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811. ALMA observations of LESS submm galaxies
ID:
ivo://CDS.VizieR/J/ApJ/768/91
Title:
ALMA observations of LESS submm galaxies
Short Name:
J/ApJ/768/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870{mu}m survey with ALMA (ALESS) has produced maps ~3x deeper and with a beam area ~200x smaller than the original LESS observations, doubling the current number of interferometrically-observed submillimeter sources. The high resolution of these maps allows us to resolve sources that were previously blended and accurately identify the origin of the submillimeter emission. We discuss the creation of the ALESS submillimeter galaxy (SMG) catalog, including the main sample of 99 SMGs and a supplementary sample of 32 SMGs. We find that at least 35% (possibly up to 50%) of the detected LABOCA sources have been resolved into multiple SMGs, and that the average number of SMGs per LESS source increases with LESS flux density. Using the (now precisely known) SMG positions, we empirically test the theoretical expectation for the uncertainty in the single-dish source positions. We also compare our catalog to the previously predicted radio/mid-infrared counterparts, finding that 45% of the ALESS SMGs were missed by this method. Our ~1.6" resolution allows us to measure a size of ~9kpcx5kpc for the rest-frame ~300{mu}m emission region in one resolved SMG, implying a star formation rate surface density of 80M_{sun}_/yr/kpc2, and we constrain the emission regions in the remaining SMGs to be <10kpc. As the first statistically reliable survey of SMGs, this will provide the basis for an unbiased multiwavelength study of SMG properties.
812. ALMA obs. of ethyl formate toward Orion KL
ID:
ivo://CDS.VizieR/J/ApJ/871/251
Title:
ALMA obs. of ethyl formate toward Orion KL
Short Name:
J/ApJ/871/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies. We wish to explore more organic molecules with increasing complexity in this region. In particular, we have searched for one of the most complex organic molecules detected in space so far, ethyl formate (C_2_H_5_OCHO). This species is the next step in chemical complexity after the simplest member of esters (methyl formate, CH_3_OCHO). The mechanisms leading to its formation are still poorly known. We have used high angular resolution (~1.5") ALMA observations covering a large bandwidth from 214 to 247GHz. We have detected 82 unblended lines of C_2_H_5_OCHO (49 and 33 of the trans- and gauche- conformers, respectively). The line images showed that C2H5OCHO arises mainly from the compact ridge and the hot core-southwest regions. The derived rotational temperatures and column densities are 122+/-34K, (0.9+/-0.3)x10^16^cm^-2^ for the hot core-SW, and 103+/-13K, (0.6+/-0.3)x10^16^cm^-2^ for the compact ridge. The comparison of spatial distribution and abundance ratios with chemically related molecules (methyl formate, ethanol, and formic acid) indicates that C_2_H_5_OCHO is likely formed on the surface of dust grains by addition of CH_3_ to functional-group radicals (CH_2_OCHO) derived from methyl formate (CH_3_OCHO).
813. ALMA obs. of giant molecular clouds in Hen 2-10
ID:
ivo://CDS.VizieR/J/ApJ/876/141
Title:
ALMA obs. of giant molecular clouds in Hen 2-10
Short Name:
J/ApJ/876/141
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new ^12^CO (J=1-0) observations of He 2-10, a blue compact dwarf galaxy about 8.7Mpc away, taken with the Atacama Large Millimeter Array. These are the highest spatial and spectral resolution observations, to date, of the molecular gas in this starburst galaxy. We measure a molecular mass of (1.2+/-0.4)x10^8^M_{sun}_ in He 2-10, and 75% of the molecular gas mass is contained within the northern region of the galaxy near the previously identified young super star clusters, which has a projected size of about 300pc. We use the CPROPS algorithm to identify 119 resolved giant molecular clouds distributed throughout the galaxy, and the molecular gas contained within these clouds makes up between 45% and 70% of the total molecular mass. The molecular clouds in He 2-10 have similar median sizes (~26pc), luminous masses (~4x10^5^M_{sun}_), and surface densities (~180M_{sun}_/pc^2^) to Milky Way clouds. However, He 2-10 clouds have velocity dispersions (~3km/s) about 50% higher than those in the Milky Way. We provide evidence that He 2-10 clouds tend to be in virial equilibrium, with the virial and luminous masses scaling according to M_vir_{propto}M_lum_^1.2+/-0.1^, similar to clouds in the Milky Way. However, we measure a scaling relationship between luminous mass and size, M_lum_{propto}R^3.0+/-0.3^, that is steeper than what is observed in Milky Way clouds. Assuming that He 2-10 molecular clouds are virialized, we infer values of the CO-to-H_2_ conversion factor ranging from 0.5 to 13 times the standard value in the solar neighborhood. Given star formation efficiencies as low as 5%, the most massive molecular clouds in He 2-10 currently have enough mass to form the next generation of super star clusters in the galaxy.
