Large Dust Masses Research Articles

The evolved circumbinary disk of AC Herculis: a radiative transfer, interferometric, and mineralogical study

We aim to constrain the structure of the circumstellar material around the post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial distribution of the amorphous as well as of the crystalline dust. We present very high-quality mid-IR interferometric data that were obtained with MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative transfer code, to find a good structure model of AC Her's circumbinary disk. We include a grain size distribution and midplane settling of dust self-consistently. The spatial distribution of crystalline forsterite in the disk is investigated with the mid-IR features, the 69~$\mu$m band and the 11.3~$\mu$m signatures in the interferometric data. All the data are well fitted. The inclination and position angle of the disk are well determined at i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about an order of magnitude larger than the dust sublimation radius. Significant grain growth has occurred, with mm-sized grains being settled to the midplane of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming {\alpha}=0.01, a good fit is obtained with a small grain size power law index of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is compatible with recent estimates employing direct gas diagnostics. The spatial distribution of the forsterite is different from the amorphous dust, as more warm forsterite is needed in the surface layers of the inner disk. The disk in AC Her is very evolved, with its small gas/dust ratio and large inner hole. Mid-IR interferometry offers unique constraints, complementary to mid-IR features, for studying the mineralogy in disks. A better uv coverage is needed to constrain in detail the distribution of the crystalline forsterite in AC Her, but we find strong similarities with the protoplanetary disk HD100546.

STAR FORMATION BIMODALITY IN EARLY-TYPE GALAXIES

We compute the properties of a sample of 221 local early-type galaxies with a spectral energy distribution (SED) modeling software, CIGALEMC. Concentrating on the star forming activity and dust contents, we derive parameters such as the specific star formation rate, the dust luminosity, dust mass and temperature. 52 % of our sample is composed of elliptical (E) galaxies and 48 % of lenticular (S0) galaxies. We find a larger proportion of S0 galaxies among galaxies with a large specific star formation rate (sSFR) and large specific dust emission. The stronger activity of S0 galaxies is confirmed by larger dust masses. We investigate the relative proportion of active galactic nuclei (AGN) and star-forming (SF) galaxies in our sample using spectroscopic SDSS data and near-infrared selection techniques, and find a larger proportion of AGN dominated galaxy in the S0 sample than the E one. This could corroborate a scenario where blue galaxies evolve into red ellipticals by passing through a S0 AGN active period while quenching its star formation. Finally, we find a good agreement comparing our estimates with color indicators.

The dust content of QSO hosts at high redshift

Infrared observations of high-z quasar (QSO) hosts indicate the presence of large masses of dust in the early universe. When combined with other observables, such as neutral gas masses and star formation rates, the dust content of z~6 QSO hosts may help constraining their star formation history. We have collected a database of 58 sources from the literature discovered by various surveys and observed in the FIR. We have interpreted the available data by means of chemical evolution models for forming proto-spheroids, investigating the role of the major parameters regulating star formation and dust production. For a few systems, given the derived small dynamical masses, the observed dust content can be explained only assuming a top-heavy initial mass function, an enhanced star formation efficiency and an increased rate of dust accretion. However, the possibility that, for some systems, the dynamical mass has been underestimated cannot be excluded. If this were the case, the dust mass can be accounted for by standard model assumptions. We provide predictions regarding the abundance of the descendants of QSO hosts; albeit rare, such systems should be present and detectable by future deep surveys such as Euclid already at z>4.

THE NEARBY, YOUNG, ISOLATED, DUSTY STAR HD 166191

We report an in-depth study of the F8-type star HD 166191, identified in an ongoing survey for stars exhibiting infrared emission above their expected photospheres in the Wide-field Infrared Survey Explorer all-sky catalog. The fractional IR luminosity measured from 3.5 to 70 $\mu$m is exceptionally high (L$_{IR}$/L$_{bol}$ $\sim$10%). Near-diffraction limited imaging observations with the T-ReCS Si filter set on the Gemini South telescope and adaptive optics imaging with the NIRC2 Lp filter on the Keck II telescope confirmed that the excess emission coincides with the star. Si-band images show a strong solid-state emission feature at $\sim$10 $\mu$m. Theoretical evolutionary isochrones and optical spectroscopic observations indicate a stellar age in the range 10-100 Myr. The large dust mass seen in HD 166191's terrestrial planet zone is indicative of a recent collision between planetary embryos or massive ongoing collisional grinding associated with planet building.

