We present a study of two molecular clouds with kinematic Galactocentric distances of 22 and 28 kpc (R⊙=8.5 kpc). These are several kiloparsecs further from the Galactic center than any previously known and apparently lie beyond the outermost massive star‐forming regions. We compare the physical properties of the clouds with molecular clouds of similar size near the solar circle, e.g., those in Taurus and Orion. Observations with the CfA 1.2 m and NRAO 12 m telescopes indicate that these distant clouds have sizes of 40–70 pc, molecular masses of 4–7×104 M⊙, and velocity widths 2–3 km s−1. They contain dense molecular clumps of sizes 7–10 pc and kinetic temperatures 15–25 K. The distant clouds are similar to molecular clouds near the solar circle in all the properties we have determined. Their primary difference is an apparent lack of embedded IRAS infrared sources.
{"title":"Properties of molecular clouds in the extreme outer Galaxy","authors":"S. Digel, P. Thaddeus, E. D. Geus","doi":"10.1063/1.43973","DOIUrl":"https://doi.org/10.1063/1.43973","url":null,"abstract":"We present a study of two molecular clouds with kinematic Galactocentric distances of 22 and 28 kpc (R⊙=8.5 kpc). These are several kiloparsecs further from the Galactic center than any previously known and apparently lie beyond the outermost massive star‐forming regions. We compare the physical properties of the clouds with molecular clouds of similar size near the solar circle, e.g., those in Taurus and Orion. Observations with the CfA 1.2 m and NRAO 12 m telescopes indicate that these distant clouds have sizes of 40–70 pc, molecular masses of 4–7×104 M⊙, and velocity widths 2–3 km s−1. They contain dense molecular clumps of sizes 7–10 pc and kinetic temperatures 15–25 K. The distant clouds are similar to molecular clouds near the solar circle in all the properties we have determined. Their primary difference is an apparent lack of embedded IRAS infrared sources.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"163 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":"115327691","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 spectrum of the Milky Way observed by the COBE FIRAS instrument shows an excess of long wavelength emission when compared to a single temperature σ∝ν2 dust model. This excess could be due to a massive population of large spherical grains or to a very small mass of fractal grains. Fractal dust grains with low equilibrium temperatures can produce the bulk of the IR emission by single photon thermal pulsing with peak temperatures of ≊20 K.
{"title":"Cold dust in the ISM","authors":"E. Wright","doi":"10.1063/1.44012","DOIUrl":"https://doi.org/10.1063/1.44012","url":null,"abstract":"The spectrum of the Milky Way observed by the COBE FIRAS instrument shows an excess of long wavelength emission when compared to a single temperature σ∝ν2 dust model. This excess could be due to a massive population of large spherical grains or to a very small mass of fractal grains. Fractal dust grains with low equilibrium temperatures can produce the bulk of the IR emission by single photon thermal pulsing with peak temperatures of ≊20 K.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"39 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":"134538814","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}
Recent developments in determining the large‐scale structure of the Galaxy with stellar tracers are discussed. Among the possible approaches, direct mapping using standard candles is emphasized because of its promise to provide the most unbiased and consistent view, especially when kinematic data is available.Candidate standard candle tracers include HII regions, planetary nebulae, Cepheid variables, and AGB stars (carbon stars, Mira variables, OH/IR stars). Current progress is briefly reviewed in turn. Mapping techniques are discussed, and as an example, the author’s experience analyzing the IRAS PSC and detection of a bar is described.Bars and similar rotating non‐axisymmetric features in the Galaxy provide observable stellar kinematic signatures, even if the perturbations are relatively weak (several percent). Therefore, only a modest velocity data set is required to place meaningful constraints. For example, the moderate‐strength bar with half‐length of 3 kpc described previously will produce a strong...
{"title":"Distribution of stars in the disk","authors":"M. Weinberg","doi":"10.1063/1.44000","DOIUrl":"https://doi.org/10.1063/1.44000","url":null,"abstract":"Recent developments in determining the large‐scale structure of the Galaxy with stellar tracers are discussed. Among the possible approaches, direct mapping using standard candles is emphasized because of its promise to provide the most unbiased and consistent view, especially when kinematic data is available.Candidate standard candle tracers include HII regions, planetary nebulae, Cepheid variables, and AGB stars (carbon stars, Mira variables, OH/IR stars). Current progress is briefly reviewed in turn. Mapping techniques are discussed, and as an example, the author’s experience analyzing the IRAS PSC and detection of a bar is described.Bars and similar rotating non‐axisymmetric features in the Galaxy provide observable stellar kinematic signatures, even if the perturbations are relatively weak (several percent). Therefore, only a modest velocity data set is required to place meaningful constraints. For example, the moderate‐strength bar with half‐length of 3 kpc described previously will produce a strong...","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"17 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":"130077323","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}
Over the past decade, the uncertainty on the H2 mass of the inner Galaxy has been reduced from a factor ∼4 to less than a factor 2, comparable to the uncertainty which still exists for H i. Gas masses beyond the solar circle remain more uncertain, owing mainly to uncertainties in the rotation curve and CO‐to‐H2 mass conversion factor there. H i and H2 masses are roughly equal within the solar circle, but H i dominates beyond. GMCs are superior to H i clouds for tracing Galactic structure, but kinematic distance errors and severe velocity crowding near the terminal velocity in the inner Galaxy remain formidable obstacles to sorting out the structure of that region.Large‐scale near‐infrared surveys of the Galactic plane, particularly those recently obtained by the COBE satellite, hold great promise for determining both distances and masses for large GMCs in the inner Galaxy. An earlier survey by the Infrared Telescope (IRT) has already revealed a remarkably tight anticorrelation between CO and near‐infrared...
