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(Abridged)We characterize gas and dust emission in Magellanic Bridge A, which has the highest 870$\mu$m excess of emission found in single dish surveys. Using the ALMA telescope, we mapped the Magellanic Bridge A molecular cloud with sub-parsec resolution, in 1.3 mm continuum and CO(2-1) line emission. We also map the cloud in 870$\mu$m continuum and CO(2-1) line emission at ~6 pc resolution with APEX. We combine the ALMA and APEX CO(2-1) line cubes to study the molecular gas emission. Magellanic Bridge A breaks up into two distinct molecular clouds in dust and CO(2-1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrarred fluxes, is ~3 K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum are ~7 and ~3 for the North and South sources respectively. Nonetheless, we do not detect the corresponding 1.3 mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits and therefore we cannot independently confirm the excess at this longer wavelength. The CO(2-1) emission is in two parsec-sized clouds with virial masses around 400 and 700 Mo each. Their volume densities are ~700-2600 cm$^{-3}$, larger than typical bulk densities of Galactic molecular clouds. The CO-to-H2 conversion factor is 6.5 and 15 M$_{\odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the North and South clouds, calculated using their respective virial masses and CO(2-1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses $M\sim1.3\times10^3$ M$_{\odot}$ and $2.9\times10^3$ M$_{\odot}$ for North and South respectively, a factor ~4 larger than the virial masses we infer from CO., Comment: Astronomy & Astrophysics in press. 14 pages, 6 figures, 7 tables

We present a multi-wavelength study of two HH objects (137 and 138) that may be associated. We use Gemini H2 (2.12 µm) and K (2.2 µm) images, as well as APEX molecular line observations and Spitzer image archives. Several H2 knots, linked to the optical chain of knots of HH 137, are identified in the Gemini and Spitzer 4.5 µm images. New shock excited regions related to the optical knots delineating HH 138 are also reported. In addition, a bright 4.5 µm 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 12CO(3-2), 13CO(3-2), C18O(3-2), HCO+ (3-2) and HCN(3-2) molecular lines with an LTE mass of 36 M . The 12CO(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 H2 and 4.5 µm shock emission knots. In fact, the outflow 2 shows an elongated 12CO blue lobe that coincides with all the H2 knots of HH 137 which end at a terminal H2 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., Los datos utilizados para este trabajo pueden accederse haciendo clic en "Documentos relacionados"., Facultad de Ciencias Astronómicas y Geofísicas

High resolution (1'' $\times$ 2'') ALMA CO(2-1) observations of the ram pressure stripped galaxy NGC 4402 in the Virgo cluster show some of the clearest evidence yet for the impacts of ram pressure on the molecular ISM of a galaxy. The eastern side of the galaxy at $r \sim 4.5$ kpc, upon which ram pressure is incident, has a large (width $\sim$1 kpc, height $\sim$1 kpc above the disk midplane) extraplanar plume of molecular gas and dust. Molecular gas in the plume region shows distinct non-circular motions in the direction of the ram pressure; the kinematic offset of up to 60 km s$^{-1}$ is consistent with acceleration by ram pressure. We also detect a small amount of gas in clouds below the plume that are spatially and kinematically distinct from the surrounding medium, and appear to be decoupled from the stripped ISM. We propose that diffuse molecular gas is directly stripped but GMC density gas is not directly stripped, and so decouples from lower density stripped gas. However, GMCs become effectively stripped on short timescales. We also find morphological and kinematic signatures of ram pressure compression of molecular gas in a region of intense star formation on the leading side at $r \sim 3.5$ kpc. We propose that the compressed and stripped zones represent different evolutionary stages of the ram pressure interaction, and that feedback from star formation in the compressed zone facilitates the effective stripping of GMCs by making the gas cycle rapidly to a lower density diffuse state., Published in ApJ Sep. 2020

The extended ultraviolet (XUV) disk galaxies are some of the most interesting objects studied in the last few years. The UV emission, revealed by GALEX, extends well beyond the optical disk after the drop in Hα emission, the usual tracer of star formation. This shows that sporadic star formation can occur in a large fraction of the HI disk at radii up to 3 or 4 times the optical radius. In most galaxies, these regions are poor in stars and are dominated by under-recycled gas; they therefore bear some similarity to the early stages of spiral galaxies and high-redshift galaxies. One remarkable example is M83, a nearby galaxy with an extended UV disk reaching 2 times the optical radius. It offers the opportunity to search for molecular gas and to characterize the star formation in outer disk regions, traced by the UV emission. We obtained CO(2-1) observations with ALMA of a small region in a 1.5′ × 3′ rectangle located at rgal = 7.85′ over a bright UV region of M83. There is no CO detection, in spite of the abundance of HI gas, and the presence of young stars traced by their HII regions. Our spatial resolution (17 pc × 13 pc) was perfectly fitted to detect giant molecular clouds (GMC), but none were detected. The corresponding upper limits occur in a region of the Kennicutt–Schmidt diagram where dense molecular clouds are expected. Stacking our data over HI-rich regions, using the observed HI velocity, we obtain a tentative detection corresponding to a H2-to-HI mass ratio of < 3 × 10−2. A possible explanation is that the expected molecular clouds are CO-dark because of the strong UV radiation field. This field preferentially dissociates CO with respect to H2, due to the small size of the star-forming clumps in the outer regions of galaxies.

