arXiv subjects

Akiko Kawamura

Publications and source records attributed to Akiko Kawamura.

At least 37 records · Page 2Linked to original sources

arXiv2020

A low-velocity bipolar outflow from a deeply embedded object in Taurus revealed by the Atacama Compact Array

The first hydrostatic core, the first quasi-hydrostatic object formed during the star formation process, is still the observational missing link between the prestellar and protostellar phases, mainly due to its short lifetime. Although we have not established a clear method to identify this rare object, recent theoretical studies predict that the first core has millimeter continuum emission and low-velocity outflow with a wide opening angle. An extensive continuum/outflow survey toward a large number of $"$starless$"$ cores in nearby star-forming regions works as a pathfinder. We observed 32 prestellar cores in Taurus with an average density of $\gtrsim$10$^5$ cm$^{-3}$ in 1.3 mm continuum and molecular lines using the Atacama Large Millimeter/submillimeter Array$-$Atacama Compact Array (ALMA$-$ACA) stand-alone mode. Among the targets, MC35-mm centered at one of the densest $"$starless$"$ cores in Taurus has blueshifted/redshifted wings in the $^{12}$CO (2-1) line, indicating that there is deeply embedded object driving molecular outflow. The observed velocities and sizes of the possible outflow lobes are 2-4 km s$^{-1}$, and $\sim$2 $\times$10$^3$ au, respectively, and the dynamical time is calculated to be $\sim$10$^3$ yr. In addition to this, the core is one of the strongest N$_2$D$^{+}$ (3-2) emitters in our sample. All of the observed signatures do not conflict with any of the theoretical predictions about the first hydrostatic core so far, and thus MC35-mm is unique as the only first-core candidate in the Taurus molecular cloud.

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arXiv2020

ALMA Observations of Giant Molecular Clouds in M33 I: Resolving Star Formation Activities in the Giant Molecular Filaments Possibly Formed by a Spiral Shock

We report molecular line and continuum observations toward one of the most massive giant molecular clouds (GMCs), GMC-16, in M33 using ALMA with an angular resolution of 0$''$44 $\times$ 0$''$27 ($\sim$2 pc $\times$ 1 pc). We have found that the GMC is composed of several filamentary structures in $^{12}$CO and $^{13}$CO ($J$ = 2-1). The typical length, width, and total mass are $\sim$50-70 pc, $\sim$5-6 pc, and $\sim$10$^{5}$ $M_{\odot}$, respectively, which are consistent with those of giant molecular filaments (GMFs) as seen in the Galactic GMCs. The elongations of the GMFs are roughly perpendicular to the direction of the galaxy's rotation, and several H$\;${\sc ii} regions are located at the downstream side relative to the filaments with an offset of $\sim$10-20 pc. These observational results indicate that the GMFs are considered to be produced by a galactic spiral shock. The 1.3 mm continuum and C$^{18}$O ($J$ = 2-1) observations detected a dense clump with the size of $\sim$2 pc at the intersection of several filamentary clouds, which is referred to as the $"$hub filament,$"$ possibly formed by a cloud-cloud collision. A strong candidate for protostellar outflow in M33 has also been identified at the center of the clump. We have successfully resolved the parsec-scale local star formation activity in which the galactic scale kinematics may induce the formation of the parental filamentary clouds.

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arXiv2019

An ALMA view of molecular filaments in the Large Magellanic Cloud II: An early stage of high-mass star formation embedded at colliding clouds in N159W-South

