The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
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DOI：
10.3847/2041-8213/aa9055
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发表时间：
2017-10
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通讯作者：
P. Blanchard;E. Berger;W. Fong;M. Nicholl;J. Leja;C. Conroy;K. Alexander;R. Margutti;P. G. Williams;Zoheyr Doctor;R. Chornock;V. Villar;P. Cowperthwaite;J. Annis;D. Brout;D. Brown;H.-Y. Chen;T. Eftekhari;J. Frieman;D. Holz;B. Metzger;A. Rest;M. Sako;M. Soares-Santos
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作者：
P. Blanchard;E. Berger;W. Fong;M. Nicholl;J. Leja;C. Conroy;K. Alexander;R. Margutti;P. G. Williams;Zoheyr Doctor;R. Chornock;V. Villar;P. Cowperthwaite;J. Annis;D. Brout;D. Brown;H.-Y. Chen;T. Eftekhari;J. Frieman;D. Holz;B. Metzger;A. Rest;M. Sako;M. Soares-Santos
本文介绍了GW 170817的宿主星系NGC 4993的性质，GW 170817是中子星星（BNS）系统合并的第一个引力波（GW）事件，也是第一个与电磁（EM）系统合并的引力波（GW）事件。我们使用档案测光和新的光学/近红外成像和光谱，连同恒星人口合成模型来推断宿主星系的全球性质。我们推断星星的形成历史在年前达到峰值，随后的指数下降导致当前星星形成率很低，为0.01 yr−1，我们将其转换为二元合并时标概率分布。我们发现合并的中位时间尺度为Gyr，90%的置信范围为。这反过来又表明了一个初始的二元分离，相当于银河系BNS系统的推断值。我们还使用新的和存档的哈勃太空望远镜图像来测量NGC 4993中心2.1 kpc（0.64re）的光学对应物的投影偏移，并对任何预先存在的发射进行限制，这排除了球状星团光度函数中较亮的一半。最后，系统的年龄和偏移表明它经历了一次适度的纳塔尔踢，上限为200 km s−1。未来对BNS合并的GW-EM观测将能够测量它们的人口延迟时间分布，这将直接告知它们作为宇宙中r过程富集的主要来源的可行性。
We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational-wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 yr−1, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of Gyr, with a 90% confidence range of . This in turn indicates an initial binary separation of , comparable to the inferred values for Galactic BNS systems. We also use new and archival Hubble Space Telescope images to measure a projected offset of the optical counterpart of 2.1 kpc (0.64re) from the center of NGC 4993 and to place a limit of mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of ∼200 km s−1. Future GW–EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of r-process enrichment in the universe.