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1
Freeman, K. C. "Galactic bulges: overview." Proceedings of the International Astronomical Union 3, S245 (July 2007): 3–10. http://dx.doi.org/10.1017/s1743921308017146.
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AbstractThis overview of galactic bulges begins with a discussion of the various kinds of bulges (classical, boxy/peanut-shaped, pseudo) and their likely formation mechanisms. Other specific topics include the Galactic bar/bulge and its chemical evolution, the bulge of M31, the relation between bulges and metal-poor halos (often lumped together as spheroids), the morphology-density relation and the formation of S0 galaxies, the color-structure bimodality, and scaling laws for bulges. Finally I will briefly discuss the current difficulty of forming bulgeless disk galaxies in ΛCDM.
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Renzini, Alvio. "Formation and evolution of stars in galactic bulges." Symposium - International Astronomical Union 153 (1993): 151–68. http://dx.doi.org/10.1017/s0074180900123174.
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A fair fraction of stars in the Galactic Bulge (a possibly in bulges in general) appears to be more metal rich than the sun. Some of the current limitations in quantitatively modelling such super metal rich (SMR) stars are briefly recalled, including the question of the helium enrichment, of the metallicity dependence of mass loss, and of the metal opacity. Recent color-magnitude diagrams for stars in the Galactic Bulge are show that the bulk of Bulge stars must be very old, although current data do not allow to determine the age with sufficient accuracy to establish the relative age of the Halo and of the Bulge. The question of the nature of the most luminous (AGB) stars in bulges and in M32 is then addressed in some detail, discussing a series of methodological aspects which would need careful consideration before using bright AGB stars as age indicators. It is concluded that — for the time being — none of the claims for the presence of an intermediate age component in the Galactic Bulge, in M32, and in the bulge of M31 is completely exempt from ambiguities, and ways for elimitating such ambiguities are suggested. Finally, from the evidence that bulges are dominated by a very old stellar population it is concluded that star formation in bulges probably started and was essentially completed before the completion of star formation in the halo: bulges are likely to on average older than halos.
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Arimoto, N. "Stellar population synthesis: Application To Galactic Bulges." Symposium - International Astronomical Union 153 (1993): 133–50. http://dx.doi.org/10.1017/s0074180900123162.
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The stellar populations give traces of the formation history of the bulges. The metallicity distribution of K-giants in the Galactic bulge resembles to that of the giant ellipticals. There seems to be no conspicuous colour-magnitude relation intrinsic to the bulges. This can be explained if the bulges formed by the dissipative collapse of central regions of proto-galaxies followed by the supernova-driven bulge wind which was induced later than the dwarf ellipticals of the similar mass (the biased wind). Unfortunately, the observational data available at present of stellar populations of the bulges are not yet sufficient to get a firm conclusion on the origin of the bulges.
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Breda, Iris, and Polychronis Papaderos. "The continuous rise of bulges out of galactic disks." Astronomy & Astrophysics 614 (June 2018): A48. http://dx.doi.org/10.1051/0004-6361/201731705.
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Context. A key subject in extragalactic astronomy concerns the chronology and driving mechanisms of bulge formation in late-type galaxies (LTGs). The standard scenario distinguishes between classical bulges and pseudo-bulges (CBs and PBs, respectively), the first thought to form monolithically prior to disks and the second gradually out of disks. These two bulge formation routes obviously yield antipodal predictions on the bulge age and bulge-to-disk age contrast, both expected to be high (low) in CBs (PBs). Aims. Our main goal is to explore whether bulges in present-day LTGs segregate into two evolutionary distinct classes, as expected from the standard scenario. Other questions motivating this study center on evolutionary relations between LTG bulges and their hosting disks, and the occurrence of accretion-powered nuclear activity as a function of bulge stellar mass ℳ⋆ and stellar surface density Σ⋆. Methods. In this study, we have combined three techniques – surface photometry, spectral modeling of integral field spectroscopy data and suppression of stellar populations younger than an adjustable age cutoff with the code REMOVEYOUNG (ℛ𝒴) – toward a systematic analysis of the physical and evolutionary properties (e.g., ℳ⋆, Σ⋆ and mass-weighted stellar age 〈t⋆〉ℳ and metallicity 〈Z⋆〉ℳ, respectively) of a representative sample of 135 nearby (≤ 130 Mpc) LTGs from the CALIFA survey that cover a range between 108.9 M⊙ and 1011.5 M⊙ in total stellar mass ℳ⋆,T. In particular, the analysis here revolves around ⟨δμ9G⟩, a new distance- and formally extinction-independent measure of the contribution by stellar populations of age ≥ 9 Gyr to the mean r-band surface brightness of the bulge. We argue that ⟨δμ9G⟩ offers a handy semi-empirical tracer of the physical and evolutionary properties of LTG bulges and a promising means for their characterization. Results. The essential insight from this study is that LTG bulges form over 3 dex in ℳ⋆ and more than 1 dex in Σ⋆ a tight continuous sequence of increasing ⟨δμ9G⟩ with increasing ℳ⋆, Σ⋆, 〈t⋆〉ℳ and 〈Z⋆〉ℳ. Along this continuum of physical and evolutionary properties, our sample spans a range of ~ 4 mag in ⟨δμ9G⟩: high-⟨δμ9G⟩ bulges are the oldest, densest and most massive ones (〈t⋆〉ℳ ~ 11.7 Gyr, Σ⋆ > 109 M⊙ kpc−2, ℳ⋆ ≥ 1010 M⊙), whereas the opposite is the case for low-⟨δμ9G⟩ bulges (〈t⋆〉ℳ ~ 7 Gyr) that generally reside in low-mass LTGs. Furthermore, we find that the bulge-to-disk age and metallicity contrast, as well as the bulge-to-disk mass ratio, show a positive trend with ℳ⋆,T, raising from, respectively, ~ 0 Gyr, ~ 0 dex and 0.25 to ~ 3 Gyr, ~ 0.3 dex and 0.67 across the mass range covered by our sample. Whereas gas excitation in lower-mass (≲ 109.7 M⊙) bulges is invariably dominated by star formation (SF), LINER- and Seyfert-specific emission-line ratios were exclusively documented in high-mass (≳ 1010 M⊙), high-Σ⋆ (≳ 109 M⊙ kpc−2) bulges. This is in agreement with previous work and consistent with the notion that the Eddington ratio or the black hole-to-bulge mass ratio scale with ℳ⋆. The coexistence of Seyfert and SF activity in ~20% of higher-ℳ⋆, high-Σ⋆ bulges being spectroscopically classified as Composites suggests that the onset of AGN-driven feedback does not necessarily lead to an abrupt termination of SF in LTG nuclei. Conclusions. The continuity both in the properties of LTG bulges themselves and in their age and metallicity contrast to their parent diskssuggests that these components evolve alongside in a concurrent process that leads to a continuum of physical and evolutionary characteristics. Our results are consistent with a picture where bulge growth in LTGs is driven by a superposition of quick-early and slow-secular processes, the relative importance of which increases with ℳ⋆,T. These processes, which presumably combine in situ SF in the bulge and inward migration of material from the disk, are expected to lead to a non-homologous radial growth of Σ⋆ and a trend for an increasing Sérsic index with increasing galaxy mass.
