The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
- Harvard-Smithsonian Ctr. Astrophys.
- Northwestern U.
- Chicago U.
- Ohio U.
- Fermilab
- Pennsylvania U.
- Syracuse U.
- Chicago U., Astron. Astrophys. Ctr.
- Fermilab; Chicago U., KICP
- Chicago U., EFI; Chicago U., KICP
- Columbia U.
- Baltimore, Space Telescope Sci.; Johns Hopkins U.
- Brandeis U.; Fermilab
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 $$\gtrsim 10\,\mathrm{Gyr}$$ ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 $${M}_{\odot }$$ yr(−)(1), which we convert into a binary merger timescale probability distribution. We find a median merger timescale of $${11.2}_{-1.4}^{+0.7}$$ Gyr, with a 90% confidence range of $$6.8\mbox{--}13.6\,\mathrm{Gyr}$$. This in turn indicates an initial binary separation of $$\approx 4.5$$ $${R}_{\odot }$$, 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 (0.64r ( )e( )) from the center of NGC 4993 and to place a limit of $${M}_{r}\gtrsim -7.2$$ 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.
- Research Organization:
- Northwestern U.; Harvard-Smithsonian Ctr. Astrophys.; Columbia U.; Johns Hopkins U.; Chicago U., EFI; Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Pennsylvania U.; Chicago U., Astron. Astrophys. Ctr.; Baltimore, Space Telescope Sci.; Chicago U., KICP; Brandeis U.; Ohio U.; Syracuse U.; Chicago U.
- Sponsoring Organization:
- US Department of Energy
- Grant/Contract Number:
- AC02-07CH11359
- OSTI ID:
- 1409349
- Report Number(s):
- FERMILAB-PUB-17-473-A-AE-CD; oai:inspirehep.net:1630798; arXiv:1710.05458
- Journal Information:
- Astrophys.J.Lett., Journal Name: Astrophys.J.Lett. Journal Issue: 2 Vol. 848
- Country of Publication:
- United States
- Language:
- English
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