Growing evidence indicate supermassive black holes (SMBHs) in a mass range of $M_{\rm BH}$$\sim 106-10^{10}M_{\odot}$ lurking in central stellar bulges of galaxies.Extensive observations reveal fairly tight power laws of $M_{\rm BH}$ versus the mean stellar velocity dispersion $σ$ of the host stellar bulge.Together with evidence for correlations between $M_{\rm BH}$ and other properties of host bulges, the dynamic evolution of a bulge and the formation of a central SMBH should be linked. In this Letter, we reproduce the empirical $M_{\rm BH}-σ$ power laws based on our recent theoretical analyses (Lou & Wang; Wang & Lou; Lou, Jiang & Jin) for a self-similar general polytropic quasi-static dynamic evolution of bulges with self-gravity and spherical symmetry and present a sensible criterion of forming a central SMBH. The key result is $M_{\rm BH}={\cal L}σ^{1/(1-n)}$ where $2/3<n<1$ and ${\cal L}$ is a proportional coefficient characteristic of different classes of host bulges. By fitting and comparing several empirical $M_{\rm BH}-σ$ power laws, we conclude that SMBHs and galactic bulges grow and evolve in a coeval manner and most likely there exist several classes of galactic bulge systems in quasi-static self-similar evolution and that to mix them together can lead to an unrealistic fitting. Based on our bulge-SMBH model, we provide explanations for intrinsic scatter in the relation and a unified scenario for the formation and evolution of SMBHs in different classes of host bulges.
We demonstrate a strong correlation between supermassive black hole (SMBH) mass and the global structure of ellipticals and bulges: more centrally concentrated bulges and ellipticals (higher Sersic index $n$) host higher-mass black holes. This correlation is as good as that previously found between SMBH mass and central velocity dispersion, with comparable scatter. In addition, by carefully modeling the bulges of disk galaxies so that bars, inner disks, and the like do not accidentally contribute to bulge light, we find that the correlation between SMBH mass and bulge or elliptical luminosity …
As a potential mechanism to build up supermassive black holes (BHs) in a spheroidal system, we consider the radiation drag effect by bulge stars, which extracts angular momentum from interstellar gas and thus allows the gas to accrete onto the galactic center. With incorporating radiation hydrodynamical equation with simple stellar evolution, it is shown that the BH-to-bulge mass ratio, $f_{BH}$, is basically determined by a fundamental constant, that is, the energy conversion efficiency for nuclear fusion of hydrogen to helium, $ε=0.007$. More specifically, $f_{BH}$ is predicted to be $0.3ε-0…
Growing evidence indicate supermassive black holes (SMBHs) in the mass range of $M_{\rm BH}$$\sim 10^6-10^{10}M_{\odot}$ lurking in central bulges of many galaxies. Extensive observations reveal fairly tight power laws of $M_{\rm BH}$ versus the mean stellar velocity dispersion $σ$ of the host bulge. The dynamic evolution of a bulge and the formation of a central SMBH should be physically linked by various observational clues. In this contribution, we reproduce the empirical $M_{\rm BH}-σ$ power laws based on a self-similar general polytropic quasi-static bulge evolution and a sensible criteri…
A variety of host galaxy (bulge) parameters are examined in order to determine their predictive power in ascertaining the masses of the supermassive black holes (SMBH) at the centers of the galaxies. Based on a sample of 23 nearby galaxies, comprised of both elliptical galaxies and spiral/lenticular bulges, we identify a strong correlation between the bulge gravitational binding energy ($E_g$), as traced by the stellar light profile, and the SMBH mass ($M_{\bullet}$), such that $M_{\bullet} \propto E_g^{0.6}$. The scatter about the relationship indicates that this is as strong a predictor of $…
Using results from structural analysis of a sample of nearly 1000 local galaxies from the Sloan Digital Sky Survey, we estimate how the mass in central black holes is distributed amongst elliptical galaxies, classical bulges and pseudo-bulges, and investigate the relation between their stellar masses and central stellar velocity dispersion sigma. Assuming a single relation between elliptical galaxy/bulge mass, M_Bulge, and central black hole mass, M_BH, we find that 55^{+8}_{-4} per cent of the mass in black holes in the local universe is in the centres of elliptical galaxies, 41^{+4}_{-2} per…
