Dust Absorption Research Articles

Ultraviolet through Infrared Spectral Energy Distributions from 1000 SDSS Galaxies: Dust Attenuation

The meaningful comparison of models of galaxy evolution to observations is critically dependent on the accurate treatment of dust attenuation. To investigate dust absorption and emission in galaxies we have assembled a sample of ~1000 galaxies with UV through IR photometry from GALEX, SDSS, and Spitzer, and optical spectroscopy from SDSS. The ratio of IR to UV emission (IRX) is used to constrain the dust attenuation in galaxies. We use the 4000 A break as a robust and useful, although coarse, indicator of star formation history (SFH). We examine the relationship between IRX and the UV spectral slope (a common attenuation indicator at high redshift) and find little dependence of the scatter on D_n(4000). We construct average UV through far-IR spectral energy distributions (SEDs) for different ranges of IRX, D_n(4000), and stellar mass (M_*) to show the variation of the entire SED with these parameters. When binned simultaneously by IRX, D_n(4000), and M_* these SEDs allow us to determine a low-resolution average attenuation curve for different ranges of M_*. The attenuation curves thus derived are consistent with a λ^(−0.7) attenuation law, and we find no significant variations with M_*. Finally, we show the relationship between IRX and the global stellar mass surface density and gas-phase metallicity. Among star-forming galaxies we find a strong correlation between IRX and stellar mass surface density, even at constant metallicity, a result that is closely linked to the well-known correlation between IRX and star formation rate.

Effect of mineral dust aerosols on the photolysis rates in the clean and polluted marine environments

This study examines the importance of spectral optical properties of mineral dust in calculations of photolysis rates in clean and polluted marine environments. A set of optical characteristics was computed with Mie theory using data on the size distribution and composition of mineral dust from recent experimental and modeling studies. These models were incorporated into the National Center for Atmospheric Research tropospheric ultraviolet‐visible radiation transfer code. The 13 analyzed photolysis reactions were classified into three groups according to their photolytic wavelengths and the vertical profile of J values in the aerosol‐free atmosphere. The photolysis reactions of O3(O1D), NO2, and NO3(NO) were selected as representative of groups I, II, and III, respectively. We find that depending on its properties, dust causes either a decrease or an increase in the spectral actinic fluxes relative to the aerosol‐free condition. The wavelength range in which the changes in actinic fluxes are negative becomes broader as the amount of dust load increases, a dust size distribution is shifted to coarse size mode, and the iron oxide content in dust aggregates increases. Changes in actinic fluxes also depend on the sun position (time of the day) and an altitude considered. As a result, dust exerts the differing impact on J values of the three photolytic groups. The diurnal cycle of dust‐affected J values of a given group is similar among the differing size distribution and dust compositions, but changes in J values vary by a factor of 1.5–2. For a given content of iron oxide, the largest changes are caused by the size distributions that are shifted to the fine size mode. A change in J values of groups I and II caused by the varying amount of iron oxide in dust aggregates (from 1% to 10%) is negative in and below the dust layer. In contrast, J values of group III increase in the presence of low absorbing dust (with 1% of iron oxide), but they decrease with increasing dust absorption. Our results indicate that the dust composition not only will be needed to accurately model a decrease in J values of groups I and II but also to determine a correct sign and value of changes of J values of group III. In the case of dust mixed with pollution, we find that the external mixing of dust and black carbon causes somewhat larger changes in J values compared to the internal mixing of these species. We conclude that regional differences in size and composition of mineral dust as well as related changes in the vertical profile and diurnal cycle of actinic fluxes and J values should be taken into account if more realistic assessments of the dust impact on photochemistry through photolysis are to be achieved.

Color variability of the blazar AO 0235+16

Multicolor (UBVRIJHK) observations of the blazar AO 0235+16 are analyzed. The light curves were compiled at the Turin Observatory from literature data and the results of observations obtained in the framework of the WEBT program (this http URL). The color variability of the blazar was studied in eight time intervals with a sufficient number of multicolor optical observations; JHK data are available for only one of these. The spectral energy distribution (SED) of the variable component remained constant within each interval, but varied strongly from one interval to another. After correction for dust absorption, the SED can be represented by a power law in all cases, providing evidence for a synchrotron nature of the variable component. We show that the variability at both optical and IR wavelengths is associated with the same variable source.

