The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 micron that is beyond the peak (~160 micron) of dust emission in most galaxies. We investigate the differences in the fitted dust temperatures and masses determined using only <200 micron data and then also including >200 micron data (new SPIRE observations) to determine how important having >200 micron data is for deriving these dust properties. We fit the 100 to 350 micron observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of the Herschel Science Demonstration phase. The dust temperatures and masses computed using only 100 and 160 micron data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 micron data. We find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350 micron fractional residuals. We find that the emission at 500 micron is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24 micron flux and the total gas surface density. This argues against a flux calibration error as the origin of the 500 micron excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at lambda > 500 micron for the origin of the 500 micron excess.
We present a multi-wavelength analysis of the infrared dust bubble S24, and its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust linked to them, and analyzing the evolutionary status of the young stellar objects (YSOs) identified there. Using APEX data, we mapped the molecular emission in the CO(2-1), $^{13}$CO(2-1), C$^{18}$O(2-1), and $^{13}$CO(3-2) lines in a region of about 5'x 5' in size around the bubble. The cold dust distribution was analyzed using ATLASGAL and Herschel images. Complementary IR and radio data were also used.The molecular gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities between -48.0 km sec$^{-1}$ and -40.0 km sec$^{-1}$. The gas distribution reveals a shell-like molecular structure of $\sim$0.8 pc in radius bordering the bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel images.The presence of extended emission at 24 $\mu$m and radio continuum emission inside the bubble indicates that the bubble is a compact HII region. Part of the molecular gas bordering S24 coincides with the extended infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the interface between S24 and G341.217-0.237. As regards G341.220-0.213, the presence of an arc-like molecular structure at the northern and eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. Several YSO candidates are found to be linked to the IR extended sources, thus confirming their nature as active star-forming regions. The total gas mass in the region and the H$_2$ ambient density amount to 10300 M$_{\odot}$ and 5900 cm$^{-3}$, indicating that G341.220-0.213, G341.217-0.237, and the S24 HII region are evolving in a high density medium. A triggering star formation scenario is also investigated.
As the first part of the ESO-Swedish SEST Key Programme on CO in the Magellanic Clouds, we have observed 12 CO J=1-0 towards 92 positions in the LMC and 42 positions in the SMC. In the SMC we searched for emission form H II regions, dark clouds and IRAS infrared sources. The generally negative detection rate of non-IRAS sources in the SMC led to an LMC source selection based on the IRAS results. In both galaxies, CO was detected towards the majority of sources observed. We also observed 13 CO J=1-0 towards the brighter 12 CO sources in the LMC (37) and SMC (9). Compared to the strength of CO lines observed in the Milky Way Galaxy with identical linear resolutions, velocity-integrated CO emission is weaker by at least a factor of three in the LMC sources and an order of magnitude in the SMC sources
Abstract To investigate the effects of stellar feedback on the gravitational state of giant molecular clouds (GMCs), we study 12 CO and 13 CO Atacama Large Millimeter/submillimeter Array maps of nine GMCs distributed throughout the Large Magellanic Cloud (LMC), the nearest star-forming galaxy to our own. We perform noise and resolution matching on the sample, working at a common resolution of 3.″5 (0.85 pc at the LMC distance of 50 kpc), and we use the Spectral Clustering for Molecular Emission Segmentation clustering algorithm to identify discrete substructure, or “clumps.” We supplement these data with three tracers of recent star formation: 8 μ m surface brightness, continuum-subtracted H α flux, and interstellar radiation field energy density inferred from dust emission. The 12 CO clumps identified cover a range of 3.6 dex in luminosity-based mass and 2.4 dex in average 8 μ m surface brightness, representative of the wide range of conditions of the interstellar medium in the LMC. Our observations suggest evidence for increased turbulence in these clouds. While the turbulent linewidths are correlated with clump surface density, in agreement with previous observations, we find even better correlation with the three star formation activity tracers considered, suggesting stellar energy injection plays a significant role in the dynamical state of the clumps. The excess linewidths we measure do not appear to result from opacity broadening. 12 CO clumps are found to be typically less gravitationally bound than 13 CO clumps, with some evidence of the kinetic-to-gravitational potential energy ratio increasing with star formation tracers. Further multiline analysis may better constrain the assumptions made in these calculations.
Context . The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. Aims . We present the CO(3-2) APEX survey at a 6 pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H 2 envelopes. Methods . We adopted the CO analysis in the SMC bar comparing the CO(3–2) survey with that of the CO(2–1) of a similar resolution. We studied the CO(3–2)-to-CO(2–1) ratio ( R 32 ), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color [70/160], and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO(3–2) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. Results . We obtained R 32 = 0.65 ± 0.02 for the SW bar and a slightly higher ratio, R 32 = 0.7 ± 0.1, for N66 in the SMC. We found that R 32 varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) R 32 tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that R 32 is correlated with the IR color [70/160] and the total IR surface brightness. This finding indicates that R 32 increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified 225 molecular clouds with sizes of R > 1.5 pc and signal-to-noise ratios (S/N) of >3, of which only 17 are well resolved CO(3–2) clouds with S/N ≳ 5. These 17 clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO(3–2) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO(3–2)-to-H 2 conversion factor of 12.6 −7 +10 M ⊙ (K km s −1 pc 2 ) −1 for the total sample.
