768 research outputs found

    The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies

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    Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically-selected samples of galaxies is inferred. We implement an efficient and optimised algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our re-analysis of the ATLAS3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the "spin" parameter proxy Lambda_Re. In particular, low spin systems have a higher occurrence of triaxiality, while high spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multi-merger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations.Comment: 15 pages, 11 figures, MNRAS in prin

    The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry

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    In order to determine the causes of kinematic asymmetry in the Hα\alpha gas in the SAMI Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved Hα\alpha velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry (vasym\overline{v_{asym}}) in nearby galaxies and environmental and stellar mass data from the GAMA survey. {We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with log(M/M)>10.0\mathrm{\log(M_*/M_\odot)}>10.0, but there is no significant correlation for galaxies with log(M/M)<10.0\mathrm{\log(M_*/M_\odot)}<10.0. Moreover, low mass galaxies (log(M/M)<9.0\mathrm{\log(M_*/M_\odot)}<9.0) have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low mass galaxies.} We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low mass galaxies. High gas fraction is linked to high σmV\frac{\sigma_{m}}{V} (where σm\sigma_m is Hα\alpha velocity dispersion and VV the rotation velocity), which is strongly correlated with vasym\overline{v_{asym}}, and galaxies with log(M/M)<9.0\log(M_*/M_\odot)<9.0 have offset σmV\overline{\frac{\sigma_{m}}{V}} from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with log(M/M)<9.0\log(M_*/M_\odot)<9.0. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.Comment: 15 pages, 20 figure

    The SHOX gene and the short stature. Roundtable on diagnosis and treatment of short stature due to SHOX haploinsufficiency: How genetics, radiology and anthropometry can help the pediatrician in the diagnostic process padova (April 20th, 2011)

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    The growth of the human body depends from a complex interaction between nutritional, environmental and hormonal factors and by a large number of different genes. One of these genes, short stature homeobox (SHOX), is believed to play a major role in growth. SHOX haploinsufficiency is associated with a wide spectrum of conditions, all characterized growth failure such as Leri-Weill dyschondrosteosis , Turner syndrome, short stature with subtle auxological and radiological findings and the so called “idiopathic short stature” (short stature with no specific findings other than growth failure). The document was prepared by a multidisciplinary team (paediatric endocrinologists, paediatrician, radiologist, geneticist and epidemiologist) to focus on the investigation of children with suspected SHOX- deficiency (SHOX-D) for an early identification and a correct diagnostic work - up of this genetic disorder. On the basis of a number of screening studies, SHOX-D appears to be a relatively frequent cause of short stature. The following recommendations were suggested by our multidisciplinary team: (i) a careful family history, measurements of body proportions and detection of any dysmorphic features are important for the suspect of a genetic disorder ,(ii)the presence of any combination of the following physical findings, such as reduced arm span/ height ratio, increased sitting height/height ratio, above average BMI, Madelung deformity, cubitus valgus, short or bowed forearm, dislocation of the ulna at the elbow, or the appearance of muscular hypertrophy, should prompt the clinician to obtain a molecular analysis of the SHOX region, (iii) it is of practical importance to recognise early or mild signs of Madelung deformity on hand and wrist radiographs, (iv) growth hormone ,after stimulation test, is usually normal . However, treatment with rhGH may improve final adult height; the efficacy of treatment is similar to that observed in those treated for Turner syndrome

    The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types

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    We take advantage of the first data from the Sydney-AAO Multi-object Integral field (SAMI) Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass (MM_{*}) to internal velocity quantified by the S0.5S_{0.5} parameter, which combines the contribution of both dispersion (σ\sigma) and rotational velocity (VrotV_{rot}) to the dynamical support of a galaxy (S0.5=0.5Vrot2+σ2S_{0.5}=\sqrt{0.5V_{rot}^{2}+\sigma^{2}}). Our results are independent of the baryonic component from which σ\sigma and VrotV_{rot} are estimated, as the S0.5S_{0.5} of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical MM_{*} vs. VrotV_{rot} and MM_{*} vs. σ\sigma relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once VrotV_{rot} and σ\sigma are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5<log(M/M)<<log(M_{*}/M_{\odot})<11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter
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