The study of the chemical abundances of HII regions in polar ring galaxies and their implications for the evolutionary scenario of these systems has been a step forward both in tracing the formation history of the galaxy and giving hints on the mechanisms at work during the building of disk by cold accretion process. It's now important to establish whether such results are typical for the class of polar disk galaxies as whole. The present work aims at checking the cold accretion of gas through a "cosmic filament" as a possible scenario for the formation of the polar structures in UGC7576 and UGC9796. If these form by cold accretion, we expect the HII regions abundances and metallicities to be lower than those of same-luminosity spiral disks, with values of the order of Z ~ 1/10 Zsun, as predicted by cosmological simulations. We have used deep long-slit spectra, obtained with DOLORES@TNG in the optical wavelengths, of the brightest HII regions associated with the polar structures to derive their chemical abundances and star formation rate. We used the "Empirical methods", based on the intensities of easily observable lines, to derive the oxygen abundance 12+log(O/H) of both galaxies. Such values are compared with those typical for different morphological galaxy types of comparable luminosity. The average metallicity values for UGC7576 and UGC9796 are Z = 0.4 Zsun and Z = 0.1 Zsun respectively. Both values are lower than those measured for ordinary spirals of similar luminosity and UGC7576 presents no metallicity gradient along the polar structure. These data, toghether with other observed features, available for the two PRGs in previous works, are compared with the predictions of simulations of tidal accretion, cold accretion and merging, to disentangle between these scenarios.
获得了M101星盘中28个H Ⅱ区的新光谱，得到了10条[O Ⅲ]λ4363极光线的新探测。从这些数据中测量的氧丰度梯度，结合以前的观测，显示出沿着星系西侧弧的局部分散度为0.15+/-0.03 dex，而盘的其余部分的分散度为0.08+/-0.01 dex。我们样本中的一个H I I区域（H27）的氧丰度明显低于周围星系，而另一个相对较近的H I I区域（H128）在银河系中的位置已经被认为具有高氧丰度。这些结果代表了边际证据的存在适度偏离化学丰度均匀性的星际介质的M101。使用各种各样的强线丰度指标，我们发现没有证据表明在整个星系盘的氧丰度的显着大规模的方位角变化。
Testing subhalo abundance matching with galaxy kinematics
University of Oxford（牛津大学）；University of Cambridge（剑桥大学）；University of Manchester（曼彻斯特大学）；University of Portsmouth（朴茨茅斯大学）；University of the Western Cape（西开普大学）
Testing the key role of the stellar mass-halo mass relation in galaxy merger rates and morphologies via DECODE, a novel Discrete statistical sEmi-empiriCal mODEl
The Structural Abundance Crisis of Massive Galaxies in Current Cosmological Simulations
Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；International Centre for Radio Astronomy Research, University of Western Australia（西澳大利亚大学国际射电天文学研究中心）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
