Draft version September 27, 2017 Preprint typeset using LATEX style AASTeX6 v. 1.0 SPATIALLY RESOLVED MANGA OBSERVATIONS OF THE HOST GALAXY OF SUPERLUMINOUS SUPERNOVA 2017EGM Ting-Wan Chen (sw,) 1, Patricia Schady1, Lin Xiao2, J.J. Eldridge2, Tassilo Schweyer1, Chien-Hsiu Lee (N見修) 3, Po-Chieh Yu (俞伯傑) 4, Stephen J. Smartt5 and Cosimo Inserra6 1Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748, Garching, Germany; [email protected] 2Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand 3Subaru Telescope National Astronomical Observatory of Japan, 650 N Aohoku Pl., Hilo, HI 96720, USA 4Graduate Institute of Astronomy, National Central University, No. 300, Zhongda Rd., Zhongli Dist., Taoyuan City 32001, Taiwan 5Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK 6Department of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK ABSTRACT Superluminous supernovae (SLSNe) are found predominantly in dwarf galaxies, indicating that their progenitors have a low metallicity. However, the most nearby SLSN to date, SN 2017egm, occurred in the spiral galaxy NGC 3191, which has a relatively high stellar mass and correspondingly high metallicity. In this paper, we present detailed analysis of the nearby environment of SN 2017egm using MaNGA IFU data, which provides spectral data on kiloparsec scales. From the velocity map we find no evidence that SN 2017egm occurred within some intervening satellite galaxy, and at the SN position most metallicity diagnostics yield a solar and above solar metallicity (12 + log (O=H) ∼ 8:8 − 9:1). Additionally we measure a small Hα equivalent width (EW) at the SN position of just 34 Å, which is one of the lowest EWs measured at any SLSN or Gamma-Ray Burst position, and indicative of the progenitor star being comparatively old. We also compare the observed properties of NGC 3191 with other SLSN host galaxies. The solar-metallicity environment at the position of SN 2017egm presents a challenge to our theoretical understanding, and our spatially resolved spectral analysis provides further constraints on the progenitors of SLSNe. Keywords: supernovae:general — supernovae:individual (SN 2017egm), galaxies:general — galax- ies:individual (NGC 3191) 1. INTRODUCTION larger sSFR, it is difficult to disentangle the relative impor- Superluminous supernovae (SLSNe)1 have been discov- tance of these properties towards the formation of SLSNe ered in recent wide field, untargeted surveys (e.g. Quimby (Perley et al. 2016; Chen et al. 2017a). From the ejecta et al. 2011). They are 100 times brighter (absolute mag- masses (Nicholl et al. 2015), and oxygen masses in the nitude of −21; Gal-Yam 2012) than typical core-collapse nebular spectra (Jerkstrand et al. 2017), it seems certain SNe, and the standard paradigm of iron-core collapse can- that the progenitors are above 20M , but whether they not account for their origin. Further constraints on the exclusively arise from higher mass stars (M > 40M ) progenitor properties arise from studying the nearby en- remains to be seen. arXiv:1708.04618v2 [astro-ph.GA] 26 Sep 2017 vironments. SLSNe appear to exclusively occur in dwarf The recent discovery of the closest SLSN to date, galaxies (Neill et al. 2011; Chen et al. 2013; Lunnan et al. SN 2017egm at z = 0:0307, which occurred in the massive, 2014; Leloudas et al. 2015; Angus et al. 2016) with less spiral galaxy NGC 3191 challenges the current hypothesis than around a half-solar metallicity (Perley et al. 2016; on the required host properties (Dong et al. 2017; Nicholl Chen et al. 2017a; Schulze et al. 2016). Their host galax- et al. 2017 and Bose et al. 2017). One major issue with ies also typically have high specific star formation rates these previous studies is they do not probe the local envi- ronment of SN 2017egm. The two available SDSS spectra (sSFR≡SFR/M∗), which may indicate that the progeni- tors are very young stars (Leloudas et al. 2015). Given analysed in Nicholl et al.