Squid gelatin obtained from inner and outer tunics was hydrolysed with Alcalase to isolate antioxidant peptide sequences. The ACE-inhibitory activity of the isolated peptides was also evaluated. ...After fractionation by ultrafiltration and size-exclusion chromatography into four fractions, the antioxidant activity of the peptide fractions was determined by radical scavenging ability and ferric reducing power. Fraction FIII showed the highest antioxidant activity, although slight differences could be expected in the antioxidant activity of the different fractions based on the amino acid composition. FIII was subjected to liquid chromatography and tandem mass spectrometry (LC–MS/MS) and two major compounds were identified: the compound with
m/
z 952.42, which could be mostly comprised by the carbohydrate fucose, and the peptide with
m/
z 1410.63. Three possible sequences were proposed and synthesised for this peptide, and the contribution of Leu or Hyp residues to the antioxidant and ACE-inhibitory activities of the resulting sequence was evaluated. The presence of Leu residues in the peptide sequence in replacement of Hyp seems to play an important role in the antioxidant and ACE-inhibitory activity.
To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxies at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: ...OII lambda3727, H beta , OIII lambda5007, H alpha , and NII lambda6584. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z approximately 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using Nu/H alpha -based metallicities from stacked spectra. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al.
Context. The study of the integrated properties of star-forming galaxies is central to understand their formation and evolution. Some of these properties are extensive and therefore their analysis ...require totally covering and spatially resolved observations. Among these properties, metallicity can be defined in spiral discs by means of integral field spectroscopy (IFS) of individual H ii regions. The simultaneous analysis of the abundances of primary elements, as oxygen, and secondary, as nitrogen, also provides clues about the star formation history and the processes that shape the build-up of spiral discs. Aims. Our main aim is to analyse simultaneously O/H and N/O abundance ratios in H ii regions in different radial positions of the discs in a large sample of spiral galaxies to obtain the slopes and the characteristic abundance ratios that can be related to their integrated properties. Methods. We analysed the optical spectra of individual selected H ii regions extracted from a sample of 350 spiral galaxies of the CALIFA survey. We calculated total O/H abundances and, for the first time, N/O ratios using the semi-empirical routine Hii-Chi-mistry, which, according to Pérez-Montero (2014, MNRAS, 441, 2663), is consistent with the direct method and reduces the uncertainty in the O/H derivation using N ii lines owing to the dispersion in the O/H-N/O relation. Then we performed linear fittings to the abundances as a function of the de-projected galactocentric distances. Results. The analysis of the radial distribution both for O/H and N/O in the non-interacting galaxies reveals that both average slopes are negative, but a non-negligible fraction of objects have a flat or even a positive gradient (at least 10% for O/H and 4% for N/O). The slopes normalised to the effective radius appear to have a slight dependence on the total stellar mass and the morphological type, as late low-mass objects tend to have flatter slopes. No clear relation is found, however, to explain the presence of inverted gradients in this sample, and there is no dependence between the average slopes and the presence of a bar. The relation between the resulting O/H and N/O linear fittings at the effective radius is much tighter (correlation coefficient ρs = 0.80) than between O/H and N/O slopes (ρs = 0.39) or for O/H and N/O in the individual H ii regions (ρs = 0.37). These O/H and N/O values at the effective radius also correlate very tightly (less than 0.03 dex of dispersion) with total luminosity and stellar mass. The relation with other integrated properties, such as star formation rate, colour, or morphology, can be understood only in light of the found relation with mass.
