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arXiv 1108.0933astro-ph.CO
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恒星爆发对z=2恒星形成的较小作用

The lesser role of starbursts for star formation at z=2

G. Rodighiero, E. Daddi, I. Baronchelli, A. Cimatti, A. Renzini, H. Aussel, P. Popesso, D. Lutz, P. Andreani, S. Berta, A. Cava, D. Elbaz, A. Feltre, A. Fontana… 展开作者

G. Rodighiero, E. Daddi, I. Baronchelli, A. Cimatti, A. Renzini, H. Aussel, P. Popesso, D. Lutz, P. Andreani, S. Berta, A. Cava, D. Elbaz, A. Feltre, A. Fontana, N. M. Forster Schreiber, A. Franceschini, R. Genzel, A. Grazian, C. Gruppioni, O. Ilbert, E. Le Floch, G. Magdis, M. Magliocchetti, B. Magnelli, R. Maiolino, H. McCracken, R. Nordon, A. Poglitsch, P. Santini, F. Pozzi, L. Riguccini, L. J. Tacconi, S. Wuyts, G. Zamorani

摘要:

已知两种主要的恒星形成模式控制着星系的生长:一种是相对稳定的盘状星系,定义了一个紧密的恒星形成率(SFR)-恒星质量序列,另一种是恒星暴模式,通常被解释为由合并驱动。这样的星暴星系是罕见的,但有更高的SFR,它是感兴趣的,以建立这两个模式的相对重要性。PACS/Herschel对整个COSMOS和GOODS-South场的观测,结合以前的光学/近红外数据,使我们能够首次准确地量化这两种模式对红移区间1.5<z<2.5的全球SFR密度的相对贡献,即,在恒星形成活动的宇宙高峰期在固定的恒星质量下,星系SFR的对数分布被高斯描述得很好,星暴星系只代表一个相对较小的偏差,这在SFR比主序星高出4倍以上时变得很明显。这样的星暴星系只占质量选择的恒星形成星系的2%,在z~2处只占宇宙SFR密度的10%。只有在SFR> 1000 M(sun)/yr的情况下,序列外源才对SFR密度有显著贡献(46+/-20%)。我们的结论是合并驱动的星爆在星系中恒星的形成中发挥了相对较小的作用,而它们可能代表了一个关键的阶段,对淬火的恒星形成和星系的形态转变。

英文摘要:

Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5<z<2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than 4 times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star forming galaxies and account for only 10% of the cosmic SFR density at z~2. Only when limited to SFR>1000M(sun)/yr, off-sequence sources significantly contribute to the SFR density (46+/-20%). We conclude that merger-driven starbursts play a relatively minor role for the formation of stars in galaxies, whereas they may represent a critical phase towards the quenching of star formation and morphological transformation in galaxies.

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