Cometary globules, dense molecular gas structures exposed to the UV radiation, are found inside HII regions. Understanding the nature and origin of these structures through a kinematic study of the molecular gas is useful to advance in our knowledge of the interplay between radiation and molecular gas. Using ASTE we carried out molecular observations towards two cometary globules (Sim129 and Sim130) in the HII region Sh2-236. We mapped two regions with the 12CO J=3-2 and HCO+ J=4-3 lines. Additionally, two single pointings of C2H (N=4-3), HNC and HCN J=4-3 were observed. We combined our observations with public infrared and optical data to analyse the distribution and kinematics of the gas. We found kinematic signatures of infalling gas in the 12CO J=3-2 and C2H J=4-3 spectra towards Sim129 . We detected HCO+, HCN, and HNC J=4-3 only towards Sim130. The HCN/HNC integrated ratio of about 3 found in Sim130 suggests that the possible star formation activity within the globule has not yet ionized the gas. The location of NVSS 052255+33315, which peaks towards the brightest border of the globule, supports this scenario. The non-detection of these molecules towards Sim129 could be due to the radiation arising from the star formation activity inside this globule. The ubiquitous presence of the C2H molecule towards both globules shows the action of nearby O-B stars irradiating their external layers. Based on mid-infrared emission, we identified two new structures: a region of diffuse emission (R1) located, in projection, in front of the head of Sim129, and a pillar-like feature (P1) placed besides Sim130. Based on 12CO J=3-2, we found molecular gas associated with Sim129, Sim130, R1 and P1 at radial velocities of -1.5, -11, +10, and +4 km/s, respectively. Therefore, while Sim129 and P1 are located at the far side of the shell, Sim130 is placed at the near side, consistent with earlier results., Comment: Accepted for publication in A&A

We report the first evidence of molecular gas in two atomic hydrogen (HI) clouds associated with gas outflowing from the Small Magellanic Cloud (SMC). We used the Atacama Pathfinder Experiment (APEX) to detect and spatially resolve individual clumps of CO(2-1) emission in both clouds. CO clumps are compact (~ 10 pc) and dynamically cold (linewidths < 1 km/s). Most CO emission appears to be offset from the peaks of the HI emission, some molecular gas lies in regions without a clear HI counterpart. We estimate a total molecular gas mass of 10^3-10^4 Msun in each cloud and molecular gas fractions up to 30% of the total cold gas mass (molecular + neutral). Under the assumption that this gas is escaping the galaxy, we calculated a cold gas outflow rate of 0.3-1.8 Msun/yr and mass loading factors of 3 -12 at a distance larger than 1 kpc. These results show that relatively weak star-formation-driven winds in dwarf galaxies like the SMC are able to accelerate significant amounts of cold and dense matter and inject it into the surrounding environment., Accepted for publication in ApJ Letters

Massive molecular clumps fragment into cores where star formation takes place, hence star-forming studies should be done at different spatial scales. Using near-IR data obtained with Gemini, data of CH3OCHO and CH3CN from the ALMA database, observations of HCN, HNC, HCO+, and C2H carried out with ASTE, and CO data from public surveys, we perform a deep study of the YSO G29.86-0.004 at core and clump spatial scales. The near-IR emission shows two nebulosities separated by a dark lane, suggesting a typical disk-jets system, but highly asymmetric. They are likely produced by scattered light in cavities carved out by jets on an infalling envelope of material, which also present line emission of H2 and [FeII]. The presence of the complex molecular species observed with ALMA confirms that we are mapping a hot molecular core. The CH3CN emission concentrates at the position of the dark lane and it appears slightly elongated from southwest to northeast in agreement with the inclination of the system as observed at near-IR. The morphology of the CH3OCHO emission is more complex and extends along some filaments and concentrates in knots and clumps, mainly southwards the dark-lane, suggesting that the southern jet is encountering a dense region. The northern jet flows more freely, generating more extended features. This is in agreement with the red-shifted molecular outflow traced by the 12CO J=3-2 line extending towards the northwest and the lack of a blue-shifted outflow. This configuration can be explained by considering that the YSO is located at the furthest edge of the molecular clump along the line of sight, which is consistent with the position of the source in the cloud mapped in the C18O J=3-2 line. The detection of HCN, HNC, HCO+, and C2H allowed us to characterize the dense gas at clump scales, yielding results that are in agreement with the presence of a high-mass protostellar object., Accepted to be published in A&A (July 13, 2020)

We present a high-sensitivity ($1\sigma, Comment: 21 pages, 11 figures, accepted for publication by ApJ

A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10-m Gran Telescopio Canarias and in the emission line of CO(1-0) with the NOEMA mm-wave interferometer. The metallicity was determined to be 12+log(O/H)=7.83+-0.09, from which we estimate a conversion factor of alpha_CO~100 Msun/pc2/(K km/s) and a molecular cloud mass of ~2.9x10^7 Msun. This is an enormous concentration of molecular mass at one end of a small galaxy, suggesting a recent accretion. The molecular cloud properties seem normal: the surface density, 120 Msun/pc2, is comparable to that of a standard giant molecular cloud, the cloud's virial ratio of ~1.8 is in the star-formation range, and the gas consumption time, 0.5 Gyr, at the present star formation rate is typical for molecular regions. The low metallicity implies that the cloud has an average visual extinction of only 0.8 mag, which is close to the threshold for molecule formation. With such an extinction threshold, molecular clouds in metal-poor regions should have high surface densities and high internal pressures. If high pressure is associated with the formation of massive clusters, then metal-poor galaxies such as dwarfs in the early universe could have been the hosts of metal-poor globular clusters., 4 pages and 4 figures. accepted by ApJL

NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5-1/10 $Z_{\odot}$ Magellanic Bridge, allowing to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics $gri$H$\alpha$ imaging of NGC 796 (at 0.5", which is ~0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore if star formation and stellar evolution varies as a function of metallicity by comparing the properties of NGC 796 to higher metallicity clusters. We find from isochronal fitting of the cluster main sequence in the colour-magnitude diagram an age of 20$^{+12}_{-5}$ Myr. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope $\alpha$ = 1.99$\pm$0.2, hinting at an metallicity and/or environmental dependence of the IMF which may lead to a top-heavy IMF in the early Universe. Study of the H$\alpha$ emission line stars reveals that Classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990$\pm200$ $M_{\odot}$, and a core radius of 1.4$\pm$0.3 pc which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge., Comment: Accepted for publication in the Astrophysical Journal. Contains 14 pages, 11 figures, and 3 tables

At a distance of 61 kpc, the Small Magellanic Cloud (SMC) affords an absolutely unique view of the low metallicity star-forming interstellar medium, providing the nearest laboratory to study processes relevant to star formation at high redshifts. We present new ALMA 7m-array maps of CO and 12CO (2-1) for one of the four observed regions in the Southwest Bar of the SMC. These maps are the first high-resolution (~6″ ~ 1.7 pc) images of CO in a molecular cloud at 1/5 Solar metallicity. We show the structure of photodissociation regions for the first time at 1/5 Solar metallicity by combining the new ALMA data with Herschel maps of [C ii] and [O i]. We present preliminary evidence that there is extended, faint 12CO (2-1) emission near where we expect the Hi-to-H2 transition. We also compare our data to the low metallicity 3D simulations by Glover & Mac Low (2011) and Shetty et al. (2011).

To test the theoretical understanding that finding bright CO emission depends primarily on dust shielding, we investigate the relationship between CO emission ($I_{\rm CO}$) and the amount of dust (estimated from IR emission and expressed as "$A_V$") across the Large Magellanic Cloud, the Small Magellanic Cloud, and the Milky Way. We show that at our common resolution of 10 pc scales, $I_{\rm CO}$ given a fixed line-of-sight $A_V$ is similar across all three systems despite the difference in metallicity. We find some evidence for a secondary dependence of $I_{\rm CO}$ on radiation field; in the LMC, $I_{\rm CO}$ at a given $A_V$ is smaller in regions of high $T_{\rm dust}$, perhaps because of an increased photodissociating radiation field. We suggest a simple but useful picture in which the CO-to-H$_2$ conversion factor (\xco) depends on two separable factors: (1) the distribution of gas column densities, which maps to an extinction distribution via a dust-to-gas ratio; and (2) the dependence of $I_{\rm CO}$ on $A_V$. Assuming that the probability distribution function (PDF) of local Milky Way clouds is universal, this approach predicts a dependence of \xco\ on $Z$ between $Z^{-1}$ and $Z^{-2}$ above about a third solar metallicity. Below this metallicity, CO emerges from only the high column density parts of the cloud and so depends very sensitively on the adopted PDF and the H$_2$/{\sc Hi} prescription. The PDF of low metallicity clouds is thus of considerable interest and the uncertainty associated with even an ideal prescription for \xco\ at very low metallicity will be large., 20 pages, 11 figures, submitted to MNRAS

Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations, they are molecular with H2 the dominant species and CO the best available. When the abundances of carbon and oxygen are low compared to hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies CO forms slowly and is easily destroyed, so it cannot accumulate inside dense clouds. Then we lose our ability to trace the gas in regions of star formation and we lose critical information on the temperatures, densities, and velocities of the material that collapses. I will report on high resolution observations with ALMA of CO clouds in the local group dwarf irregular galaxy WLM, which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold and the properties derived of very small dense CO clouds mapped..

New sensitive CO(2-1) observations of the 30 Doradus region in the Large Magellanic Cloud are presented. We identify a chain of three newly discovered molecular clouds we name KN1, KN2 and KN3 lying within 2--14 pc in projection from the young massive cluster R136 in 30 Doradus. Excited H$_2$ 2.12$\mu$m emission is spatially coincident with the molecular clouds, but ionized Br$\gamma$ emission is not. We interpret these observations as the tails of pillar-like structures whose ionized heads are pointing towards R136. Based on infrared photometry, we identify a new generation of stars forming within this structure., Comment: Accepted for publication in ApJ (includes 13 pages, 8 figures). For higher resolution figures please see http://www.das.uchile.cl/~vkalari/staplervk.pdf

