NGC 253 starburst galaxy at low radio frequencies Anna D. Kapińska ICRAR/University of Western Australia CAASTRO Introduction: NGC 253 – the Sculptor galaxy Archetypal nuclear starburst galaxy. Located in the nearby Sculptor Group at a distance ~3.9 Mpc, cz = 240 km/s ESO (R,V,Hα,OIII) Introduction: NGC 253 – the Sculptor galaxy Archetypal nuclear starburst galaxy. ➢ 10 Located in the nearby Sculptor Group stellar mass 4 x 10 M⊙ ➢ 9 at a distance ~3.9 Mpc, cz = 240 km/s stellar halo of 2.5 x 10 M⊙ ➢ star formation rate ~5 M⊙/yr (Bailin+2011; Lucero+2015) ESO (R,V,Hα,OIII) G.Meurer (Hα) GaLactic and Extragalactic All-sky MWA Survey – GLEAM Murchison Radio Observatory Western Australia ➢ 72 – 230 MHz (20 bands) ➢ sky south of declination +30° Kapinska ➢ depth: ~10 mJy/beam @200MHz ➢ resolution: ~2 arcmin @200MHz GLEAM: Wayth+ 2015 Data Release 1 (DR1): Hurley-Walker+ 2017 Hurley-Walker Talk outline ➢ Synchroton radio halo ➢ Broadband radio spectral energy distribution (SED) ➢ Spectral index map (α) & multi-frequency context NGC 253 – low frequency radio GLEAM MWA/EoR0 Offringa+2016, MWA/EoR collab. GLEAM Hα + GLEAM 200 MHz contours Synchrotron radio halo 78.5° Projected scale-height (maximum vertical extent) Spectral energy distribution – radio Kapinska et al. ApJ under review Total flux density Central starburst (300-500 pc) Spectral energy distribution – radio Kapinska et al. ApJ under review GLEAM EoR Total flux density TGSS Central starburst (300-500 pc) Spectral energy distribution – radio Kapinska et al. ApJ under review Disk & halo Central starburst Radio emission – models synchrotron emission free-free emission absorption at low frequencies optically thick regime self-absorption Radio emission – models synchrotron emission free-free emission absorption at low frequencies optically thick regime Internal or external free-free absorption of synchrotron emission self-absorption galaxy Line of sight H II galaxy external internal Spectral energy distribution – radio Kapinska et al. ApJ under review Disk & halo curved synchrotron emission cf. Carilli 1996 Central starburst – internal free-free absorbed synchrotron emission, turnover: ~230 MHz Radio spectral index map Kapinska et al. ApJ under review α 200 MHz – 1.46 GHz Multiwavelength view Kapinska et al. ApJ under review Soft X-ray (<1 keV; Bauer+2008) Extraplanar HI (KAT-7; Lucero+2015) Spectral index (0.2–1.46 GHz) Multiwavelength view Kapinska et al. ApJ under review Soft X-ray (<1 keV; Bauer+2008) Extraplanar HI (KAT-7; Lucero+2015) Spectral index (0.2–1.46 GHz) Spectral flattening * e– low-frequency cut off? * strong superwind collimating cold gas? → extraplanar HI Summary ● New, deep low-frequency radio images of NGC 253 → amazing capabilities of MWA – SKA precursor! ● Radio emission at MHz frequencies a combination of central starburst (internally free-free absorbed synchrotron) and extended emission of disk and halo (synchrotron flattening at low radio frequencies) ● Spectral turnover of central starburst for the first time statistically constrained, at ~230 MHz ● Extensive synchrotron radio halo of NGC 253 imaged by MWA, extending up to 8 kpc at 200 MHz.