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Presentation v2
- 1. The role of core collapse supernovae in the context of dust production in the early universe Mikkel Juhl Hobert Dark Cosmology Centre, Niels Bohr Institute Master’s thesis Supervisor: Darach Watson Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 1
- 2. Table of Contents Introduction • Cosmic dust in the early universe • Core collapse supernovae and supernova remnants My project • Dust emission and dust models • Cold dust in young core collapse supernova remnants in the Large Magellanic Cloud Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 2
- 3. Cosmic dust Complex structures of one or more elements. Only about 0.1% of interstellar matter. Absorbs and scatters light (extinction). Reemits absorbed light as infrared radiation. Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 3
- 4. Dust in the early universe Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 4 One or more processes must produce large amounts of dust, fast and efficiently.
- 5. • Death of high mass stars. • Different elements burn in the star until the core reaches iron. • Nuclear fusion in the core stops. The star starts to collapse. • Inner core is compressed into neutrons and neutrinos. • Outer material bounces on the degenerated core creating a shock. • Shock initially halts but is revived by neutrino heating. • Outer material is blasted away leaving a stellar remnant behind. Core collapse supernovae Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 5
- 6. Supernova remnants • Free expansion phase Lasts for ~102 − 103 yr. • Adiabatic phase Lasts for ~2 × 104 yr. • Radiative phase Lasts for ~105 − 106 yr. Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 6
- 7. Dust emission Emits thermally, not as a black body 𝐹𝜈 = 𝐵𝜈 𝑇𝑑 𝑀 𝑑 𝐷2 𝜅 𝜈 = 𝜅0 𝜈 𝜈0 𝛽 𝐹𝜈 ∝ 𝜈2 Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 7 𝜅 𝜈 +𝛽 Emits thermally as a gray body (Rayleigh-Jeans regime)
- 8. Dust models Astronomical silicates (AS) (minerals rich in Mg, Si and O) Amorphous carbon (e.g. coal and soot, rich in C). i. ACAR sample ii. BE sample Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 8
- 9. Observing cold dust Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 9 Spitzer Space Telescope Herschel Space Observatory Mid infrared (MIPS) Far infrared and submillimeter (PACS and SPIRE)
- 10. Young core collapse supernova remnants in the Large Magellanic Cloud Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 10 Large Magellanic Cloud • Small and well-known distance, 𝐷 = 50 kpc • Face-on geometry • Rich in gas and dust • Rapid star formation • Many supernovae and supernova remnants Sample criteria • Young core collapse supernova remnants • Must be in regions with little contamination • Must be distinguishable from the background
- 11. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 11 Subtracting the background with an annulus Subtracting the background with a median filter Aperture photometry Uniform background Varying background
- 12. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 12 24 𝜇m 70 𝜇m 100 𝜇m 160 𝜇m 250 𝜇m 350 𝜇m 500 𝜇m
- 13. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 13 N49
- 14. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 14 24 𝜇m 70 𝜇m 100 𝜇m 160 𝜇m 250 𝜇m 350 𝜇m 500 𝜇m 70 𝜇m 100 𝜇m 160 𝜇m 250 𝜇m 350 𝜇m 500 𝜇m 24 𝜇m
- 15. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 15 N132D
- 16. Cold dust in the supernova remnants Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 16 SNR AS 𝑴 𝒅 𝑻 𝒅 (𝑴☉) (K) ACAR 𝑴 𝒅 𝑻 𝒅 (𝑴☉) (K) BE 𝑴 𝒅 𝑻 𝒅 (𝑴☉) (K) SN1987A 3.0−0.4 +0.5 17.1−0.5 +0.5 0.6−0.08 +0.09 19.8−0.6 +0.6 1.1−0.1 +0.2 19.0−0.6 +0.6 N11L 0.05−0.05 +0.1 30.5−12.0 +6.8 0.03−0.03 +0.2 18.0−0.02 +16.2 0.03−0.03 +0.2 23.0−05.0 +13.3 N23 0.08−0.08 +0.1 30.4−12.4 +7.2 0.02−0.02 +0.02 35.4−17.4 +7.8 0.03−0.02 +0.05 35.7−17.6 +7.0 N132D 0.9−0.5 +2.1 30.8−8.6 +10.7 0.2−0.1 +0.4 40.7−15.9 +11.3 0.3−0.2 +0.8 37.6−13.4 +11.3 N49 9.5−1.5 +1.8 32.1−1.3 +1.1 1.9−0.3 +0.3 40.4−1.4 +1.5 3.5−0.5 +0.6 37.7−1.2 +1.3 N63A 18.2−2.9 +3.3 28.7−0.9 +0.9 3.4−0.5 +0.6 35.5−1.1 +1.2 6.5−1.0 +1.1 33.3−1. +1.1
- 17. Dust from swept-up interstellar matter Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 17 𝑛HI (neutral) 𝑛HII (ionized) 𝑛H2 (molecular)
- 18. Dust from swept-up interstellar matter SNR 𝒏 𝐇𝐈 (𝐜𝐦−𝟑) 𝒏 𝐇𝐈𝐈 (𝐜𝐦−𝟑) 𝒏 𝐇 𝟐 (𝐜𝐦−𝟑 ) 𝒏 𝐇 (𝐜𝐦−𝟑) D2G* (𝟏𝟎−𝟑) 𝑴 𝒅,𝐈𝐒𝐌 (𝑴☉) SN1987A ... ... ... 1 4.15 6 × 10−6 N11L 2.64 0.81 ... 3.45 4.17 1.0 N23 1.38 0.66 ... 2.04 4.44 0.2 N132D 1.34 0.87 0.21 2.63 8.26 4.5 N49 3.14 1.96 0.13 5.36 6.25 6.2 N63A 0.28 2.1 ... 2.38 9.62 2.0 Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 18 *Temim et al. (2015)