We have conducted ALMA CO isotopes and 1.3 mm continuum observations toward filamentary molecular clouds of the N159W-South region in the Large Magellanic Cloud with an angular resolution of $\sim$0"25 ($\sim$0.07 pc). Although the previous lower-resolution ($\sim$1") ALMA observations revealed that there is a high-mass protostellar object at an intersection of two line-shaped filaments in $^{13}$CO with the length scale of $\sim$10 pc, the spatially resolved observations, in particular, toward the highest column density part traced by the 1.3 mm continuum emission, the N159W-South clump, show complicated hub-filamentary structures. We also discovered that there are multiple protostellar sources with bipolar outflows along the massive filament. The redshifted/blueshifted components of the $^{13}$CO emission around the massive filaments/protostars have complementary distributions, which is considered to be a possible piece of evidence for a cloud-cloud collision. We propose a new scenario in which the supersonically colliding gas flow triggers the formation of both the massive filament and protostars. This is a modification of the earlier scenario of cloud-cloud collision, by Fukui et al., that postulated the two filamentary clouds occur prior to the high-mass star formation. A recent theoretical study of the shock compression in colliding molecular flows by Inoue et al. demonstrates that the formation of filaments with hub structure is a usual outcome of the collision, lending support for the present scenario. The theory argues that the filaments are formed as dense parts in a shock compressed sheet-like layer, which resembles $"$an umbrella with pokes.$"$

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arXiv2019

An ALMA view of molecular filaments in the Large Magellanic Cloud I: The formation of high-mass stars and pillars in the N159E-Papillon Nebula triggered by a cloud-cloud collision

We present the ALMA observations of CO isotopes and 1.3 mm continuum emission toward the N159E-Papillon Nebula in the Large Magellanic Cloud (LMC). The spatial resolution is 0"25-0"28 (0.06-0.07 pc), which is a factor of 3 higher than the previous ALMA observations in this region. The high resolution allowed us to resolve highly filamentary CO distributions with typical widths of $\sim$0.1 pc (full width half maximum) and line masses of a few 100 $M_{\odot}$ pc$^{-1}$. The filaments (more than ten in number) show an outstanding hub-filament structure emanating from the nebular center toward the north. We identified for the first time two massive protostellar outflows of $\sim$10$^4$ yr dynamical age along one of the most massive filaments. The observations also revealed several pillar-like CO features around the Nebula. The H II region and the pillars have a complementary spatial distribution and the column density of the pillars is an order of magnitude higher than that of the pillars in the Eagle nebula (M16) in the Galaxy, suggesting an early stage of pillar formation with an age younger than $\sim$10$^5$ yr. We suggest that a cloud-cloud collision triggered the formation of the filaments and protostar within the last $\sim$2 Myr. It is possible that the collision is more recent, as part of the kpc-scale H I flows come from the tidal interaction resulting from the close encounter between the LMC and SMC $\sim$200 Myr ago as suggested for R136 by Fukui et al.

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arXiv2019

Complex Organic Molecules in Star-Forming Regions of the Magellanic Clouds

The Large and Small Magellanic Clouds (LMC and SMC), gas-rich dwarf companions of the Milky Way, are the nearest laboratories for detailed studies on the formation and survival of complex organic molecules (COMs) under metal poor conditions. To date, only methanol, methyl formate, and dimethyl ether have been detected in these galaxies - all three toward two hot cores in the N113 star-forming region in the LMC, the only extragalactic sources exhibiting complex hot core chemistry. We describe a small and diverse sample of the LMC and SMC sources associated with COMs or hot core chemistry, and compare the observations to theoretical model predictions. Theoretical models accounting for the physical conditions and metallicity of hot molecular cores in the Magellanic Clouds have been able to broadly account for the existing observations, but fail to reproduce the dimethyl ether abundance by more than an order of magnitude. We discuss future prospects for research in the field of complex chemistry in the low-metallicity environment. The detection of COMs in the Magellanic Clouds has important implications for astrobiology. The metallicity of the Magellanic Clouds is similar to galaxies in the earlier epochs of the Universe, thus the presence of COMs in the LMC and SMC indicates that a similar prebiotic chemistry leading to the emergence of life, as it happened on Earth, is possible in low-metallicity systems in the earlier Universe.

