We have obtained multislit spectroscopic observations from 3700 to 9200Å with Low Resolution Imaging Spectrometer at the Keck I telescope for 31 Hii regions in the disc of the Andromeda galaxy (M31), ...spanning a range in galactocentric distance from 3.9 to 16.1kpc. In nine Hii regions we measure one or several auroral lines (Oiii λ4363, Nii λ5755, Siii λ6312, Oii λ7325) from which we determine the electron temperature (Te) of the gas and derive chemical abundances using the direct Te-based method. We analyse, for the first time in M31, abundance trends with galactocentric radius from the direct method, and find that the Ne/O, Ar/O, N/O and S/O abundance ratios are consistent with a constant value across the M31 disc, while the O/H abundance ratio shows a weak gradient. We have combined our data with all spectroscopic observations of Hii regions in M31 available in the literature, yielding a sample of 85 Hii regions spanning distances from 3.9 to 24.7kpc (0.19-1.2R25) from the galaxy centre. We have tested a number of empirical calibrations of strong emission line ratios. We find that the slope of the oxygen abundance gradient in M31 is -0.023 ± 0.002dexkpc-1, and that the central oxygen abundance is in the range 12+log(O/H) 8.71-8.91dex (i.e. between 1.05 and 1.66 times the solar value, for 12+log(O/H) = 8.69), depending on the calibration adopted. The Hii region oxygen abundances are compared with the results from other metallicity indicators (supergiant stars and planetary nebulae). The comparison shows that Hii region O/H abundances are systematically 0.3dex below the stellar ones. This discrepancy is discussed in terms of oxygen depletion on to dust grains and possible biases affecting Te-based oxygen abundances at high metallicity. PUBLICATION ABSTRACT
We have obtained multislit spectroscopic observations from 3700 to 9200 Å with Low Resolution Imaging Spectrometer at the Keck I telescope for 31 H ii regions in the disc of the Andromeda galaxy ...(M31), spanning a range in galactocentric distance from 3.9 to 16.1 kpc. In nine H ii regions we measure one or several auroral lines (O iii λ4363, N ii λ5755, S iii λ6312, O ii λ7325) from which we determine the electron temperature (T
e) of the gas and derive chemical abundances using the direct
T
e-based method. We analyse, for the first time in M31, abundance trends with galactocentric radius from the direct method, and find that the Ne/O, Ar/O, N/O and S/O abundance ratios are consistent with a constant value across the M31 disc, while the O/H abundance ratio shows a weak gradient. We have combined our data with all spectroscopic observations of H ii regions in M31 available in the literature, yielding a sample of 85 H ii regions spanning distances from 3.9 to 24.7 kpc (0.19-1.2 R
25) from the galaxy centre. We have tested a number of empirical calibrations of strong emission line ratios. We find that the slope of the oxygen abundance gradient in M31 is −0.023 ± 0.002 dex kpc−1, and that the central oxygen abundance is in the range 12+log(O/H) 8.71-8.91 dex (i.e. between 1.05 and 1.66 times the solar value, for 12+log(O/H)⊙ = 8.69), depending on the calibration adopted. The H ii region oxygen abundances are compared with the results from other metallicity indicators (supergiant stars and planetary nebulae). The comparison shows that H ii region O/H abundances are systematically ∼0.3 dex below the stellar ones. This discrepancy is discussed in terms of oxygen depletion on to dust grains and possible biases affecting T
e-based oxygen abundances at high metallicity.
ABSTRACT
We present here the second part of a project that aims at solving the controversy regarding the issue of the bar effect on the radial distribution of metals in the gas-phase of spiral ...galaxies. In Paper I, we presented a compilation of more than 2800 H ii regions belonging to 51 nearby galaxies for which we derived chemical abundances and radial abundance profiles from a homogeneous methodology. In this paper, we analyse the derived gas-phase radial abundance profiles of 12+log (O/H) and log (N/O), for barred and unbarred galaxies separately, and find that the differences in slope between barred and unbarred galaxies depend on galaxy luminosity. This is due to a different dependence of the abundance gradients (in dex kpc−1) on luminosity for the two types of galaxies: in the galaxy sample under consideration the gradients appear to be considerably shallower for strongly barred galaxies in the whole luminosity range, while profile slopes for unbarred galaxies become steeper with decreasing luminosity. Therefore, we only detect differences in slope for the lower luminosity (lower mass) galaxies (MB ≳ −19.5 or M* ≲ 1010.4 M⊙). We discuss the results in terms of the disc evolution and radial mixing induced by bars and spiral arms. Our results reconcile previous discrepant findings that were biased by the luminosity (mass) distribution of the sample galaxies and possibly by the abundance diagnostics employed.
Incompressible materials, such as filled rubbers and biological tissues, may exhibit high nonlinear and anisotropic inelastic responses induced by deformations when subject to large strains. The ...constitutive modeling area has focused on describing the anisotropic behavior of viscosity and damage. However, coupled anisotropic inelastic effects are still a major challenge, with few contributions in the literature. This paper then presents a variational full-network framework capable of representing coupled anisotropic damage and viscoelasticity responses induced by deformation. The proposal extends a variational family to include the advantages of the full-network framework to deal with anisotropic behaviors. Approximations of the potential energies used on the full-network integration scheme associate the inelastic scalar variables at each material point with the quadrature points directions, resulting naturally in a set of scalar minimization problems. Numerical tests are presented to show the ability of the framework to represent anisotropic damage and viscoelasticity. Two variational models, specialized for filled rubber and soft biological tissues, are also implemented on finite element software to assess the model into practical applications. The results show the proposed model’s versatility to simulate anisotropic viscoelasticity, anisotropic mechanical damage, and viscous and damage coupled phenomena, maintaining accuracy for large strain and time increments.
