A Distinct Structure inside the Galactic Bar

Nishiyama, Shogo; Nagata, T.; Baba, Daisuke; Haba, Y.; Kadowaki, Ryota; Kato, Daisuke; Kurita, Mikio; Nagashima, Chie; Nagayama, Takahiro; Murai, Yuka; Nakajima, Yasushi; Tamura, Motohide; Nakaya, Hidehiko; Sugitani, Koji; Naoi, Takahiro; Matsunaga, Noriyuki; Tanabé, Toshihiko; Kusakabe, Nobuhiko; Sato, Shuji

doi:10.1086/429291

Cited by 110 publications

(154 citation statements)

References 35 publications

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“…We only show here that a flaring bar can be a realistic explanation for the double-clump and that it is dynamically reasonable, as in the Pfenniger (1985) simulations. In a future paper we plan a more complete analysis of the shape of the flare using VVV data, for example, by comparing simulations with the density plots from Saito et al (2011) in order to specify the characteristics of this flare more accurately as a function of the galacto-centric distance.…”

Section: Resulting Colour-magnitude Diagrams and Double-clump Featurementioning

confidence: 73%

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

Robin

Marshall

Schultheis

et al. 2012

A&A

247

314

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Exploring the bulge region of our Galaxy is an interesting but challenging quest because of its complex structure and the highly variable extinction. We re-analyse photometric near-infrared data in order to investigate why it is so hard to reach a consensus on the shape and density law of the bulge, as witnessed in the literature. The apparent orientation of the bulge seems to vary with the range of longitude, latitude, and the population considered. To solve the problem we have used the Besançon galaxy model to provide a scheme for parameter fitting of the structural characteristics of the bulge region. The fitting process allows the shape of the bulge's main structure to be determined. We explore various parameters and shapes for the bulge population, based on Ferrer's ellipsoids, and fit the shape of the inner disc in the same process. The results show that the main structure has a standard triaxial boxy shape with an orientation of about 13• with respect to the Sun-Galactic centre direction. But the fit is greatly improved when we add a second structure, which is a longer and thicker ellipsoid. We emphasize that our first ellipsoid represents the main boxy bar of the Galaxy and that the thick bulge population could be either (i) a classical bulge slightly flattened by the effect of the bar's potential; or (ii) an inner thick disc counterpart. With Ferrer's ellipsoid, the model shows a general agreement with 2MASS data at the level of 10% in the whole bulge region but does not produce the "double clump" feature. However, we show that the double clump seen at intermediate latitudes can be reproduced by adding a slight flare to the bar. To characterize the populations better, we further simulate several fields that have been surveyed in spectroscopy and for which a metallicity distribution function (MDF) are available. The model agrees well with these MDF measured along the minor axis if we assume that the main bar has a mean solar metallicity and the second thicker population has a lower metallicity. It then naturally creates a vertical metallicity gradient by mixing the two populations. In the process of model fitting, we also determine the thin disc parameters. The thin disc is found to have a scale length of 2.2 kpc, in good agreement with previous estimates towards the anticentre, but with a large hole of scale length 1.3 kpc, giving a maximum density in the plane for this population at about 2.3 kpc from the Galactic centre. In the very central part of the bulge on top of our two populations, and by subtracting the fitted ellipsoids, we find evidence of an extra population in the nuclear region, at 2• in longitude and 1• of latitude from the Galactic centre. Its location corresponds well to the central molecular zone, and to the Alard nuclear bar.

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Section: Resulting Colour-magnitude Diagrams and Double-clump Featurementioning

confidence: 73%

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

Robin

Marshall

Schultheis

et al. 2012

A&A

247

314

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“…As shown in Nishiyama et al (2005), the mean magnitude of RC stars weakly depends on the Galactic longitude. However, for changing the ratios of total-to-selective extinction A K S /E K S −λ , it is required that the distance to the stars needs to be highly correlated with the reddening.…”

Section: Resultsmentioning

confidence: 87%

“…It is on the assumptions of the same mean distance and magnitude of the RC star population among the small fields, of the agreement of the central positions of the spatial distributions of the RC and RGB stars, and that the upper RGB stars have colors varying only with luminosity. The distance to the RC stars seems to be rather constant (Nishiyama et al 2005) in this range of Galactic longitudes, and it seems reasonable to assume that the RC and RGB stars have similar spatial distributions. The upper RGB has been used for determining the interstellar reddening and extinction by many investigators.…”

Section: Introductionmentioning

confidence: 88%

INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III:J,H,K_SBANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 μm IN THESPITZER/IRAC SYSTEM