814. ALMA obs. of massive clouds in the CMZ
ID:
ivo://CDS.VizieR/J/ApJ/894/L14
Title:
ALMA obs. of massive clouds in the CMZ
Short Name:
J/ApJ/894/L14
Date:
19 Jan 2022 13:10:58
Publisher:
CDS
Description:
We report Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 continuum observations of 2000au resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy. To study gas fragmentation, we use the dendrogram method to identify cores as traced by the dust continuum emission. The four clouds exhibit different fragmentation states at the observed resolution despite having similar masses at the cloud scale (~1-5pc). Assuming a constant dust temperature of 20K, we construct core mass functions of the clouds and find a slightly top-heavy shape as compared to the canonical initial mass function, but we note several significant uncertainties that may affect this result. The characteristic spatial separation between the cores as identified by the minimum spanning tree method, ~10^4^au, and the characteristic core mass, 1-7M_{sun}_, are consistent with predictions of thermal Jeans fragmentation. The three clouds showing fragmentation may be forming OB associations (stellar mass ~10^3^M_{sun}_). None of the four clouds under investigation seem to be currently able to form massive star clusters like the Arches and the Quintuplet (>~10^4^M_{sun}_), but they may form such clusters by further gas accretion onto the cores.
815. ALMA obs. of polarization in the IM Lup disk
ID:
ivo://CDS.VizieR/J/ApJ/860/82
Title:
ALMA obs. of polarization in the IM Lup disk
Short Name:
J/ApJ/860/82
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 870{mu}m ALMA observations of polarized dust emission toward the Class II protoplanetary disk IM Lup. We find that the orientation of the polarized emission is along the minor axis of the disk, and that the value of the polarization fraction increases steadily toward the center of the disk, reaching a peak value of ~1.1%. All of these characteristics are consistent with models of self-scattering of submillimeter-wave emission from an optically thin inclined disk. The distribution of the polarization position angles across the disk reveals that, while the average orientation is along the minor axis, the polarization orientations show a significant spread in angles; this can also be explained by models of pure scattering. We compare the polarization with that of the Class I/II source HL Tau. A comparison of cuts of the polarization fraction across the major and minor axes of both sources reveals that IM Lup has a substantially higher polarization fraction than HL Tau toward the center of the disk. This enhanced polarization fraction could be due a number of factors, including higher optical depth in HL Tau, or scattering by larger dust grains in the more evolved IM Lup disk. However, models yield similar maximum grain sizes for both HL Tau (72{mu}m) and IM Lup (61{mu}m, this work). This reveals continued tension between grain-size estimates from scattering models and from models of the dust emission spectrum, which find that the bulk of the (unpolarized) emission in disks is most likely due to millimeter-sized (or even centimeter-sized) grains.
816. ALMA obs. of polarized dust emission from Ser-emb 8
ID:
ivo://CDS.VizieR/J/ApJ/842/L9
Title:
ALMA obs. of polarized dust emission from Ser-emb 8
Short Name:
J/ApJ/842/L9
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (~80000au) to disk (~100au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvenic (weakly magnetized) to sub-Alfvenic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ~100au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence-not the magnetic field-that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.
817. ALMA obs. of star-forming regions toward NGC6334I
ID:
ivo://CDS.VizieR/J/ApJ/883/129
Title:
ALMA obs. of star-forming regions toward NGC6334I
Short Name:
J/ApJ/883/129
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relative column densities of the structural isomers methyl formate, glycolaldehyde, and acetic acid are derived for a dozen positions toward the massive star-forming regions MM1 and MM2 in the NGC 6334I complex, which are separated by ~4000au. Relative column densities of these molecules are also gathered from the literature for 13 other star-forming regions. In this combined data set, a clear bimodal distribution is observed in the relative column densities of glycolaldehyde and methyl formate. No such distribution is evident with acetic acid. The two trends are comprised of star-forming regions with a variety of masses, suggesting that there must be some other common parameter that is heavily impacting the formation of glycolaldehyde. This is indicative of some demonstrable differentiation in these cores; studying the abundances of these isomers may provide a clue as to the integral chemical processes ongoing in a variety of protostellar environments.
