ATOMS: ALMA three-millimeter observations of massive star-forming regions -- XVIII. On the origin and evolution of dense gas fragments in molecular shells of compact HII regions
Fragmentation and evolution for the molecular shells of the compact HII regions are less explored compared to their evolved counterparts. We map nine compact HII regions with a typical diameter of 0.4 pc that are surrounded by molecular shells traced by CCH. Several to a dozen dense gas fragments probed by H13CO+ are embedded in these molecular shells. These gas fragments, strongly affected by the HII region, have a higher surface density, mass, and turbulence than those outside the shells but within the same pc-scale natal clump. These features suggest that the shells swept up by the early HII regions can enhance the formation of massive dense structures that may host the birth of higher-mass stars. We examine the formation of fragments and find that fragmentation of the swept-up shell is unlikely to occur in these early HII regions, by comparing the expected time scale of shell fragmentation with the age of HII region. We propose that the appearance of gas fragments in these shells is probably the result of sweeping up pre-existing fragments into the molecular shell that has not yet fragmented. Taken together, this work provides a basis for understanding the interplay of star-forming sites with an intricate environment containing ionization feedback such as those observed in starburst regions.
The ionization feedback from HII regions modifies the properties of high-mass starless clumps (HMSCs, of several hundred to a few thousand solar masses with a size of ~0.1-1 pc), such as temperature and turbulence, on the clump scale. The question of whether the presence of HII regions modifies the core-scale fragmentation and star formation in HMSCs remains to be explored. We aim to investigate the difference of 0.025 pc-scale fragmentation between candidate HMSCs that are strongly impacted by HII regions and less disturbed ones. We also search for evidence of mass shaping and induced star fo…
We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate Hot Molecular Cores (HMCs) showing rich spectra (N>20lines) of complex organic molecules (COMs) but not associated with H/U…
The study of hyper-compact (HC) or ultra-compact (UC) HII regions is fundamental to understanding the process of massive (> 8 M_sun) star formation. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4 mm Cycle 6 observations to investigate at high angular resolution (~0.050", corresponding to 330 au) the HC HII region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. We used the H30alpha emission and different molecular lines of CH3CN and 13CH3CN to study the kinematics of the ionized and molecular gas, respectively. At the center of the HC HII region,…
We have observed the compact HII region complex nearest to the dynamical center of the Galaxy, G-0.02-0.07, using ALMA in the H42a recombination line, CS J=2-1, H13CO+ J=1-0, and SiO v=0, J=2-1 emission lines, and 86 GHz continuum emission. The HII regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright-half and a dark-half in the recombination line and continuum emission. The absorption features in the molecular emission lines show that HII-A, B and C are located on the near side of the 50 km/s Molecular Cloud (50MC) but HII-D is located on the far s…
Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$α$, He40$α$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$α$ emission. The basic parameters for these UC H{\sc ii} regions such as electron density, emission measure, electron temperature, ionic abundance ratio (n$_{\rm He^+}$/n$_{\rm H^+}$), and line width are derived. The median electron density and the median n$_…
The spectral energy distribution (SED) in the millimetre (mm) to centimetre (cm) range is a useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. While many studies have been carried out towards low- and high-mass protostars, little exists so far about solar-type protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. We focus here on the OMC-2/3 solar-type protostars, which are bounded by nearby HII regions and which are, therefore, potentia…
The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory (OVRO), Atacama Large Millimetric Array (ALMA), and the infrared \textit{Spitzer} observatories, are powerful facilities to study massive star formation regions and related objects such as ultra--compact (UC) \hii regions, molecular clumps, and cores. We used these telescopes to study the \uchiir G43.89--0.78. The morphological study at arcminute scales using NVSS and \textit{Spitzer} data shows that this region is similar to those observed in the \textit{ bubble--like} structures revealed by \textit{Spitzer} observations. …
Electron temperature and emission measure of HII regions in the central molecular zone (CMZ) from H40 αrecombination line and continuum emissions by ALMA CMZ Exploration Survey - ACES -
