Mem. S.A.It. Vol. 83, 77
c SAIt 2012

Memorie dellaSupernovae as sources of dust in the early
universe
T. Nozawa1 , T. Kozasa2 , H. Umeda3 , K. Maeda1 , K. Nomoto1 , N. Tominaga4 ,D. Ỹamasawa2 , A. Habe2 , and H. Hirashita51

Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa,
Chiba 277-8583, Japan, e-mail: takaya.nozawa@ipmu.jp
2
Department of Cosmosciences, Graduate School of Science, Hokkaido University,
Sapporo 060-0810, Japan3
Department of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo
113-0033, Japan
4
Department of Physics, Faculty of Science and Engineering, Konan University, Okamoto,
Kobe 658-8501, Japan
5
Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei
10617, Taiwan

Abstract. We report the mass and size distribution of dust ejected from supernovae (SNe)that are considered to be important sources of dust in the early universe. We find that Type
II-P SNe supply ∼0.1–1.0 M of dust and enrich the interstellar medium (ISM) with large
grains of ≥0.01 µm. Hence, if SNe are dominant dust sources at high redshift, the interstellar
extinction curve is expected to be flat. We also demonstrate that the size distribution ofdust controls the formation of H2 molecules on the grain surfaces and greatly affects theevolution of galaxies. Finally, we examine the formation and evolution of dust in envelopedeficient Type IIb/Ib/Ia SNe and show that they are unlikely to be efficient sources of dust.
Dust, extinction – ISM: supernova remnants – Shock waves – Stars:
Population III – Supernovae: general – Ultraviolet: ISM
Key words.

1. Introduction
Submillimeter and millimeter observations
have detected the rest-frame infrared (IR)emission from dust in the host galaxies ofquasars at redshift z > 5 (see Nozawa et al.
2009 for a review). The observed total IR luminosity exceeds 1013 L , and the estimatedmass of the dust is well above 108 M . This
indicates that the high-redshift quasar systems
Send offprint requests to: T. Nozawa

have been already enriched with dust up to thelevel comparable to or more than nearby dusty
galaxies. Thus, this discovery has raised an important question about the origin of an enormous amount of dust in the early universe.
It has been considered that, at z ≥ 5 when
the cosmic age is younger than about 1 Gyr,interstellar dust can be only supplied by supernovae (SNe) evolving from short-lived massive stars. In this scenario, ∼1.0 M of dust
must be ejected by each SN for explaining thedust mass observed in the high-z quasars (e.g.,

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Nozawa: Dust in the early universe

Dwek et al. 2007). In contrast, recent chemical
evolution models argue that, even in such an
early epoch, grain growth in molecular clouds,
as well as dust production by asymptotic giant
branch stars, would make great contributions todust budget, as is the case in our Galaxy (Gallet al. 2011 and references therein).
On the other hand, the properties of dust
at high redshift seem to be different fromthose at low redshift. In general, the extinction curves of quasars at z ≤ 4 are describedby the interstellar extinction law in the Small
Magellanic Cloud (SMC, e.g., Hopkins et al.
2004). However, the extinction curves obtained
for several quasars at z >∼ 5 are flatter than the
SMC extinction curve and show no bump at
2200 Å that is seen in our Galaxy (Maiolino
et al. 2004; Gallerani et al. 2010). Thus, theextinction properties at z >∼ 5 are incompatible with the nearby ones, suggesting different
origin and evolution of dust at high redshift.
In this paper, we present the mass and sizeof dust grains injected from SNe which are expected to be major sources of dust in the early
universe. Then we discuss the roles that suchdust grains play in interstellar extinction andstar formation history (SFH) in young galaxies.
Finally we describe the formation and ejection
processes of dust in various types of SNe.

2. Dust ejection from primordial SNe
A single massive star whose initial metallicity (Zpr ) is very low could not undergo intensive mass loss during the evolution stage (e.g.,
Heger et al. 2003). Thus, it is expected thatmetal-poor massive stars with the progenitor
mass of Mpr = 8–40 M explode as Type II-P
SNe (SNe II-P) retaining massive H envelopes.
Moreover, in the early universe, very massive
stars with Mpr = 140–260 M are believed to
explode as pair-instability SNe (PISNe, Umeda& Nomoto 2002; Heger et al. 2002).
Several theoretical studies investigated thecondensation of dust in these types of primordial (Zpr = 0) SNe (Todini & Ferrara 2002;
Nozawa et al. 2003; Schneider et al. 2004, seealso Cherchneff & Dwek 2010). All of thesestudies conclude that the total mass of dust

