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NGC 2770: High Supernova Rate Due to Interaction

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NGC 2770: High Supernova Rate Due to Interaction Astronomy & Astrophysics manuscript no. ms c ESO 2020 August 20, 2020 NGC 2770: High supernova rate due to interaction Michał J. Michałowski1, 2, 3, Christina Thöne4, Antonio de Ugarte Postigo4, 5, Jens Hjorth5, Aleksandra Lesniewska´ 1, Natalia Gotkiewicz6, Wojciech Dimitrov1, Maciej P. Koprowski6, Peter Kamphuis7 1 Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, ul. Słoneczna 36, 60-286 Poznan,´ Poland [email protected] 2 TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA 3 Fulbright Senior Award Fellow 4 Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía, s/n, E-18008, Granada, Spain 5 DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark 6 Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudzia¸dzka 5, 87-100 Torun,´ Poland 7 Ruhr-Universität Bochum, Faculty of Physics and Astronomy, Astronomical Institute, 44780 Bochum, Germany August 20, 2020 ABSTRACT Context. Galaxies that hosted many core-collapse supernova (SN) explosions can be used to study the conditions necessary for the formation of massive stars. NGC 2770 was dubbed an SN factory because it hosted four core-collapse SNe in 20 years (three type Ib and one type IIn). Its star formation rate (SFR) was reported to not be enhanced and, therefore, not compatible with such a high SN rate. Aims. We aim to explain the high SN rate of NGC 2770. Methods. We used archival Hi line data for NGC 2770 and reinterpreted the Hα and optical continuum data. Results. Even though the continuum-based SFR indicators do not yield high values, the dust-corrected Hα luminosity implies a high SFR, consistent with the high SN rate. Such a disparity between the SFR estimators is an indication of recently enhanced star formation activity because the continuum indicators trace long timescales of the order of 100 Myr, unlike the line indicators, which trace timescales of the order of 10 Myr. Hence, the unique feature of NGC 2770 compared to other galaxies is the fact that it was observed very shortly after the enhancement of the SFR. It also has high dust extinction, E(B − V) above 1 mag. We provide support for the hypothesis that the increased SFR in NGC 2770 is due to the interaction with its companion galaxies. We report an Hi bridge between NGC 2770 and its closest companion and the existence of a total of four companions within 100 kpc (one identified for the first time). There are no clear Hi concentrations close to the positions of SNe in NGC 2770 such as those detected for hosts of gamma-ray bursts (GRBs) and broad-lined SNe type Ic (IcBL). This suggests that the progenitors of type Ib SNe are not born out of recently accreted atomic gas, as was suggested for GRB and IcBL SN progenitors. Key words. galaxies: evolution — galaxies: individual: NGC 2770 — galaxies: ISM — galaxies: star formation — supernovae: individual: 1999eh, 2007uy, 2008D, 2015bh — radio lines: galaxies 1. Introduction not compatible with such a high SN rate (Thöne et al. 2009). In 2015, a fourth SN (type IIn) exploded, bringing the current rate Due to their very short lifetimes, the properties and numbers to four over the last 20 years. of massive stars in a galaxy can be used to infer the details of star formation. Individual stars can only be detected in the most SN1999eh was the first SN discovered in NGC2770 nearby galaxies, so massive stars in most galaxies can only be (Hurstet al. 1999; Armstrong 2000) and was classified as studied when they explodeas core-collapse supernovae(SNe).In type Ib (Jha et al. 1999). Similarly, SN 2007uy was classified the context of using SNe to study star formation, it is especially as a type Ib (vanderHorstetal. 2011; Royetal. 2013) pe- arXiv:2008.08091v1 [astro-ph.HE] 18 Aug 2020 promising to study galaxies with multiple SNe, as their high SN culiar (Modjazet al. 2014) SN. The discovery of SN2008D rates should be connected with conditions necessary for a given (also classified as type Ib) in the early phase during the ob- type of stellar explosion. For example, Li & Li (1995) showed servations of SN2007uy allowed the detection of signatures that the number of galaxies hosting multiple SNe does not de- of SN shock breakout (Mazzali et al. 2008; Soderberget al. viate significantly from a Poissonian distribution, so the hosts 2008; Chevalier & Fransson 2008; Bietenholz et al. 2009; of multiple SNe are not inherently different