Hard X-ray emission from giant molecular clouds NGC 6334 and M17

1999 ◽  
Vol 320 (4-5) ◽  
pp. 323-323 ◽  
Author(s):  
K. Matsuzaki ◽  
Y. Sekimoto ◽  
T. Kamae ◽  
S. Yamamoto ◽  
K. Tatematsu ◽  
...  
1998 ◽  
Vol 188 ◽  
pp. 230-231
Author(s):  
M. Nakano

The signs of the active star formation in the Orion region are mainly found in the direction of the two giant molecular clouds - Ori A and Ori B -. Recent objective prism survey in the Orion region shows large number of Hα emission-line stars distributed outside of the giant molecular clouds (Nakano et al., 1995). Many weak-lined T Tauri star candidates are also discovered by the discrimination analysis of the X-ray sources found in the ROSAT all sky survey (RASS) (Sterzik et al., 1995). Although such huge number of pre-main sequence stars outside of the molecular cloud was not expected, their nature is still in controversial (Neuhäuser, 1997). To know the X-ray properties of these sources in the Orion region, we have carried out the ASCA observations.


2011 ◽  
Vol 740 (2) ◽  
pp. 103 ◽  
Author(s):  
Hirokazu Odaka ◽  
Felix Aharonian ◽  
Shin Watanabe ◽  
Yasuyuki Tanaka ◽  
Dmitry Khangulyan ◽  
...  

2001 ◽  
Vol 372 (2) ◽  
pp. 651-662 ◽  
Author(s):  
L. Sidoli ◽  
S. Mereghetti ◽  
A. Treves ◽  
A. N. Parmar ◽  
R. Turolla ◽  
...  

2003 ◽  
Vol 324 (S1) ◽  
pp. 125-131 ◽  
Author(s):  
Hiroshi Murakami ◽  
Atsushi Senda ◽  
Yoshitomo Maeda ◽  
Katsuji Koyama

1991 ◽  
Vol 148 ◽  
pp. 415-420 ◽  
Author(s):  
R. S. Booth ◽  
Th. De Graauw

In this short review we describe recent new observations of millimetre transitions of molecules in selected regions of the Magellanic Clouds. The observations were made using the Swedish-ESO Submillimetre Telescope, SEST, (Booth et al. 1989), the relatively high resolution of which facilitates, for the first time, observations of individual giant molecular clouds in the Magellanic Clouds. We have mapped the distribution of the emission from the two lowest rotational transitions of 12CO and 13CO and hence have derived excitation conditions for the molecule. In addition, we have observed several well-known interstellar molecules in the same regions, thus doubling the number of known molecules in the Large Magellanic Cloud (LMC). The fact that all the observations have been made under controlled conditions with the same telescope enables a reasonable intercomparison of the molecular column densities. In particular, we are able to observe the relative abundances among the different isotopically substituted species of CO.


Author(s):  
Yingtian Chen ◽  
Hui Li ◽  
Mark Vogelsberger

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.


1983 ◽  
Vol 100 ◽  
pp. 133-134
Author(s):  
Frank N. Bash

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.


2021 ◽  
Vol 502 (2) ◽  
pp. 2364-2380
Author(s):  
Nilanjan Banik ◽  
Jo Bovy ◽  
Gianfranco Bertone ◽  
Denis Erkal ◽  
T J L de Boer

ABSTRACT New data from the Gaia satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyse the stellar density variations in the GD-1 stream and show that they cannot be due to known baryonic structures such as giant molecular clouds, globular clusters, or the Milky Way’s bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses ≈107–$10^9 \ \rm {M}_{\odot }$. We infer a total abundance of dark subhaloes normalized to standard cold dark matter $n_{\rm sub}/n_{\rm sub, CDM} = 0.4 ^{+0.3}_{-0.2}$ (68 per cent), which corresponds to a mass fraction contained in the subhaloes $f_{\rm {sub}} = 0.14 ^{+0.11}_{-0.07} {{\ \rm per\ cent}}$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.


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