The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform

Jes K. Jørgensen - One of the best experts on this subject based on the ideXlab platform.

  • Evidence for the start of planet formation in a young circumstellar disk
    Nature Astronomy, 2018
    Co-Authors: Daniel Harsono, Per Bjerkeli, Matthijs H. D. Van Der Wiel, Jon P. Ramsey, Luke T. Maud, Lars E. Kristensen, Jes K. Jørgensen
    Abstract:

    Evidence for the earliest phase of planet formation, dust grain growth, has been seen in the very young and Massive circumstellar disk around low-mass protostar TMC1A. Such systems, still rich in gas, are responsible for the high-mass end of the exoplanet mass distribution. The growth of dust grains in protoplanetary disks is a necessary first step towards planet formation^ 1 . This growth has been inferred from observations of thermal dust emission^ 2 towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to Neptune^ 3 . In contrast, the majority of confirmed exoplanets are heavier than Neptune^ 4 . Given that young protoplanetary disks are more Massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a Massive Reservoir in young disks remains scarce. Here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner ~15 au of a very young (age ~100,000 years) disk around the solar-type protostar TMC1A. By using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. This suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass Reservoir sufficient for giant planet formation. Hence, planet formation starts during the earliest, embedded phases in the life of young stars.

  • Evidence for the start of planet formation in a young circumstellar disk
    Nature Astronomy, 2018
    Co-Authors: Daniel Harsono, Per Bjerkeli, Matthijs H. D. Van Der Wiel, Jon P. Ramsey, Luke T. Maud, Lars E. Kristensen, Jes K. Jørgensen
    Abstract:

    © 2018, The Author(s). The growth of dust grains in protoplanetary disks is a necessary first step towards planet formation1. This growth has been inferred from observations of thermal dust emission2towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to Neptune3. In contrast, the majority of confirmed exoplanets are heavier than Neptune4. Given that young protoplanetary disks are more Massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a Massive Reservoir in young disks remains scarce. Here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner ~15 au of a very young (age ~100,000 years) disk around the solar-type protostar TMC1A. By using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. This suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass Reservoir sufficient for giant planet formation. Hence, planet formation starts during the earliest, embedded phases in the life of young stars.

Geraint Lewis - One of the best experts on this subject based on the ideXlab platform.

  • A Massive Reservoir of low-excitation molecular gas at high redshift
    Nature, 2001
    Co-Authors: Padeli Papadopoulos, Rob Ivison, Chris Carilli, Geraint Lewis
    Abstract:

    Molecular hydrogen (H_2) is an important component of galaxies because it fuels star formation and the accretion of gas onto active galactic nuclei (AGN), the two processes that can generate the large infrared luminosities of gas-rich galaxies^ 1 , 2 . Observations of spectral-line emission from the tracer molecule carbon monoxide (CO) are used to probe the properties of this gas. But the lines that have been studied in the local Universe—mostly the lower rotational transitions of J = 1 → 0 and J = 2 → 1—have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar APM08279+5255 at redshift z = 3.91, using the two lowest excitation lines of ^12CO ( J = 1 → 0 and J = 2 → 1). The maps confirm the presence of hot and dense gas near the nucleus^ 3 , and reveal an extended Reservoir of molecular gas with low excitation that is 10 to 100 times more Massive than the gas traced by the higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may exist in the environments of high-redshift ( z > 3) galaxies.

Daniel Harsono - One of the best experts on this subject based on the ideXlab platform.

  • Evidence for the start of planet formation in a young circumstellar disk
    Nature Astronomy, 2018
    Co-Authors: Daniel Harsono, Per Bjerkeli, Matthijs H. D. Van Der Wiel, Jon P. Ramsey, Luke T. Maud, Lars E. Kristensen, Jes K. Jørgensen
    Abstract:

    Evidence for the earliest phase of planet formation, dust grain growth, has been seen in the very young and Massive circumstellar disk around low-mass protostar TMC1A. Such systems, still rich in gas, are responsible for the high-mass end of the exoplanet mass distribution. The growth of dust grains in protoplanetary disks is a necessary first step towards planet formation^ 1 . This growth has been inferred from observations of thermal dust emission^ 2 towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to Neptune^ 3 . In contrast, the majority of confirmed exoplanets are heavier than Neptune^ 4 . Given that young protoplanetary disks are more Massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a Massive Reservoir in young disks remains scarce. Here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner ~15 au of a very young (age ~100,000 years) disk around the solar-type protostar TMC1A. By using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. This suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass Reservoir sufficient for giant planet formation. Hence, planet formation starts during the earliest, embedded phases in the life of young stars.

