By measuring the dimensionless product (σz/vc)2R0/h one can estimate the ratio of disk mass to total mass interior to the Sun’s orbit, where σz is velocity dispersion perpendicular to the disk appropriate to some tracer population, h is the scale height of that tracer, and vc is the circular velocity at the Sun’s distance from the center of the Milky Way, R0. While there are model dependent factors of order unity which render this ratio uncertain, it is difficult to avoid the conclusion that there is significant dark matter interior to the Sun’s orbit. Beyond the solar circle radial velocity data for disk stars are consistent with a flat rotation curve out to 2R0. Beyond that the interpretation of radial velocity data for blue horizontal branch stars, globular clusters, and satellite galaxies requires assumptions about their transverse velocities. Proper motion measurements less uncertain than 0.5 mas/yr might resolve this ambiguity.By measuring the dimensionless product (σz/vc)2R0/h one can estimate the ratio of disk mass to total mass interior to the Sun’s orbit, where σz is velocity dispersion perpendicular to the disk appropriate to some tracer population, h is the scale height of that tracer, and vc is the circular velocity at the Sun’s distance from the center of the Milky Way, R0. While there are model dependent factors of order unity which render this ratio uncertain, it is difficult to avoid the conclusion that there is significant dark matter interior to the Sun’s orbit. Beyond the solar circle radial velocity data for disk stars are consistent with a flat rotation curve out to 2R0. Beyond that the interpretation of radial velocity data for blue horizontal branch stars, globular clusters, and satellite galaxies requires assumptions about their transverse velocities. Proper motion measurements less uncertain than 0.5 mas/yr might resolve this ambiguity.
{"title":"Evidence for dark matter","authors":"P. Schechter","doi":"10.1063/1.43941","DOIUrl":"https://doi.org/10.1063/1.43941","url":null,"abstract":"By measuring the dimensionless product (σz/vc)2R0/h one can estimate the ratio of disk mass to total mass interior to the Sun’s orbit, where σz is velocity dispersion perpendicular to the disk appropriate to some tracer population, h is the scale height of that tracer, and vc is the circular velocity at the Sun’s distance from the center of the Milky Way, R0. While there are model dependent factors of order unity which render this ratio uncertain, it is difficult to avoid the conclusion that there is significant dark matter interior to the Sun’s orbit. Beyond the solar circle radial velocity data for disk stars are consistent with a flat rotation curve out to 2R0. Beyond that the interpretation of radial velocity data for blue horizontal branch stars, globular clusters, and satellite galaxies requires assumptions about their transverse velocities. Proper motion measurements less uncertain than 0.5 mas/yr might resolve this ambiguity.By measuring the dimensionless product (σz/vc)2R0/h one can estimate the ratio of disk mass to total mass interior to the Sun’s orbit, where σz is velocity dispersion perpendicular to the disk appropriate to some tracer population, h is the scale height of that tracer, and vc is the circular velocity at the Sun’s distance from the center of the Milky Way, R0. While there are model dependent factors of order unity which render this ratio uncertain, it is difficult to avoid the conclusion that there is significant dark matter interior to the Sun’s orbit. Beyond the solar circle radial velocity data for disk stars are consistent with a flat rotation curve out to 2R0. Beyond that the interpretation of radial velocity data for blue horizontal branch stars, globular clusters, and satellite galaxies requires assumptions about their transverse velocities. Proper motion measurements less uncertain than 0.5 mas/yr might resolve this ambiguity.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"406 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":"124320595","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}
E. Ladd, J. Deane, J. Goldader, D. Sanders, C. Wynn-Williams
We report on submillimeter observations of the star forming region W51 on 11 pc size scales with 0.7 pc resolution. These observations show at least nine emission centers, each of which has enough luminosity to be a potential site for massive star formation. We also detect a region of extended emission surrounding these emission centers. This extended emission component has a steeper submillimeter spectrum, suggesting that it is warmer than the star forming cores.
