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The aim of this master thesis is to investigate the influence of intergalactic duston astronomical observations. The current cosmological paradigm of an acceleratingcosmic expansion is supported by observations of Type Ia supernovae. However, thelight emitted by these and other cosmological sources is not only redshifted by cosmicexpansion but will also interact with matter along the light path which affects the light.Especially intergalactic dust can lead to additional reddening and dimming of distantsources due to light scattering or absorption. This yields systematic contaminations tocosmological measurements. Using quasars as backlight sources we seek to estimate theattenuation of their observed spectra caused by intergalactic dust in order to determinethe existence and properties of the intergalactic dust. In this thesis we will analysethe methods and tools used as well as discussing the dust properties and how theyaffect the results. This thesis shows that intergalactic dust exist, and has a notableeffect on cosmological measurements and favors dust grains consisting of silicate witha size around 0.1 µm with Ωdust around 5 − 7 × 10^−6. The conclusion is in agreementwith previous studies of the same matter. With the increasing precision of cosmologicalmeasurements systematic effects such as intergalactic dust is a factor that has to betaken into account. Syftet med denna masteruppsats är att undersöka de effekter intergalaktiskt stofthar på astronomiska observationer. Den ledande kosmologiska moddellen som säger attuniversum expanderar är stöttad av observationer av Typ 1a supernovor. Ljuset somkommer från supernovorna är däremot inte bara påverkade av den kosmiska expansionen men kommer också interagera med materia på vägen som påverkar ljuset. Specielltintergalaktiskt stoft kan leda till ytterligare dimning av ljuset och att ljuset blir rödare.Detta är på grund av spridningen eller absorptionen av ljuset när ljuset interagerar medstoftpartiklarna. Detta leder till systematiska fel i kosmologiska mätningar. Genomatt använda kvasarer som en ljuskälla försöker vi uppskatta ljusdämpningen på derasspektrum som orsakats av intergalaktiskt stoft. Detta görs för att bestämma ifall intergalaktiskt stoft existerar och vad dess egenskaper är. I denna uppsats gjordes enanalys av metoden, beräkningsverktygen som användes och några egenskaper hos stoft.Slutsatsen av denna analys visar på att intergalaktiskt stoft existerar och har en mätbar effekt på kosmologiska observationer. Resultatet visar att modellen föredrar stoftav silikat med storlekar runt 0.1 µm med Ωdust runt 5 − 7 × 10^−6vilket stämmer överens med tidigare studier. Med den ökade pressionen av kosmologiska mätningar blirsystematiska effekter, som den från intergalaktiskt stoft, ännu viktigare att ta i hänsyn.

We have investigated effects of dust attenuation on quasar luminosity functions using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, about 2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fueling to a central black hole starts some time after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical timescale of their host bulges or the dust covering factor is as small as 0.1., 5 pages, 4 figures, 1 tables. Accepted for publication by MNRAS Letters

The effect of the primeval sources of radiation and particles on the thermodynamical state of the intergalactic medium during the Epoch of Reionisation is still unclear. In this work, we explore the contribution of electrons accelerated in the jets of high-redshift microquasars to heating and ionising the intergalactic medium. We develop Monte Carlo simulations of the propagation and energy deposition of these electrons as they travel away from their sources. We find that microquasars contribute significantly to heating the intergalactic medium and are effective ionisers only near the galaxies. Their effect on heating is of the same order of magnitude than that of CRs from SNe., 13 pages, 13 figures, accepted for publication in MNRAS

Recently, large samples of visually classified early-type galaxies (ETGs) containing dust have been identified using space-based infrared observations with the Herschel Space Telescope. The presence of large quantities of dust in massive ETGs is peculiar as X-ray halos of these galaxies are expected to destroy dust in 10 Myr (or less). This has sparked a debate regarding the origin of the dust: is it internally produced by asymptotic giant branch (AGB) stars, or is it accreted externally through mergers? We examine the 2D stellar and ionised gas kinematics of dusty ETGs using IFS observations from the SAMI galaxy survey, and integrated star-formation rates, stellar masses, and dust masses from the GAMA survey. Only 8% (4/49) of visually-classified ETGs are kinematically consistent with being dispersion-supported systems. These "dispersion-dominated galaxies" exhibit discrepancies between stellar and ionised gas kinematics, either offsets in the kinematic position angle or large differences in the rotational velocity, and are outliers in star-formation rate at a fixed dust mass compared to normal star-forming galaxies. These properties are suggestive of recent merger activity. The remaining 90% of dusty ETGs have low velocity dispersions and/or large circular velocities, typical of "rotation-dominated galaxies". These results, along with the general evidence of published works on X-ray emission in ETGs, suggest that they are unlikely to host hot, X-ray gas consistent with their low stellar mass when compared to dispersion-dominated galaxies. This means dust will be long lived and thus these galaxies do not require external scenarios for the origin of their dust content., 13 pages, 9 figures, accepted for publication in MNRAS