The hierarchical build-up of galactic bulges should lead to the build-up of present-day supermassive black holes by a mixture of gas accretion and merging of supermassive black holes. The tight relation between black hole mass and stellar velocity dispersion is thereby a strong argument that the supermassive black holes in merging galactic bulges do indeed merge. Otherwise the ejection of supermassive black holes by gravitational slingshot would lead to excessive scatter in this relation. At high redshift the coalescence of massive black hole binaries is likely to be driven by the accretion of…
We highlight the correlation between a galaxy's supermassive black hole mass and the Sersic-index of the host spheroid or bulge component. From our bulge-disk decompositions of 10 095 galaxies, drawn from the Millennium Galaxy Catalogue, we construct the local (z < 0.18) mass function of supermassive black holes. We compare our results to those of McLure & Dunlop (2004) and conclude that the mass density of supermassive black holes may be marginally higher than previously supposed. This increase is predominantly due to the inclusion of low mass and later-type bulges. More details will be prese…
We quantitatively scrutinize the effects of the radiation drag arising from the radiation fields in a galactic bulge in order to examine the possibility that the radiation drag could be an effective mechanism to extract angular momentum in a spheroidal system like a bulge and allow plenty of gas to accrete onto the galactic center. For this purpose, we numerically solve the relativistic radiation hydrodynamical equation coupled with the accurate radiative transfer and quantitatively assess the radiation drag efficiency. As a result, we find that in an optically thick regime the radiation drag …
We present a simple scenario where the formation of galactic bulges was regulated by the dark halo gravity and regulated the growth of the central supermassive black hole. Assuming the angular momentum is low, we suggest that bulges form in a runaway collapse due to the "gravothermal" instability once the central gas density or pressure exceeds certain threshold (Xu & Zhao 2007). We emphasize that the threshold is nearly universal, set by the background NFW dark matter gravity $g_{DM} \sim 1.2 \times 10^{-8}{\rm cm} {\rm sec}^{-2}$ in the central cusps of halos. Unlike known thresholds for gra…
The growth of supermassive black holes by merging and accretion in hierarchical models of galaxy formation is studied by means of Monte Carlo simulations. A tight linear relation between masses of black holes and masses of bulges arises if if the mass accreted by supermassive black holes scales linearly with the mass forming stars and if the redshift evolution of mass accretion tracks closely that of star formation. Differences in redshift evolution between black hole accretion and star formation introduce considerable scatter in this relation. A non-linear relation between black hole accretio…
Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and STIS spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M_sun. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated…
The masses of supermassive black holes correlate almost perfectly with the velocity dispersions of their host bulges, M(BH) ~ sigma^alpha, where alpha =4.8 +/- 0.5$. The relation is much tighter than the relation between M(BH) and bulge luminosity, with a scatter no larger than expected on the basis of measurement error alone. Black hole masses estimated by Magorrian et al. (1998) lie systematically above the M(BH)-sigma relation defined by more accurate mass estimates, some by as much as two orders of magnitude. The tightness of the M(BH)-sigma relation implies a strong link between black hol…
