Polarization simulations of stellar wind bow shock nebulae – II. The case of dust scattering

ABSTRACT We study the polarization produced by scattering from dust in a bow shock-shaped region of enhanced density surrounding a stellar source, using the Monte Carlo radiative transfer code SLIP. Bow shocks are structures formed by the interaction of the winds of fast-moving stars with the interstellar medium. Our previous study focused on the polarization produced in these structures by electron scattering; we showed that polarization is highly dependent on inclination angle and that multiple scattering changes the shape and degree of polarization. In contrast to electron scattering, dust scattering is wavelength-dependent, which changes the polarization behaviour. Here, we explore different dust particle sizes and compositions and generate polarized spectral energy distributions for each case. We find that the polarization spectral energy distribution behaviour depends on the dust composition and grain size. Including dust emission leads to polarization changes with temperature at higher optical depth in ways that are sensitive to the orientation of the bow shock. In various scenarios and under certain assumptions, our simulations can constrain the optical depth and dust properties of resolved and unresolved bow shock-shaped scattering regions. Constraints on optical depth can provide estimates of local interstellar medium density for observed bow shocks. We also study the impact of dust grains filling the region between the star and bow shock. We see that as the density of dust between the star and bow shock increases, the resulting polarization is suppressed for all the optical depth regimes.

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A thin shell of ionized gas as the explanation for infrared excess among classical Cepheids

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935848 ◽

2020 ◽

Vol 633 ◽

pp. A47 ◽

Cited By ~ 4

Author(s):

V. Hocdé ◽

N. Nardetto ◽

E. Lagadec ◽

G. Niccolini ◽

A. Domiciano de Souza ◽

...

Keyword(s):

Thin Shell ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Spectral Energy ◽

Ionized Gas ◽

Infrared Excess ◽

Interstellar Clouds ◽

Classical Cepheids ◽

Extragalactic Distance Scale ◽

The Impact

Context. The infrared (IR) excess of classical Cepheids is seldom studied and poorly understood despite observational evidence and the potential for its contribution to induce systematics on the period-luminosity (PL) relation used in the calibration of the extragalactic distance scale. Aims. This study aims to understand the physical origin of the IR excess found in the spectral energy distribution (SED) of 5 Cepheids: RS Pup (P = 41.46d), ζ Gem (P = 10.15d), η Aql (P = 7.18d), V Cen (P = 5.49d) and SU Cyg (P = 3.85d). Methods. A time series of atmospheric models along the pulsation cycle were fitted to a compilation of data, including optical and near-IR photometry, Spitzer spectra (secured at a specific phase), interferometric angular diameters, effective temperature estimates, and radial velocity measurements. Herschel images in two bands were also analyzed qualitatively. In this fitting process, based on the SPIPS algorithm, a residual was found in the SED, whatever the pulsation phase, and for wavelengths larger than about 1.2 μm, which corresponds to the so-determined infrared excess of Cepheids. This IR excess was then corrected from interstellar medium absorption in order to infer the presence (or absence) of dust shells and was, ultimately, used in order to fit a model for a shell of ionized gas. Results. For all Cepheids, we find a continuum IR excess increasing up to approximately −0.1 magnitudes at 30 μm, which cannot be explained by a hot or cold dust model of CircumStellar Environment (CSE). However, a weak but significant dust emission at 9.7 μm is found for ζ Gem, η Aql and RS Pup, while clear interstellar clouds are seen in the Herschel images for V Cen and RS Pup. We show, for the first time, that the IR excess of Cepheids can be explained by free–free emission from a thin shell of ionized gas, with a thickness of ≃15% of the star radius, a mass of 10−9−10−7M⊙ and a temperature ranging between 3500 and 4500 K. Conclusions. The presence of a thin shell of ionized gas around Cepheids must be tested with interferometers operating in the visible or mid-IR, or using radio telescopes. The impact of such CSEs of ionized gas on the PL relation of Cepheids also calls for further investigation.

