Colour jumps across the spiral arms of Hubble Ultra Deep Field galaxies

We have measured, at various wavelengths, the spiral arm pitch angles of a sample of distant spiral galaxies from the Hubble Space Telescope eXtreme Deep Field (XDF). According to density wave theory, we should detect colour jumps from red-to-blue across the spiral arms. Colour jumps are a consequence of large-scale shocks, which also generate the classic blue-to-red age/colour gradients, and have only been detected until now in nearby spiral galaxies. Our results indicate that colour jumps and gradients have been occurring in distant galaxies for at least the last 8 Gyr, in agreement with density wave theory.Comment: Accepted for publication in MNRA

Effects of Non-Circular Motions on Azimuthal Color Gradients

Assuming that density waves trigger star formation, and that young stars preserve the velocity components of the molecular gas where they are born, we analyze the effects that non-circular gas orbits have on color gradients across spiral arms. We try two approaches, one involving semi-analytical solutions for spiral shocks, and another with magnetohydrodynamic (MHD) numerical simulation data. We find that, if non-circular motions are ignored, the comparison between observed color gradients and stellar population synthesis models would in principle yield pattern speed values that are systematically too high for regions inside corotation, with the difference between the real and the measured pattern speeds increasing with decreasing radius. On the other hand, image processing and pixel averaging result in systematically lower measured spiral pattern speed values, regardless of the kinematics of stellar orbits. The net effect is that roughly the correct pattern speeds are recovered, although the trend of higher measured $\Omega_p$ at lower radii (as expected when non-circular motions exist but are neglected) should still be observed. We examine the Martinez-Garcia et al. (2009) photometric data and confirm that this is indeed the case. The comparison of the size of the systematic pattern speed offset in the data with the predictions of the semi-analytical and MHD models corroborates that spirals are more likely to end at Outer Lindblad Resonance, as these authors had already found.Comment: 32 pages, 15 figures, accepted to Ap

The relation between dynamics and star formation in barred galaxies

We analyze optical and near-infrared data of a sample of 11 barred spiral galaxies, in order to establish a connection between star formation and bar/spiral dynamics. We find that 22 regions located in the bars, and 20 regions in the spiral arms beyond the end of the bar present azimuthal color/age gradients that may be attributed to star formation triggering. Assuming a circular motion dynamic model, we compare the observed age gradient candidates with stellar populations synthesis models. A link can then be established with the disk dynamics that allows us to obtain parameters like the pattern speed of the bar or spiral, as well as the positions of resonance radii. We subsequently compare the derived pattern speeds with those expected from theoretical and observational results in the literature (e.g., bars ending near corotation). We find a tendency to overestimate bar pattern speeds derived from color gradients in the bar at small radii, away from corotation; this trend can be attributed to non-circular motions of the young stars born in the bar region. In spiral regions, we find that ~ 50% of the color gradient candidates are "inverse", i.e., with the direction of stellar aging contrary to that of rotation. The other half of the gradients found in spiral arms have stellar ages that increase in the same sense as rotation. Of the 9 objects with gradients in both bars and spirals, six (67%) appear to have a bar and a spiral with similar Omega_p, while three (33%) do not.Comment: Accepted for publication in Ap

Natural and artificial feeding management before weaning promote different rumen microbial colonization but not differences in gene expression levels at the rumen epithelium of newborn goats

The aim of this work was to evaluate the effect of feeding management during the first month of life (natural with the mother, NAT, or artificial with milk replacer, ART) on the rumen microbial colonization and the host innate immune response. Thirty pregnant goats carrying two fetuses were used. At birth one kid was taken immediately away from the doe and fed milk replacer (ART) while the other remained with the mother (NAT). Kids from groups received colostrum during first 2 days of life. Groups of four kids (from ART and NAT experimental groups) were slaughtered at 1, 3, 7, 14, 21 and 28 days of life. On the sampling day, after slaughtering, the rumen content was sampled and epithelial rumen tissue was collected. Pyrosequencing analyses of the bacterial community structure on samples collected at 3, 7, 14 and 28 days showed that both systems promoted significantly different colonization patterns (P = 0.001). Diversity indices increased with age and were higher in NAT feeding system. Lower mRNA abundance was detected in TLR2, TLR8 and TLR10 in days 3 and 5 compared to the other days (7, 14, 21 and 28). Only TLR5 showed a significantly different level of expression according to the feeding system, presenting higher mRNA abundances in ART kids. PGLYRP1 showed significantly higher abundance levels in days 3, 5 and 7, and then experienced a decline independently of the feeding system. These observations confirmed a highly diverse microbial colonisation from the first day of life in the undeveloped rumen, and show that the colonization pattern substantially differs between pre-ruminants reared under natural or artificial milk feeding systems. However, the rumen epithelial immune development does not differentially respond to distinct microbial colonization patterns.publishersversionPeer reviewe