Spectral aerosol optical properties from AERONET Sun-photometric measurements over West Africa

Aerosol optical properties including Aerosol Optical Depth (AOD, τ aλ), Angstrom exponent (α), size distribution, single scattering albedo ( w o ) were examined using long-term ground-based radiometric measurements at five West African sites; Dakar (14°42'N 17°29′W), Banizoumbou (13°45′N, 02°39′E), Agoufou (15°21'N,1°29′W), Ilorin (08°32′N, 04°34′E), and Ouagadougou (12°22′N, 1°31′W). Also included were observations made at the Cape Verde Islands (16° 45′N, 22° 57′W) to investigate the aerosol transport over the Atlantic Ocean. Results from multiyear observations show that monthly average AOD generally exhibits primary and secondary maximum in March and June respectively except Ilorin that shows peak value in January. The seasonal cycle of Angström exponent (α 440–870 nm) shows that minimum values are often associated with dust storm in all sites however, the monthly mean α 440–870 nm yields high values at Ilorin, even for peak dust seasons. It suggests that fine mode aerosols dominate the daily aerosol optical influence even during the ‘harmattan’ season when biomass/urban pollution aerosol mixes with coarse mode dust originating aerosols at the sites. The retrieved aerosol size distributions for predominately fine mode particles (cases with α 440–870 nm> 0.5) at Ilorin and Cape Verde show an obvious steady increase in particle size as τ a440 nm increased in both the modal maximum value and expansion of the fine mode boundary towards larger radius. The volume median radius of the size distribution of the coarse mode desert dust at Ilorin ranged from ∼ 1.9 to 3.2 μm with geometric standard deviation of 1.61 to 1.83. The coarse particle mode at Cape Verde shows very little dynamic changes as a function of aerosol optical depth. Results from estimated single scattering albedo ( w o) show wide differences in the observed magnitudes of the fine/coarse mode particle absorption at the sites under study. The differences in dust absorption may be adduced to the possible interactions between dust and fine mode pollution aerosols and variability of the dust optical properties from different source regions in West Africa. Air mass backward trajectories based on multiyear data were developed to explain the transport and identification of different aerosol types in this region of study.

JASMINE data analysis

AbstractJapan Astrometry Satellite Mission for Infrared Exploration (JASMINE) aims to construct a map of the Galactic bulge with a 10 μas accuracy. We use z-band CCD or K-band array detector to avoid dust absorption, and observe about 10 × 20 degrees area around the Galactic bulge region.In this poster, we show the observation strategy, reduction scheme, and error budget. We also show the basic design of the software for the end-to-end simulation of JASMINE, named JASMINE Simulator.

Measuring the cosmic star-formation rate density using deep radio surveys

There is now good agreement between the various methods of estimating the space density of the star-formation rate (SFRD) at low redshifts (z < 1), with uncertainties around 30–50%. However, the situation at higher redshifts remains much less clear, with uncertainties in the SFRD, due to e.g. poorly known dust absorption corrections, of as much as 300–500%. Radio emission from star-forming galaxies is unaffected by absorption and scales linearly with star-formation rate, thus the radio luminosity of star-forming galaxies provides an excellent independent, unbiased measure of their star-formation rate. The current deepest ‘blank field’ radio surveys (reaching <10 μJy rms at 1.4 GHz) are sensitive enough to detect starburst galaxies out to z ~ 3, and so potentially offer an excellent way to measure the SFRD. Indeed, modelling of the sub-mJy source counts requires an additional population of faint steep spectrum objects, that are very likely to be starburst galaxies.

JASMINE – design and method of data reduction

AbstractJapan Astrometry Satellite Mission for Infrared Exploration (JASMINE) aims to construct a map of the Galactic bulge with 10 μ arc sec accuracy. We use z-band CCD for avoiding dust absorption, and observe about 10 × 20 degrees area around the Galactic bulge region. Because the stellar density is very high, each FOVs can be combined with high accuracy. With 5 years observation, we will construct 10 μ arc sec accurate map.In this poster, I will show the observation strategy, design of JASMINE hardware, reduction scheme, and error budget. We also construct simulation software named JASMINE Simulator. We also show the simulation results and design of software.