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Physical Processes in the Large Scale ISM from Dust Observations

Symposium - International Astronomical Union ◽

10.1017/s0074180900128475 ◽

1998 ◽

Vol 179 ◽

pp. 153-164

Author(s):

F. Boulanger

Keyword(s):

Interstellar Medium ◽

Large Scale ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Dust Particles ◽

Spectral Energy ◽

Interstellar Clouds ◽

Aromatic Molecules ◽

Formation Efficiency ◽

Small Dust

Over the last two decades observations of dust emission in the infrared have played an important role in the development of research on the interstellar medium. The study of the spectral energy distribution has led to the discovery of small dust particles including the large aromatic molecules (PAHs). Infrared sky images have been used to study the structure of interstellar matter, the evolution of dust within the interstellar medium and the star formation efficiency of interstellar clouds.

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Interstellar medium magnetic field in bow shock modelling

Aircraft Engineering and Aerospace Technology ◽

10.1108/aeat-01-2018-0004 ◽

2018 ◽

Vol 92 (3) ◽

pp. 386-389

Author(s):

Jan Kotlarz ◽

Romana Ratkiewicz ◽

Wojciech Konior

Keyword(s):

Magnetic Field ◽

Interstellar Medium ◽

Design Methodology ◽

Numerical Models ◽

Bow Shock ◽

Content Type ◽

Astrophysical Objects ◽

Bow Shocks ◽

The Impact ◽

Practical Implications

Purpose This paper aims to demonstrate the impact of interstellar (IS) magnetic field on stellar shocks existence, shape and size in the stellar wind (SW) vs interstellar medium (ISM) numerical models. Design/methodology/approach Comparison of hydrodynamics (HD) and magnetohydrodynamic (MHD) models results with or without ISM magnetic field, its intensity and ISM parameters. Findings ISM magnetic field facilitates formation and stabilises bow shocks around all astrophysical objects. ISM magnetic field may also be one of the reasons for a bow shock existence around the Sun. Practical implications ISM magnetic field should be implemented in MHD and future kinetic numerical models of the SW interaction with ISM plasma. Originality/value This paper presents the results of HD and MHD models of bow shocks and the importance of ISM magnetic field implementation, according to astronomical bow shock observations. The study also presents a review of the most important papers showing the numerical results of bow shock formation.

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Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731117 ◽

2017 ◽

Vol 604 ◽

pp. A52 ◽

Cited By ~ 20

Author(s):

A. Bracco ◽

P. Palmeirim ◽

Ph. André ◽

R. Adam ◽

P. Ade ◽

...

Keyword(s):

Star Formation ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Class Ii ◽

Spectral Energy ◽

Relevant Parameter ◽

Mass Star ◽

Radial Temperature ◽

Dust Temperature ◽

Prestellar Cores

The characterization of dust properties in the interstellar medium is key for understanding the physics and chemistry of star formation. Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds. However, most of these estimates rely on dust models that need further observational constraints to capture the relevant parameter variations depending on the local environment: from clouds to prestellar and protostellar cores. We present results of a new study of dust emissivity changes based on millimeter continuum data obtained with the NIKA camera at the IRAM-30 m telescope. Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index, β, in the Rayleigh-Jeans tail of the dust spectral energy distribution far from its peak emission, where the contribution of other parameters (i.e. dust temperature) is more important. Focusing on the Taurus molecular cloud, one of the most famous low-mass star-forming regions in the Gould Belt, we analyze the emission properties of several distinct objects in the B213 filament. This subparsec-sized region is of particular interest since it is characterized by a collection ofevolutionary stages of early star formation: three prestellar cores, two Class 0/I protostellar cores and one Class II object. We are therefore able to compare dust properties among a sequence of sources that likely derive from the same parent filament. By means of the ratio of the two NIKA channel maps, we show that in the Rayleigh-Jeans approximation, βRJ varies among the objects: it decreases from prestellar cores (βRJ ~ 2) to protostellar cores (βRJ ~ 1) and the Class II object (βRJ ~ 0). For one prestellar and two protostellar cores, we produce a robust study using available Herschel data to constrain the dust temperature of the sources. By using the Abel transform inversion technique we derive accurate radial temperature profiles that allow us to obtain radial β profiles. We find systematic spatial variations of β in the protostellar cores that are not observed in the prestellar core. While in the former case β decreases toward the center (with β varying between 1 and 2), in the latter it remains constant (β = 2.4 ± 0.3). Moreover, the dust emissivity index appears anticorrelated with the dust temperature. We discuss the implication of these results in terms of dust grain evolution between pre- and protostellar cores.