The possibility that the masses of supermassive black holes (SBHs) correlate with the total gravitational mass of their host galaxy, or the mass of the dark matter halo in which they presumably formed, is investigated using a sample of 16 spiral and 20 elliptical galaxies. The bulge velocity dispersion, typically defined within an aperture of size less than 0.5 kpc, is found to correlate tightly with the galaxy's circular velocity, the latter measured at distances from the galactic center at which the rotation curve is flat, 20 to 80kpc. By using the well known M-sigma relation for SBHs, and a…
Motivated by the observed correlation between black hole masses $\mbh$ and the velocity dispersion $σ$ of host galaxies, we develop a theoretical model of black hole formation in galactic bulges (this paper generalizes an earlier ApJ Letter). The model assumes an initial state specified by a a uniform rotation rate $Ω$ and a density distribution of the form $ρ= \aeff^2 / 2 πG r^2$ (so that $\aeff$ is an effective transport speed). The black hole mass is determined when the centrifugal radius of the collapse flow exceeds the capture radius of the central black hole (for Schwarzschild geometry).…
Dynamical searches find central dark objects - candidate supermassive black holes (BHs) - in at least 34 galaxies. The demographics of these objects lead to the following conclusions: (1) BH mass correlates with the luminosity of the bulge component of the host galaxy, albeit with considerable scatter. The median BH mass fraction is 0.15 % of the mass of the bulge. The quartiles are 0.09 % and 0.7 %. (2) BH mass correlates with the mean velocity dispersion of the bulge component inside its effective radius, i.e., with how strongly the bulge stars are gravitationally bound to each other. For th…
We present evidence for a strong correlation between the concentration of bulges and the mass of their central supermassive black hole (M_bh) -- more concentrated bulges have more massive black holes. Using C_{r_e}(1/3) from Trujillo, Graham & Caon (2001b) as a measure of bulge concentration, we find that log (M_bh/M_sun) = 6.81(+/-0.95)C_{r_e}(1/3) + 5.03(+/-0.41). This correlation is shown to be marginally stronger (Spearman's r_s=0.91) than the relationship between the logarithm of the stellar velocity dispersion and log M_bh (Spearman's r_s=0.86), and has comparable, or less, scatter (0.31…
We study observed correlations between supermassive black hole (BHs) and the properties of their host galaxies, and show that the observations define a BH 'fundamental plane' (BHFP), of the form M_BH sigma^(3.0+-0.3)*R_e^(0.43+-0.19), or M_BH M_bulge^(0.54+-0.17)*sigma^(2.2+-0.5), analogous to the FP of elliptical galaxies. The BHFP is preferred over a simple relation between M_BH and any of sigma, M_bulge, M_dyn, or R_e alone at >99.9% significance. The existence of this BHFP has important implications for the formation of supermassive BHs and the masses of the very largest black holes, and i…
We report the discovery of a strong correlation between the shape of a bulge's light-profile and the mass of its central supermassive black hole (M_{bh}). We find that log(M_{bh}/M_{sun}) = 2.91(+/-0.38)log(n) + 6.37(+/-0.21), where `n' is the Sersic r^{1/n} shape index of the bulge. This correlation is marginally stronger than the relationship between the logarithm of the stellar velocity dispersion and log(M_{bh}) and has comparable scatter. It therefore offers a cheap (in terms of telescope time) alternative to estimating the masses of supermassive black holes.
The evolution of the dark matter distribution at the Galactic center is analyzed, which is caused by the combination of gravitational scattering on Galactic bulge stars and absorption by a supermassive black hole at the center of the bulge. Attention is focused on the boundary condition on the black hole. It is shown that its form depends on the energy of dark matter particles. The modified flux of dark matter particles onto the black hole is calculated. Estimates of the amount of dark matter absorbed show that the fraction of dark matter in the total mass of the black hole may be significant.…
Here, we present our on-going work on the determination of stellar parameters of giants in the Galactic Disks and Bulge observed with UVES on the VLT. We present some preliminarily results.
We review current knowledge on the structure, properties and evolution of galactic bulges, considering particularly common preconceptions in the light of recent observational results.