818. ALMA obs. of UDS and GOODS-S massive galaxies
ID:
ivo://CDS.VizieR/J/ApJ/901/74
Title:
ALMA obs. of UDS and GOODS-S massive galaxies
Short Name:
J/ApJ/901/74
Date:
18 Feb 2022 09:10:36
Publisher:
CDS
Description:
We present 0.2 resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations at 870um in a stellar mass-selected sample of 85 massive (M*>10^11^M_{sun}_) star-forming galaxies (SFGs) at z=1.9-2.6 in the CANDELS/3D-Hubble Space Telescope fields of UDS and GOODS-S. We measure the effective radius of the rest-frame far-infrared (FIR) emission for 62 massive SFGs. They are distributed over wide ranges of FIR size from R_e,FIR_=0.4kpc to R_e,FIR_=6kpc. The effective radius of the FIR emission is smaller by a factor of 2.3_-1.0_^+1.9^ than the effective radius of the optical emission and is smaller by a factor of 1.9_-1.0_^+1.9^ than the half-mass radius. Taking into account potential extended components, the FIR size would change only by ~10%. By combining the spatial distributions of the FIR and optical emission, we investigate how galaxies change the effective radius of the optical emission and the stellar mass within a radius of 1kpc, M_1kpc_. The compact starburst puts most of the massive SFGs on the mass-size relation for quiescent galaxies (QGs) at z~2 within 300Myr if the current star formation activity and its spatial distribution are maintained. We also find that within 300Myr, ~38% of massive SFGs can reach the central mass of M_1kpc_=10^10.5^M_{sun}_, which is around the boundary between massive SFGs and QGs. These results suggest an outside-in transformation scenario in which a dense core is formed at the center of a more extended disk, likely via dissipative in-disk inflows. Synchronized observations at ALMA 870um and James Webb Space Telescope 3-4um will explicitly verify this scenario.
819. ALMA obs. of 70um dark high-mass clumps (ASHES)
ID:
ivo://CDS.VizieR/J/ApJ/886/102
Title:
ALMA obs. of 70um dark high-mass clumps (ASHES)
Short Name:
J/ApJ/886/102
Date:
08 Mar 2022 13:24:32
Publisher:
CDS
Description:
The ALMA Survey of 70{mu}m dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive (>500M_{sun}_), cold (<=15K), 3.6-70{mu}m dark prestellar clump candidates, embedded in infrared dark clouds, were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We have mosaicked each clump (~1arcmin^2^) in continuum and line emission with the 12m, 7m, and Total Power (TP) arrays at 224GHz (1.34mm), resulting in ~1.2" resolution (~4800au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass (<1M_{sun}_) cores and no high-mass (>30M_{sun}_) prestellar cores (maximum mass 11M_{sun}_). From the prestellar core mass function, we derive a power-law index of 1.17+/-0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.
820. ALMaQUEST. IV. ALMA-MaNGA QUEnching & star formation
ID:
ivo://CDS.VizieR/J/ApJ/903/145
Title:
ALMaQUEST. IV. ALMA-MaNGA QUEnching & star formation
Short Name:
J/ApJ/903/145
Date:
15 Mar 2022
Publisher:
CDS
Description:
The ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey is a program with spatially resolved 12CO(1-0) measurements obtained with the Atacama Large Millimeter Array (ALMA) for 46 galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) DR15 optical integral-field spectroscopic survey. The aim of the ALMaQUEST survey is to investigate the dependence of star formation activity on the cold molecular gas content at kiloparsec scales in nearby galaxies. The sample consists of galaxies spanning a wide range in specific star formation rate (sSFR), including starburst (SB), main-sequence (MS), and green valley (GV) galaxies. In this paper, we present the sample selection and characteristics of the ALMA observations and showcase some of the key results enabled by the combination of spatially matched stellar populations and gas measurements. Considering the global (aperture-matched) stellar mass, molecular gas mass, and star formation rate of the sample, we find that the sSFR depends on both the star formation efficiency (SFE) and the molecular gas fraction (f_H_2__), although the correlation with the latter is slightly weaker. Furthermore, the dependence of sSFR on the molecular gas content (SFE or f_H_2__) is stronger than that on either the atomic gas fraction or the molecular-to-atomic gas fraction, albeit with the small Hi sample size. On kiloparsec scales, the variations in both SFE and f_H_2__ within individual galaxies can be as large as 1-2dex, thereby demonstrating that the availability of spatially resolved observations is essential to understand the details of both star formation and quenching processes.