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arXiv2019

A centrally concentrated sub-solar mass starless core in the Taurus L1495 filamentary complex

The formation scenario of brown dwarfs is still unclear because observational studies to investigate its initial condition are quite limited. Our systematic survey of nearby low-mass star-forming regions using the Atacama Compact Array (aka Morita array) and the IRAM 30 m telescope in 1.2 mm continuum has identified a centrally concentrated starless condensation with a central H$_2$ volume density of $\sim$10$^6$ cm$^{-3}$, MC5-N, connected to a narrow (width $\sim$0.03 pc) filamentary cloud in the Taurus L1495 region. The mass of the core is $\sim$0.2-0.4 $M_{\odot}$, which is an order of magnitude smaller than typical low-mass prestellar cores. Taking into account a typical core to star formation efficiency for prestellar cores ($\sim$20%-40%) in nearby molecular clouds, brown dwarf(s) or very low-mass star(s) may be going to be formed in this core. We have found possible substructures at the high-density portion of the core, although much higher angular resolution observation is needed to clearly confirm them. The subsequent N$_2$H$^+$ and N$_2$D$^+$ observations using the Nobeyama 45 m telescope have confirmed the high-deuterium fractionation ($\sim$30%). These dynamically and chemically evolved features indicate that this core is on the verge of proto-brown dwarf or very low-mass star formation and is an ideal source to investigate the initial conditions of such low-mass objects via gravitational collapse and/or fragmentation of the filamentary cloud complex.

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arXiv2019

Formation of High-Mass stars in an isolated environment in the Large Magellanic Cloud

The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud (LMC). High-mass stars usually form in Giant Molecular Clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12CO (J = 1-0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high-density and high-temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ~ 40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.

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arXiv2018

The Dust-Selected Molecular Clouds in the Northeast Region of the Small Magellanic Cloud

We present a high-sensitivity ($1σ<1.6~\mathrm{mJy~beam^{-1}}$) continuum observation in a 343 arcmin$^2$ area of the northeast region in the Small Magellanic Cloud at a wavelength of 1.1 mm, conducted using the AzTEC instrument on the ASTE telescope. In the observed region, we identified 20 objects by contouring $10σ$ emission. Through spectral energy distribution (SED) analysis using 1.1 mm, $Herschel$, and $Spitzer$ data, we estimated the gas masses of $5\times 10^3-7\times 10^4~\mathrm{M_\odot}$, assuming a gas-to-dust ratio of 1000. Dust temperature and the index of emissivity were also estimated as $18-33$ K and $0.9-1.9$, respectively, which are consistent with previous low resolution studies. The relation between dust temperature and the index of emissivity shows a weak negative linear correlation. We also investigated five CO-detected dust-selected clouds in detail. The total gas masses were comparable to those estimated from the Mopra CO data, indicating that the assumed gas-to-dust ratio of 1000 and the $X_\mathrm{CO}$ factor of $1\times10^{21}~\mathrm{cm^{-2}~(K~km~s^{-1})^{-1}}$, with uncertainties of a factor of 2, are reliable for the estimation of the gas masses of molecular or dust-selected clouds. Dust column density showed good spatial correlation with CO emission, except for an object that associates with bright young stellar objects. The $8~\mathrm{μm}$ filamentary and clumpy structures also showed similar spatial distribution with the CO emission and dust column density, supporting the fact that polycyclic aromatic hydrocarbon emissions arise from the surfaces of dense gas and dust clouds.

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arXiv2018

Warm CO gas generated by possible turbulent shocks in a low-mass star-forming dense core in Taurus

We report ALMA Cycle 3 observations in CO isotopes toward a dense core, MC27/L1521F in Taurus, which is considered to be at an early stage of multiple star formation in a turbulent environment. Although most of the high-density parts of this core are considered to be as cold as $\sim$10 K, high-angular resolution ($\sim$20 au) observations in $^{12}$CO ($J$ = 3--2) revealed complex warm ($>$15--60 K) filamentary/clumpy structures with the sizes from a few tens of au to $\sim$1,000 au. The interferometric observations of $^{13}$CO and C$^{18}$O show that the densest part with arc-like morphologies associated with the previously identified protostar and condensations are slightly redshifted from the systemic velocity of the core. We suggest that the warm CO clouds may be consequences of shock heating induced by interactions among the different density/velocity components that originated from the turbulent motions in the core. However, such a small-scale and fast turbulent motion does not correspond to a simple extension of the line-width-size relation (i.e., Larson'{}s law), and thus the actual origin remains to be studied. The high-angular resolution CO observations are expected to be essential in detecting small-scale turbulent motions in dense cores and to investigate protostar formation therein.