One of the central features of the last 8 to 10 billion years of cosmic history has been the emergence of a well-populated red sequence of non-star-forming galaxies. A number of models of galaxy formation and evolution have been devised to attempt to explain this behavior. Most current models require feedback from supermassive black holes (AGN feedback) to quench star formation in galaxies in the centers of their dark matter halos (central galaxies). Such models make the strong prediction that all quenched central galaxies must have a large supermassive black hole (and, by association, a promi…
We have investigated past measurements of the local supermassive black hole mass density, correcting for hitherto unknown dependencies on the Hubble constant, which, in some cases, had led to an underestimation of the mass density by factors of ~2. Correcting for this, we note that the majority of past studies yield a local supermassive black hole mas density that is consistent with the range 4.4-5.9 x 10^5 f(H_0) M_Sun / Mpc^3 (when using H_0 = 70 km/s/Mpc). In addition, we address a number of ways in which these past estimates can be further developed. In particular, we tabulate realistic bu…
High quality spectrophotometric observations of 30 Planetary Nebulae in the Galactic Bulge have been made. Accurate reddenings, plasma parameters, and abundances of He,O,N,S,Ar,Cl are derived. We find the abundances of O,S,Ar in the Planetary Nebulae in the Galactic Bulge to be comparable with the abundances of the Planetary Nebulae in the Disk, high abundances being maybe slightly more frequent in the Bulge. The distribution of the N/O ratio does not present in the Galactic Bulge Planetary Nebulae the extension to high values that it presents in the Disk Planetary Nebulae. We interpret this a…
We present a series of simulations of the self--regulated growth of supermassive black holes (SMBHs) in galaxies via three different fueling mechanisms: major mergers, minor mergers, and disk instabilities. The SMBHs in all three scenarios follow the same black hole fundamental plane (BHFP) and correlation with bulge binding energy seen in simulations of major mergers, and observed locally. Furthermore, provided that the total gas supply is significantly larger than the mass of the SMBH, its limiting mass is not influenced by the amount of gas available or the efficiency of black hole growth. …
We present spatially extended gas kinematics at parsec-scale resolution for the nuclear regions of four nearby disk galaxies, and model them as rotation of a gas disk in the joint potential of the stellar bulge and a putative central black hole. The targets were selected from a larger set of long-slit spectra obtained with the Hubble Space Telescope as part of the Survey of Nearby Nuclei with STIS (SUNNS). They represents the 4 galaxies (of 24) that display symmetric gas velocity curves consistent with a rotating disk. We derive the stellar mass distribution from the STIS acquisition images ad…
We reinvestigate the correlation between black hole mass and bulge concentration. With an increased galaxy sample, updated estimates of galaxy distances, black hole masses, and Sersic indices `n' - a measure of concentration - we perform a least-squares regression analysis to obtain a relation suitable for the purpose of predicting black hole masses in other galaxies. In addition to the linear relation, log(M_bh) = 7.81(+/-0.08) + 2.69(+/-0.28)[log(n/3)] with epsilon_(intrin)=0.31 dex, we investigated the possibility of a higher order M_bh-n relation, finding the second order term in the best-…
Recent observations and theories suggest that extreme horizontal branch (EHB) stars and their progeny should be the cause of the UV excess seen in the spectra of many elliptical galaxies. Since the Galactic Bulge is the closest representation of an old, metal-rich spheroid in which we are able to study the EHB scenario in detail, we obtained spectra of bulge EHB star candidates and we confirm their status as hot evolved stars. It is the first time that such stars are unambiguously identified in the Galactic Bulge.
The observed spectra of the microlensed sources towards the Galactic bulge may be used as a tool for studying the kinematics and extinction effects in the Galactic bulge. In this paper, we first investigate the expected distribution of the microlensed sources as a function of depth within the Galactic bulge. Our analysis takes a magnitude limited microlensing survey into account, and includes the effects of extinction. We show that, in the current magnitude limited surveys, the probability that the source lies at the far side of the bulge is larger than the probability that the source lies at …
We compare the populations of Red Giant stars and Planetary Nebulae in the Galactic Bulge, in the light of recent determinations of their abundances patterns. We find both populations to be compatible. From the planetary nebulae, we find evidences that the Bulge did not form stars recently. The whole abundances pattern remains however puzzling, some elements favoring a quick evolution of the Galactic Bulge (Mg and Ti), and others a much slower one (He, O, Si, S, Ar and Ca).
