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Register a new userEnhanced dust emissivity power-law index along the western H$alpha$ filament of NGC 1569
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We used a data set from AKARI and Herschel images at wavelengths from 7 $mu$m to 500 $mu$m to catch the evidence of dust processing in galactic winds in NGC 1569. Images show a diffuse infrared (IR) emission extending from the galactic disk into the halo region. The most prominent filamentary structure seen in the diffuse IR emission is spatially in good agreement with the western H$alpha$ filament (western arm). The spatial distribution of the $F_mathrm{350}/F_mathrm{500}$ map shows high values in regions around the super-star clusters (SSCs) and towards the western arm, which are not found in the $F_mathrm{250}/F_mathrm{350}$ map. The color-color diagram of $F_mathrm{250}/F_mathrm{350}$-$F_mathrm{350}/F_mathrm{500}$ indicates high values of the emissivity power-law index ($beta_mathrm{c}$) of the cold dust component in those regions. From a spectral decomposition analysis on a pixel-by-pixel basis, a $beta_mathrm{c}$ map shows values ranging from $sim1$ to $sim2$ over the whole galaxy. In particular, high $beta_mathrm{c}$ values of $sim2$ are only observed in the regions indicated by the color-color diagram. Since the average cold dust temperature in NGC 1569 is $sim30$ K, $beta_mathrm{c}<2.0$ in the far-IR and sub-mm region theoretically suggests emission from amorphous grains, while $beta_mathrm{c}=2.0$ suggests that from crystal grains. Given that the enhanced $beta_mathrm{c}$ regions are spatially confined by the HI ridge that is considered to be a birthplace of the SSCs, the spatial coincidences may indicate that dust grains around the SSCs are grains of relatively high crystallinity injected by massive stars originating from starburst activities and that those grains are blown away along the HI ridge and thus the western arm.
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We present new measurements of the dust emissivity index, beta, for the high-mass, star-forming OMC 2/3 filament. We combine 160-500 um data from Herschel with long-wavelength observations at 2 mm and fit the spectral energy distributions across a ~ 2 pc long, continuous section of OMC 2/3 at 15000 AU (0.08 pc) resolution. With these data, we measure beta and reconstruct simultaneously the filtered-out large-scale emission at 2 mm. We implement both variable and fixed values of beta, finding that beta = 1.7 - 1.8 provides the best fit across most of OMC 2/3. These beta values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that beta values derived from spatial filtered emission maps agree well with those values from unfiltered data at the same resolution. Our results contradict the very low beta values (~ 0.9) previously measured in OMC 2/3 between 1.2 mm and 3.3 mm data, which we attribute to elevated fluxes in the 3.3 mm observations. Therefore, we find no evidence or rapid, extensive dust grain growth in OMC 2/3. Future studies with Herschel data and complementary ground-based long-wavelength data can apply our technique to obtain robust determinations of beta in nearby cold molecular clouds.
We present ALMA CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in the 2A 0335+096 galaxy cluster (z = 0.0346). The total molecular gas mass of (1.13+/-0.15) x 10^9 M_sun is divided into two components: a nuclear region and a 7 kpc long dusty filament. The central molecular gas component accounts for (3.2+/-0.4) x 10^8 M_sun of the total supply of cold gas. Instead of forming a rotationally-supported ring or disk, it is composed of two distinct, blueshifted clumps south of the nucleus and a series of low-significance redshifted clumps extending toward a nearby companion galaxy. The velocity of the redshifted clouds increases with radius to a value consistent with the companion galaxy, suggesting that an interaction between these galaxies <20 Myr ago disrupted a pre-existing molecular gas reservoir within the BCG. Most of the molecular gas, (7.8+/-0.9) x 10^8 M_sun, is located in the filament. The CO emission is co-spatial with a 10^4 K emission-line nebula and soft X-rays from 0.5 keV gas, indicating that the molecular gas has cooled out of the intracluster medium over a period of 25-100 Myr. The filament trails an X-ray cavity, suggesting that the gas has cooled from low entropy gas that has been lifted out of the cluster core and become thermally unstable. We are unable to distinguish between inflow and outflow along the filament with the present data. Cloud velocities along the filament are consistent with gravitational free-fall near the plane of the sky, although their increasing blueshifts with radius are consistent with outflow.
