Dust Absorption Research Articles

THE SUPERNOVA IMPOSTOR IMPOSTOR SN 1961V:SPITZERSHOWS THAT ZWICKY WAS RIGHT (AGAIN)

SN 1961V, one of Zwicky's defining Type V supernovae (SN), was a peculiar transient in NGC 1058 that has variously been categorized as either a true core collapse SN leaving a black hole (BH) or neutron star (NS) remnant, or an eruption of a luminous blue variable (LBV) star. The former case is suggested by its association with a decaying non-thermal radio source, while the latter is suggested by its peculiar transient light curve and its low initial expansion velocities. The crucial difference is that the star survives a transient eruption but not an SN. All stars identified as possible survivors are significantly fainter, L_opt ~ 10^5 Lsun, than the L_opt ~ 3 10^6 Lsun progenitor star at optical wavelengths. While this can be explained by dust absorption in a shell of material ejected during the transient, the survivor must then be present as a L_IR ~ 3 10^6 Lsun mid-infrared source. Using archival Spitzer observations of the region, we show that such a luminous mid-IR source is not present. The brightest source of dust emission is only L_IR ~ 10^5 Lsun and does not correspond to the previously identified candidates for the surviving star. The dust cannot be made sufficiently distant and cold to avoid detection unless the ejection energy, mass and velocity scales are those of a SN or greater. We conclude that SN 1961V was a peculiar, but real, supernova. Its peculiarities are probably due to enhanced mass loss just prior to the SN, followed by the interactions of the SN blast wave with this ejecta. This adds to the evidence that there is a population of SN progenitors that have major mass loss episodes shortly before core collapse. The progenitor is a low metallicity, ~1/3 solar, high mass, M_ZAMS > 80 Msun, star, which means either that BH formation can be accompanied by an SN or that surprisingly high mass stars can form a NS.

KECK DEEP FIELDS. IV. LUMINOSITY-DEPENDENT CLUSTERING AND GALAXY DOWNSIZING IN UV-SELECTED GALAXIES ATz= 4, 3, AND 2

We investigate the luminosity dependent clustering of rest-frame UV selected galaxies at z~4, 3, 2.2, and 1.7 in the Keck Deep Fields (KDFs), which are complete to R = 27 and cover 169 arcmin^2. We find that at z~4 and 3, UV-bright galaxies cluster more strongly than UV-faint ones, but at z~2.2 and 1.7, the UV-bright galaxies are no longer the most strongly clustered. We derive mass estimates for objects in our sample by comparing our measurements to the predicted clustering of dark matter haloes in the Millennium Simulation. From these estimates, we infer relationships between halo mass and star formation rate (SFR), and find that the most massive dark matter haloes in our sample host galaxies with high SFRs (M_1700 < -20, or > 50 M_sun/yr) at z~3 and 4, moderate SFRs (-20<M_1700<-19, or ~20 M_sun/yr) at z~2.2, and lower SFRs (-19<M_1700<-18, or ~2 M_sun/yr) at z~1.7. We believe our measurements may provide a new line of evidence for galaxy downsizing by extending that concept from stellar to halo mass. We also find that the objects with blue UV colors in our sample are much more strongly clustered than those with red UV colors, and we propose that this may be due to the presence of the 2175A dust absorption bump in more massive halos, which contain the older stellar populations and dust needed to produce the feature. The relatively small area covered by the survey means that the absolute values of the correlation lengths and halo masses we derive are heavily dependent on the "integral constraint" correction, but the uniformly deep coverage across a large redshift interval allows us to detect several important trends that are independent of this correction.

Is GRB 050904 at z = 6.3 absorbed by dust?