在过去的十年中，银河系内部H2质量的不确定性已经从1 ~ 4降低到小于2，与仍然存在的H2质量的不确定性相当。太阳圈以外的气体质量仍然不确定，主要是由于旋转曲线和CO - to - H2质量转换因子的不确定性。在太阳圈内，氢和氢的质量大致相等，但在太阳圈外，氢占主导地位。gmc在追踪星系结构方面优于H - i云，但运动距离误差和银河系内部接近终端速度的严重速度拥挤仍然是整理该区域结构的巨大障碍。银河平面的大规模近红外巡天，特别是最近由COBE卫星获得的巡天，为确定银河系内部大型gmc的距离和质量带来了巨大的希望。红外望远镜(IRT)的早期调查已经揭示了CO与近红外…
{"title":"The distribution of neutral gas in the Milky Way","authors":"T. Dame","doi":"10.1063/1.43985","DOIUrl":"https://doi.org/10.1063/1.43985","url":null,"abstract":"Over the past decade, the uncertainty on the H2 mass of the inner Galaxy has been reduced from a factor ∼4 to less than a factor 2, comparable to the uncertainty which still exists for H i. Gas masses beyond the solar circle remain more uncertain, owing mainly to uncertainties in the rotation curve and CO‐to‐H2 mass conversion factor there. H i and H2 masses are roughly equal within the solar circle, but H i dominates beyond. GMCs are superior to H i clouds for tracing Galactic structure, but kinematic distance errors and severe velocity crowding near the terminal velocity in the inner Galaxy remain formidable obstacles to sorting out the structure of that region.Large‐scale near‐infrared surveys of the Galactic plane, particularly those recently obtained by the COBE satellite, hold great promise for determining both distances and masses for large GMCs in the inner Galaxy. An earlier survey by the Infrared Telescope (IRT) has already revealed a remarkably tight anticorrelation between CO and near‐infrared...","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"7 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":"114618698","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}
Globular clusters are the oldest known stellar system in our Galaxy. It is therefore surprising that they are found to contain relatively large numbers of millisecond pulsars, since these pulsars have a limited active lifetime. Globular cluster pulsars are preferentially found in clusters with massive and dense cores and are often binary with another star. These properties suggest that they are neutron stars which have been captured by a cluster star or binary system and ‘‘recycled,’’ that is, spun up to their present short periods by accretion of mass from the companion. Based on the observed sample of 30 or so pulsars, it is estimated that the total number of pulsars in globular clusters is about 1000. This is about two orders of magnitude greater than the observed number of low‐mass X‐ray binary systems, which places limits on the lifetime of these systems if they are the progenitors of millisecond pulsars. Some pulsars lying close to the core of dense clusters are observed to be accelerated in the clu...
{"title":"Globular clusters and pulsars","authors":"R. Manchester","doi":"10.1063/1.43928","DOIUrl":"https://doi.org/10.1063/1.43928","url":null,"abstract":"Globular clusters are the oldest known stellar system in our Galaxy. It is therefore surprising that they are found to contain relatively large numbers of millisecond pulsars, since these pulsars have a limited active lifetime. Globular cluster pulsars are preferentially found in clusters with massive and dense cores and are often binary with another star. These properties suggest that they are neutron stars which have been captured by a cluster star or binary system and ‘‘recycled,’’ that is, spun up to their present short periods by accretion of mass from the companion. Based on the observed sample of 30 or so pulsars, it is estimated that the total number of pulsars in globular clusters is about 1000. This is about two orders of magnitude greater than the observed number of low‐mass X‐ray binary systems, which places limits on the lifetime of these systems if they are the progenitors of millisecond pulsars. Some pulsars lying close to the core of dense clusters are observed to be accelerated in the clu...","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"18 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":"115461068","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 non‐circular velocities of gas in the inner few degrees of our Galaxy would arise naturally if the Milky Way had a small bar at its center. Recent studies suggest that this bar is more rapidly rotating than had been previously suggested; corotation probably lies near R=2.4 kpc. The circular speed associated with the Galaxy’s monopole component must rise as vc∼R1/8 in the inner kiloparsec or so. It seems likely that the bar is the peanut‐shaped object seen by COBE, and formed by spontaneous thickening of a bar‐unstable disk. The lop‐sidedness of the distribution of molecular gas at ‖l‖≲2° suggests that the gas flow at the Center is unsteady. This unsteadiness may be an important clue to the correct technique for simulating the large‐scale dynamics of the interstellar medium, which displays a wealth of unresolvable structure.