We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII region radiative transfer. We confirm that in the higher-metallicity Large Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in the nebular Lyman continuum: objects identified as optically thin candidates based on nebular ionization structure show 6 times lower median 8-mic surface brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2 mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively), which is driven by the association between the very small dust grains and higher density gas found at higher nebular optical depths. In contrast, PAH and dust formation in the low-metallicity Small Magellanic Cloud is strongly inhibited such that we find no variation in either 8-mic or 24-mic emission between our optically thick and thin samples. This is attributable to extremely low PAH and dust production together with high, corrosive UV photon fluxes in this low-metallicity environment. The dust mass surface densities and gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey data support this interpretation., Comment: Accepted to ApJ, May 15, 2017. 10 pages, 9 figures

Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations, they are molecular with H_2 the dominant species and CO the best available tracer. When the abundances of carbon and oxygen are low compared to hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies, CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds. Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H_2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact., 10 pages, 3 figures

The Magellanic Clouds provide the only laboratory to study the effect of metallicity and galaxy mass on molecular gas and star formation at high (~20 pc) resolution. We use the dust emission from HERITAGE Herschel data to map the molecular gas in the Magellanic Clouds, avoiding the known biases of CO emission as a tracer of H$_{2}$. Using our dust-based molecular gas estimates, we find molecular gas depletion times of ~0.4 Gyr in the LMC and ~0.6 SMC at 1 kpc scales. These depletion times fall within the range found for normal disk galaxies, but are shorter than the average value, which could be due to recent bursts in star formation. We find no evidence for a strong intrinsic dependence of the molecular gas depletion time on metallicity. We study the relationship between gas and star formation rate across a range in size scales from 20 pc to ~1 kpc, including how the scatter in molecular gas depletion time changes with size scale, and discuss the physical mechanisms driving the relationships. We compare the metallicity-dependent star formation models of Ostriker, McKee, and Leroy (2010) and Krumholz (2013) to our observations and find that they both predict the trend in the data, suggesting that the inclusion of a diffuse neutral medium is important at lower metallicity., Comment: 24 pages, 14 figures, accepted for publication in ApJ. FITS files of the dust-based estimates of the H2 column densities for the LMC and SMC (shown in Figures 2 and 3) will be available online through ApJ

Aims. We present a multiwavelength analysis of the infrared dust bubble S 24 and the extended IR sources G341.220-0.213 and G341.217-0.237 located in its environs. We aim to investigate the characteristics of the molecular gas and the interstellar dust linked to them and analyze the evolutionary state of the young stellar objects identified there and the relation of the bubble to S 24 and the IR sources. Methods. Using the APEX telescope, we mapped the molecular emission in the CO(2-1), 13CO(2-1), C18O(2-1), and 13CO(3-2) lines in a region of about 5′ × 5′ in size around the bubble. The cold dust distribution was analyzed using submillimeter continuum images from ATLASGAL and Herschel. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium in the region. Results. The molecular gas distribution shows that gas linked to the S 24 bubble and to G341.220-0.213 and G341.217-0.237 has velocities of between -48.0 km s-1 and -40.0 km s-1, compatible with the kinematical distance of 3.7 kpc that is generally adopted for the region. The gas distribution reveals a shell-like molecular structure of ∼0.8 pc in radius bordering the S 24 bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel-SPIRE images. The weak extended emission at 24 μm from warm dust and radio continuum emission projected inside the bubble indicates exciting sources and that the bubble is a compact Hii region. Part of the molecular gas bordering the S 24 Hii region coincides with the extended infrared dust cloud SDC341.194-0.221. A molecular and cold dust clump is present at the interface between the S 24 Hii region and G341.217-0.237, shaping the eastern border of the IR bubble. The arc-like molecular structure encircling the northern and eastern sections of the IR source G341.220-0.213 indicates that the source is interacting with the molecular gas. The analysis of the available IR point source catalogs reveals some young stellar object candidates linked to the IR-extended sources, thus confirming their nature as active star-forming regions. Gas and dust masses were estimated for the different features. The total gas mass in the region and the H2 ambient density amount to 10 300 M⊙ and 5900 cm-3, indicating that G341.220-0.213, G341.217-0.237, and the S 24 Hii region are evolving in a high-densit © ESO, 2015., Facultad de Ciencias Astronómicas y Geofísicas

We combine Spitzer and Herschel data of the star-forming region N11 in the Large Magellanic Cloud to produce detailed maps of the dust properties in the complex and study their variations with the ISM conditions. We also compare APEX/LABOCA 870um observations with our model predictions in order to decompose the 870um emission into dust and non-dust (free-free emission and CO(3-2) line) contributions. We find that in N11, the 870um can be fully accounted for by these 3 components. The dust surface density map of N11 is combined with HI and CO observations to study local variations in the gas-to-dust mass ratios. Our analysis leads to values lower than those expected from the LMC low-metallicity as well as to a decrease of the gas-to-dust mass ratio with the dust surface density. We explore potential hypotheses that could explain the low observed gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas or of optically thick HI or variations in the dust abundance in the dense regions). We finally decompose the local SEDs using a Principal Component Analysis (i.e. with no a priori assumption on the dust composition in the complex). Our results lead to a promising decomposition of the local SEDs in various dust components (hot, warm, cold) coherent with that expected for the region. Further analysis on a larger sample of galaxies will follow in order to understand how unique this decomposition is or how it evolves from one environment to another., 24 pages, 16 figures, accepted for publication in MNRAS

