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Maiolino et al. laboratories to investigate the properties be fitted with a non-BAL (unreddened) of dust. quasar template with a slope α = −2.1 α By means of low resolution near-IR (Fλ ∝ λ ), which is shown with a dot- spectroscopic observations we have re- ted line in Fig.1. Such a blue slope is cently identified a few BAL quasars at consistent with the intrinsic slope of – z ≈ 5 − 6 (Maiolino et al. 2004). The 2.01 inferred by Reichard et al. (2003)13 most distant among them is the LoBAL for BAL quasars. The observed spec- quasar SDSSJ104845.05+463718.3 (here- trum deviates significantly from the non- after SDSS1048+46). At a redshift z = BAL unreddened template only at λrest < 6.193 (based on a new medium resolution 1700 A.˚ While such a deviation was ini- spectrum around MgIIλ2798; Maiolino et tially ascribed to a severe blend of the al. in prep), this is the only LoBAL CIV and SiIV troughs in the low resolu- at z > 5 currently known, and offers a tion spectrum, the new medium resolu- unique chance of investigating the dust tion spectrum (whose unsmoothed and en- extinction curve at z ≈ 6. This quasar larged version is shown in Fig. 1b) clearly was re-observed at higher spectral reso- shows that this is not the case. The con- lution with the goal of de-blending the tinuum outside the troughs is indeed red- deep troughs characterizing its spectrum der than expected by the extrapolation of and of estimating the reddening of the the longer spectrum through continuum. Observations were obtained the unreddened quasar template (dotted in February 2004 with the Near Infrared line). If such reddening at short wave- Camera Spectrometer (NICS18) at the lengths is due to dust, then the extinc- Telescopio Nazionale Galileo (Canary Is- tion curve must be quite unusual: rela- lands). SDSS1048+46 was observed for tively flat at λ> 1700 A˚ and steeply rising a total of 3 hours, with a slit of 1.5′′ at shorter wavelengths. We can quantita- oriented along the parallactic angle. We tively derive the extinction curve by using used a grism covering the spectral region the equation Aλ = −2.5 log(Fobs/Fintr), 0.8 − 1.45µm. where Fobs is the observed spectrum and Fig. 1a shows the observed spectrum Fintr is the intrinsic spectrum. We avoided (solid line) smoothed to a lower resolution spectral regions contaminated by emis- for sake of clarity, and combined with a sion/absorption features by interpolating previous low resolution spectrum17 of the the continuum from the nearby regions. 26 full wavelength range 0.8 − 2.4µm. At The blend of FeII lines makes more un- the quasar’s redshift our data cover the certain the description of the continuum wavelength range 1200 < λrest < 3300A˚ in the spectral region between 2300A˚ and in the rest frame of the emitted radia- 3050A;˚ however, the latter spectral re- tion. The observed spectrum is much gion is not critical within the context of bluer than LoBAL quasars observed at this paper, since the most important as- z <4, whose average spectrum is shown pect is that the extinction curve must be with the dashed line13. In particular, rather flat in the region between 1700A˚ SDSS1048+46 is bluer than any known and 3300A,˚ and increase rapidly at λrest < LoBAL quasar13 at z <4. Since the red 1700A.˚ For the intrinsic spectrum we used shape of LoBAL quasars at z<4 is ascribed the non-BAL template obtained by the 13 to dust reddening, the much bluer slope of SLOAN survey (this choice is appropri- SDSS1048 already indicates a large varia- ate since non-BAL quasars at z∼6 have 17 tion of dust extinction and reddening from spectra similar to those at z<4) , with z < 4 to z ≈ 6. slopes ranging from α = −2.1 (the red- The continuum at λrest >1700 A˚ can dest slope compatible with our observed A SUPERNOVA ORIGIN FOR DUST IN A HIGH-REDSHIFT QUASAR 3 spectrum at λrest > 1700A)˚ to α = −2.5 of silicates (Mg2SiO4 and MgSiO3), amor- (only 1% of quasars have slopes bluer than phous carbon (AC), magnetite (Fe3O4) 13 this value ). The resulting extinction and corundum (Al2O3). The typical grain curve is shown in Fig. 2 (thick solid line sizes range between 5 A˚ to 0.1 µm, with and shaded region). As expected, the ex- smaller grains being predominantly com- tinction curve inferred for this quasar at posed of silicates and magnetite (sizes ≈5– z =6.2 is quite different with respect to 15 A)˚ and larger ones by amorphous car- the SMC curve which applies to quasars bon (sizes ≈ 100 − 200 A).