arXiv subjects

H. L. Gomez

Publications and source records attributed to H. L. Gomez.

At least 19 recordsLinked to original sources

arXiv2026

HCO$^+$ and the Effect of Mixing in SN 1987A

We present high angular resolution observations of the HCO$^+$ emission in the central ejecta of the supernova remnant SN 1987A using the Atacama Large Millimeter Array (ALMA). We use this to infer the degree and type of mixing required within the ejecta in order to form HCO$^+$. The distribution of the $J=3-2$ HCO$^+$ emission is co-spatial with that of the $J=2-1$ CO emission, with an overlap between their brightest peaks. The correlation between the two molecules is strong and suggests that HCO$^+$ could form from reactions involving CO. We obtain additional observations of the $J=4-3$ HCO$^+$ emission to calculate the mass of HCO$^+$. The estimated HCO$^+$ mass is $3\text{--}9 \times 10^{-6}\,M_{\odot}$. The relatively large fractional abundance of HCO$^+$ with respect to CO ($M_{\mathrm{HCO}^+}/M_{\mathrm{CO}} = 3 \times 10^{-6}\text{--}3 \times 10^{-4}$) suggests that a moderate amount of hydrogen was mixed into the carbon- and oxygen-rich nuclear zones of the ejecta prior to and during the supernova explosion, in addition to large-scale macroscopic mixing.

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arXiv2026

3D insights into SN 1987A: ALMA observations compared to hydrodynamical explosion simulations

We obtain three-dimensional distributions of CO and SiO molecules from high spatial resolution (0.03--0.06") ALMA observations of SN 1987A at two different epochs. The evolution between these two epochs is consistent with homologous expansion. From these 3D maps, we reconstruct the 3D mass distributions of the ejecta in CO and SiO molecules, which we compare with those obtained by state-of-the-art, long-time hydrodynamical supernova explosion models computed with the Prometheus-HotB code for 10 different progenitors, including both red and blue supergiants. The models which best match the mass distributions correspond to explosions of binary-merger blue supergiant progenitors; at least two such models approximately reproduce the observed CO morphology. In contrast, the SiO velocity distribution and morphology are not as well reproduced in these models, indicating insufficient mixing of Si into the outer layers already at the progenitor stage. The theoretical models suggest a strong correlation between the centre of mass of the densest carbon- and oxygen-rich ejecta and the direction of the neutron-star kick. If such a correlation also applies to the CO emission in the ejecta of SN 1987A, the kick of the compact remnant is expected to point towards the observer, at an angle of approximately $45^\circ$ to the north.

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arXiv2024

Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec- IFU spectroscopy of the young supernova remnant Cassiopeia A (Cas A). We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the reformation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3 - 5.5 microns) were obtained toward two representative knots in the NE and S fields. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar VI] and relatively weaker, variable strength ejecta lines of [Si IX], [Ca IV], [Ca V] and [Mg IV]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudo-continuum underneath, which is attributed to the high-velocity widths of CO lines. The CO also shows high J lines at different vibrational transitions. Our results with LTE modeling of CO emission indicate a temperature of 1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae, and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

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arXiv2024

Deep JWST/NIRCam imaging of Supernova 1987A

JWST/NIRCam obtained high angular-resolution (0.05-0.1''), deep near-infrared 1--5 micron imaging of Supernova (SN) 1987A taken 35 years after the explosion. In the NIRCam images, we identify: 1) faint H2 crescents, which are emissions located between the ejecta and the equatorial ring, 2) a bar, which is a substructure of the ejecta, and 3) the bright 3-5 micron continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1-2.3 micron images is mostly due to line emission, which is mostly emitted in the ejecta and in the hot spots within the equatorial ring. In contrast, the NIRCam 3-5 micron images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time scales are shorter than the synchrotron cooling time scale, and the time scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time scale. With the advent of high sensitivity and high angular resolution images provided by JWST/NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how a SN evolves.

