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NGC 253 starburst galaxy at low radio frequencies Anna D. Kapi ska - - PowerPoint PPT Presentation
NGC 253 starburst galaxy at low radio frequencies Anna D. Kapi ska - - PowerPoint PPT Presentation
NGC 253 starburst galaxy at low radio frequencies Anna D. Kapi ska ICRAR/University of Western Australia CAASTRO Introduction: NGC 253 the Sculptor galaxy Archetypal nuclear starburst galaxy. Located in the nearby Sculptor Group at a
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Introduction: NGC 253 – the Sculptor galaxy
ESO (R,V,Hα,OIII) G.Meurer (Hα)
Archetypal nuclear starburst galaxy. Located in the nearby Sculptor Group at a distance ~3.9 Mpc, cz = 240 km/s
➢ stellar mass 4 x 1010 M⊙ ➢ stellar halo of 2.5 x 109 M⊙ ➢ star formation rate ~5 M⊙/yr
(Bailin+2011; Lucero+2015)
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GaLactic and Extragalactic All-sky MWA Survey – GLEAM
Hurley-Walker
Kapinska
➢ 72 – 230 MHz (20 bands) ➢ sky south of declination +30° ➢ depth: ~10 mJy/beam @200MHz ➢ resolution: ~2 arcmin @200MHz
GLEAM: Wayth+ 2015 Data Release 1 (DR1): Hurley-Walker+ 2017
Murchison Radio Observatory Western Australia
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Talk outline
➢ Synchroton radio halo ➢ Broadband radio spectral energy distribution (SED) ➢ Spectral index map (α) & multi-frequency context
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NGC 253 – low frequency radio
Offringa+2016, MWA/EoR collab.
MWA/EoR0 GLEAM GLEAM Hα + GLEAM 200 MHz contours
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Synchrotron radio halo
78.5°
Projected scale-height (maximum vertical extent)
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Spectral energy distribution – radio
Total flux density
Central starburst (300-500 pc)
Kapinska et al. ApJ under review
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Spectral energy distribution – radio
GLEAM
Total flux density
Central starburst (300-500 pc)
Kapinska et al. ApJ under review EoR TGSS
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Spectral energy distribution – radio
Kapinska et al. ApJ under review
Central starburst Disk & halo
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Radio emission – models
synchrotron emission free-free emission absorption at low frequencies
- ptically thick regime
self-absorption
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Radio emission – models
synchrotron emission free-free emission absorption at low frequencies
- ptically thick regime
self-absorption Internal or external free-free absorption of synchrotron emission external
Line of sight galaxy
internal
H II
galaxy
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Spectral energy distribution – radio
Kapinska et al. ApJ under review
Central starburst – internal free-free absorbed synchrotron emission, turnover: ~230 MHz
- cf. Carilli 1996
Disk & halo curved synchrotron emission
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Radio spectral index map
Kapinska et al. ApJ under review
α
200 MHz – 1.46 GHz
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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)
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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
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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