Amount of intergalactic dust: constraints from distant supernovae and the thermal history of the intergalactic medium

The amount and properties of high-redshift galactic and intergalactic (IG) dust are largely unknown, but could be investigated using multi-wavelength photometry of high-z objects that have a known intrinsic spectrum. Observations of gamma-ray burst (GRB) afterglows appear to support the theoretical model of an adiabatic blast wave expanding into an external medium. In this model, the synchrotron peak flux is independent of frequency, providing a flat spectrum when observed over time, and therefore allowing straightforward measurement of the relative attenuation of afterglow flux in widely separated bands. Applying this method to dust extinction, we show that for a sample of afterglows which have been corrected by galactic extinction, comparison between the number counts of peak fluxes in X-ray versus optical can provide constraints on an intergalactic component of dust. A similar technique can probe the redshift-dependence of extinction in GRB-forming regions without requiring an assumed relation between extinction and reddening by the dust. Probing systematic changes in extinction with redshift - particularly in IG and/or non-reddening dust - is crucial to a proper interpretation of the Type Ia Supernova Hubble diagram and similar observations, and useful in understanding GRB progenitor environments.

Distant supernovae have been observed to be fainter than what is expected in a matterdominated universe. The most likely explanation is that the universe is dominated by anenergy component with negative pressure, namely dark energy. However, there are severalastrophysical processes that could, in principle, affect the measurements andin order to be able to take advantage of the growing supernova statistics, thecontrol of systematic effects is crucial. We discuss two of these; extinction due tointergalactic grey dust and dimming due to photon–axion oscillations and show howtheir effect on supernova observations can be constrained using observed quasarcolours and spectra. For a wide range of intergalactic dust models, we are ableto rule out any dimming larger than 0.2 magnitudes for a type Ia supernova atz = 1. The corresponding limit for intergalactic Milky Way type dust is 0.03 magnitudes. For themore speculative model of photons mixing with axions, we find that the effect isindependent of photon energy for certain combinations of parameter values and a dimmingas large as 0.6 magnitudes cannot be ruled out. These effects can have profoundimplications for the possibility of constraining dark energy properties using supernovaobservations.

Aeolian dust has a significant environmental impact on the ocean biogeochemical cycles in different timescales. However, spatial and temporal variations of dust transported on long distances in the upper troposphere by the westerly jet, in particular over orbital-millennial timescales, have not been resolved yet. In this study, we present the evidence for changes in the main axis and path of westerly jet over East Asia at millennial-orbital scale during the last glacial period (~60 ka). We examine the grain size characteristics of sediment core LV53-23 collected from the central Japan (East) Sea, which lies the downwind of westerly jet to discuss the evolution of westerly jet since the last glacial period. Our results show that core sediments are composed mainly of silt characterized of eolian dust, which is consistent with those sediment cores discussed in previous studies from the Japan Sea. The median grain-size of silt fraction has similar pattern with environmentally sensitive grain size extracted by standard deviation/grain-size method. The median grain size in silt fraction increased in stadial periods and decreased in interstadial periods, which might be related to changes in the path of westerly jet. During the stadial, the westerly jet mostly located in the the south of the Tibetan Plateau. It can influence the northern part of the Tibetan Plateau extending to 50°N with high speed, which is prerequisite of dust raised to westerlies in northern China and thus carried the coarser dust from nearby Mongolian Gobi and northeastern China to the Japan Sea. During the interstadial, the provenance of the finer aeolian dust was from Taklimakan Desert when westerly jet migrated northward and concentrated within a narrow band at northern Tibetan Plateau with a longer duration. We found the multi-millennial time scales variations during DOI 8, 12, 14, 16 in cores LV53-23 and MD01-2407 located in the southwestern Japan Sea based on the results of NGRIP and GISP 2 Greenland ice cores. Contrasting with grain size variations of the loess-paleosol records (e.g., Gulang Loess sequence), the lowest grain size during the Last Glacial Maximum confirm that the silt fraction of Japan Sea sediment was mostly transported by westerlies instead of East Asian Winter Monsoon. The mechanism driving the orbital scale variability in grain size of aeolian dust in the Japan Sea is mainly forced by variations of ice volume due to summer insolation in the Northern Hemisphere. A southward migration in the main axis of westerly jet and its influential area was affected by a decrease of summer insolation and increase of ice volume in Northern Hemisphere. During the Last Glacial Maximum, although the cold surges and dust storms were intensive, the southward path of westerly jet may decreased the dust entrainment ability transported by westerlies so that downwind received finer grain size eolian dust. This argument is consistent with findings showing that the location of subarctic front in North Pacific during the Last Glacial Maximum was caused by a southward shift of the path of Kuroshio Current which is controlled by westerly jet. During the glacial period, the decreasing grain size of dust in northern site is explained by weaker westerlies in higher latitudes (40°–50°N) caused by the southward shift of westerly jet main axis, while the increase grain size in the southern site is controlled by the increasing of dust transport path because of westerlies speed in lower latitudes.