{"title":"Dynamics of the galactic bulge‐bar","authors":"J. Binney, O. Gerhard","doi":"10.1063/1.43925","DOIUrl":"https://doi.org/10.1063/1.43925","url":null,"abstract":"The non‐circular velocities of gas in the inner few degrees of our Galaxy would arise naturally if the Milky Way had a small bar at its center. Recent studies suggest that this bar is more rapidly rotating than had been previously suggested; corotation probably lies near R=2.4 kpc. The circular speed associated with the Galaxy’s monopole component must rise as vc∼R1/8 in the inner kiloparsec or so. It seems likely that the bar is the peanut‐shaped object seen by COBE, and formed by spontaneous thickening of a bar‐unstable disk. The lop‐sidedness of the distribution of molecular gas at ‖l‖≲2° suggests that the gas flow at the Center is unsteady. This unsteadiness may be an important clue to the correct technique for simulating the large‐scale dynamics of the interstellar medium, which displays a wealth of unresolvable structure.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"174 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":"114738049","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}
T. Oka, T. Hasegawa, M. Hayashi, T. Handa, S. Sakamoto
We report a large scale mapping observation of the Galactic center region in the CO (J=2−1) line using the Tokyo‐NRO 60 cm survey telescope. Distribution of the CO (J=2−1) emission in the I‐V plane suggests that molecular clouds forms a huge complex (Nuclear Molecular cloud Complex, NMC). Tracers of star formation activities in the last 106–108 years show that star formation has occurred in a ring ∼100 pc in radius. Relative to this Star Forming Ring, the molecular gas is distributed mainly on the positive longitude side. This may indicate that much of the gas in NMC is in transient orbit to fall into the star forming ring or to the nucleus in the near future.
我们报告了使用东京- NRO 60厘米巡天望远镜在CO (J=2−1)线上对银河系中心区域进行的大比例尺测绘观测。CO (J=2−1)在I - V平面的发射分布表明分子云形成了一个巨大的复合体(核分子云复合体，NMC)。过去106-108年间恒星形成活动的示踪剂显示，恒星形成发生在半径约100pc的环内。相对于这个恒星形成环，分子气体主要分布在正经度侧。这可能表明，在不久的将来，NMC中的大部分气体在瞬态轨道上落入恒星形成环或核心。
{"title":"CO (J=2−1) observations of the molecular cloud complex in the Galactic center","authors":"T. Oka, T. Hasegawa, M. Hayashi, T. Handa, S. Sakamoto","doi":"10.1063/1.43927","DOIUrl":"https://doi.org/10.1063/1.43927","url":null,"abstract":"We report a large scale mapping observation of the Galactic center region in the CO (J=2−1) line using the Tokyo‐NRO 60 cm survey telescope. Distribution of the CO (J=2−1) emission in the I‐V plane suggests that molecular clouds forms a huge complex (Nuclear Molecular cloud Complex, NMC). Tracers of star formation activities in the last 106–108 years show that star formation has occurred in a ring ∼100 pc in radius. Relative to this Star Forming Ring, the molecular gas is distributed mainly on the positive longitude side. This may indicate that much of the gas in NMC is in transient orbit to fall into the star forming ring or to the nucleus in the near future.","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"117 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":"121446386","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":"A pessimist’s view of Galactic structure","authors":"S. Tremaine","doi":"10.1063/1.43946","DOIUrl":"https://doi.org/10.1063/1.43946","url":null,"abstract":"","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"99 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":"124088340","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":"The radiative support of Galactic HI","authors":"A. Ferrara","doi":"10.1063/1.43933","DOIUrl":"https://doi.org/10.1063/1.43933","url":null,"abstract":"","PeriodicalId":310353,"journal":{"name":"Back to the Galaxy","volume":"26 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":"121981106","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":"Chemical homogeneity within the old open cluster M 67","authors":"B. Hufnagel, Graeme H. Smith","doi":"10.1063/1.44033","DOIUrl":"https://doi.org/10.1063/1.44033","url":null,"abstract":"","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":"124676537","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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