The vertical distribution of gas in disk galaxies is studied using analytical and numerical methods. If the sound speed of gas or the velocity dispersion of clouds is only weakly dependent on galactic radius, then the gas flares outward, perpendicular to the galactic plane. The rate of this flaring is determined by the galactic potential and constrains the mass distribution differently from rotation curves. In principle, therefore, high resolution measurements of the widths of HI layers in external edge—on galaxies could be used in conjunction with measured rotation curves to infer the shapes and masses of dark matter halos. This paper investigates the dependence of flaring on the flattening of the halo, ratio of halo‐to‐disk mass, and extent of the halo. We conclude that flaring can in principle be used to constrain the vertical scale‐height of the non‐gaseous disk material, as well as the axis ratios of dark matter halos.
{"title":"Flaring of gas in galactic disks","authors":"T. Kundić, L. Hernquist, J. Gunn","doi":"10.1063/1.43945","DOIUrl":"https://doi.org/10.1063/1.43945","url":null,"abstract":"The vertical distribution of gas in disk galaxies is studied using analytical and numerical methods. If the sound speed of gas or the velocity dispersion of clouds is only weakly dependent on galactic radius, then the gas flares outward, perpendicular to the galactic plane. The rate of this flaring is determined by the galactic potential and constrains the mass distribution differently from rotation curves. In principle, therefore, high resolution measurements of the widths of HI layers in external edge—on galaxies could be used in conjunction with measured rotation curves to infer the shapes and masses of dark matter halos. This paper investigates the dependence of flaring on the flattening of the halo, ratio of halo‐to‐disk mass, and extent of the halo. We conclude that flaring can in principle be used to constrain the vertical scale‐height of the non‐gaseous disk material, as well as the axis ratios of dark matter halos.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"25 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":"126317839","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}
J. Weiland, M. Hauser, T. Kelsall, E. Dwek, S. Moseley, R. Silverberg, M. Mitra, N. Odegard, W. Spiesman, T. J. Sodroski, S. W. Stemwedel, H. Freudenreich, C. Lisse
Near‐infrared observations of the Galactic bulge from the Diffuse Infrared Background Experiment (DIRBE) on‐board NASA’s Cosmic Background Explorer (COBE) satellite are discussed. Emphasis is placed on preliminary analysis of asymmetries in the brightness distribution of the bulge, and the implications for the presence of a stellar bar in the bulge region.
{"title":"Dirbe observations of the Galactic bulge","authors":"J. Weiland, M. Hauser, T. Kelsall, E. Dwek, S. Moseley, R. Silverberg, M. Mitra, N. Odegard, W. Spiesman, T. J. Sodroski, S. W. Stemwedel, H. Freudenreich, C. Lisse","doi":"10.1063/1.44023","DOIUrl":"https://doi.org/10.1063/1.44023","url":null,"abstract":"Near‐infrared observations of the Galactic bulge from the Diffuse Infrared Background Experiment (DIRBE) on‐board NASA’s Cosmic Background Explorer (COBE) satellite are discussed. Emphasis is placed on preliminary analysis of asymmetries in the brightness distribution of the bulge, and the implications for the presence of a stellar bar in the bulge region.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"79 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":"122872505","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 outer parts of the Galaxy disk are observed to bend away from the plane of the inner material. The warp is most obvious in neutral hydrogen, but also involves molecular gas and stars. Models for the bending of a self‐gravitating disk are discussed with reference to the Galactic warp.