  • Evidence for the start of planet formation in a young circumstellar disk
    Nature Astronomy, 2018
    Co-Authors: Daniel Harsono, Per Bjerkeli, Matthijs H. D. Van Der Wiel, Jon P. Ramsey, Luke T. Maud, Lars E. Kristensen, Jes K. Jørgensen
    Abstract:

    © 2018, The Author(s). The growth of dust grains in protoplanetary disks is a necessary first step towards planet formation1. This growth has been inferred from observations of thermal dust emission2towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to Neptune3. In contrast, the majority of confirmed exoplanets are heavier than Neptune4. Given that young protoplanetary disks are more Massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a Massive Reservoir in young disks remains scarce. Here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner ~15 au of a very young (age ~100,000 years) disk around the solar-type protostar TMC1A. By using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. This suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass Reservoir sufficient for giant planet formation. Hence, planet formation starts during the earliest, embedded phases in the life of young stars.

Ya. I. Rodionov - One of the best experts on this subject based on the ideXlab platform.

  • Charge relaxation resistance in the cotunneling regime of multichannel Coulomb blockade: Violation of Korringa-Shiba relation
    Physical Review B, 2015
    Co-Authors: Igor S. Burmistrov, Ya. I. Rodionov
    Abstract:

    We study the low frequency admittance of a small metallic island coupled to a gate electrode and to a Massive Reservoir via a \emph{multi channel} tunnel junction. The ac current is caused by a slowly oscillating gate voltage. We focus on the regime of inelastic cotunneling in which the dissipation of energy (the real part of the admittance) is determined by two-electron tunneling with creation of electron-hole pairs on the island. We demonstrate that at finite temperatures but low frequencies the energy dissipation is ohmic whereas at zero temperature it is super-ohmic. We find that (i) the charge relaxation resistance (extracted from the real part of the admittance) is strongly temperature dependent, (ii) the imaginary and real parts of the admittance do not satisfy the Korringa-Shiba relation. At zero temperature the charge relaxation resistance vanishes in agreement with the recent zero temperature analysis [M. Filippone and C. Mora, Phys. Rev. B {\bf 86}, 125311 (2012) and P. Dutt, T. L. Schmidt, C. Mora, and K. Le Hur, Phys. Rev. B {\bf 87}, 155134 (2013)].

  • Out-of-equilibrium admittance of single electron box under strong Coulomb blockade
    JETP Letters, 2010
    Co-Authors: Ya. I. Rodionov, Igor S. Burmistrov
    Abstract:

    We study admittance and energy dissipation in an out-of-equilibrium single electron box. The system consists of a small metallic island coupled to a Massive Reservoir via single tunneling junction. The potential of electrons in the island is controlled by an additional gate electrode. The energy dissipation is caused by an AC gate voltage. The case of a strong Coulomb blockade is considered. We focus on the regime when electron coherence can be neglected but quantum fluctuations of charge are strong due to Coulomb interaction. We obtain the admittance under the specified conditions. It turns out that the energy dissipation rate can be expressed via charge relaxation resistance and renormalized gate capacitance even out of equilibrium. We suggest the admittance as a tool for a measurement of the bosonic distribution corresponding collective excitations in the system.

  • Charge relaxation resistance in the Coulomb blockade problem
    Physical Review B, 2009
    Co-Authors: Ya. I. Rodionov, Igor S. Burmistrov, A. S. Ioselevich
    Abstract:

    We study the dissipation in a system consisting of a small metallic island coupled to a gate electrode and to a Massive Reservoir via single tunneling junction. The dissipation of energy is caused by a slowly oscillating gate voltage. We compute it in the regimes of weak and strong Coulomb blockade. We focus on the regime of not very low temperatures when electron coherence can be neglected but quantum fluctuations of charge are strong due to Coulomb interaction. The answers assume a particularly transparent form while expressed in terms of specially chosen physical observables. We discovered that the dissipation rate is given by a universal expression in both limiting cases.

Padeli Papadopoulos - One of the best experts on this subject based on the ideXlab platform.

  • A Massive Reservoir of low-excitation molecular gas at high redshift
    Nature, 2001
    Co-Authors: Padeli Papadopoulos, Rob Ivison, Chris Carilli, Geraint Lewis
    Abstract:

    Molecular hydrogen (H_2) is an important component of galaxies because it fuels star formation and the accretion of gas onto active galactic nuclei (AGN), the two processes that can generate the large infrared luminosities of gas-rich galaxies^ 1 , 2 . Observations of spectral-line emission from the tracer molecule carbon monoxide (CO) are used to probe the properties of this gas. But the lines that have been studied in the local Universe—mostly the lower rotational transitions of J = 1 → 0 and J = 2 → 1—have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar APM08279+5255 at redshift z = 3.91, using the two lowest excitation lines of ^12CO ( J = 1 → 0 and J = 2 → 1). The maps confirm the presence of hot and dense gas near the nucleus^ 3 , and reveal an extended Reservoir of molecular gas with low excitation that is 10 to 100 times more Massive than the gas traced by the higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may exist in the environments of high-redshift ( z > 3) galaxies.