Energy Distribution of Individual Quasars from Far‐Ultraviolet to X‐Rays. I. Intrinsic Ultraviolet Hardness and Dust Opacities

Using Chandra and HST archival data, we have studied the individual Spectral Energy Distribution (SED) of 11 quasars. All UV spectra show a spectral break around 1100A. 5 X-ray spectra show the presence of a ``soft excess'' and 7 spectra showed an intrinsic absorption. We found that for most quasars a simple extrapolation of the far-UV powerlaw into the X-ray domain generally lies below the X-ray data and that the big blue bump and the soft X-ray excess do not share a common physical origin. We explore the issue of whether the observed SED might be dust absorbed in the far and near-UV. We fit the UV break, assuming a powerlaw that is absorbed by cubic nanodiamond dust grains. We then explore the possibility of a universal SED (with a unique spectral index) by including further absorption from SMC-like extinction. Using this approach, satisfactory fits to the spectra can be obtained. The hydrogen column densities required by either nanodiamonds or amorphous dust models are all consistent, except for one object, with the columns deduced by our X-ray analysis, provided that the C depletion is ~0.6. Because dust absorption implies a flux recovery in the extreme UV (<700A), our modeling opens the possibility that the intrinsic quasar SED is much harder and more luminous in the extreme UV than inferred from the near-UV data, as required by photoionization models of the broad emission line region. We conclude that the intrinsic UV SED must undergo a sharp turn-over before the X-ray domain.

Dust absorption over the “Great Indian Desert” inferred using ground‐based and satellite remote sensing

Mineral dust is the single largest contributor of natural aerosols over land. Dust aerosols exhibit high variability in their radiative effects because their composition varies locally. This arises because of the regional distinctiveness of the soil characteristics as well as the accumulation of other aerosol species, such as black carbon, on dust while airborne. To accurately estimate the climate impact of dust, spatial and temporal distribution of its radiative properties are essential. However, this is poorly understood over many regions of the world, including the Indian region. In this paper, infrared (IR) radiance (10.5–12.5 μm) acquired from METEOSAT‐5 satellite (∼5‐km resolution) is used to retrieve dust aerosol characteristics over the “Great Indian Desert” and adjacent regions. The infrared radiance depression on account of the presence of dust in the atmosphere has been used as an index of dust load, called the Infrared Difference Dust Index (IDDI). Simultaneous, ground‐based spectral optical depths estimated at visible and near‐infrared wavelengths (using a multiwavelength solar radiometer) are used along with the IDDI to infer the dust absorption. The inferred single scattering albedo of dust was in the range of 0.88–0.94. We infer that dust over the Indian desert is of more absorbing nature (compared with African dust). Seasonally, the absorption is least in summer and most in winter. The large dust absorption leads to lower atmospheric warming of 0.7–1.2 K day−1.

SpitzerObservations of 3C Quasars and Radio Galaxies: Mid‐Infrared Properties of Powerful Radio Sources

We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS instruments on the Spitzer Space Telescope. Powerful emission (L_24micron > 10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the Spitzer data as well as other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 microns, quasars are typically four times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of non-thermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anti-correlated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 microns for objects with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R < 10^-2, it is 1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.

Simulating the Formation of Molecular Clouds. II. Rapid Formation from Turbulent Initial Conditions

In this paper we present results from a large set of numerical simulations that demonstrate that H2 formation occurs rapidly in turbulent gas. Starting with purely atomic hydrogen, large quantities of molecular hydrogen can be produced on timescales of 1-2 Myr, given turbulent velocity dispersions and magnetic field strengths consistent with observations. Moreover, as our simulations underestimate the effectiveness of H2 self-shielding and dust absorption, we can be confident that the molecular fractions that we compute are strong lower limits on the true values. The formation of large quantities of molecular gas on the timescale required by rapid cloud formation models therefore appears to be entirely plausible. We also investigate the density and temperature distributions of gas in our model clouds. We show that the density probability distribution function is approximately lognormal, with a dispersion that agrees well with the prediction of Padoan and coworkers. The temperature distribution is similar to that of a polytrope, with an effective polytropic index γeff 0.8, although at low gas densities, the scatter of the actual gas temperature around this mean value is considerable, and the polytropic approximation does not capture the full range of behavior of the gas.