5
Rich, R. Michael. "The Stellar Population of the Galactic Bulge." Symposium - International Astronomical Union 171 (1996): 19–22. http://dx.doi.org/10.1017/s0074180900232105.
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How old is the bulge? Are bulges in general as old as halos? Do bulges form rapidly or slowly? Are they formed from disks via dynamical instabilities, or perhaps by starbursts? In general, do luminous spheroids form at the same time as the oldest stars?
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Barbuy, Beatriz, Cristina Chiappini, and Ortwin Gerhard. "Chemodynamical History of the Galactic Bulge." Annual Review of Astronomy and Astrophysics 56, no. 1 (September 14, 2018): 223–76. http://dx.doi.org/10.1146/annurev-astro-081817-051826.
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The Galactic Bulge can uniquely be studied from large samples of individual stars and is therefore of prime importance for understanding the stellar population structure of bulges in general. Here the observational evidence on the kinematics, chemical composition, and ages of Bulge stellar populations based on photometric and spectroscopic data is reviewed. The bulk of Bulge stars are old and span a metallicity range of −1.5≲[Fe/H]≲+0.5. Stellar populations and chemical properties suggest a star-formation timescale below ∼2 Gyr. The overall Bulge is barred and follows cylindrical rotation, and the more metal-rich stars trace a box/peanut (B/P) structure. Dyna-mical models demonstrate the different spatial and orbital distributions of metal-rich and metal-poor stars. We discuss current Bulge-formation scenarios based on dynamical, chemical, chemodynamical, and cosmological models. Despite impressive progress, we do not yet have a successful fully self-consistent chemodynamical Bulge model in the cosmological framework, and we will also need a more extensive chrono-chemical-kinematic 3D map of stars to better constrain such models.
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Martinez-Valpuesta, Inma, and E. Athanassoula. "Boxy/peanut bulges, vertical buckling and galactic bars." Proceedings of the International Astronomical Union 3, S245 (July 2007): 103–6. http://dx.doi.org/10.1017/s1743921308017390.
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AbstractBoxy/peanut bulges in disk galaxies have been associated to stellar bars. In this talk, we discuss the different properties of such bulges and their relation with the corresponding bar, using a very large sample of a few hundred numerical N-body simulations. We present and inter-compare various methods of measuring the boxy/peanut bulge properties, namely its strength, shape and possible asymmetry. Some of these methods can be applied to both simulations and observations. Our final goal is to get correlations that will allow us to obtain information on the boxy/peanut bulge for a galaxy viewed face-on as well as information on the bars of galaxies viewed edge-on.
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Ballero, Silvia K., Francesca Matteucci, and Luca Ciotti. "Chemical evolution of Seyfert galaxies." Proceedings of the International Astronomical Union 3, S245 (July 2007): 231–32. http://dx.doi.org/10.1017/s1743921308017729.
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AbstractWe computed the chemical evolution of Seyfert galaxies, residing in spiral bulges, based on an updated model for the Milky Way bulge with updated calculations of the Galactic potential and of the feedback from the central supermassive black hole (BH) in a spherical approximation. We followed the evolution of bulges of masses 2 × 109 − 1011M⊙ by scaling the star-formation efficiency and the bulge scalelenght as in the inverse-wind scenario for ellipticals. We successfully reproduced the observed relation between the BH mass and that of the host bulge, and the observed peak nuclear bolometric luminosity. The observed metal overabundances are easily achieved, as well as the constancy of chemical abundances with the redshift.
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Gargiulo, Ignacio D., Antonela Monachesi, Facundo A. Gómez, Robert J. J. Grand, Federico Marinacci, Rüdiger Pakmor, Simon D. M. White, Eric F. Bell, Francesca Fragkoudi, and Patricia Tissera. "The prevalence of pseudo-bulges in the Auriga simulations." Monthly Notices of the Royal Astronomical Society 489, no. 4 (September 11, 2019): 5742–63. http://dx.doi.org/10.1093/mnras/stz2536.
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ABSTRACT We study the galactic bulges in the Auriga simulations, a suite of 30 cosmological magneto-hydrodynamical zoom-in simulations of late-type galaxies in Milky Way sized dark matter haloes performed with the moving-mesh code arepo. We aim to characterize bulge formation mechanisms in this large suite of galaxies simulated at high resolution in a fully cosmological context. The bulges of the Auriga galaxies show a large variety in their shapes, sizes, and formation histories. According to observational classification criteria, such as Sérsic index and degree of ordered rotation, the majority of the Auriga bulges can be classified as pseudo-bulges, while some of them can be seen as composite bulges with a classical component; however, none can be classified as a classical bulge. Auriga bulges show mostly an in situ origin, $21{{\ \rm per\ cent}}$ of them with a negligible accreted fraction (facc < 0.01). In general, their in situ component was centrally formed, with ${\sim}75{{\ \rm per\ cent}}$ of the bulges forming most of their stars inside the bulge region at z = 0. Part of their in situ mass growth is rapid and is associated with the effects of mergers, while another part is more secular in origin. In $90{{\ \rm per\ cent}}$ of the Auriga bulges, the accreted bulge component originates from less than four satellites. We investigate the relation between the accreted stellar haloes and the bulges of the Auriga simulations. The total bulge mass shows no correlation with the accreted stellar halo mass, as in observations. However, the accreted mass of bulges tends to correlate with their respective accreted stellar halo mass.
