Mapping the three-dimensional density of the galactic bulge with VVV red clump stars
01 Nov 2013-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 435, Iss: 3, pp 1874-1887
TL;DR: In this paper, the authors measured the angle of the bar-bulge to the line-of-sight to be (27+-2)deg, where the dominant error is systematic arising from the details of the deconvolution process.
Abstract: The inner Milky Way is dominated by a boxy, triaxial bulge which is believed to have formed through disk instability processes. Despite its proximity, its large-scale properties are still not very well known, due to our position in the obscuring Galactic disk. Here we make a measurement of the three-dimensional density distribution of the Galactic bulge using red clump giants identified in DR1 of the VVV survey. Our density map covers the inner (2.2x1.4x1.1)kpc of the bulge/bar. Line-of-sight density distributions are estimated by deconvolving extinction and completeness corrected K-band magnitude distributions. In constructing our measurement, we assume that the three-dimensional bulge is 8-fold mirror triaxially symmetric. In doing so we measure the angle of the bar-bulge to the line-of-sight to be (27+- 2)deg, where the dominant error is systematic arising from the details of the deconvolution process. The resulting density distribution shows a highly elongated bar with projected axis ratios ~(1:2.1) for isophotes reaching ~2kpc along the major axis. Along the bar axes the density falls off roughly exponentially, with axis ratios (10:6.3:2.6) and exponential scale-lengths (0.70:0.44:0.18)kpc. From about 400pc above the Galactic plane, the bulge density distribution displays a prominent X-structure. Overall, the density distribution of the Galactic bulge is characteristic for a strongly boxy/peanut shaped bulge within a barred galaxy.
Citations
More filters
Posted Content•
TL;DR: Kormendy and Ho as mentioned in this paper proposed a method to estimate the BH masses for galaxies with active nuclei (AGNs) based on the observational criteria that are used to classify classical and pseudo bulges.
Abstract: This is the Supplemental Material to Kormendy and Ho 2013, ARAA, 51, 511 (arXiv:1304.7762). Section S1 summarizes indirect methods that are used to estimate black hole (BH) masses for galaxies with active nuclei (AGNs). Section S2 lists the observational criteria that are used to classify classical and pseudo bulges. The (pseudo)bulge classifications used in the main paper are not based on physical interpretation; rather, they are based on these observational criteria. Section S3 supplements the BH database in Section 5 of the main paper and Section S4 here. It discusses corrections to galaxy and BH parameters, most importantly to 2MASS K-band apparent magnitudes. It presents evidence that corrections are needed because 2MASS misses light at large radii when the images of galaxies subtend large angles on the sky or have shallow outer brightness gradients. Section S4 reproduces essentially verbatim the first part of Section 5 in the main paper, the BH database. It includes the list of BH and host-galaxy properties (Tables 2 and 3). Its most important purpose is to provide all of the notes on individual objects.
1,774 citations
TL;DR: In this paper, the authors review the key integrated, structural and kinematic parameters of the Galaxy, and point to uncertainties as well as directions for future progress, and show that the Galaxy is a luminous (L⋆) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo.
Abstract: Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be studied using the full distribution of stars from faint dwarfs to supergiants. The oldest components provide us with unique insight into how galaxies form and evolve over billions of years. The Galaxy is a luminous (L⋆) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global properties, it falls in the sparsely populated “green valley” region of the galaxy color-magnitude diagram. Here we review the key integrated, structural and kinematic parameters of the Galaxy, and point to uncertainties as well as directions for future progress. Galactic studies will continue to play a fundamental role far into the future because there are measurements that can only be made in the near field and much of contemporary astrophysics depends on such observations.
1,084 citations
26 Sep 2019
526 citations
Cites background or methods from "Mapping the three-dimensional densi..."
...Data from Wegg & Gerhard (2013); figure after Portail et al. (2015b)....
[...]
...Figure 7c shows that the density distributions inside ∼1 kpc are nearly exponential, with scale lengths (hx : hy : hz) = (0.70 : 0.44 : 0.18) kpc and axis ratios (10 : 6.3 : 2.6) (Wegg & Gerhard 2013)....
[...]
...Adapted from Wegg & Gerhard (2013) with permission....
[...]
...Portail et al. (2015b) removed a best-matched ellipsoidal density from the 3D RCG bulge density of Wegg & Gerhard (2013), finding that 24% of the bulge stellar mass remained in the residual X shape....
[...]
...NIR RCG star counts at b = ± 1◦ have confirmed a structural change in the RCG longitude profiles at |l | 4◦ (Nishiyama et al. 2005, Gonzalez et al. 2011a, Wegg & Gerhard 2013)....
[...]
TL;DR: In this paper, the authors derived the mean proper motions and space velocities of 154 Galactic globular clusters and the velocity dispersion profiles of 141 Globular clusters based on a combination of Gaia DR2 proper motions with ground-based line-of-sight velocity.