We investigate the evolution of interstellar dust in the Universe by means of chemical evolution models of galaxies of different morphological types, reproducing the main observed features of present day galaxies. We adopt the most updated prescriptions for dust production from supernovae and asymptotic giant branch (AGB) stars as well as for dust accretion and destruction processes. Then, we study the cosmic dust rate in the framework of three different cosmological scenarios for galaxy formation: i) a pure luminosity scenario (PLE), ii) a number density evolution scenario (DE), as suggested by the classical hierarchical clustering scenario and iii) an alternative scenario, in which both spirals and ellipticals are allowed to evolve in number on an observationally motivated basis. Our results give predictions about the evolution of the dust content in different galaxies as well as the cosmic dust rate as a function of redshift. Concerning the cosmic dust rate, the best scenario is the alternative one, which predicts a peak at 2 < z < 3 and reproduces the cosmic star formation rate. We compute the evolution of the comoving dust density parameter �� dust and find agreement with data for z < 0.5 in the framework of DE and alternative scenarios. Finally, the evolution of the average cosmic metallicity is presented and it shows a quite fast increase in each scenario, reaching the solar value at the present time, although most of the heavy elements are incorporated into solid grains, and therefore not observable in the gas phase., 15 pages, 7 figures. Accepted for publication by MNRAS

I examine a possible spectral distortion of the Cosmic Microwave Background (CMB) due to its absorption by galactic and intergalactic dust. I show that even subtle intergalactic opacity of $1 \times 10^{-7}\, \mathrm{mag}\, h\, \mathrm{Gpc}^{-1}$ at the CMB wavelengths in the local Universe causes non-negligible CMB absorption and decline of the CMB intensity because the opacity steeply increases with redshift. The CMB should be distorted even during the epoch of the Universe defined by redshifts $z < 10$. For this epoch, the maximum spectral distortion of the CMB is at least $20 \times 10^{-22} \,\mathrm{Wm}^{-2}\, \mathrm{Hz}^{-1}\, \mathrm{sr}^{-1}$ at 300 GHz being well above the sensitivity of the COBE/FIRAS, WMAP or Planck flux measurements. If dust mass is considered to be redshift dependent with noticeable dust abundance at redshifts 2-4, the predicted CMB distortion is even higher. The CMB would be distorted also in a perfectly transparent universe due to dust in galaxies but this effect is lower by one order than that due to intergalactic opacity. The fact that the distortion of the CMB by dust is not observed is intriguing and questions either opacity and extinction law measurements or validity of the current model of the Universe., 5 pages, 4 figures

Theoretical models predict that core-collapse supernovae (CCSNe) can be efficient dust producers (0.1-1.0 Msun), potentially accounting for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g., SN1987A, Crab Nebula). In this paper, we revisit the dust mass produced in Cassiopeia A (Cas A), a ~330-year old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data at a common resolution of ~0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 micron with a four-component interstellar medium (ISM) and supernova (SN) dust model. We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3-0.5 Msun of silicate grains freshly produced in the SNR, with a lower limit of >=0.1-0.2 Msun. For a mixture of 50% of silicate-type grains and 50% of carbonaceous grains, we derive a total SN dust mass between 0.4 Msun and 0.6 Msun. These dust mass estimates are higher than from most previous studies of Cas A and support the scenario of supernova dominated dust production at high redshifts. We furthermore derive an interstellar extinction map for the field around Cas A which towards Cas A gives average values of A_V=6-8 mag, up to a maximum of A_V=15 mag., 37 pages, 24 figures, Manuscript published in MNRAS, including minor corrections. Accepted on 01/11/2016. Deposited on 08/01/2017

We have recently suggested that dust growth in the cold gas phase dominates the dust abundance in elliptical galaxies while dust is efficiently destroyed in the hot X-ray emitting plasma (hot gas). In order to understand the dust evolution in elliptical galaxies, we construct a simple model that includes dust growth in the cold gas and dust destruction in the hot gas. We also take into account the effect of mass exchange between these two gas components induced by active galactic nucleus (AGN) feedback. We survey reasonable ranges of the relevant parameters in the model and find that AGN feedback cycles actually produce a variety in cold gas mass and dust-to-gas ratio. By comparing with an observational sample of nearby elliptical galaxies, we find that, although the dust-to-gas ratio varies by an order of magnitude in our model, the entire range of the observed dust-to-gas ratios is difficult to be reproduced under a single parameter set. Variation of the dust growth efficiency is the most probable solution to explain the large variety in dust-to-gas ratio of the observational sample. Therefore, dust growth can play a central role in creating the variation in dust-to-gas ratio through the AGN feedback cycle and through the variation in dust growth efficiency., 14 pages, 9 figures, accepted for publication in Planetary and Space Science (special issue for Cosmic Dust IX)

We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by AGB stars and Type II SNe, destruction and accretion (gas condensation in clouds). We then apply our model to Damped Lyman-Alpha systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf galaxies. ii) We find that the process of dust accretion plays a fundamental role in the evolution of dust and in certain cases it becomes the dominant process in the dust cycle. On the other hand, dust destruction seems to be a negligible process in irregulars. iii) Concerning Damped Lyman-Alpha systems, we show that the observed gas-phase abundances of silicon, normalized to volatile elements (zinc and sulfur), are in agreement with our model. iv) The abundances of iron and silicon in DLA systems suggest that the two elements undergo a different history of dust formation and evolution. Our work casts light on the nature of iron-rich dust: the observed depletion pattern of iron is well reproduced only when an additional source of iron dust is considered. Here we explore the possibility of a contribution from Type Ia SNe as well as an efficient accretion of iron nano-particles., Comment: Accepted for publication by MNRAS, 20 pages, 11 figures