Fig. 1. Total mass of dust ejected from primordial
SNe II-P with Mpr = 13, 20, 25, and 30 M (unmixed case). The results after destruction by the reverse shock are shown for nH,0 = 0.1 (blue), 1.0(red), and 10 cm−3 (green). Dust masses at the timeof dust formation are connected by the dashed line.

formed in the ejecta is 0.1–1.0 M for SNe II-P
and a few tens M for PISNe.
However, dust grains condensed in theejecta are subsequently swept up by the reverse
shock and are processed through destruction
due to sputtering in the shocked gas (Bianchi& Schneider 2007; Nozawa et al. 2007). The
destruction efficiency of dust depends on theinitial size distribution of dust, as well as thegas density in the ISM. Hence, to estimate theproperties of dust finally ejected from SNe, it isnecessary to investigate the formation of dustin the SN ejecta and the destruction of dust by
the reverse shock, self-consistently.
Here we focus on the properties of dust thatis formed in the unmixed ejecta of primordial
SNe II-P and then is released to the ISM; there
has been no clear evidence for the presenceof PISNe (Nagao et al. 2008). Figure 1 shows
the total mass of dust that can survive the destruction by the reverse shock and be injected
into the ISM for the interstellar hydrogen number density of nH,0 = 0.1, 1.0, and 10 cm−3
(Nozawa et al. 2007). Dust destruction is more
efficient for higher ISM density, and more than
80 % of the initial mass are destroyed for nH,0
= 10 cm−3 . Meanwhile, if nH,0 ≤ 1.0 cm−3 ,the dust mass ejected from SNe II-P is 0.07–
0.8 M , which would be high enough to make

Nozawa: Dust in the early universe

79

Fig. 2. Comparison of size distribution function ofFig. 3. Extinction curves derived from the dust

dust before destruction (dashed line) and after destruction (solid lines) by the reverse shock for the
SN II-P model of Mpr = 20 M and Zpr = 0. The results after destruction are shown for nH,0 = 0.1 cm−3
(blue) and 1.0 cm−3 (red). The vertical axis represents the mass of dust in units of M with md (a) being differential dust mass spectrum.

models for the SN II-P with Mpr = 20 M and
Zpr = 0. The results for the dust models after destruction by the reverse shock are shown for nH,0 =0.1 cm−3 (blue) and 1.0 cm−3 (red), while the result
for the dust model before destruction is indicatedby the dashed line. The SMC extinction curve takenfrom Gordon et al. (2003) is given for comparison.

large contributions to a huge amount of dust
detected in the high-z quasars.
Figure 2 compares the dust size distributions summed up over all grain species before and after destruction by the reverse shock.
Before destruction, the radii of newly formed
grains span a wide range from 0.0005 µm to
1.0 µm. However, once these newly formed
grains are swept up by the reverse shock, thesmall grains are trapped in the shocked hot gas
and are predominantly destroyed by sputtering.
Thus, only large grains of >0.01 µm are finallysupplied from SNe II-P to the ISM.
Figure 3 shows the extinction curves calculated on the basis of the size distribution of dustin Figure 2 (Hirashita et al. 2005, 2008). Since
the average radius of dust at the time of formation is relatively large ('0.06 µm), the extinction curve is flatter than the SMC extinction
curve in UV region (1/λ > 4 µm−1 ). On theother hand, the size distributions after destruction are dominated by large grains of >∼0.01 µmwith still larger average radii (>0.1 µm). As aresult, the extinction curves become even flatter, being almost independent of wavelengths.
The size distribution of dust also plays a
key role in the SFH. The surfaces of dust grainprovide formation sites of H2 molecules, which
promotes the formation of stars in metal-poorgalaxies (Hirashita & Ferrara 2002). Figure 4
illustrates how the SFH can be changed by thedifference in the dust size distribution under theassumption that the star formation rate (SFR) is
proportional to the amount of H2 (Yamasawa et
al. 2011). For the size distribution without destruction, which includes a significant numberof small grains, the ratio of the total surface
area to the total dust volume is large. Thus, H2
molecules form very efficiently, and the SFR
is enhanced rapidly with time. However, as
shown in the lower panel of Figure 4, the intensive destruction of small grains due to sputtering substantially suppresses the H2 formation,and the SFR does not increase remarkably.
In summary, SNe II-P are actually efficient
sources of dust in the early universe, supplying∼0.1–1.0 M of dust grains to the ISM. The
grain radii are relatively large, which makes
the extinction curve quite flat and prevents H2
molecules from forming much enough to elevate the SFR dramatically. We emphasize thatthe size distribution of dust heavily affects theSFH, so its effect should be taken into accountin modelling the evolution of galaxies.

