Gas is observed to extend far from the disk of the Galaxy, with a scale height that increases with ionization state of the gas. Recent observations have shown that a substantial amount of the halo gas is hot. This gas could be either heated internally, by halo supernovae for example, and/or it could be energized by gas venting from superbubbles in the Galactic disk—a Galactic fountain. Calculation of the UV emission and absorption spectrum of a Galactic fountain shows good agreement with observation; in the absence of conduction, agreement with x‐ray observations requires fine tuning of the initial temperature of the fountain. The superbubbles that provide the mass and energy of the gaseous halo in fountain models are created by OB associations in the disk. A recent calculation of the luminosity distribution of Galactic OB associations is described. The filling factor of superbubbles in the disk is estimated to be of order 0.1; combined with observations of H I and C IV, this suggests a mass flow of sever...
{"title":"Fountains, bubbles, and hot gas","authors":"C. McKee","doi":"10.1063/1.43978","DOIUrl":"https://doi.org/10.1063/1.43978","url":null,"abstract":"Gas is observed to extend far from the disk of the Galaxy, with a scale height that increases with ionization state of the gas. Recent observations have shown that a substantial amount of the halo gas is hot. This gas could be either heated internally, by halo supernovae for example, and/or it could be energized by gas venting from superbubbles in the Galactic disk—a Galactic fountain. Calculation of the UV emission and absorption spectrum of a Galactic fountain shows good agreement with observation; in the absence of conduction, agreement with x‐ray observations requires fine tuning of the initial temperature of the fountain. The superbubbles that provide the mass and energy of the gaseous halo in fountain models are created by OB associations in the disk. A recent calculation of the luminosity distribution of Galactic OB associations is described. The filling factor of superbubbles in the disk is estimated to be of order 0.1; combined with observations of H I and C IV, this suggests a mass flow of sever...","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116302049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Regions of massive star formation can be identified as IRAS point‐like sources with characteristic FIR colors in the Galactic plane. The close association of these sources with molecular clouds provides a way of determining their kinematic distances and therefore luminosities. The mean radial distribution of the FIR luminosity generated by embedded massive stars in the IV Galactic quadrant is strongly peaked at the position of the molecular annulus. The FIR surface luminosity appears to be proportional to the 2nd power of the H2 surface density in the Galactic disk. At least 13% of the total FIR emission from massive star forming molecular clouds is produced in their dense cores, with typical sizes of 1–2 pc, in the close neighborhood of embedded OB stars. We present here a CS (2‐1) map and near‐infrared images of one of such regions, at 5.7 kpc of the Sun, associated with a strongly self‐absorbed CO (1‐0) profile.
{"title":"Massive stars embedded in GMC’s in the southern galaxy","authors":"L. Bronfman, J. May","doi":"10.1063/1.43981","DOIUrl":"https://doi.org/10.1063/1.43981","url":null,"abstract":"Regions of massive star formation can be identified as IRAS point‐like sources with characteristic FIR colors in the Galactic plane. The close association of these sources with molecular clouds provides a way of determining their kinematic distances and therefore luminosities. The mean radial distribution of the FIR luminosity generated by embedded massive stars in the IV Galactic quadrant is strongly peaked at the position of the molecular annulus. The FIR surface luminosity appears to be proportional to the 2nd power of the H2 surface density in the Galactic disk. At least 13% of the total FIR emission from massive star forming molecular clouds is produced in their dense cores, with typical sizes of 1–2 pc, in the close neighborhood of embedded OB stars. We present here a CS (2‐1) map and near‐infrared images of one of such regions, at 5.7 kpc of the Sun, associated with a strongly self‐absorbed CO (1‐0) profile.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116683658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Shear, tides, and cloud formation in spiral arms","authors":"C. Gammie","doi":"10.1063/1.44004","DOIUrl":"https://doi.org/10.1063/1.44004","url":null,"abstract":"","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123364072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have simulated the evolution of a supernova remnant embedded in a galactic magnetic field using 2D numerical MHD. The calculation generalizes the spherically symmetric results of Slavin and Cox (1992) to 2D axisymmetric geometry. We follow the evolution of the remnant for 5×106 yr—sufficiently long for the effects of magnetic shaping and radiative cooling of the hot bubble to become important. We find that: (1) the shock wave becomes increasingly oblate and the hot bubble becomes increasingly prolate with respect to the magnetic axis with time; (2) the radiative shell remains thick except at the magnetic poles due to magnetic pressure support; (3) near the magnetic poles a dense polar cap of HI forms at the bubble apex; (4) a complex shock system including a shock ‘‘dimple’’ forms near the magnetic axis when the shock speed has dropped to slightly greater than the ambient Alfven speed; (5) after 5 Myr the hot bubble collapses to a slender, 400 pc‐long cylinder with T≊107 K.