from other galax- Malesani et al. 2009; Maund et al. 2009; Modjaz et al. 2009; ies; they just have higher star formation rates (SFRs). Moreover, Tanaka et al. 2009; Gorosabel et al. 2010; Couch et al. 2011). Anderson & Soto (2013) find that galaxieswith multiple SNe are SN2015bh was a type IIn SN or a significant outburst of a lu- preferentially of later morphological types, pointing to the likely minous blue variable (LBV) star. It was proceeded by 20 years connection with young stellar populations. of outbursting activity (Elias-Rosa et al. 2016; Ofek et al. 2016; NGC 2770 (UGC 4806) was dubbed an SN Ib factory Thöne et al. 2017; Boian & Groh 2018). (Thöne et al. 2009) because it hosted three type Ib SNe in ten In the single-star progenitor channel, SNe of both types Ib/c years. Its SFR was reported to not be enhanced and, therefore, (Woosley et al. 2002) and IIn (Kiewe et al. 2012) are believed Article number, page 1 of 8 A&A proofs: manuscript no. ms 140 70 0 Velocity (km/s) -70 NGC 2770C 2008D Ib tidal tail NGC 2770C 2008D Ib tidal tail -140 2015bh IIn 1999eh Ib 2015bh IIn 1999eh Ib 2007uy IbPec NGC 2770B 2007uy IbPec NGC 2770B tidal tail tidal tail 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin 140 70 0 Velocity (km/s) -70 NGC 2770C 2008D Ib tidal tail NGC 2770C 2008D Ib tidal tail -140 2015bh IIn 1999eh Ib 2015bh IIn 1999eh Ib 2007uy IbPec NGC 2770B 2007uy IbPec NGC 2770B tidal tail tidal tail 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin 140 70 0 Velocity (km/s) -70 NGC 2770C 2008D Ib tidal tail NGC 2770C 2008D Ib tidal tail -140 2015bh IIn 1999eh Ib 2015bh IIn 1999eh Ib 2007uy IbPec NGC 2770B 2007uy IbPec NGC 2770B tidal tail tidal tail 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin Fig. 1. Atomic gas distribution in NGC 2770. The data are at resolutions of 24′′ × 13′′ (top), 36′′ × 30′′ (middle), and 65′′ × 56′′ (bottom). Left: zeroth moment maps (integrated emission). Right: first moment maps (velocity fields) relative to z = 0.00649 (1945.65 km s−1). The positions of SNe are marked by grey circles, whereas the black cross shows the position of the optical centre of the galaxy. Each panel is 6.7′ per side. North is up and east is to the left. NGC 2770B is at the right edge of the panels and connected to NGC 2770 by a tidal feature. NGC 2770C is at the left edge of the panels. Article number, page 2 of 8 Michałowski et al.: NGC 2770 NGC 2770C tidal tail NGC 2770C tidal tail NGC 2770B NGC 2770B tidal tail tidal tail 140 70 0 Velocity (km/s) -70 NGC 2770D NGC 2770D -140 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin NGC 2770C tidal tail NGC 2770C tidal tail NGC 2770B NGC 2770B tidal tail tidal tail 140 70 0 Velocity (km/s) -70 NGC 2770D NGC 2770D -140 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin NGC 2770C tidal tail NGC 2770C tidal tail NGC 2770B NGC 2770B tidal tail tidal tail 140 70 0 Velocity (km/s) -70 NGC 2770D NGC 2770D -140 8.0 kpc 8.0 kpc 1 arcmin 1 arcmin Fig. 2. As in Fig. 1, but zoomed out to show the environment of NGC 2770. Each panel is 16.7′ per side. NGC 2770B and C are ∼ 3′ (24 kpc) to the west and east from the centre of NGC 2770, respectively, whereas NGC 2770D is ∼ 12′ (96 kpc) to the south-east. There are tidal features extending from both endpoints of the NGC 2770 disc. NGC 2770E is outside the panels to the east of NGC 2770. Article number, page 3 of 8 A&A proofs: manuscript no. ms Fig. 3. Optical colour image of the NGC 2770 group with all detected companions. For the figure we use g′ (blue), r′ (yellow), and i′ (red) filters from the SDSS DR 16 in a mosaic of 13 plates. On the left we show zoomed in images of the four companions. The different scales are indicated in the images. to be connected with the endpoints of the evolution of the most The third is to test whether the environment of NGC2770 might massive stars (of the order of > 25 M⊙), likely Wolf-Rayet stars have been responsible for its high SN rate. for the type Ib/c (Gaskell et al. 1986). On the other hand, the We adopted a redshift for NGC2770 of z = 0.00649 double-star channel for SNe type Ib/c involves a less massive (Haynes et al. 1997), a luminosity distance of 27.9Mpc, and a −1 star (8–20 M⊙) with the hydrogen envelope removed through in- corresponding scale of 0.134kpc arcsec . This assumes a cos- −1 −1 teraction in a binary system (Podsiadlowski et al. 1992). This mological model with H0 = 70 km s Mpc , ΩΛ = 0.7, and double-star channel was also claimed for type IIb SNe, that is Ωm = 0.3.
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