Abstract: We have derived the mean proper motions and space velocities of 154 Galactic globular clusters and the velocity dispersion profiles of 141 globular clusters based on a combination of Gaia DR2 proper motions with ground-based line-of-sight velocities. Combining the velocity dispersion profiles derived here with new measurements of the internal mass functions allows us to model the internal kinematics of 144 clusters, more than 90 per cent of the currently known Galactic globular cluster population. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass-loss and dynamical friction. We find a correlation between the stellar mass function of a globular cluster and the amount of mass lost from the cluster, pointing to dynamical evolution as one of the mechanisms shaping the mass function of stars in clusters. The mass functions also show strong evidence that globular clusters started with a bottom-light initial mass function. Our simulations show that the currently surviving globular cluster population has lost about 80 per cent of its mass since the time of formation. If globular clusters started from a lognormal mass function, we estimate that the Milky Way contained about 500 globular clusters initially, with a combined mass of about 2.5 × 10 M. For a power-law initial mass function, the initial mass in globular clusters could have been a factor of three higher.
363 citations
Cites background from "Mapping the three-dimensional densi..."
...It has been suggested that a large fraction of the Milky Way bulge stars have formed through disc instability processes and are not part of a classical bulge formed through mergers early in the formation of the Galaxy (e.g. Wegg & Gerhard 2013)....
[...]
TL;DR: In this paper, the authors investigated the long bar of the Milky Way using red clump giant (RCG) stars from UKIDSS, 2MASS, VVV, and GLIMPSE.
Abstract: While it is incontrovertible that the inner Galaxy contains a bar, its structure near the Galactic plane has remained uncertain, where extinction from intervening dust is greatest. We investigate here the Galactic bar outside the bulge, the long bar, using red clump giant (RCG) stars from UKIDSS, 2MASS, VVV, and GLIMPSE. We match and combine these surveys to investigate a wide area in latitude and longitude, |b|<9deg and |l|<40deg. We find: (1) The bar extends to l~25deg at |b|~5deg from the Galactic plane, and to l~30deg at lower latitudes. (2) The long bar has an angle to the line-of-sight in the range (28-33)deg, consistent with studies of the bulge at |l|<10deg. (3) The scale-height of RCG stars smoothly transitions from the bulge to the thinner long bar. (4) There is evidence for two scale heights in the long bar. We find a ~180pc thin bar component reminiscent of the old thin disk near the sun, and a ~45pc super-thin bar component which exists predominantly towards the bar end. (5) Constructing parametric models for the RC magnitude distributions, we find a bar half length of 5.0+-0.2kpc for the 2-component bar, and 4.6+-0.3kpc for the thin bar component alone. We conclude that the Milky Way contains a central box/peanut bulge which is the vertical extension of a longer, flatter bar, similar as seen in both external galaxies and N-body models.
314 citations
Cites background or methods or result from "Mapping the three-dimensional densi..."
...5 that the bar angle between 10◦ l 20◦ was close to the α ≈ 27◦ found in the B/P Bulge....
[...]
...The fitted bar angle is α = 28.4◦ in agreement with the bar angle in the bulge region found by Wegg & Gerhard (2013) of α = (27±2)◦....
[...]
...This is consistent with being aligned to the Milky Way’s Bulge (e.g. Wegg & Gerhard 2013; Cao et al. 2013)....
[...]
...We homogenise the analysis of the surveys using a common photometric system and identify RCGs statistically in magnitude distributions rather than in colour-magnitude diagrams since this has worked well in the bulge (e.g. Nataf et al. 2013; Wegg & Gerhard 2013)....
[...]
...This is consistent with alignment with the angle found in the central |l|< 10◦ in Wegg & Gerhard (2013) of α = (27±2)◦ which is our assumed N-body bulge angle, and with α = (29− 32)◦ found by Cao et al. (2013) for a simpler parametric Dwek et al. (1995) bulge model....
[...]
References
More filters
TL;DR: In this article, the average extinction law over the 3.5 micron to 0.125 wavelength range was derived for both diffuse and dense regions of the interstellar medium. And the validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature.
Abstract: The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.
11,704 citations
"Mapping the three-dimensional densi..." refers background or methods in this paper
...This is because the Cardelli et al. (1989) extinction law is less steep in the NIR and therefore appears to overcorrect the extinction....
[...]
...We therefore urge caution in interpreting the corners of the map i.e. near |x|= 2kpc , |y|= 1kpc. (D) We change the extinction law to that given by Cardelli et al. (1989) from our standard extinction law taken from Nishiyama et al. (2006)....
[...]
TL;DR: In this paper, the uncertainty inherent in any observational estimate of the IMF is investigated by studying the scatter introduced by Poisson noise and the dynamical evolution of star clusters, and it is found that this apparent scatter reproduces quite well the observed scatter in power-law index determinations, thus defining the fundamental limit within which any true variation becomes undetectable.
Abstract: A universal initial mass function (IMF) is not intuitive, but so far no convincing evidence for a variable IMF exists. The detection of systematic variations of the IMF with star-forming conditions would be the Rosetta Stone for star formation.