˚ The pre- at z < 4. The dot-dashed line in Fig. 1b dicted grain properties for different Type- indicates the non-BAL template absorbed II SNe have then been averaged over the with the extinction curve inferred by us in stellar Initial Mass Function (IMF). We Fig.2, which nicely matches the observed adopted a Salpeter IMF, but even higher- spectrum (except for the emission and ab- mass weighted Larson-like IMFs22 do not < sorption lines, whose intensity and shape change significantly the results ( ∼ 2% in depend on the physics of the ionized gas). the extinction curve). The extinction A required to match 3000A˚ The SN dust extinction properties have the observed spectrum is in the range 0.4- been derived using the standard Mie the- 0.8 mag. ory for spherical grains. Grains made The extinction curve inferred from the of AC are the main contributors to ex- most distant LoBAL can also reproduce tinction. We used the optical properties the shape of the second most distant for AC produced in an inert atmosphere BAL SDSS1044-01, a High Ionization (ACAR23), which is appropriate for the BAL (HiBAL)17 at z =5.78. The lat- SN ejecta environment. Other important ter quasar presents much lower reddening contributors to extinction were found to 24,25 than SDSS1048-46 and therefore cannot be Mg2SiO4 and Fe3O4 grains . be used to provide tight constraints on the Fig.2 shows the resulting extinction extinction curve. Nonetheless, similarly to curves, which are in a much better agree- SDSS1048-46, it is characterized a rather ment with the observations than the usual blue continuum at λrest > 1700A˚ and a SMC curve. The extinction curves were reddening at λrest < 1700A,˚ which can be obtained for various initial stellar metal- nicely fitted by using the same extinction licities. The best agreement is found for −2 −4 curve derived above and shown in Fig. 2. the Z = 10 Z⊙ and 10 Z⊙ mod- In order to interpret the observations, els, although the other models do not dif- we have computed the SN dust extinc- fer strongly and are still within the ob- tion curve by using the model proposed by servational uncertainties. We also show Todini & Ferrara (2001)6 which describes the case of dust formed in the ejecta of −4 dust formation in the ejecta of Type-II a single 25 M⊙, Z = 10 Z⊙ Type-II SN; SNe as a function of the progenitor mass the agreement for this case is excellent at and metallicity. In spite of the uncer- most wavelenghts. The plateau between tainties, the model has been successfully 1700 A˚ and 3000 A˚ is due to a local min- applied to interpret the observed prop- imum between two broad absorption fea- erties of SN 1987A6 and of the young, tures caused by AC grains, with the added 20 metal-poor dwarf SBS 0335-052 . flat contribution from Fe3O4 grains. Sili- A grid of SN models has been consid- cate grains contribute to the rise at shorter ered, with different initial stellar progen- wavelenghts. itor masses (12 M⊙ ≤ M ≤ 40 M⊙) We conclude that our analysis, com- 21 and metallicities (0 ≤ Z/Z⊙ ≤ 1) . bined with observations, provides the first The resulting SN dust grains are made direct evidence for dust produced in SN 4 R. Maiolino et al. ejecta, rather than in evolved stars, in an 8. Schneider, R., Ferrara, A., Salvaterra, R., object at z > 6. In particular, we find Dust Formation in Very Massive Primor- that dust purely produced by Type-II SNe dial Supernovae. Mon. Not. R. Astron. can explain very well the observed extinc- Soc. accepted astro-ph/0307087 (2004). tion curve. By implication, we conclude 9. Moseley, S. H., Dwek, E., Glaccum, that much of the dust seen at high red- W., Graham, J. R., Loewenstein, R. F. shifts probably has the same origin. The Far-infrared observations of thermal dust properties of high redshift dust are there- emission from supernova 1987A Nature fore noticeably different from those found 340, 697-699 (1989). at later cosmic times: grains are typically 10. Dunne, L., Eales, S., Ivison, R., Morgan, smaller, due to their different formation H., & Edmunds, M. Type II supernovae history and to the short time available to as a significant source of interstellar dust. subsequently accrete heavy atoms and co- Nature 424, 285-287 (2003). agulate with other grains. 11. Morgan, H. L., Dunne, L., Eales, S. A., Ivison, R. J., & Edmunds, M. G. Cold Received 25 August 2018; Accepted —. Dust in Kepler’s Supernova Remnant. As- trophys. J. 597, L33-L36 (2003). 1. Hirashita, H., Ferrara, A. Effects of dust grains on early galaxy evolution Mon. Not. 12. Richards, G. T., et al. Red and Reddened R. Astron. Soc. 337, 921-937 (2002). Quasars in the . Astron. J. 126, 1131-1147 (2003). 2. Schneider, R., Ferrara, A., Salvaterra, R., Omukai, K., & Bromm, V. Low-mass 13. Reichard, T. A., et al. Continuum and relics of early formation. Nature 422, Emission-Line Properties of Broad Ab- 869-871 (2003). sorption Line Quasars Astron. J. 126, 2594-2607 (2003). 3. Whittet, D. C. B. Dust in the galactic environment. Institute of Physics (IOP) 14. Hopkins, P., Strauss, M. A., Hall, P. B., Publishing, Bristol, 2003, Series in As- et al. Astrophys. J., in press. (2003, astro- tronomy & . ph/0406293) 15. Gaskell, C. M., Goosmann, R. W., An- 4. Bertoldi, F., Carilli, C. L., Cox, P., Fan, tonucci, R. R. J., Whysong, D. H., X., Strauss, M. A., Beelen, A., Omont, A., & Zylka, R. Dust emission from the The Nuclear Reddening Curve for Ac- tive Galactic Nuclei and the Shape of most distant quasars. Astron. Astroph. the Infra-Red to X-Ray Spectral 406, L55-L58 (2003). DistributionAstroph. J. submitted, astro- 5. Priddey, R. S., Isaak, K. G., McMahon, ph/0309595 (2003) R. G., Robson, E. I., & Pearson, C. P. 16. Maiolino, R., Marconi, A., Salvati, M., Quasars as probes of the submillimetre Risaliti, G., Severgnini, P., Oliva, E., La cosmos at z > 5 - I. Preliminary SCUBA Franca, F., & Vanzi, L. Dust in active nu- Mon. Not. R. Astron. Soc. photometry. clei. I. Evidence for “anomalous” proper- 344, L74-L78 (2003). ties. Astron. Astroph. 365, 28-36 (2001).