We study the dust content of galaxies from $z=0$ to $z=9$ in semi-analytic models of galaxy formation that include new recipes to track the production and destruction of dust. We include condensation of dust in stellar ejecta, the growth of dust in the interstellar medium (ISM), the destruction of dust by supernovae and in the hot halo, and dusty winds and inflows. The rate of dust growth in the ISM depends on the metallicity and density of molecular clouds. Our fiducial model reproduces the relation between dust mass and stellar mass from $z=0$ to $z=7$, the number density of galaxies with dust masses less than $10^{8.3}\,\rm{M}_\odot$, and the cosmic density of dust at $z=0$. The model accounts for the double power-law trend between dust-to-gas (DTG) ratio and gas-phase metallicity of local galaxies and the relation between DTG ratio and stellar mass. The dominant mode of dust formation is dust growth in the ISM, except for galaxies with $M_*, Accepted for publication in MNRAS

Dwarf spheroidal galaxies are among the most numerous galaxy population in the Universe, but their main formation and evolution channels are still not well understood. The three dwarf spheroidal satellites (NGC147, NGC185, and NGC205) of the Andromeda galaxy are characterised by very different interstellar medium (ISM) properties, which might suggest them being at different galaxy evolutionary stages. While the dust content of NGC205 has been studied in detail by De Looze et al. (2012), we present new Herschel dust continuum observations of NGC147 and NGC185. The non-detection of NGC147 in Herschel SPIRE maps puts a strong constraint on its dust mass (< 128 Msun). For NGC185, we derive a total dust mass M_d = 5.1 x 10^3 Msun, which is a factor of ~2-3 higher than that derived from ISO and Spitzer observations and confirms the need for longer wavelength observations to trace more massive cold dust reservoirs. We, furthermore, estimate the dust production by asymptotic giant branch (AGB) stars and supernovae (SNe). For NGC147, the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population. In NGC185 and NGC205, the observed dust content is one order of magnitude higher compared to the estimated dust production by AGBs and SNe. Efficient grain growth, and potentially longer dust survival times (3-6 Gyr) are required to account for their current dust content. Our study confirms the importance of grain growth in the gas phase to account for the current dust reservoir in galaxies., 17 pages, 7 figures, accepted in MNRAS

We present full volume cosmological simulations using the moving-mesh code AREPO to study the coevolution of dust and galaxies. We extend the dust model in AREPO to include thermal sputtering of grains and investigate the evolution of the dust mass function, the cosmic distribution of dust beyond the interstellar medium, and the dependence of dust-to-stellar mass ratio on galactic properties. The simulated dust mass function is well-described by a Schechter fit and lies closest to observations at $z = 0$. The radial scaling of projected dust surface density out to distances of $10 \, \text{Mpc}$ around galaxies with magnitudes $17 < i < 21$ is similar to that seen in Sloan Digital Sky Survey data, albeit with a lower normalisation. At $z = 0$, the predicted dust density of $\Omega_\text{dust} \approx 1.3 \times 10^{-6}$ lies in the range of $\Omega_\text{dust}$ values seen in low-redshift observations. We find that dust-to-stellar mass ratio anti-correlates with stellar mass for galaxies living along the star formation main sequence. Moreover, we estimate the $850 \, \mu\text{m}$ number density functions for simulated galaxies and analyse the relation between dust-to-stellar flux and mass ratios at $z = 0$. At high redshift, our model fails to produce enough dust-rich galaxies, and this tension is not alleviated by adopting a top-heavy initial mass function. We do not capture a decline in $\Omega_\text{dust}$ from $z = 2$ to $z = 0$, which suggests that dust production mechanisms more strongly dependent on star formation may help to produce the observed number of dusty galaxies near the peak of cosmic star formation., Comment: 18 pages, 12 figures. Accepted by MNRAS

A majority of early-type galaxies contain interstellar dust, yet the origin of this dust, and why the dust sometimes exhibits unusual polycyclic aromatic hydrocarbon (PAH) ratios, remains a mystery. If the dust is internally produced, it likely originates from the large number of AGB stars associated with the old stellar population. We present GALEX and WISE elliptical aperture photometry of $\sim310$ early-type galaxies with Spitzer mid-infrared spectroscopy and/or ancillary data from ATLAS3D, to characterize their circumstellar dust and the shape of the radiation field that illuminates the interstellar PAHs. We find that circumstellar dust is ubiquitous in early-type galaxies, which indicates some tension between stellar population age estimates and models for circumstellar dust production in very old stellar populations. We also use dynamical masses from ATLAS3D to show that WISE W1 (3.4 $\mu$m) mass-to-light ratios are consistent with the initial mass function variation found by previous work. While the stellar population differences in early-type galaxies correspond to a range of radiation field shapes incident upon the diffuse dust, the ratio of the ionization-sensitive $7.7\mu$m to $11.3\mu$m PAH feature does not correlate with the shape of the radiation field, nor to variations with the size-sensitive $11.3\mu$m to $17\mu$m ratio. The $7.7\mu$m to $11.3\mu$m PAH ratio does tend to be smaller in galaxies with proportionally greater $H_2$ emission, which is evidence that processing of primarily smaller grains by shocks is responsible for the unusual ratios, rather than substantial differences in the overall PAH size or ionization distribution., Comment: 19 pages, 17 figures, 2 tables, Published in MNRAS