{"title":"Submillimeter images of W51","authors":"E. Ladd, J. Deane, J. Goldader, D. Sanders, C. Wynn-Williams","doi":"10.1063/1.43982","DOIUrl":"https://doi.org/10.1063/1.43982","url":null,"abstract":"We report on submillimeter observations of the star forming region W51 on 11 pc size scales with 0.7 pc resolution. These observations show at least nine emission centers, each of which has enough luminosity to be a potential site for massive star formation. We also detect a region of extended emission surrounding these emission centers. This extended emission component has a steeper submillimeter spectrum, suggesting that it is warmer than the star forming cores.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"22 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":"123510823","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 significant fraction of the diffuse galactic γ‐ray emission could be due to γ‐rays from individually undetected pulsars. Using the polar cap model of pulsar γ‐ray emission, the contribution of aging radio pulsars to the diffuse galactic γ‐ray glow is estimated. We calculate photon flux maps for a dynamically evolving pulsar population and, using COS‐B data, we derive constraints on the Galactic birth rate of pulsars. We emphasize the value of analyzing the collective contribution of pulsars that perhaps individually are too faint to be detected by the Compton Observatory.
{"title":"Diffuse Galactic gamma‐rays from pulsars","authors":"D. Hartmann, L. Brown, N. Schnepf","doi":"10.1063/1.43961","DOIUrl":"https://doi.org/10.1063/1.43961","url":null,"abstract":"A significant fraction of the diffuse galactic γ‐ray emission could be due to γ‐rays from individually undetected pulsars. Using the polar cap model of pulsar γ‐ray emission, the contribution of aging radio pulsars to the diffuse galactic γ‐ray glow is estimated. We calculate photon flux maps for a dynamically evolving pulsar population and, using COS‐B data, we derive constraints on the Galactic birth rate of pulsars. We emphasize the value of analyzing the collective contribution of pulsars that perhaps individually are too faint to be detected by the Compton Observatory.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"91 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120825244","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}
Good evidence for the existence of a bar at the center of the Milky Way was available nearly twenty years ago, but it is only in the last several years that its existence has become compelling. Previous evidence for the existence of a bar is reviewed, and the recent photometric evidence is discussed. The system of metal‐rich globular clusters is shown to exhibit an elongation and orientation consistent with the bar determined by other means. It is argued that the reason that the bar was not previously embraced is that it conflicted with the prevailing idea that the non‐circular motions of the gas near the center is due to explosions, which had an influential proponent in Jan Oort.
{"title":"Photometric evidence for the bar","authors":"L. Blitz","doi":"10.1063/1.43926","DOIUrl":"https://doi.org/10.1063/1.43926","url":null,"abstract":"Good evidence for the existence of a bar at the center of the Milky Way was available nearly twenty years ago, but it is only in the last several years that its existence has become compelling. Previous evidence for the existence of a bar is reviewed, and the recent photometric evidence is discussed. The system of metal‐rich globular clusters is shown to exhibit an elongation and orientation consistent with the bar determined by other means. It is argued that the reason that the bar was not previously embraced is that it conflicted with the prevailing idea that the non‐circular motions of the gas near the center is due to explosions, which had an influential proponent in Jan Oort.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"278 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":"129668682","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 conducted a survey of the 800 μm continuum emission from ∼15°×0.2° area around the Galactic center. The 800 μm continuum emission, which traces temperature weighted column density of dust, shows a strong asymmetry between the positive and negative galactic longitudes, similar to that seen in the molecular data; the bulk of the emission occurs at the positive galactic longitudes. One of the most interesting features in the 800 μm map is a clumpy ridge of emission apparently connecting Sgr B2 and the Radio Continuum Arc. A molecular counterpart of this ridge can be seen in the CS J=2→1 data. The ridge contains a number of dust cores without identified far–infrared sources or compact H II regions. These dust cores may be unusually cold.
