far-IR Dust Emission Research Articles

The intrinsic reddening of the Magellanic Clouds as traced by background galaxies – II. The Small Magellanic Cloud

ABSTRACT We present a map of the total intrinsic reddening across ≃34 deg2 of the Small Magellanic Cloud (SMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created using a subsample of 29 274 galaxies with low levels of intrinsic reddening based on the lephare χ2 minimization SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts [ΔE(B − V) ≃ 0.3 mag]. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC sampled, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased samples in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorizations of extragalactic sources behind the SMC and as such we provide the lephare outputs for our full sample of ∼500 000 sources.

The dust in M31

Abstract We have analysed Herschel observations of M31, using the ppmap procedure. The resolution of ppmap images is sufficient ($\sim 31\, {\rm pc}$ on M31) that we can analyse far-IR dust emission on the scale of giant molecular clouds. By comparing ppmap estimates of the far-IR emission optical depth at $300\, \mu {\rm m}\, (\tau _{{300}})$, and the near-IR extinction optical depth at $1.1\, \mu {\rm m}\, (\tau _{{1.1}})$ obtained from the reddening of Red Giant Branch (RGB) stars, we show that the ratio ${\cal R}^{\mathrm{ obs.}}_\tau \equiv \tau _{{1.1}}/\tau _{{300}}$ falls in the range $500\lesssim {\cal R}^{\mathrm{ obs.}}_\tau \lesssim 1500$. Such low values are incompatible with many commonly used theoretical dust models, which predict values of ${\cal R}^{\mathrm{ model}}_\kappa \equiv \kappa _{{1.1}}/\kappa _{{300}}$ (where κ is the dust opacity coefficient) in the range $2500\lesssim {\cal R}^{\mathrm{ model}}_\kappa \lesssim 4000$. That is, unless a large fraction, $\gtrsim 60{{\ \rm per\ cent}}$, of the dust emitting at $300\, \mu {\rm m}$ is in such compact sources that they are unlikely to intercept the lines of sight to a distributed population like RGB stars. This is not a new result: variants obtained using different observations and/or different wavelengths have already been reported by other studies. We present two analytic arguments for why it is unlikely that $\gtrsim 60{{\ \rm per\ cent}}$ of the emitting dust is in sufficiently compact sources. Therefore it may be necessary to explore the possibility that the discrepancy between observed values of ${\cal R}^{\mathrm{ obs.}}_\tau$ and theoretical values of ${\cal R}^{\mathrm{ model}}_\kappa$ is due to limitations in existing dust models. ppmap also allows us to derive optical-depth weighted mean values for the emissivity index, β ≡ −dln (κλ)/dln (λ), and the dust temperature, T, denoted ${\bar{\beta }}$ and ${\bar{T}}$. We show that, in M31, ${\cal R}^{\mathrm{ obs.}}_\tau$ is anticorrelated with ${\bar{\beta }}$ according to ${\cal R}^{\mathrm{ obs.}}_\tau \simeq 2042(\pm 24)-557(\pm 10){\bar{\beta }}$. If confirmed, this provides a challenging constraint on the nature of interstellar dust in M31.

Stacking analysis of HERITAGE data to statistically study far-IR dust emission from evolved stars

AbstractWe aim to analyse the co-added Herschel images of various categories of evolved stars in the LMC and SMC from the Herschel HERITAGE survey in order to identify, in a statistical sense, a cool historic dust mass component emitted by these sources. The fluxes derived from the co-added stacks can then be compared with those predicted by the GRAMS model grid in order to refine the DPRs estimated for the SMC and LMC.

FOREGROUND BIAS FROM PARAMETRIC MODELS OF FAR-IR DUST EMISSION

ABSTRACT We use simple toy models of far-IR dust emission to estimate the accuracy to which the polarization of the cosmic microwave background can be recovered using multi-frequency fits, if the parametric form chosen for the fitted dust model differs from the actual dust emission. Commonly used approximations to the far-IR dust spectrum yield CMB residuals comparable to or larger than the sensitivities expected for the next generation of CMB missions, despite fitting the combined CMB + foreground emission to precision 0.1% or better. The Rayleigh–Jeans approximation to the dust spectrum biases the fitted dust spectral index by and the inflationary B-mode amplitude by . Fitting the dust to a modified blackbody at a single temperature biases the best-fit CMB by if the true dust spectrum contains multiple temperature components. A 13-parameter model fitting two temperature components reduces this bias by an order of magnitude if the true dust spectrum is in fact a simple superposition of emission at different temperatures, but fails at the level for dust whose spectral index varies with frequency. Restricting the observing frequencies to a narrow region near the foreground minimum reduces these biases for some dust spectra but can increase the bias for others. Data at THz frequencies surrounding the peak of the dust emission can mitigate these biases while providing a direct determination of the dust temperature profile.