Nishiyama

Tamura

Hatano

et al. 2009

ApJ

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397

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We have determined interstellar extinction law toward the Galactic center (GC) at the wavelength from 1.2 to 8.0 μm, using point sources detected in the IRSF/SIRIUS near-infrared (NIR) survey and those in the Two Micron All Sky Survey (2MASS) and Spitzer/IRAC/GLIMPSE II catalogs. The central region | l | 3.• 0 and | b | 1.• 0 has been surveyed in the J, H, and K S bands with the IRSF telescope and the SIRIUS camera whose filters are similar to the Mauna Kea Observatories (MKO) NIR photometric system. Combined with the GLIMPSE II point source catalog, we made K S versus K S −λ color-magnitude diagrams (CMDs) where λ = 3.6, 4.5, 5.8, and 8.0 μm. The K S magnitudes of bulge red clump stars and the K S − λ colors of red giant branches are used as a tracer of the reddening vector in the CMDs. From these magnitudes and colors, we have obtained the ratios of total-to-selective extinction This confirms the flattening of the extinction curve at λ 3 μm from a simple extrapolation of the powerlaw extinction at shorter wavelengths, in accordance with recent studies. The extinction law in the 2MASS J, H, and K S bands has also been calculated, and good agreement with that in the MKO system is found. Thus, it is established that the extinction in the wavelength range of J, H, and K S is well fitted by a power law of steep decrease A λ ∝ λ −2.0 toward the GC. In nearby molecular clouds and diffuse interstellar medium, the lack of reliable measurements of the total-to-selective extinction ratios hampers unambiguous determination of the extinction law; however, observational results toward these lines of sight cannot be reconciled with a single extinction law.

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“…The X-shape is a pronounced boxy/peanut (B/P) structure that, in its inner region A&A 562, A66 (2014) (|b| < 5), becomes a bar, hereafter the main bar. Closer yet to the center (|l| < 4, |b| < 2) the main bar changes its apparent inclination with respect to the line of sight (Nishiyama et al 2005;Gonzalez et al 2011a), most likely due to the presence of either a distinct, smaller bar, or a more axysimmetric structure . The presence of a longer bar, extending to longitudes |l| > 7 (Hammersley et al 2000;Cabrera-Lavers et al 2007López-Corredoira et al 2007;Churchwell et al 2009;Amôres et al 2013) has been interpreted by theoreticians as most likely being an extension of the main bar itself (e.g., Martinez-Valpuesta & Gerhard 2011;Athanassoula 2012).…”

Section: Introductionmentioning

confidence: 99%

The GIRAFFE Inner Bulge Survey (GIBS)

Zoccali

Gonzalez

Vásquez

et al. 2014

A&A

140

199

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Context. The Galactic bulge is a massive, old component of the Milky Way. It is known to host a bar, and it has recently been demonstrated to have a pronounced boxy/peanut structure in its outer region. Several independent studies suggest the presence of more than one stellar populations in the bulge, with different origins and a relative fraction changing across the bulge area. Aims. This is the first of a series of papers presenting the results of the Giraffe Inner Bulge Survey, carried out at the ESO-VLT with the multifibre spectrograph FLAMES. Spectra of ∼5000 red clump giants in 24 bulge fields have been obtained at resolution R = 6500, in the infrared Calcium triplet wavelength region at ∼8500 Å. They are used to derive radial velocities and metallicities, based on new calibration specifically devised for this project. Radial velocities for another ∼1200 bulge red clump giants, obtained from similar archive data, have been added to the sample. Higher resolution spectra have been obtained for ∼450 additional stars at latitude b = −3.5, with the aim of investigating chemical abundance patterns variations with longitude, across the inner bulge. In total we present here radial velocities for 6392 red clump stars. Methods. We present here the target selection criteria, observing strategy and the catalog with radial velocity measurements for all the target stars. Results. We derive a radial velocity, and velocity dispersion map of the Milky Way bulge, useful to be compared with similar maps of external bulges, and to infer the expected velocities and dispersion at any line of sight. The K-type giants kinematics is consistent with the cylindrical rotation pattern of M-giants from the BRAVA survey. Our sample enables to extend this result to latitude b = −2, closer to the Galactic plane than probed by previous surveys. Finally, we find strong evidence for a velocity dispersion peak at (0, −1) and (0, −2), possibily indicative of a high density peak in the central ∼250 pc of the bulge.

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A Distinct Structure inside the Galactic Bar

Cited by 110 publications

References 35 publications

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III:J,H,K_SBANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 μm IN THESPITZER/IRAC SYSTEM

The GIRAFFE Inner Bulge Survey (GIBS)

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A Distinct Structure inside the Galactic Bar

Cited by 110 publications

References 35 publications

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data

INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III:J,H,KSBANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 μm IN THESPITZER/IRAC SYSTEM

The GIRAFFE Inner Bulge Survey (GIBS)

Contact Info

Product

Resources

About

INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III:J,H,K_SBANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 μm IN THESPITZER/IRAC SYSTEM