{"title":"The warp of the Milky Way","authors":"L. Sparke","doi":"10.1063/1.43967","DOIUrl":"https://doi.org/10.1063/1.43967","url":null,"abstract":"The outer parts of the Galaxy disk are observed to bend away from the plane of the inner material. The warp is most obvious in neutral hydrogen, but also involves molecular gas and stars. Models for the bending of a self‐gravitating disk are discussed with reference to the Galactic warp.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"1 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":"131616881","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}
A remarkable enhancement of the 6.7 keV line emission and associated thermal continuum emission from the Galactic ridge toward the Galactic center discovered recently by Ginga satellite opens new opportunity of exploring high‐energy phenomena in the Galaxy. This emission is thought to originate in a hot optically thin gas, and the central enhancement seems to be associated with an ultra hot (T≊108 K), rarefied [n∼(3−6)⋅10−2 cm−3] interior of the 200‐pc expanding molecular ring in the Galactic center. Assuming that this interior is a superbubble resulting from an adiabatic explosion, we analyze the dynamics of the explosive phenomenon. Some implications of the presence of a cold (molecular) and a warm (radio emitting) gas between us and the ultra hot superbubble, such as fluorescence of iron lines in the cold gas and scattering of iron lines in warm (hot) gas are discussed.
{"title":"Ultra hot gas in the Galaxy: possible origins and implications","authors":"L. Ozernoy, L. Titarchuk, R. Ramaty","doi":"10.1063/1.43952","DOIUrl":"https://doi.org/10.1063/1.43952","url":null,"abstract":"A remarkable enhancement of the 6.7 keV line emission and associated thermal continuum emission from the Galactic ridge toward the Galactic center discovered recently by Ginga satellite opens new opportunity of exploring high‐energy phenomena in the Galaxy. This emission is thought to originate in a hot optically thin gas, and the central enhancement seems to be associated with an ultra hot (T≊108 K), rarefied [n∼(3−6)⋅10−2 cm−3] interior of the 200‐pc expanding molecular ring in the Galactic center. Assuming that this interior is a superbubble resulting from an adiabatic explosion, we analyze the dynamics of the explosive phenomenon. Some implications of the presence of a cold (molecular) and a warm (radio emitting) gas between us and the ultra hot superbubble, such as fluorescence of iron lines in the cold gas and scattering of iron lines in warm (hot) gas are discussed.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"33 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":"132192890","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 relation between the projected face‐on velocity‐integrated CO(1‐0) brightness ICO and the 20‐cm non‐thermal radio continuum brightness T20 is shown to be virtually constant as a function of radius in the Galactic disk. Averaged in 1 kpc annuli, the ratio ICO/T20 has a mean value of 1.51±0.34 km s−1 from 2 to 10 kpc. This value is very close to that reported recently for the disks of 8 normal spiral galaxies, where 〈ICO/T20〉=1.3±0.6 km s−1 in spite of the fact that the values of surface brightness in CO and radio continuum in the sample vary by more than a factor of 100.An explanation of this correlation is given in the framework of the hypothesis that both ICO and TNT have a common origin in the local density of cosmic rays in galaxy disks. The inner disk of M31 is apparently deficient in cosmic rays; the molecular clouds there are likely to be very cold, and may have temperatures close to the cosmic microwave background, rendering them nearly invisible in emission.