We use cosmological hydrodynamic simulations to investigate formation of galactic bulges within the framework of hierarchical clustering in a representative CDM cosmological model. We show that largest objects forming at cosmological redshifts z~4 resemble observed bulges of spiral galaxies or moderate size ellipticals in their general properties like sizes, shapes, and density profiles. This is consistent with observational data indicating the existence of ``old'' bulges and ellipticals at more moderate redshifts. These bulges are gas dominated at redshift z=3, with high rates of star formati…
We present our on-going work on the determination of elemental abundances of giants in the Galactic Bulge by means of infrared spectroscopy. We show a preliminarily reduced spectrum and a synthetic spectrum fit of the Bulge giant Arp 4203 recorded with the near-infrared, high-resolution Crires spectrograph mounted on the VLT during its science verification run in August 2006. Abundances derived from this spectrum are discussed.
In this work we report spectrophotometric observations of a planetary nebula sample towards the galactic bulge. A total of 45 PNe was observed and their physical parameters (electron density and temperature) were derived. Ionic abundances were calculated using a three-level atom model and abundances were derived through ionisation correction factors. Results show low abundance objects at high galactic latitudes, indicating a possible vertical gradient inside the bulge. A few objects with low N/O ratio were found, which could originated from old, low mass progenitors.
DENIS observations in the J (1.2 micron) and K_S (2.15 micron) bands together with isochrones calculated for the RGB and AGB phase are used to draw an extinction map of the inner Galactic Bulge. The uncertainty in this method is mainly limited by the optical depth of the Bulge itself. A comparison with fields of known extinction shows a very good agreement. We present an extinction map for the inner Galactic Bulge (approx. 20 sq. deg.)
We present an analysis of the Galactic bulge emission observed by the RXTE/PCA during a set of scans over the Galactic Center field, performed in 1999-2001. The total exposure time of these observations is close to 700 ksec. We construct the distribution of Galactic ridge emission intensity and spectral parameters up to Galactic latitudes b=-10deg;+9deg. We show that the intensity distribution of the ridge emission at |b|>2deg could be well described by an exponential model with e-folding width b_0~ 3.3deg. Best-fit spectral parameters do not show statistically significant changes over Galacti…
We compare abundances patterns in the Bulge for elements observed in stars and in planetary nebulae. Some alpha elements, like Mg and Ti, are overabundant respect to Fe, and others are not, like He, O, Si, S, Ar, Ca. The first ones favor a quick evolution of the Galactic Bulge, and the seconds a much slower one.
We present the Catalog of microlensing events detected toward the Galactic bulge in three observing seasons, 1997--1999, during the OGLE-II microlensing survey. The search for microlensing events was performed using a database of about 4*10^9 photometric measurements of about 20.5 million stars from the Galactic bulge. The Catalog comprises 214 cases of microlensing events found in the fields covering about 11 square degrees on the sky and distributed in different parts of the Galactic bulge. The sample includes 20 binary microlensing events, 14 of them are caustic crossing. In one case a doub…
We 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 {\sl 2MASS}-selected M giant stars in the Galactic bulge, observed with the CTIO 4m Hydra multi-object spectrograph. This program is to test…
Adopting a single-zone framework, with accretion of primordial gas on a free-fall timescale, the chemical evolution of the Galactic bulge is calculated, assuming (i) a corresponding rapid timescale for star formation, and (ii) an initial mass function biased towards massive stars. We emphasise here the uncertainties associated with the underlying physics (specifically, stellar nucleosynthesis) and how those uncertainties are manifest in the predicted abundance ratio patterns in the resulting present-day Galactic bulge stellar populations.
We review the motivation and search for supermassive black holes (BHs) in galaxies. Energetic nuclear activity provides indirect but compelling evidence for BH engines. Ground-based dynamical searches for central dark objects are reviewed in Kormendy & Richstone (1995, ARA&A, 33, 581). Here we provide an update of results from the HST. As of 2001 March, dynamical BH detections are available for at least 37 galaxies. The demographics of these objects lead to the following conclusions: (1) BH mass correlates with the luminosity of the bulge component of the host galaxy. The median BH mass fracti…
AIMS: We spectroscopically characterize the Galactic Bulge to infer its star formation timescale, compared to the other Galactic components, through the chemical signature on its individual stars. METHODS: We derived iron and oxygen abundances for 50 K giants in four fields towards the Galactic bulge. High resolution (R=45,000) spectra for the target stars were collected with FLAMES-UVES at the VLT. RESULTS: Oxygen, as measured from the forbidden line at 6300 Å, shows a well-defined trend with [Fe/H], with [O/Fe] higher in bulge stars than in thick disk ones, which were known to be more oxygen…
We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive.