Institute of Astronomy, The University of Tokyo（东京大学天文学研究所）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；CCosmic Origins Of Life (COOL)（宇宙生命起源中心（COOL））；UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, Oxford Road, The University of Manchester（曼彻斯特大学约德尔银行天体物理学中心英国ALMA区域中心节点）；Department of Astronomy, University of Florida（佛罗里达大学天文学系）；Max Planck Institute for Astronomy（马克斯·普朗克天体物理学研究所）；Center for Astrophysics and Space Astronomy（科罗拉多大学博尔德分校天体物理学与空间天文中心；天体物理与行星科学系）；Department of Astrophysical and Planetary Sciences；University of Colorado, Boulder
This paper presents a multiwavelength investigation of the Galactic HII IRAS 17149$-$3916. Using the Giant Meterwave Radio Telescope, India, first low-frequency radio continuum observations at 610 and 1280 MHz for this region are presented. The ionized gas emission displays an interesting cometary morphology which is likely powered by the early type source, E4 (IRS-1). The origin of the cometary morphology is discussed under the framework of the widely accepted bow shock, champagne flow, and clumpy cloud mechanisms. The mid- and far-infrared data from Spitzer-GLIMPSE and Herschel-Hi-GAL reveal…
We present a detailed characterization of the population of compact radio-continuum sources in W51 A using subarcsecond VLA and ALMA observations. We analyzed their 2-cm continuum, the recombination lines (RL's) H77$α$ and H30$α$, and the lines of $\rm H_{2}CO(3_{0,3}-2_{0,2})$, $\rm H_{2}CO(3_{2,1}-2_{2,0})$, and $\rm SO(6_{5}-5_{4})$. We derive diameters for 10/20 sources in the range $D \sim 10^{-3}$ to $\sim 10^{-2}$ pc, thus placing them in the regime of hypercompact HII regions (HC HII's). Their continuum-derived electron densities are in the range $n_{\rm e} \sim 10^4$ to $10^5$ cm$^{-3…
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 tha…
We present the highest resolution (1") $^{12}$CO(1-0) observations of molecular gas in the dwarf starburst galaxy NGC 625, to date, obtained with ALMA. Molecular gas is distributed in discrete clouds within an area of $0.4$ kpc$^2$ and does not have well-ordered large-scale motions. We measure a total molecular mass in NGC 625 of $5.3\times 10^6 M_\odot$, assuming a Milky Way CO-to-H$_2$ conversion factor. We use the CPROPS package to identify molecular clouds and measure their properties. The 19 resolved CO clouds have a median radius of 20 pc, a median line width 2.5 km s$^{-1}$, and a media…
We present 250~GHz continuum and H29alpha line data toward W49N:A2, a hypercompact HII region ionized by an O9 star. The data obtained with ALMA at a resolution of ~0"05 (600 au) confirmed the presence of an ionized ring with a radius of~700 au inclined by ~50degree (0degree for pole-on). It has a width of ~1000 au and is relatively flat with a scale height of less than several hundred au. The tilted ring, or the apparent ellipse, has a prominent velocity difference between its NW and SE ridges along the minor axis, suggesting that it is expanding in the equatorial plane at a velocity of 13.2 …
We observed the high-mass star-forming region G335.579-0.292 with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz with an angular resolution of 0.3'' ($\sim 1000$ au resolution at the source distance). G335.579-0.292 hosts one of the most massive cores in the Galaxy (G335-MM1). The continuum emission shows that G335-MM1 fragments into at least five sources, while molecular line emission is detected in two of the continuum sources (ALMA1 and ALMA3). We found evidence of large and small scale infall in ALMA1 revealed by an inverse P-Cygni profile and the presence of a blue-shi…
Unveiling Stellar Feedback and Cloud Structure in the $ρ$ Ophiuchi A Region with ALMA and JWST: Discovery of Substellar Cores, C$^{18}$O Striations, and Protostellar Outflows
High-mass stars form in much richer environments than those associated with isolated low-mass stars, and once they reach a certain mass, produce ionised (HII) regions. The formation of these pockets of ionised gas are unique to the formation of high-mass stars (M $>8$ M$_\odot$), and present an excellent opportunity to study the final stages of accretion, which could include accretion through the HII region itself. This study of the dynamics of the gas on both sides of these ionisation boundaries in very young HII regions aims to quantify the relationship between the HII regions and their imme…
Little is known about how high-mass stars form. Around 30\% of the young high-mass stars in the Galaxy are observed at the edges of ionized (HII) regions. Therefore these are places of choice to study the earliest stages of high-mass star formation, especially towards the most massive condensations. High-spatial resolution observations in the millimeter range might reveal how these stars form and how they assemble their mass. We want to study the fragmentation process down to the 0.01~pc scale in the most massive condensation observed at the south-western edge of the HII region RCW~120 where t…
