [O III] 4363 emission line was detected at least at a 2sigma level, allowing abundance determination by direct methods. The oxygen abundance 12+logO/H of the SDSS galaxies lies in the range from ~7.1 (Z_{sun}_/30) to ~8.5 (0.7Z_{sun}_). The SDSS sample is merged with a sample of 109 blue compact dwarf (BCD) galaxies with high quality spectra, which contains extremely low-metallicity objects. We use the merged sample to study the abundance patterns of low-metallicity emission-line galaxies. We find that extremely metal-poor galaxies (12+logO/H<7.6, i.e. Z<Z_{sun}_/12) are rare in the SDSS sample. The alpha element to oxygen abundance ratios do not show any significant trends with oxygen abundance, in agreement with previous studies, except for a slight increase of Ne/O with increasing metallicity, which we interpret as due to a moderate depletion of O onto grains in the most metal-rich galaxies. The Fe/O abundance ratio is smaller than the solar value, by up to 1 dex at the high metallicity end. We also find that Fe/O increases with decreasing Hbeta equivalent width EW(Hbeta). We interpret this as a sign of strong depletion onto dust grains, and gradual destruction of those grains on a time scale of a few Myr. All the galaxies are found to have logN/O>-1.6, implying that they have a different nature than the subsample of high-redshift damped Lyalpha systems with log N/O of ~-2.3 and that their ages are larger than 100-300Myr. We confirm the apparent increase in N/O with decreasing EW(Hbeta), already shown in previous studies, and explain it as the signature of gradual nitrogen ejection by massive stars from the most recent starburst.
- ID:
- ivo://CDS.VizieR/J/AZh/79/867
- Title:
- Abundances of HII regions in blue galaxies
- Short Name:
- J/AZh/79/867
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New expression for the ionization correction factors (ICF) are used to find the nebular-gas compositions in HII regions in blue compact dwarf galaxies (BCD). The abundances of He, N, O, Ne, S, and Ar in 41 HII regions are determined.