We attempt to interpret existing data on the evolution of the UV luminosity function and UV colours, $\beta$, of galaxies at $5 \leq z \leq 8$, to improve our understanding of their dust content and ISM properties. To this aim, we post-process the results of a cosmological hydrodynamical simulation with a chemical evolution model, which includes dust formation by supernovae and intermediate mass stars, dust destruction in supernova shocks, and grain growth by accretion of gas-phase elements in dense gas. We find that observations require a steep, Small Magellanic Cloud-like extinction curve and a clumpy dust distribution, where stellar populations younger than 15 Myr are still embedded in their dusty natal clouds. Investigating the scatter in the colour distribution and stellar mass, we find that the observed trends can be explained by the presence of two populations: younger, less massive galaxies where dust enrichment is mainly due to stellar sources, and massive, more chemically evolved ones, where efficient grain growth provides the dominant contribution to the total dust mass. Computing the IR-excess - UV color relation we find that all but the dustiest model galaxies follow a relation shallower than the Meurer et al. (1999) one, usually adopted to correct the observed UV luminosities of high-$z$ galaxies for the effects of dust extinction. As a result, their total star formation rates might have been over-estimated. Our study illustrates the importance to incorporate a proper treatment of dust in simulations of high-$z$ galaxies, and that massive, dusty, UV-faint galaxies might have already appeared at $z \lesssim 7$., Comment: accepted in MNRAS

We combine Spitzer and Herschel data of the star-forming region N11 in the Large Magellanic Cloud to produce detailed maps of the dust properties in the complex and study their variations with the ISM conditions. We also compare APEX/LABOCA 870um observations with our model predictions in order to decompose the 870um emission into dust and non-dust (free-free emission and CO(3-2) line) contributions. We find that in N11, the 870um can be fully accounted for by these 3 components. The dust surface density map of N11 is combined with HI and CO observations to study local variations in the gas-to-dust mass ratios. Our analysis leads to values lower than those expected from the LMC low-metallicity as well as to a decrease of the gas-to-dust mass ratio with the dust surface density. We explore potential hypotheses that could explain the low observed gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas or of optically thick HI or variations in the dust abundance in the dense regions). We finally decompose the local SEDs using a Principal Component Analysis (i.e. with no a priori assumption on the dust composition in the complex). Our results lead to a promising decomposition of the local SEDs in various dust components (hot, warm, cold) coherent with that expected for the region. Further analysis on a larger sample of galaxies will follow in order to understand how unique this decomposition is or how it evolves from one environment to another., 24 pages, 16 figures, accepted for publication in MNRAS

We interpret recent ALMA observations of z > 6 normal star forming galaxies by means of a semi-numerical method, which couples the output of a cosmological hydrodynamical simulation with a chemical evolution model which accounts for the contribution to dust enrichment from supernovae, asymptotic giant branch stars and grain growth in the interstellar medium. We find that while stellar sources dominate the dust mass of small galaxies, the higher level of metal enrichment experienced by galaxies with Mstar > 10^9 Msun allows efficient grain growth, which provides the dominant contribution to the dust mass. Even assuming maximally efficient supernova dust production, the observed dust mass of the z = 7.5 galaxy A1689-zD1 requires very efficient grain growth. This, in turn, implies that in this galaxy the average density of the cold and dense gas, where grain growth occurs, is comparable to that inferred from observations of QSO host galaxies at similar redshifts. Although plausible, the upper limits on the dust continuum emission of galaxies at 6.5 < z < 7.5 show that these conditions must not apply to the bulk of the high redshift galaxy population, Comment: 5 pages, 2 figures, accepted for publication as a Letter to MNRAS

Interstellar dust plays decisive roles in the conversion of neutral to molecular hydrogen (H_2), the thermodynamical evolution of interstellar medium (ISM), and the modification of spectral energy distributions (SEDs) of galaxies. These important roles of dust have not been self-consistently included in previous numerical simulations of galaxy formation and evolution. We have therefore developed a new model by which one can investigate whether and how galaxy formation and evolution can be influenced by dust-related physical processes such as photo-electric heating, H_2 formation on dust, and stellar radiation pressure on dust in detail. A novel point of the model is that different dust species in a galaxy are represented by `live dust' particles (i.e., not test particles). Therefore, dust particles in a galaxy not only interact gravitationally with all four components of the galaxy (i.e., dark matter, stars, gas, and dust) but also are grown and destroyed through physical processes of ISM. First we describe a way to include dust-related physical processes in Nbody+hydrodynamical simulations of galaxy evolution in detail. Then we show some preliminary results of dust-regulated galaxy evolution. The preliminary results suggest that the evolution of dust distributions driven by radiation pressure of stars is very important for the evolution of star formation rates, chemical abundances, H_2 fractions, and gas distributions in galaxies., 27 pages, 16 figures, accepted for publication in MNRAS (The last figure C3 illustrates the new simulations with dust physics.)