Recent observations of Type Ia SNe at redshifts 0 < z <1 reveal a progressive dimming which has been interpreted as evidence for a cosmological constant of Omega_Lambda ~ 0.7. An alternative explanation of the SN results is an open universe with Omega_Lambda=0 and the presence of > 0.1 micron dust grains with a mass density of Omega_dust ~ (few) * 10^{-5} in the intergalactic (IG) medium. The same dust that dims the SNe absorbs the cosmic UV/optical background radiation around ~ 1 micron, and re-emits it at far infrared (FIR) wavelengths. Here we compare the FIR emission from IG dust with observations of the cosmic microwave (CMB) and cosmic far infrared backgrounds (FIRB) by the DIRBE/FIRAS instruments. We find that the emission would not lead to measurable distortion to the CMB, but would represent a substantial fraction (> 75%) of the measured value of the FIRB in the 300-1000 micron range. This contribution would be marginally consistent with the present unresolved fraction of the observed FIRB in an open universe. However, we find that IG dust probably could not reconcile the standard Omega=1 CDM model with the SN observations, even if the necessary quantity of dust existed. Future observations able to reliably resolve the FIRB to a flux limit of ~0.5 mJy, along with a more precise measure of the coarse-grained FIRB, will provide a definitive test of the IG dust hypothesis in all cosmologies.

We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8<z<1.1. The model can also be used to improve spectroscopic identification algorithms, and derive photometric redshifts of distant Type Ia supernovae.

Estimates of the cosmic star formation rate and of cluster metallicities independently imply that at z 0.5 the gas in the universe has substantial average metallicity: 1/10 Z/Z☉ 1/3 for Ωgas = 0.05. This metal density probably cannot be contained in known solar-metallicity galaxies of density parameter Ω* ≈ 0.004, implying significant enrichment of the intergalactic medium (IGM) by ejection of metals and dust from galaxies via winds, in mergers or in dust efflux driven by radiation pressure. Galaxies have a dust-to-metal ratio of ~0.5 in their interstellar media, but some fraction (1 - f) > 0 of this must be destroyed in the IGM or during the ejection process. Assuming the Draine & Lee dust model and preferential destruction of small grains (as destruction by sputtering would provide), I calculate the reddening and extinction of a uniform cosmological dust component in terms of f and the minimum grain size amin. Very small grains provide most of the reddening but less than half of the opacity for optical extinction. For f 0.3 and amin 0.1 μm, the intergalactic dust would be too gray to have been detected by its reddening, yet dense enough to be cosmologically important: it could account for the recently observed Type Ia supernova dimming at z ~ 0.5 without cosmic acceleration. It would also have implications for galaxy counts and evolutionary studies and would contribute significantly to the cosmic infrared background (CIB). The importance of gray intergalactic dust of the described type can be tested by observations of z = 0.5 supernovae in (rest) R-band or longer wavelengths and by the fluxes of a large sample of supernovae at z > 1.

We compare the rise times of nearby and distant Type Ia supernovae (SNe Ia) as a test for evolution using 73 high-redshift spectroscopically-confirmed SNe Ia from the first two years of the five year Supernova Legacy Survey (SNLS) and published observations of nearby SN. Because of the ``rolling'' search nature of the SNLS, our measurement is approximately 6 times more precise than previous studies, allowing for a more sensitive test of evolution between nearby and distant supernovae. Adopting a simple $t^2$ early-time model (as in previous studies), we find that the rest-frame $B$ rise times for a fiducial SN Ia at high and low redshift are consistent, with values $19.10^{+0.18}_{-0.17}({stat}) \pm 0.2 ({syst})$ and $19.58^{+0.22}_{-0.19}$ days, respectively; the statistical significance of this difference is only 1.4 \sg . The errors represent the uncertainty in the mean rather than any variation between individual SN. We also compare subsets of our high-redshift data set based on decline rate, host galaxy star formation rate, and redshift, finding no substantive evidence for any subsample dependence.