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MacArthur, Lauren A., Richard S. Ellis, and Tommaso Treu. "The fundamental plane of bulges at intermediate redshift." Proceedings of the International Astronomical Union 3, S245 (July 2007): 443–46. http://dx.doi.org/10.1017/s1743921308018322.
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AbstractWe report on a new study aimed at understanding the diversity and evolutionary properties of distant galactic bulges in the context of well-established trends for pure spheroidal galaxies. Bulges have been isolated for a sample of 137 spiral galaxies in the GOODS fields within the redshift range 0.1 < z < 1.2. Using proven photometric techniques we determine for each galaxy the characteristic parameters (size, surface brightness, profile shape) in the 4 GOODS-ACS imaging bands of both the disk and bulge components. Using the DEIMOS spectrograph on Keck, precision stellar velocity dispersions were secured for a sizeable fraction of the bulges. This has enabled us to compare the Fundamental Plane of our distant bulges with that of field spheroidal galaxies in a similar redshift range. Bulges in spiral galaxies with a bulge-to-total luminosity ratio (B/T) > 0.2 show very similar patterns of evolution to those seen for low luminosity spheroidals. To first order, their recent mass assembly histories are equivalent.
11
Rich, R. Michael. "Element Abundance Ratios in Galactic Bulge Stars." Highlights of Astronomy 11, no. 1 (1998): 66–69. http://dx.doi.org/10.1017/s1539299600019997.
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I review the current status of measurements of element ratios in metal rich stars. These include giants in the Galactic bulge, metal rich Galactic globular clusters, and high velocity dwarfs in the Solar vicinity. There is evidence for enhancement of Mg and Ti in the bulge. While s-process elements have Solar abundance in bulge giants, they are deficient in the metal rich, high velocity dwarfs. There are no secure measurements of oxygen abundance in the bulge, but present data indicate no evidence either for extremely low or high [O/Fe] in bulge giants. The current data are limited by resolution and S/N, and I outline goals for observations with the next generation of ground-based telescopes.If the central bulge of the Milky Way formed rapidly, one would expect that enrichment could occur only through massive star SNe, with little or no contribution from core deflagration SNe. In this scenario, one expects alpha-capture elements to be enhanced at a given [Fe/H] compared to the Solar vicinity: element abundance ratios may record something of the history of star formation. The idea is developed in Wheeler, Sneden & Truran (1989) and its application to bulges and elliptical galaxies is developed in Matteucci & Brocato (1990). As Kraft reviews in this volume, the stellar evolution effects that modify surface abundances in globular cluster stars do not appear to be a problem for field giants.
12
Binney, James. "Symposium summary: dynamics." Proceedings of the International Astronomical Union 3, S245 (July 2007): 455–58. http://dx.doi.org/10.1017/s1743921308018358.
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AbstractPseudobulges form from unstable disks, while classical bulges form in violent episodes of star formation when a merger sweeps cold gas to a galactic centre. It seems unlikely that smashed disks contribute much to classical bulges. During mergers central black holes make cusps shallower and inflate kinematically decoupled cores. The abundance of galaxies with no detected classical bulge can perhaps be understood if galaxies exchange gas with the IGM more freely than is often supposed.
13
Milone, A., and B. Barbuy. "TiO bands in composite systems." Symposium - International Astronomical Union 153 (1993): 313–14. http://dx.doi.org/10.1017/s0074180900123393.
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TiO bands at λ 620 nm are synthesized. The behaviour of these bands as a function of stellar parameters is studied. Application to composite spectra of one galactic bulge globular cluster and to bulges of elliptical galaxies is also carried out. TiO bands may be useful metallicity indicators.
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Dwek, E. "Morphology of the Galactic Bulge from COBE DIRBE Observations." Symposium - International Astronomical Union 169 (1996): 61–69. http://dx.doi.org/10.1017/s0074180900229537.
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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).
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Zhao, HongSheng. "A Self-Consistent Dynamical Model for the COBE Observed Galactic Bar and Its Application to Microlensing." International Astronomical Union Colloquium 157 (1996): 549–53. http://dx.doi.org/10.1017/s0252921100050417.
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AbstractA self-consistent stellar dynamical model for the Galactic bar is constructed from about 500 numerically computed orbits with an extension of the Schwarzschild technique. The model fits the COBE found asymmetric boxy light distribution and the observed stellar kinematics of the bulge. The model potential is also consistent with the non-circular motions of the HI and CO velocity maps of the inner Galaxy. We also use the stellar bar model to construct an N-body model to study stability and a microlensing map towards the bulge, which can account for the observed optical depth and the event duration by the MACHO and OGLE collaborations. The technique used here can be applied to interpret light and velocity data of external bulges/bars and galactic nuclei.
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Pfenniger, Daniel. "Delayed formation of bulges by dynamical processes." Symposium - International Astronomical Union 153 (1993): 387–90. http://dx.doi.org/10.1017/s0074180900123721.
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Two mechanisms involving purely dynamical processes can lead to the formation of a bulge after its disc: 1) small bulges (1 – 2 kpc), including box-shaped bulges and mildly triaxial bulges, can result from the formation and destruction of a bar; 2) big bulges (> 2kpc) à la Sombrero can grow following the accretion of small satellites. Fully consistent N-body simulations show that the fraction of galaxy mass accreted in this way needs to be larger than about 5%. Less accretion does not create smaller bulges, but heats the whole disc. These dynamical effects transforming Hubble types from SB to SA and vice-versa over ≈ 1 – 2 Gyr also indicate, by the secular growth of bulges, a general sense of galactic evolution from Sd to Sa.
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Zhang, Xiaolei. "1.7. Secular dynamical evolution of spiral galaxies and the formation of galactic bulges." Symposium - International Astronomical Union 184 (1998): 29–30. http://dx.doi.org/10.1017/s0074180900083868.
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We show that a recently discovered spiral-induced radial mass accretion process could account for the formation of the Galactic Bulge in a Hubble time. This process is thus expected to be important in the formation of bulges in spiral galaxies, and in the secular evolution of galaxies along the Hubble sequence from late to earlier types.