{"title":"Magnetic shaping of SNRs and their bubbles","authors":"M. Norman","doi":"10.1063/1.43936","DOIUrl":"https://doi.org/10.1063/1.43936","url":null,"abstract":"We have simulated the evolution of a supernova remnant embedded in a galactic magnetic field using 2D numerical MHD. The calculation generalizes the spherically symmetric results of Slavin and Cox (1992) to 2D axisymmetric geometry. We follow the evolution of the remnant for 5×106 yr—sufficiently long for the effects of magnetic shaping and radiative cooling of the hot bubble to become important. We find that: (1) the shock wave becomes increasingly oblate and the hot bubble becomes increasingly prolate with respect to the magnetic axis with time; (2) the radiative shell remains thick except at the magnetic poles due to magnetic pressure support; (3) near the magnetic poles a dense polar cap of HI forms at the bubble apex; (4) a complex shock system including a shock ‘‘dimple’’ forms near the magnetic axis when the shock speed has dropped to slightly greater than the ambient Alfven speed; (5) after 5 Myr the hot bubble collapses to a slender, 400 pc‐long cylinder with T≊107 K.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"217 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134438209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The circular velocity of the thick disc is investigated using data in the 5 dimensional space (V, B‐V, U‐B, μl, μb) in a direction at intermediate latitude. We show that using a discriminant analysis we are able to distinguish the thick disc from the disc and the halo and that these data constrain the asymmetric drift of this population. It is found to be 80±20 km/s at a 2 sigmas level.
{"title":"The circular velocity of the thick disc","authors":"A. Robin, Bingqiu Chen","doi":"10.1063/1.43956","DOIUrl":"https://doi.org/10.1063/1.43956","url":null,"abstract":"The circular velocity of the thick disc is investigated using data in the 5 dimensional space (V, B‐V, U‐B, μl, μb) in a direction at intermediate latitude. We show that using a discriminant analysis we are able to distinguish the thick disc from the disc and the halo and that these data constrain the asymmetric drift of this population. It is found to be 80±20 km/s at a 2 sigmas level.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"152 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131965308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Interstellar gas moving in elliptical streamlines is used to model the observed terminal velocities of neutral hydrogen gas in the I. and IV. galactic quadrant. The excentricity of the orbits decreases with increasing r, and they are well aligned with a position angle of 40° for r≤3 kpc indicating the existence of a bar in that region. Plotting the orbits in the galactic plane spiral‐arm‐like features are marked by orbital crowding effects. This spiral arm system is 4‐armed for 3≤r≤6 kpc, and two‐armed outside of this and it agrees reasonably well in position with the spiral structure outlined by Georgelin and Georgelin (1976). The strong peak of the galactic rotation curve found amongst others by Rohlfs and Kreitschmann (1987) near r=500 pc is seen to be caused by the alignment of the elliptical orbits and not to be a feature of the dynamics.
{"title":"Galactic elliptical streamlines and their large‐scale organization","authors":"K. Rohlfs, H. Kampmann","doi":"10.1063/1.44019","DOIUrl":"https://doi.org/10.1063/1.44019","url":null,"abstract":"Interstellar gas moving in elliptical streamlines is used to model the observed terminal velocities of neutral hydrogen gas in the I. and IV. galactic quadrant. The excentricity of the orbits decreases with increasing r, and they are well aligned with a position angle of 40° for r≤3 kpc indicating the existence of a bar in that region. Plotting the orbits in the galactic plane spiral‐arm‐like features are marked by orbital crowding effects. This spiral arm system is 4‐armed for 3≤r≤6 kpc, and two‐armed outside of this and it agrees reasonably well in position with the spiral structure outlined by Georgelin and Georgelin (1976). The strong peak of the galactic rotation curve found amongst others by Rohlfs and Kreitschmann (1987) near r=500 pc is seen to be caused by the alignment of the elliptical orbits and not to be a feature of the dynamics.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131980422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Current issues in the study of the large‐scale properties of the Milky Way","authors":"J. Ostriker, F. Verter","doi":"10.1063/1.43923","DOIUrl":"https://doi.org/10.1063/1.43923","url":null,"abstract":"","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"138 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128076319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mosaics at 60 μm and 100 μm have been constructed of the 60°×60° area covering the Galactic center, bulge, molecular ring, and nearby clouds of emitting dust. We examine the relationship between various tracers of the interstellar medium and the fine‐scale structure that is evident in these mosaics. We pay special attention to the nearby Ophiucus cloud complex, a spectacular showcase for interactions between hot stars and dense interstellar matter. Here, the CO emission correlates well with much of the warm dust emission, whereas the Hα and FIR emission appear mostly uncorrelated. The warmest FIR colors are associated with the positions of young hot stars. Closer to the Galactic plane, the FIR fine structure is more likely tracing enhancements of warm dust in the more distant molecular ring and central bulge.
