En México, la presencia de hongos fitopatógenos ocasiona severos daños en frutos de durazno (Prunus persica L.), después de la cosecha, causando disminución en la exportación de productos procesados ...y en vida de anaquel. El objetivo de este trabajo fue describir el rango de hospedantes de hongos foliares en frutos de manzano (Malus domestica Borkh), fresa (Fragaria spp.), ciruela (Prunus domestica L.), pera (Pyrus communis L.) y membrillo (Cydonia oblonga Mill.), y en hojas de variedades de durazno. Para la prueba de patogenicidad se utilizó la técnica de aspersión y las enfermedades se valoraron mediante la escala de severidad de 5 grados de 0 a ≥75 % de presencia de síntomas sobre el fruto y del 10 a ≥60% para hoja desprendida y porcentaje de incidencia. Se inocularon conidios de Fusarium spp, Alternaria spp, Epicoccum spp, Collectotrichum spp y Monilinia spp., en todos los frutos y las hojas de las variedades de durazno amarillo, prisco y blanco, con siete repeticiones, dejando un testigo con agua destilada estéril para cada uno de los tratamientos; se colocaron en cámara húmeda en condiciones asépticas, a 27°C ± 1 y se sometieron a regímenes de 14 horas oscuridad y 10 horas luz, por 4, 7, 10 y 12 días. Los datos se sometieron a un análisis de varianza utilizando la comparación de medias de Tukey (P≤0.05). La variedad amarillo de durazno presentó mayor susceptibilidad a todos los hongos, los cuales fueron patogénicos a los hospedantes con severidad de 0 a 97,14 %.
Abstract
Understanding the connection between nuclear activity and galaxy environment remains critical in constraining models of galaxy evolution. By exploiting the extensive cataloged data from the ...Galaxy and Mass Assembly survey, we identify a representative sample of 205 quasars at 0.1 <
z
< 0.35 and establish a comparison sample of galaxies, closely matched to the quasar sample in terms of both stellar mass and redshift. On scales <1 Mpc, the galaxy number counts and group membership of quasars appear entirely consistent with those of the matched galaxy sample. Despite this, we find that quasars are ∼1.5 times more likely to be classified as the group center, indicating a potential link between quasar activity and cold gas flows or galaxy interactions associated with rich group environments. On scales of ∼a few Mpc, the clustering strengths of both samples are statistically consistent, and beyond 10 Mpc, we find no evidence that quasars trace large-scale structures any more than the galaxy control sample. Both populations are found to prefer intermediate-density sheets and filaments to either very high-density environments or very low-density environments. This weak dependence of quasar activity on galaxy environment supports a paradigm in which quasars represent a phase in the lifetime of all massive galaxies and in which secular processes and a group-centric location are the dominant triggers of quasars at low redshift.
ABSTRACT We present a pilot analysis of the influence of galaxy stellar mass and cluster environment on the probability of slow rotation in 22 central galaxies at mean redshift z = 0.07. This ...includes new integral-field observations of five central galaxies selected from the Sloan Digital Sky Survey, observed with the SPIRAL integral-field spectrograph on the Anglo-Australian Telescope. The composite sample presented here spans a wide range of stellar masses, log( , and are embedded in halos ranging from groups to clusters, log( . We find a mean probability of slow rotation in our sample of P(SR) %. Our results show an increasing probability of slow rotation in central galaxies with increasing stellar mass. However, when we examine the dependence of slow rotation on host cluster halo mass, we do not see a significant relationship. We also explore the influence of cluster dominance on slow rotation in central galaxies. Clusters with low dominance are associated with dynamically younger systems. We find that cluster dominance has no significant effect on the probability of slow rotation in central galaxies. These results conflict with a paradigm in which halo mass alone predetermines central galaxy properties.