- 19. Summary • Each target must produce, on average, 0.4 𝑀☉ of dust (Dwek et al., 2007). • Low amounts of observed dust in N11L and N23. • High amounts of observed dust in SN1987A and N63A. • Dust in N132D and N49 is probably swept up. • Total dust mass strongly depends on i. The specific dust model. ii. The accuracy of the background subtraction. • Still uncertainty surrounding core collapse supernovae as key contributors of dust. • They are likely not the only significant sources of dust. Dark Cosmology Centre, Niels Bohr Institute 3/22/2016 Dias 19
Editor's Notes
- Thank you all for coming here today. For the next 30 minutes I will talk about my project which is titled [TITLE].
- First I will be talking about [1]. Then I’ll try to explain what [2] are and some physics behind it. Finally I’ll talk a little bit about [3] before I reach the main work of my project; [4].
- Dust is larger complex structures of solid often consisting of multiple elements. It’s basically smoke-like particles. In interstellar space, it’s only a small fraction of normal matter, but it’s still a very important component of the universe. However, cosmic dust is currently not very well understood. What we do understand is that it absorbs and scatters light. It absorbs blue light better than it absorbs red light, so when we observe an object behind it, the object will typically appear more red to us. It then reemits the absorbed light as infrared radiation.
- In recent years, people have observed large amounts of dust in galaxies at a time when the universe was very young. For example, over 100 million solar masses of dust has been seen in a galaxy only around 400 million years after the first stars in the universe ignited. This is the similar to if you were sitting in your spotless living room and went to the kitchen and came back two minutes later to find that your room was suddenly filled with dust. This would raise the question: How did the dust appear? Something must have made the dust and put it there, fast and efficiently.
- The major candidates are core collapse supernovae of high mass stars. High mass stars live and die almost instantenously and they also produce a lot of the heavy elements that make up the dust. In fact it’s estimated that each core collapse on average must contribute about 0.4 solar masses of dust if they are the only contributing source. Core collapse supernovae are the death of high mass stars. In its lifetime, a star burns fuel in its interior in order to sustain its own gravity and keep it from collapsing upon itself. However, at some point the fuel burning in the core reaches iron which cannot be burned any further so the star starts to collapse. As it collapses, the inner core is compressed tightly and material is converted to neutrons and neutrinos by a process known as electron capture. At some point, the core becomes so dense that it cannot be squeezed anymore and the compression stops. Outer materials falls in and bounces on the surface and sends out a shockwave. The shock doesn’t have enough energy to blow away the outer material so it initially stops but is suddenly revived again when it’s heated by neutrinos anti-neutrinos created from pair productions. Finally the outer material is expelled in a supernova remnant, leaving behind a neutron star or black hole.
- After the core collapse, the material starts to propagate out as a shock front in the ambient medium. This is what we call a supernova remnant. A supernova remnant is typically divided into three evolutionary phases. In the free expansion phase the shock propagates uninterrupted through the interstellar medium which it sweeps up along the way. At some point, the accumulated mass becomes so large that it slows down the expansion rate. A contact discontinuity between the accumulated and interior material sends back a reverse shock which heats the interior to such high temperatures that the atoms become ionized and unable to recombine. Hence radiation losses are negligible and so the remnant expands and cools adiabatically. This is known as the adiabatic phase. When the remnant has cooled enough, atoms will again be able to recombine and significantly cool via radiation and the expansion rate slows down even further. Ambient matter continues to accumulate and finally after a few hundred thousand years, the remnant disperses into the interstellar medium. This is the radiation phase. Here is a real example of a supernova remnant from a core collapse supernova called the Crab Nebula which is associated with the supernova SN 1054 recorded by Chinese astronomers around a 1000 years ago.
