・・・・・今後の宇宙進化コロキウム/ OUTAP colloquium・・・・・
直近の宇宙進化コロキウム/ Next OUTAP colloquium
Date : 1/24 (Wed) 15:00~
Speaker : Mr. Ryohei Naktani (University of Tokyo)
Title : Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks by Ultraviolet/X-ray Radiation: Metallicity Dependence
Abstract: Protoplanetary disks are thought to have lifetimes of several million years in the solar neighborhood, but recent observations suggest that the disk lifetimes are shorter in a low metallicity environment. We perform a suite of radiation hydrodynamics simulations of photoevaporation of protoplanetary disks to study the disk structure and its long-term evolution of ∼ 10000 years, and the metallicity dependence of mass-loss rate. Our simulations follow hydrodynamics, extreme and far ultra-violet/X-ray radiative transfer, and non-equilibrium chemistry in a self-consistent manner. Dust grain temperatures are also calculated consistently by solving the radiative transfer of the stellar irradiation and grain (re-)emission. We vary the disk gas metallicity over a wide range of 10−4 Z⊙ ≤ Z ≤ 10 Z⊙. Without X-rays, the photoevaporation rate is lower with higher metallicity in the range of 10−0.5 Z⊙ ≲ Z ≲ 10 Z⊙, because dust shielding effectively prevents far-ultraviolet (FUV) photons from penetrating into and heating the dense regions of the disk. The photoevaporation rate sharply declines at even lower metallicities in 10−1.5 Z⊙ ≲ Z ≲ 10−0.5 Z⊙, because FUV photoelectric heating becomes less effective than dust-gas collisional cooling. The temperature in the neutral region decreases, and photoevaporative flows are excited only in an outer region of the disk. At 10−4 Z⊙ ≤ Z ≲ 10−1.5 Z⊙, H I photoionization heating acts as a dominant gas heating process and drives photoevaporative flows at roughly a constant rate. X-ray itself does not drive a photoevaporative flow but it enhances FUV heating and thus photoevaporation rates in low metallicity 10−2.5 Z⊙ ≤ Z ≲ 10−0.5 Z⊙. The typical disk lifetime is shorter at Z = 0.2 Z⊙ than at Z = Z⊙, being consistent with recent observations of the extreme outer galaxy.
Date : 12/21 (Thu) 15:00~
Speaker : Prof. Yoichi Tamura (Nagoya University)
Title : ALMA reveals early metal enrichment in a Lyman break galaxy at z = 8
Abstract: We present the Atacama Large Millimeter/submillimeter Array (ALMA) detection of the [O III] 88 um line and dust continuum emission in a z ~ 8 Lyman break galaxy (LBG) lying behind the Frontier Field cluster MACS J0416.1-2403. This [O III] detection confirms the spectroscopic redshift of the LBG to be z = 8.3118 ± 0.0003, making this galaxy one of the furtherst galaxies ever identified spectroscopically. The delensed 850 um flux density of 0.1 mJy corresponds to a far-infrared (FIR) luminosity of 1.7 * 10^11 L_Sun if assuming a dust temperature of T_dust = 50 K and an emissivity index of beta = 1.5, yielding a large dust mass of 4 * 10^6 M_Sun. The apparent [O III] flux and line width are 71 ± 17 mJy km s^-1 and 141 ± 21 km s^-1, respectively. The inferred [O III]-to-FIR luminosity ratio is very low (~ 1 * 10^-3) and is comparable to dusty starbursts even if the uncertainty in dust temperature is taken into account. The ultraviolet-to-FIR spectral energy distribution along with the [O III] flux suggests a relatively high metallicity which may attenuates ionizing photons while help dust grain growth through interstellar accretion of gas-phase metals.
Date : 12/21 (Thu) 10:30~
Speaker : Mr. Jeong-Gyu Kim (Seoul National University)
Title : Dispersal of Giant Molecular Clouds by UV Radiation Feedback from Massive Stars
Abstract: Almost all stars in the present-day universe are believed to form in clusters embedded in giant molecular clouds. Although scarce in numbers, massive stars profoundly affect the evolution of natal clouds by emitting copious UV photons that excite H II regions and drive their expansion. In this talk, I will present results of radiation hydrodynamic simulations of star cluster formation in turbulent molecular clouds. I will focus on the effects of photoionization and radiation pressure on regulating the net star formation efficiency and lifetime of clouds, as well as their relative dominance in a range of environments.
コロキウムの予定表はこちら/ Schedule of colloquium
・・・・・過去の宇宙進化コロキウム/ Previous OUTAP colloquium・・・・・
2017年度の宇宙進化コロキウム/OUTAP colloquium (2017)