Claim of dust extinction for this GRB has been debated in the past. We suggest that the discrepant results occur primarily because most of previous studies have not simultaneously investigated the X-ray to near-IR spectral energy distribution of this GRB. The difficulty with this burst is that the X-ray afterglow is dominated by strong flares at early times and is poorly monitored at late times. In addition, the Z band photometry, which is the most sensitive to dust extinction, has been found to be affected by strong systematics. In this paper we carefully re-analyze the Swift/XRT afterglow observations of this GRB, using extensive past studies of X-ray flare properties when computing the X-ray afterglow flux level and exploiting the recent reanalysis of the optical (UV rest frame) data of the same GRB. We extract the X-ray to optical/near-IR afterglow SED for the three epochs where the best spectral coverage is available: 0.47, 1.25, and 3.4 days after the trigger. A spectral power-law model has been fitted to the extracted SEDs. We discuss that no spectral breaks or chromatic temporal breaks are expected in the epochs of interest. To fit any UV rest-frame dust absorption, we tested the Small Magellanic Cloud (SMC) extinction curve, the mean extinction curve (MEC) found for a sample of QSO at $z>4$ and its corresponding attenuation curve, as well as a starburst attenuation curve, and the extinction curve consistent with a supernova dust origin (SN-type). The SMC extinction curve and the SN-type one provide good fit to the data at all epochs, with an average amount of dust absorption at $\lambda_{rest} = 3000 \AA$ of $A_{3000} = 0.25\pm 0.07$ mag. These results indicate that the primeval galaxy at $z = 6.3$ hosting this GRB has already enriched its ISM with dust.

CLARA’s view on the escape fraction of Lyman α photons in high-redshift galaxies

Using CLARA (Code for Lyman Alpha Radiation Analysis) we constrain the escape fraction of Lyman-Alpha radiation in galaxies in the redshift range 5<z<7, based on the MareNostrum High-z Universe, a SPH cosmological simulation with more than 2 billion particles. We approximate Lyman-Alpha Emitters (LAEs) as dusty gaseous slabs with Lyman-Alpha radiation sources homogeneously mixed in the gas. Escape fractions for such a configuration and for different gas and dust contents are calculated using our newly developed radiative transfer code CLARA. The results are applied to the MareNostrum High-z Universe numerical galaxies. The model shows a weak redshift evolution and good agreement with estimations of the escape fraction as a function of reddening from observations at z \sim 2.2 and z \sim 3. We extend the slab model by including additional dust in a clumpy component in order to reproduce the UV con- tinuum luminosity function and UV colours at redshifts z>~5. The LAE Luminosity Function (LF) based on the extended clumpy model reproduces broadly the bright end of the LF derived from observations at z \sim 5 and z \sim 6. At z \sim 7 our model over-predicts the LF by roughly a factor of four, presumably because the effects of the neutral intergalactic medium are not taken into account. The remaining tension between the observed and simulated faint end of the LF, both in the UV-continuum and Lyman-Alpha at redshifts z \sim 5 and z \sim 6 points towards an overabundance of simulated LAEs hosted in haloes of masses 1.0x10^10h-1Msol < Mh < 4.0x10^10h-1Msol. Given the difficulties in explaining the observed overabundance by dust absorption, a probable origin of the mismatch are the high star formation rates in the simulated haloes around the quoted mass range. A more efficient supernova feedback should be able to regulate the star formation process in the shallow potential wells of these haloes.

Megamaser detection and nuclear obscuration in Seyfert galaxies

We revisit the relation between H2O maser detection rate and nuclear obscuration for a sample of 114 Seyfert galaxies, drawn from the CfA, 12um and IRAS F25/F60 catalogs. These sources have mid-infrared spectra from the Spitzer Space Telescope and they are searched for X-ray and [O III], 5007Angstrom fluxes from the literature. We use the strength of the [O IV], 25.9um emission line as tracer for the intrinsic AGN strength. After normalization by [O IV] the observed X-ray flux provides information about X-ray absorption. The distribution of X-ray / [O IV] flux ratios is significantly different for masers and non-masers: The maser detected Seyfert-2s (Sy 1.8-2.0) populate a distinct X-ray / [O IV] range which is, on average, about a factor four lower than the range of Seyfert-2 non-masers and about a factor of ten lower than the range of Seyfert-1s (Sy 1.0-1.5). Non-masers are almost equally distributed over the entire X-ray / [O IV] range. This provides evidence that high nuclear obscuration plays a crucial role for the probability of maser detection. Furthermore, after normalization with [O IV], we find a similar but weaker trend for the distribution of the maser detection rate with the absorption of the 7um dust continuum. This suggests that the obscuration of the 7 um continuum occurs on larger spatial scales than that of the X-rays. Hence, in the AGN unified model, at moderate deviation from edge-on, the 7um dust absorption may occur without proportionate X-ray absorption. The absorption of [O III] appears unrelated to maser detections. The failure to detect masers in obscured AGN is most likely due to insufficient observational sensitivity.