The discovery with the {\it Herschel Space Observatory} of bright far infrared and submm emission from the ejecta of the core collapse supernova SN\,1987A has been interpreted as indicating the presence of some 0.4--0.7\,M$_\odot$ of dust. We have constructed radiative transfer models of the ejecta to fit optical to far-infrared observations from the literature at epochs between 615 days and 24 years after the explosion, to determine when and where this unexpectedly large amount of dust formed. We find that the observations by day 1153 are consistent with the presence of 3$\times$10$^{-3}$M$_\odot$ of dust. Although this is a larger amount than has previously been considered possible at this epoch, it is still very small compared to the amount present in the remnant after 24 years, and significantly higher dust masses at the earlier epochs are firmly ruled out by the observations, indicating that the majority of the dust must have formed at very late times. By 8515-9200 days after the explosion, 0.6--0.8\,M$_\odot$ of dust is present, and dust grains with radii greater than 2\,$\mu$m are required to obtain a fit to the observed SED. This suggests that the dust mass increase at late times was caused by accretion onto and coagulation of the dust grains formed at earlier epochs. These findings provide further confirmation that core collapse supernovae can create large quantities of dust, and indicate that the reason for small dust masses being estimated in many cases is that the vast majority of the dust forms long after most supernovae have been detectable at mid-infrared wavelengths., Comment: 13 pages, 16 figures. Accepted for publication in MNRAS

In this paper we consider the implications of the distributions of dust and metals in the disc of M31. We derive mean radial dust distributions using a dust map created from Herschel images of M31 sampling the entire far-infrared (FIR) peak. Modified blackbodies are fit to approximately 4000 pixels with a varying, as well as a fixed, dust emissivity index (beta). An overall metal distribution is also derived using data collected from the literature. We use a simple analytical model of the evolution of the dust in a galaxy with dust contributed by stellar sources and interstellar grain growth, and fit this model to the radial dust-to-metals distribution across the galaxy. Our analysis shows that the dust-to-gas gradient in M31 is steeper than the metallicity gradient, suggesting interstellar dust growth is (or has been) important in M31. We argue that M31 helps build a case for cosmic dust in galaxies being the result of substantial interstellar grain growth, while the net dust production from stars may be limited. We note, however, that the efficiency of dust production in stars, e.g., in supernovae (SNe) ejecta and/or stellar atmospheres, and grain destruction in the interstellar medium (ISM) may be degenerate in our simple model. We can conclude that interstellar grain growth by accretion is likely at least as important as stellar dust production channels in building the cosmic dust component in M31., 12 pages, 7 figures. Published in MNRAS 444, 797. This version is updated to match the published version

The origin of dust in galaxies is still a mystery. The majority of the refractory elements are produced in supernova explosions but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1-0.5 solar masses of dust in nearby supernova remnants suggests in situ dust formation, while other observations reveal very little dust in supernovae the first few years after explosion. Observations of the bright SN 2010jl have been interpreted as pre-existing dust, dust formation or no dust at all. Here we report the rapid (40-240 days) formation of dust in its dense circumstellar medium. The wavelength dependent extinction of this dust reveals the presence of very large (> 1 micron) grains, which are resistant to destructive processes. At later times (500-900 days), the near-IR thermal emission shows an accelerated growth in dust mass, marking the transition of the supernova from a circumstellar- to an ejecta-dominated source of dust. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media., 62 pages, 13 figures, 1 table. Author version of the Letter to Nature, published online July 9 2014 (Nature, 511, 7509, pp. 326-329 (2014)), prior to the final editorial changes to conform to Journal style; includes Methods and Extended Data Figures and the Supplementary Information. See published version http://www.nature.com/nature/journal/v511/n7509/full/nature13558.html

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., 22 pages, 8 figures, MNRAS, accepted

In order to examine the line-blanketing effect due to gaseous clouds at high redshifts, we have calculated the ionization states of gas clouds of subgalactic mass scale exposed to a UV radiation field that can reproduce the ionization states of the Lyman limit systems (LLSs) along the line of sight to quasar HS1700+6416. We also adopted the integrated UV radiation from the observed quasars modified by the intervening absorption due to the Lyman alpha forest and LLSs as an ionizing spectrum. Our photoionization models can explain the observed HI column-density distribution, the observed CIV/HI ratio and the observed optical depths of HI and HeII. We conclude that the integrated UV background models can well explain the ionization states of both the IGM and Lyman alpha clouds at z ~ 2--3. The gaseous mass of the Lyman alpha clouds follows a power-law form as dn/dM_c ~ M_c(-delta ) with delta ~ 2--2.5 in the 10(8) --10(11) MO range. The majority of the dark baryon probably consists of the IGM.