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arXiv2022

Properties of shocked dust grains in supernova remnants

Shockwaves driven by supernovae both destroy dust and reprocess the surviving grains, greatly affecting the resulting dust properties of the interstellar medium (ISM). While these processes have been extensively studied theoretically, observational constraints are limited. We use physically-motivated models of dust emission to fit the infrared (IR) spectral energy distributions of seven Galactic supernova remnants, allowing us to determine the distribution of dust mass between diffuse and dense gas phases, and between large and small grain sizes. We find that the dense ($\sim 10^3 \,{\rm cm}^{-3}$), relatively cool ($\sim 10^3 \, {\rm K}$) gas phase contains $>90\%$ of the dust mass, making the warm dust located in the X-ray emitting plasma ($\sim 1 \,{\rm cm}^{-3}$/$10^6 \, {\rm K}$) a negligible fraction of the total, despite dominating the mid-IR emission. The ratio of small ($\lesssim 10 \, {\rm nm}$) to large ($\gtrsim 0.1 \, {\rm μm}$) grains in the cold component is consistent with that in the ISM, and possibly even higher, whereas the hot phase is almost entirely devoid of small grains. This suggests that grain shattering, which processes large grains into smaller ones, is ineffective in the low-density gas, contrary to model predictions. Single-phase models of dust destruction in the ISM, which do not account for the existence of the cold swept-up material containing most of the dust mass, are likely to greatly overestimate the rate of dust destruction by supernovae.

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arXiv2021

A High-Resolution Investigation of the Multi-Phase ISM in a Galaxy during the First Two Billion Years

We have carried out the first spatially-resolved investigation of the multi-phase interstellar medium (ISM) at high redshift, using the z=4.24 strongly-lensed sub-millimetre galaxy H-ATLASJ142413.9+022303 (ID141). We present high-resolution (down to ~350 pc) ALMA observations in dust continuum emission and in the CO(7-6), H_2O (2_{1,1} - 2_{0,2}), CI(1-0) and CI(2-1) lines, the latter two allowing us to spatially resolve the cool phase of the ISM for the first time. Our modelling of the kinematics reveals that the system appears to be dominated by a rotationally-supported gas disk with evidence of a nearby perturber. We find that the CI(1-0) line has a very different distribution to the other lines, showing the existence of a reservoir of cool gas that might have been missed in studies of other galaxies. We have estimated the mass of the ISM using four different tracers, always obtaining an estimate in the range (3.2-3.8) x 10^{11} M_sol, significantly higher than our dynamical mass estimate of (0.8-1.3) x 10^{11} M_sol. We suggest that this conflict and other similar conflicts reported in the literature is because the gas-to-tracer ratios are ~4 times lower than the Galactic values used to calibrate the ISM in high-redshift galaxies. We demonstrate that this could result from a top-heavy initial mass function and strong chemical evolution. Using a variety of quantitative indicators, we show that, extreme though it is at z=4.24, ID141 will likely join the population of quiescent galaxies that appears in the Universe at z~3.

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arXiv2021

Dust continuum, CO, and [C I] 1-0 lines: self-consistent H2 mass estimates and the possibility of globally CO-dark galaxies at $z = 0.35$

We present ALMA observations of a small but statistically complete sample of twelve 250 micron selected galaxies at $z=0.35$ designed to measure their dust submillimeter continuum emission as well as their CO(1-0) and atomic carbon [CI](3P1-3P0) spectral lines. This is the first sample of galaxies with global measures of all three $H_2$-mass tracers and which show star formation rates (4-26 Msun yr$^{-1}$) and infra-red luminosities ($1-6\times10^{11}$ Lsun) typical of star forming galaxies in their era. We find a surprising diversity of morphology and kinematic structure; one-third of the sample have evidence for interaction with nearby smaller galaxies, several sources have disjoint dust and gas morphology. Moreover two galaxies have very high $L_{CI}/L_{CO}$ ratios for their global molecular gas reservoirs; if confirmed, such extreme intensity ratios in a sample of dust selected, massive star forming galaxies presents a challenge to our understanding of ISM. Finally, we use the emission of the three molecular gas tracers, to determine the carbon abundance, $X_{ci}$, and CO-$\rm{H_2}$ conversion $α_{co}$ in our sample, using a weak prior that the gas-to-dust ratio is similar to that of the Milky Way for these massive and metal rich galaxies. Using a likelihood method which simultaneously uses all three gas tracer measurements, we find mean values and errors on the mean of $α_{co}=3.0\pm0.5\,\rm{Msun\,(K\,kms^{-1}\,pc^2)^{-1}}$ and $X_{ci}=1.6\pm0.1\times 10^{-5}$ (or $α_{ci}=18.8\,K kms^{-1}\,pc^2 (Msun)^{-1}$) and $δ_{GDR}=128\pm16$ (or $α_{850}=5.9\times10^{12}\,\rm{W\,Hz^{-1}\, Msun^{-1}}$), where our starting assumption is that these metal rich galaxies have an average gas-to-dust ratio similar to that of the Milky Way centered on $δ_{GDR}=135$.

