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JWST View of the Supernebula in NGC 5253. II. Nebular Lines

Sara C. Beck, Jean L. Turner, Elm Zweig, John H. Black, Paul T. P. Ho, David S. Meier, Sergiy Silich, Daniel P. Cohen, S. Michelle Consiglio, Nicholas G. Ferraro

Abstract

The nearby dwarf starburst NGC 5253 is dominated by a compact radio-infrared supernebula powered by a very young and bright embedded Super Star Cluster (SSC) of $\sim 10^9 L_\odot$. We observed this source and its surroundings over the 5-25$μ$m range with MIRI/MRS on JWST and in Paper I presented the JWST view of the region and its continuum features. We now present the more than 70 emission lines of HI, $H_2$ and metal ions detected by MIRI/MRS. We derive the extinction by comparing HI recombination to the free-free radio continuum and find that it is very flat, i.e., almost independent of wavelength, over this spectral range. Nebular conditions are consistent with young ($\lesssim5\times10^6$ years) and very massive stars. All regions show high excitation, but the spatial distribution of the high excitation lines suggests that photons with energies close to 50eV are escaping the supernebula core in spite of 35 magnitudes of visual extinction.

JWST View of the Supernebula in NGC 5253. II. Nebular Lines

Abstract

The nearby dwarf starburst NGC 5253 is dominated by a compact radio-infrared supernebula powered by a very young and bright embedded Super Star Cluster (SSC) of . We observed this source and its surroundings over the 5-25m range with MIRI/MRS on JWST and in Paper I presented the JWST view of the region and its continuum features. We now present the more than 70 emission lines of HI, and metal ions detected by MIRI/MRS. We derive the extinction by comparing HI recombination to the free-free radio continuum and find that it is very flat, i.e., almost independent of wavelength, over this spectral range. Nebular conditions are consistent with young ( years) and very massive stars. All regions show high excitation, but the spatial distribution of the high excitation lines suggests that photons with energies close to 50eV are escaping the supernebula core in spite of 35 magnitudes of visual extinction.

Paper Structure

This paper contains 17 sections, 4 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Data Analysis and Reduction
  3. The HII Regions of the NGC 5253 Starburst Region
  4. Mid-Infrared Emission Lines
  5. Extinction Law in the Mid-infrared
  6. Calculating Extinction from HI lines and Radio Flux
  7. Extinction to the Individual Regions
  8. The Silicate Feature in NGC 5253 Does Not Correlate Simply with the Extinction
  9. Fine Structure Lines and Nebular Conditions in the NGC 5253 Starburst
  10. Spatial Distribution of the Fine Structure Lines
  11. Fine structure Line Ratios and Conditions in the Sources
  12. High Excitation Lines
  13. Contribution of Mid-Infrared Lines to Total Cooling and Luminosity
  14. Elemental Abundances in the NGC 5253 Starburst
  15. A mystery feature
  16. ...and 2 more sections

Figures (8)

  • Figure 1: The JWST chip (rectangular outline) and the regions used for spectral extraction are displayed as solid circles and ellipses labeled D1, D2, D4, D6, Ellipse and Chip and overlaid on images of the source at H$\alpha$ (HST image), 107 GHz ALMA image and the integrated flux of the ALMA CO(3-2) line turner2017consiglio2017. Dashed contours trace the 7$\mu m$ continuum emission from the JWST MIRI/MRSpaperi.
  • Figure 2: Apparent extinction as determined by the comparison of observed flux to flux predicted from 107 GHz free-free flux. Color is coded to signal-to-noise for each panel, from low (black) to high (pink), and error bars are shown. The best fit linear regression is shown with 95% confidence levels for predictions. The MIRI/MRS datapoints near 5 in D1 and Ellipse are from high level 7-series lines near the band edge, where instrumental response is degraded.
  • Figure 3: Apparent extinction from the near-infrared to mid-infrared as determined by the comparison of observed flux to flux predicted from 107 GHz free-free flux, including HST and Keck near-infrared fluxes for $\lambda<5$turner2003alonso-herrero2004 as well as JWST MIRI/MRS fluxes. Signal-to-noise is indicated by color from low (black) to high (pink) and error bars. A loess-smoothed fit from R (span 75%) with 95% confidence levels for predictions is shown. The lines around 5 are from high levels of the n-7 series, which has large scatter due to the instrumental response at the band edge (see Paper 1) creates large scatter in the fluxes.
  • Figure 4: Spectra of the individual regions.
  • Figure 5: Emission from the giant H$\,$ II region, NGC$\,$5253-D1. Contours are of Pf $\alpha$ emission, 1.5, 5, 15 GJy/sr. (Left) HST 656N image, H $\alpha$. (Middle) Continuum-free line map of Pf $\alpha$, HI 6-5. (Right) Continuum-free line map of [Ne III].
  • ...and 3 more figures