Dust masses of young disks: constraining the initial solid reservoir for planet formation

Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk mass distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ9 mm = 0.28 cm2 g−1, the median dust masses of the embedded disks in Perseus are 158 M⊕ for Class 0 and 52 M⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M⊕ and 12 M⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ1.3 mm = 2.3 cm2 g−1. The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.

Unveiling the physical conditions of the youngest disks

Context. Protoplanetary disks have been studied extensively, both physically and chemically, to understand the environment in which planets form. However, the first steps of planet formation are likely to occur already when the protostar and disk are still embedded in their natal envelope. The initial conditions for planet formation may thus be provided by these young embedded disks, of which the physical and chemical structure is poorly characterized. Aims. We aim to constrain the midplane temperature structure, one of the critical unknowns, of the embedded disk around L1527. In particular, we set out to determine whether there is an extended cold outer region where CO is frozen out, as is the case for Class II disks. This will show whether young disks are indeed warmer than their more evolved counterparts, as is predicted by physical models. Methods. We used archival ALMA data of 13CO J = 2–1, C18O J = 2–1 and N2D+J = 3–2 to directly observe the midplane of the near edge-on L1527 disk. The optically thick CO isotopologues allowed us to derive a radial temperature profile for the disk midplane, while N2D+, which can only be abundant when CO is frozen out, provides an additional constraint on the temperature. Moreover, the effect of CO freeze-out on the 13CO, C18O and N2D+ emission was investigated using 3D radiative transfer modeling. Results. Optically thick 13CO and C18O emission is observed throughout the disk and inner envelope, while N2D+ is not detected. Both CO isotopologues have brightness temperatures ≳25 K along the midplane. Disk and envelope emission can be disentangled kinematically, because the largest velocities are reached in the disk. A power law radial temperature profile constructed using the highest midplane temperature at these velocities suggest that the temperature is above 20 K out to at least 75 au, and possibly throughout the entire 125 au disk. The radiative transfer models show that a model without CO freeze-out in the disk matches the C18O observations better than a model with the CO snowline at ~70 au. In addition, there is no evidence for a large (order of magnitude) depletion of CO. Conclusions. The disk around L1527 is likely to be warm enough to have CO present in the gas phase throughout the disk, suggesting that young embedded disks can indeed be warmer than the more evolved Class II disks.

Unveiling the physical and chemical conditions in the young disk around L1527

Planets form in disks around young stars. The planet formation process may start when the protostar and disk are still deeply embedded within their infalling envelope. However, unlike more evolved protoplanetary disks, the physical and chemical structure of these young embedded disks are still poorly constrained. We have analyzed ALMA data for 13CO, C18O and N2D+ to constrain the temperature structure, one of the critical unknowns, in the disk around L1527. The spatial distribution of 13CO and C18O, together with the kinetic temperature derived from the optically thick 13CO emission and the non-detection of N2D+, suggest that this disk is warm enough (≳ 20 K) to prevent CO freeze-out.

Homology stability for symmetric diffeomorphism and mapping class groups

For any smooth compact manifold W with boundary of dimension of at least two we prove that the classifying spaces of its group of diffeomorphisms which fix a set of k points or k embedded disks (up to permutation) satisfy homology stability. The same is true for so-called symmetric diffeomorphisms of W connected sum with k copies of an arbitrary compact smooth manifold Q of the same dimension. The analogues for mapping class groups as well as other generalisations will also be proved.

Embedded disks around low-mass protostars

The time evolution of protostellar disks in the embedded phase of star formation (EPSF) is reviewed based on numerical hydrodynamics simulations of the gravitational collapse of two cloud cores with distinct initial masses. Special emphasis is given to disk, stellar, and envelope masses and also mass accretion rates onto the star. It is shown that accretion is highly variable in the EPSF, in agreement with recent theoretical and observational expectations. Protostellar disks quickly accumulate mass upon formation and may reach a sizeable fraction of the envelope mass (~35%) by the end of the Class 0 phase. Systems with disk-to-star mass ratio ξ≈0.5 are common but systems with ξ≥1.0 are rare because the latter quickly evolve into binary or multiple systems. Embedded disks are characterized by radial pulsations, the amplitude of which increases with growing core mass.

Metallicity gradients in dwarf elliptical galaxies

We discuss the relations between the metallicity gradients and the other characteristics of a set of dwarf elliptical galaxies in different environments. We suggest that dEs have typically metallicity gradients of −0.30 ± 0.25 dex/re, unrelated to their mass. Dwarf elliptical galaxies with embedded disks, or dS0, may have flat metallicity gradients.