Examining the Effects of Dust Aerosols on Satellite Sea Surface Temperatures in the Mediterranean Sea Using the Medspiration Matchup Database

Abstract Dust aerosol plumes from the Sahara cover the Mediterranean Sea regularly during the summer months (June–August) and occasionally during other seasons. Dust can absorb infrared longwave radiation, thus causing a drop in sea surface temperature (SST) retrievals from satellite. To quantify the magnitude of this absorption and to understand the sources of the biases that might be introduced when trying to validate SST algorithms with in situ bulk temperatures, the effects of the dust absorption are studied using the Medspiration Match-up Database. This database provides in situ and satellite SSTs derived from the Advanced Very High Resolution Radiometer (AVHRR) and the Advanced Along-Track Scanning Radiometer (AATSR), and the difference between skin and bulk measurements is calculated in order to obtain errors or residuals, which are classified by ranges and compared to an aerosol optical thickness product derived from the sensors. The behavior of the residuals is studied and there is clear correspondence between higher residual values and higher aerosol concentrations, though in some cases this relation is not so evident, especially during autumn months. Residuals for this period are then related to other atmospheric effects and layer boundary physical processes by using ancillary data (e.g., soundings).

Host galaxy-active galactic nucleus alignments in the Sloan Digital Sky Survey Data Release 7

We determine the intrinsic shapes and orientations of 27,450 type I and II active galactic nucleus (AGN) galaxies in the spectroscopic sample of the SDSS DR7, by studying the distribution of projected axis ratios of AGN hosts. Our aim is to study possible alignments between the AGN and host galaxy systems (e.g. the accretion disc and the galaxy angular momentum) and the effect of dust obscuration geometry on the AGN type. We define control samples of non-AGN galaxies that mimic the morphology, colour, luminosity and concentration distributions of the AGN population, taking into account the effects of dust extinction and reddening. Assuming that AGN galaxies have the same underlying three-dimensional shape distribution as their corresponding control samples, we find that the spiral and elliptical type I AGN populations are strongly skewed toward face-on galaxies, while ellipticals and spirals type II AGN are skewed toward edge-on orientations. These findings rule out random orientations for AGN hosts at high confidence for type I spirals (delta chi^2~230) and type II ellipticals (delta chi^2~15), while the signal for type I ellipticals and type II spirals is weaker (delta chi^2~3 and delta chi^2~6, respectively). We obtain a much stronger tendency for the type II spirals to be edge-on when just high [OIII] equivalent width (EW) AGN are considered, suggesting that >20% of low [OIII] EW edge-on type II AGN may be missing from the optical sample. Galactic dust absorption of the broad-line region alone cannot explain the observed inclination angle and projected axis ratio distributions of type I and II Seyfert types, implying that obscuration by a small-scale circumnuclear torus is necessary. These results favour a scenario in which the angular momentum of the material which feeds the black hole retains a memory of its original gas source at least to some small, non-negligible degree.

A dual-frequency sub-arcsecond study of proto-planetary disks at mm wavelengths: first evidence for radial variations of the dust properties

(Abridged) We attempt to characterize the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws. We used the IRAM PdBI interferometer to provide very high angular resolution (down to 0.4" in some sources) observations of the continuum at 1.3 mm and 3 mm around a sample of T Tauri stars in the Taurus-Auriga region. The sample includes single and multiple systems, with a total of 23 individual disks. We used track-sharing observing mode to minimize the biases. We fitted these data with two kinds of models: a "truncated power law" model and a model presenting an exponential decay at the disk edge ("viscous" model). ect evidence for tidal truncation is found in the multiple systems. The temperature of the mm-emitting dust is constrained in a few systems. Unambiguous evidence for large grains is obtained by resolving out disks with very low values of the dust emissivity index Beta. In most disks that are sufficiently resolved at two different wavelengths, we find a radial dependence of Beta, which appears to increase from low values (as low as 0) at the center to about 1.7 -- 2 at the disk edge. The same behavior could apply to all studied disks. It introduces further ambiguities in interpreting the brightness profile, because the regions with apparent Beta = 0 can also be interpreted as being optically thick when their brightness temperature is high enough. Despite the added uncertainty on the dust absorption coefficient, the characteristic size of the disk appears to increase with a higher estimated star age. These results provide the first direct evidence of the radial dependence of the grain size in proto-planetary disks.