Quasar feedback in the early Universe: The case of SDSS J1148+5251

Abstract Galaxy-scale gas outflows triggered by active galactic nuclei have been proposed as a key physical process to regulate the co-evolution of nuclear black holes and their host galaxies. The recent detection of a massive gas outflow in one of the most distant quasars, SDSS J1148+5251 at z= 6.4, presented by Maiolino et al., strongly supports this idea and suggests that strong quasar feedback is already at work at very early times. In a previous work, Valiante et al., we have presented a hierarchical semi-analytical model, GAMETE/QSOdust, for the formation and evolution of high-redshift quasars, and we have applied it to the quasar SDSS J1148+5251, with the aim of investigating the star formation history, the nature of the dominant stellar populations and the origin and properties of the large dust mass observed in the host galaxy. A robust prediction of the model is that the evolution of the nuclear black hole and of the host galaxy are tightly coupled by quasar feedback in the form of strong galaxy-scale winds. In the present Letter, we show that the gas outflow rate predicted by GAMETE/QSOdust is in good agreement with the lower limit of 3500M⊙yr−1 inferred by the observations. According to the model, the observed outflow at z= 6.4 is dominated by quasar feedback, as the outflow rate has already considerably depleted the gas content of the host galaxy, leading to a downturn in the star formation rate at z &amp;lt; 7–8. Hence, we predict that supernova explosions give a negligible contribution to the observed winds at z= 6.4.

Dust in the early Universe: evidence for non-stellar dust production or observational errors?

Observations have revealed unexpectedly large amounts of dust in high-redshift galaxies and its origin is still much debated. Valiante et al. (2009, MNRAS, 397, 1661) suggested the net stellar dust production of the quasar host galaxy SDSS J1148+5251 may be sufficient to explain the large dust mass detected in this galaxy, albeit under some very special assumptions (e.g., 'closed box' evolution and a rather high gas mass). Here it is shown that since accretion of essentially pristine material may lower the efficiency of dust formation significantly, and the observationally derived dust-to-gas ratios for these high-redshift galaxies are remarkably high, stellar dust production is likely insufficient. A model including metallicity-dependent, non-stellar dust formation ('secondary dust') is presented. The required contribution from this non-stellar dust component appears too large, however. If all observational constraints are to be met, the resultant dust-to-metals ratio is close to unity, which means that almost all interstellar metals exist in the form dust. This is a very unlikely situation and suggests the large dust-to-gas ratios at high-redshifts may be due to observational uncertainties and/or or incorrect calibration of conversion factors for gas and dust tracers.

The Herschel Space Observatory View of the Gas and Dust Properties of Dwarf Galaxies

The Herschel Dwarf Galaxy Survey investigates the metal enrichment of the dust and gas in galaxies through observations of the local universe dwarf galaxies via the new far-infrared (FIR) and submillimetre imaging spectroscopic and photometric observations from the recently launched Herschel Space Observatory. The dust spectral energy distributions can now be constrained out to submm wavelengths and often show a submm excess in the low metallicity galaxies, which, if tracing very cold dust, could highlight large dust masses, sometimes not easily reconciled with their low-metallicity and observed gas mass. Additionally, Herschel observations of the FIR fine-structure lines probe the low density ionised gas, the HII regions and photodissociation regions. L [ CII ] /L CO is remarkably high in dwarf galaxies – typically an order of magnitude larger than more metal-rich starburst galaxies, pointing to a potentially significant reservoir of H 2 not traced by CO but shielded in the C + -emitting envelopes. Thus a more accurate estimate of the molecular gas mass in low metallicity galaxies will be via the ( CO + [ CII ]) to H 2 conversion factor. The 88 μm [OIII] line is the brightest of all FIR lines in low-metallicity galaxies, sometimes 1.5 to 2 time brighter than the 158 μm [CII] line which is usually the dominate FIR coolant in normal spiral and starburst galaxies. The 88 μm [OIII] line may become the workhorse diagnostic for the high-redshift low-metallicity galaxies which will be targets for future submm observatories, such as ALMA. Further observations from The Herschel Dwarf Galaxy survey will provide a more complete picture of the nature of the dust and gas in low metallicity galaxies and thus a more comprehensive view of the chemical evolution of galaxies.