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Feltzing, S. "1.12. Structure of the inner galactic disk and the bulge - first results." Symposium - International Astronomical Union 184 (1998): 39–40. http://dx.doi.org/10.1017/s0074180900083911.
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Is there an age and/or a metallicity gradient in the Bulge? This is a notoriously difficult question because of the well known age-metallicity-distance degeneracy in colour magnitude diagrams (CMD) as well as the severe crowding and large reddening towards the Galactic Bulge. The current observational data on the bulge in our galaxy and bulges in other spiral galaxies point in disparate directions, that is evidence for both early (e.g. existence of very old halo and bulge globular clusters) and late formation (e.g. Sgr dSph and bar instabilities) can be found as well as the existence and non-existence of metallicity gradients (for a review of the observational status see Wyse, Gilmore & Franx 1997). We here present the CMDs for two fields, Baade's window and SGR-I, Fig.1c and d. Both these regions have low extinction. To determine the age and metallicity for these stars we compare the CMDs with CMDs of globular clusters, also observed with WFPC2, of known metallicity and age, Fig.1a and b. This method enables us to work entirely in the in-flight magnitude system of WFPC2 and there is no need for transformations to standard colours and magnitudes, something which is not straight forward for WFPC2 passbands.
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Costantin, L., J. Méndez-Abreu, E. M. Corsini, M. C. Eliche-Moral, T. Tapia, L. Morelli, E. Dalla Bontà, and A. Pizzella. "The intrinsic shape of bulges in the CALIFA survey." Astronomy & Astrophysics 609 (January 2018): A132. http://dx.doi.org/10.1051/0004-6361/201731823.
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Context.The intrinsic shape of galactic bulges in nearby galaxies provides crucial information to separate bulge types.Aims.We aim to derive accurate constraints to the intrinsic shape of bulges to provide new clues on their formation mechanisms and set new limitations for future simulations.Methods.We retrieved the intrinsic shape of a sample of CALIFA bulges using a statistical approach. Taking advantage of GalMer numerical simulations of binary mergers we estimated the reliability of the procedure. Analyzing thei-band mock images of resulting lenticular remnants, we studied the intrinsic shape of their bulges at different galaxy inclinations. Finally, we introduced a new (B/A,C/A) diagram to analyze possible correlations between the intrinsic shape and the properties of bulges.Results.We tested the method on simulated lenticular remnants, finding that for galaxies with inclinations of 25° ≤θ≤ 65° we can safely derive the intrinsic shape of their bulges. We found that our CALIFA bulges tend to be nearly oblate systems (66%), with a smaller fraction of prolate spheroids (19%), and triaxial ellipsoids (15%). The majority of triaxial bulges are in barred galaxies (75%). Moreover, we found that bulges with low Sérsic indices or in galaxies with low bulge-to-total luminosity ratios form a heterogeneous class of objects; additionally, bulges in late-type galaxies or in less massive galaxies have no preference for being oblate, prolate, or triaxial. On the contrary, bulges with high Sérsic index, in early-type galaxies, or in more massive galaxies are mostly oblate systems.Conclusions.We concluded that various evolutionary pathways may coexist in galaxies, with merging events and dissipative collapse being the main mechanisms driving the formation of the most massive oblate bulges and bar evolution reshaping the less massive triaxial bulges.
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Breda, Iris, Polychronis Papaderos, and Jean-Michel Gomes. "Indications of the invalidity of the exponentiality of the disk within bulges of spiral galaxies." Astronomy & Astrophysics 640 (August 2020): A20. http://dx.doi.org/10.1051/0004-6361/202037889.
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Context. A fundamental subject in extragalactic astronomy concerns the formation and evolution of late-type galaxies (LTGs). The standard scenario envisages a two-phase build-up for these systems, comprising the early assembly of the bulge followed by disk accretion. However, recent observational evidence points to a joint formation and perpetual coevolution of these structural components. Our current knowledge on the properties of the bulge and the disk is, to a large degree, founded on photometric decomposition studies, which sensitively depend on the adopted methodology and enclosed assumptions on the structure of LTGs. A critical assumption whose validity had never been questioned before is that galactic disks conserve their exponential nature up to the galactic center. This, although seemingly plausible, implies that bulge and disk coexist without significant dynamical interaction and mass exchange over nearly the entire Hubble time. Aims. Our goal is to examine the validity of the standard assumption that galactic disks preserve their exponential intensity profile inside the bulge radius (RB) all the way to the galactic center, as is generally assumed in photometric decomposition studies. Methods. We developed a spectrophotometric bulge-disk decomposition technique that provides an estimation for the net (i.e., disk-subtracted) spectrum of the bulge. Starting from an integral field spectroscopy (IFS) data cube, this tool computes the integrated spectrum of the bulge and the disk, scales the latter considering the light fraction estimated from photometric decomposition techniques, and subtract it from the former, thereby allowing for the extraction of the net-bulge spectrum. Considering that the latter depends on the underlying assumption for the disk luminosity profile, checking its physical plausibility (for instance, positiveness and spectral slope) places indirect constraints on the validity of the disk’s assumed profile inside the radius R⋆ < RB. In this pilot study, we tested the following three different disk configurations: the standard exponential disk profile as well as a centrally flattened or down-bending exponential disk profile. Results. A systematic application of our spectrophotometric bulge-disk decomposition tool to a representative sample of 135 local LTGs from the CALIFA survey yields a significant fraction (up to ∼30 (20)%) of unphysical net-bulge spectra when a purely exponential (centrally flattened) intensity profile is assumed for the disk. This never occurs for disks’ profiles involving a centrally decreasing intensity. Conclusions. The obtained results suggest that, for a significant fraction of LTGs, the disk component shows a down-bending beneath the bulge. If proven to be true, this result will call for a substantial revision of structural decomposition studies for LTGs and it will have far-reaching implications in our understanding of the photometric properties of their bulges. Given its major relevance, it appears worthwhile to explore the central stellar surface density of galactic disks further, through an improved version of the spectrophotometric decomposition tool presented here and its application combining deep surface photometry, spatially resolved spectral synthesis, and kinematical analyses.
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Izquierdo-Villalba, David, Silvia Bonoli, Massimo Dotti, Alberto Sesana, Yetli Rosas-Guevara, and Daniele Spinoso. "From galactic nuclei to the halo outskirts: tracing supermassive black holes across cosmic history and environments." Monthly Notices of the Royal Astronomical Society 495, no. 4 (May 21, 2020): 4681–706. http://dx.doi.org/10.1093/mnras/staa1399.