•A constitutive model for anisotropic damage and viscoelasticity induced by strain.•Extends a family of variational models using an approximation of potential energies.•The model fills a gap in the area by coupling anisotropic damage and viscoelasticity.•Evaluate the accuracy of an integration scheme to solve large inelastic increments.
In the era of precision cosmology, it is essential to determine the Hubble constant empirically with an accuracy of one per cent or better
. At present, the uncertainty on this constant is dominated ...by the uncertainty in the calibration of the Cepheid period-luminosity relationship
(also known as the Leavitt law). The Large Magellanic Cloud has traditionally served as the best galaxy with which to calibrate Cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale
. Eclipsing binary systems composed of late-type stars offer the most precise and accurate way to measure the distance to the Large Magellanic Cloud. Currently the limit of the precision attainable with this technique is about two per cent, and is set by the precision of the existing calibrations of the surface brightness-colour relation
. Here we report a calibration of the surface brightness-colour relation with a precision of 0.8 per cent. We use this calibration to determine a geometrical distance to the Large Magellanic Cloud that is precise to 1 per cent based on 20 eclipsing binary systems. The final distance is 49.59 ± 0.09 (statistical) ± 0.54 (systematic) kiloparsecs.
Abstract
We present deep spectrophotometry of 18 H ii regions in the nearby massive spiral galaxies M 101 and M 31. We have obtained direct determinations of electron temperature in all the nebulae. ...We detect the C ii 4267 Å line in several H ii regions, permitting to derive the radial gradient of C/H in both galaxies. We also determine the radial gradients of O/H, N/O, Ne/O, S/O, Cl/O and Ar/O ratios. As in other spiral galaxies, the C/H gradients are steeper than those of O/H producing negative slopes of the C/O gradient. The scatter of the abundances of O with respect to the gradient fittings do not support the presence of significant chemical inhomogeneities across the discs of the galaxies, especially in the case of M101. We find trends in the S/O, Cl/O and Ar/O ratios as a function of O/H in M101 that can be reduced using Te indicators different from the standard ones for calculating some ionic abundances. The distribution of the N/O ratio with respect to O/H is rather flat in M31, similarly to previous findings for the Milky Way. Using the disc effective radius – Re – as a normalization parameter for comparing gradients, we find that the latest estimates of Re for the Milky Way provide an excess of metallicity in apparent contradiction with the mass-metallicity relation; a value about two times larger might solve the problem. Finally, using different abundance ratios diagrams we find that the enrichment timescales of C and N result to be fairly similar despite their different nucleosynthetic origin.
We present the mass-metallicity (MZ) and luminosity-metallicity (LZ) relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary Probe 2 survey. We determine stellar masses by ...fitting the spectral energy distribution inferred from photometry with current stellar population synthesis models. This work raises the number of galaxies with metallicities at z ~0.8 by more than an order of magnitude. We investigate the evolution in the MZ and LZ relations in comparison with local MZ and LZ relations determined in a consistent manner using ~2,000 galaxies in the Sloan Digital Sky Survey. We show that high stellar mass galaxies (M ~ 1010.6 M ) at z ~0.8 have attained the chemical enrichment seen in the local universe, while lower stellar mass galaxies (M ~ 109.2 M ) at z ~0.8 have lower metallicities ( Delta *Dlog(O/H) ~ 0.15 dex) than galaxies at the same stellar mass in the local universe. We find that the LZ relation evolves in both metallicity and B-band luminosity between z ~0.8 and z ~ 0, with the B-band luminosity evolving as a function of stellar mass. We emphasize that the B-band luminosity should not be used as a proxy for stellar mass in chemical evolution studies of star-forming galaxies. Our study shows that both the metallicity evolution and the B-band luminosity evolution for emission-line galaxies between the epochs are a function of stellar mass, consistent with the cosmic downsizing scenario of galaxy evolution.
ABSTRACT Low-resolution (4.5-5 ) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques ...to determine stellar temperatures, gravities, and metallicities (from iron peak and -elements). A metallicity gradient of −0.22 0.06 dex/R25 is detected. The central metallicity on a logarithmic scale relative to the Sun is Z = −0.37 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity-luminosity relationship is used to determine a distance modulus of 26.85 0.10 mag.
We acquired spectra of 141 H ii 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.
High-quality spectra of 90 blue supergiant stars in the Large Magellanic Cloud are analyzed with respect to effective temperature, gravity, metallicity, reddening, extinction, and extinction law. An ...average metallicity, based on Fe and Mg abundances, relative to the Sun of Z = −0.35 0.09 dex is obtained. The reddening distribution peaks at = 0.08 mag, but significantly larger values are also encountered. A wide distribution of the ratio of extinction to reddening is found ranging from = 2 to 6. The results are used to investigate the blue supergiant relationship between flux-weighted gravity, gf g/ , and absolute bolometric magnitude Mbol. The existence of a tight relationship, the Flux-weighted Gravity-Luminosity Relationship (FGLR), is confirmed. However, in contrast to previous work, the observations reveal that the FGLR is divided into two parts with a different slope. For flux-weighted gravities larger than 1.30 dex, the slope is similar to that found in previous work, but the relationship becomes significantly steeper for smaller values of the flux-weighted gravity. A new calibration of the FGLR for extragalactic distance determinations is provided.
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