scholarly journals Morphology of the Galactic Bulge from COBE DIRBE Observations

1996 ◽  
Vol 169 ◽  
pp. 61-69
Author(s):  
E. Dwek
Keyword(s):  
Interstellar Dust ◽  
Galactic Center ◽  
Galactic Plane ◽  
Star Formation History ◽  
Galactic Bulge ◽  
Stellar Content ◽  
The Galaxy ◽  
Infrared Background ◽  
History Of ◽  
Sweeping Gas

The Diffuse Infrared Background Experiment (DIRBE) on-board the Cosmic Background Explorer (COBE) satellite has provided striking new images of the Galactic bulge at effective wavelengths of 1.25, 2.2, 3.5, and 4.9μ (Hauser 1993, plate 3; Arendt et al. 1994; Weiland et al. 1994). The bulge, defined here as the spheroid within the |l| < 20° and |b| < 10° region around the Galactic center, and its stellar content have been subjects of considerable interest since they contain important clues about the dynamical and star-formation history of our Galaxy. The morphology of the Galactic bulge is much harder to ascertain than that of bulges in many external galaxies, because of our location in the Galactic plane amid the obscuration by interstellar dust. In spite of this difficulty, there has recently been an accumulating body of evidence that the stellar distribution in the bulge is bar shaped, i.e. that the bulge is not rotationally symmetric in the plane of the disk (see Blitz 1993 for a review of the subject). The existence of a bar in our Galaxy would have important implications for the dynamics of the Galaxy. A bar would provide a mechanism for sweeping gas from the disk into the Galactic center “feeding” a central black hole (e.g. Shlosman, Frank, & Begelman 1989). It would also provide a mechanism for generating spiral arms, and a basis for estimating the mass of the halo relative to that of the disk (e.g. Combes & Sanders 1981 and references therein).

scholarly journals The chemodynamics of prograde and retrograde Milky Way stars

2020 ◽  
Vol 643 ◽  
pp. A69
Author(s):  
Georges Kordopatis ◽  
Alejandra Recio-Blanco ◽  
Mathias Schultheis ◽  
Vanessa Hill
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Azimuthal Velocity ◽  
Mixed Population ◽  
Photometric Data ◽  
Rotating Stars ◽  
The Galaxy ◽  
History Of ◽  
Different Populations

Context. The accretion history of the Milky Way is still unknown, despite the recent discovery of stellar systems that stand out in terms of their energy-angular momentum space, such as Gaia-Enceladus-Sausage. In particular, it is still unclear how these groups are linked and to what extent they are well-mixed. Aims. We investigate the similarities and differences in the properties between the prograde and retrograde (counter-rotating) stars and set those results in context by using the properties of Gaia-Enceladus-Sausage, Thamnos/Sequoia, and other suggested accreted populations. Methods. We used the stellar metallicities of the major large spectroscopic surveys (APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE, SEGUE) in combination with astrometric and photometric data from Gaia’s second data-release. We investigated the presence of radial and vertical metallicity gradients as well as the possible correlations between the azimuthal velocity, vϕ, and metallicity, [M/H], as qualitative indicators of the presence of mixed populations. Results. We find that a handful of super metal-rich stars exist on retrograde orbits at various distances from the Galactic center and the Galactic plane. We also find that the counter-rotating stars appear to be a well-mixed population, exhibiting radial and vertical metallicity gradients on the order of ∼ − 0.04 dex kpc−1 and −0.06 dex kpc−1, respectively, with little (if any) variation when different regions of the Galaxy are probed. The prograde stars show a vϕ − [M/H] relation that flattens – and, perhaps, even reverses as a function of distance from the plane. Retrograde samples selected to roughly probe Thamnos and Gaia-Enceladus-Sausage appear to be different populations yet they also appear to be quite linked, as they follow the same trend in terms of the eccentricity versus metallicity space.

scholarly journals The origin of the galaxy color bimodality

2014 ◽  
Vol 11 (S308) ◽  
pp. 383-389
Author(s):  
M. A. Aragón-Calvo ◽  
Mark C. Neyrinck ◽  
Joseph Silk
Keyword(s):  
Spatial Configuration ◽  
Star Formation History ◽  
Star Forming ◽  
Complex Processes ◽  
Complex Process ◽  
Formation History ◽  
Density Relation ◽  
The Galaxy ◽  
Color Density ◽  
History Of

AbstractThe star formation history of galaxies is a complex process usually considered to be stochastic in nature, for which we can only give average descriptions such as the color-density relation. In this work we follow star-forming gas particles in a hydrodynamical N-body simulation back in time in order to study their initial spatial configuration. By keeping record of the time when a gas particle started forming stars we can produce Lagrangian gas-star isochrone surfaces delineating the surfaces of accreting gas that begin producing stars at different times. These surfaces form a complex a network of filaments in Eulerian space from which galaxies accrete cold gas. Lagrangian accretion surfaces are closely packed inside dense regions, intersecting each other, and as a result galaxies inside proto-clusters stop accreting gas early, naturally explaining the color dependence on density. The process described here has a purely gravitational / geometrical origin, arguably operating at a more fundamental level than complex processes such as AGN and supernovae, and providing a conceptual origin for the color-density relation.

scholarly journals Hidden infrared star clusters in our Galaxy: follow-up observations

2009 ◽  
Vol 5 (S266) ◽  
pp. 366-366
Author(s):  
Jura Borissova ◽  
Radostin Kurtev ◽  
Margaret M. Hanson ◽  
Leonid Georgiev ◽  
Valentin Ivanov ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Star Cluster ◽  
Open Clusters ◽  
Star Formation History ◽  
Stellar Disk ◽  
Physical Parameters ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Infrared Star

