Astrofísica

We present an exact γ=5/3 spherical accretion solution which modifies the Bondi boundary condition of ρ→const. as r→∞ to ρ→0 as r→∞. This change allows for simple power law solutions on the density and infall velocity fields, ranging from a cold empty free-fall condition where pressure tends to zero, to a hot hydrostatic equilibrium limit with no infall velocity. As in the case of the Bondi solution, a maximum accretion rate appears. As in the γ=5/3 case of the Bondi solution, no sonic radius appears, this time however, because the flow is always characterised by a constant Mach number. This number equals 1 for the case of the maximum accretion rate, diverges towards the cold empty state, and becomes subsonic towards the hydrostatic equilibrium limit. It can be shown that in the limit as { r→0}, the Bondi solution tends to the new solution presented, { extending the validity of the Bondi accretion value to} cases where the accretion density profile does not remain at a fixed constant value out to infinity. We then explore small deviations from sphericity and the presence of angular momentum through an analytic perturbative analysis. Such perturbed solutions yield a rich phenomenology through density and velocity fields in terms of Legendre polynomials, which we begin to explore for simple angular velocity boundary conditions having zeros on the plane and pole. The new solution presented provides complementary physical insight into accretion problems in general.

The origin of stellar masses is a central open issue in astrophysics. In a pilot survey using ALMA millimeter observations, we showed that in extreme environments of our Galaxy the mass distribution of cores (CMFs) present an excess of high-mass objects compared to the canonical IMF. In this talk, I will introduce the ALMA-IMF Large Program, whose goal is to determine if and how the origin of the IMF depends on the cloud characteristics. Its first results, obtained from a large sample of cores without significant bias, suggest that CMFs of high-mass proto-clusters generally do not follow the canonical IMF. I will also present our detailed ALMA-IMF studies of the W43 molecular complex. We propose that top-heavy CMFs are associated with spatially and temporally limited bursts of star formation. In addition, the identification of molecular outflows in CO(2-1) enables us to assess that a very large fraction of high-mass cores are protostellar, and thus that most cores in this region do not go through a high-mass prestellar core phase. We also find that the slope of the protostellar CMF is significantly flatter than that of the prestellar CMF, which questions the processes of core mass growth.

Title: "Chemical Links among NH2CHO, HNCO, and H2CO in Hot Core Regions" Abstract: Formamide (NH2CHO) is the simplest possible amid and contains a peptide bond that connects amino acids to form proteins. Then, it is important for understanding the formation processes of biological molecules to reveal the chemistry of such a simple amide. We have analyzed ALMA Band 6 data toward 30 high-mass star-forming regions containing hot core(s). We have identified a total of 44 hot cores and investigated chemical links among NH2CHO, HNCO, and H2CO using a partial correlation test. Strong correlation coefficients have been derived for pairs of NH2CHO-HNCO and NH2CHO-H2CO, which means that they are chemically linked. Our chemical simulation can reproduce the observational results, which enables us to reveal their gas-phase chemical links. Title: "Initial results of commissioning observations in 2019 with Band 4 Receiver (B4R) on the LMT 50m telescope" Abstract: We have been working on commissioning observations with the B4R receiver on the LMT 50m telescope. Unfortunately, we could not work at the LMT site during this visit, but we plan to update the B4R system. In this presentation, I'll talk about the update plan of the B4R system and the initial results of mapping observations toward the Orion KL region obtained in the last commissioning in November 2019. Various complex organic molecules(COMs) have been detected in this region, and I have analyzed the chemical composition and distribution. Title: "Bright Extragalactic ALMA Redshift Survey (BEARS): Gas physical properties of the bright Herschel-selected galaxies at high-redshift" We present Atacama Large Millimetre/submillimetre Array (ALMA) Bands 3 and 4 observations of 85 high-redshift 500 μm sources selected from the Herschel Astrophysical Terahertz Large Area Survey with the primary goal of identifying their spectroscopic redshifts. Through the detections of CO, [C I], or H2O emission lines, we have determined reliable spectroscopic redshifts for 71 ALMA continuum sources. We created a deep stacked spectrum spanning 220 to 890 GHz at rest-frame frequencies, and we can identify the faint lines such as HCN(4–3). Stacked results and most of our targets are consistent with the mean CO line ratios for Planck-selected lensed dusty star-forming galaxies shown by Harrington et al. (2021). This result means both galaxy populations have similar gas conditions. Using [C I] (3P1 ‒ 3P0) and CO emission lines as a tracer of molecular gas mass, we investigate the Schmidt-Kennicutt relation and compare it with previous works. We find that our galaxies are not simply scaled-up versions of the normal star-forming systems although have slightly longer depletion time scales than other submillimetre-selected galaxies. Our sources could be biased to bright CO or [CI] luminous, i.e. large amount of molecular gas, however, they could have more extended gas.

NGC628 is the first nearby galaxy for which JWST data became available to the public. The most striking characteristic of the publicly released MIRI image is the presence of a large number of "holes" in an otherwise bright mid-infrared (MIR) emitting disk. This porous structure has given it a popular nickname "phantom galaxy". The "holes" are most often expanding bubbles or superbubbles that are created by the mechanical power output by the massive stars in young star clusters. However, few cases exist where the stellar population that was responsible for the creation of the bubble was unambiguously identified. We here analyze the largest of the bubbles in the JWST/MIRI image of NGC628, measuring 1.3 kpc in diameter to understand the origin of such large bubbles. We combined the JWST NIRCam and MIRI dataset with archival images from the HST, ALMA, VLA and MUSE, to identify the resolved population that might be responsible for the creation of the bubble, and to map the multiphase morphology and kinematics of the gas in the shell surrounding the bubble. The bubble is dominated by the molecular gas and is expanding at 12 km/s velocity. We find conclusive evidence for the presence of a resolved stellar population of ages between 5 to 50 Myr inside the bubble, whose collective mechanical power output is sufficient to explain the presently observed radius, velocity and the shell mass. In the talk, I will discuss the star formation scenario inside the bubble and the conditions that favour the formation of large superbubbles.