投影的面朝速度积分CO(1‐0)亮度ICO与20‐cm非热射电连续体亮度T20之间的关系，作为银河系圆盘半径的函数，实际上是恒定的。在1 kpc环空范围内，ICO/T20的平均值为1.51±0.34 km s−1。这个值非常接近最近报道的8个正常螺旋星系盘的值，其中< ICO/T20 > =1.3±0.6 km s−1，尽管样品中CO和射电连续体的表面亮度值相差超过100倍。在假设的框架中给出了这种相关性的解释，即ICO和TNT在星系盘中宇宙射线的局部密度中具有共同的起源。M31的内盘显然缺乏宇宙射线;那里的分子云很可能非常寒冷，温度可能接近宇宙微波背景，使它们在发射中几乎看不见。
{"title":"The ICO/TNT relation in the Galaxy and in other Galaxies","authors":"R. Allen","doi":"10.1063/1.43988","DOIUrl":"https://doi.org/10.1063/1.43988","url":null,"abstract":"The relation between the projected face‐on velocity‐integrated CO(1‐0) brightness ICO and the 20‐cm non‐thermal radio continuum brightness T20 is shown to be virtually constant as a function of radius in the Galactic disk. Averaged in 1 kpc annuli, the ratio ICO/T20 has a mean value of 1.51±0.34 km s−1 from 2 to 10 kpc. This value is very close to that reported recently for the disks of 8 normal spiral galaxies, where 〈ICO/T20〉=1.3±0.6 km s−1 in spite of the fact that the values of surface brightness in CO and radio continuum in the sample vary by more than a factor of 100.An explanation of this correlation is given in the framework of the hypothesis that both ICO and TNT have a common origin in the local density of cosmic rays in galaxy disks. The inner disk of M31 is apparently deficient in cosmic rays; the molecular clouds there are likely to be very cold, and may have temperatures close to the cosmic microwave background, rendering them nearly invisible in emission.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"16 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":"134398572","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 behavior and interactions of one or more core black holes is described for the mass density environment of the galaxy core and comparisons made between this environment and that of a large spherical stellar system typical of an active galaxy. Data is presented for a range of galaxy types in local galaxy clusters that indicates jetting with kinetic energy greater than 1055 ergs from a collapsed object or system of objects in the galaxy core may have occurred during the very early phase of development of the Milky Way but is unlikely in later epochs.
{"title":"The Milky Way: An active galaxy?","authors":"W. C. Oelfke","doi":"10.1063/1.43950","DOIUrl":"https://doi.org/10.1063/1.43950","url":null,"abstract":"The behavior and interactions of one or more core black holes is described for the mass density environment of the galaxy core and comparisons made between this environment and that of a large spherical stellar system typical of an active galaxy. Data is presented for a range of galaxy types in local galaxy clusters that indicates jetting with kinetic energy greater than 1055 ergs from a collapsed object or system of objects in the galaxy core may have occurred during the very early phase of development of the Milky Way but is unlikely in later epochs.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"76 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":"115004686","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 obtained UBV CCD‐magnitudes for stars in eight distant, young groups in the third Galactic quadrant. Comparison with theoretical isochrones yields ages and distances of significantly improved precision compared to previous studies. One of the best observed groups (in the faint H ii region S 289) is located twice as far from the Galactic center as the Sun, at the outer limit of active star formation in the Galactic disk. Together with published radial velocities and allowing for a metallicity gradient, the new distances harden the evidence for a flat Galactic rotation curve out to R≂16 kpc.
{"title":"Remote young stellar groups and the rotation of the outer Galactic disk","authors":"L. Turbide, A. Moffat","doi":"10.1063/1.43970","DOIUrl":"https://doi.org/10.1063/1.43970","url":null,"abstract":"We have obtained UBV CCD‐magnitudes for stars in eight distant, young groups in the third Galactic quadrant. Comparison with theoretical isochrones yields ages and distances of significantly improved precision compared to previous studies. One of the best observed groups (in the faint H ii region S 289) is located twice as far from the Galactic center as the Sun, at the outer limit of active star formation in the Galactic disk. Together with published radial velocities and allowing for a metallicity gradient, the new distances harden the evidence for a flat Galactic rotation curve out to R≂16 kpc.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"129 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":"123260050","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 warm ionized component of the interstellar medium is characterized by widespread regions of nearly fully ionized hydrogen with an electron density ne≂0.1 cm−3 and a temperature T≂8000 K. The regions occupy at least 20% of the volume within a layer of half‐thickness H≂1 kpc and have a mass surface density approximately one‐third that of the H I. The required ionizing power is 1×10−4 ergs s−1 per cm2 of the Galactic disk near the solar circle. These results have been derived from a relatively small number of sight lines that sample a region of radius 3‐4 kpc about the sun. The temperature and ionization state have been probed at low Galactic latitudes near the midplane, while the scale height, density, filling fraction, and power requirement are derived from data at high latitudes.