Both fuelling of a central black hole and the build-up of bulges are -- at least theoretically -- facilitated by non-axisymmetric potentials. It is argued here that the recently established surface brightness division between bulge-dominated galaxies that dominate the local type 2 AGN luminosity function, and disk-dominated galaxies that host (at best) weak AGN can be understood in terms of a simple bar-instability criterion.
We argue that the observed correlations between central black holes masses M_{BH} and galactic bulge velocity dispersions σ_e in the form M_{BH}\proptoσ_e^4 may witness on the pregalactic origin of massive black holes. Primordial black holes would be the centers for growing protogalaxies which experienced multiple mergers with ordinary galaxies. This process is accompanied by the merging of black holes in the galactic nuclei.
We estimate the optical depth to self-lensing by stars in the Galactic bulge using the HST star counts of Holtzman et al and Zoccali et al as extrapolated by Gould into the brown-dwarf and remnant regimes and deprojected along the line of sight using the model of Dwek et al. We find a self-lensing optical depth tau(bulge-bulge)=0.98 x 10^{-6}. When combined with the lensing of bulge stars by foreground stars in the disk, this yields tau(bulge-total)=1.63 x 10^{-6}, in reasonable agreement with the estimates of tau=2.13 +/- 0.40 x 10^{-6} and tau=1.08 +/- 0.30 x 10^{-6} based on observations of…
We present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum $V$-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, we derive the selective extinction coefficient $R_{V,VR}=A_V/E(V-R) = 4.3 \pm 0.2$. This value is what is expected for a standard extinction law with $R_{V,BV} = 3.1 \pm 0.3$.
This article gives a brief overview of the direct and indirect evidence in support of the standard paradigm that active galactic nuclei are powered by supermassive black holes.
Surface brightness maps at 12 microns, derived from observations with the Infrared Astronomical Satellite (IRAS), are used to estimate the integrated flux at this wavelength from the Galactic bulge as a function of galactic latitude along the minor axis. A simple model was used to remove Galactic disk emission (e.g. unresolved stars and dust) from the IRAS measurements. The resulting estimates are compared with predictions for the 12 micron bulge surface brightness based on observations of complete samples of optically identified M giants in several minor axis bulge fields. No evidence is foun…
The chemical evolution of the Galactic bulge is treated here in the context of an inside-out model for the Galaxy formation. We assume that this central region evolved even faster than the Galactic halo and test the effect of changing the slope of the IMF on the predicted stellar metallicity distribution for bulge stars. An IMF favoring the formation of massive stars is found to improve the agreement with the most recently observed metallicity distribution of bulge K giants. Then, we make specific predictions about temporal evolution of several light and heavy species in the Galactic bulge. We…
We present follow-up observations of a gravitational microlensing candidate found by the MACHO collaboration in the Galactic bulge. The photometric data cover a period near the maximum of the event and may be used to construct complete light curve. The position of the lensed star in the color magnitude diagram suggests that it is a Galactic bulge star located on the subgiant branch.
