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Register a new userTowards a More Complex Understanding of Natal Super Star Clusters with Multiwavelength Observations
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Henize 2-10 (He 2-10) is a nearby (D = 9 Mpc) starbursting blue compact dwarf galaxy that boasts a high star formation rate and a low luminosity AGN. He 2-10 is also one of the first galaxies in which embedded superstar clusters (SSCs) were discovered. SSCs are massive, compact star clusters that will impact their host galaxies dramatically when their massive stars evolve. Here, we discuss radio, submillimeter, and infrared observations of He 2-10 from 1.87 microns to 6 cm in high angular resolution (~0.3 arcsec), which allows us to disentangle individual clusters from aggregate complexes as identified at lower resolution. These results indicate the importance of spatial resolution to characterize SSCs, as low resolution studies of SSCs average over aggregate complexes that may host SSCs at different stages of evolution. We explore the thermal, non-thermal, and dust emission associated with the clusters along with dense molecular tracers to construct a holistic review of the natal SSCs that have yet to dramatically disrupt their parent molecular clouds. We assess the production rate of ionizing photons, extinction, total mass, and the star formation efficiency associated with the clusters. Notably, we find that the star formation efficiency for the some of the natal clusters is high (>70%), which suggests that these clusters could remain bound even after the gas is dispersed from the system from stellar feedback mechanisms. If they remain bound, these SSCs could survive to become objects indistinguishable from globular clusters.
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We present ALMA observations of the dwarf starburst galaxy Henize 2-10 in combination with previous SMA CO observations to probe the molecular environments of natal super star clusters. These observations include the HCO$^+$(1-0), HCN(1-0), HNC(1-0), and CCH(1-0) molecular lines, as well as 88 GHz continuum with a spatial resolution of $1.7times 1.6$. After correcting for the contribution from free-free emission to the 88 GHz continuum flux density ($sim$ 60% of the 88 GHz emission), we derive a total gas mass for He~2-10 of $M_{gas} = 4-6times10^8$ M$_{odot}$, roughly 5-20% of the dynamical mass. Based on a principle component analysis, HCO$^+$ is found to be the best general tracer of molecular emission. The line widths and luminosities of the CO emission suggests that the molecular clouds could either be as small as $sim 8$ pc, or alternately have enhanced line widths. The CO emission and 88 GHz continuum are anti-correlated, suggesting that either the dust and molecular gas are not cospatial, which could reflect the 88 GHz continuum is dominated by free-free emission. The CO and CCH emission are also relatively anti-correlated, which is consistent with the CCH being photo-enhanced, and/or the CO being dissociated in the regions near the natal super star clusters. The molecular line ratios of regions containing the natal star clusters are different from the line ratios observed for regions elsewhere in the galaxy. In particular, the regions with thermal radio emission all have CO(2-1)/HCO$^+(1-0) < 16$, and the HCO$^+$/CO ratio appears to be correlated with the evolutionary stage of the clusters.
We present a multiwavelength study of the extended green object, G12.42+0.50 in this paper. The associated ionized, dust, and molecular components of this source are studied in detail employing various observations at near-, mid- and far-infrared, submillimeter and radio wavelengths. Radio continuum emission mapped at 610 and 1390 MHz, using the Giant Meterwave Radio Telescope, India, advocates for a scenario of coexistence of an UC H II region and an ionized thermal jet possibly powered by the massive young stellar object, IRAS 18079-1756 with an estimated spectral type of B1 - B0.5. Shock-excited lines of H2 and [FeII], as seen in the near-infrared spectra obtained with UKIRT-UIST, lend support to this picture. Cold dust emission shows a massive clump of mass 1375 M{sun} enveloping G12.42+0.50. Study of the molecular gas kinematics using the MALT90 and JCMT archival data unravels the presence of both infall activity and large-scale outflow suggesting an early stage of massive star formation in G12.42+0.50. A network of filamentary features are also revealed merging with the massive clump mimicking a hub-filament layout. Velocity structure along these indicate bulk inflow motion.