AHerschel-SPIRE survey of the Mon R2 giant molecular cloud: analysis of the gas column density probability density function

We present a far-IR survey of the entire Mon R2 GMC with $Herschel-SPIRE$ cross-calibrated with $Planck-HFI$ data. We fit the SEDs of each pixel with a greybody function and an optimal beta value of 1.8. We find that mid-range column densities obtained from far-IR dust emission and near-IR extinction are consistent. For the entire GMC, we find that the column density histogram, or N-PDF, is lognormal below $\sim$10$^{21}$ cm$^{-2}$. Above this value, the distribution takes a power law form with an index of -2.16. We analyze the gas geometry, N-PDF shape, and YSO content of a selection of subregions in the cloud. We find no regions with pure lognormal N-PDFs. The regions with a combination of lognormal and one power law N-PDF have a YSO cluster and a corresponding centrally concentrated gas clump. The regions with a combination of lognormal and two power law N-PDF have significant numbers of typically younger YSOs but no prominent YSO cluster. These regions are composed of an aggregate of closely spaced gas filaments with no concentrated dense gas clump. We find that for our fixed scale regions, the YSO count roughly correlates with the N-PDF power law index. The correlation appears steeper for single power law regions relative to two power law regions with a high column density cut-off, as a greater dense gas mass fraction is achieved in the former. A stronger correlation is found between embedded YSO count and the dense gas mass among our regions.

HERSCHELOBSERVATIONS OF A NEWLY DISCOVERED UX Ori STAR IN THE LARGE MAGELLANIC CLOUD

The LMC star, SSTISAGE1C J050756.44-703453.9, was first noticed during a survey of EROS-2 lightcurves for stars with large irregular brightness variations typical of the R Coronae Borealis (RCB) class. However, the visible spectrum showing emission lines including the Balmer and Paschen series as well as many Fe II lines is emphatically not that of an RCB star. This star has all of the characteristics of a typical UX Ori star. It has a spectral type of approximately A2 and has excited an H II region in its vicinity. However, if it is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows irregular drops in brightness of up to 2 mag, and displays the reddening and "blueing" typical of this class of stars. Its spectrum, showing a combination of emission and absorption lines, is typical of a UX Ori star that is in a decline caused by obscuration from the circumstellar dust. SSTISAGE1C J050756.44-703453.9 has a strong IR excess and significant emission is present out to 500 micron. Monte Carlo radiative transfer modeling of the SED requires that SSTISAGE1C J050756.44-703453.9 has both a dusty disk as well as a large extended diffuse envelope to fit both the mid- and far-IR dust emission. This star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only the second such star to be discovered in the LMC.

Herschelobservations of the W43 “mini-starburst”

<i>Aims. <i/>To explore the infrared and radio properties of one of the closest Galactic starburst regions.<i>Methods. <i/>Images obtained with the <i>Herschel<i/> Space Observatory at wavelengths of 70, 160, 250, 350, and 500 <i>μ<i/>m using the PACS and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8 <i>μ<i/>m images from the <i>Spitzer<i/> Space Observatory. The morphology of the far-infrared emission is combined with radial velocity measurements of millimeter and centimeter wavelength transitions to identify features likely to be associated with the W43 complex.<i>Results. <i/>The W43 star-forming complex is resolved into a dense cluster of protostars, infrared dark clouds, and ridges of warm dust heated by massive stars. The 4 brightest compact sources with <i>L<i/> > 1.5 × 10<sup>4<sup/> embedded within the <i>Z<i/>-shaped ridge of bright dust emission in W43 remain single at 4” (0.1 pc) resolution These objects, likely to be massive protostars or compact clusters in early stages of evolution are embedded in clumps with masses of 10<sup>3<sup/> to 10<sup>4<sup/> , but contribute only 2% to the 3.6 × 10<sup>6<sup/> far-IR luminosity of W43 measured in a 16 by 16 pc box. The total mass of gas derived from the far-IR dust emission inside this region is ~10<sup>6<sup/> . Cometary dust clouds, compact 6 cm radio sources, and warm dust mark the locations of older populations of massive stars. Energy release has created a cavity blowing-out below the Galactic plane. Compression of molecular gas in the plane by the older H ii region near G30.684–0.260 and the bipolar structure of the resulting younger W43 H ii region may have triggered the current mini-star burst.

Recent star formation at low metallicities. The star-forming region NGC 346/N66 in the Small Magellanic Cloud from near-infrared VLT/ISAAC observations

We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC in order to locate the centres of active high- and intermediate-mass star formation through the identification of near-IR bright objects as candidate stellar sources under formation.We use archived imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 and we construct the near-IR colour-magnitude (CMD) and colour-colour diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We select, thus, the best candidates for being young stellar sources. Based on their near-IR colours we select 263 candidate young stellar sources. This sample comprises a variety of objects such as intermediate-mass PMS and Herbig Ae/Be stars and possibly massive YSOs, providing original near-IR colours for them. The spatial distribution of the selected candidate sources shows that they are located along the dusty filamentary structures of N66 seen in mid- and far-IR dust emission and agrees very well with that of previously detected candidate YSOs and PMS stars. Our study provides an original accurate set of near-IR colours for candidate young stellar sources. While this adds significant information on the star formation process in NGC 346/N66, it is still necessary to reveal the exact nature of these objects, a process that requires the combination of multi-wavelength data, so that complete Spectral Energy Distributions can be constructed for individual sources. This would be a quite important follow-up study to that presented here.

