- ID:
- ivo://CDS.VizieR/J/A+A/645/A139
- Title:
- ALMA mm observations of VLMS in Taurus
- Short Name:
- J/A+A/645/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of giant planets orbiting very low mass stars (VLMS) and the recent observed substructures in disks around VLMS is challenging planet formation models. Specifically, radial drift of dust particles is a catastrophic barrier in these disks, which prevents the formation of planetesimals and therefore planets. We aim to estimate if structures, such as cavities, rings, and gaps, are common in disks around VLMS and to test models of structure formation in these disks. We also aim to compare the radial extent of the gas and dust emission in disks around VLMS, which can give us insight about radial drift. We studied six disks around VLMS in the Taurus star-forming region using ALMA Band 7 (~340GHz) at a resolution of ~0.1". The targets were selected because of their high disk dust content in their stellar mass regime. Our observations resolve the disk dust continuum in all disks. In addition, we detect the ^12^CO (J=3-2) emission line in all targets and ^13^CO (J=3-2) in five of the six sources. The angular resolution allows the detection of dust substructures in three out of the six disks, which we studied by using UV-modeling. Central cavities are observed in the disks around stars MHO6 (M5.0) and CIDA1 (M4.5), while we have a tentative detection of a multi-ringed disk around J0433. We estimate that a planet mass of 0.1M_Jup_ or 0.4M_Saturn_ is required for a single planet to create the first gap in J0433. For the cavities of MHO6 and CIDA1, a Saturn-mass planet (0.3M_Jup_) is required. The other three disks with no observed structures are the most compact and faintest in our sample, with the radius enclosing 90% of the continuum emission varying between 13-21au. The emission of ^12^CO and ^13^CO is more extended than the dust continuum emission in all disks of our sample. When using the ^12^CO emission to determine the gas disk extension Rgas, the ratio of Rgas/Rdust in our sample varies from 2.3 to 6.0. One of the disks in our sample, CIDA7, has the largest Rgas/Rdust ratio observed so far, which is consistent with models of radial drift being very efficient around VLMS in the absence of substructures. Given our limited angular resolution, substructures were only directly detected in the most extended disks, which represent 50% of our sample, and there are hints of unresolved structured emission in one of the bright smooth sources. Our observations do not exclude giant planet formation on the substructures observed. A comparison of the size and luminosity of VLMS disks with their counterparts around higher mass stars shows that they follow a similar relation .
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/831/125
- Title:
- ALMA 887{mu}m obs. of ChaI star-forming region
- Short Name:
- J/ApJ/831/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887{mu}m survey of the disk population around objects from ~2 to 0.03M_{sun}_ in the nearby ~2Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887{mu}m flux densities into dust disk masses, hereafter M_dust_. We find that the M_dust_-M_*_ relation is steeper than linear and of the form M_dust_{propto}(M_*_)^1.3-1.9^, where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same M_dust_-M_*_ relation, while the 10 Myr old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/126
- Title:
- ALMA observation of 152 1-11Myr aged stars
- Short Name:
- J/ApJ/895/126
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We utilize ALMA archival data to estimate the dust disk size of 152 protoplanetary disks in Lupus (1-3Myr), Chamaeleon I (2-3Myr), and Upper-Sco (5-11Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. We use these 199 homogeneously derived disk sizes to identify empirical disk-disk and disk-host property relations as well as to search for evolutionary trends. In agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. We find that disks in the 2-3Myr old ChaI are not smaller than disks in other regions of similar age, and confirm the Barenfeld et al. finding that the 5-10Myr USco disks are smaller than disks belonging to younger regions. Finally, we find that the outer edge of the solar system, as defined by the Kuiper Belt, is consistent with a population of dust disk sizes which have not experienced significant truncation.
- ID:
- ivo://CDS.VizieR/J/ApJ/783/84
- Title:
- ALMA observations in 107 galaxies at z=0.2-2.5
- Short Name:
- J/ApJ/783/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The use of submillimeter dust continuum emission to probe the mass of interstellar dust and gas in galaxies is empirically calibrated using samples of local star-forming galaxies, Planck observations of the Milky Way, and high-redshift submillimeter galaxies. All of these objects suggest a similar calibration, strongly supporting the view that the Rayleigh-Jeans tail of the dust emission can be used as an accurate and very fast probe of the interstellar medium (ISM) in galaxies. We present ALMA Cycle 0 observations of the Band 7 (350GHz) dust emission in 107 galaxies from z=0.2 to 2.5. Three samples of galaxies with a total of 101 galaxies were stellar-mass-selected from COSMOS to have M_*_=~10^11^M_{sun}_:37 at z~0.4, 33 at z~0.9, and 31 at z=2. A fourth sample with six infrared-luminous galaxies at z=2 was observed for comparison with the purely mass-selected samples. From the fluxes detected in the stacked images for each sample, we find that the ISM content has decreased by a factor ~6 from 1 to 2x10^10^M_{sun}_ at both z=2 and 0.9 down to ~2x10^9^M_{sun}_at z=0.4. The infrared-luminous sample at z=2 shows a further ~4 times increase in M_ISM_compared with the equivalent non-infrared-bright sample at the same redshift. The gas mass fractions are ~2%+/-0.5%, 12%+/-3%, 14%+/-2%, and 53%+/-3% for the four subsamples (z=0.4, 0.9, and 2 and infrared-bright galaxies).