We present the results of a new study of the molecular gas associated with the "extended green object" (EGO) G35.03+0.35. This object, very likely a massive young stellar object, is embedded in a molecular cloud at the border of an HII region. The observations were performed with the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO and 13CO J=3-2, HCO+ J=4-3, and CS J=7-6 lines with an angular resolution about 22". From the 12CO J=3-2 line we discovered outflowing activity of the massive young stellar object. We obtained a total mass and kinetic energy for the outflows of 30 M_sun and 3000 M_sun (km/s)^2 (6 x 10^{46} ergs), respectively. We discovered a HCO+ and CS clump towards the EGO G35.03+0.35. The detection of these molecular species supports the presence of molecular outflows and a dense molecular envelope with temperatures and densities above 40 K and 6 x 10^{6} cm^{-3}, respectively. Using public near- and mid-IR, and sub-mm data we investigated the spectral energy distribution confirming that EGO G35.03+0.35 is a massive young stellar object at the earliest evolutionary stage (i.e. a class I young stellar object). By anlysing radio continuum archival data we found three radio sources towards the object, suggesting the presence of several young stellar objects in the region. Our radio continuum analysis is consistent with the presence of at least one ultracompact HII region and an hypercompact HII region or a constant-velocity ionized wind source.

We present HK spectra of three sources located in the N66 region of the Small Magellanic Cloud. The sources display prominent stellar Br Gamma and extended H2 emission, and exhibit infrared excesses at lambda > 2 micron. Based on their spectral features, and photometric spectral energy distributions, we suggest that these sources are massive young stellar objects (mYSOs). The findings are interpreted as evidence of on-going high mass star formation in N66., Accepted for publication on Astronomy and Astrophysics Journal, acceptance date 21/03/2018 (includes 12 pages, 5 figures)

The amount of molecular gas is a key for understanding the future star formation in a galaxy. However, this quantity is difficult to infer as the cold H2 is almost impossible to observe and, especially at low metallicities, CO only traces part of the clouds, keeping large envelopes of H2 hidden from observations. In this context, millimeter dust emission tracing the cold and dense regions can be used as a tracer to unveil the total molecular gas masses. I present studies of a sample of giant molecular clouds in the Small Magellanic Cloud. These clouds have been observed in the millimeter and sub-millimeter continuum of dust emission: with SIMBA/SEST at 1.2 mm and the new LABOCA bolometer on APEX at 870 μm. Combining these with radio data for each cloud, the spectral energy distribution of dust emission are obtained and gas masses are inferred. The molecular cloud masses are found to be systematically larger than the virial masses deduced from CO emission. Therefore, the molecular gas mass in the SMC has been underestimated by CO observations, even through the dynamical masses. This result confirms what was previously observed by Bot et al. (2007). We discuss possible interpretations of the mass discrepancy observed: in the giant molecular clouds of the SMC, part of cloud's support against gravity could be given by a magnetic field. Alternatively, the inclusion of surface terms in the virial theorem for turbulent clouds could reproduce the observed results and the giant molecular clouds could be transient structures.

Aims. Our goal is to determine the physical properties of molecular gas located in different environments of the SMC – from near the vicinity of hot H II regions to cold, quiescent clouds – via modelling and simulations, and compare with the properties of molecular gas found in similar environments in the LMC. Methods. We present observations of the 12 CO (1–0), (2–1), (3–2), 13 CO (1–0), (2–1), and CS (2–1), (3–2) line emission toward six molecular clouds in the SMC: N 66, N 88, Lirs 36, Lirs 49, Hodge 15, and SMC-B1#1. These data, as well as published data on three clouds of the LMC: 30 Dor-10, N 159-W, and N 159-S, are analysed to estimate gas kinetic temperatures, column densities, and surface filling factors using a Mean Escape Probability approximation of the radiative transfer equations. The solutions are restricted using the $\chi^2$ approach. Results. Assuming that the [ 12 CO/ 13 CO] abundance ratio is similar in both galaxies, we find that the CO and CS column densities of SMC clouds are a magnitude smaller than those of LMC clouds, mirroring the metallicity differences. Our analysis suggests the existence of a lower limit for the 12 CO/ 13 CO isotope ratio of 50 in both galaxies. The surface filling factors of the CO emission in the SMC clouds are a factor of a few smaller than in the LMC and seem to decrease with increasing UV radiation fields, i.e., more vigorous star formation activity. A simple model, which assumes a spherical cloud with uniform physical parameters immersed in the CMB radiation field, provides a reasonably good fit to the observed properties of the (supposedly) quiescent clouds SMC-B1#1 and N 159-S. For all other clouds considered, this model gives large values of $\chi^2$, strongly indicating the need for a more complex model. We present some results from 2-component modelling, e.g., for Lirs 36 a mixture of 20 K gas with high optical depth and a less dense gas with temperatures of 100 K reproduces well the main features of the CO data.