We present a detailed 2D study of the ionized ionized interstellar medium (ISM) of IZw18 using new Potsdam Multi-Aperture Spectrophotometer-integral field unit (PMAS-IFU) optical observations. IZw18 ...is a high-ionization galaxy which is among the most metal-poor starbursts in the local Universe. This makes IZw18 a local benchmark for understanding the properties most closely resembling those prevailing at distant starbursts. Our IFU aperture (∼1.4 × 1.4 kpc2) samples the entire IZw18 main body and an extended region of its ionized gas. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located close to the north-west knot and thereabouts. We detect a Wolf–Rayet feature near the north-west knot. We derive spatially resolved and integrated physical–chemical properties for the ionized gas in IZw18. We find no dependence between the metallicity indicator R23 and the ionization parameter (as traced by O iii/O ii) across IZw18. Over ∼0.30 kpc2, using the O iii λ4363 line, we compute T
eO iii values (∼15 000–25 000 K), and oxygen abundances are derived from the direct determinations of T
eO iii. More than 70 per cent of the higher-T
eO iii (≳22 000 K) spaxels are He iiλ4686-emitting spaxels too. From a statistical analysis, we study the presence of variations in the ISM physical–chemical properties. A galaxy-wide homogeneity, across hundreds of parsecs, is seen in O/H. Based on spaxel-by-spaxel measurements, the error-weighted mean of 12 + log(O/H) = 7.11 ± 0.01 is taken as the representative O/H for IZw18. Aperture effects on the derivation of O/H are discussed. Using our IFU data we obtain, for the first time, the IZw18 integrated spectrum.
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.
Abstract
In Montero-Dorta et al., we show that luminous red galaxies (LRGs) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at z ∼ 0.55 can be divided into two groups based on their ...star formation histories. So-called fast-growing LRGs assemble 80 per cent of their stellar mass at z ∼ 5, whereas slow-growing LRGs reach the same evolutionary state at z ∼ 1.5. We further demonstrate that these two subpopulations present significantly different clustering properties on scales of ∼1−30 Mpc. Here, we measure the mean halo mass of each subsample using the galaxy–galaxy lensing technique, in the ${\sim }190\deg ^2$ overlap of the LRG catalogue and the CS82 and CFHTLenS shear catalogues. We show that fast- and slow-growing LRGs have similar lensing profiles, which implies that they live in haloes of similar mass: $\log (M_{\rm halo}^{\rm fast}/h^{-1}\mathrm{M}_{{\odot }}) = 12.85^{+0.16}_{-0.26}$ and $\log (M_{\rm halo}^{\rm slow}/h^{-1}\mathrm{M}_{{\odot }}) =12.92^{+0.16}_{-0.22}$. This result, combined with the clustering difference, suggests the existence of galaxy assembly bias, although the effect is too subtle to be definitively proven, given the errors on our current weak-lensing measurement. We show that this can soon be achieved with upcoming surveys like DES.
ABSTRACT Extremely metal-poor (XMP) galaxies are defined to have a gas-phase metallicity smaller than a tenth of the solar value ( ). They are uncommon, chemically and possibly dynamically primitive, ...with physical conditions characteristic of earlier phases of the universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time, high electron temperature objects are selected; metals are a main coolant of the gas, so metal-poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788,677 spectra to select 1281 galaxies that have particularly intense O iiiλ4363 with respect to O iiiλ5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample has a mean stellar mass around , with the dust mass for typical star-forming regions. In agreement with previous findings, XMPs show a tendency to be tadpole-like or cometary. Their underlying stellar continuum corresponds to a fairly young stellar population ( ), although young and aged stellar populations coexist at the low-metallicity starbursts. About 10% of the XMPs show large N/O. Based on their location in constrained cosmological numerical simulations, XMPs have a strong tendency to appear in voids and to avoid galaxy clusters. The puzzling 2%-solar low-metallicity threshold exhibited by XMPs remains.
ABSTRACT Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers ...are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter halos. Although these predictions are unambiguous, the observational support has been indirect so far. Here, we report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local universe, taking the form of localized starbursts associated with gas having low metallicity. Detailed abundance analyses based on Gran Telescopio Canarias optical spectra of 10 XMPs show that the galaxy hosts have metallicities around 60% solar, on average, while the large star-forming regions that dominate their integrated light have low metallicities of some 6% solar. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr), the observed metallicity inhomogeneities are only possible if the metal-poor gas fell onto the disk recently. We analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. If this interpretation is correct, XMPs trace the cosmic web gas in their surroundings, making them probes to examine its properties.
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