Under this proposal, we have been undertaking a calibration of rate of change of the expansion rate of the Universe as a function of cosmic look-back time using the high-precision standard candles, Type Ia supernovae, as observed in their rest-frame near-infrared wavelengths. The apparent acceleration of the Universe, as discovered earlier using these same types of supernovae, was both unanticipated and extremely profound in its implications. Not only does the acceleration mean that the Universe is unbound, but it also implies the existence of a new constituent of the Universe (so-called 'dark energy') that is many orders of magnitude stronger than what physicists can easily accommodate in their standard theories of particle physics. A result with such wide-ranging and important implications must be checked, and all sources of systematic error and uncertainty must be evaluated and accounted for. At increasingly higher redshifts the objects being observed are seen at earlier cosmic times and the radiation that reaches Earth is shifted to longer and longer wavelengths. What leaves a supernova event at one time in the past as an optical photon is downgraded by cosmic expansion into a red or infrared photon by the time it is detected here. Optical images of distant supernovae seen now, began their lives as ultraviolet photons. The ultraviolet properties of nearby supernovae are not well understood, so comparing supernova across time and space becomes complicated and uncertain. Moreover it is well known that the systematic effects of interstellar dust are larger and more variable from place to place in the ultraviolet than they are at longer wavelengths. To mitigate both the uncertainty of the ultraviolet calibration and the certainty of variable dust extinction along the line of sight, the Carnegie Supernova Program (CSP) has been observing the distant supernovae at groundbased infrared wavelengths that more closely match restframe (emitted) optical wavelengths at the supernova event itself. Not only does this allow us to compare local (calibrating) supernovae with distant supernovae without the uncertainty of shifting between uncertain physical regimes, but it also actively reduces both the impact and the uncertainty of interstellar dust on the apparent magnitudes of the tagert supernovae and their calibrators. Infrared radiation penetrates dust and gas much more efficiently than optical and ultraviolet photons. This has been possible because Carnegie operates very large-aperture telescopes at the Las Campanas Observatory in Chile, equipped with state-of-the-art, wide-field near-infrared detectors capable of detecting and measuring distant supernovae (discovered by collaborating surveys) early in their evolution. With support from the DOE through this grant the Carnegie Supernova Project has observed 70 Type Ia supernovae from Chile obtaining near-infrared light curves which, when combined with the discovery images provide high-quality data on the rest-frame, near-infrared magnitudes of these supernovae at the time of maximum light. The peak luminosity of Type Ia supernovae can then be used to estimate their distances (once corrected for decline rate and residual reddening effects). Those distances when compared to their expansion velocities give us the systematic departures from pure Hubble expansion that lie at the heart of the detection of dark energy in the Universe. A paper summarizing the techniques and methods used by the CSP in measuring high-redshift supernovae is in the final stages of circulating amongst the team members. We expect to submit it to the Astrophysical Journal before the end of 2008. Half of the data on the full sample observed supernovae has been fully reduced for this paper. We already have a new measurement of the dark energy contribution to cosmic acceleration. We find a value of w = -1.05 {+-} 0.08 (statistical) {+-} 0.08 (systematic). This value is consistent with, but completely independent of and has a smaller systematic uncertainty than, other studies to date.

Observations of high-redshift Type Ia supernovae (SNe Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat Λ cold dark matter (ΛCDM) cosmological model based on baryon acoustic oscillations and cosmic microwave background measurements, redshift dependent deviations of SN Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a $0.03 \pm 0.01 \, {(\rm {stat})}$ mag discrepancy in the distant supernova distance moduli relative to the ΛCDM model anchored by supernovae at z &amp;lt; 0.05. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is entirely due to dimming by dust, the measurements can be modelled with a cosmic dust density $\Omega _{\rm IGM}^{\rm dust} = 8 \times 10^{-5} (1+z)^{-1}$, corresponding to an average attenuation of 2 × 10−5 mag Mpc−1 in V band. Forthcoming SN Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.