Here we present H i line and 20-cm radio continuum data of the nearby galaxy pair NGC 1512/1510 as obtained with the Australia Telescope Compact Array (ATCA). These are complemented by GALEX (Galaxy ...Evolution Explorer) ultraviolet (UV)-, SINGG Hα- and Spitzer mid-infrared images, allowing us to compare the distribution and kinematics of the neutral atomic gas with the locations and ages of the stellar clusters within the system. For the barred, double-ring galaxy NGC 1512 we find a very large H i disc, ∼four times its optical diameter, with two pronounced spiral/tidal arms. Both its gas distribution and the distribution of the star-forming regions are affected by gravitational interaction with the neighbouring blue compact dwarf galaxy NGC 1510. While the inner disc of NGC 1512 shows quite regular rotation, deviations are visible along the outer arms and at the position of NGC 1510. From the H i rotation curve of NGC 1512 we estimate a dynamical mass of Mdyn≳ 3 × 1011 M⊙, compared to an H i mass of MH i= 5.7 × 109 M⊙ (∼2 per cent Mdyn). The two most distant H i clumps, at radii of ∼80 kpc, show signs of star formation (SF) and are likely tidal dwarf galaxies (TDGs). Both lie along an extrapolation of the eastern-most H i arm, with the most compact H i cloud located at the tip of the arm. The 20-cm radio continuum map indicates extended SF activity not only in the central regions of both galaxies but also in between them. SF in the outer disc of NGC 1512 is revealed by deep optical- and two-colour UV images. Using the latter we determine the properties of ≳200 stellar clusters and explore their correlation with dense H i clumps in the even larger 2X-H i disc. Outside the inner star-forming ring of NGC 1512, which must contain a large reservoir of molecular gas, H i turns out to be an excellent tracer of SF activity. The multiwavelength analysis of the NGC 1512/1510 system, which is probably in the first stages of a minor merger having started ∼400 Myr ago, links stellar and gaseous galaxy properties on scales from 1 to 100 kpc.
We demonstrate that the space formed by the star formation rate (SFR), gas-phase metallicity (Z), and stellar mass (M sub(sstarf)) can be reduced to a plane, as first proposed by Lara-Lopez et al. We ...study three different approaches to find the best representation of this 3D space, using a principal component analysis (PCA), a regression fit, and binning of the data. The PCA shows that this 3D space can be adequately represented in only two dimensions, i.e., a plane. We find that the plane that minimizes the chi super(2) for all variables, and hence provides the best representation of the data, corresponds to a regression fit to the stellar mass as a function of SFR and Z, M sub(sstarf) = f(Z, SFR). We find that the distribution resulting from the median values in bins for our data gives the highest ?2. We also show that the empirical calibrations to the oxygen abundance used to derive the Fundamental Metallicity Relation have important limitations, which contribute to the apparent inconsistencies. The main problem is that these empirical calibrations do not consider the ionization degree of the gas. Furthermore, the use of the N2 index to estimate oxygen abundances cannot be applied for 12 + log(O/H) gap 8.8 because of the saturation of the NII lambda6584 line in the high-metallicity regime. Finally, we provide an update of the Fundamental Plane derived by Lara-Lopez et al.
We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star ...formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.
We present a study of the properties of star-forming regions within a sample of seven Wolf-Rayet (WR) galaxies. We analyse their morphologies, colours, star-formation rates (SFRs), metallicities and ...stellar populations, combining broad-band and narrow-band photometry with low-resolution optical spectroscopy. The UBVRI observations were made with the 2-m HCT (Himalayan Chandra Telescope) and 1-m ARIES telescope. The spectroscopic data were obtained using the Hanle Faint Object Spectrograph Camera (HFOSC) mounted on the 2-m HCT. The observed galaxies are NGC 1140, IRAS 07164+5301, NGC 3738, UM 311, NGC 6764, NGC 4861 and NGC 3003. The optical spectra were used to search for the faint WR features, to confirm that the ionization of the gas is caused by the massive stars, and to quantify the oxygen abundance of each galaxy using several independent empirical calibrations. We detected broad features originating in WR stars in NGC 1140 and 4861 and used them to derive the massive star populations. For these two galaxies we also derived the oxygen abundance using a direct estimation of the electron temperature of the ionized gas. The N/O ratio in NGC 4861 is ∼0.25-0.35 dex higher than expected, which may be a consequence of the chemical pollution by N-rich material released by WR stars. Using our Hα images we identified tens of star-forming regions within these galaxies, for which we derived the SFR. Our Hα-based SFR usually agrees with the SFR computed using the far-infrared and the radio-continuum flux. For all regions we found that the most recent star-formation event is 3-6 Myr old. We used the optical broad-band colours in combination with Starburst99 models to estimate the internal reddening and the age of the dominant underlying stellar population within all these regions. Knots in NGC 3738, 6764 and 3003 generally show the presence of an important old (400-1000 Myr) stellar population. However, the optical colours are not able to detect stars older than 20-50 Myr in the knots of the other four galaxies. This fact suggests that both the current intensity of the starbursts and the star-formation activity have been ongoing for at least a few tens of millions of years in these objects.