- Typically, an object that emits thermally will radiate as a black body. Here the flux density of the source depends on its mass and distance to us as well as the Planck black body spectrum. However, dust doesn’t emit as a black body but instead as what we call a gray body, which is in this mass absorption coefficient. The mass extinction coefficient depends on the frequency and typically it can be parametrized as such for long wavelengths. Here, the parameters also strongly depend on the geometrical and internal properties of the dust grains (shape, size, density etc.). So basically if we measure the flux and distance to the dust, we can estimate its temperature and mass if we assume some specific dust composition.
- In my project I have assumed three different dust compositions. Astronomical silicates and amorphous carbon for which I’ve used two different samples. Here on the right we see how the mass absorption coefficient depends on the wavelength for the three models.
- Since dust emits infrared light, I’ve used data from the two space telescopes you see here. The Spitzer Space Telescope has the onboard instrument MIPS that observes mid infrared light. The Herschel Space Observatory observes far infrared and submillimeter light with the instruments PACS and SPIRE.
- I’ve chosen a sample of young supernova remnants from core collapse supernovae in the nearby Large Magellanic Cloud galaxy, which has been observed with the Spitzer and Herschel telescopes. The Large Magellanic Cloud is an excellent stellar laboratory for multiple reasons. First of all, the distance is very well known and galaxy is almost seen face-on. It’s also rich in gas and dust, has rapid star formation and contains many supernovae and supernova remnants. I’ve imposed some criteria on my sample. The remnants must be relatively young, they must be in regions with little contamination and they must be distinguishable from the background. Here on the right I’ve marked the young core collapse supernova remnants´in the Large Magellanic Cloud. The ones that satisfy my criteria are marked in green. The red names are the one I ultimately excluded.
- I measured the flux with a standard astronomical procedure called aperture photometry. Typically when we have an object we can count the flux coming from within an aperture around the target. The target sits on top of a background field which we have to subtract. Typically if the background is fairly uniform, we can estimate the background from an annulus centered the target and subtract it from the total flux. If the background varies a lot, however, it can be more useful to create a median filter. A median filter imitates the large scale structure in the picture which we can then subtract from the image.
- Here we see the standard annulus background subtraction where my supernova remnant, inside the aperture, is in a relatively uniform background. The different images corresponds to different wavelengths.
- After the background subtraction we can count the flux from the aperture for each wavelength to create the Spectral Energy Distribution function of the target and fit it with our modified black body function for our three dust models. I’ve actually fitted with both a warm and a cold component for each dust type, however, only the cold component is shown.
- Here, another target sits in a significantly varying background which we can see by the increasing density, so hence I’ve subtracted it with a median filter, shown in the lower two row, before counting the flux from the aperture.
- This is the corresponding Spectral Energy Distribution Function, also for a double component modified black body for warm and cold dust, where only the cold component is shown. Notice that the uncertainty in the long wavelength bands become increasingly large, probably owing to both the increasingly lower image resolutions and to general difficulties in accurately determining the background.
- Here are my results for the cold dust components for my 6 supernova remnants. I want to draw your attention to the dust masses for the three dust models and notice that they vary a lot for each distinct model. These two remnants appear to have a relatively significant amounts of cold dust. These two have overwhelmingly large amounts, especially compared to the rest.
- It seems unlikely that over 10 solar masses of dust can be produced by a single core collapse supernova, so I’ve examined how much of it comes from swept-up interstellar matter. I’ve done this by examining the interstellar gas densities around the remnants. The hydrogen gas exists in three forms; neutral, ionized and molecular hydrogen. I’ve then calculated the total gas masses in the remnants and transformed them to total swept-up dust masses using local estimates of a quantity we call the dust-to-gas mass ratios.
- Here we the see total swept-up dust in the remnants. The swept-up masses in N132D and N49 appear to be relatively large so the dust we see is most likely swept-up material. SN1987A and N63A have relatively low swept-up masses, however, and so the dust we see has likely been produced following the core collapse.
- Each target must produce, on average, 0.4 solar masses of dust. The dust observed in N11L and N23 is significantly lower than this. However, the dust observed in SN1987A and N63A is significantly larger than this. The dust seen in N132D and N49 is probably swept up interstellar material. The measured total dust masses strongly depend both on the specific dust model and also the accuracy of the background subtraction, which some of my results is indicative of that I wasn’t able to do sufficiently. All in all, the conclusion of my project is that it’s still uncertain whether core collapse supernovae are the key contributors of dust. However, from the results I’ve represented I personally don’t think it’s likely that they are the only significant sources of dust.