The Elusive ISM of Dwarf Galaxies: Excess Submillimetre Emission &amp; CO-Dark Molecular Gas

The Herschel Dwarf Galaxy Survey investigates the interplay of star formation activity and the the metal-poor gas and dust of dwarf galaxies using FIR and submillimetre imaging spectroscopic and photometric observations in the 50 to 550mu window of the Herschel Space Observatory. The dust SEDs are well constrained with the new Herschel and MIR Spitzer data. A submillimetre excess is often found in low metallicity galaxies, which,if tracing very cold dust, would highlight large dust masses not easily reconciled in some cases, given the low metallicities and expected gas-to-dust mass ratios. The galaxies are also mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122 and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regions and photodissociation regions. While still early in the Herschel mission we can already see, along with earlier studies, that line ratios in the metal-poor ISM differ remarkably from those in the metal-rich starburst environments. In dwarf galaxies, L[CII]/L(CO) (>10^4) is at least an order of magnitude greater than in the most metal-rich starburst galaxies. The enhanced [CII] arises from the larger photodissociation region where H2, not traced by the CO, can exist. The 88mu [OIII] line usually dominates the FIR line emission over galaxy-wide scales in dwarf galaxies, not the 158mu [CII] line which is the dominant FIR cooling line in metal-rich galaxies. All of the FIR lines together can contribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey will provide statistical information on the nature of the dust and gas in low metallicity galaxies, elucidating the origin of the submm excess in dwarf galaxies, and help determine a ([CII] +CO) to H2 conversion factor, thus providing observational constraints on chemical evolution models of galaxies.

Crystallization of ice in Comet 17P/Holmes: Probably not responsible for the explosive 2007 megaburst

Our work was inspired by the recent brightening of Comet 17P/Holmes. The recently observed increase in brightness of this comet was correlated with emission of dust, probably larger in mass than the dust mantle of the nucleus. We analyzed the hypothesis that the comet can eject a large mass of dust due to non-uniform crystallization of amorphous water ice. For this purpose, we simulated the evolution of a model nucleus on the orbit of Comet 17P/Holmes. The nucleus is composed of water ice and dust and has the shape of an elongated ellipsoid. The simulations include crystallization of amorphous ice in the nucleus, changes in the dust mantle thickness, and changes in the nucleus orientation in space. Our computations indicate that: (i) ejection of the dust cover triggers crystallization of ice independently on the material properties of the nucleus; (ii) moderate changes in the nucleus orientation (∼50°) may result in an acceleration of the crystallization of ice in the northern hemisphere, while a rather large change in the orientation (∼120°) is needed to cause a significant jump of the crystallization front in the southern hemisphere, where the emission of dust during the recent brightening was strongest. We investigated the possible reason for an explosion and we have found that the crystallization of the water ice itself is probably not sufficient.

MILLIMETER OBSERVATIONS OF A SAMPLE OF HIGH-REDSHIFT OBSCURED QUASARS

We present observations at 1.2 mm with MAMBO-II of a sample of z>~2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. Five out of 21 sources (24%) are detected at a significance of >=3sigma. Stacking all sources leads to a statistical detection of <S_1.2mm>= 0.96+-0.11 mJy and stacking only the non-detections also yields a statistical detection, with <S_1.2mm>= 0.51+-0.13 mJy. This corresponds to a typical far-infrared luminosity L_FIR~4x10^12 Lsol. If the far-infrared luminosity is powered entirely by star-formation, and not by AGN-heated dust, then the characteristic inferred star-formation rate is ~700 Msol yr-1. This far-infrared luminosity implies a dust mass of M_dust~3x10^8 Msol. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. We present dust SEDs for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. There is a hint that the host galaxies of obscured quasars must have higher far-infrared luminosities and cool-dust masses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z=2.767, we detect the CO(3-2) transition, with S_CO Delta nu=630+-50 mJy km s-1, corresponding to L_CO(3-2)= 3.2x10^7 Lsol, or L'_CO(3-2)=2.4x10^10 K km s-1 pc2. For another source at z=4.17, the lack of detection of the CO(4-3) line yields a limit of L'_CO(4-3)<1x10^10 K km s-1 pc2. Molecular gas masses, gas depletion timescales and gas-to-dust ratios are estimated (Abridged).