AbstractWe are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.

scholarly journals Measurements of Isotopic Abundances in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 397-404 ◽  
Author(s):  
Arno A. Penzias
Keyword(s):  
Molecular Clouds ◽  
General Framework ◽  
Galactic Center ◽  
Galactic Plane ◽  
Giant Molecular Clouds ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
Isotopic Abundances ◽  
Si Isotopes

While an examination of the available data reveals some seemingly contradictory results, a general framework having the following outlines can be put forward:1. With the exception of the two galactic center sources SgrA and SgrB, the relative isotopic abundances exhibited by the giant molecular clouds in our Galaxy exhibit few, if any, significant variations from the values obtained by averaging the data from all these sources.2. The 13C/12C and 14N/15N abundance ratios are ∼130% and ∼150%, respectively, of their terrestrial values throughout the galactic plane and somewhat higher, ∼300%, near the galactic center.3. The 16O/18O and 17O/18O abundance ratios are ∼130% and ∼160%, respectively, of their terrestrial values throughout the Galaxy, although the former may be somewhat lower near the galactic center.4. The S and Si isotopes have generally terrestrial abundances.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Did the Bulge Form All at Once?

1996 ◽  
Vol 169 ◽  
pp. 403-410
Author(s):  
R.M. Rich
Keyword(s):  
Galaxy Evolution ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Field Population ◽  
Dynamical Instability ◽  
Galactic Bulge ◽  
Recent Developments ◽  
Order Of Magnitude ◽  
History Of

It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

scholarly journals The Nucleus of Our Home Galaxy: A Remnant of an Active or a Starburst Galaxy?

1994 ◽  
Vol 159 ◽  
pp. 351-354
Author(s):  
Leonid M. Ozernoy
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Radiation Spectrum ◽  
Seyfert Galaxy ◽  
Star Formation History ◽  
Starburst Galaxy ◽  
Formation History ◽  
History Of ◽  
Sgr A ◽  
Radio Band

To resolve the above dilemma, two essentially different approaches are undertaken: First, a new, detailed analysis of the entire radiation spectrum of Sgr A∗, from radio band up to gamma-rays, is reviewed, which enables us to put substantial constraints on the mass of a putative black hole. The derived upper limit turns out to be too small to allow the black hole to serve as an ‘engine’ for a Seyfert galaxy. Second, analyses of recent data on the 10 KeV gas in the central 200 pc and on star formation history at the Galactic center both make a star burst the likely episode in a recent past. Taken together, the two approaches seem to indicate that the history of the central part of our Galaxy can be better described as that of a starburst, rather than a Seyfert, galaxy.

scholarly journals 1.16. 4.5 to 11.7 microns spectrophotometric observations of the Galactic bulge by the MIRS/IRTS

1998 ◽  
Vol 184 ◽  
pp. 47-47
Author(s):  
Kin-Wing Chan ◽  
T. L. Roellig ◽  
T. Onaka ◽  
I. Yamamura ◽  
T. Tanabé
Keyword(s):  
Interstellar Medium ◽  
Mass Loss Rate ◽  
Life Time ◽  
High Mass ◽  
Galactic Latitude ◽  
Galactic Bulge ◽  
Stellar Content ◽  
Mid Infrared ◽  
Evolved Stars ◽  
Infrared Background

Using the Mid-Infrared (MIRS) on board the Infrared Telescope in Space (IRTS) we obtained the 4.5 to 11.7 μm spectra of the stellar populations and diffuse interstellar medium in the Galactic bulge (l ≈ 8.7°, b ≈ 2.9, 4.0, 4.7, and 5.7°). Below galactic latitute of 4.0° the mid-infrared background spectra in the bulge are similar to the spectrum of M and K giants. The UIR bands (6.2, 7.7, 8.6, and 11.3 μm) are also detected in these regions and they are likely arising from the diffuse interstellar medium in the bulge. Above galactic latitude of 4.0°, the mid-infrared background spectra are similar to the spectrum of those evolved stars with high mass-loss rate detected by IRAS. One likely interpretation is that this background emission arises predominantly from these stars with very low luminosities that have not been detected by IRAS. The main-sequence life time for such low luminosity evolved stars is at least 10 Gyr, even in the metal poor cases. If these low luminosity evolved stars are metal-rich then the age would be much older. Thus, the existence of a large number (~ 75) of such low luminosity evolved stars in a small region (8′ × 8′) in the bulge would have significant impact on our understanding of the stellar content and the age of the Galactic bulge.

scholarly journals Spatial variations in the star formation history of the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 281-286
Author(s):  
Carme Gallart ◽  
Ingrid Meschin ◽  
Antonio Aparicio ◽  
Peter B. Stetson ◽  
Sebastián L. Hidalgo
Keyword(s):  
Star Formation ◽  
Outer Part ◽  
Large Magellanic Cloud ◽  
Star Formation History ◽  
Wide Field ◽  
Galactocentric Distance ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Star Formation Histories

AbstractBased on the quantitative analysis of a set of wide-field color—magnitude diagrams reaching the old main sequence-turnoffs, we present new LMC star-formation histories, and their variation with galactocentric distance. Some coherent features are found, together with systematic variations of the star-formation history among the three fields analyzed. We find two main episodes of star formation in all three fields, from 1 to 4 and 7 to 13 Gyr ago, with relatively low star formation around ≃ 4–7 Gyr ago. The youngest age in each field gradually increases with galactocentric radius; in the innermost field, LMC 0514–6503, an additional star formation event younger than 1 Gyr is detected, with star formation declining, however, in the last ≃ 200 Myr. The population is found to be older on average toward the outer part of the galaxy, although star formation in all fields seems to have started around 13 Gyr ago.

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