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arXiv2018

A multiline study of a high-mass young stellar object in the Small Magellanic Cloud with ALMA: The detection of methanol gas at 0.2 solar metallicity

We report the results of subparsec-scale submillimeter observations towards an embedded high-mass young stellar object in the Small Magellanic Cloud (SMC) with ALMA. Complementary infrared data obtained with the AKARI satellite and the Gemini South telescope are also presented. The target infrared point source is spatially resolved into two dense molecular cloud cores; one is associated with a high-mass young stellar object (YSO core), while another is not associated with an infrared source (East core). The two cores are dynamically associated but show different chemical characteristics. Emission lines of CS, C33S, H2CS, SO, SO2, CH3OH, H13CO+, H13CN, SiO, and dust continuum are detected from the observed region. Tentative detection of HDS is also reported. The first detection of CH3OH in the SMC has a strong impact on our understanding of the formation of complex organic molecules in metal-poor environments. The gas temperature is estimated to be ~10 K based on the rotation analysis of CH3OH lines. The fractional abundance of CH3OH gas in the East core is estimated to be (0.5-1.5) x 10^(-8), which is comparable with or marginally higher than those of similar cold sources in our Galaxy despite a factor of five lower metallicity in the SMC. This work provides observational evidence that an organic molecule like CH3OH, which is largely formed on grain surfaces, can be produced even in a significantly lower metallicity environment compared to the solar neighborhood. A possible origin of cold CH3OH gas in the observed dense core is discussed.

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arXiv2018

The Detection of Hot Cores and Complex Organic Molecules in the Large Magellanic Cloud

We report the first extragalactic detection of the complex organic molecules (COMs) dimethyl ether (CH$_3$OCH$_3$) and methyl formate (CH$_3$OCHO) with the Atacama Large Millimeter/submillimeter Array (ALMA). These COMs together with their parent species methanol (CH$_3$OH), were detected toward two 1.3 mm continuum sources in the N 113 star-forming region in the low-metallicity Large Magellanic Cloud (LMC). Rotational temperatures ($T_{\rm rot}\sim130$ K) and total column densities ($N_{\rm rot}\sim10^{16}$ cm$^{-2}$) have been calculated for each source based on multiple transitions of CH$_3$OH. We present the ALMA molecular emission maps for COMs and measured abundances for all detected species. The physical and chemical properties of two sources with COMs detection, and the association with H$_2$O and OH maser emission indicate that they are hot cores. The fractional abundances of COMs scaled by a factor of 2.5 to account for the lower metallicity in the LMC are comparable to those found at the lower end of the range in Galactic hot cores. Our results have important implications for studies of organic chemistry at higher redshift.

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arXiv2017

A Detached Protostellar Disk around a $\sim$0.2$M_{\odot}$ protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus

We report ALMA observations in 0.87 mm continuum and $^{12}$CO ($J$ = 3--2) toward a very low-luminosity ($<$0.1 $L_{\odot}$) protostar, which is deeply embedded in one of the densest core MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to $\sim$20 AU, and we have clearly detected blueshifted/redshifted gas in $^{12}$CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of $\sim$10 AU, a disk mass of $\sim$10$^{-4}$ $M_{\odot}$ and a central stellar mass of $\sim$0.2 $M_{\odot}$. The observed disk seems to be detached from the surrounding dense gas, although it is still embedded at the center of the core whose density is $\sim$10$^{6}$ cm$^{-3}$. The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of $\sim$0.2 $M_{\odot}$ protostar. However, we cannot explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar ($\sim$0.65 $R_\odot$). These facts may challenge our current understanding of the low mass star formation, in particular the mass accretion process onto the protostar and the circumstellar disk.