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ABSTRACT We study the mass assembly and spin evolution of supermassive black holes (BHs) across cosmic time as well as the impact of gravitational recoil on the population of nuclear and wandering BHs (wBHs) by using the semi-analytical model L-Galaxies run on top of Millennium merger trees. We track spin changes that BHs experience during both coalescence events and gas accretion phases. For the latter, we assume that spin changes are coupled with the bulge assembly. This assumption leads to predictions for the median spin values of z = 0 BHs that depend on whether they are hosted by pseudo-bulges, classical bulges or ellipticals, being $\overline{a} \sim 0.9$, 0.7 and 0.4, respectively. The outcomes of the model display a good consistency with $z \le 4$ quasar luminosity functions and the $z = 0$ BH mass function, spin values, and BH correlation. Regarding the wBHs, we assume that they can originate from both the disruption of satellite galaxies (orphan wBH) and ejections due to gravitational recoils (ejected wBH). The model points to a number density of wBHs that increases with decreasing redshift, although this population is always $\rm {\sim}2\, dex$ smaller than the one of nuclear BHs. At all redshifts, wBHs are typically hosted in $\rm {\it M}_{halo} \gtrsim 10^{13} \, M_{\odot }$ and $\rm {\it M}_{stellar} \gtrsim 10^{10} \, M_{\odot }$, being orphan wBHs the dominant type. Besides, independently of redshift and halo mass, ejected wBHs inhabit the central regions (${\lesssim}\rm 0.3{\it R}_{200}$) of the host DM halo, while orphan wBH linger at larger scales (${\gtrsim}\rm 0.5{\it R}_{200}$). Finally, we find that gravitational recoils cause a progressive depletion of nuclear BHs with decreasing redshift and stellar mass. Moreover, ejection events lead to changes in the predicted local BH–bulge relation, in particular for BHs in pseudo-bulges, for which the relation is flattened at $\rm {\it M}_{bulge} \gt 10^{10.2}\, M_{\odot }$ and the scatter increase up to ${\sim}\rm 3\, dex$.
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Thomas, Daniel, and Roger L. Davies. "Rejuvenation of spiral bulges." Proceedings of the International Astronomical Union 3, S245 (July 2007): 289–92. http://dx.doi.org/10.1017/s1743921308017936.
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AbstractWe seek to understand whether the stellar populations of galactic bulges show evidence of secular evolution triggered by the presence of the disc. To this end we re-analyse the sample of Proctor & Sansom (2002), deriving stellar population ages and element abundances from absorption line indices as functions of central velocity dispersion and Hubble type. In agreement with other studies in the literature, we find that bulges have relatively low luminosity weighted ages, the lowest age derived being 1.3 Gyr. Hence bulges are not generally old, but actually rejuvenated systems. We discuss evidence that this might be true also for the bulge of the Milky Way. The smallest bulges are the youngest with the lowest α/Fe ratios indicating the presence of significant star formation events involving 10 − 30 per cent of their total mass in the past 1 − 2 Gyr. No significant correlations of the stellar population parameters with Hubble Type are found. We show that the above relationships with σ coincide perfectly with those of early-type galaxies. At a given velocity dispersion, bulges and elliptical galaxies are indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudobulge formation must be restricted to spirals of types later than Sbc.
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Breda, Iris, Polychronis Papaderos, Jean Michel Gomes, José Manuel Vílchez, Bodo L. Ziegler, Michaela Hirschmann, Leandro S. M. Cardoso, Patricio Lagos, and Fernando Buitrago. "Stellar age gradients and inside-out star formation quenching in galaxy bulges." Astronomy & Astrophysics 635 (March 2020): A177. http://dx.doi.org/10.1051/0004-6361/201937193.
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Radial age gradients hold the cumulative record for the multitude of physical processes driving the build-up of stellar populations and the ensuing star formation (SF) quenching process in galaxy bulges and, therefore, potentially sensitive discriminators between competing theoretical concepts on bulge formation and evolution. Based on spectral modeling of integral field spectroscopy (IFS) data from the CALIFA survey, we derived mass- and light-weighted stellar age gradients (∇(t⋆, B)ℒ, ℳ) within the photometrically determined bulge radius (RB) of a representative sample of local face-on late-type galaxies that span 2.6 dex in stellar mass (8.9 ≤ log ℳ⋆, T ≤ 11.5). Our analysis documents a trend of decreasing ∇(t⋆, B)ℒ, ℳ with increasing ℳ⋆, T, with high-mass bulges predominantly showing negative age gradients and vice versa. The inversion from positive to negative ∇(t⋆, B)ℒ, ℳ occurs at log ℳ⋆, T ≃ 10, which roughly coincides with the transition from lower-mass bulges whose gas excitation is powered by SF to bulges classified as composite, LINER, or Seyfert. We discuss two simple limiting cases for the origin of radial age gradients in massive late-type galaxy bulges. The first one assumes that the stellar age in the bulge is initially spatially uniform (∇(t⋆, B)ℒ, ℳ ≈ 0), thus the observed age gradients (∼ − 3 Gyr/RB) arise from an inside-out SF quenching (ioSFQ) front that is radially expanding with a mean velocity vq. In this case, the age gradients for massive bulges translate into a slow (vq ∼1–2 km s−1) ioSFQ that lasts until z ∼ 2, suggesting mild negative feedback by SF or an active galactic nucleus (AGN). If, on the other hand, negative age gradients in massive bulges are not due to ioSFQ but primarily due to their inside-out formation process, then the standard hypothesis of quasi-monolithic bulge formation has to be discarded in favor of another scenario. This would involve a gradual buildup of stellar mass over 2–3 Gyr through, for instance, inside-out SF and inward migration of SF clumps from the disk. In this case, rapid (≪1 Gyr) AGN-driven ioSFQ cannot be ruled out. While the ℳ⋆, T versus ∇(t⋆, B)ℒ, ℳ relation suggests that the assembly history of bulges is primarily regulated by galaxy mass, its large scatter (∼1.7 Gyr/RB) reflects a considerable diversity. This calls for an in-depth examination of the role of various processes (e.g., negative and positive AGN feedback, bar-driven gas inflows) with higher-quality IFS data in conjunction with advanced spectral modeling codes.