Abstract We use deep spectroscopy from the SAMI Galaxy Survey to explore the precision of the fundamental plane of early-type galaxies (FP) as a distance indicator for future single-fibre ...spectroscopy surveys. We study the optimal trade-off between sample size and signal-to-noise ratio (SNR), and investigate which additional observables can be used to construct hyperplanes with smaller intrinsic scatter than the FP. We add increasing levels of random noise (parametrised as effective exposure time) to the SAMI spectra to study the effect of increasing measurement uncertainties on the FP- and hyperplane-inferred distances. We find that, using direct-fit methods, the values of the FP and hyperplane best-fit coefficients depend on the spectral SNR, and reach asymptotic values for a mean 〈SNR〉 = 40 Å−1. As additional variables for the FP we consider three stellar-population observables: light-weighted age, stellar mass-to-light ratio and a novel combination of Lick indices (Iage). For a 〈SNR〉 = 45 Å−1 (equivalent to 1-hour exposure on a 4-m telescope), all three hyperplanes outperform the FP as distance indicators. Being an empirical spectral index, Iage avoids the model-dependent uncertainties and bias underlying age and mass-to-light ratio measurements, yet yields a 10 per cent reduction of the median distance uncertainty compared to the FP. We also find that, as a by-product, the Iage hyperplane removes most of the reported environment bias of the FP. After accounting for the different signal-to-noise ratio, these conclusions also apply to a 50 times larger sample from SDSS-III. However, in this case, only age removes the environment bias.
From a volume-limited sample of 45 542 galaxies and 6000 groups with z ≤ 0.213, we use an adapted minimal spanning tree algorithm to identify and classify large-scale structures within the Galaxy And ...Mass Assembly (GAMA) survey. Using galaxy groups, we identify 643 filaments across the three equatorial GAMA fields that span up to 200 h
−1 Mpc in length, each with an average of eight groups within them. By analysing galaxies not belonging to groups, we identify a secondary population of smaller coherent structures composed entirely of galaxies, dubbed 'tendrils' that appear to link filaments together, or penetrate into voids, generally measuring around 10 h
−1 Mpc in length and containing on average six galaxies. Finally, we are also able to identify a population of isolated void galaxies. By running this algorithm on GAMA mock galaxy catalogues, we compare the characteristics of large-scale structure between observed and mock data, finding that mock filaments reproduce observed ones extremely well. This provides a probe of higher order distribution statistics not captured by the popularly used two-point correlation function.
ABSTRACT The metallicity of the progenitor system producing a type Ia supernova (SN Ia) could play a role in its maximum luminosity, as suggested by theoretical predictions. We present an ...observational study to investigate if such a relationship exists. Using the 4.2 m William Herschel Telescope (WHT) we have obtained intermediate-resolution spectroscopy data of a sample of 28 local galaxies hosting SNe Ia, for which distances have been derived using methods independent of those based on SN Ia parameters. From the emission lines observed in their optical spectra, we derived the gas-phase oxygen abundance in the region where each SN Ia exploded. Our data show a trend, with an 80% of chance not being due to random fluctuation, between SNe Ia absolute magnitudes and the oxygen abundances of the host galaxies, in the sense that luminosities tend to be higher for galaxies with lower metallicities. This result seems likely to be in agreement with both the theoretically expected behavior and with other observational results. This dependence MB-Z might induce systematic errors when it is not considered when deriving SNe Ia luminosities and then using them to derive cosmological distances.
PDF