{"title":"Dust emission in the Galactic center","authors":"D. Lis, J. Carlstrom","doi":"10.1063/1.43931","DOIUrl":"https://doi.org/10.1063/1.43931","url":null,"abstract":"We conducted a survey of the 800 μm continuum emission from ∼15°×0.2° area around the Galactic center. The 800 μm continuum emission, which traces temperature weighted column density of dust, shows a strong asymmetry between the positive and negative galactic longitudes, similar to that seen in the molecular data; the bulk of the emission occurs at the positive galactic longitudes. One of the most interesting features in the 800 μm map is a clumpy ridge of emission apparently connecting Sgr B2 and the Radio Continuum Arc. A molecular counterpart of this ridge can be seen in the CS J=2→1 data. The ridge contains a number of dust cores without identified far–infrared sources or compact H II regions. These dust cores may be unusually cold.","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":"127612893","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 considered radial velocities of galactic H II regions with known distances to analyze the velocity field of these regions along the galactic plane. A radial velocity is taken as the average of optical and radio data existing in the literature. A limiting value of 14 km kpc−1 s−1 for Oort’s constant A is attained with a least squares solutions, as we incorporate regions with ever larger distances from the sun. The data also suggest an overall radial contraction of the H II regions towards the galactic center of about 6 km s−1.
我们考虑了已知距离的星系H II区的径向速度，以分析这些区域沿星系平面的速度场。视向速度取文献中光学和无线电数据的平均值。奥尔特常数A的极限值为14 km kpc−1 s−1，这是通过最小二乘解得到的，因为我们将距离太阳越来越远的区域纳入其中。数据还表明，H II区域向银河系中心的整体径向收缩约为6 km s - 1。
{"title":"A kinematic study of galactic HII regions. Indication of a contraction towards the center","authors":"P. Pişmiş, E. Moreno","doi":"10.1063/1.43968","DOIUrl":"https://doi.org/10.1063/1.43968","url":null,"abstract":"We have considered radial velocities of galactic H II regions with known distances to analyze the velocity field of these regions along the galactic plane. A radial velocity is taken as the average of optical and radio data existing in the literature. A limiting value of 14 km kpc−1 s−1 for Oort’s constant A is attained with a least squares solutions, as we incorporate regions with ever larger distances from the sun. The data also suggest an overall radial contraction of the H II regions towards the galactic center of about 6 km s−1.","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":"132973944","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 report first results on the photoproduction of the species H I, Al III, Si IV, and C IV kinematically associated with the Galactic intermediate‐velocity (IV) arch. We find that photoionization of solar abundance gas cannot reproduce the observed column densities of these species, while models using stellar radiation fields and the observed x‐ray background can reproduce the observed columns in gas having depleted metal abundances. The pattern of metal depletions required is consistent with their incorporation into standard interstellar grains. Limits on the intensity of the halo radiation field indicate that the material of the IV arch is smoothly distributed, having a local density ∼10−2 cm−3 and filling factor of order unity. These results suggest that photoionization plays a key role in the production of at least some of the high‐ionization species Si IV and C IV in the Galactic halo.
我们报告了与银河系中速(IV)拱相关的H I, Al III, Si IV和C IV类光产生的初步结果。我们发现太阳丰度气体的光电离不能再现这些物种观测到的柱密度，而使用恒星辐射场和观测到的x射线背景的模型可以再现金属丰度耗尽的气体中观测到的柱密度。所需的金属消耗模式与它们融入标准星际颗粒是一致的。对光晕辐射场强度的限制表明，IV弓的材料分布均匀，局部密度为~ 10−2 cm−3，填充因子为阶单位。这些结果表明，在银晕中至少有一些高电离物质Si IV和C IV的产生中，光电离起着关键作用。
{"title":"The formation of high-ionization species associated with Galactic, intermediate velocity H I","authors":"J. Sokolowski, L. Danly","doi":"10.1063/1.43932","DOIUrl":"https://doi.org/10.1063/1.43932","url":null,"abstract":"We report first results on the photoproduction of the species H I, Al III, Si IV, and C IV kinematically associated with the Galactic intermediate‐velocity (IV) arch. We find that photoionization of solar abundance gas cannot reproduce the observed column densities of these species, while models using stellar radiation fields and the observed x‐ray background can reproduce the observed columns in gas having depleted metal abundances. The pattern of metal depletions required is consistent with their incorporation into standard interstellar grains. Limits on the intensity of the halo radiation field indicate that the material of the IV arch is smoothly distributed, having a local density ∼10−2 cm−3 and filling factor of order unity. These results suggest that photoionization plays a key role in the production of at least some of the high‐ionization species Si IV and C IV in the Galactic halo.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"125 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":"133334891","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}
H. Freudenreich, T. J. Sodroski, G. Berriman, E. Dwek, B. Franz, M. Hauser, T. Kelsall, S. Moseley, N. Odegard, R. Silverberg, G. Toller, J. Weiland
A large‐scale warp in the surface brightness distribution of the Galactic disk has been found in the data of the Diffuse Infrared Background Experiment (DIRBE) of the Cosmic Background Explorer. In the far‐infrared it is seen in seen in thermal emission by dust. In the near‐infrared it is seen in starlight. The far‐infrared warp matches that of the velocity‐integrated HI. The near‐infrared warp has approximately the same orientation, but has a smaller amplitude, which increases with increasing wavelength. This is consistent with the stellar disk of the Galaxy being bent in the same way as the HI layer.