Context. CO observations have been the best way so far to trace molecular gas in external galaxies, but in low metallicity environments the gas mass deduced could be largely underestimated due to enhanced photodissociation of the CO molecule. Large envelopes of H2 could therefore be missed by CO observations. Aims. At present, the kinematic information of CO data cubes are used to estimate virial masses and trace the total mass of the molecular clouds. Millimeter dust emission can also be used as a dense gas tracer and could unveil H2 envelopes lacking CO. These different tracers must be compared in different environments. Methods. This study compares virial masses to masses deduced from millimeter emission, in two GMC samples: the local molecular clouds in our Galaxy (10 4 −10 5 M� ), and their equivalents in the Small Magellanic Cloud (SMC), one of the nearest low metallicity dwarf galaxies. Results. In our Galaxy, mass estimates deduced from millimeter (FIRAS) emission are consistent with masses deduced from gamma ray analysis and therefore trace the total mass of the clouds. Virial masses are systematically larger (twice on average) than mass estimates from millimeter dust emission. This difference decreases toward high masses and has been reported in previous studies. This is not the case for SMC giant molecular clouds: molecular cloud masses deduced from SIMBA millimeter observations are systematically higher (twice on average for conservative values of the dust to gas ratio and dust emissivity) than the virial masses from SEST CO observations. The observed excess cannot be accounted for by any plausible change of dust properties. Taking a general form for the virial theorem, we show that a magnetic field strength of ∼15 µG in SMC clouds could provide additional support for the clouds and explain the difference observed. Conclusions. We conclude that masses of SMC molecular clouds have so far been underestimated. Magnetic pressure may contribute significantly to their support.

[Abridged] We present the analysis of ISOCAM-CVF and NIR photometry data of the HII region complex N4 in LMC. The aim is twofold: 1) to study the connection between the ISM and the star content of this region; 2)to investigate the effects of the lower than galactic metallicity on dust properties. A dust features -- gas lines -- continuum fitting technique on the data, allows the production of images in each single emission and the detailed analysis of dust, and ionized gas. The NIR photometry provides, for the first time, information on the stellar content of N4. The images in single dust feature bands and gas lines clearly show that the HII region core is completely devoid of the carriers responsible for the Aromatic Features (AFs). On the other hand, the ionized gas arises almost completely in this dust cavity, where also the two main exciting stars of N4 are located. We find evidences that the effect of lower than Galactic metallicity on the carriers responsible for the AFs, is not to prevent their formation or to modify their chemical properties, but to enhance their destruction by the high and hard ISRF. We show that this mechanism is more efficient on smaller dust particles/molecules thus affecting the dust-size distribution. We argue that effects on dust--size distribution, rather than thedifferent dust properties due to a lower metallicity, should be taken into account when analyzing more distant relatively low metallicity galaxies. Finally, the analysis of the stellar content of N4 reveals 7 stars: 4 reddened O MS stars and 3 stars with envelopes. In particular, one of these, seems to be an Ultra Compact HII region containing an embedded YSO.

We present the initial results from the Spitzer Survey of the Small Magellanic Cloud (S3MC), which imaged the star-forming body of the Small Magellanic Cloud (SMC) in all seven MIPS and IRAC wavebands. We find that the F_8/F_24 ratio (an estimate of PAH abundance) has large spatial variations and takes a wide range of values that are unrelated to metallicity but anticorrelated with 24 um brightness and F_24/F_70 ratio. This suggests that photodestruction is primarily responsible for the low abundance of PAHs observed in star-forming low-metallicity galaxies. We use the S3MC images to compile a photometric catalog of ~400,000 mid- and far-infrared point sources in the SMC. The sources detected at the longest wavelengths fall into four main categories: 1) bright 5.8 um sources with very faint optical counterparts and very red mid-infrared colors ([5.8]-[8.0]>1.2), which we identify as YSOs. 2) Bright mid-infrared sources with mildly red colors (0.16, Comment: Accepted for publication in The Astrophysical Journal. Given the draconian figure file-size limits implemented in astro-ph, readers are encouraged to download the manuscript with full quality images from http://celestial.berkeley.edu/spitzer/publications/s3mcsurvey.pdf

We present results obtained towards the HII regions N159, N166, and N132 from the emission of several molecular lines in the 345 GHz window. Using ASTE we mapped a 2.4' $\times$ 2.4' region towards the molecular cloud N159-W in the $^{13}$CO J=3-2 line and observed several molecular lines at an IR peak very close to a massive young stellar object. $^{12}$CO and $^{13}$CO J=3-2 were observed towards two positions in N166 and one position in N132. The $^{13}$CO J=3-2 map of the N159-W cloud shows that the molecular peak is shifted southwest compared to the peak of the IR emission. Towards the IR peak we detected emission from HCN, HNC, HCO$^{+}$, C$_{2}$H J=4-3, CS J=7-6, and tentatively C$^{18}$O J=3-2. This is the first reported detection of these molecular lines in N159-W. The analysis of the C$_{2}$H line yields more evidence supporting that the chemistry involving this molecular species in compact and/or UCHII regions in the LMC should be similar to that in Galactic ones. A non-LTE study of the CO emission suggests the presence of both cool and warm gas in the analysed region. The same analysis for the CS, HCO$^{+}$, HCN, and HNC shows that it is very likely that their emissions arise mainly from warm gas with a density between $5 \times 10^5$ to some $10^6$ cm$^{-3}$. The obtained HCN/HNC abundance ratio greater than 1 is compatible with warm gas and with an star-forming scenario. From the analysis of the molecular lines observed towards N132 and N166 we propose that both regions should have similar physical conditions, with densities of about 10$^3$ cm$^{-3}$., Comment: accepted in MNRAS (October 5, 2015)