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Dust properties and star formation of approximately a thousand local galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834553 ◽

2019 ◽

Vol 631 ◽

pp. A38 ◽

Cited By ~ 1

Author(s):

S. Lianou ◽

P. Barmby ◽

A. A. Mosenkov ◽

M. Lehnert ◽

O. Karczewski

Keyword(s):

Star Formation ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Distribution Functions ◽

Spectral Energy ◽

Emission Properties ◽

Galaxy Type ◽

Dust Mass ◽

The Galaxy ◽

Stellar Masses

Aims. We derived the dust properties for 753 local galaxies and examine how these relate to some of their physical properties. We present the derived dust emission properties, including model spectral energy distribution (SEDs), star formation rates (SFRs) and stellar masses, as well as their relations. Methods. We modelled the global dust-SEDs for 753 galaxies, treated statistically as an ensemble within a hierarchical Bayesian dust-SED modelling approach, so as to derive their infrared (IR) emission properties. To create the observed dust-SEDs, we used a multi-wavelength set of observations, ranging from near-IR to far-IR-to-submillimeter wavelengths. The model-derived properties are the dust masses (Mdust), the average interstellar radiation field intensities (Uav), the mass fraction of very small dust grains (“QPAH” fraction), as well as their standard deviations. In addition, we used mid-IR observations to derive SFR and stellar masses, quantities independent of the dust-SED modelling. Results. We derive distribution functions of the properties for the galaxy ensemble and as a function of galaxy type. The mean value of Mdust for the early-type galaxies (ETGs) is lower than that for the late-type and irregular galaxies (LTGs and Irs, respectively), despite ETGs and LTGs having stellar masses spanning across the whole range observed. The Uav and “QPAH” fraction show no difference among different galaxy types. When fixing Uav to the Galactic value, the derived “QPAH” fraction varies across the Galactic value (0.071). The specific SFR increases with galaxy type, while this is not the case for the dust-specific SFR (SFR/Mdust), showing an almost constant star formation efficiency per galaxy type. The galaxy sample is characterised by a tight relationship between the dust mass and the stellar mass for the LTGs and Irs, while ETGs scatter around this relation and tend towards smaller dust masses. While the relation indicates that Mdust may fundamentally be linked to M⋆, metallicity and Uav are the second parameter driving the scatter, which we investigate in a forthcoming work. We used the extended Kennicutt–Schmidt (KS) law to estimate the gas mass and the gas-to-dust mass ratio (GDR). The gas mass derived from the extended KS law is on average ∼20% higher than that derived from the KS law, and a large standard deviation indicates the importance of the average star formation present to regulate star formation and gas supply. The average GDR for the LTGs and Irs is 370, and including the ETGs gives an average of 550.

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Temporal correlation between the optical and γ-ray flux variations in the blazar 3C 454.3

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz941 ◽

2019 ◽

Vol 486 (2) ◽

pp. 1781-1795 ◽

Cited By ~ 8

Author(s):

Bhoomika Rajput ◽

C S Stalin ◽

S Sahayanathan ◽

Suvendu Rakshit ◽

Amit Kumar Mandal

Keyword(s):

