High angular resolution ALMA images of dust and molecules in the SN 1987A ejecta

Abstract: We present high angular resolution (~80 mas) ALMA continuum images of the SN 1987A system, together with CO $J$=2 $!\rightarrow!$ 1, $J$=6 $!\rightarrow!$ 5, and SiO $J$=5 $!\rightarrow!$ 4 to $J$=7 $!\rightarrow!$ 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in H$\alpha$ images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO $J$=6 $!\rightarrow!$ 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO $J$=6 $!\rightarrow!$ 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO $J$=2 $!\rightarrow!$ 1 and SiO $J$=5 $!\rightarrow!$ 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared--millimeter spectral energy distribution give ejecta dust temperatures of 18--23K. We revise the ejecta dust mass to $\mathrm{M_{dust}} = 0.2-0.4$M$\odot$ for carbon or silicate grains, or a maximum of $<0.7$M$\odot$ for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.

• The paper details high-resolution ALMA imaging that maps asymmetric dust and clumpy molecular distributions in SN 1987A ejecta.
• The paper utilizes RADEX modeling to derive molecular excitation conditions, highlighting temperature and density variations.
• The paper’s SED analysis constrains dust temperatures (18–23 K) and masses (up to 0.7 M⊙), advancing supernova dust formation theories.

High Angular Resolution ALMA Images of Dust and Molecules in the Ejecta of SN 1987A

The study of supernova 1987A (SN 1987A) provides key insights into the aftermath of stellar explosions and the evolution of supernova remnants (SNRs). The paper presents high-resolution images from the Atacama Large Millimeter/submillimeter Array (ALMA) detailing the properties of dust and molecules in SN 1987A, over three decades post-explosion. This analysis focuses on observations at frequencies of 315 GHz (Band 7) and 679 GHz (Band 9), targeting continuum dust emission and spectral lines from CO and SiO molecules.

Key Observations and Findings

1. Dust and Molecular Distributions: The dust in SN 1987A's ejecta is distributed asymmetrically, exhibiting clumps that fill the spatial void seen in Hα images. The CO and SiO molecules are also clumpy, with emission peaks that vary between different line transitions. Notably, a dust peak is found coincident with a previously identified molecular hole, suggesting spatial and possible chemical interactions.
2. Molecular Line Ratios and Models: Using the RADEX non-LTE radiative transfer code, the paper models the molecular excitation conditions. The line ratios of SiO and CO transitions indicate that the molecular gas might have varying kinetic temperatures and densities. Regions with strong CO emission often coincide with weaker dust emission, which points towards complex interplay in the supernova's chemical environment.
3. Spectral Energy Distribution (SED) Analysis: The study fits the observed SED of the ejecta with various dust grain models. The inferred dust temperature ranges from 18 to 23 K, with dust masses between 0.2 and 0.4$M_\mathrm{\odot}$ for carbon or silicate compositions. A total dust mass of up to 0.7$M_\mathrm{\odot}$ is suggested for a mixture of grain species. These findings are consistent with nucleosynthesis yield predictions, revealing substantial dust formation in supernovae.
4. Implications for Dust Formation: The observations suggest that carbonaceous dust may have formed following CO dissociation, contrary to prevailing chemical models, which predominantly predict silicate formation. This highlights a potential need to revisit supernova dust formation theories, particularly concerning CO dissociation mechanisms.
5. Detection and Properties of the Dust "Blob": A significant concentration of dust ("the blob") correlates spatially with molecular holes, suggesting a region of heated dust and gas. This blob might be heated by a nascent compact source, possibly a neutron star or a pulsar wind nebula, which has yet to be observed directly.

Implications and Future Research Directions

The findings bring forward new perspectives on the interaction between dust, molecules, and the underlying remnant structure in SN 1987A. The detection of significant dust masses helps elucidate the role of supernovae as dust producers in the cosmos. Future observations are required to enhance our understanding of the dust formation mechanisms and the identification of potential compact sources in such environments.

The combinations of diverse grain compositions used to fit the SED underscore the complexity in modeling the dust output of SNRs. This study underlines the importance of high spatial resolution in untangling the intricate chemistry of the ejecta and advancing our knowledge of the late stages of supernovae.

Overall, this paper demonstrates the crucial role of ALMA in advancing our understanding of supernova remnants, setting the stage for future investigations into the lifecycle of stellar debris and contributing to broader astrophysical questions regarding matter recycling in galaxies.