Home > VLBIコロキウム | 国立天文台野辺山談話会 > 2013.2.18-2.24

# 2013.2.18-2.24

## 2月20日(水)

キャンパス

セミナー名
VLBIコロキウム

2月20日（水曜日）15時00分～16時00分

タイトル
ALMA observations for Orion-KL region
Abstract
Orion-KL is one of the most-studied massive star forming region. Especially, maser observations with VLBI have revealed the kinematics of disk/outflow system around Source I. However, there are still unsolved-problems such as the origin of high-velocity outflow in this region and the relationship between Source I and high-velocity outflow. Recently, ALMA observations are shedding light on the complex kinematics of outflows in this region. I will briefly summarize the VLBI observations toward Orion-KL, and introduce some studies with ALMA of this region.

名前：志野 渚

テレビ参加：可能

## 2月21日(木)

キャンパス

セミナー名

2月21日（木曜日）16時00分～17時00分

ヘリオ会議室

タイトル
Giant Molecular Clouds Formation in a Barred Galaxy
Abstract
Star formation is one of the key processes governing the evolution of galaxies. Many observations of nearby disk galaxies indicate an empirical relation, the Kennicutt-Schmidt relation, between the gas surface density and the star formation rate surface density. However, with the advance of higher resolution observations, it has been seen that barred galaxies show different star formation activity in the bar and spiral arm regions, even if the gas surface density is comparable in both areas(Momose et al. 2010). What is the physical process that creates this difference? Almost all stars are formed in giant molecular clouds (GMCs). The properties of the GMCs, the number of the GMCs, or the interaction between the GMCs might therefore be suspected to be quite different in these regions of the galaxies. We performed a three-dimensional hydrodynamical simulation of the nearby barred galaxy M83 (NGC5236) using $\it{Enzo}$, an adaptive mesh refinement code. We analysed the properties of the GMCs in the bar, spiral arm, disc, and inter-arm region. We found that there were differences in the properties of clouds in each regions. The one-dimensional velocity dispersion and the virial parameter, which is the measure of gravitational binding of clouds, are highest in the bar region. Also, the number of clouds is highest in the bar region. To make the formation and the evolution of GMCs clear, we tracked the motion of all GMCs in the galaxy and calculated the cloud formation rate, cloud-cloud merger rate, and cloud dissipation rate. The merger rate is highest in the bar region and the time scale for a cloud merger is about 12 Myr. Using the analytical star formation models, we compared our Kennicutt-Schmidt relations and observational results. We used three star formation models based on conversion of gas from free-fall collapse, GMC turbulence and cloud-cloud collisions. All three models agreed well with the observed Kennicutt-Schmidt relation. These difference in the cloud properties, the number of clouds, and the number of cloud collisions are a possible explanation for the difference in star formation activity in a barred galaxy.

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