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arXiv2017

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

We present high-resolution (sub-parsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in $^{12}$CO(2-1) and high column density regions in $^{13}$CO(2-1). Our target is a quiescent cloud (PGCC G282.98-32.40, which we refer to as the "Planck cold cloud" or PCC) in the southern outskirts of the galaxy where star-formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and 5 times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface density structures tend to exhibit super-virial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures ("leaves") of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the small-scale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-linewidth relationships.

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arXiv2017

Molecular-Cloud-Scale Chemical Composition II: Mapping Spectral Line Survey toward W3(OH) in the 3 mm Band

In order to study a molecular-cloud-scale chemical composition, we have conducted a mapping spectral line survey toward the Galactic molecular cloud W3(OH), which is one of the most active star forming regions in the Perseus arm, with the NRO 45 m telescope. We have observed the area of 16' $\times$ 16', which corresponds to 9.0 pc $\times$ 9.0 pc. The observed frequency ranges are 87--91, 96--103, and 108--112 GHz. We have prepared the spectrum averaged over the observed area, in which 8 molecular species CCH, HCN, HCO$^+$, HNC, CS, SO, C$^{18}$O, and $^{13}$CO are identified. On the other hand, the spectrum of the W3(OH) hot core observed at a 0.17 pc resolution shows the lines of various molecules such as OCS, H$_2$CS CH$_3$CCH, and CH$_3$CN, in addition to the above species. In the spatially averaged spectrum, emission of the species concentrated just around the star-forming core such as CH$_3$OH and HC$_3$N is fainter than in the hot core spectrum, whereas emission of the species widely extended over the cloud such as CCH is relatively brighter. We have classified the observed area into 5 subregions according to the integrated intensity of $^{13}$CO, and have evaluated the contribution to the averaged spectrum from each subregion. The CCH, HCN, HCO$^+$, and CS lines can be seen even in the spectrum of the subregion with the lowest $^{13}$CO integrated intensity range ($< 10$ K km s$^{-1}$). Thus, the contributions of the spatially extended emission is confirmed to be dominant in the spatially averaged spectrum.

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arXiv2017

ALMA observations of N83C in the early stage of star formation in the Small Magellanic Cloud

We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in $^{12}$CO($J=2-1$), $^{13}$CO($J=2-1$), C$^{18}$O($J=2-1$), $^{12}$CO($J=3-2$), $^{13}$CO($J=3-2$), and CS($J=7-6$) lines toward the active star-forming region N83C in the Small Magellanic Cloud (SMC), whose metallicity is $\sim$ 1/5 of the Milky Way (MW). The ALMA observations first reveal sub-pc scale molecular structures in $^{12}$CO($J=2-1$) and $^{13}$CO($J=2-1$) emission. We found strong CO peaks associated with young stellar objects (YSOs) identified by the $Spitzer$ Space Telescope, and also found that overall molecular gas is distributed along the edge of the neighboring HII region. We derived a gas density of $\sim 10^4$ cm$^{-3}$ in molecular clouds associated with YSOs based on the virial mass estimated from $^{12}$CO($J=2-1$) emission. This high gas density is presumably due to the effect of the HII region under the low-metallicity (accordingly small-dust content) environment in the SMC; far-UV radiation from the HII region can easily penetrate and photo-dissociate the outer layer of $^{12}$CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in $^{12}$CO emission. We obtained the CO-to-H$_2$ conversion factor $X_{\rm CO}$ of $7.5 \times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ in N83C based on virial masses and CO luminosities, which is four times larger than that in the MW, 2 $\times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We also discuss the difference in the nature between two high-mass YSOs, each of which is associated with a molecular clump with a mass of about a few $\times 10^3 M_{\odot}$.