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Rich, R. Michael. "1.1. The Galactic bulge." Symposium - International Astronomical Union 184 (1998): 11–18. http://dx.doi.org/10.1017/s0074180900083807.
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I review current work on the Galactic bulge, with emphasis on issues that may connect to the environment of the Galactic Center. There is growing evidence that the field population of the bulge at RGC > 500pc is as old as the metal rich Galactic center globular clusters, and that field and clusters have the same spatial and metallicity distribution. We suggest that by analogy, extragalactic metal rich cluster systems, which also tend to follow the spheroid light, are old. On the other hand, there has been long standing evidence for an age gradient toward the Galactic center, and recent observations confirm without doubt that there is active star formation there. If a long-lived bar has been funneling gas (and inducing star formtion) in the central 100 pc, the star formation history there will be complicated and interesting.
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Petrovskaya, I. V., and S. Ninković. "The contribution of the Galactic Bulge to the Galactic rotation curve." Symposium - International Astronomical Union 153 (1993): 353–54. http://dx.doi.org/10.1017/s0074180900123575.
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It is not always clear what the bulge of the Galaxy is: a region close to the centre, a subsystem formed by a distinct population, or a mixture of populations but characterised by its own mass distribution. We consider the bulge of the Milky Way as a subsystem and thus contributing to the galactic gravitation field. We want to estimate the contribution of the galactic bulge to the rotation curve.
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Tsujimoto, Takuji, and Kenji Bekki. "Metal-rich infall onto the inner disk through the interaction between bulge winds and gaseous halos." Proceedings of the International Astronomical Union 5, S265 (August 2009): 384–85. http://dx.doi.org/10.1017/s1743921310001043.
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AbstractWe demonstrate for the first time that gaseous halos of disk galaxies can play a vital role in recycling metal-rich gas ejected from the bulges and thus in promoting the chemical evolution of the disks. Our numerical simulations show that metal-rich bulge winds can be accreted onto the thin disks owing to hydrodynamical interaction between the gaseous ejecta and the gaseous halos. Accordingly, we anticipate that chemical abundances of the inner disk stars are significantly influenced by the enriched winds. About ~1% of gaseous ejecta from the bulges can be accreted onto the middle disk corresponding to the sun's position. We discuss these results in the context of the origin of super metal-rich stars in the solar neighborhood as well as an observed flattening of the abundance gradient in the Galactic disk.
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Gadotti, Dimitri Alexei. "The structural parameters of bulges, bars and discs in the local Universe." Proceedings of the International Astronomical Union 3, S245 (July 2007): 117–20. http://dx.doi.org/10.1017/s1743921308017420.
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AbstractImage decomposition of galaxies is now routinely used to estimate the structural parameters of galactic components. In this work, I address questions on the reliability of this technique. In particular, do bars and AGN need to be taken into account to obtain the structural parameters of bulges and discs? And to what extent can we trust image decomposition when the physical spatial resolution is relatively poor? With this aim, I performed multi-component (bar/bulge/disc/AGN) image decomposition of a sample of very nearby galaxies and their artificially redshifted images, and verified the effects of removing the bar and AGN components from the models. Neglecting bars can result in a overestimation of the bulge-to-total luminosity ratio of a factor of two, even if the resolution is low. Similar effects result when bright AGN are not considered in the models, but only when the resolution is high. I also show that the structural parameters of more distant galaxies can in general be reliably retrieved, at least up to the point where the physical spatial resolution is ≈ 1.5 Kpc, but bulge parameters are prone to errors if its effective radius is small compared to the seeing radius, and might suffer from systematic effects. I briefly discuss the consequences of these results to our knowledge of the stellar mass budget in the local universe, and finish by showing preliminary results from a large SDSS sample on the dichotomy between classical and pseudo-bulges.
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Bisnovatyi-Kogan, Gennady, and Alexei Pozanenko. "Annihilation line from the galactic bulge due to action of low-mass flare stars." International Journal of Modern Physics D 27, no. 10 (July 2018): 1844003. http://dx.doi.org/10.1142/s0218271818440030.
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We consider the low-mass flare stars which form the bulk of the population in the galactic bulge as a source of the positrons needed to form the observed narrow annihilation line from the galactic bulge. Estimates based on the observed flares in low-mass stars, together with observations of the annihilation line in solar flares, show that the rate of production of positrons in flares in the stars in the bulge may be sufficient to explain the formation of the narrow stationary annihilation line observed from the region of the galactic bulge.
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Wyse, Rosemary F. G., Gerard Gilmore, and Marijn Franx. "GALACTIC BULGES." Annual Review of Astronomy and Astrophysics 35, no. 1 (September 1997): 637–75. http://dx.doi.org/10.1146/annurev.astro.35.1.637.
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Mollá, Mercedes, Federico Ferrini, and Giacomo Gozzi. "Galactic bulges." Monthly Notices of the Royal Astronomical Society 316, no. 2 (August 2000): 345–56. http://dx.doi.org/10.1046/j.1365-8711.2000.03497.x.
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Tasca, Lidia A. M., and Laurence Tresse. "Where is the Light? Tracing the Evolution of Bulges and Disks since z ~ 0.8." Proceedings of the International Astronomical Union 6, S277 (December 2010): 282–86. http://dx.doi.org/10.1017/s1743921311022940.
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AbstractThe chronology of galactic bulge and disk formation is studied by analysing the relative contributions of these components to the B band rest–frame luminosity density (LD) at two different cosmological epochs. The luminosity function (LF) of the bulge and disk components at z ~ 0.8 is computed on a galaxy subsample of the final zCOSMOS “bright” catalogue of roughly 20,000 objects with spectroscopic redshift in the COSMOS field. The comparison is then performed on galaxies in the local universe. Our preliminary results show that the LD in the disk component strongly decreases from ~ 80% at z ~ 0.8 to ~ 50% at z = 0, the bulges having a specular behaviour. The observational constraints provided in this work are aimed to discriminate among competing scenarios of galaxy formation and evolution. An appropriate comparison with hydrodynamical semianalytical models will be considered in a future study to understand further the formation and evolution of galaxies.
