In this analysis, we illustrate how the relatively new emission mechanism, known as spinning dust, can be used to characterize dust grains in the interstellar medium. We demonstrate this by using ...spinning dust emission observations to constrain the abundance of very small dust grains (a ≲ 10 nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1 cm for four different very small dust grain abundances, which we constrain by comparing to 1 cm CARMA observations. For all of our cores, we find a depletion of very small grains, which we suggest is due to the process of grain growth. This work represents the first time that spinning dust emission has been used to constrain the physical properties of interstellar dust grains.
We have analyzed a uniform sample of 16 evolved H II regions located in a 2degrees x 2degrees Galactic field centered at (l,b) = (30degrees, 0degrees) and observed as part of the Herschel Hi-GAL ...survey. The evolutionary stage of these H II regions was established using ancillary radio-continuum data. By combining Hi-GAL PACS (70 mum, 160 mum) and SPIRE (250 mum, 350 mum, and 500 mum) measurements with MIPSGAL 24 mum data, we built spectral energy distributions of the sources and showed that a two-component gray-body model is a good representation of the data. In particular, wavelengths > 70 mum appear to trace a cold dust component, for which we estimated an equilibrium temperature of the big grains (BGs) in the range 20-30 K, while for lambda < 70 mum, the data indicate the presence of a warm dust component at temperatures of the order of 50-90 K. This analysis also revealed that dust is present in the interior of H II regions, although likely not in a large amount. In addition, the data seem to corroborate the hypothesis that the main mechanism responsible for the (partial) depletion of dust in H II regions is radiation-pressure-driven drift. In this framework, we speculated that the 24 mum emission that spatially correlates with ionized gas might be associated with either very small grain or BG replenishment, as recently proposed for the case of wind-blown bubbles. Finally, we found that evolved H II regions are characterized by distinctive far-IR and submillimeter colors, which can be used as diagnostics for their identification in unresolved Galactic and extragalactic regions.
Anomalous microwave emission is known to exist in the Perseus cloud. One of the most promising candidates to explain this excess of emission is electric dipole radiation from rapidly rotating very ...small dust grains, commonly referred to as spinning dust. Photometric data obtained with the Spitzer Space Telescope have been reprocessed and used in conjunction with the dust emission model dustem to characterize the properties of the dust within the cloud. This analysis has allowed us to constrain spatial variations in the strength of the interstellar radiation field (χISRF), the mass abundances of the polycyclic aromatic hydrocarbons (PAHs) and the very small grains (VSGs) relative to the big grains (Y
PAH and Y
VSG), the column density of hydrogen (N
H) and the equilibrium dust temperature (T
dust). The parameter maps of Y
PAH, Y
VSG and χISRF are the first of their kind to be produced for the Perseus cloud, and we used these maps to investigate the physical conditions in which anomalous emission is observed. We find that in regions of anomalous emission the strength of the ISRF, and consequently the equilibrium temperature of the dust, is enhanced while there is no significant variation in the abundances of the PAHs and the VSGs or the column density of hydrogen. We interpret these results as an indication that the enhancement in χISRF might be affecting the properties of the small stochastically heated dust grains resulting in an increase in the spinning dust emission observed at 33 GHz. This is the first time that such an investigation has been performed, and we believe that this type of analysis creates a new perspective in the field of anomalous emission studies, and represents a powerful new tool for constraining spinning dust models.
We present the first far infrared (FIR) dust emission polarization map covering the full extent of Milky Way’s central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne ...experiment, covers the Galactic center region − 2° < ℓ < 2°, − 4° < b < 3° at a wavelength of 240 μm and an angular resolution of 2.2′. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky (POS) that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of ≃22° clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonally to the field traced by GHz radio synchrotron emission in the Galactic center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 and 50 km s−1 molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. The low polarization fraction in the Galactic center region measured with Planck at 353 GHz combined with a highly ordered projected field orientation is unusual. This feature actually extends to the whole inner Galactic plane. We propose that it could be caused by the increased number of turbulent cells for the long lines of sight towards the inner Galactic plane or to dust properties specific to the inner regions of the Galaxy. Assuming equipartition between magnetic pressure and ram pressure, we obtain magnetic field strength estimates of the order of 1 mG for several CMZ molecular clouds.
We present the first search for spinning dust emission from a sample of 34 Galactic cold cores, performed using the CARMA interferometer. For each of our cores, we use photometric data from the ...Herschel Space Observatory to constrain
$\bar{N}_{\mathrm{H}}$
,
$\bar{T}_{\mathrm{d}}$
,
$\bar{n}_{\mathrm{H}}$
, and
$\bar{G}_{\mathrm{0}}$
. By computing the mass of the cores and comparing it to the Bonnor–Ebert mass, we determined that 29 of the 34 cores are gravitationally unstable and undergoing collapse. In fact, we found that six cores are associated with at least one young stellar object, suggestive of their protostellar nature. By investigating the physical conditions within each core, we can shed light on the cm emission revealed (or not) by our CARMA observations. Indeed, we find that only three of our cores have any significant detectable cm emission. Using a spinning dust model, we predict the expected level of spinning dust emission in each core and find that for all 34 cores, the predicted level of emission is larger than the observed cm emission constrained by the CARMA observations. Moreover, even in the cores for which we do detect cm emission, we cannot, at this stage, discriminate between free–free emission from young stellar objects and spinning dust emission. We emphasize that although the CARMA observations described in this analysis place important constraints on the presence of spinning dust in cold, dense environments, the source sample targeted by these observations is not statistically representative of the entire population of Galactic cores.
