Astrophysics of Galaxies (astro-ph.GA)

Abstract: Interstellar dust extinction law is essential for interpreting observations. In this work, we investigate the ultraviolet (UV)--mid-infrared (IR) extinction law of the Taurus molecular cloud and its possible variations. We select 504,988 dwarf stars (4200 K < Teff < 8000 K) and 4,757 giant stars (4200 K < Teff < 5200 K) based on the stellar parameters of Gaia DR3 as tracers. We establish the Teff--intrinsic color relations and determine the intrinsic color indices and color excesses for different types of stars. In the determination of color excess ratios (CERs), we analyze and correct the curvature of CERs and derive the UV--mid-IR CERs of 16 bands. We consider different effective wavelengths for different types of stars when converting CERs to relative extinction, and obtain the extinction law with a better wavelength resolution. In addition, we analyze the possible regional variation of extinction law and derive the average extinction law of Rv=3.13+-0.32 for the Taurus molecular cloud. Only 0.9% of subregions have deviations >3sigma, indicating limited regional variation in the extinction law. We also discuss the effect of Gaia Teff overestimation on the determination of the Taurus extinction law and find that the effect is negligible.

Abstract: Many interstellar complex organic molecules (COMs) are believed to be produced on the surfaces of icy grains at low temperatures. Atomic carbon is considered responsible for the skeletal evolution processes, such as C-C bond formation, via insertion or addition reactions. Before reactions, C atoms must diffuse on the surface to encounter reaction partners; therefore, information on their diffusion process is critically important for evaluating the role of C atoms in the formation of COMs. In situ detection of C atoms on ice was achieved by a combination of photostimulated desorption and resonance enhanced multiphoton ionization methods. We found that C atoms weakly bound to the ice surface diffused approximately above 30 K and produced C2 molecules. The activation energy for C-atom surface diffusion was experimentally determined to be 88 meV (1,020 K), indicating that the diffusive reaction of C atoms is activated at approximately 22 K on interstellar ice. The facile diffusion of C at T > 22 K atoms on interstellar ice opens a previously overlooked chemical regime where the increase in complexity of COMs as driven by C atoms. Carbon addition chemistry can be an alternative source of chemical complexity in translucent clouds and protoplanetary disks with crucial implications in our current understanding on the origin and evolution of organic chemistry in our Universe.

Abstract: An open supercluster (OSC) is defined as a cluster of at least six open clusters (OCs) born from the same giant molecular cloud (GMC). We survey the recent catalogs of OCs based on Gaia data and relevant literature to find 17 OSCs of the third galactic quadrant, along with 190 likely members of them. OSCs are frequent enough to be considered an extra class of objects in the hierarchy of star formation. Some of these supersystems are new and most of them contain more members than previously thought. The detailed study of some OSCs has leaded to the discovery of four new young clusters that are members of them, named Casado-Hendy 2 to 5. In certain instances, subgroups with distinct PMs or 3D positions have been found within an OSC, suggesting the presence of multiple generations of stars formed from several bursts of star formation within the same GMC. OSCs are typically unbound and tend to disintegrate on timescales of 0.1 Gyr. The present results support the Primordial Group hypothesis (Casado 2022) and suggest that globular clusters are not formed from the accretion of open superclusters, at least in the local Universe at late times.

Abstract: We investigate the disk formation process in the TNG50 simulation, examining the profiles of SFR surface density ($\Sigma_{\rm SFR}$), gas inflow and outflow, and the evolution of the angular momentum of inflowing gas particles. The TNG50 galaxies tend to have larger star-forming disks, and also show larger deviations from exponential profiles in $\Sigma_{\rm SFR}$ when compared to real galaxies in the MaNGA (Mapping Nearby Galaxies at APO) survey. The stellar surface density of TNG50 galaxies show good exponential profiles, which is found to be the result of strong radial migration of stars over time. However, this strong radial migration of stars in the simulation produces flatter age profiles in TNG50 disks compared to observed galaxies. The star formation in the simulated galaxies is sustained by a net gas inflow and this gas inflow is the primary driver for the cosmic evolution of star formation, as expected from simple gas-regulator models of galaxies. There is no evidence for any significant loss of angular momentum for the gas particles after they are accreted on to the galaxy, which may account for the large disk sizes in the TNG50 simulation. Adding viscous processes to the disks, such as the magnetic stresses from magneto-rotational instability proposed by Wang & Lilly 2022, will likely reduce the sizes of the simulated disks and the tension with the sizes of real galaxies, and may produce more realistic exponential profiles.