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Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993

Palmese, A. and Eifler, T. F. (2017) Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993. Astrophysical Journal Letters, 849 (2). Art. No. L34. ISSN 2041-8213.

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We present a study of NGC 4993, the host galaxy of the GW170817 gravitational-wave event, the GRB 170817A short gamma-ray burst (sGRB), and the AT 2017gfo kilonova. We use Dark Energy Camera imaging, AAT spectra, and publicly available data, relating our findings to binary neutron star (BNS) formation scenarios and merger delay timescales. NGC 4993 is a nearby early-type galaxy, with an i-band Sérsic index n = 4.0 and low asymmetry (A = 0.04 ± 0.01). These properties are unusual for sGRB hosts. However, NGC 4993 presents shell-like structures and dust lanes indicative of a recent galaxy merger, with the optical transient located close to a shell. We constrain the star formation history (SFH) of the galaxy assuming that the galaxy merger produced a star formation burst, but find little to no ongoing star formation in either spatially resolved broadband SED or spectral fitting. We use the best-fit SFH to estimate the BNS merger rate in this type of galaxy, as R^(gal)_(NSM) = 5.7^(+0.57)_(-3.3) x 10^(-6) yr^(-1). If star formation is the only considered BNS formation scenario, the expected number of BNS mergers from early-type galaxies detectable with LIGO during its first two observing seasons is 0.038^(+0.004)_(-0.022), as opposed to ~0.5 from all galaxy types. Hypothesizing that the binary formed due to dynamical interactions during the galaxy merger, the subsequent time elapsed can constrain the delay time of the BNS coalescence. By using velocity dispersion estimates and the position of the shells, we find that the galaxy merger occurred t_(mer) ≾ 200 Myr prior to the BNS coalescence.

Item Type:Article
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Alternate Title:DECam and DES perspective of the GW170817 host, NGC 4993: indication for dynamically-driven formation of binary neutron star in early type galaxies
Additional Information:© 2017 The American Astronomical Society. Received 2017 October 18; revised 2017 October 25; accepted 2017 October 25; published 2017 November 9. Funding for the DES Projects has been provided by the DOE and NSF (USA), MEC/MICINN/MINECO (Spain), STFC(UK), HEFCE (UK), NCSA (UIUC), KICP (U. Chicago), CCAPP (Ohio State), MIFPA (Texas A&M), CNPQ, FAPERJ, FINEP (Brazil), DFG (Germany), and the Collaborating Institutions in the Dark Energy Survey. The Collaborating Institutions are Argonne Lab, UC Santa Cruz, University of Cambridge, CIEMAT-Madrid, University of Chicago, University College London, DES-Brazil Consortium, University of Edinburgh, ETH Zürich, Fermilab, University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona, Lawrence Berkeley Lab, LMU München and the associated Excellence Cluster Universe, University of Michigan, NOAO, University of Nottingham, Ohio State University, University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sussex, Texas A&M University, and the OzDES Membership Consortium. Based in part on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The DES Data Management System is supported by the NSF under grant numbers AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. This Letter has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this Letter, or allow others to do so, for United States Government purposes. A.P., W.H., and O.L. are supported by ERC Advanced Grant FP7/291329. Based in part on data acquired through the Australian Astronomical Observatory. Based on data obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts.
Funding AgencyGrant Number
Department of Energy (DOE)UNSPECIFIED
Ministerio de Educación y Ciencia (MEC)UNSPECIFIED
Ministerio de Ciencia e Innovación (MCINN)UNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)UNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Higher Education Funding Council for EnglandUNSPECIFIED
National Center for Supercomputing Applications (NCSA) UNSPECIFIED
Kavli Institute for Cosmological Physics (KICP)UNSPECIFIED
Center of Cosmology and Astro Particle Physics (CCAPP)UNSPECIFIED
Mitchell Institute for Fundamental Physics and Astronomy (MIFPA)UNSPECIFIED
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)UNSPECIFIED
Financiadora de Estudos e Projetos (FINEP)UNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2015-71825
Ministerio de Economía, Industria y Competitividad (MINECO)ESP2015-66861
Ministerio de Economía, Industria y Competitividad (MINECO)FPA2015-68048
Centro de Excelencia Severo OchoaSEV-2016-0588
Centro de Excelencia Severo OchoaSEV-2016-0597
Ministerio de Economía, Industria y Competitividad (MINECO)MDM-2015-0509
European Regional Development FundUNSPECIFIED
Generalitat de CatalunyaUNSPECIFIED
European Research Council (ERC)240672
European Research Council (ERC)291329
European Research Council (ERC)306478
Australian Research CouncilCE110001020
Department of Energy (DOE)DE-AC02-07CH11359
European Research Council (ERC)291329
Subject Keywords:galaxies: individual (NGC 4993) – galaxies: evolution – galaxies: structure – gravitational waves
Issue or Number:2
Record Number:CaltechAUTHORS:20171114-153319090
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Official Citation:A. Palmese et al 2017 ApJL 849 L34
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83207
Deposited By: Tony Diaz
Deposited On:15 Nov 2017 00:34
Last Modified:03 Oct 2019 19:03

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