6. Todini, P. & Ferrara, A. Dust formation in 17. Maiolino, R., Oliva, E., Ghinassi, F., primordial Type II supernovae. Mon. Not. Pedani, M., Mannucci, F., Mujica, R. R. Astron. Soc. 325, 726-736 (2001). & Juarez, Y. Extreme gas properties in the most distant quasars. Astron. Astroph. 7. Nozawa, T., Kozasa, T., Umeda, H., 420, 889-897 (2004) Maeda, K. Nomoto, K. Dust in the Early Universe: Dust Formation in the Ejecta of 18. Baffa, C., et al. NICS: The TNG Near In- Population III Supernovae. Astrophys. J. frared Camera Spectrometer. Astron. As- 598, 785-803 (2003). troph. 378, 722-728 (2001). A SUPERNOVA ORIGIN FOR DUST IN A HIGH-REDSHIFT QUASAR 5 19. Maiolino, R., Juarez, Y., Mujica, R., Na- comments. This work was partially sup- gar, N. M., & Oliva, E. Early star forma- ported by the Italian Ministry of Research tion traced by the highest redshift quasars. (MIUR) and by the National Institute for Astrophys. J. 596, L155-L158 (2003). Astrophysics (INAF). 20. Hirashita, H., Hunt, L. K., Ferrara, A. Dust and hydrogen molecules in the ex- Competing interests statement The tremely metal-poor SBS authors declare that they have no compet- 0335-052 Mon. Not. R. Astron. Soc. 330, ing financial interests. L19-L23 (2002). 21. Woosley, S. E., & Weaver, T. A., The evo- lution and explosion of massive stars. II. Explosive hydrodynamics and nucleosyn- thesis. Astrophys. J. Supp. 101, 181-235 (1995). 22. Early and the evolution of the stellar initial mass function in galaxies Mon. Not. R. Astron. Soc. 301, 569-581 (1998). 23. Zubko, V. G., Mennella, V., Colangeli, L., Bussoletti, E. Optical constants of cosmic carbon analogue grains - I. Simulation of clustering by a modified continuous distri- bution of ellipsoids. Mon. Not. R. Astron. Soc. 282, 1321-1329 (1996). 24. Scott, A., Duley, W. W. Ultraviolet and Infrared Refractive Indices of Amorphous Silicates Astrophys. J. Supp. 105, 401-405 (1996). 25. Mukai, T. Cometary Dust and Interplan- etary Particles in Evolution of Interstel- lar Dust and Related Topics Bonetti, A., Greenberg, J. M., Aiello, S. eds., (Elese- vier Publishers, New York, 1989), 397- 26. Maiolino, R., Juarez, Y., Mujica, R., Na- gar, N., Oliva, E. Early Star Formation Traced by the Highest-Redshift Quasars Astroph. J. 596, L155-L158 (2003)