A detailed study of the Hourglass Nebula in the M8 star forming region is presented. The study is mainly based on recent subarcsec-resolution JHKs images taken at Las Campanas Observatory and complemented with archival HST images and longslit spectroscopy retrieved from the ESO Archive Facility. Using the new numerical code CHORIZOS, we estimate the distance to the earliest stars in the region to be 1.25 kpc. Infrared photometry of all the sources detected in the field is given. From analysis of the JHKs colour-colour diagrams, we find that an important fraction of these sources exhibit significant infrared excess. These objects are candidates to be low- and intermediate-mass pre-main sequence stars. Based on HST observations, the spatial distribution of gas, dust and stars in the region is analyzed. The morphological analysis of these images also reveals a rich variety of structures related to star formation (proplyds, jets, bow shocks), similar to those observed in M16 and M42, along with the detection of the first four Herbig-Haro objects in the region. Furthermore, a longslit spectrum obtained with NTT confirms the identification of one of them (HH 870) in the core of the Hourglass nebula, providing the first direct evidence of active star formation by accretion in M8.
We present a multi-wavelength study of two HH objects (137 and 138) that may be associated. We use Gemini H$_2$ (2.12 $\mu$m) and K (2.2 $\mu$m) images, as well as APEX molecular line observations and Spitzer image archives. Several H$_2$ knots, linked to the optical chain of knots of HH 137, are identified in the Gemini and Spitzer 4.5 $\mu$m images. New shock excited regions related to the optical knots delineating HH 138 are also reported. In addition, a bright 4.5 $\mu$m 0.09 pc-long arc-shaped structure, roughly located mid-way between HH 137 and HH 138, is found to be associated with two Spitzer Class I/II objects, which are likely to be the exciting stars. These sources are almost coincident with a high-density molecular clump detected in $^{12}$CO(3-2), $^{13}$CO(3-2), C$^{18}$O(3-2), HCO$^{+}$(3-2) and HCN(3-2) molecular lines with an LTE mass of 36 M$_{\odot}$. The $^{12}$CO(3-2) emission distribution over the observed region reveals molecular material underlying three molecular outflows. Two of them (outflows 1 and 2) are linked to all optical knots of HH 137 and HH 138 and to the H$_2$ and 4.5 $\mu$m shock emission knots. In fact, the outflow 2 shows an elongated $^{12}$CO blue lobe that coincides with all the H$_2$ knots of HH 137 which end at a terminal H$_2$ bow shock. We propose a simple scenario that connects the outflows to the dust clumps detected in the region. A third possible outflow is located to the north-east projected towards a secondary weak and cold dust clump.
We present UBVRIz' optical images taken with MOSAIC on the CTIO 4 m telescope of the 0.32 deg2 Extended Hubble Deep Field-South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z = 3, active galactic nucleus (AGN) demographics, and Galactic structure. Our methods used for astrometric calibration, weighted image combination, and photometric calibration in AB magnitudes are described. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62,968 objects is complete to a total magnitude of RAB = 25, with R-band counts consistent with results from the literature. We select z ≃ 3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4 arcmin-2 and an angular correlation function w(θ) = (2.3 ± 1.0)θ-0.8, consistent with previous findings that high-redshift Lyman break galaxies reside in massive dark matter halos. Our images and catalogs are available online.
We provide a corrected Table 4 that lists the total galaxy fluxes for the HERTIAGE bands and corresponding Figure 19 which plots these fluxes in comparison to prior measurements These corrected fluxes differ by up to 41% to what we reported in the original paper. These revised fluxes utilize a more appropriate subtraction of the Milky Way Foreground Cirrus emission which contaminates especially the PACS 100 and 160 micron bands. The subtraction process uses the HI 21 cm emission to develop a model for the MW cirrus dust emission. In addition, the better subtraction process corrected for an over subtraction of the background in the SPIRE images of the SMC that occurred during the original data processing. The need for these better foreground subtractions was realized while working on an analysis of the dust masses and gas-to-dust ratios in the LMC and SMC reported by Gordon et al. (2014) and Roman-Duval et al. (2014). After the subtraction has been done, the fluxes were derived by simply summing up all the pixels in the image. The errors we quote for the fluxes reflect the absolute flux calibration errors for extended sources which are approx.10% for PACS and approx. 8% for SPIRE. In the revised Figure 19, we confirm that these corrected global fluxes remain within the range of prior global measurements for both the LMC and SMC. Indeed, the shape of the corrected spectral energy distributions appears better aligned with prior measurements.
Shocks and torques produced by non-axisymmetric structures such as spiral arms and bars may transport gas to galaxy central regions. We test this hypothesis by studying the dependence of the concentration of CO luminosity ( C CO ) and molecular gas ( C mol ) and the star formation rate ( C SFR ) in the central ∼2 kpc on the strength of non-axisymmetric disk structure using a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. The C mol is calculated using a CO-to-H 2 conversion factor that decreases with higher metallicity and higher stellar surface density. We find that C mol is systematically 0.22 dex lower than C CO . We confirm that high C mol and strong non-axisymmetric disk structure are more common in barred galaxies than in unbarred galaxies. However, we find that spiral arms also increase C mol . We show that there is a good correlation between C mol and the strength of non-axisymmetric structure (which can be due to a bar, spiral arms, or both). This suggests that the stronger the bars and spirals, the more efficient the galaxy is at transporting cold gas to its center. Despite the small subsample size, the C mol of the four Seyferts are not significantly reduced compared to inactive galaxies of similar disk structure, implying that the active galactic nucleus feedback in Seyferts may not notably affect the molecular gas distribution in the central ∼2 kpc. We find that C SFR tightly correlates with C mol in both unbarred and barred galaxies. Likewise, elevated C SFR is found in galaxies with strong disk structure. Our results suggest that the disk structure, either spirals or bars, can transport gas to the central regions, with higher inflow rates corresponding to stronger structure, and consequently boost central star formation. Both spirals and bars play, therefore, an essential role in the secular evolution of disk galaxies.