Spectral Energy Distribution ◽

Broad Band ◽

Temporal Correlation ◽

Lorentz Factor ◽

Degree Of Polarization ◽

Spectral Energy ◽

Long Duration ◽

Γ Ray ◽

Optical Flux ◽

Optical Flare

ABSTRACT Blazars show optical and γ-ray flux variations that are generally correlated, although there are exceptions. Here we present anomalous behaviour seen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data at optical, ultraviolet, X-ray, and γ-ray energies, spanning about 9 yr from 2008 August to 2017 February. We have identified four time intervals (epochs), A, B, D, and E, when the source showed large-amplitude optical flares. In epochs A and B the optical and γ-ray flares are correlated, while in D and E corresponding flares in γ-rays are weak or absent. In epoch B the degree of optical polarization strongly correlates with changes in optical flux during a short-duration optical flare superimposed on one of long duration. In epoch E the optical flux and degree of polarization are anticorrelated during both the rising and declining phases of the optical flare. We carried out broad-band spectral energy distribution (SED) modelling of the source for the flaring epochs A,B, D, and E, and a quiescent epoch, C. Our SED modelling indicates that optical flares with absent or weak corresponding γ-ray flares in epochs D and E could arise from changes in a combination of parameters, such as the bulk Lorentz factor, magnetic field, and electron energy density, or be due to changes in the location of the γ-ray-emitting regions.

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SUPER

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833520 ◽

2018 ◽

Vol 620 ◽

pp. A82 ◽

Cited By ~ 11

Author(s):

C. Circosta ◽

V. Mainieri ◽

P. Padovani ◽

G. Lanzuisi ◽

M. Salvato ◽

...

Keyword(s):

Star Formation ◽

Adaptive Optics ◽

High Redshift ◽

Spectral Energy Distribution ◽

Host Galaxy ◽

Spectral Energy ◽

Distribution Fitting ◽

X Ray ◽

Narrow Component ◽

The Impact

Theoretical models of galaxy formation suggest that the presence of an active galactic nucleus (AGN) is required to regulate the growth of its host galaxy through feedback mechanisms, produced by, for example, AGN-driven outflows. Although many observational studies have revealed that such outflows are common both at low and high redshift, a comprehensive picture is still missing. In particular, the peak epoch of galaxy assembly (1 < z < 3) has been poorly explored so far, and current observations in this redshift range are mostly limited to targets with high chances to be in an outflowing phase. This paper introduces SUPER (a SINFONI Survey for Unveiling the Physics and Effect of Radiative feedback), an ongoing ESO’s VLT/SINFONI Large Programme. SUPER will perform the first systematic investigation of ionized outflows in a sizeable and blindly-selected sample of 39 X-ray AGN at z ∼ 2, which reaches high spatial resolutions (∼2 kpc) thanks to the adaptive optics-assisted IFS observations. The outflow morphology and star formation in the host galaxy will be mapped through the broad component of [O III]λ5007 and the narrow component of Hα emission lines. The main aim of our survey is to infer the impact of outflows on the on-going star formation and to link the outflow properties to a number of AGN and host galaxy properties. We describe here the survey characteristics and goals, as well as the selection of the target sample. Moreover, we present a full characterization of its multi-wavelength properties: we measure, via spectral energy distribution fitting of UV-to-FIR photometry, stellar masses (4 × 109 − 2 × 1011 M⊙), star formation rates (25 − 680 M⊙ yr−1) and AGN bolometric luminosities (2 × 1044 − 8 × 1047 erg s−1), along with obscuring column densities (up to 2 × 1024 cm−2) and luminosities in the hard 2 − 10 keV band (2 × 1043 − 6 × 1045 erg s−1) derived through X-ray spectral analysis. Finally, we classify our AGN as jetted or non-jetted according to their radio and FIR emission.

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The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834002 ◽

2019 ◽

Vol 621 ◽

pp. A139 ◽

Cited By ~ 12

Author(s):

K. Tisanić ◽

V. Smolčić ◽

J. Delhaize ◽

M. Novak ◽

H. Intema ◽

...