Polycyclic aromatic hydrocarbon selected galaxies

<i>Context. <i/>This is the fourth in a series of papers based on the ISOCAM Parallel Survey at 6.7 <i>μ<i/>m. While the first three papers have been devoted to active galactic nuclei (AGN), here we report on emission-line galaxies without AGN signatures in their optical spectra. <i>Aims. <i/> Polycyclic aromatic hydrocarbon (PAH) emission has been found in both starbursts and modestly starforming galaxies, but the relation between starforming activity and PAH luminosity is still a matter of debate. The different correlation degrees could be caused by the variety of optical and far-infrared sample selection criteria. In order to obtain a census of the typical properties of PAH emitting galaxies, we here study moderately distant galaxies which have been selected by their PAH emission.<i>Methods. <i/>Combining the ISOCAM Parallel Survey at 6.7 <i>μ<i/>m with 2MASS we have colour-selected a sample of 120 candidates for strong PAH emission. We obtained optical and mid-infrared spectra of 75 and 19 sources, respectively, and analysed IRAS-ADDSCANs and available Spitzer 3.6–160 <i>μ<i/>m photometry. <i>Results. <i/> The Spitzer mid-infrared spectra exhibit clear PAH features and corroborate that our photometric selection criteria trace the PAH emission of galaxies fairly well. The optical spectra show emission lines, at median redshift , as well as H and Ca II absorption, indicating ongoing starformation as well as post-starbursts. The mid- and far-infrared spectral energy distributions (SEDs) provide evidence for a broad range of far-infrared (FIR) luminosities (), but in general the dust is colder ( K, ) than for starburst galaxies like M 82 ( K). For most galaxies the monocromatic luminosity peaks at about equal height at optical, 6.7 <i>μ<i/>m (PAH) and FIR wavelengths. In about 15% of the sources the FIR luminosity exceeds the optical and PAH energy output by about a factor 5–10 despite the cool dust temperature; in these galaxies a large dust mass of 10<sup>8<sup/>–10<sup>9<sup/> is inferred. <i>Conclusions. <i/>At moderate distance (), PAH selected galaxies turn out to be a quite heterogeneous population of dust-rich, partly infrared-luminous galaxies but mostly cool with a range of post-starburst signatures and starforming activity which appears to be rather modest relative to the entire gas content (derived from the dust mass and assuming a standard gas/dust ratio). Our results on PAH selected galaxies question the often expressed interpretation that the majority of high redshift galaxies detected in 15 and 24 <i>μ<i/>m surveys are dominated by powerful ongoing starbursts with high starforming efficiency.

THE LOCAL ENVIRONMENT OF THE FU-ORIONIS-LIKE OBJECTS AR 6A AND 6B

We present new 12CO J = 3–2 and HCN J = 3–2 molecular line maps of the region surrounding the young star AR 6 using the 15 m James Clerk Maxwell Telescope (JCMT). AR 6 was previously found to be a double source with both components exhibiting several characteristics of FU Orionis (FUor) eruptive variable stars. The aims of this investigation were to determine if the AR 6 sources are associated with molecular outflows and if a significant reservoir of natal molecular gas and dust exists around the stars. These observations form a part of a large-scale study of the outflow and circumstellar environment characteristics of FUors and FUor-like objects to place constrains on the age and evolutionary state of sources exhibiting FUor-like tendencies. Our data indicate that AR 6, like FUor itself, does not possess a CO outflow and likewise, does not show evidence for large amounts of molecular gas in its circumstellar environment. In fact, AR 6 seems to lie in a local minimum of HCN emission. This is also found in 850 μm dust emission seen in JCMT archival data. We conclude that from the near-infrared to the sub-millimeter, AR 6 is similar to FUor in several respects. We interpret the lack of significant dust and molecular gas in the circumstellar environment of AR 6, together with the large near-infrared (NIR) thermal excess, as evidence that the sources have exhausted their natal envelopes, that they have at least small hot circumstellar disks, and that they are more evolved than Class I protostars. This, in itself, suggests that, since FUor eruptions have also been observed in stars with large dust mass envelopes (e.g., V346 Nor) and with CO outflows (e.g., L1551 IRS5), FUor events probably occur at many different stages in the early, formative phase of a star's life, and lends support to the idea that FUor outbursts are repetitive like their shorter-lived relatives occurring in EXor eruptive variables. Finally, we study the stellar environment around AR 6 using Two Micron All Sky Survey, Spitzer Infrared Array Camera, and Chandra ACIS images and show that, being part of the "Spokes" young stellar cluster, AR 6 is unlike many FUors which are typically located in more sparsely populated regions.