In this work we present high resolution spectroscopic data of the giant star-forming region of N11, obtained with the GIRAFFE instrument at the Very Large Telescope. By using this data set, we find that most of the H$\alpha$ emission lines profiles in this complex can be fitted by a single Gaussian, however, multiple emission line profiles can be observed in the central region of N11. By adding all the spectra, we derive the integrated H$\alpha$ profile of this complex, which displays a width ($\sigma$) of about 12 km s$^{-1}$ (corrected by instrumental and thermal width). We find that a single Gaussian fit on the integrated H$\alpha$ profile leaves remaining wings, which can be fitted by a secondary broad Gaussian component. In addition, we find high velocity features, which spatially correlate with soft diffuse X-ray emission., Comment: Proceedings of IAU Symposium 309, Vienna, ed. B.L. Ziegler, F. Combes, H. Dannerbauer, M. Verdugo

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.

The rate at which interstellar gas is converted into stars, and its dependence on environment, is one of the pillars on which our understanding of the visible Universe is build. We present a comparison of the surface density of young stars (Sigma_*) and dust surface density (Sigma_d) across NGC346 (N66) in 115 independent pixels of 6x6 pc^2. We find a correlation between Sigma_* and Sigma_d with a considerable scatter. A power law fit to the data yields a steep relation with an exponent of 2.6+-0.2. We convert Sigma_d to gas surface density (Sigma_g) and Sigma_* to star formation rate (SFR) surface densities (Sigma_SFR), using simple assumptions for the gas-to-dust mass ratio and the duration of star formation. The derived total SFR (4+-1 10^-3 M_sun/yr) is consistent with SFR estimated from the Ha emission integrated over the Ha nebula. On small scales the Sigma_SFR derived using Ha systematically underestimates the count-based Sigma_SFR, by up to a factor of 10. This is due to ionizing photons escaping the area, where the stars are counted. We find that individual 36 pc^2 pixels fall systematically above integrated disc-galaxies in the Schmidt-Kennicutt diagram by on average a factor of ~7. The NGC346 average SFR over a larger area (90 pc radius) lies closer to the relation but remains high by a factor of ~3. The fraction of the total mass (gas plus young stars) locked in young stars is systematically high (~10 per cent) within the central 15 pc and systematically lower outside (2 per cent), which we interpret as variations in star formation efficiency. The inner 15 pc is dominated by young stars belonging to a centrally condensed cluster, while the outer parts are dominated by a dispersed population. Therefore, the observed trend could reflect a change of star formation efficiency between clustered and non-clustered star-formation., Accepted for publication in MNRAS

Aims. We present here a study of the cold dust in the close environs of the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, which was probably triggered by the expansion of the ionization front against its environment. Methods. We make use of 870 μm emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 μm emission provides an excellent probe of mass and density of dense molecular clouds. The obtained LABOCA image was compared to archival infrared, radio continuum, and optical images. Results. The 870 μm emission follows the 8 μm (Spitzer), 250 μm, and 500 μm (Herschel) emission distributions showing the classical morphology of a two-dimensional projection of a spherical shell. We use the 870 μm and 250 μm images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 M⊙ and 2800 M⊙, and volume densities between 1.1 × 103 cm-3 and ~2.04 × 105 cm-3. The total mass of the clumps is ~37 600 M⊙. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the Hii region it reaches ~40 K. The clump mass distribution for the sample is fitted by a power law dN/dlog (M/M⊙) ∝ M-α, with α = 0.93 ± 0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 μm emission shows that only 37% of them lie in or above the high-mass star formation threshold. Most of this 37% have candidate YSOs projected inside their limits. A comparison of the dynamical age of the Hii region with the fragmentation time, allowed us to conclude that the collect-and-collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may be acting simultaneously. The position of the identified young stellar objects in the region is also a strong indicator that the collect-and-collapse process is acting., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

We review the present knowledge of molecular line studies and its relation to interstellar medium properties in the Large and Small Magellanic Clouds. The physical and chemical properties of the molecular gas together with the abundance of different molecular species will be discussed.

Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such 'low-metallicity' galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases.

The second largest HII region in the Large Magellanic Cloud, N11B has been surveyed in the near IR.We present JHKs images of the N11B nebula.These images are combined with CO(1-0) emission line data and with archival NTT and HST/WFPC2 optical images to address the star formation activity of the region.IR photometry of all the IR sources detected is given.We confirm that a second generation of stars is currently forming in the N11B region. Our IR images show the presence of several bright IR sources which appear located towards the molecular cloud as seen from the CO emission in the area.Several of these sources show IR colours with YSO characteristics and they are prime candidates to be intermediate-mass Herbig Ae/Be stars.For the first time an extragalactic methanol maser is directly associated with IR sources embedded in a molecular core.Two IR sources are found at 2"(0.5 pc) of the methanol maser reported position.Additionally, we present the association of the N11A compact HII region to the molecular gas where we find that the young massive O stars have eroded a cavity in the parental molecular cloud, typical of a champagne flow. The N11 region turns out to be a very good laboratory for studying the interaction of winds, UV radiation and molecular gas.Several photodissociation regions are found., 11 figures, accepted in Astronomical Journal (April 2003), needs AASTEX package

(Abridged) We present the analysis of the main FIR fine structure lines emission in NGC1313 and NGC6946. We calculate that a component probably associated with the diffuse disks contributes