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arXiv2021

BEDE: Bayesian Estimates of Dust Evolution For Nearby Galaxies

We build a rigorous statistical framework to provide constraints on the chemical and dust evolution parameters for nearby late-type galaxies with a wide range of gas fractions ($3\%<f_g<94\%$). A Bayesian Monte Carlo Markov Chain framework provides statistical constraints on the parameters used in chemical evolution models. Nearly a million one-zone chemical and dust evolution models were compared to 340 galaxies. Relative probabilities were calculated from the $χ^2$ between data and models, marginalised over the different time steps, galaxy masses and star formation histories. We applied this method to find `best fitting' model parameters related to metallicity, and subsequently fix these metal parameters to study the dust parameters. For the metal parameters, a degeneracy was found between the choice of initial mass function, supernova metal yield tables and outflow prescription. For the dust parameters, the uncertainties on the best fit values are often large except for the fraction of metals available for grain growth, which is well constrained. We find a number of degeneracies between the dust parameters, limiting our ability to discriminate between chemical models using observations only. For example, we show that the low dust content of low-metallicity galaxies can be resolved by either reducing the supernova dust yields and/or including photo-fragmentation. We also show that supernova dust dominates the dust mass for low metallicity galaxies and grain growth dominates for high metallicity galaxies. The transition occurs around $12+\log({\rm O/H})=7.75$, which is lower than found in most studies in the literature.

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arXiv2020

Revisiting the dust destruction efficiency of supernovae

Dust destruction by supernovae is one of the main processes removing dust from the interstellar medium (ISM). Estimates of the efficiency of this process, both theoretical and observational, typically assume a shock propagating into a homogeneous medium, whereas the ISM possesses significant substructure in reality. We self-consistently model the dust and gas properties of the shocked ISM in three supernova remnants (SNRs), using X-ray and infrared (IR) data combined with corresponding emission models. Collisional heating by gas with properties derived from X-ray observations produces dust temperatures too high to fit the far-IR fluxes from each SNR. An additional colder dust component is required, which has a minimum mass several orders of magnitude larger than that of the warm dust heated by the X-ray emitting gas. Dust-to-gas mass ratios indicate that the majority of the dust in the X-ray emitting material has been destroyed, while the fraction of surviving dust in the cold component is plausibly close to unity. As the cold component makes up virtually all the total dust mass, destruction timescales based on homogeneous models, which cannot account for multiple phases of shocked gas and dust, may be significantly overestimating actual dust destruction efficiencies, and subsequently underestimating grain lifetimes.

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arXiv2020

S2COSMOS: Evolution of Gas Mass with Redshift Using Dust Emission

We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850$μ$m. We use stacking methodologies on the 850$μ$m S2COSMOS map to derive the gas mass fraction of galaxies out to high redshifts, 0 <= $z$ <= 5, for galaxies with stellar masses of $10^{9.5} < M_* (\rm M_{\odot}) < 10^{11.75}$. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around $z$ ~ 2.5-3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas.

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arXiv2019

Herschel-ATLAS: Revealing dust build-up and decline across gas, dust and stellar mass selected samples: I. Scaling relations

We present a study of the dust, stars and atomic gas (HI) in an HI-selected sample of local galaxies (z<0.035) in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) fields. This HI-selected sample reveals a population of very high gas fraction (>80 per cent), low stellar mass sources that appear to be in the earliest stages of their evolution. We compare this sample with dust and stellar mass selected samples to study the dust and gas scaling relations over a wide range of gas fraction (proxy for evolutionary state of a galaxy). The most robust scaling relations for gas and dust are those linked to NUV-r (SSFR) and gas fraction, these do not depend on sample selection or environment. At the highest gas fractions, our additional sample shows the dust content is well below expectations from extrapolating scaling relations for more evolved sources, and dust is not a good tracer of the gas content. The specific dust mass for local galaxies peaks at a gas fraction of ~75 per cent. The atomic gas depletion time is also longer for high gas fraction galaxies, opposite to the trend found for molecular gas depletion timescale. We link this trend to the changing efficiency of conversion of HI to H2 as galaxies increase in stellar mass surface density as they evolve. Finally, we show that galaxies start out barely obscured and increase in obscuration as they evolve, yet there is no clear and simple link between obscuration and global galaxy properties.