TYPE Ia SUPERNOVA LIGHT CURVE INFERENCE: HIERARCHICAL MODELS IN THE OPTICAL AND NEAR-INFRARED

We have constructed a comprehensive statistical model for Type Ia supernova (SN Ia) light curves spanning optical through near-infrared (NIR) data. A hierarchical framework coherently models multiple random and uncertain effects, including intrinsic supernova (SN) light curve covariances, dust extinction and reddening, and distances. An improved BayeSN Markov Chain Monte Carlo code computes probabilistic inferences for the hierarchical model by sampling the global probability density of parameters describing individual SNe and the population. We have applied this hierarchical model to optical and NIR data of 127 SNe Ia from PAIRITEL, CfA3, Carnegie Supernova Project, and the literature. We find an apparent population correlation between the host galaxy extinction AV and the ratio of total-to-selective dust absorption RV. For SNe with low dust extinction, AV ≲ 0.4, we find RV ≈ 2.5–2.9, while at high extinctions, AV ≳ 1, low values of RV < 2 are favored. The NIR luminosities are excellent standard candles and are less sensitive to dust extinction. They exhibit low correlation with optical peak luminosities, and thus provide independent information on distances. The combination of NIR and optical data constrains the dust extinction and improves the predictive precision of individual SN Ia distances by about 60%. Using cross-validation, we estimate an rms distance modulus prediction error of 0.11 mag for SNe with optical and NIR data versus 0.15 mag for SNe with optical data alone. Continued study of SNe Ia in the NIR is important for improving their utility as precise and accurate cosmological distance indicators.

“Novel” brominated flame retardants in Belgian and UK indoor dust: Implications for human exposure

Concentrations of several “novel” brominated flame retardants (NBFRs) are reported in indoor dust samples from Belgian houses ( n = 39) and offices ( n = 6) and from day-care centers and schools in the West Midlands of the UK ( n = 36). Using a GC-ECNI/MS method, the following NBFRs were quantified: decabromodiphenyl ethane (DBDPE) (range <20–2470 ng g −1), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) (range <0.5–1740 ng g −1), tetrabromobisphenol A-bis(2,3-dibromopropylether) (TBBPA-DBPE) (range <20–9960 ng g −1), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) (range <2–436 ng g −1) and bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate (TBPH) (range <2–6175 ng g −1). Hexachlorocyclopentadienyl-dibromocyclooctane (HCDBCO), another NBFR, was below the detection limit of 2 ng g −1 dust in all dust samples. No correlation was detected between concentrations of NBFRs and PBDEs. The ratio of TBB:TBPH in the dust samples ranged from 0.01 to 4.77 (average 0.42), compared to the ratio present in the commercial flame retardant product FM 550 (TBB:TBPH = 4:1). Furthermore, no correlation was detected between concentrations in dust of TBB and TBPH. This may suggest different sources of these NBFRs, or similar sources but compound-specific differences in their indoor fate and transport. Exposure via dust ingestion was estimated for both adults and toddlers under low-end (5th percentile), typical (median), and high-end (95th percentile concentrations) scenarios. These were calculated assuming 100% absorption of intake dust and using mean dust ingestion (adults = 20 mg d −1; for toddlers = 50 mg d −1) and high dust ingestion (adults = 50 mg d −1; for toddlers = 200 mg d −1). Typical exposure with high dust ingestion estimates for adults were 0.01, 0.2, 0.01, 0.02 and 0.08 ng kg −1 bw d −1 and for toddlers 0.05, 1.9, 0.08, 0.4 and 1.12 ng kg −1 bw d −1 for BTBPE, DBDPE, TBB, TBPH and TBBPA-DBPE, respectively. Our results showed that, similar to PBDEs, toddlers have higher exposure to NBFRs than adults. This study documents the presence of NBFRs in indoor environments, and emphasizes the need to evaluate the health implications of exposure to such chemicals.