(2017) were from spectrograph that low mass and metal-poor galaxies have typically fibers that did not cover the SN site. Here we present a detailed analysis of the host galaxy of SN 2017egm 1 In this paper we use the term SLSN to refer only to hydrogen- poor, Type I SLSNe 0 90 2 70 100 2 0 ◦ 0 6 6 4 2 70 80 2 0 ◦ 0 6 3 4 2 70 60 2 0 ◦ 0 6 0 4 2 70 40 2 0 ◦ 0 6 7 4 1 70 20 2 0 ◦ 0 6 4 4 1 0 70 2 0 ◦ 0 6 1 SN2017egm km/s 4 1 20 70 2 0 ◦ 0 6 8 4 0 0 40 Declination (J2000) 7 2 0 ◦ 0 6 5 4 0 60 70 2 0 ◦ 0 6 2 80 4 0 70 2 ◦ 6 100 4 s s s s s s s s s s 5 2 9 6 3 0 7 4 1 8 . 6 6 5 5 5 5 4 4 4 3 m 0 m 0 m 0 m 0 m 0 m 0 m 0 m 0 m 0 m 0 9 9 9 9 9 9 9 9 9 9 h 1 h 1 h 1 h 1 h 1 h 1 h 1 h 1 h 1 h 1 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 Right Ascension (J2000) 2 Chen et al. Figure 1 redshift of just redward of the H masked-out the area where this unidentified feature appears. : Left: using SDSS/MaNGA z at APO; Bundy et al. 2015) data= obtained0 MaNGA from FOV the ofSDSS NGC 3191. Data Release 14 2016-Jan-17. The MaNGA field-of-view:031 provides spec- tral measurements across a large area of NGC 3191 (Fig. In the top right region of the map there are about 30 pixels that show an additional feature 1). Using these data, we present the direct measurement of metallicity at this SLSN site, use the EW to studyα the progenitor properties, and compare the gas-phase line that is clearly not intrinsic to the nebular line emission from NGC 3191, we therefore properties of NGC 3191 with other SLSN host galaxies. 2 3 . The observationsurvey (Mapping was conducted Nearby on Galaxies 2. RESULTS OF THE MANGA DATA OF NGC 3191 MaNGAWe datacube,used our own following inhouse a similar tools to procedure analyze as the de- large scribed in Krühler et al.(2017). To separate the stellar and gas-phase components of the galaxy, we used the spec- Right: tral synthesis code 2009) to fit stellar population models to each spaxel. By subtracting the best-fit stellar template from the observed Velocity map inferred from the position of the H spectra, we were left with a datacube only containing the contribution of the gas-phase, which we then used to derive the velocity and metallicity maps. starlight 2 3 http://www.sdss.org/surveys/manga http://skyserver.sdss.org/dr14/en/home.aspx satelliteMany galaxies spiral (e.g.galaxies the are Magellanic often accompanied satellites ofby the dwarf Milky Way), and thus SN 2017egm might reside in a (e.g. Cid Fernandes et al. nearby dwarf satellite galaxy along the line-of-sight, rather 2.1. than in NGC 3191 itself. Such a kinematically distinct galaxy (200-300 km s Velocity map served in emission lines if the SFR of the satellite were high enough. of theWe created a velocity map by measuring the position at each spatial pixel, assuming a redshift of As shown in Fig.1, the velocity map is smooth across α the SN 2017gemH explosion site with no indication of a α line relative a kinematically distinct component. Using the line with respect to the rest-frame− wavelength the SN position to derive our sensitivity to the detection1 of a foreground dwarf galaxy, we place a conservativemight be expected) could be ob- upper limit of corresponds to SFR limit with a nearby ( et al. 2017a), and only 2 of 19 hosts may have a SFR less than our limit (the remaining 17 hosts have SFRs > would0 be the true host galaxy, it is at the lowest end of the : f host SFR distribution.01 On the other hand,H the satellite would have to beM many times larger thanα the spatial < < yr 1 − 0 :9 1 z < :002 ). Therefore, if a line-of-sight× satellite 10 0 M z : − 3 16 = 0 ) SLSNyr host sample (Chen − erg s 1 :0307 ). We compared this H − α 1 . cm flux at − 2 (which Host galaxy of SLSN 2017egm 3 9. 20 a) b) 60 9. 16 1 ) 10− 2 9. 12 − 3 50 c 9. 08 2 p R ) k 1 9. 04 H / 40 − r O ( y 9. 00 g ¯ SN2017egm SN2017egm o 30 8. 96 l M + ( 8. 92 2 1 R 20 2 F 8. 88 10− S PSF PSF 8. 84 10 1 kpc 1 kpc 8. 80 10 20 30 40 50 60 0. 50 3. 0 c) d) 60 0. 45 2. 7 0. 40 2. 4 50 0. 35 2. 1 ) g a 1. 8 0. 30 40 m ( 1. 5 0. 25 SN2017egm V SN2017egm − 30 1. 2 0. 20 B E 0. 9 0. 15 log([SIII]/[SII]) 20 0. 6 0. 10 PSF PSF 0. 3 10 1 kpc 0. 05 1 kpc 10 20 30 40 50 60 e) f) 60 Hα 60 [OIII]λ5007 102 50 50 ) ) 101 40 Å 40 Å ( ( W W SN2017egm 1 SN2017egm 10 E E 30 30 20 20 PSF PSF 10 1 kpc 10 1 kpc 100 100 10 20 30 40 50 60 10 20 30 40 50 60 Figure 2: Reconstructed images of NGC 3191 from the MaNGA data cube.