We present multi-scale and multi-wavelength data of the Galactic HII region G25.4-0.14 (hereafter G25.4NW, distance ~5.7 kpc). The SHARC-II 350 micron continuum map displays a hub-filament configuration containing five parsec scale filaments and a central compact hub. Through the 5 GHz radio continuum map, four ionized clumps (i.e., Ia-Id) are identified toward the central hub, and are powered by massive OB-stars. The Herschel temperature map depicts the warm dust emission (i.e., Td ~23-39 K) toward the hub. High resolution Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum m…
We present Karl G. Jansky Very Large Array (VLA) Ka band (33 GHz) and Atacama Large Millimeter Array (ALMA) Band 3 (94.5 GHz) continuum images covering the nucleus and two extranuclear star-forming regions within the nearby galaxy NGC 3627 (M 66), observed as part of the Star Formation in Radio Survey (SFRS). Both images achieve an angular resolution of $\lesssim$2\arcsec, allowing us to map the radio spectral indices and estimate thermal radio fractions at a linear resolution of $\lesssim$90 pc at the distance of NGC 3627. The thermal fraction at 33 GHz reaches unity at and around the peaks o…
During the transition phase from a prestellar to a protostellar cloud core, one or several protostars can form within a single gas core. The detailed physical processes of this transition, however, still remain unclear. We present 1.3 mm dust continuum and molecular line observations with the Atacama Large Millimeter/submillimeter Array (ALMA) toward 43 protostellar cores in the Orion Molecular Cloud Complex ($λ$ Orionis, Orion B, and Orion A) with an angular resolution of $\sim$ 0.35" ($\sim$ 140 au). In total, we detect 13 binary/multiple systems. We derive an overall multiplicity frequency …
Millimeter emission from debris disks around stars of different ages provides constraints on the collisional evolution of planetesimals. We present ALMA 1.3 millimeter observations of a sample of 76 Solar-type stars in the ~115 Myr old Pleiades star cluster. These ALMA observations complement previous infrared observations of this sample by providing sensitivity to emission from circumstellar dust at lower temperatures, corresponding to debris at radii comparable to the Kuiper Belt and beyond. The observations obtain a beam size of 1.5 arcsec (200 au) and a median rms noise of 54 mircoJy/beam,…
Using the Atacama Large Millimetre/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), we observed the Extended Green Object (EGO) G19.01$-$0.03 with sub-arcsecond resolution from 1.05 mm to 5.01 cm wavelengths. Our $\sim0.4''\sim1600$ AU angular resolution ALMA observations reveal a velocity gradient across the millimetre core MM1, oriented perpendicular to the previously known bipolar molecular outflow, that is consistently traced by 20 lines of 8 molecular species with a range of excitation temperatures, including complex organic molecules (COMs). Kinematic modelling s…
We present results of the $^{12}$CO (1--0) mosaic observations of the nearby barred-spiral galaxy M83 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). The total flux is recovered by combining the ALMA data with single-dish data obtained using the Nobeyama 45-m telescope. The combined map covers a $\sim$13 kpc$^{2}$ field that includes the galactic center, eastern bar, and spiral arm with a resolution of \timeform{2''.03} $\times$ \timeform{1''.1} ($\sim$45 pc $\times$ $\sim$25 pc). With a resolution comparable to typical sizes of giant molecular clouds (GMCs), the CO dist…
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of $\mathrm{^{13}CO(J=1-0)}$ line and 104 GHz continuum emission from NGC 604, a giant HII region (GHR) in the nearby spiral galaxy M33. Our high spatial resolution images ( 3.2"$\times$ 2.4", corresponding to $13 \times 10$ pc physical scale) allow us to detect fifteen molecular clouds. We find spatial offsets between the $^{13}CO$ and 104 GHz continuum emission and also detect continuum emission near the centre of the GHR. The identified molecular clouds have sizes ranging from 5-21 pc, linewidths of 0.3-3.0 $\mathrm…
We present a detailed study of the massive star-forming region G35.2-0.74N with ALMA 1.3 mm multi-configuration observations. At 0.2" (440 au) resolution, the continuum emission reveals several dense cores along a filamentary structure, consistent with previous ALMA 0.85 mm observations. At 0.03" (66 au) resolution, we detect 22 compact sources, most of which are associated with the filament. Four of the sources are associated with compact centimeter continuum emission, and two of these are associated with H30α recombination line emission. The H30α line kinematics show ordered motion of the io…
Filaments play an important role in star formation, but the formation process of filaments themselves is still unclear. The high-mass star forming clump G286.21+0.17 (G286 for short) that contains an "L" type filament was thought to undergo global collapse. Our high resolution ALMA band 3 observations resolve the gas kinematics of G286 and reveal two sub-clumps with very different velocities inside it. We find that the "blue profile" (an indicator of gas infall) of HCO+ lines in single dish observations of G286 is actually caused by gas emission from the two sub-clumps rather than gas infall. …