Comparative Assessment of Human Exposure to Phthalate Esters from House Dust in China and the United States

Because of volatilization and leaching from their application in consumer and personal care products, phthalate esters are ubiquitous contaminants in the indoor environment. In this study, we measured concentrations and profiles of 9 phthalate esters in indoor dust samples collected from six cities in China (n = 75). For comparison, we also analyzed samples collected from Albany, New York, USA (n = 33). The results indicated that concentrations, except for dicyclohexyl phthalate (DCHP) and bis(2-ethylhexyl) phthalate (DEHP), and profiles of phthalate esters varied significantly between the two countries. Concentrations of diethyl phthalate (DEP), di-n-hexyl phthalate (DNHP), and benzyl butyl phthalate (BzBP) were 5 to 10 times higher in dust samples collected from Albany than those from the Chinese cities. In contrast, concentrations of di-iso-butyl phthalate (DIBP) in dust samples from Albany were 5 times lower than those from the Chinese cities. We estimated the daily intake (DI) of phthalate esters through the routes of dust ingestion and dermal dust absorption. The extent of contribution of indoor dust to human exposures varied, depending on the type of phthalate esters. The contribution of dust to DEHP exposure was 2-5% and 10-58% of the estimated total DIs in China and the USA, respectively. On the basis of the estimates of total DIs of phthalates, extrapolated from urinary metabolite concentrations, the contributions of inhalation, dermal absorption, and dietary intake to total DIs were estimated. The results indicated that dietary intake is the main source of exposure to DEHP (especially in China), whereas dermal exposure was a major source for DEP. This is the first study to elucidate sources of human exposure to phthalates among the general population in China.

ICES IN THE QUIESCENT IC 5146 DENSE CLOUD

This paper presents spectra in the 2 to 20 micron range of quiescent cloud material located in the IC 5146 cloud complex. The spectra were obtained with NASA's Infrared Telescope Facility (IRTF) SpeX instrument and the Spitzer Space Telescope's Infrared Spectrometer. We use these spectra to investigate dust and ice absorption features in pristine regions of the cloud that are unaltered by embedded stars. We find that the H2O-ice threshold extinction is 4.03+/-0.05 mag. Once foreground extinction is taken into account, however, the threshold drops to 3.2 mag, equivalent to that found for the Taurus dark cloud, generally assumed to be the touchstone quiescent cloud against which all other dense cloud and embedded young stellar object observations are compared. Substructure in the trough of the silicate band for two sources is attributed to CH3OH and NH3 in the ices, present at the ~2% and ~5% levels, respectively, relative to H2O-ice. The correlation of the silicate feature with the E(J-K) color excess is found to follow a much shallower slope relative to lines of sight that probe diffuse clouds, supporting the previous results by Chiar et al. (2007).

Extended dust shell of the carbon star U Hydrae observed with AKARI

Context. Low- to intermediate-mass stars lose a significant fraction of their mass while they are on the asymptotic giant branch (AGB). This mass loss is considered to determine the final stages of their evolution. The material ejected from the stellar photosphere forms a circumstellar envelope in its surroundings. Layers of circumstellar envelope constitute the footprint of mass-loss history. Aims. Our aim is to probe the mass-loss history in the carbon star U Hya in the last ∼10 4 years by investigating the distribution of dust in the circumstellar envelope with high spatial resolution. Methods. We observed U Hya in the far-infrared (FIR) at 65, 90, 140, and 160 μm simultaneously, using the slow scan observing mode of the far-infrared surveyor (FIS) aboard the infrared astronomical satellite AKARI. It produced a map of ∼10 � × 40 � in size in each band. Results. The FIS maps reveal remarkably circular, ring-like emission structure almost centered on the star, showing the presence of a detached, spherical dust shell. A hollow dust shell model gives the inner radius Rin of 101–107 �� [(2.5–2.6) × 10 17 cm], thickness that covers a half of the total dust mass ΔRhm of 16–23 �� [(3.8–5.6) × 10 16 cm], which gives ΔRhm/Rin ∼ 0.2, and the power-law index of the dust opacity distribution of 1.10–1.15. The dust mass in the shell is well-constrained to be (0.9–1.4) × 10 −4 (κ100/25) −1 M� , where κ100 is the dust absorptivity at 100 μm in units of cm 2 g −1 . The dust mass-loss rate at Rin is found to be (1.8–

