Simple relations for deriving the oxygen abundance in H ii
regions with intensities of the three strong emission lines R
2, R
3, and N
2 (R calibration) or S
2, R
3, and N
2 (S calibration) in their ...spectra are suggested. A sample of 313 reference H ii regions of the counterpart method (C method) is used as calibrating data points. Relations for the determination of nitrogen abundances, the R calibration, are also constructed. We find that the oxygen and nitrogen abundances in high-metallicity H ii regions can be estimated using the intensities of the two strong lines R
2 and N
2 (or S
2 and N
2 for oxygen) only. The corresponding two-dimensional relations are provided. There are considerable advantages of the suggested calibration relations as compared to the existing ones. First, the oxygen and nitrogen abundances estimated through the suggested calibrations agree with the T
e
-based abundances within ∼0.1 dex over the whole metallicity range, i.e. the relative accuracy of the calibration-based abundances is 0.1 dex. Although we constructed distinct relations for high- and low-metallicity objects, the separation between these two can be simply obtained from the intensity of the N
2 line. Moreover, the applicability ranges of the high- and low-metallicity relations overlap for adjacent metallicities, i.e. the transition zone disappears. Secondly, the oxygen abundances produced by the two suggested calibrations are in remarkable agreement with each other. In fact, the R-based and S-based oxygen abundances agree within ∼0.05 dex in the majority of cases for more than three thousand H ii region spectra.
We considered two sequences of spiral galaxies with different shapes of the radial gas-phase oxygen abundance distributions from the galaxies in the survey Mapping Nearby Galaxies
at Apache Point ...Observatory (MaNGA): (1) Galaxies in which the gradient is well approximated by a single linear relation across the whole disc, that is, galaxies with an S (slope)
gradients, (2) galaxies in which the metallicity in the inner region of the disc is at a nearly constant level and the gradient is negative at larger radii, that is, galaxies with
level-slope (LS) gradients. We also selected galaxies with a nearly uniform oxygen abundance across the whole galaxy, that is, galaxies with level (L) gradients (or O/H uniform
galaxies) with a high oxygen abundance that can be the final evolutionary stage of the two galaxy sequences described above. The radial nitrogen abundance distributions
in galaxies with LS oxygen abundance distributions also show breaks at radii smaller than the O/H distribution breaks. The observed behaviour of the oxygen and nitrogen
abundances with radius in these galaxies can be explained by the time delay between the nitrogen and oxygen enrichment together with the variation in the star formation history
along the radius. These galaxies clearly show the effect of the inside-out disc evolution model, which predicts that the galactic centre evolves more rapidly than
the regions at greater galactocentric distances. We find that the shape of the radial abundance distribution in a galaxy is not related to its macroscopic characteristics (rotation
velocity, stellar mass, isophotal radius, and star formation rate) and is independent of its present-day environment.
The correlations between the gradient slopes and macroscopic characteristics of galaxies are weak in the sense that the scatter of the points in each diagram is large.
The galaxies with different abundance distributions (S, LS, or L) in our sample are located within the main sequence of the star-forming
galaxies in the diagram of star formation rate -- stellar mass. We also examined the properties of the Milky Way in the context of the considered galaxy samples.
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, NGC4625 and NGC628. PUBLICATION ABSTRACT
Abstract
We suggest a new way of determining abundances and electron temperatures in H ii regions from strong emission lines. Our approach is based on the standard assumption that H ii regions with ...similar intensities of strong emission lines have similar physical properties and abundances. A 'counterpart' for a studied H ii region may be chosen among H ii regions with well-measured abundances (reference H ii regions) by comparison of carefully chosen combinations of strong-line intensities. Then the abundances in the investigated H ii region can be assumed to be the same as those in its counterpart. In other words, we suggest to determine the abundances in H ii regions 'by precedent'. To get more reliable abundances for the considered H ii region, a number of reference H ii regions are selected and then the abundances in the target H ii 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 H ii 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.
We determine the radial abundance distributions across the discs of 14 irregular galaxies of the types Sm and Im (morphological T types 9 and 10) as traced by their H ii regions. The oxygen and ...nitrogen abundances in H ii regions are estimated through the T... method or/and with the counterpart method (C method). Moreover, we examine the correspondence between the radial abundance gradient and the surface brightness profile. We find that irregular galaxies with a flat inner profile (flat or outwardly increasing surface brightness in the central region) show shallow (if any) radial abundance gradients. On the other hand, irregular galaxies with a steep inner profile (with or without a bulge or central star cluster) usually show rather steep radial abundance gradients. This is in contrast to the widely held belief that irregular galaxies do not usually show a radial abundance gradient. (ProQuest: ... denotes formulae/symbols omitted.)
Oxygen abundance maps of CALIFA galaxies Zinchenko, I A; Pilyugin, L S; Grebel, E K ...