Keyword(s):

Survival Analysis ◽

Energy Distribution ◽

Power Law ◽

Rest Frame ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Radio Luminosity ◽

Star Forming ◽

The Impact ◽

Frame Frequency

We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z ∼ 4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared–radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies’ (SFGs) SED. To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published Very Large Array observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (z ∈ [0.3, 4], SFR ≥ 100 M⊙ yr−1) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from α1 = 0.42 ± 0.06 below a rest-frame frequency of 4.3 GHz to α2 = 0.94 ± 0.06 above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs ( SFR > 10 M⊙ yr−1) that show the SED of HSFGs to differ from the SED found for normal SFGs ( SFR < 10 M⊙ yr−1). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free–free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q − z trend in SFGs.

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Properties of LBGs with [OIII] detection at z ∼ 3.5

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935975 ◽

2019 ◽

Vol 631 ◽

pp. A123 ◽

Cited By ~ 1

Author(s):

Fang-Ting Yuan ◽

Denis Burgarella ◽

David Corre ◽

Veronique Buat ◽

Médéric Boquien ◽

...

Keyword(s):

Physical Properties ◽

Emission Line ◽

Near Infrared ◽

Spectral Energy Distribution ◽

Formation Rate ◽

Line Emission ◽

Stellar Mass ◽

Spectral Energy ◽

Emission Data ◽

The Impact

Context. Nebular emission lines are critical to measure physical properties in the ionized gas (e.g., metallicity, the star formation rate, or dust attenuation). They also account for a significant fraction of broadband fluxes, in particular at the highest redshifts, and therefore can strongly affect the determination of other physical properties, such as the stellar mass, which are crucial in shaping our understanding of galaxy formation and evolution. Aims. We investigate a sample of 51 Lyman break galaxies at 3.0 < zspec < 3.8 with detected [OIII] line emissions and estimated the physical properties of these galaxies to examine the impact of including nebular emission data in the Spectral energy distribution (SED) fitting. Methods. We used the Code Investigating GALaxy Emission (CIGALE) to fit the rest-frame ultraviolet-to-near-infrared SEDs of these galaxies and their emission line data simultaneously. We ran CIGALE with and without the nebular model or the emission line data, and compare the results to show the importance of including the nebular emission line data in the SED fitting. Results. We find that without the nebular model, the SED fitting overestimates the stellar mass due to the strong [OIII] lines that are redshifted to the Ks-band, which is consistent with previous results. The emission line data are necessary to constrain the nebular model in the SED fitting. We examine the Ks-band excess, which is mostly used to estimate the emissions of the [OIII]+Hβ lines when there is no spectral data, and we find that the estimation and observation are statistically consistent. However, the difference can reach up to more than 1 dex in some catastrophic cases, which shows the importance of obtaining spectroscopic measurements for these lines. We also estimate the equivalent width of the Hβ absorption and find it negligible compared to the Hβ emission. Conclusions. Line emission is important to constrain the nebular models and to obtain reliable estimates of the physical properties of galaxies. These data should be taken into account in the SED fitting.

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ISM Diagnostics: Dust

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313001324 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 259-266 ◽

Cited By ~ 2

Author(s):

Takashi Onaka

Keyword(s):

Vibration Mode ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Diagnostic Methods ◽

Spectral Energy ◽

Significant Information ◽

Physical Conditions ◽

Band Emission ◽

Small Grains ◽

The Universe

AbstractInfrared (IR) observations provide significant information on the lifecycle of dust grains in the interstellar medium (ISM), which is crucial for the understanding of the evolution of matter in the universe. The IR spectral energy distribution (SED) of the dust emission tells us the relative abundance of sub-micron grains, very small grains, and carriers of the unidentified infrared (UIR) emission bands, since they emit the far-IR, the mid-IR, and the UIR bands from the near- to mid-IR, respectively. On the other hand, the UIR emission bands themselves offer a useful means to probe the physical conditions from which the band emission arises because each band is assigned to a specific C-H or C-C vibration mode and because its relative intensity should reflect the properties of the band carriers and the physical conditions of the environment. Here the two diagnostic methods using IR observations are briefly described together with examples of the observational results. Implications for the dust lifecycle are also discussed.

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