{"title":"Far‐infrared fine structure and its interstellar counterparts","authors":"F. Boulanger, W. Waller","doi":"10.1063/1.44029","DOIUrl":"https://doi.org/10.1063/1.44029","url":null,"abstract":"Mosaics at 60 μm and 100 μm have been constructed of the 60°×60° area covering the Galactic center, bulge, molecular ring, and nearby clouds of emitting dust. We examine the relationship between various tracers of the interstellar medium and the fine‐scale structure that is evident in these mosaics. We pay special attention to the nearby Ophiucus cloud complex, a spectacular showcase for interactions between hot stars and dense interstellar matter. Here, the CO emission correlates well with much of the warm dust emission, whereas the Hα and FIR emission appear mostly uncorrelated. The warmest FIR colors are associated with the positions of young hot stars. Closer to the Galactic plane, the FIR fine structure is more likely tracing enhancements of warm dust in the more distant molecular ring and central bulge.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"9 27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127272673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Sanders, N. Scoville, R. Tilanus, Z. Wang, S. Zhou
A survey of the Galactic Plane in the (2→1) and (3→2) rotational transitions of CO and 13CO has been carried out using the 10 m telescope of the Caltech Submillimeter Observatory (CSO). These data, plus previous observations of (1→0) emission from CO and 13CO obtained with at the Five College Radio Astronomy Observatory (FCRAO), have been used to determine the excitation properties of the molecular gas [Tk, n(H2)] throughout the disk of the Milky Way. The bulk of the molecular gas outside the galactic center (R/R⊙≳0.05 kpc) appears to be slightly colder, Tk=10–15 °K, and denser, n(H2)=103–104 cm−3, than previously assumed. There are no obvious gradients in temperature and cloud H2 density with galactocentric radius, although the molecular clouds in the galactic center and near the peak of the galactic ring at R/R⊙=0.4–0.6 are on average warmer (Tk∼15–20 °K) than the molecular material at other radii. The large H2 volume density derived from the CO data implies that a general internal property of molecular...
{"title":"A multi‐transition CO and 13CO survey of the Galactic Plane","authors":"D. Sanders, N. Scoville, R. Tilanus, Z. Wang, S. Zhou","doi":"10.1063/1.43993","DOIUrl":"https://doi.org/10.1063/1.43993","url":null,"abstract":"A survey of the Galactic Plane in the (2→1) and (3→2) rotational transitions of CO and 13CO has been carried out using the 10 m telescope of the Caltech Submillimeter Observatory (CSO). These data, plus previous observations of (1→0) emission from CO and 13CO obtained with at the Five College Radio Astronomy Observatory (FCRAO), have been used to determine the excitation properties of the molecular gas [Tk, n(H2)] throughout the disk of the Milky Way. The bulk of the molecular gas outside the galactic center (R/R⊙≳0.05 kpc) appears to be slightly colder, Tk=10–15 °K, and denser, n(H2)=103–104 cm−3, than previously assumed. There are no obvious gradients in temperature and cloud H2 density with galactocentric radius, although the molecular clouds in the galactic center and near the peak of the galactic ring at R/R⊙=0.4–0.6 are on average warmer (Tk∼15–20 °K) than the molecular material at other radii. The large H2 volume density derived from the CO data implies that a general internal property of molecular...","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124798156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Kinematical constraints on the dynamically determined local mass density of the Galaxy","authors":"B. Fuchs, R. Wielen","doi":"10.1063/1.43942","DOIUrl":"https://doi.org/10.1063/1.43942","url":null,"abstract":"","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123841893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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