- ID:
- ivo://CDS.VizieR/J/ApJ/813/45
- Title:
- ALMA observations in z~0.5-3 quasars
- Short Name:
- J/ApJ/813/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Atacama Large Millimeter/submillimeter Array (ALMA) 870 {mu}m (345 GHz) data for 49 high-redshift (0.47<z<2.85), luminous (11.7<log(L_bol_/L_{sun}_)<14.2) radio-powerful active galactic nuclei (AGNs), obtained to constrain cool dust emission from starbursts concurrent with highly obscured radiative-mode black hole (BH) accretion in massive galaxies that possess a small radio jet. The sample was selected from the Wide-field Infrared Survey Explorer with extremely steep (red) mid-infrared colors and with compact radio emission from NVSS/FIRST. Twenty-six sources are detected at 870 {mu}m, and we find that the sample has large mid- to far-infrared luminosity ratios, consistent with a dominant and highly obscured quasar. The rest-frame 3 GHz radio powers are 24.7<log(P_3.0GHz_/W/Hz)<27.3 and all sources are radio-intermediate or radio-loud. BH mass estimates are 7.7<log(M_BH_/M_{sun}_)<10.2. The rest-frame 1-5 {mu}m spectral energy distributions are very similar to the "Hot DOGs" (hot dust-obscured galaxies), and steeper (redder) than almost any other known extragalactic sources. ISM masses estimated for the ALMA-detected sources are 9.9<log(M_ISM_/M_{sun}_)<11.75 assuming a dust temperature of 30 K. The cool dust emission is consistent with star formation rates reaching several thousand M_{sun}_/yr, depending on the assumed dust temperature, but we cannot rule out the alternative that the AGN powers all the emission in some cases. Our best constrained source has radiative transfer solutions with approximately equal contributions from an obscured AGN and a young (10-15 Myr) compact starburst.
- ID:
- ivo://CDS.VizieR/J/A+A/556/L1
- Title:
- ALMA observations of 12CO/13CO around R Scl
- Short Name:
- J/A+A/556/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detached-shell source R Scl, displaying CO emission from recent mass loss, in a binary-induced spiral structure as well as in a clumpy shell produced during a thermal pulse, provides a unique laboratory for studying the differences in CO isotope abundances throughout its recent evolution. We observed both the ^12^CO(J=3-2) and the ^13^CO(J=3-2) line using ALMA. We find significant variations in the ^12^CO/^13^CO intensity ratios and consequently in the abundance ratios. The average CO isotope abundance ratio is at least a factor three lower in the shell (~19) than that in the present-day (<~300yr) mass loss (>60). Additionally, variations in the ratio of more than an order of magnitude are found in the shell itself. We attribute these variations to the competition between selective dissociation and isotope fractionation in the shell, of which large parts cannot be warmer than ~35K. However, we also find that the ^12^CO/^13^CO ratio in the present-day mass loss is significantly higher than the ^12^C/^13^C ratio determined in the stellar photosphere from molecular tracers (~19). The origin of this discrepancy is still unclear, but we speculate that it is due to an embedded source of UV-radiation that is primarily photo-dissociating ^13^CO. This radiation source could be the hitherto hidden companion. Alternatively, the UV-radiation could originate from an active chromosphere of R Scl itself. Our results indicate that caution should be taken when directly relating the ^12^CO/^13^CO intensity and ^12^C/^13^C abundance ratios for specific asymptotic giant branch stars, in particular binaries or stars that display signs of chromospheric stellar activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/827/142
- Title:
- ALMA observations of GKM stars in Upper Sco
- Short Name:
- J/ApJ/827/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88mm continuum and ^12^CO J=3-2 line fluxes of disks around low-mass (0.14-1.66M_{sun}_) stars at an age of 5-11Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, five are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area (<~40au), or if the CO is heavily depleted by a factor of at least ~1000 relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of M_dust_{propto}M_*_^1.67+/-0.37^. Disk dust masses in Upper Sco are compared to those measured in the younger Taurus star-forming region to constrain the evolution of disk dust mass. We find that the difference in the mean of log(M_dust_/M*) between Taurus and Upper Sco is 0.64+/-0.09, such that M_dust_/M* is lower in Upper Sco by a factor of ~4.5.
- 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.
- 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).
- 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.