Dust around red supergiants in the Magellanic Clouds

AbstractIt is both surprising and exciting to find that young galaxies at high redshift contain large dust masses. For galaxies at z &gt; 5, after only 1 Gyr, there has not been time for low-mass stars to have evolved to the AGB phase and produce dust. In such galaxies, Type II SNe and red supergiants (RSGs) may even dominate the dust production rate. It has long been known that RSG atmospheres produce dust, but little is known about it. We are pursuing three parallel studies to better understand RSG dust. First, we are using optical spectra and JHK photometry to characterize the optical and near-IR extinction curves of the RSGs. Second, we are using the optical spectra combined with 2MASS, IRAC and MIPS photometry to estimate the dust mass loss rates from Local Group RSGs. In addition, we will use our Monte Carlo radiative transfer models to analyze the emission from dust in the circumstellar shells. Third, the final piece of the puzzle is being provided by obtaining new IRS spectra of LMC and SMC RSGs. We plan to use the IRS to make a systematic study of the dust properties in RSG shells in the LMC and SMC so that we can probe how they may vary with a large range of galactic metallicities. The derived stellar SEDs and extinction curves will be combined with Spitzer IRAC and MIPS photometry and IRS spectra for use as inputs to our Monte Carlo codes which will be used to study the composition, size distributions and clumpiness of the dust.

Deep Submillimeter Observations of Two Lyα‐emitting Galaxies atz∼ 6.5

We present deep submillimeter imaging of two spectroscopically confirmed z~6.5 Lyman-alpha emitters (LAEs) in the Subaru Deep Field. Although we reach the nominal confusion limit at 850 micron, neither LAE is detected at 850 micron nor 450 micron, thus we conclude that the LAEs do not contain large dust masses (<2.3e8 Msun and <5.7e8 Msun). The limit on their average L(FIR)/L(UV) ratios (<~35) is substantially lower than seen for most submillimeter selected galaxies at z~3, and is within the range of values exhibited by Lyman-break galaxies. We place upper-limits on their individual star formation rates of <~248 Msun/yr and <~613 Msun/yr, and on the cosmic star formation rate density of the z~6.5 LAE population of <~0.05 Msun/yr/Mpc^3. In the two submm pointings, we also serendipitously detect seven sources at 850 micron that we estimate to lie at 1<z<5.

Submillimetre emission from Carinae

We present critical, long-wavelength observations of ? Carinae in the submillimetre using Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope at 850 and 450 ?m to confirm the presence of a large mass of warm dust around the central star. We fit a two-component blackbody to the infrared-submm spectral energy distribution and estimate between 0.3 and 0.7 M? of dust exists in the nebula depending on the dust absorption properties and the extent of contamination from free–free emission at the SCUBA wavelengths. These results provide further evidence that ? Car's circumstellar nebula contains >10 M? of gas, although this may have been ejected on a longer time-scale than previously thought.

Subaru Telescope Observations of Deep Impact

The impact cratering process on a comet is controversial but holds the key for interpreting observations of the Deep Impact collision with comet 9P/Tempel 1. Mid-infrared data from the Cooled Mid-Infrared Camera and Spectrometer (COMICS) of the Subaru Telescope indicate that the large-scale dust plume ejected by the impact contained a large mass (approximately 10(6) kilograms) of dust and formed two wings approximately +/-45 degrees from the symmetric center, both consistent with gravity as the primary control on the impact and its immediate aftermath. The dust distribution in the inner part of the plume, however, is inconsistent with a pure gravity control and implies that evaporation and expansion of volatiles accelerated dust.