The Epoch of Reionization (EoR) heralded the advent of the Universe we recognize today, containing stars, galaxies and super-massive black holes. A number of experiments to detect the red-shifted hydrogen signature of the atomic component of the intergalactic medium (IGM) are on-going (e.g. PAPER, MWA, LOFAR). Due to the faintness of the signal, the bright foregrounds, and the challenge of instrumental systematics, multiple techniques are essential to create a more robust detection and to provide the complete picture on the evolution of early galaxies.

Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky. Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6 ± 0.2 (that is, a cosmic age of 490 ± 15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ≲14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium.

The Stephan's Quintet (SQ, HCG92) was observed with the Far-Infrared Surveyor (FIS) aboard AKARI in four far-infrared (IR) bands at 65, 90, 140, and 160 um. The AKARI four-band images of the SQ show far-IR emission in the intergalactic medium (IGM) of the SQ. In particular, the 160 um band image shows single peak emission in addition to the structure extending in the North-South direction along the shock ridge as seen in the 140 um band, H2 emission and X-ray emission. Whereas most of the far-IR emission in the shocked region comes from the cold dust component, shock-powered [CII]158um emission can significantly contribute to the emission in the 160 um band that shows a single peak at the shocked region. In the shocked region, the observed gas-to-dust mass ratio is in agreement with the Galactic one. The color temperature of the cold dust component (~20 K) is lower than that in surrounding galaxies (~30 K). We discuss a possible origin of the intergalactic dust emission., Comment: 14 pages, 4 figures, accepted for publication in the ApJ Letters

New observations with Herschel allow accurate measurement of the equilibrium temperature of large dust grains heated by the interstellar radiation field (ISRF), which is critical in deriving dust column density and masses. We present temperature maps derived from the Herschel SPIRE and PACS data in two fields along the Galactic plane, obtained as part of the Hi-GAL survey during the Herschel science demonstration phase (SDP). We analyze the distribution of the dust temperature spatially, as well as along the two lines-of-sight (LOS) through the Galaxy. The zero-level offsets in the Herschel maps were established by comparison with the IRAS and Planck data at comparable wavelengths. We derive maps of the dust temperature and optical depth by adjusting a detailed model for dust emission at each pixel. The dust temperature maps show variations in the ISRF intensity and reveal the intricate mixture of the warm dust heated by massive stars and the cold filamentary structures of embedded molecular clouds. The dust optical depth at 250 μm is well correlated with the gas column density, but with a significantly higher dust emissivity than in the solar neighborhood. We correlate the optical depth with 3-D cubes of the dust extinction to investigate variations in the ISRF strength and dust abundance along the line of sight through the spiral structure of the Galaxy. We show that the warmest dust along the LOS is located in the spiral arms of the Galaxy, and we quantify their respective IR contribution.

Conservation of the phase-space density of photons plus Lorentz invariance requires that the cosmological luminosity distance be larger than the angular diameter distance by a factor of $(1+z)^2$, where $z$ is the redshift. Because this is a fundamental symmetry, this prediction--known sometimes as the "Etherington relation" or the "Tolman test"--is independent of world model, or even the assumptions of homogeneity and isotropy. It depends, however, on Lorentz invariance and transparency. Transparency can be affected by intergalactic dust or interactions between photons and the dark sector. Baryon acoustic feature and type Ia supernovae measures of the expansion history are differently sensitive to the angular diameter and luminosity distances and can therefore be used in conjunction to limit cosmic transparency. At the present day, the comparison only limits the change $\Delta\tau$ in the optical depth from redshift 0.20 to 0.35 at visible wavelengths to $\Delta\tau < 0.13$ at 95% confidence. In a model with a constant comoving number density $n$ of scatterers of constant proper cross-section $\sigma$, this limit implies $n \sigma< 2\times10^{-4} h \Mpc^{-1}$. These limits depend weakly on the cosmological world model. Within the next few years, the limits could extend to redshifts $z\approx2.5$ and improve to $n \sigma, Comment: 14 pages, 2 figures, revised to match the published version

Pseudobulges form from unstable disks, while classical bulges form in violent episodes of star formation when a merger sweeps cold gas to a galactic centre. It seems unlikely that smashed disks contribute much to classical bulges. During mergers central black holes make cusps shallower and inflate kinematically decoupled cores. The abundance of galaxies with no detected classical bulge can perhaps be understood if galaxies exchange gas with the IGM more freely than is often supposed.