{"title":"The warm ionized medium","authors":"R. J. Reynolds","doi":"10.1063/1.44005","DOIUrl":"https://doi.org/10.1063/1.44005","url":null,"abstract":"The warm ionized component of the interstellar medium is characterized by widespread regions of nearly fully ionized hydrogen with an electron density ne≂0.1 cm−3 and a temperature T≂8000 K. The regions occupy at least 20% of the volume within a layer of half‐thickness H≂1 kpc and have a mass surface density approximately one‐third that of the H I. The required ionizing power is 1×10−4 ergs s−1 per cm2 of the Galactic disk near the solar circle. These results have been derived from a relatively small number of sight lines that sample a region of radius 3‐4 kpc about the sun. The temperature and ionization state have been probed at low Galactic latitudes near the midplane, while the scale height, density, filling fraction, and power requirement are derived from data at high latitudes.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"21 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":"120952886","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}
Infrared emission from Hii regions has been extracted from the IRAS databases for a sample of Galactic Hii regions identified by radio continuum and recombination line surveys. This investigation, based on a sample of radio Hii regions, should lessen the bias towards local Hii regions which are larger and brighter on average. The infrared luminosity, color, and physical properties have been extracted from this data set as a function of Galactocentric distance. The global infrared properties of the Hii regions are quite uniform with some very interesting exceptions.
{"title":"Infrared emission of Galactic Hii regions","authors":"T. Kuchar","doi":"10.1063/1.43983","DOIUrl":"https://doi.org/10.1063/1.43983","url":null,"abstract":"Infrared emission from Hii regions has been extracted from the IRAS databases for a sample of Galactic Hii regions identified by radio continuum and recombination line surveys. This investigation, based on a sample of radio Hii regions, should lessen the bias towards local Hii regions which are larger and brighter on average. The infrared luminosity, color, and physical properties have been extracted from this data set as a function of Galactocentric distance. The global infrared properties of the Hii regions are quite uniform with some very interesting exceptions.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"157 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":"132827229","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}
S. Sakamoto, T. Hasegawa, M. Hayashi, T. Handa, T. Oka
A large‐area CO(J=2−1) map of the Orion A and B clouds is presented. The J=2−1/J=1−0 intensity ratio of CO varies systematically over the whole extent of these clouds, i.e., the ratio is ∼1 in their main ridges and declines to ∼0.5 in their peripheries. This variation of the intensity ratio is understood in terms of the variation of the surface gas density of clumps which is ≳3×103 cm−3 for those in the ridges and ∼1×102 cm−3 for those in the peripheries. The peripheral regions seen in low‐J transitions of 12CO is more surface‐filling (≳0.7) than expected.The J=2−1/J=1−0 luminosity ratio for the Orion A and B clouds is 0.75 and 0.62, respectively. These values are consistent with those observed typically along the Solar circle and are significantly lower than large values often observed in the inner Galaxy and the Galactic center.
{"title":"A large area CO(J=2−1) mapping of the Orion giant molecular clouds","authors":"S. Sakamoto, T. Hasegawa, M. Hayashi, T. Handa, T. Oka","doi":"10.1063/1.43995","DOIUrl":"https://doi.org/10.1063/1.43995","url":null,"abstract":"A large‐area CO(J=2−1) map of the Orion A and B clouds is presented. The J=2−1/J=1−0 intensity ratio of CO varies systematically over the whole extent of these clouds, i.e., the ratio is ∼1 in their main ridges and declines to ∼0.5 in their peripheries. This variation of the intensity ratio is understood in terms of the variation of the surface gas density of clumps which is ≳3×103 cm−3 for those in the ridges and ∼1×102 cm−3 for those in the peripheries. The peripheral regions seen in low‐J transitions of 12CO is more surface‐filling (≳0.7) than expected.The J=2−1/J=1−0 luminosity ratio for the Orion A and B clouds is 0.75 and 0.62, respectively. These values are consistent with those observed typically along the Solar circle and are significantly lower than large values often observed in the inner Galaxy and the Galactic center.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"1 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":"128449187","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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