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Mizerski, Tomasz. "Multiperiodic RR Lyrae stars in the Galactic Bulge and the SMC." International Astronomical Union Colloquium 193 (2004): 124–27. http://dx.doi.org/10.1017/s0252921100010460.
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AbstractI have performed a detailed analysis of multiperiodic RR Lyr stars of the Galactic Bulge and the Small Magellanic Cloud. In the rich OGLE-II database on the Galactic Bulge objects I detected more than 2500 RR Lyr stars, with almost 600 of them exhibiting multiperiodic behavior of various, sometimes unique, kinds. Many of them can only be explained by excitation of nonradial modes. There are two major, striking differences between the two discussed stellar systems: the incidence rate of RRd double mode pulsators is over 30 times higher in the SMC than in the Galactic Bulge, and there are more than twice as many Blazhko stars in the Galactic Bulge as in the SMC.
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Walton, N. A., M. J. Barlow, and R. E. S. Clegg. "Chemical Abundances in Galactic Bulge Pn." Symposium - International Astronomical Union 155 (1993): 581. http://dx.doi.org/10.1017/s0074180900172559.
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We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity Galactic bulge. The sample abundances are also contrasted with the abundances found for PN in the Galactic disk. The mean C/O ratio for the bulge PN is significantly lower than that found for Galactic disk PN. Further, we present an abundance analysis of the very metal-poor bulge PN M2-29. From an analysis of the differential extinction found from the observed ratios of the He ii 1640,4686Å lines, we find that the ultraviolet reddening law towards the bulge is steeper than in the solar neighbourhood.
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Gouda, N., Y. Kobayashi, Y. Yamada, T. Yano, T. Tsujimoto, M. Suganuma, Y. Niwa, and M. Yamauchi. "JASMINE: constructor of the dynamical structure of the Galactic bulge." Proceedings of the International Astronomical Union 3, S245 (July 2007): 355–58. http://dx.doi.org/10.1017/s1743921308018103.
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AbstractWe introduce a Japanese space astrometry project which is called JASMINE. JASMINE (Japan Astrometry Satellite Mission for INfrared Exploration) will measure distances and tangential motions of stars in the Galactic bulge with yet unprecedented precision. JASMINE will operate in z-band whose central wavelength is 0.9 micron. It will measure parallaxes, positions with accuracy of about 10 micro-arcsec and proper motions with accuracy of about 10 micro- arcsec/year for the stars brighter than z=14 mag. The number of stars observed by JASMINE with high accuracy of parallaxes in the Galactic bulge is much larger than that observed in other space astrometry projects operating in optical bands. With the completely new “map of the Galactic bulge” including motions of bulge stars, we expect that many new exciting scientific results will be obtained in studies of the Galactic bulge. One of them is the construction of the dynamical structure of the Galactic bulge. Kinematics and distance data given by JASMINE are the closest approach to a view of the exact dynamical structure of the Galactic bulge.Presently, JASMINE is in a development phase, with a target launch date around 2016. We comment on the outline of JASMINE mission, scientific targets and a preliminary design of JASMINE in this paper.
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Rich, R. Michael, Christian Howard, David B. Reitzel, HongSheng Zhao, and Roberto de Propris. "Kinematics and composition of the Galactic bulge: recent progress." Proceedings of the International Astronomical Union 3, S245 (July 2007): 333–38. http://dx.doi.org/10.1017/s174392130801805x.
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AbstractWe present recent results from a Keck study of the composition of the Galactic bulge, as well as results from the bulge Bulge Radial Velocity Assay (BRAVA). Culminating a 10 year investigation, Fulbright, McWilliam, & Rich (2006, 2007) solved the problem of deriving the iron abundance in the Galactic bulge, and find enhanced alpha element abundances, consistent with the earlier work of McWilliam & Rich (1994). We also report on a radial velocity survey of 2MASS-selected M giant stars in the Galactic bulge, observed with the CTIO 4m Hydra multi-object spectrograph. This program is to test dynamical models of the bulge and to search for and map any dynamically cold substructure in the Galactic bulge. We show initial results on fields at −10° < l < + 10° and b = −4°. We construct a longitude-velocity plot for the bulge stars and the model data, and find that contrary to previous studies, the bulge does not rotate as a solid body; from −5° < l < + 5° the rotation curve has a slope of ≈ 100 km s−1 and flattens considerably at greater l and reaches a maximum rotation of 45 km s−1 (heliocentric) or ~ 70 km s−1 (Galactocentric). This rotation is slower than that predicted by the dynamical model of Zhao (1996).
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Origlia, Livia. "A review of the chemical abundances and kinematics of the Galactic bulge." Proceedings of the International Astronomical Union 9, S298 (May 2013): 28–39. http://dx.doi.org/10.1017/s1743921313006170.
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AbstractThis review will attempt to draw a state of the art observational picture of the Galactic bulge. The main chemical, kinematic and evolutionary properties of the gas and stellar populations in the barred bulge and towards the Galactic center region will be discussed in the context of the possible formation scenarios. Future perspectives for our comprehension of the complex structure of the Galactic bulge from ongoing and foreseen optical and infrared surveys will be also highlighted.
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Habing, H. J. "Stellar Populations in the Galactic Bulge." Symposium - International Astronomical Union 169 (1996): 317–27. http://dx.doi.org/10.1017/s0074180900229859.
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In this review I discuss stars in the bulge of our Milky Way, but I exclude stars within a few parsec from Sgr A West; they are the subject of other reviews at this Symposium. We should, however, not forget that there may be an intimate connection between the central cluster and the bulge: bulge stars may eject matter that feeds the monster at the center and eruptions by this monster may have an important effect on the bulge.
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Kim, J. W., H. I. Kim, and Y. J. Sohn. "Red-giant branch morphology of metal-poor globular clusters in the Galactic bulge." Proceedings of the International Astronomical Union 3, S245 (July 2007): 363–64. http://dx.doi.org/10.1017/s1743921308018139.