Monthly Notices of the Royal Astronomical Society,
11/2016, Letnik:
462, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We construct maps of the oxygen abundance distribution across the discs of 88 galaxies using Calar Alto Legacy Integral Field Area survey (CALIFA) Data Release 2 (DR2) spectra. The position of the ...centre of a galaxy (coordinates on the plate) was also taken from the CALIFA DR2. The galaxy inclination, the position angle of the major axis, and the optical radius were determined from the analysis of the surface brightnesses in the Sloan Digital Sky Survey (SDSS) g and r bands of the photometric maps of SDSS Data Release 9. We explore the global azimuthal abundance asymmetry in the discs of the CALIFA galaxies and the presence of a break in the radial oxygen abundance distribution. We found that there is no significant global azimuthal asymmetry for our sample of galaxies, i.e. the asymmetry is small, usually lower than 0.05 dex. The scatter in oxygen abundances around the abundance gradient has a comparable value, ...0.05 dex. A significant (possibly dominant) fraction of the asymmetry can be attributed to the uncertainties in the geometrical parameters of these galaxies. There is evidence for a flattening of the radial abundance gradient in the central part of 18 galaxies. We also estimated the geometric parameters (coordinates of the centre, the galaxy inclination and the position angle of the major axis) of our galaxies from the analysis of the abundance map. The photometry-map-based and the abundance-map-based geometrical parameters are relatively close to each other for the majority of the galaxies but the discrepancy is large for a few galaxies with a flat radial abundance gradient. (ProQuest: ... denotes formulae/symbols omitted.)
We performed a compilation of more than 1000 published spectra of H II regions in spiral galaxies. The oxygen and nitrogen abundances in each H II region were recomputed in a homogeneous way, using ...the P-method. The radial distributions of oxygen and nitrogen abundances were derived. The correlations between oxygen abundance and macroscopic properties are examined. We found that the oxygen abundance in spiral galaxies correlates with its luminosity, rotation velocity, and morphological type: the correlation with the rotation velocity may be slightly tighter. There is a significant difference between the luminosity-metallicity relationship obtained here and that based on the oxygen abundances determined through the R sub(23)-calibrations. The oxygen abundance of NGC 5457 recently determined using direct measurements of T sub(e) (Kennicutt et al. 2003) agrees with the luminosity-metallicity relationship derived in this paper, but is in conflict with the luminosity-metallicity relationship derived with the R sub(23)-based oxygen abundances. The obtained luminosity-metallicity relation for spiral galaxies is compared to that for irregular galaxies. Our sample of galaxies shows evidence that the slope of the O/H - M sub(B) relationship for spirals (-0.079 plus or minus 0.018) is slightly more shallow than that for irregular galaxies (-0.139 plus or minus 0.011). The effective oxygen yields were estimated for spiral and irregular galaxies. The effective oxygen yield increases with increasing luminosity from M sub(B) similar to -11 to M sub(B) similar to -18 (or with increasing rotation velocity from V sub(rot) similar to 10 km s super(-1) to V sub(rot) similar to 100 km s super(-1)) and then remains approximately constant. Irregular galaxies from our sample have effective oxygen yields lowered by a factor of 3 at maximum, i.e. irregular galaxies usually keep at least 1/3 of the oxygen they manufactured during their evolution.
We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method, via the ...direct T
e-method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the T
e-method underestimates the oxygen abundances by up to ∼2 dex (with averaged value of ∼0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called ‘temperature problem’ in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (∼2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.
ABSTRACT
In the local Universe, there are a handful of dwarf compact star-forming galaxies with extremely low oxygen abundances. It has been proposed that they are young, having formed a large ...fraction of their stellar mass during their last few hundred Myr. However, little is known about the fraction of young stellar populations in more massive galaxies. In a previous article, we analysed 404 000 Sloan Digital Sky Survey spectra to identify a surprisingly large sample of more massive very young galaxies (VYGs), defined to have formed at least $50{{\ \rm per\ cent}}$ of their stellar mass within the last 1 Gyr. Here, we investigate in detail the properties of a subsample of 207 galaxies that are VYGs according to all three of our spectral models. We compare their properties with those of control sample galaxies (CSGs). We find that VYGs tend to have higher surface brightness and to be more compact, dusty, asymmetric, and clumpy than CSGs. Analysis of a subsample with H i detections reveals that VYGs are more gas rich than CSGs. VYGs tend to reside more in the inner parts of low-mass groups and are twice as likely as CSGs to be interacting with a neighbour galaxy. On the other hand, VYGs and CSGs have similar gas metallicities and large-scale environments (relative to filaments and voids). These results suggest that gas-rich interactions and mergers are the main mechanisms responsible for the recent triggering of star formation in low-redshift VYGs, except for the lowest mass VYGs, where the starbursts would arise from a mixture of mergers and gas infall.
We have compared the oxygen and nitrogen abundances derived from global emission-line Sloan Digital Sky Survey (SDSS) spectra of galaxies using (1) the T
e method and (2) two recent strong-line ...calibrations: the ON and NS calibrations. Using the T
e method, anomalously high N/O abundance ratios have been found in some SDSS galaxies. To investigate this, we have Monte Carlo simulated the global spectra of composite nebulae by a mix of spectra of individual components, based on spectra of well-studied H ii regions in nearby galaxies. We found that the T
e method results in an underestimated oxygen abundance (and hence in an overestimated nitrogen-to-oxygen ratio) if H ii regions with different physical properties contribute to the global spectrum of composite nebulae. This effect is somewhat similar to the small-scale temperature fluctuations in H ii regions discussed by Peimbert. Our work thus suggests that the high T
e-based N/O abundance ratios found in SDSS galaxies may not be real. However, such an effect is not expected to be present in dwarf galaxies since they generally have a uniform chemical composition. The ON and NS calibrations give O and N abundances in composite nebulae which agree with the mean luminosity-weighted abundances of their components to within ∼0.2 dex.
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