The giant HII region W31 hosts the populous star cluster W31-CL and others projected on or in the surroundings. The most intriguing object is the stellar cluster SGR1806-20, which appears to be related to a Luminous Blue Variable (LBV) - a luminous supergiant star. We used the deep VVV J-,H-and K$_s$-bands photometry combined with 2MASS data in order to address the distance andother physical and structural properties of the clusters W31-CL, BDS 113 and SGR1806-20. Field-decontaminated photometry was used to analyse colour-magnitude diagrams and stellar radial density profiles, using procedures that our group has developed and employed in previous studies. We concludethat the clusters W31-CL and BDS113 are located at 4.5kpc and 4.8kpc and have ages of 0.5Myr and 1Myr, respectively. This result, together with the pre-main sequence (PMS) distribution in the colour-magnitude diagram, characterises them as members of the W31 complex. The present photometry detects the stellar content, addressed in previous spectroscopic classifications, in the direction of thecluster SGR1806-20, including the LBV, WRs, and foreground stars. We derive an age of 10$pm$4Myr and a distance of d=8.0$pm$1.95kpc. The cluster is extremely absorbed, with AV= 25mag. Thepresent results indicate that SGR1806-20 is more distant by a factor 1.8 with respect to the W31 complex, and thus not physically related to it.
We present a multiwavelength study of 28 Galactic massive star-forming H II regions. For 17 of these regions, we present new distance measurements based on Gaia DR2 parallaxes. By fitting a multicomponent dust, blackbody, and power-law continuum model to the 3.6 $mu$m through 10 mm spectral energy distributions, we find that ${sim}34$% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ${sim}68$% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates $N_C ge 10^{50}~{rm s}^{-1}$ and dust-processed $L_{rm TIR}ge 10^{6.8}$ L$_{odot}$) have on average higher percentages of absorbed Lyman continuum photons ($sim$51%) and reprocessed starlight ($sim$82%) compared to less luminous regions. Luminous H II regions show lower average PAH fractions than less luminous regions, implying that the strong radiation fields from early-type massive stars are efficient at destroying PAH molecules. On average, the monochromatic luminosities at 8, 24, and 70 $mu$m combined carry 94% of the dust-reprocessed $L_{rm TIR}$. $L_{70}$ captures ${sim}52$% of $L_{rm TIR}$, and is therefore the preferred choice to infer the bolometric luminosity of dusty star-forming regions. We calibrate SFRs based on $L_{24}$ and $L_{70}$ against the Lyman continuum photon rates of the massive stars in each region. Standard extragalactic calibrations of monochromatic SFRs based on population synthesis models are generally consistent with our values.
We present the study of deuteration of cyanoacetylene (HC$_3$N) towards a sample of 28 high-mass star-forming cores divided into different evolutionary stages, from starless to evolved protostellar cores. We report for the first time the detection of DC$_3$N towards 15 high-mass cores. The abundance ratios of DC$_3$N with respect HC$_3$N range in the interval 0.003$-$0.022, lower than those found in low-mas protostars and dark clouds. No significant trend with the evolutionary stage, or with the kinetic temperature of the region, has been found. We compare the level of deuteration of HC$_3$N with those of other molecules towards the same sample, finding weak correlation with species formed only or predominantly in gas phase (N$_2$H$^+$ and HNC, respectively), and no correlation with species formed only or predominantly on dust grains (CH$_3$OH and NH$_3$, respectively). We also present a single-dish map of DC$_3$N towards the protocluster IRAS 05358+3543, which shows that DC$_3$N traces an extended envelope ($sim$0.37 pc) and peaks towards two cold condensations separated from the positions of the protostars and the dust continuum. The observations presented in this work suggest that deuteration of HC$_3$N is produced in the gas of the cold outer parts of massive star-forming clumps, giving us an estimate of the deuteration factor prior to the formation of denser gas.
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