Modulation of the aerosol absorption and single‐scattering albedo due to synoptic scale and sea breeze circulations: United Arab Emirates experiment perspective

The spectral aerosol absorption properties in the Arabian Gulf region were observed during the United Arab Emirates Unified Aerosol Experiment (UAE2). Measurements were taken at a coastal region of the Arabian Gulf located 60 km northeast of Abu Dhabi, the capital of the United Arab Emirates, allowing characterization of pollution and dust absorption properties in a highly heterogeneous environment. A large observed change of the diurnal signal during the period under study (27 August through 30 September 2004) was due to (1) strong sea and land breeze and (2) changes in prevailing synoptic‐scale flow. During the night, stagnating air resulted in gradual accumulation of pollution with maximum absorption in the early morning hours. The rising sun increased both the depth of the boundary layer and the temperature of the interior desert, resulting in strong and sudden sea breeze onset which ventilated the polluted air accumulated during the night. Our observations show that the onshore winds brought cleaner air resulting in decreasing values of the absorption coefficient and increasing values of the single‐scattering albedo (SSA). The mean value of the absorption coefficient at 550 nm measured during the sea breeze was 10.2 ± 0.9 Mm−1, while during the land breeze it was 13.8 ± 1.2 Mm−1. Synoptic‐scale transport also strongly influenced particle fine/coarse partition with “northern” flow bringing pollution particles and “southern” flow bringing more dust.

Lyα emission in high-redshift galaxies

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on theSpitzer Space Telescope. II. TheIRASBright Galaxy Sample

We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38 micron region of the ten Ultraluminous Infrared Galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample. Among the BGS ULIRGs, we find a factor of 50 spread in the rest-frame mid to far-infrared spectral slope. The 9.7 micron silicate optical depths range from less than 0.4 more than 4.2, implying line of sight extinctions of A(V) ~ 8 - 78 mag. There is evidence for water ice and hydrocarbon absorption and C2H2 and HCN absorption features in four and possibly six of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [NeV] emission in three of the ten BGS ULIRGs, at flux levels of 5-18E-14 erg/cm^2/sec and [NeV] 14.3/[NeII] 12.8 line flux ratios of 0.12-0.85. The remaining BGS ULIRGs have limits on their [NeV]/[NeII] line flux ratios which range from less than 0.15 to less than 0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [NeV]/[NeII] or [OIV]/[NeII] line flux ratios (or their upper limits) are significantly lower than implied by the MIR slope or EQW of the 6.2 micron PAH feature. Fitting the SEDs, we see evidence for hot (T > 300K) dust in five of the BGS ULIRGs, with the fraction of hot dust to total dust luminosity ranging from ~1-23%, before correcting for extinction. When integrated over the IRAC-8, IRS blue peakup, and MIPS-24 filter bandpasses, the IRS spectra imply very blue colors for some ULIRGs at z ~ 1.3. This is most extreme for sources with significant amounts of warm dust and deep silicate absorption.

A Spitzer IRS Low‐Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies: A Constraint on Geometry between Energy Sources and Dust