An Astrophysical Peek into Einstein’s Static Universe: No Dark Energy

It is shown that in order that the fluid pressure and acceleration are uniform and finite in Einstein’s Static Universe (ESU), , the cosmological constant, is zero.   being a fundamental constant, should be the same everywhere including the Friedman model. Independent proofs show that it must be so. Accordingly, the supposed acceleration of the universe and the attendant concept of a “Dark Energy” (DE) could be an illusion; an artifact of explaining cosmological observations in terms of an oversimplified model which is fundamentally inappropriate. Indeed observations show that the actual universe is lumpy and inhomogeneous at the largest scales. Further in order that there is no preferred centre, such an inhomogeneity might be expressed in terms of infinite hierarchial fractals. Also, the recent finding that the Friedman model intrinsically corresponds to zero pressure (and hence zero temperature) in accordance with the fact that an ideal Hubble flow implies no collision, no randomness (Mitra, Astrophys. Sp. Sc., 333,351, 2011) too shows that the Friedman model cannot represent the real universe having pressure, temperature and radiation. Dark Energy might also be an artifact of the neglect of dust absorption of distant Type 1a supernovae coupled with likely evolution of supernovae luminosities or imprecise calibration of cosmic distance ladders or other systemetic errors (White, Rep. Prog. Phys., 70, 883, 2007). In reality, observations may not rule out an inhomogeneous static universe (Ellis, Gen. Rel. Grav. 9, 87, 1978), if the fundamental “constant”s are indeed constant.

The visibility of Lyman α emitters during reionization

We present the first Lyman Alpha Emitter (LAE) study that combines: (i) cosmological SPH simulations run using GADGET-2, (ii) radiative transfer simulations (CRASH), and (iii) a previously developed LAE model. This complete LAE model accounts for the intrinsic LAE Lyman Alpha/continuum luminosity, dust enrichment and Lyman Alpha transmission through the intergalactic medium (IGM), to quantify the effects of reionization, dust and velocity fields on the Lyman Alpha and UV Luminosity Functions (LF). We find that a model neglecting dust sorely fails to reproduce either the slope or the magnitude of the observed Lyman Alpha and UV LFs. Clumped dust is required to simultaneously fit the observed UV and Lyman Alpha LFs, such that the intrinsic Lyman Alpha-to-continuum luminosity is enhanced by a factor f_alpha/f_c ~ 1.5 (3.7) excluding (including) peculiar velocities. The higher value including velocity fields arises since LAEs reside in large potential wells and inflows decrease their Lyman Alpha transmission. For the first time, a degeneracy is found between the the ionization state of the IGM and the clumping of dust inside high-redshift galaxies. The Lyman Alpha LF at z ~ 5.7 can be well reproduced (to within a 5 sigma error) by a wide range of IGM average neutral hydrogen fraction, 3.4/10^3 to 0.16, provided that the increase in the Lyman Alpha transmission through a more ionized IGM is compensated by a decrease in the Lyman Alpha escape fraction from the galaxy due to dust absorption. The physical properties of LAEs are presented, along with a discussion of the assumptions adopted.

AKARIIRC INFRARED 2.5-5 μm SPECTROSCOPY OF A LARGE SAMPLE OF LUMINOUS INFRARED GALAXIES

We present the results of our systematic infrared 2.5–5 μm spectroscopy of 60 luminous infrared galaxies (LIRGs) with infrared luminosities LIR = 1011–1012 L☉ and 54 ultraluminous infrared galaxies (ULIRGs) with LIR ⩾ 1012 L☉, using the AKARI Infrared Camera (IRC). AKARI IRC slit-less spectroscopy allows us to probe the full range of emission from these galaxies, including spatially extended components. The 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission features, hydrogen recombination emission lines, and various absorption features are detected and used to investigate the properties of these galaxies. Because of the relatively small effect of dust extinction in the infrared range, quantitative discussion of these dusty galaxy populations is possible. For sources with clearly detectable Brβ (2.63 μm) and Brα (4.05 μm) emission lines, the flux ratios are found to be similar to those predicted by case B theory. Starburst luminosities are estimated from both 3.3 μm PAH and Brα emission, which roughly agree with each other. In addition to the detected starburst activity, a significant fraction of the observed sources display signatures of obscured active galactic nuclei (AGNs), such as low PAH equivalent widths, large optical depths of dust absorption features, and red continuum emission. The energetic importance of optically elusive buried AGNs in optically non-Seyfert galaxies tends to increase with increasing galaxy infrared luminosity, from LIRGs to ULIRGs.

Agglomeration processes in carbonaceous dusty plasmas, experiments and numerical simulations

This paper deals with carbon dust agglomeration in radio frequency acetylene/argon plasma. Two studies, an experimental and a numerical one, were carried out to model dust formation mechanisms. Firstly, in situ transmission spectroscopy of dust clouds in the visible range was performed in order to observe the main features of the agglomeration process of the produced carbonaceous dust. Secondly, numerical simulation tools dedicated to understanding the achieved experiments were developed. A first model was used for the discretization of the continuous population balance equations that characterize the dust agglomeration process. The second model is based on a Monte Carlo ray-tracing code coupled to a Mie theory calculation of dust absorption and scattering parameters. These two simulation tools were used together in order to numerically predict the light transmissivity through a dusty plasma and make comparisons with experiments.