We study the resolved radio-continuum spectral energy distribution of the dwarf irregular galaxy, NGC 1569, on a beam-by-beam basis to isolate and study its spatially resolved radio emission characteristics. Utilizing high quality NRAO Karl G. Jansky Very Large Array (VLA) observations that densely sample the 1--34,GHz frequency range, we adopt a Bayesian fitting procedure, where we use H$alpha$ emission that has not been corrected for extinction as a prior, to produce maps of how the separated thermal emission, non-thermal emission and non-thermal spectral index vary across NGC,1569s main disk. We find a higher thermal fraction at 1,GHz than is found in spiral galaxies ($26^{+2}_{-3}%$) and find an average non-thermal spectral index $alpha = -0.53pm0.02$, suggesting that a young population of cosmic ray electrons is responsible for the observed non--thermal emission. By comparing our recovered map of the thermal radio emission with literature H$alpha$ maps, we estimate the total reddening along the line of sight to NGC,1569 to be $E(B-V) = 0.49 pm 0.05$, which is in good agreement with other literature measurements. Spatial variations in the reddening indicate that a significant portion of the total reddening is due to internal extinction within NGC,1569.
Recent observations from the MUSTANG2 instrument on the Green Bank Telescope have revealed evidence of enhanced long-wavelength emission in the dust spectral energy distribution (SED) in the Orion Molecular Cloud (OMC) 2/3 filament on 25 ($sim$0.1 pc) scales. Here we present a measurement of the dust SED on larger spatial scales (map size 0.5-3 degrees or roughly 3-20pc), at somewhat lower resolution (120, corresponding to 0.25 pc at the distance of 400pc) using data from the Herschel satellite and Atacama Cosmology Telescope (ACT). We then extend these 120-scale investigations to other regions covered in the Herschel Gould Belt Survey (HGBS) specifically: the dense filaments in the southerly regions of Orion A and its tail; Orion B; and Serpens-S. Our dataset in aggregate covers approximately 10 deg$^2$, with continuum photometry spanning from 160 um to 3mm. These data also show an excess of emission at 3mm, though somewhat weaker (8.5% excess) compared to what is seen at higher resolution. More strikingly, we find that the enhancement is present even more strongly in the other filaments we targeted, with an average enhancement of 24.9% compared to a standard MBB fit to lambda $leq$2mm data. By applying this analysis to the other targeted regions we lay the groundwork for future high-resolution observations and analysis. Finally, we also consider a two-component dust model motivated by Planck results and an amorphous grain dust model. While both of these have been proposed to explain deviations in emission from a generic modified blackbody, we find that they do not perform significantly better than a MBB spectrum for fitting the SEDs.
Variations in the dust emissivity are critical for gas mass determinations derived from far-infrared observations, but also for separating dust foreground emission from the Cosmic Microwave Background (CMB). Hi-GAL observations allow us for the first time to study the dust emissivity variations in the inner regions of the Galactic plane at resolution below 1 degree. We present maps of the emissivity spectral index derived from the combined Herschel PACS 160 mu m, SPIRE 250 mu m, 350 mu m, and 500 mu m data, and the IRIS 100 mu m data, and we analyze the spatial variations of the spectral index as a function of dust temperature and wavelength in the two Science Demonstration Phase Hi-GAL fields, centered at l=30{deg} and l=59{deg}. Applying two different methods, we determine both dust temperature and emissivity spectral index between 100 and 500 mu m, at an angular resolution of 4. Combining both fields, the results show variations of the emissivity spectral index in the range 1.8-2.6 for temperatures between 14 and 23 K. The median values of the spectral index are similar in both fields, i.e. 2.3 in the range 100-500 mu m, while the median dust temperatures are equal to 19.1 K and 16.0 K in the l=30{deg} and l=59{deg} field, respectively. Statistically, we do not see any significant deviations in the spectra from a power law emissivity between 100 and 500 mu m. We confirm the existence of an inverse correlation between the emissivity spectral index and dust temperature, found in previous analyses.
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