We present the results of Spitzer IRS low-resolution infrared 5-35 micron spectroscopy of nearby ultraluminous infrared galaxies (ULIRGs) at z < 0.15. We focus on the search for the signatures of buried active galactic nuclei (AGNs) in the complete sample of ULIRGs classified optically as non-Seyferts (LINERs or HII-regions). In addition to polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 micron, 7.7 micron, and 11.3 micron, the conventional tool of starburst-AGN separation, we use the optical depths of the 9.7 micron and 18 micron silicate dust absorption features to infer the geometry of energy sources and dust at the nuclei of these ULIRGs, namely, whether the energy sources are spatially well mixed with dust(a normal starburst) or are more centrally concentrated than the dust (a buried AGN). Infrared spectra of at least 30%, and possibly 50%, of the observed optical non-Seyfert ULIRGs are naturally explained by emission consisting of (1) energetically insignificant, modestly obscured (Av < 20-30 mag) PAH-emitting normal starbursts, and (2) energetically dominant, highly dust-obscured, centrally concentrated energy sources with no PAH emission. We interpret the latter component as a buried AGN. The fraction of ULIRGs showing some buried AGN signatures is higher in LINER ULIRGs than in HII-region ULIRGs. Most of the luminous buried AGN candidates are found in ULIRGs with cool far-infrared colors. Where the absorption-corrected intrinsic AGN luminosities are derivable with little uncertainty, they are found to be of the order of 10^12Lsun, accounting for the bulk of the ULIRGs' luminosities. The 5-35 micron spectroscopic starburst/AGN classifications are generally consistent with our previous classifications based on 3-4 micron spectra for the same sample.

Atmospheric warming due to dust absorption over Afro‐Asian regions

There have been several investigations to understand the impact of Saharan dust layer on radiative heat balance. However, there are few studies on the impact of dust over Asian regions which is unique in aerosol perspective because of co‐existence of natural and anthropogenic aerosols. Here, we examine the surface cooling and lower atmospheric warming (and hence heating rate) due to dust over Afro‐Asian regions using collocated data from METEOSAT (of ESA) and MODIS (of NASA). Large reduction of surface reaching solar radiation as much as 10 to 15 W m−2 due to dust was observed simultaneous with a lower atmospheric warming of 0.3 to 0.5 K/day. During local noon warming was as large as 3K over desert regions. The large dust heating at source regions and its impact over ocean due to transported dust raises several issues which need to be understood.

Reevaluation of Mineral aerosol radiative forcings suggests a better agreement with satellite and AERONET data

Abstract. Modelling studies and satellite retrievals do not agree on the amplitude and/or sign of the direct radiative perturbation from dust. Modelling studies have systematically overpredicted mineral dust absorption compared to estimates based upon satellite retrievals. In this paper we first point out the source of this discrepancy, which originates from the shortwave refractive index of dust used in models. The imaginary part of the refractive index retrieved from AERONET over the range 300 to 700 nm is 3 to 6 times smaller than that used previously to model dust. We attempt to constrain these refractive indices using a mineralogical database and varying the abundances of iron oxides (the main absorber in the visible). We first consider the optically active mineral constituents of dust and compute the refractive indices from internal and external mixtures of minerals with relative amounts encountered in parent soils. We then compute the radiative perturbation due to mineral aerosols for internally and externally mixed minerals for 3 different hematite contents, 0.9%, 1.5% and 2.7% by volume. These constant amounts of hematite allow bracketing the influence of dust aerosol when it is respectively an inefficient, standard and a very efficient absorber. These values represent low, central and high content of iron oxides in dust determined from the mineralogical database. Linke et al. (2006) determined independently that iron-oxides represent 1.0 to 2.5% by volume using x-Ray fluorescence on 4 different samples collected over Morocco and Egypt. Based upon values of the refractive index retrieved from AERONET, we show that the best agreement between 440 and 1020 nm occurs for mineral dust internally mixed with 1.5% volume weighted hematite. This representation of mineral dust allows us to compute, using a general circulation model, a new global estimate of mineral dust perturbation between –0.47 and –0.24 Wm−2 at the top of the atmosphere, and between –0.81 and –1.13 Wm−2 at the surface for both shortwave and longwave wavelengths. The anthropogenic dust fraction is thought to account for between 10 and 50% of the total dust load present in the atmosphere. We estimate a top of the atmosphere forcing between –0.03 and –0.25 Wm−2, which is markedly different that the IPCC range of –0.6 to +0.4 Wm−2 (IPCC, 2001). The 24-h average atmospheric heating by mineral dust during summer over the tropical Atlantic region (15° N–25° N; 45° W–15° W) is in the range +22 to +32 Wm−2 τ−1 which compares well with the 30±4 Wm−2 τ−1 measured by Li et al. (2004) over that same region. The refractive indices from Patterson et al. (1977) and from Volz (1973) overestimate by a factor of 2 the energy absorbed in the column during summer over the same region. This discrepancy is due to too large absorption in the visible but we could not determine if this is linked to the sample studied by Patterson et al. (1997) or to the method used in determining the refractive index.