We explore the possibility that the steepening observed shortward of 1000A in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities as found in carbonaceous chondrite meteorites, such as Allende, is successful in reproducing the sharp break observed. The intergalactic dust model is partially successful in explaining the shape of the composite energy distribution, but must be discarded in the end, as the amount of crystalline dust required is unreasonable and would imply an improbable fine tuning among the dust formation processes. The alternative intrinsic dust model requires a mixture of both cubic diamonds and Allende nanodiamonds and provide a better fit of the UV break. The gas column densities implied are of the order 10^{20} cm^{-2} assuming solar metallicity for carbon and full depletion of carbon into dust. The absorption only occurs in the ultraviolet and is totally negligible in the visible. The minimum dust mass required is of the order ~ 0.003 r_{pc}^{2}M_o, where r_{pc} is the distance in parsec between the dust screen and the continuum source. The intrinsic dust model reproduces the flux {\it rise} observed around 660A in key quasar spectra quite well. We present indirect evidence of a shallow continuum break near 670A (18.5 eV), which would be intrinsic to the quasar continuum., 13 COLOR figures, 6 BW figures, ACCEPTED in ApJ (June 2005)

The detection of the IR emission from individual galaxy clusters is a difficult task due to the extremely low level of this emission and the fluctuations of the IR sky, galactic cirrus and background galaxies. We have statistically detected a significant IR emission toward galaxy clusters at 12 μm, 25 μm, 60 μm and 100 μm by co-adding the IRAS maps toward a total of 11 507 galaxy clusters extracted from the CDS database. This process averages the sky fluctuations of the astrophysical sky and the survey noise to a very low level in all four bands. We have obtained an averaged central detection at all wavelengths, with an intensity of 2685 ± 573 Jy/sr, 2127 ± 742 Jy/sr, 16 253 ± 670 Jy/sr and 34 011 ± 1391 Jy/sr respectively. These detections have been confirmed against possible spurious or systematic signals using different test methods. The origin of this detected IR emission is discussed. The free-free contribution to the IR emission can be ruled out. Both the level of the emission and its spectrum favor an interpretation in terms of dust emission. However the exact location of this dust remains unknown: is this emission due to intergalactic dust, or simply the dust included in the galaxies of the clusters? This last question will be discussed in a forthcoming paper.

Magnetic fields of unknown origin appear to permeate the Universe on all large scales. We suggest that the winds and cosmic rays, which are produced by the spherical ejecta and jets from supernova explosions, magnetize the interstellar medium in galaxies, the intracluster medium in galaxy clusters, and the intergalactic space. We show that, if the cosmic rays generate magnetic fields in rough energy equipartition with the cosmic rays, the predicted magnetic-field strengths coincide with the ones observed.

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 has probably the same origin., To Appear in Nature, September 30, 2004

International audience; We present preliminary analysis and considerations of the impact of dust on the measurement of cosmological parameters based on Type Ia supernovae. This analysis relies on the models of Commins [this proceedings, 2003] and employs subtraction of median extinction values from the measured magnitudes of Type Ia supernovae found in spiral galaxies, but combined with observational selection effects. Then, we estimate corrections to cosmological parameters. This work generally supports the SCP and Hi-Z team discovery of a non-zero Lambda. One of the goals of some of the dust treatments was to find a solution to the dust corrections that could "re-center" the fit to cosmological parameters from supernovae on the Omega tot=1 line segment in the Omega m-Omega Lambda plane. Such a "solution" was found and requires more dust in distant SCP cosmological supernovae than in nearby galaxies (the Calan-Tololo supernovae). Other host galaxy dust scenarios with differing amounts of dust and consequences for cosmology are explored. No convincing scenario of dust has yet been able to be developed for host galaxies in the observed SCP data which include observational selection that yields a Lambda=0 universe.

This paper examines the allowed amount of IG (intergalactic) dust, which is constrained by extinction and reddening of distant SNe and thermal history of IGM (intergalactic medium) affected by dust photoelectric heating. Based on the observational cosmic star formation history, we find an upper bound of $\chi$, the mass ratio of the IG dust to the total metal in the Universe, as $\chi\la 0.1$ for $10 {\rm \AA} \la a \la 0.1 \micron$ and $\chi\la 0.1(a/0.1 \micron)^{-1}$ for $0.1 \micron\la a\la1\micron$, where $a$ is a characteristic grain size of the IG dust. This upper bound of $\chi\sim0.1$ suggests that the dust-to-metal ratio in the IGM is smaller than the current Galactic value. The corresponding allowed density of the IG dust increases from $\sim10^{-34}$ g cm$^{-3}$ at $z=0$ to $\sim10^{-33}$ g cm$^{-3}$ at $z\sim1$, and keeps almost the value toward higher redshift. This causes IG extinction of $\la 0.2$ mag at the observer's $B$-band for $z\sim 1$ sources and that of $\la 1$ mag for higher redshift sources. Furthermore, if $E(B-V)\sim 0.1$ mag at the observer's frame against $z\ga1$ sources is detected, we can conclude that a typical size of the IG dust is $\la 100$ \AA. The 2175 \AA absorption feature of small graphite may be found as a local minimum at $z\sim2.5$ in a plot of the observed $E(B-V)$ as a function of the source redshift. Finally, the IGM mean temperature at $z\la1$ can be still higher than $10^{4}$ K, provided the size of the IG dust is $\la100$ \AA., Comment: 33 pages, 14 figures, MNRAS accepted

Colour measurements of quasars are used to constrain the abundance and properties of intergalactic dust and the related extinction effects on high-z sources. For Type Ia supernovae at z = 1, we derive an upper limit on the possible dimming from intergalactic dust of dm=0.2, ruling out the ``grey'' dust scenario as being solely responsible for the observed faintness of high-z SNIa., 11 pages, 4 figures, reference added, minor changes, matches accepted JCAP version