THE WARM MOLECULAR GAS AROUND THE CLOVERLEAF QUASAR

We present the first broadband lambda = 1 mm spectrum toward the z=2.56 Cloverleaf Quasar, obtained with Z-Spec, a 1-mm grating spectrograph on the 10.4-meter Caltech Submillimeter Observatory. The 190-305 GHz observation band corresponds to rest-frame 272 to 444 microns, and we measure the dust continuum as well as all four transitions of carbon monoxide (CO) lying in this range. The power-law dust emission, F_nu = 14 mJy (nu/240GHz)^3.9 is consistent with the published continuum measurements. The CO J=6->5, J=8->7, and J=9->8 measurements are the first, and now provide the highest-J CO information in this source. Our measured CO intensities are very close to the previously-published interferometric measurements of J=7->6, and we use all available transitions and our 13CO upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2-50x10^9 Msun) of highly-excited gas with thermal pressure nT > 10^6 Kcm^-3. The ratio of the total CO cooling to the far-IR dust emission exceeds that in the local dusty galaxies, and we investigate the potential heating sources for this bulk of warm molecular gas. We conclude that both UV photons and X-rays likely contribute, and discuss implications for a top-heavy stellar initial mass function arising in the X-ray-irradiated starburst. Finally we present tentative identifications of other species in the spectrum, including a possible detection of the H20 2_0,2->1_1,1 transition at lambda_rest = 303 microns.

The Extended Dust Emission around GK Per

GK Per, a classical nova system that erupted in 1901, is one of the more unusual examples of its type. It has the longest known orbital period for a classical nova (1.997d; Crampton, Cowley &amp; Fisher 1986); and it contains a white dwarf primary with an evolved K2 sub-giant secondary. Most remarkably, the IRAS Sky Survey (1991) reveals that GK Per exhibits far-IR dust emission extending ~ 17′ to the NW and SE of the nova (Bode et al. 1987; Seaquist et al. 1989). We have re-analysed the IRAS data using maximum entropy reconstruction (Bontekoe et al. 1991; Bontekoe, Koper &amp; Kester 1994) to resolve structures at a spatial resolution approaching the diffraction limit of IRAS, which is 1′ at 60 μm and 1.7′ at 100/μm.

The dust in the hydrogen-poor ejecta of Abell 30

view Abstract Citations (50) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Dust in the Hydrogen-poor Ejecta of Abell 30 Borkowski, Kazimierz J. ; Harrington, J. Patrick ; Blair, William P. ; Bregman, Jesse D. Abstract We present new optical and near-infrared images of the hydrogen-poor planetary nebula Abell 30 and produce detailed models that account for the major observed morphological and IR properties. By imaging the nebula in the K band, we confirm the presence of hot dust in an expanding equatorial ring of H-poor gas. No emission was detected from the H-poor polar knots, suggesting a dust deficiency there relative to the equatorial ring. The near-IR emission is attributed to small carbonaceous dust grains which are stochastically heated by stellar ultraviolet photons. Using an adaptive version of a matrix method devised by Guhathakurta & Draine (1989) to model stochastic heating, we find that the near-IR spectrum observed by Dinerstein & Lester (1984) requires the presence of dust grains down to approximately 0.0007 microns in radius. This minimum grain radius is in excellent agreement with our calculations of the grain destruction by energetic stellar UV photons: we find that carbon clusters with less than approximately 140 atoms (0.0007 microns in radius) are destroyed by stellar UV photons in approximately 1000 yr, the kinematic age of H-poor ejecta. Modeling of the far-IR dust emission implies that the bulk of the dust mass in A30 must reside at distances several times greater than the distance of the equatorial ring from the central star. This spatial dust distribution is attributed to the interaction of the stellar wind with the inhomogeneous H-poor ejecta. Most of the H-poor gas and dust has been apparently carried outward by the stellar wind, leaving behing dense, H-poor knots with prominent wind-blown tails in the equatorial ring and in the polar knots. This picture is supported by the presence of a stellar wind-blown bubble within the H-rich envelope in our optical images. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174849 Bibcode: 1994ApJ...435..722B Keywords: Hydrogen; Interplanetary Dust; Interplanetary Magnetic Fields; Planetary Nebulae; Stellar Atmospheres; Stellar Spectra; Astronomical Observatories; Emission Spectra; Infrared Imagery; Morphology; Numerical Analysis; Astronomy; ISM: ABUNDANCES; ISM: DUST; EXTINCTION; ISM: PLANETARY NEBULAE: INDIVIDUAL NAME: ABELL 30; STARS: MASS LOSS full text sources ADS | data products SIMBAD (2)