We study the molecular and the ionized gas in a possible precursor of an UC HII region to contribute to the understanding of how high-mass stars build-up their masses once they have reached the zero-age main secuence. We carried out molecular observations toward the position of the Red MSX source G052.9221-00.4892, using ASTE in the 12CO, 13CO, and C18O J=3-2, and HCO+ J=4-3 lines. We also present radio continuum observations at 6 GHz carried out with the JVLA interferometer. Combining these observations with public infrared data allowed us to inquire about the nature of the source. The analysis of the molecular observations reveals the presence of a kinetic temperature and H2 column density gradients across the molecular clump in which the source is embedded, with the hotter and less dense gas in the inner region. The 12CO J=3-2 emission shows evidence of misaligned massive molecular outflows, with the blue lobe in positional coincidence with a jet-like feature seen at 8 um. The radio continuum emission shows a slightly elongated compact radio source in positional coincidence with the Red MSX source. The polar-like morphology of this compact radio source perfectly matches the hourglass-like morphology exhibited by the source in the Ks-band. The axes of symmetry of the radio source and the near-IR nebula are perfectly aligned. Based on the multiwavelength analysis, we suggest that the analyzed source could be transiting a HC HII region phase, in which the young central star emits winds and ionizing radiation through the poles. By the other hand, according to a comparison between the Br-gamma and the radio flux density, the source would be in a more evolved evolutionary stage of an optically thin UC HII region in photoionization equilibrium. If this is the case, from the radio continuum emission, we can conjecture upon the spectral type of its exciting star which would be a B0.5V., Comment: Accepted in A&A. August 22, 2017

The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micron. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power- law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submm excess; defined as the submillimeter (submm) emission above that expected from SMBB models fit to observations < 200 micron. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 micron submm excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our the fitting results shows that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submm excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 +/- 1.7) x 10^5 and (8.3 +/- 2.1) times 10^4 M(sun) for the LMC and SMC, respectively. We find significant correlations between the submm excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations., 20 pages, 9 figures, accepted for publication in the ApJ

Aims. We analyze the distribution of the molecular gas and dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped HII region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and of investigating the evolutionary state of the young stellar objects identified there. Methods. Using the APEX telescope, we mapped the molecular emission in the J = 3-2 transition of three CO isotopologues, 12CO, 13CO and C18O, over a 1. 5 × 1. 5 region around the IRAS position. We also observed the high-density tracers CS and HCO+ toward the source. The cold-dust distribution was analyzed using submillimeter continuum data at 870 μm obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium. Results. The molecular gas distribution reveals a cavity and a shell-like structure of ~0.32 pc in radius centered at the position of the IRAS source, with some young stellar objects projected onto the cavity. The total molecular mass in the shell and the mean H2 volume density are ~40 M and ~(1-2) × 103 cm-3. The cold-dust counterpart of the molecular shell has been detected in the far-IR at 870 μm and in Herschel data at 350 μm. Weak extended emission at 24 μm from warm dust is projected onto the cavity, as well as weak radio continuum emission. Conclusions. A comparison of the distribution of cold and warm dust, and molecular and ionized gas allows us to conclude that a compact HII region has developed in the molecular clump, indicating that this is an area of recent massive star formation. Probable exciting sources capable of creating the compact HII region are investigated. The 2MASS source 10380461-5846233 (MSX G286.3773-00.2563) seems to be responsible for the formation of the HII region.., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and Hα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380{sub −130}{sup +250} ± 3 in the LMC, and 1200{sub −420}{sup +1600} ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M {sub ☉} pc{sup –2} in the LMC and 0.03 M {sub ☉} pc{sup –2} in the SMC, corresponding to A {sub V} ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H{sub 2} conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X {sub CO} to be 6 × 10{sup 20} cm{sup –2} K{sup –1} km{sup –1} s in the LMC (Z = 0.5 Z {sub ☉}) at 15 pc resolution, and 4 × 10{sup 21} cm{sup –2} K{sup –1} km{sup –1} s in the SMC (Z = 0.2 Z {sub ☉})more » at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H{sub 2} in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H{sub 2}. Within the expected 5-20 times Galactic X {sub CO} range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling and observations are required to break the degeneracy between dust grain coagulation, accretion, and CO-dark H{sub 2}. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emission.« less

In order to elucidate star formation in the LMC, we made a complete study of CO clouds with NANTEN. In the present paper, we compare 55 giant molecular clouds (GMCs), whose physical quantities were well determined, with young objects, such as young stellar clusters and H II regions. We find that the GMCs are actively forming stars and clusters; 23 and 40 are found to be associated with the clusters and the H II regions, respectively. The clusters associated with the GMCs are significantly young; ∼ 85% of them are younger than∼ 10Myr. In addition, compact groups of the young clusters are often found at the peak position of the GMCs, e.g., N 159 and N 44, while much looser groups are away from the GMCs. This suggests that the clusters are formed in groups and disperse as they become old. The distributions of the CO, [C II], and UV indicate that the GMCs are likely to be rapidly dissipated within several Myr due to UV photons from the clusters. We also estimate the evolutionary time scale of the GMCs; they form stars in a few Myr after their birth, and form clusters during the next few Myr, and are dissipated in the subsequent few Myr.