We present spectroscopic and photometric observations of SN 1992ar, the most distant supernova (SN) in the Calán/Tololo Survey. We compare its spectrum with those of nearby Type Ia and Ic SNe and conclude that the latter type is a better match to SN 1992ar. Using K-corrections based on the spectra of well-observed Type Ic and Ia SNe, we compute different possible rest-frame light curves of SN 1992ar and compare them with those of representative SNe of each type observed in the nearby universe. From the photometry and the spectra, we are able to conclude that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even though the data set collected is fairly complete (one spectrum and 10 photometric points), it is not possible to decide whether SN 1992ar was a fast Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V magnitudes at maximum implied by each of these possibilities are -19.2 and -20.2, respectively. The latter would make SN 1992ar one of the brightest SNe on record. SN 1992ar, hence, illustrates the problem of contamination faced by the high-z Type Ia SNe samples whose luminosity distances are used to determine the cosmological parameters of the universe. We present observational criteria to distinguish the two SN types when the Si II 6355 Å line is redshifted out of the sensitivity range of typical CCD detectors and discuss the effect that these luminous Type Ic SNe would have on the measured cosmological parameters, if not removed from the high-z Type Ia SN samples.

Lunar dust charging by photoelectric emissions

The ultimate fate of the universe, infinite expansion or a big crunch, can be determined by measuring the redshifts, apparent brightnesses, and intrinsic luminosities of very distant supernovae. Recent developments have provided tools that make such a program practicable: (1) Studies of relatively nearby Type Ia supernovae (SNe Ia) have shown that their intrinsic luminosities can be accurately determined; (2) New research techniques have made it possible to schedule the discovery and follow-up observations of distant supernovae, producing well over 50 very distant (z = 0.3 -- 0.7) SNe Ia to date. These distant supernovae provide a record of changes in the expansion rate over the past several billion years. By making precise measurements of supernovae at still greater distances, and thus extending this expansion history back far enough in time, we can distinguish the slowing caused by the gravitational attraction of the universe's mass density Omega_M from the effect of a possibly inflationary pressure caused by a cosmological constant Lambda. We report here the first such measurements, with our discovery of a Type Ia supernova (SN 1997ap) at z = 0.83. Measurements at the Keck II 10-m telescope make this the most distant spectroscopically confirmed supernova. Over two months of photometry of SN 1997ap with the Hubble Space Telescope and ground-based telescopes, when combined with previous measurements of nearer SNe Ia, suggests that we may live in a low mass-density universe. Further supernovae at comparable distances are currently scheduled for ground and space-based observations.

Effects of initial axion production and photon–axion oscillation on type Ia supernova dimming

This Letter investigates the amount of dust in the intergalactic medium (IGM). The dust photoelectric heating can be the most efficient heating mechanism in the IGM where the density is very small and there are a lot of hard ultraviolet photons. Comparing the observational thermal history of IGM with a theoretical one taking into account the dust photoelectric heating, we can put an upper limit on the dust-to-gas ratio, ${\cal D}$, in the IGM. Since the rate of the dust photoelectric heating depends on the size of dust, we find the following results: If the grain size is $\ga 100$ \AA, ${\cal D}$ at $z \sim 3$ is $\la 1/100$ Galactic value corresponding to $\Omega_{\rm dust}^{\rm IGM}\la 10^{-5}$. On the other hand, if the grain size is as small as $\sim 10$ \AA, ${\cal D}$ is $\la 1/1000$ Galactic value corresponding to $\Omega_{\rm dust}^{\rm IGM}\la 10^{-6}$.

The light from distant supernovae (SNe) can be magnified through gravitational lensing when a foreground galaxy is located along the line of sight. This line-up allows for detailed studies of SNe at high redshift that otherwise would not be possible. Spectroscopic observations of lensed high-redshift Type Ia supernovae (SNe Ia) are of particular interest since they can be used to test for evolution of their intrinsic properties. The use of SNe Ia for probing the cosmic expansion history has proven to be an extremely powerful method for measuring cosmological parameters. However, if systematic redshift-dependent properties are found, their usefulness for future surveys could be challenged. We investigate whether the spectroscopic properties of the strongly lensed and very distant SN Ia PS1-10afx at $z=1.4$ deviates from the well-studied populations of normal SNe Ia at nearby or intermediate distance. We created median spectra from nearby and intermediate-redshift spectroscopically normal SNe Ia from the literature at -5 and +1 days from light-curve maximum. We then compared these median spectra to those of PS1-10afx. We do not find signs of spectral evolution in PS1-10afx. The observed deviation between PS1-10afx and the median templates are within what is found for SNe at low- and intermediate-redshift. There is a noticeable broad feature centred at $\rm \lambda\sim 3500$~\AA{}, which is present only to a lesser extent in individual low and intermediate redshift SN Ia spectra. From a comparison with a recently developed explosion model, we find this feature to be dominated by iron peak elements, in particular, singly ionized cobalt and chromium.