The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

Journal Article · Mon Oct 16 04:00:00 UTC 2017 · Astrophys.J.Lett.

DOI: https://doi.org/10.3847/2041-8213/aa9055 · OSTI ID:1409349

Blanchard, P. K. ^[1]; Berger, E.  ^[1]; Fong, W.  ^[2]; Nicholl, M.  ^[1]; Leja, J.  ^[1]; Conroy, C.  ^[1]; Alexander, K. D.  ^[1]; Margutti, R. ^[2]; Williams, P. K.G. ^[1]; Doctor, Z. ^[3]; Chornock, R. ^[4]; Villar, V. A. ^[1]; Cowperthwaite, P. S. ^[1]; Annis, J.  ^[5]; Brout, D.  ^[6]; Brown, D. A.  ^[7]; Chen, H.-Y. ^[8]; Eftekhari, T. ^[1]; Frieman, J. A.  ^[9]; Holz, D. E. ^[10] ; Metzger, B. D. ^[11]; Rest, A. ^[12]; Sako, M. ^[6]; Soares-Santos, M.  ^[13]

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1. Harvard-Smithsonian Ctr. Astrophys.
2. Northwestern U.
3. Chicago U.
4. Ohio U.
5. Fermilab
6. Pennsylvania U.
7. Syracuse U.
8. Chicago U., Astron. Astrophys. Ctr.
9. Fermilab; Chicago U., KICP
10. Chicago U., EFI; Chicago U., KICP
11. Columbia U.
12. Baltimore, Space Telescope Sci.; Johns Hopkins U.
13. 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