Planck observations of M33 Tibbs, C T; Israel, F P; Laureijs, R J ...
Monthly Notices of the Royal Astronomical Society,
07/2018, Letnik:
477, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
We have performed a comprehensive investigation of the global integrated flux density of M33 from radio to ultraviolet wavelengths, finding that the data between ∼100 GHz and 3 THz are ...accurately described by a single modified blackbody curve with a dust temperature of Tdust = 21.67 ± 0.30 K and an effective dust emissivity index of βeff = 1.35 ± 0.10, with no indication of an excess of emission at millimetre/submillimetre wavelengths. However, subdividing M33 into three radial annuli, we found that the global emission curve is highly degenerate with the constituent curves representing the subregions of M33. We also found gradients in Tdust and βeff across the disc of M33, with both quantities decreasing with increasing radius. Comparing the M33 dust emissivity with that of other Local Group members, we find that M33 resembles the Magellanic Clouds rather than the larger galaxies, i.e. the Milky Way and M31. In the Local Group sample, we find a clear correlation between global dust emissivity and metallicity, with dust emissivity increasing with metallicity. A major aspect of this analysis is the investigation into the impact of fluctuations in the cosmic microwave background (CMB) on the integrated flux density spectrum of M33. We found that failing to account for these CMB fluctuations would result in a significant overestimate of Tdust by ∼5 K and an underestimate of βeff by ∼0.4.
We have observed the H II region RCW175 with the 64 m Parkes telescope at 8.4 GHz and 13.5 GHz in total intensity, and at 21.5 GHz in both total intensity and polarization. High angular resolution ...ranging from 1 to 2.4 arcmin, high sensitivity, and polarization capability enable us to perform a detailed study of the different constituents of the H II region. For the first time, we resolve three distinct regions at microwave frequencies, two of which are part of the same annular diffuse structure. Our observations enable us to confirm the presence of anomalous microwave emission (AME) from RCW175. Fitting the integrated flux density across the entire region with the currently available spinning dust models, using physically motivated assumptions, indicates the presence of at least two spinning dust components: a warm component (T sub(gas) = 5800 K) with a relatively large hydrogen number density n sub(H) = 26.3/cm super(3) and a cold component (T sub(gas) = 100 K) with a hydrogen number density of n sub(H) = 150/cm super(3). The present study is an example highlighting the potential of using high angular-resolution microwave data to break model parameter degeneracies. Thanks to the spectral coverage and angular resolution of the Parkes observations, we have been able to derive one of the first AME/excess maps, at 13.5 GHz, showing clear evidence that the bulk of the anomalous emission arises in particular from one of the source components, with some additional contribution from the diffuse structure. A cross-correlation analysis with thermal dust emission has shown a high degree of correlation with one of the regions within RCW175. In the center of RCW175, we find an average polarized emission at 21.5 GHz of 2.2 + or - 0.2(rand.) + or - 0.3(sys.)% of the total emission, where we have included both systematic and statistical uncertainties at 68% CL. This polarized emission could be due to sub-dominant synchrotron emission from the region and is thus consistent with very faint or non-polarized emission associated with AME.
The Herschel survey of the Galactic plane (Hi-GAL) provides a unique opportunity to study star formation over large areas of the sky and different environments in the Milky Way. We use the ...best-studied Hi-GAL fields to date, two 2degrees 2degrees tiles centered on (l, b) = (30degrees, 0degrees) and (l, b) = (59degrees, 0degrees), to study the star formation activity in these regions of the sky using a large sample of well-selected young stellar objects (YSOs). The source-counting method gives results that are only valid for the particular region under consideration In contrast the construction of the JR indicator leads to results that can be extrapolated to the whole Galaxy. By means of the candidate YSO-counting method, it will then be possible to calibrate an SFR Galactic indicator and to test the validity of the extragalactic estimators.
Lynds dark cloud LDN1622 represents one of the best examples of anomalous dust emission, possibly originating from small spinning dust grains. We present Cosmic Background Imager (CBI) 31-GHz data of ...LDN1621, a diffuse dark cloud to the north of LDN1622 in a region known as Orion East. A broken ring-like structure with diameter ≈20 arcmin of diffuse emission is detected at 31 GHz, at ≈20–30 mJy beam−1 with an angular resolution of ≈5 arcmin. The ring-like structure is highly correlated with far-infrared (FIR) emission at 12–100 μm with correlation coefficients of r≈ 0.7–0.8, significant at ∼10σ. The FIR-correlated emission at 31 GHz therefore appears to be mostly due to radiation associated with dust. Multifrequency data are used to place constraints on other components of emission that could be contributing to the 31-GHz flux. An analysis of the GB6 survey maps at 4.85 GHz yields a 3σ upper limit on free–free emission of 7.2 mJy beam−1 (≲30 per cent of the observed flux) at the CBI resolution. The bulk of the 31-GHz flux therefore appears to be mostly due to dust radiation. Aperture photometry, at an angular resolution of 13 arcmin and with an aperture of diameter 30 arcmin, allowed the use of IRAS maps and the Wilkinson Microwave Anisotropy Probe 5-yr W-band map at 93.5 GHz. A single modified blackbody model was fitted to the data to estimate the contribution from thermal dust, which amounts to ∼10 per cent at 31 GHz. In this model, an excess of 1.52 ± 0.66 Jy (2.3σ) is seen at 31 GHz. Correlations with the IRAS 100 μm gave a coupling coefficient of 18.1 ± 4.4 μK (MJy sr−1)−1, consistent with the values found for LDN1622.
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