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Fig. 4. Upper panel: Star formation and dust enrichment histories as a function of galaxy age inthe case where dust destruction is not considered.
Shown are the mass fraction of H2 molecules ( fH2 ),star formation rate (ψ) in units of M yr−1 , starto-gas mass ratio (Mstar /(Mgas + Mstar )), total dust
cross section per unit volume (σd−20 ), and dust-togas mass ratio (Dd−2 ) in units of 10−2 . Lower panel:Same as the upper panel, but in the case where dust
destruction for nH,0 = 1.0 cm−3 is considered.

3. Dust from various types of SNe
3.1. Type IIb/Ib SNe
In contrast to SNe II-P, SNe IIb/Ib have lost
almost all of the H envelopes before the explosions, so that the ratio of the explosion energy
to the ejecta mass is quite large. As a result,the expansion velocities of SNe IIb/Ib are very
high, which causes three orders of magnitude
lower gas densities than in SNe II-P.
The results of dust formation calculations(Nozawa et al. 2008, 2010) show that, becauseof the low gas density in the ejecta, dust grains
cannot grow to the radii larger than 0.01 µm.
This indicates that the radius of newly formed
dust depends on the mass of H envelope andis significantly smaller in SNe IIb/Ib with lessmassive envelopes than in SNe II-P with more
massive envelopes. The total masses of dust
formed in SNe IIb/Ib are 0.1–1.5 M , whichis in the range of dust mass for SNe II-P.
However, these dust grains cannot be injected into the ISM. The calculations of dust
destruction in the SN IIb show that, for typical ISM density (nH,0 ≥ 0.1 cm−3 ), the newly
formed grains are entirely destroyed inside the
SN remnant (SNR) before 106 yr. This is due tosmall size of newly formed dust and due to theearly arrival of the reverse shock at the dustforming region, both of which result from thethin H envelope. Thus, envelope-stripped SNe
IIb/Ib are likely to be minor sources of dust.
Here it would be worth noticing that themodel of dust formation and evolution in the
SN IIb can naturally reproduce the IR observations of Cas A SNR. The model finds that
the IR emission of Cas A comes from shockheated warm dust of 0.008 M and unshocked
cool (∼40 K) dust of 0.072 M (Nozawa et al.
2010). Soon after this work, the presence of theunshocked dust component was confirmed by
far-IR observations of Cas A with the AKARIand Herschel, which detected cool dust withtemperature of ∼35 K and mass of 0.06–0.075
M (Sibthorpe et al. 2010, Barlow et al. 2010).

3.2. Type Ia SNe
Type Ia SNe (SNe Ia) are considered to be thermonuclear explosions of white dwarfs with the
Chandrasekhar mass. SNe Ia can be potential
sources of interstellar dust in the early universe
if there exists a prompt component of SNe Ia
with ages shorter than 0.1 Gyr.
The calculations of dust formation in theejecta of SNe Ia (Nozawa et al. 2011) find that
∼0.1 M of dust can condense within one year

Nozawa: Dust in the early universe

after the explosion. However, as a result of thesmall ejecta mass ('1.4 M ), the gas density ismuch lower than SNe II-P, and dust grains form
with radii smaller than 0.01 µm. Therefore, as
is the case of SNe IIb/Ib, these small grains
cannot survive the destruction within SNRs for
nH,0 > 0.1 cm−3 . This allows us to conclude
that SNe Ia are poor sources of interstellar dust.

4. Discussion
JIM BEALL: What is the physical cause ofsuch a flat extinction curve?
TAKAYA NOZAWA: Extinction curve represents the wavelength-dependence of extinction properties of interstellar dust. According
to Babinet’s theorem, the extinction efficiencyof dust approaches two when 2πa/λ  1.
Thus, for grain radii of a >∼ 0.1 µm, the optical–
UV extinction curve is independent of grain radius and becomes flat.
MAURI VALTONEN: Could a similar flat extinction curve arise also in galaxy mergers innearby universe?
TAKAYA NOZAWA: Galaxy mergers trigger
starburst where numerous SNe are expected tooccur. SNe II-P primarily supply large grains,so the extinction curves in merging galaxies
may be more or less flat. In fact, the spectralenergy distribution of star-forming galaxies atz ∼ 1 can be well reproduced by the flat extinction curve obtained from our SN-dust model(Kawara et al. 2011; Shimizu et al. 2011).
Acknowledgements. This research has been supported in part by World Premier International
Research Center Initiative (WPI Initiative), MEXT,
Japan, and by the Grant-in-Aid for Scientific
Research of the Japan Society for the Promotion of
Science (20340038, 22684004).

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