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arXiv2017

Molecular-Cloud-Scale Chemical Composition I: Mapping Spectral Line Survey toward W51 in the 3 mm Band

We have conducted a mapping spectral line survey toward the Galactic giant molecular cloud W51 in the 3 mm band with the Mopra 22 m telescope in order to study an averaged chemical composition of the gas extended over a molecular cloud scale in our Galaxy. We have observed the area of $25' \times 30'$, which corresponds to 39 pc $\times$ 47 pc. The frequency ranges of the observation are 85.1 - 101.1 GHz and 107.0 - 114.9 GHz. In the spectrum spatially averaged over the observed area, spectral lines of 12 molecular species and 4 additional isotopologues are identified. An intensity pattern of the spatially-averaged spectrum is found to be similar to that of the spiral arm in the external galaxy M51, indicating that these two sources have similar chemical compositions. The observed area has been classified into 5 sub-regions according to the integrated intensity of $^{13}$CO($J=1-0$) ($I_{\rm ^{13}CO}$), and contributions of the fluxes of 11 molecular lines from each sub-region to the averaged spectrum have been evaluated. For most of molecular species, 50 % or more of the flux come from the sub-regions with $I_{\rm ^{13}CO}$ from 25 K km s$^{-1}$ to 100 K km s$^{-1}$, which does not involve active star forming regions. Therefore, the molecular-cloud-scale spectrum observed in the 3 mm band hardly represents the chemical composition of star forming cores, but mainly represents the chemical composition of an extended quiescent molecular gas. The present result constitutes a sound base for interpreting the spectra of external galaxies at a resolution of a molecular cloud scale ($\sim10$ pc) or larger.

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arXiv2017

The 1.1 mm Continuum Survey of the Small Magellanic Cloud: Physical Properties and Evolution of the Dust-selected Clouds

The first 1.1 mm continuum survey toward the Small Magellanic Cloud (SMC) was performed using the AzTEC instrument installed on the ASTE 10-m telescope. This survey covered 4.5 deg$^2$ of the SMC with $1σ$ noise levels of $5-12$ mJy beam$^{-1}$, and 44 extended objects were identified. The 1.1 mm extended emission has good spatial correlation with $Herschel$ 160 $\mathrm{μm}$, indicating that the origin of the 1.1 mm extended emission is thermal emission from a cold dust component. We estimated physical properties using the 1.1 mm and filtered $Herschel$ data (100, 160, 250, 350, and 500 $\mathrm{μm}$). The 1.1 mm objects show dust temperatures of $17-45$ K and gas masses of $4\times10^3-3\times10^5~M_\odot$, assuming single-temperature thermal emission from the cold dust with an emissivity index, $β$, of 1.2 and a gas-to-dust ratio of 1000. These physical properties are very similar to those of giant molecular clouds (GMCs) in our galaxy and the Large Magellanic Cloud. The 1.1 mm objects also displayed good spatial correlation with the $Spitzer$ 24 $\mathrm{μm}$ and CO emission, suggesting that the 1.1 mm objects trace the dense gas regions as sites of massive star formation. The dust temperature of the 1.1 mm objects also demonstrated good correlation with the 24 $\mathrm{μm}$ flux connected to massive star formation. This supports the hypothesis that the heating source of the cold dust is mainly local star-formation activity in the 1.1 mm objects. The classification of the 1.1 mm objects based on the existence of star-formation activity reveals the differences in the dust temperature, gas mass, and radius, which reflects the evolution sequence of GMCs.

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arXiv2016

Molecular Shocks and the Gamma-ray Clouds of the W28 Supernova Remnant

Interstellar medium clouds in the W28 region are emitting gamma-rays and it is likely that the W28 supernova remnant is responsible, making W28 a prime candidate for the study of cosmic-ray acceleration and diffusion. Understanding the influence of both supernova remnant shocks and cosmic rays on local molecular clouds can help to identify multi-wavelength signatures of probable cosmic-ray sources. To this goal, transitions of OH, SiO, NH3, HCO+ and CS have complemented CO in allowing a characterization of the chemically rich environment surrounding W28. This remnant has been an ideal test-bed for techniques that will complement arcminute-scale studies of cosmic-ray source candidates with future GeV-PeV gamma-ray observations.

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