In this contribution an average or Galactic-field IMF is defined, stressing that there is evidence for a change in the power-law index at only two masses: near 0.5 M⊙ and near 0.08 M⊙. Using this supposed universal IMF, the uncertainty inherent in any observational estimate of the IMF is investigated by studying the scatter introduced by Poisson noise and the dynamical evolution of star clusters. It is found that this apparent scatter reproduces quite well the observed scatter in power-law index determinations, thus defining the fundamental limit within which any true variation becomes undetectable. The absence of evidence for a variable IMF means that any true variation of the IMF in well-studied populations must be smaller than this scatter.
Determinations of the power-law indices α are subject to systematic errors arising mostly from unresolved binaries. The systematic bias is quantified here, with the result that the single-star IMFs for young star clusters are systematically steeper by Δα≈0.5 between 0.1 and 1 M⊙ than the Galactic-field IMF, which is populated by, on average, about 5-Gyr-old stars. The MFs in globular clusters appear to be, on average, systematically flatter than the Galactic-field IMF (Piotto & Zoccali; Paresce & De Marchi), and the recent detection of ancient white-dwarf candidates in the Galactic halo and the absence of associated low-mass stars (Ibata et al.; Mendez & Minniti) suggest a radically different IMF for this ancient population. Star formation in higher metallicity environments thus appears to produce relatively more low-mass stars. While still tentative, this is an interesting trend, being consistent with a systematic variation of the IMF as expected from theoretical arguments.
6,784 citations
"Mapping the three-dimensional densi..." refers methods in this paper
...We use a Salpeter IMF, which is equivalent to a Kroupa (2001) IMF for the range of masses consider....
[...]
TL;DR: A database of parameters for globular star clusters in the Milky Way is described which is available in electronic form through the WorldWideWeb as discussed by the authors. The information in the catalog includes up-to-date measurements for cluster distance, reddening, luminosity, colors and spectral types, velocity, structural and dynamical parameters, horizontal branch morphology, metallicity, and other quantities.
Abstract: A database of parameters for globular star clusters in the Milky Way is described which is available in electronic form through the WorldWideWeb. The information in the catalog includes up-to-date measurements for cluster distance, reddening, luminosity, colors and spectral types, velocity, structural and dynamical parameters, horizontal branch morphology, metallicity, and other quantities. This catalog will be updated regularly and maintained in electronic form for widest possible accessibility. Associated Articles Source Paper Catalog Description Catalog Description
4,741 citations
TL;DR: In this paper, the authors proposed a more accurate general mathematical model for ET where an unknown emission density generates, and is to be reconstructed from, the number of counts n*(d) in each of D detector units d. Within the model, they gave an algorithm for determining an estimate? of? which maximizes the probability p(n*|?) of observing the actual detector count data n* over all possible densities?.
Abstract: Previous models for emission tomography (ET) do not distinguish the physics of ET from that of transmission tomography. We give a more accurate general mathematical model for ET where an unknown emission density ? = ?(x, y, z) generates, and is to be reconstructed from, the number of counts n*(d) in each of D detector units d. Within the model, we give an algorithm for determining an estimate ? of ? which maximizes the probability p(n*|?) of observing the actual detector count data n* over all possible densities ?. Let independent Poisson variables n(b) with unknown means ?(b), b = 1, ···, B represent the number of unobserved emissions in each of B boxes (pixels) partitioning an object containing an emitter. Suppose each emission in box b is detected in detector unit d with probability p(b, d), d = 1, ···, D with p(b, d) a one-step transition matrix, assumed known. We observe the total number n* = n*(d) of emissions in each detector unit d and want to estimate the unknown ? = ?(b), b = 1, ···, B. For each ?, the observed data n* has probability or likelihood p(n*|?). The EM algorithm of mathematical statistics starts with an initial estimate ?0 and gives the following simple iterative procedure for obtaining a new estimate ?new, from an old estimate ?old, to obtain ?k, k = 1, 2, ···, ?new(b)= ?old(b) ?Dd=1 n*(d)p(b,d)/??old(b?)p(b?,d),b=1,···B.
4,288 citations
"Mapping the three-dimensional densi..." refers background in this paper
...(8) c© 2012 RAS, MNRAS 000, 1–14 Provided Lucy-Richardson deconvolution (Richardson 1972; Lucy 1974) converges, it converges to the maximum likelihood deconvolution for Poisson distributed errors, and is therefore an appropriate choice (Shepp & Vardi 1982)....
[...]
TL;DR: An iterative method of restoring degraded images was developed by treating images, point spread functions, and degraded images as probability-frequency functions and by applying Bayes’s theorem.
Abstract: An iterative method of restoring degraded images was developed by treating images, point spread functions, and degraded images as probability-frequency functions and by applying Bayes’s theorem. The method functions effectively in the presence of noise and is adaptable to computer operation.
3,869 citations
"Mapping the three-dimensional densi..." refers background in this paper
...(8) c© 2012 RAS, MNRAS 000, 1–14 Provided Lucy-Richardson deconvolution (Richardson 1972; Lucy 1974) converges, it converges to the maximum likelihood deconvolution for Poisson distributed errors, and is therefore an appropriate choice (Shepp & Vardi 1982)....
[...]