In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulse - asymptotic giant branch stars by using a population synthesis code. The effects of the oxygen overabundance and the mass loss rate on the ratio of the number of carbon stars to that of oxygen stars in the Galactic bulge are discussed. We find that the oxygen overabundance which is about twice as large as that in the solar neighbourhood (close to the present observations) is insufficient to explain the rareness of carbon stars in the bulge. We suggest that the large mass loss rat…
We analyse velocity, chemical abundance and spatial distribution data for some 1500 K- and M- giants in the Galactic Bulge. The bulge has a well-determined linear rotation curve over the range $\rm 700pc \le R \le 3500pc$ with amplitude ${\rm \sim 25 km s^{-1} kpc^{-1}}$. The oblate isotropic bulge model of Kent (1992) is in reasonable agreement with our data. We do not find a significant requirement for asymmetry or a bar. The metallicity distribution of K giants in a subset of our fields, using the Mg$b$ feature, has mean ${\rm [Fe/H] \approx -0.3}$ with no variation. That is, there is no de…
New observations and derived chemical abundances are reported for a sample of 57 bulge planetary nebulae (PN). Together with our previous results, a total of over a hundred objects have been analyzed, which constitute one of the largest samples of bulge nebulae studied under homogeneous conditions, including equipment and reduction procedures. In general, our data show a good agreement with some recent results in the literature, in the sense that the average abundances of bulge PN are similar to those from disk objects, however showing a larger dispersion.
We present preliminary results of an optical survey for Planetary Nebulae (PNe) in the northern part of the Galactic Bulge. In particular, observations at wavelengths corresponding to the [O III] 5007 emission line have been carried out with the 0.3 m telescope at Skinakas Observatory, where we have detected several new PNe and have rediscovered known and known-possible PNe from that region.
Detailed studies of Be stars in environments with different metallicities like the Magellanic Clouds or the Galactic bulge are necessary to understand the formation and evolution mechanisms of the circumstellar disks. However, a detailed study of Be stars in the direction of the bulge of our own galaxy has not been performed until now. We report the first systematic search for Be star candidates in the direction of the Galactic Bulge. We present the catalogue, give a brief description of the stellar variability seen, and show some light curve examples. We searched for stars matching specific c…
We present I-band light curves of 54 Population II Cepheids identified in the OGLE-II catalog of variable objects in the Galactic bulge fields. Their periods range from a fraction of a day to several days. Their light curves show very close similarity to the light curves of classical Cepheids with periods a few times longer. We analyze location of the newly identified Population II Cepheids in the color--magnitude diagram. The position of these objects confirms recent discovery that the interstellar extinction toward the Galactic bulge might be anomalous. The slope of the reddening line obtain…
The Galactic Bulge has long been assumed to be a largely old stellar population. However, some recent studies based on observations with the HST WF/PC-1 and WFPC2 of stars in the Galactic Bulge have concluded that the old population may not make up more then 30% of the total. Other studies using HST/WFPC2 differential studies of `Bulge' globular clusters and field stars have found the bulge to be comparable in age to the Galactic Halo. A complication in all these studies is the presence of a substantial population of stars which mimic a young bulge population, but which may be, and are often a…
We summarise some recent results about nearby galactic bulges that are relevant to their formation. We highlight a number of significant advances in our understanding of the surface brightness profiles, stellar populations, and especially the very centers of spiral galaxies. We also view our own Milky Way as if it were an external galaxy. Our main conclusions are that bulges of early-type spirals (S0 -- Sb) contain central nuclear components, just like late-type spirals and most other types of galaxies. The luminosities of these central components correlate best with total bulge luminosity, an…
Electron temperatures, densities, ionic and elemental abundances of helium, nitrogen, oxygen, argon, sulfur and neon were derived for a sample of bulge planetary nebulae, representative of its intermediate mass population. Using these results as constraints, a model for the chemical evolution of the galactic bulge was developed. The results indicate that the best fit is achieved using a double-infall model, where the first one is a fast collapse of primordial gas and the second is slower and enriched by material ejected by the bulge itself during the first episode.
The bulge is a region of the Galaxy of tremendous interest for understanding galaxy formation. However measuring photometry and kinematics in it raises several inherent issues, such as severe crowding and high extinction in the visible. Using the Besancon Galaxy model and a 3D extinction map, we estimate the stellar density as a function of longitude, latitude and apparent magnitude and we deduce the possibility of reaching and measuring bulge stars with Gaia. We also present an ongoing analysis of the bulge using the Canada-France-Hawaii Telescope.