{"title":"Dirbe evidence for a warp in the Galaxy","authors":"H. Freudenreich, T. J. Sodroski, G. Berriman, E. Dwek, B. Franz, M. Hauser, T. Kelsall, S. Moseley, N. Odegard, R. Silverberg, G. Toller, J. Weiland","doi":"10.1063/1.43975","DOIUrl":"https://doi.org/10.1063/1.43975","url":null,"abstract":"A large‐scale warp in the surface brightness distribution of the Galactic disk has been found in the data of the Diffuse Infrared Background Experiment (DIRBE) of the Cosmic Background Explorer. In the far‐infrared it is seen in seen in thermal emission by dust. In the near‐infrared it is seen in starlight. The far‐infrared warp matches that of the velocity‐integrated HI. The near‐infrared warp has approximately the same orientation, but has a smaller amplitude, which increases with increasing wavelength. This is consistent with the stellar disk of the Galaxy being bent in the same way as the HI layer.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"20 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":"133682710","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}
Low frequency scintillation observations of the nearby pulsar 0950+08 show that C2n, the amplitude of the electron density fluctuation spectrum, is ≂10−4.5 m−20/3 along the line of sight, a value which is 5 to 10 times smaller that C2n measured towards other pulsars within a few kpc of Earth. Since the line of sight to PSR 0950+08 is contained mostly within the local X‐ray bubble we can conclude that the coronal phase of the interstellar medium is weakly scattering.
{"title":"Turbulence in the coronal interstellar medium","authors":"J. Phillips, A. Clegg","doi":"10.1063/1.44006","DOIUrl":"https://doi.org/10.1063/1.44006","url":null,"abstract":"Low frequency scintillation observations of the nearby pulsar 0950+08 show that C2n, the amplitude of the electron density fluctuation spectrum, is ≂10−4.5 m−20/3 along the line of sight, a value which is 5 to 10 times smaller that C2n measured towards other pulsars within a few kpc of Earth. Since the line of sight to PSR 0950+08 is contained mostly within the local X‐ray bubble we can conclude that the coronal phase of the interstellar medium is weakly scattering.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"364 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":"114503588","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}
Using radio continuum and infrared surface brightness maps we surveyed galactic worms—structures perpendicular to the galactic plane. For the first time, the structures were resolved and distances determined. We find two main classes based on radio spectral index, and suggest an evolutionary sequence.
{"title":"Galactic worms: Infrared and radio maps of the first quadrant","authors":"W. Reach, C. Heiles, B. Koo","doi":"10.1063/1.43935","DOIUrl":"https://doi.org/10.1063/1.43935","url":null,"abstract":"Using radio continuum and infrared surface brightness maps we surveyed galactic worms—structures perpendicular to the galactic plane. For the first time, the structures were resolved and distances determined. We find two main classes based on radio spectral index, and suggest an evolutionary sequence.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"28 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":"133397968","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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