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 $\Omega_{\rm dust}^{\rm IGM}\la 10^{-6}$., Comment: 5 pages, 2 figures; accepted for publication in MNRAS pink pages

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., 9 pages, 2 figures, ApJ in press

If the background universe is observed through a significant amount of diffusely distributed foreground dust, then studies at optical wavelengths may be severely biased. Previous studies investigating effects of foreground dust on background sources assumed the dust to be ``compactly'' distributed, ie. on scales comparable to the visible extent of normal galaxies. We show however that diffuse dust is more effective at obscuring background sources. Galaxy clusters are a likely location for ``large-scale'' diffusely distributed dust, and its effect on the counts of background sources is explored. We also explore the implications of a hypothesised diffuse intergalactic dust component uniformly distributed to high redshift with comoving mass density equal to that associated with local galaxies. In this case, we predict a deficit in background sources about three times greater than that found in previous studies., 15 pages, 2 figures, to appear in September 1998 Issue of the Publications of the Astronomical Society of Australia

We have identified ten candidate intergalactic planetary nebulae in the Fornax galaxy cluster. These objects were found during observations in 1992 and 1993 in three fields chosen well away from any Fornax galaxy at 15 arcmin, 30 arcmin, and 45 arcmin from the centre of Fornax. We used the usual method of blinking images taken in a narrow OIII filter, with images taken in an adjacent broad filter. The measured fluxes in the narrow, broad, and I bands are consistent with these unresolved objects being planetary nebulae immersed in an intergalactic population of stars. Such a population is expected to arise as a consequence of tidal encounters between galaxies, and our findings strengthen the case for the existence of such tidal debris. The confirmation of some or all of these ten candidates as planetary nebulae would imply that intergalactic stars constitute a substantial fraction of all the stars in Fornax, up to an estimated 40 per cent. Intergalactic planetary nebulae could prove useful in probing the underlying cluster potential, since they would be far more abundant than galaxies. We discuss possible contamination of the sample by emission-line galaxies, but conclude that planetary nebulae is the most likely identification for the detected objects. keywords: intergalactic medium-- galaxies: interactions -- planetary nebulae: general -- clusters: individual: Fornax, 5 pages, latex (mn.sty), 3 figures (figure 1 is a jpeg image), to be published by MNRAS

The cocoons surrounding powerful radio sources can be extensive if the jet that feeds the cocoon is light and supersonic. They have been shown to remain overpressured with respect to the ambient medium for most of the life time of the sources. The observed lobes of the radio sources form parts of these extensive cocoons. We show that observations of the lobes of giant radio sources allow one to estimate the {\it density} of the intergalactic medium (IGM) in which the lobes are embedded. We estimate the IGM density to be of the order of a few percent of the closure density of the universe. We further calculate the radio power of the overpressured cocoon as a function of time and the ambient density., 10 pages, Standard Latex file and 1 postscript figure, uuencoded file. To appear in Monthly Notices of RAS

Measurements at a wavelength of 1.25 mm have been obtained for 17 IRAS galaxies selected on the basis of high far-infrared luminosity. These measurements are used to estimate the lower and upper limits to the mass of cold dust in infrared galaxies. As a lower limit on dust mass, all of the galaxies can be successfully modeled without invoking any dust colder than the dust responsible for the 60 and 100 micron emission that was detected by IRAS. As an upper limit, it is possible that the dust mass in a number of the galaxies may actually be dominated by cold dust. This large difference between the lower and upper limits is due primarily to uncertainty in the long-wavelength absorption efficiency of the astrophysical dust grains.

An excess of higher redshift galaxies, relative to the brightest member, in loose groups, was discovered by Arp in 1970, and was later confirmed by several authors. This effect is found to be present also in nearby small groups, identified by Tully in the Nearby Galaxy Catalogue. The asymmetry found is not likely to be ascribed to contamination by interlopers. A significant anticorrelation has also been found between the color excess E(B-V)(0)T and the velocity difference, with an associated E(B-V)(0)T variation on the order of 0.1-0.2. Such anticorrelation is not induced by obvious selection effects, such as the color-magnitude relation. A possible explanation is that groups are still collapsing and contain diffuse dust in the intragroup medium, with a mean optical depth, in the blue bland, on the order of 0.1-0.2. The mean dust density inside groups would be about 4 x 10 exp -31 g/cu cm; if the presence of dust is not only a local effect, the deduced cosmological density Omega(dust) would be in the range 10 exp -4 to 10 exp -5.

10 43 positrons per second annihilate in a compact spherical region around the centre of the Milky Way. At present, known astrophysical sources cannot account for this signal. In Ref. [1] we propose a novel scenario in which extragalactic positron sources such as radio jets of active galactic nuclei (AGN) fill the intergalactic medium (IGM) with MeV-scale e + e - pairs, which are then accreted into galaxies like the Milky Way. Interpreting the diffuse cosmic radio background (CRB) as arising from synchrotron radiation by such sources suggests that the intergalactic positron-to-electron ratio may be as high as 10-6. Assuming a simple spherical accretion model, this could account for the 511 keV emission of the galaxy.

International audience