Correspondence and requests for materials should be ad- dressed to Roberto Maiolino (e-mail: [email protected]).

Acknowledgements All authors have contributed equally to this paper. We are grateful to J. Brucato for providing the optical constant of ACAR grains and we are grateful to M. Walmsley for useful 6 R. Maiolino et al. λ µ obs [ m ] a) 0.9 1.2 1.5 1.8 2.1 Lyα 3 NV CIV Observed (z=6.2) SiIV Non−BAL quasars (z<4, α=−2.1)

] LoBAL (z<4) −1 s −2 2 Al III CIII] erg cm −13

[10 HeII FeII MgII

λ 1

F Al III FeII

MgII 0 SiIV CIV 1500 2000 2500 3000 λ rest [ Å ]

b) Lyα 3 NV CIV Absorbed quasar SiIV (SN dust) ] −1 s −2 2 Al III erg cm −13 [10 λ HeII

F 1

Al III

0 SiIV CIV 1200 1400 1600 1800 λ rest [ Å ] Figure 1. Spectrum of the quasar SDSS1048+46 at redshift 6.2, compared with quasar templates at lower redshift. a) The solid line shows the low resolution near-IR spectrum of the Low Ionization Broad Absorption Line (LoBAL) quasar SDSS1048+46. It is the composition of a previous low resolution λ/∆λ = 75 spectrum17 (shown only for λ > 1.4µm), and the new medium resolution λ/∆λ = 350 spectrum smoothed to a resolution of 75 for sake of clarity. Cross-calibration between the two spectra is ensured by matching the common parts. Upper labels identify the emission lines while lower labels identify the blueshifted absorption features. The presence of strong absorption from the high ionization species CIVλ1549 and SIVλ1397, along with absorption by the low ionization species AlIIIλ1857 and MgIIλ2798 classifies this as a LoBAL quasar. The missing parts of the spectrum are due to the regions of bad atmospheric transmission. The dotted line is the average spectrum of (unreddened) non-BAL quasars at z < 4 with a slope α = −2.1. The dashed line is the average spectrum of LoBAL quasars at z < 4. b) Same as above, but where the solid line shows only the (unsmoothed) medium resolution spectrum (λ/∆λ = 350) of SDSS1048+46. It is important to note the continuum level outside the troughs at λ < 1700A,˚ which is well below the extrapolation of the continuum at longer wavelenghts in the case of no dust reddening (dotted line). Both low and high resolution spectra allow the identification of the spectral regions for the continuum fitting (required to derive the extinction curve), and more specifically: 1275–1290A,˚ 1325–1340A,˚ 1417–1434A,˚ 1482–1489A,˚ 1577–1590A,˚ 1567–1677A,˚ 1708–1782A,˚ 1815–1845A,˚ 2015–2270A,˚ 3050–3255A.˚ The dot–dashed line in panel b) shows the effect of absorbing the non-BAL template with the extinction curve inferred by us and shown in Fig. 2 (thick solid line). A SUPERNOVA ORIGIN FOR DUST IN A HIGH-REDSHIFT QUASAR 7

λ rest [ Å ] 3000 2500 2000 1500 1200 3.0 Z=Z Z=10−2 Z Z=10−4 Z 2.5 Z=0 SMC Z=10−4 Z (z < 4) M=25M 2.0 3000Å / A λ

A 1.5

1.0 Observed z ~ 6 0.5 3 4 5 6 7 8 λ µ −1 1 / rest [ m ]

Figure 2. Extinction curve observed in the quasar SDSS1048+46 at z = 6.2 compared with the extinction curve observed in quasars at z<4 and with the extinction curve expected from supernova (SN) dust. The thick solid line shows the extinction curve inferred for SDSS1048+46. The shaded area shows the associated uncertainty, which includes the range of intrinsic spectral slopes (this uncertainty dominates at short wavelenghts, λ < 1700A),˚ the uncertanty on the continuum interpolation (in particular around the FeII hump between 2300A˚ and 3050A),˚ and the noise in the spectrum. The thin solid line shows the Small Magellanic Cloud (SMC) extinction curve, which applies to quasars at z < 4 (including BAL quasars). The other lines indicate theoretical predictions for dust produced by SNe. More specifically: dot-dashed, long-dashed, short-dashed and dotted lines represent the extinction curves produced by SNe obtained assuming that stars form according to a Salpeter IMF and initial −4 −2 metallicities 0, 10 , 10 , and 1 Z⊙, respectively. We also show the case of dust formed in the ejecta −4 of a single 25 M⊙, Z = 10 Z⊙ Type-II SN (triple-dot-dashed line).