Orion Source I (`SrcI') is the protostar at the center of the Kleinmann-Low Nebula. ALMA observations of SrcI with 0.2" angular resolution were made at 350 and 660 GHz to search for the H26alpha and H21alpha hydrogen recombination lines and to measure the continuum flux densities. The recombination lines were not detected, ruling out the possibility that SrcI is a hypercompact HII region. The deconvolved size of the continuum source is approximately 0.23 x 0.07" (100 x 30 AU); it is interpreted as a disk viewed almost edge-on. Optically thick thermal emission from ~500 K dust is the most plaus…
The ALMA-QUARKS Survey: Properties of Hot Molecular Fragments in the Massive Protocluster IRAS 17233-3606
Yunnan University（云南大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Indian Institute of Astrophysics（印度天体物理研究所）
The star-forming activity in the HII region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 $\times$ 10$^6$ L$_{\odot}$. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India and shows a large expanse of the HII region, spanning $20\times 15$ pc$^2$. The average electron number density in the region is estimated to be $\sim70$ cm$^{-3}$, which suggests an average ionization fraction o…
We report ALMA observations of $^{12}$CO(3-2) and $^{13}$CO(3-2) in the gas-poor dwarf galaxy NGC 5253. These 0.3"(5.5 pc) resolution images reveal small, dense molecular gas clouds that are located in kinematically distinct, extended filaments. Some of the filaments appear to be falling into the galaxy and may be fueling its current star formation. The most intense CO(3-2) emission comes from the central $\sim$100 pc region centered on the luminous radio-infrared HII region known as the supernebula. The CO(3-2) clumps within the starburst region are anti-correlated with H$α$ on $\sim$5 pc sca…
We present the results based on the 2.5 arcsec-resolution observations using Atacama Large Millimeter/submillimeter Array (ALMA) of the Galactic Center Molecular Cloud G-0.02-0.07, or the 50 km/s Molecular Cloud (50MC), in the SO (N_J=2_2-1_1) line and 86-GHz continuum emission, the combination of which is considered to trace "hot molecular core candidates" (HMCCs) appearing in the early stage of massive star formation. In the 86-GHz continuum image, we identified nine dust cores in the central part of the 50MC, in which four famous compact HII regions are located. No new ultra-compact HII reg…
To unravel the star formation process, we present a multi-scale and multi-wavelength study of the filamentary infrared dark cloud (IRDC) G333.73+0.37, which hosts previously known two HII regions located at its center. Each HII region is associated with a mid-infrared source, and is excited by a massive OB star. Two filamentary structures and a hub-filament system (HFS) associated with one HII region are investigated in absorption using the Spitzer 8.0 $μ$m image. The $^{13}$CO(J = 2-1) and C$^{18}$O(J = 2-1) line data reveal two velocity components (around $-$35.5 and $-$33.5 km s$^{-1}$) tow…
We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from the optical interferometer GH$α$FaS (Galaxy H$α$ Fabry-Perot System). The two sets of observations have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds (GMCs) and 303 HII regions. We have measured, and compared, their basic physical properties (radius, velocity dispersion, luminosity). For the HII regions, we find two physical regimes, one for masses $>10^{5.4} \mathrm{M_{\odot}}$ of ionized gas, where …
We present high angular resolution 0.2 arcsec continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220GHz) taken as part of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of 400au the main continuum core is essentially unresolved and isolated from other strong and compact emission peaks. At a resolution of 400au the main continuum core is essentially unresolved and isolated from other strong and compact emission peaks. We detect SiO (5-4) emission that is marginally resolved and el…
The ALMA-IMF Large Program imaged a total noncontiguous area of 53pc2, covering 15 extreme, nearby protoclusters of the Milky Way. They were selected to span relevant early protocluster evolutionary stages. Our 1.3mm and 3mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of 0.2 and 0.6Msun, respectively, with a matched spatial resolution of 2000au. We also detect lines that probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores. We classify ALMA-IMF protoclusters as Young, Inter…
With the aim of understanding the role of outflows in star formation, we performed a statistical study of the physical parameters of outflows in eleven massive protoclusters associated with ultra-compact HII regions. A total of 106 outflow lobes are identified in these protoclusters using the ALMA CO (3-2), HCN (4-3) and HCO+ (4-3) line observations. Although the position angles of outflow lobes do not differ in these three tracers, HCN and HCO+ tend to detect lower terminal velocity of the identified outflows compared to CO. The majority of the outflows in our targets are young with typical d…
