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arXiv 1807.02534astro-ph.GA
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星系和质量集合体(GAMA):0.02 < z < 0.3时大质量超紧星系的精确数密度和环境

Galaxy and Mass Assembly (GAMA): Accurate number densities & environments of massive ultracompact galaxies at 0.02 < z < 0.3

F. Buitrago, I. Ferreras, L. S. Kelvin, I. K. Baldry, L. Davies, J. Angthopo, S. Khochfar, A. M. Hopkins, S. P. Driver, S. Brough, J. Sabater, C. J. Conselice, … 展开作者

F. Buitrago, I. Ferreras, L. S. Kelvin, I. K. Baldry, L. Davies, J. Angthopo, S. Khochfar, A. M. Hopkins, S. P. Driver, S. Brough, J. Sabater, C. J. Conselice, J. Liske, B. W. Holwerda, M. N. Bremer, S. Phillipps, A. R. Lopez-Sanchez, A. W. Graham

摘要:

大质量超紧星系(MUG)在z=2-3时很常见,但在附近的宇宙中非常罕见。模拟预测,少数幸存的MUG应该居住在星系团中,其大的相对速度阻止它们合并,从而保持其原始属性(即恒星星族,质量,大小和动力学状态)。我们利用高完整性,大面积光谱GAMA调查,并与KiDS和VIKING调查的更深入成像进行补充。我们发现了一组22个真正的MUG,定义为具有高恒星质量(> 8 × 10^10 M_Sun)和紧凑的尺寸(R_e<2 Kpc),在0.02 < z < 0.3。根据典型的质量不确定性,另外一组7个较低质量的天体(6x10^10 < M_star/M_Sun < 8x10^10)也是潜在的候选者。在低红移(z < 0.3)下,MUG的共动数密度被限制在$(1.0 \pm 0.4)x 10^-6 Mpc^-3,与星系演化模型一致。然而,我们发现一个混合分布的老星系和年轻星系,与四分之一的样本代表(旧)遗物。MUG主要具有早期/膨胀盘的形态(Sersic指数1&lt;n&lt;2.5),具有高的恒星表面密度(<Sigma_e>~ 10^10 M_Sun Kpc^-2)。有趣的是,很大一部分的特征是亲密的同伴-至少在投影中-表明许多(但不是全部)居住在群体的中心区域。晕质量表明这些星系居住在平均质量的群体中。由于MUG被发现几乎均匀地分布在不同质量的环境中,它们的相对比例在更大质量的超密度中更高,这与其中一些星系在早期落入这些区域的预期相匹配。然而,必须有另一个通道,导致这些星系中的一些星系的合并历史异常低,因为我们的样本显示了一些不居住在特别密集的环境中的物体。(节略)

英文摘要:

Massive Ultracompact Galaxies (MUGs) are common at z=2-3, but very rare in the nearby Universe. Simulations predict that the few surviving MUGs should reside in galaxy clusters, whose large relative velocities prevent them from merging, thus maintaining their original properties (namely stellar populations, masses, sizes and dynamical state). We take advantage of the high-completeness, large-area spectroscopic GAMA survey, complementing it with deeper imaging from the KiDS and VIKING surveys. We find a set of 22 bona-fide MUGs, defined as having high stellar mass (>8x10^10 M_Sun) and compact size (R_e<2 Kpc) at 0.02 < z < 0.3. An additional set of 7 lower-mass objects (6x10^10 < M_star/M_Sun < 8x10^10) are also potential candidates according to typical mass uncertainties. The comoving number density of MUGs at low redshift (z < 0.3) is constrained at $(1.0\pm 0.4)x 10^-6 Mpc^-3, consistent with galaxy evolution models. However, we find a mixed distribution of old and young galaxies, with a quarter of the sample representing (old) relics. MUGs have a predominantly early/swollen disk morphology (Sersic index 1<n<2.5) with high stellar surface densities (<Sigma_e> ~ 10^10 M_Sun Kpc^-2). Interestingly, a large fraction feature close companions -- at least in projection -- suggesting that many (but not all) reside in the central regions of groups. Halo masses show these galaxies inhabit average-mass groups. As MUGs are found to be almost equally distributed among environments of different masses, their relative fraction is higher in more massive overdensities, matching the expectations that some of these galaxies fell in these regions at early times. However, there must be another channel leading some of these galaxies to an abnormally low merger history because our sample shows a number of objects that do not inhabit particularly dense environments. (abridged)

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