Study of the Sensitivity of Optical Properties of Mineral Dust to the Direct Aerosol Radiative Perturbation Using a Global Aerosol Transport Model

The sensitivity of optical properties of mineral dust aerosol to its direct radiative effect was investigated using four dust optical datasets (ADEC-1, ADEC-2, OPAC-MD and Dust-Like) with a global aerosol transport model. The annual and global mean direct aerosol radiative perturbation (DARP) by dust at the top of the atmosphere (TOA) can be positive or negative (-0.52 to +0.11 W m -2) depending on the absorptive property of dust aerosol dataset. The annual and global mean DARP at the surface is negative for all the dust optical datasets (-1.25 to -0.27 W m -2). If dust is strongly absorptive, DARP at the TOA over oceans at high latitude (> 40°) is positive due to the vertical configuration of dust and clouds. The longwave heating at the surface is strong and can exceed the shortwave cooling over desert regions if the absorption of dust is weak. Over a surface with high dust loading, the annual mean shortwave (longwave) DARP can reach -28 W m -2 (+16 W m -2). The global mean DARP values both at the TOA and surface are almost proportional to the imaginary part of the refractive index of dust. Seasonal variations of global mean DARP at the TOA significantly depend on the optical properties of dust.

A New Chemodynamical Galaxy Formation Model with Radiative Transfer

We integrate three fundamental physical processes, i.e. star formation, structure formation, and radiative transfer inside galaxies, into our chemodynamical model. Our model simulates dynamical evolution in N -body SPH method, and simulates star formation as well as radiative gas cooling, feedback processes from stellar wind and supernovae. Furthermore, we implement radiative transfer in the galaxy so that we can simulate gas photoionization heating by ultraviolet (UV) photons emitted by OB stars inside the galaxy, and so that we can obtain the whole spectral energy distribution after dust absorption without assumption on dust, gas and stellar geometry, even if the simulated galaxy has very irregular morphology. We simulate seven galaxies. Our model galaxies with photoionization by UV photons show two differences from model galaxies without them. UV photons invoke gas outflow from the system, and result in smaller star formation rate at z z = 4.5 and 3.0 > z > 2.8, and satisfies the criteria of BzK at 3.0 > z > 2.0. Then the model galaxy enters into the short passively evolving ERO phase at z = 1.6 and finally evolves to a passively evolving elliptical galaxy. In all our simulations, evolutionary path from LBGs at z = 4, through the BzK phase at 3 > z > 1.8, to passively evolving elliptical galaxies at z < 0.8, are universal.

Detection of Martian dust clouds by SPICAM UV nadir measurements during the October 2005 regional dust storm

The SPICAM UV spectrometer onboard Mars Express observed two regional dust storms: on October 24, 2005, near Argyre Planitia and on July 9, 2005, in Hellas Planitia. The measurements were performed in nadir mode. The spectral domain 210–310 nm is considered. A comparison with a prior orbit which passed above almost the same path 6 days before the storm near Argyre Planitia has shown a significant decrease of the radiance factor. The difference grows at shorter wavelengths and shows significant dust absorption in the UV. The data have been used to retrieve the dust optical thickness τ, single scattering albedo w and asymmetry factor g. The fitting of the spectra by a radiative transfer code has revealed a set of solutions which could be constrained by Mie modeling of the parameters τ, w, and g for a gamma particle size distribution. The following estimates of the dust optical parameters are obtained: w = 0.64 ± 0.04 at λ = 300 nm and decreases to 0.6 ± 0.045 at 213 nm, g = 0.86 ± 0.03 at 300 nm and slightly grows to 0.88 ± 0.04 at 213 nm, τ = 2.5 ± 0.5 for the first dust event and τ = 2.0 ± 0.5 for the second one. The obtained values of single scattering albedo are consistent with the Hubble Space Telescope and Mariner 9 results.