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arXiv2019

The unusual ISM in Blue and Dusty Gas Rich Galaxies (BADGRS)

The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV-K < 3.5), dust-rich galaxies with high gas fractions (f_HI = M_HI/(M*+M_HI)>0.5)). Dubbed `Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep CO(J_up=1,2,3) observations across the central and outer disk regions. We find very low CO brightnesses (Tp=15-30 mK), despite the bright far-infrared emission and metallicities in the range 0.5<Z/Z_sun<1.0. The CO line ratios indicate a range of conditions with R_21=0.6-2.1 and R_31=0.2-1.2. Using a metallicity dependent conversion from CO luminosity to molecular gas mass we find M_H2/M_d=7-27 and Sigma_H2=0.5-6 M_sun pc^-2, around an order of magnitude lower than expected. The BADGRS have lower molecular gas depletion timescales (tau_d = 0.5 Gyr) than other local spirals, lying offset from the Kennicutt-Schmidt relation by a similar factor to Blue Compact Dwarf galaxies. The cold diffuse dust temperatures in BADGRS (13-16 K) require an interstellar radiation field 10-20 times lower than that inferred from their observed surface brightness. We speculate that the dust in these sources has either a very clumpy geometry or a very different opacity in order to explain the cold temperatures and lack of CO emission. BADGRS also have low UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-beta space as z=5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.

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arXiv2019

The dust content of the Crab Nebula

We have modelled the near-infrared to radio images of the Crab Nebula with a Bayesian SED model to simultaneously fit its synchrotron, interstellar and supernova dust emission. We infer an interstellar dust extinction map with an average $A_{\text{V}}$=1.08$\pm$0.38 mag, consistent with a small contribution (<22%) to the Crab's overall infrared emission. The Crab's supernova dust mass is estimated to be between 0.032 and 0.049 M$_{\odot}$ (for amorphous carbon grains) with an average dust temperature $T_{\text{dust}}$=41$\pm$3K, corresponding to a dust condensation efficiency of 8-12%. This revised dust mass is up to an order of magnitude lower than some previous estimates, which can be attributed to our different interstellar dust corrections, lower SPIRE flux densities, and higher dust temperature than were used in previous studies. The dust within the Crab is predominantly found in dense filaments south of the pulsar, with an average V-band dust extinction of $A_{\text{V}}$=0.20-0.39 mag, consistent with recent optical dust extinction studies. The modelled synchrotron power-law spectrum is consistent with a radio spectral index $α_{\text{radio}}$=0.297$\pm$0.009 and an infrared spectral index $α_{\text{IR}}$=0.429$\pm$0.021. We have identified a millimetre excess emission in the Crab's central regions, and argue that it most likely results from two distinct populations of synchrotron emitting particles. We conclude that the Crab's efficient dust condensation (8-12%) provides further evidence for a scenario where supernovae can provide substantial contributions to the interstellar dust budgets in galaxies.

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arXiv2018

A Dust Twin of Cas A: Cool Dust and 21-micron Silicate Dust Feature in the Supernova Remnant G54.1+0.3

We present infrared (IR) and submillimeter observations of the Crab-like supernova remnant (SNR) G54.1+0.3 including 350 micron (SHARC-II), 870 micron (LABOCA), 70, 100, 160, 250, 350, 500 micron (Herschel) and 3-40 micron (Spitzer). We detect dust features at 9, 11 and 21 micron and a long wavelength continuum dust component. The 21 micron dust coincides with [Ar II] ejecta emission, and the feature is remarkably similar to that in Cas A. The IRAC 8 micron image including Ar ejecta is distributed in a shell-like morphology which is coincident with dust features, suggesting that dust has formed in the ejecta. We create a cold dust map that shows excess emission in the northwestern shell. We fit the spectral energy distribution of the SNR using the continuous distributions of ellipsoidal (CDE) grain model of pre-solar grain SiO2 that reproduces the 21 and 9 micron dust features and discuss grains of SiC and PAH that may be responsible for the 10-13 micron dust features. To reproduce the long-wavelength continuum, we explore models consisting of different grains including Mg2SiO4, MgSiO3, Al2O3, FeS, carbon, and Fe3O4. We tested a model with a temperature-dependent silicate absorption coefficient. We detect cold dust (27-44 K) in the remnant, making this the fourth such SNR with freshly-formed dust. The total dust mass in the SNR ranges from 0.08-0.9 Msun depending on the grain composition, which is comparable to predicted masses from theoretical models. Our estimated dust masses are consistent with the idea that SNe are a significant source of dust in the early Universe.