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AbstractUsing the (J − K, K) color-magnitude diagrams (CMDs) of 16 metal-poor globular clusters in the Galactic bulge, we investigate the morphological properties of their red-giant branch (RGB), comparing with those of metal-rich clusters in the Galactic bulge and metal-poor clusters in the Galactic halo. The RGB morphological parameters, such as colors at fixed magnitudes, magnitudes at a fixed color, the RGB slope, and a difference of color indices at two fixed magnitudes have been derived from the near-IR CMDs for each cluster. Metal-poor Galactic bulge clusters follow the previous empirical relations between colors at fixed magnitudes and magnitudes at a fixed color of the RGB and the cluster's metallicity. However, the RGB slope and the color difference parameters of some bulge clusters deviate slightly from the previous empirical linear relations for the other globular clusters, implying that the metal-poor bulge clusters may have different formation origin from the other globular clusters in the Galaxy.
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Busso, Giorgia, and Sabine Moehler. "The UV spectrum of the Galactic Bulge." Proceedings of the International Astronomical Union 5, S262 (August 2009): 311–12. http://dx.doi.org/10.1017/s1743921310002991.
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AbstractThe aim of this work is to investigate the possible existence of the UV-excess in the Milky Way bulge and its correlation with the presence of sdB stars in the bulge. The integrated spectrum of a bulge region from the UV to the optical was constructed. Results show that this bulge region has only a very weak UV excess
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Vallenari, A., S. Ragaini, and G. Bertelli. "The position angle of the Galactic bulge." Proceedings of the International Astronomical Union 3, S245 (July 2007): 371–76. http://dx.doi.org/10.1017/s1743921308018176.
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AbstractWe present a study of the structure of the Galactic Bulge in the region −6° < b < 3°,−17° < l < 17° using 2MASS archive data. More than 100 fields are used. We make use of the red clump method to derive the distance of the Bulge in the studied regions. We derive a position angle of the Galactic Bulge going from 42° ± 11 to 35° ± 10 depending on the adopted bulge mass distribution.
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Ryde, Nils A. E. "CNO abundances in the Galactic bulge." Proceedings of the International Astronomical Union 5, S265 (August 2009): 285–88. http://dx.doi.org/10.1017/s174392131000075x.
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AbstractThe carbon, nitrogen, and oxygen abundances and trends in the bulge are discussed in the context of our recent analysis of these elements in an on-going project based on near-IR spectra (Ryde et al. 2009). We obtained these using the CRIRES spectrometer on the VLT. The formation and evolution of the Milky Way bulge can be constrained by studying elemental abundances of bulge stars. Due to the large and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred.
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Aronica, G., M. Bureau, E. Athanassoula, and R. J. Dettmar. "Vertical surface brightness profiles of boxy bulges." Proceedings of the International Astronomical Union 3, S245 (July 2007): 129–30. http://dx.doi.org/10.1017/s1743921308017456.
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AbstractThe thickening of the bar in barred disk galaxies has a strong influence in shaping the morphology in the inner regions of a disk galaxy above the galactic plane. The result of such a secular evolutionary process can be observed in galaxies with box/peanut shaped (b/ps) bulges. We have applied a one–dimensional fitting method to our sample of 30 edge–on disk galaxies using different fitting function approaches. A clear increase in scale height can be observed in the area of the most prominent b/ps isophotes compared to the neighbouring disk and bulge areas, in agreement with the predictions of the bar thickening model.
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Morrison, Heather L., and Paul Harding. "The Galactic bulge and halo." Publications of the Astronomical Society of the Pacific 105 (September 1993): 977. http://dx.doi.org/10.1086/133267.
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Minniti, Dante, Simon D. M. White, Edward W. Olszewski, and John M. Hill. "Rotation of the Galactic bulge." Astrophysical Journal 393 (July 1992): L47. http://dx.doi.org/10.1086/186448.
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Han, Cheongho. "Galactic Bulge Pixel‐lensing Events." Astrophysical Journal 556, no. 1 (July 20, 2001): 461–67. http://dx.doi.org/10.1086/321539.
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King, Ivan R. "Review of the Galactic Bulge." Symposium - International Astronomical Union 153 (1993): 3–20. http://dx.doi.org/10.1017/s0074180900123083.
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Zeeuw, Tim De. "Dynamics of the Galactic Bulge." Symposium - International Astronomical Union 153 (1993): 191–208. http://dx.doi.org/10.1017/s0074180900123198.
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Recent work on the intrinsic shape, the internal kinematics of stars and gas, and the dynamics of the Galactic Bulge is discussed. Starcounts, measurements of the integrated light and the kinematics of the atomic and molecular gas all provide strong evidence that the Bulge is triaxial, and is rotating fairly rapidly. To date, there is little evidence for triaxiality in the stellar kinematics: the available stellar velocities are consistent with Kent's (1992) oblate model. This unsatisfactory situation is expected to improve rapidly.
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Udalski, Andrzej, Michal Szymanski, Janusz Kaluzny, Marcin Kubiak, Mario Mateo, George Preston, Wojciece Krzeminski, and Bohdan Paczynski. "Microlensing towards the Galactic Bulge." Symposium - International Astronomical Union 153 (1993): 311–12. http://dx.doi.org/10.1017/s0074180900123381.
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We describe an ongoing survey to search for dark matter via lensing events of stars in the Galactic Bulge. The principal properties of the survey are described, and some preliminary results are shown for newly-discovered variables. We discuss some of the projects related to the study of the Galactic Bulge that can be addressed using these data, and describe the future plans for the survey over the coming few years.
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Minniti, Dante, and Manuela Zoccali. "The Galactic bulge: a review." Proceedings of the International Astronomical Union 3, S245 (July 2007): 323–32. http://dx.doi.org/10.1017/s1743921308018048.
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AbstractThe Milky Way is the only galaxy for which we can resolve individual stars at all evolutionary phases, from the Galactic center to the outskirt. The last decade, thanks to the advent of near IR detectors and 8 meter class telescopes, has seen a great progress in the understanding of the Milky Way central region: the bulge. Here we review the most recent results regarding the bulge structure, age, kinematics and chemical composition. These results have profound implications for the formation and evolution of the Milky Way and of galaxies in general. This paper provides a summary on our current understanding of the Milky Way bulge, intended mainly for workers on other fields.
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Barbuy, B., A. Alves-Brito, S. Ortolani, M. Zoccali, V. Hill, J. Meléndez, M. Asplund, et al. "Abundances in the Galactic bulge." Physica Scripta T133 (December 2008): 014032. http://dx.doi.org/10.1088/0031-8949/2008/t133/014032.
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