A DUSTY Mg II ABSORBER ASSOCIATED WITH THE QUASAR SDSS J003545.13+011441.2

We report on a dusty Mg~II absorber associated with the quasar SDSSJ003545.13+011441.2 (hereafter J0035+0114) at $z$=1.5501, which is the strongest one among the three Mg~II absorbers along the sight line of quasar. The two low redshift intervening absorbers are at $z$=0.7436, 0.5436, respectively. Based on the photometric and spectroscopic data of Sloan Digital Sky Survey (hereafter SDSS), we infer the rest frame color excess E(\bv) due to the associated dust is more than 0.07 by assuming a Small Magellanic Cloud (hereafter SMC) type extinction curve. Our follow-up moderate resolution spectroscopic observation at the 10-m Keck telescope with the ESI spectrometer enable us to reliably identify most of the important metal elements, such as Zn, Fe, Mn, Mg, Al, Si, Cr, and Ni in the associated system. We measure the column density of each species and detect significant dust depletion. In addition, we develop a simulation technique to gauge the significance of 2175-{\AA} dust absorption bump on the SDSS quasar spectra. By using it, we analyze the SDSS spectrum of J0035+0114 for the presence of a associated 2175-{\AA} extinction feature and report a tentative detection at $\sim$2$\sigma$ significant level.

Martian dust devil electron avalanche process and associated electrochemistry

Mars' dynamic atmosphere displays localized dust devils and larger, global dust storms. Based on terrestrial analog studies, electrostatic modeling, and laboratory work, these features will contain large electrostatic fields formed via triboelectric processes. In the low‐pressure Martian atmosphere, these fields may create an electron avalanche and collisional plasma due to an increase in electron density driven by the internal electrical forces. To test the hypothesis that an electron avalanche is sustained under these conditions, a self‐consistent atmospheric process model is created including electron impact ionization sources and electron losses via dust absorption, electron dissociation attachment, and electron/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves simultaneously nine continuity equations describing the evolution of the primary gaseous chemical species involved in the electrochemistry. DDEAM monitors the evolution of the electrons and primary gas constituents, including electron/water interactions. We especially focus on electron dynamics and follow the electrons as they evolve in the E field driven collisional gas. When sources and losses are self‐consistently included in the electron continuity equation, the electron density grows exponentially with increasing electric field, reaching an equilibrium that forms a sustained time‐stable collisional plasma. However, the character of this plasma differs depending upon the assumed growth rate saturation process (chemical saturation versus space charge). DDEAM also shows the possibility of the loss of atmospheric methane as a function of electric field due to electron dissociative attachment of the hydrocarbon. The methane destruction rates are presented and can be included in other larger atmospheric models.

Cloud cover increase with increasing aerosol absorptivity: A counterexample to the conventional semidirect aerosol effect

We reexamine the aerosol semidirect effect using a general circulation model and four cases of the single‐scattering albedo of dust aerosols. Contrary to the expected decrease in low cloud cover due to heating by tropospheric aerosols, we find a significant increase with increasing absorptivity of soil dust particles in regions with high dust load, except during Northern Hemisphere winter. The strongest sensitivity of cloud cover to dust absorption is found over land during Northern Hemisphere summer. Here even medium and high cloud cover increase where the dust load is highest. The cloud cover change is directly linked to the change in relative humidity in the troposphere as a result of contrasting changes in specific humidity and temperature. More absorption by aerosols leads to larger diabatic heating and increased warming of the column, decreasing relative humidity. However, a corresponding increase in the specific humidity exceeds the temperature effect on relative humidity. The net effect is more low cloud cover with increasing aerosol absorption. The higher specific humidity where cloud cover strongly increases is attributed to an enhanced convergence of moisture driven by dust radiative heating. Although in some areas our model exhibits a reduction of low cloud cover due to aerosol heating consistent with the conventional description of the semidirect effect, we conclude that the link between aerosols and clouds is more varied, depending also on changes in the atmospheric circulation and the specific humidity induced by the aerosols. Other absorbing aerosols such as black carbon are expected to have a similar effect.