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arXiv2018

GAMA/H-ATLAS: The Local Dust Mass Function and Cosmic Density as a Function of Galaxy Type - A Benchmark for Models of Galaxy Evolution

We present the dust mass function (DMF) of 15,750 galaxies with redshift $z< 0.1$, drawn from the overlapping area of the GAMA and {\it H-}ATLAS surveys. The DMF is derived using the density corrected $V_{\rm max}$ method, where we estimate $V_{\rm max}$ using: (i) the normal photometric selection limit ($pV_{\rm max}$) and (ii) a bivariate brightness distribution (BBD) technique, which accounts for two selection effects. We fit the data with a Schechter function, and find $M^{*}=(4.65\pm0.18)\times 10^{7}\,h^2_{70}\, M_{\odot}$, $α=(1.22\pm 0.01)$, $ϕ^{*}=(6.26\pm 0.28)\times 10^{-3}\,h^3_{70}\,\rm Mpc^{-3}\,dex^{-1}$. The resulting dust mass density parameter integrated down to $10^4\,M_{\odot}$ is $Ω_{\rm d}=(1.11 \pm0.02)\times 10^{-6}$ which implies the mass fraction of baryons in dust is $f_{m_b}=(2.40\pm0.04)\times 10^{-5}$; cosmic variance adds an extra 7-17\,per\,cent uncertainty to the quoted statistical errors. Our measurements have fewer galaxies with high dust mass than predicted by semi-analytic models. This is because the models include too much dust in high stellar mass galaxies. Conversely, our measurements find more galaxies with high dust mass than predicted by hydrodynamical cosmological simulations. This is likely to be from the long timescales for grain growth assumed in the models. We calculate DMFs split by galaxy type and find dust mass densities of $Ω_{\rm d}=(0.88\pm0.03)\times 10^{-6}$ and $Ω_{\rm d}=(0.060\pm0.005)\times 10^{-6}$ for late-types and early-types respectively. Comparing to the equivalent galaxy stellar mass functions (GSMF) we find that the DMF for late-types is well matched by the GMSF scaled by $(8.07\pm0.35) \times 10^{-4}$.

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arXiv2018

The Herschel-ATLAS Data Release 2 Paper II: Catalogues of far-infrared and submillimetre sources in the fields at the south and north Galactic Poles

The {\it Herschel} Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 660 deg$^2$ with the PACS and SPIRE cameras in five photometric bands: 100, 160, 250, 350 and 500\mic. This is the second of three papers describing the data release for the large fields at the south and north Galactic poles (NGP and SGP). In this paper we describe the catalogues of far-infrared and submillimetre sources for the NGP and SGP, which cover 177 deg$^2$ and 303 deg$^2$, respectively. The catalogues contain 153,367 sources for the NGP field and 193,527 sources for the SGP field detected at more than 4$σ$ significance in any of the 250, 350 or 500\mic\ bands. The source detection is based on the 250\mic\ map, and we present photometry in all five bands for each source, including aperture photometry for sources known to be extended. The rms positional accuracy for the faintest sources is about 2.4 arc seconds in both right ascension and declination. We present a statistical analysis of the catalogues and discuss the practical issues -- completeness, reliability, flux boosting, accuracy of positions, accuracy of flux measurements -- necessary to use the catalogues for astronomical projects.

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arXiv2017

Can planet formation resolve the dust budget crisis in high redshift galaxies?

The process of planet formation offers a rich source of dust production via grain growth in protostellar discs, and via grinding of larger bodies in debris disc systems. Chemical evolution models, designed to follow the build up of metals and dust in galaxies, do not currently account for planet formation. We consider the possibility that the apparent under-prediction of dust mass in high redshift galaxies by chemical evolution models could be in part, due to these models neglecting this process, specifically due to their assumption that a large fraction of the dust mass is removed from the interstellar medium during star formation (so-called astration). By adding a planet formation phase into galaxy chemical evolution, we demonstrate that the dust budget crisis can be partially ameliorated by a factor of 1.3-1.5 only if a) circumstellar discs prevent a large fraction of the dust mass entering the star during its birth, and b) that dust mass is preferentially liberated via jets, winds and outflows rather than accreted into planetary-mass bodies.

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arXiv2017

Very Deep Inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D

Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outwards through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud (LMC) is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array (ALMA) are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

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