A Starfish Preplanetary Nebula: IRAS 19024+0044

Using the Hubble Space Telescope, we have imaged the OH/IR star IRAS 19024+0044 (I19024) at 0.6, 0.8, 1.1, and 1.6 μm, as part of our surveys of candidate preplanetary nebulae. The images show a multipolar nebula of size ~3farcs7 × 2farcs3, with at least six elongated lobes emanating from the center of the nebula. Two of the lobes show limb-brightened tips having point-symmetric structure with respect to the expected location of the central star. The central region shows two dark bands southwest and northeast of a central shallow maximum that may be either two inclined dusty toroidal structures or the dense parts of a single wide, inhomogeneous, toroid. A very faint, surface brightness-limited, diffuse halo surrounds the lobes. Long-slit/echelle optical spectroscopy obtained at the Mount Palomar and Keck observatories shows a spatially compact source of Hα emission; the Hα line shows a strong, narrow, central core with very broad (±1000 km s^(-1)), weak wings, and a narrower blueshifted absorption feature signifying the presence of a ~100 km s^(-1) outflow. The spectrum is characterized by a strong, relatively featureless, continuum and lacks the strong forbidden emission lines characteristic of planetary nebulae, confirming that IRAS 19024 is a preplanetary nebula; the spectral type for the central star, although uncertain, is most likely early G. Interferometric observations of the CO J = 1-0 line emission with the Owens Valley Radio Interferometer show a marginally resolved molecular envelope (size 5farcs5 × 4farcs4) with an expansion velocity of 13 km s^(-1), resulting from the asymptotic giant granch (AGB) progenitor's dense, slow wind. We derive a kinematic distance of 3.5 kpc to I19024, based on its radial velocity. The bolometric flux is 7.3 × 10^(9-) ergs s^(-1) cm^(-2), and the luminosity 2850 L_☉. The relatively low luminosity of I19024, in comparison with stellar evolutionary models, indicates that the initial mass of its central star was ~1-1.5 M_☉. The lobes, which appear to be hollow structures with dense walls, have a total mass greater than or equal to about 0.02 M_☉. The dusty tori in the center have masses of a few times 10^(-3) M_☉. The faint halo has a power-law radial surface brightness profile with an exponent of about -3 and most likely represents the remnant spherical circumstellar envelope formed as a result of constant mass loss during the AGB phase over the past several thousand years. From the CO data we infer a molecular mass ≳ 0.025 M_☉ and an expansion age ≾ 2870 yr, giving a mass-loss rate ≳ 10^(-5) M_☉ yr^(-1). The far-infrared fluxes of I19024 indicate the presence of a large mass of dust in the nebula; from a simple model we infer the presence of cool (109 K) and warm (280 K) components of dust mass 5.7 × 10^(-4) and 1.5 × 10^(-7) M_☉. We discuss our results for I19024 in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass-ejecta as AGB stars evolve into planetary nebulae.

A supernova origin for dust in a high-redshift quasar.

Interstellar dust plays a crucial role in the evolution of the Universe by assisting the formation of molecules, by triggering the formation of the first low-mass stars, and by absorbing stellar ultraviolet-optical light and subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass stars. This picture has, however, recently been brought into question by the discovery of large masses of dust in the host galaxies of quasars at redshift z > 6, when the age of the Universe was less than 1 Gyr. Theoretical studies, corroborated by observations of nearby supernova remnants, have suggested that supernovae provide a fast and efficient dust formation environment in the early Universe. Here we report infrared observations of a quasar at redshift 6.2, which are used to obtain directly its dust extinction curve. We then show that such a curve is in excellent agreement with supernova dust models. This result demonstrates a supernova origin for dust in this high-redshift quasar, from which we infer that most of the dust at high redshifts probably has the same origin.

Submillimetre observations of z &gt; 6 quasars

We report on submillimetre (submm) observations of three high-redshift quasars (z > 6) made using the SCUBA camera on the James Clerk Maxwell Telescope (JCMT). Only one of the sample was detected (>10σ significance) at 850 μm – SDSS J1148+5251 (z= 6.43). It was also detected at 450 μm (>3σ significance), one of the few quasars at z > 4 for which this has been the case. In combination with existing millimetric data, the 850- and 450-μm detections allow us to place limits on the temperature of the submm-emitting dust. The dust temperature is of no trivial importance given the high redshift of the source, since a cold temperature would signify a large mass of dust to be synthesized in the little time available (as an extreme upper limit in only 0.9 Gyr since z=∞). We find, however, that the combined millimetre and submm data for the source cannot simply be characterized using the single-temperature greybody fit that has been used at lower redshifts. We discuss the results of the observing and modelling, and speculate as to the origin of the deviations.

The Submillimeter Properties of Broad Absorption Line Quasars

We have carried out the first systematic survey of the submillimeter properties of broad absorption line (BAL) quasars. Thirty BAL quasars drawn from a homogeneously selected sample from the Sloan Digital Sky Survey at redshifts 2 < z < 2.6 were observed with the SCUBA array at the JCMT to a typical rms sensitivity of 2.5 mJy. Eight quasars were detected at greater than 2 σ significance, four of which are at greater than 3 σ significance. The far-infrared luminosities of these quasars are greater than 1013 L☉. There is no correlation of submillimeter flux with either the strength of the broad absorption feature or with absolute magnitude in our sample. We compare the submillimeter flux distribution of the BAL quasar sample with that of a sample of quasars that do not show BAL features in their optical spectra and find that the two are indistinguishable. BAL quasars do not have higher submillimeter luminosities than non-BAL quasars. These findings are consistent with the hypothesis that all quasars would contain a BAL if viewed along a certain line of sight. The data are inconsistent with a model in which the BAL phenomenon indicates a special evolutionary stage that coincides with a large dust mass in the host galaxy and a high submillimeter luminosity. Our work provides constraints on alternative evolutionary explanations of BAL quasars.