Mapping the outer bulge with RRab stars from the VVV Survey

Gran, F.; Minniti, D.; Saito, R. K.; Zoccali, M.; Gonzalez, O. A.; Navarrete, C.; Catelan, M.; Ramos, R. Contreras; Elorrieta, Felipe; Eyheramendy, S.; Jordán, Andrés

doi:10.1051/0004-6361/201527511

Cited by 58 publications

(87 citation statements)

References 51 publications

(89 reference statements)

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“…The distance distributions of the RR Lyrae in our sample compared with 1019 RR Lyrae type ab recently discovered in the outer bulge from the VVV survey (Gran et al 2016) have consistent peak values. The distribution of the present sample is very concentrated, much more so than the observed distribution of RR Lyrae in the inner and outer bulge.…”

Section: Distancessupporting

confidence: 78%

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Discovery of Rr Lyrae Stars in the Nuclear Bulge of the Milky Way

Minniti

Ramos

Zoccali

et al. 2016

ApJL

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Galactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.

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Section: Distancessupporting

confidence: 78%

“…VVV near-infrared color-magnitude diagram for the Galactic center region showing the position of the nuclear bulge RR Lyrae (black stars). For comparison, the unreddened outer bulge RR Lyrae Gran et al (2016) are shown to the left of the color-magnitude diagram (white dots). The direction of the reddening vector is also shown.…”

Section: Metallicitiesmentioning

confidence: 99%

Discovery of Rr Lyrae Stars in the Nuclear Bulge of the Milky Way

Minniti

Ramos

Zoccali

et al. 2016

ApJL

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“…Its spatial distribution seems to be uncorrelated with the bar position, appearing as an extended, centrally concentrated and possibly spheroidal component. This is supported by the distribution found for other tracers of metalpoor old populations such as RR Lyrae stars (Pietrukowicz et al 2012;Dékány et al 2013;Kunder et al 2016;Gran et al 2016; but see also Pietrukowicz et al 2015). On the chemical abundance side, α-abundance ratios with respect to iron are systematically enhanced over its whole metallicity range.…”

Section: Introductionsupporting

confidence: 58%

“…Moreover, from the observed mass-metallicity relation for galactic spheroids (Gallazzi et al 2005), a system with mean metallicity around [Fe/H] = −0.4 dex, as our metal-poor component is, should have a mass of ∼10 10 M , which is comparable to the total bulge mass as estimated from observations (Valenti et al 2016). Furthermore, RR Lyrae stars, as tracers of metal-poor old stellar populations, have been shown to display an axisymmetric spatial distribution, uncorrelated with the bar position angle (Dékány et al 2013;Gran et al 2016), and a high-velocity dispersion of around 130 km s −1 (Gratton 1987;Kunder et al 2016). However, this is still under debate; a recent analysis of OGLE data suggests that the RR Lyrae distribution might be elongated with a pivot angle comparable to that of the main bar (Pietrukowicz et al 2015).…”

Section: Discussionmentioning

confidence: 52%

The Gaia-ESO Survey: Exploring the complex nature and origins of the Galactic bulge populations

Rojas-Arriagada

Recio–Blanco

Laverny

et al. 2017

A&A

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112

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Context. As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge -and especially of the metal-poor bulgeand their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data samples. Aims. We used the fourth internal data release of the Gaia-ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous sampling of the different Galactic populations provided by the Gaia-ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg/Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities.Methods. We obtained spectroscopic data for ∼2500 red clump stars in 11 bulge fields, sampling the area −10• ≤ l ≤ +8• and −10• from the fourth internal data release of the Gaia-ESO survey. A sample of ∼6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a sample of stars likely located in the bulge region.Results. From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole sampled area. The relative ratio between the two modes of the MDF changes as a function of b, with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. = −0.37 ± 0.09, being 0.06 dex higher than that of the thick disk. Although this difference is inside the error bars, it suggest a higher star formation rate (SFR) for the bulge than for the thick disk. We estimate an upper limit for this difference of ∆[Fe/H] knee = 0.24 dex. Finally, we present a chemical evolution model that suitably fits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of stellar formation that takes place at early epochs. Conclusions. We associate metal-rich stars with the bar boxy/peanut bulge formed as the product of secular evolution of the early thin disk. On the other hand, the metal-poor subpopulation might be the product of an early prompt dissipative collapse dominated by massive stars. Nevertheless, our results do not allow us to firmly rule out the possibility that these stars come from the secular evolution of the early thick disk. This is the first time that an analysis of the bulge MDF and α-abundances has been performed in a large area on the basis of a homogeneous, fully spectroscopic analysis of high-resolution, high S/N data.

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“…Dékány et al 2013, Gran et al 2016. We have found hundreds of RRab stars located in a thin strip across the Galactic disk (Minniti et al 2017), at Galactic latitudes −2.24 < b < −1.05 deg, and Galactic longitudes (295 < l < 350 deg).…”

Section: Introductionmentioning

confidence: 96%

FSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars

Minniti

Palma

Dékány

et al. 2017

ApJL

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We use deep multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to search for RR Lyrae stars towards the Southern Galactic plane. Here we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster, that matches the position of the previously known star cluster FSR 1716. The stellar density map of the field yields a > 100 sigma detection for this candidate globular cluster, that is centered at equatorial coordinates RA J2000 =16:10:30.0, DEC J2000 = −53:44:56; and galactic coordinates l =329.77812, b = −1.59227. The color-magnitude diagram of this object reveals a well populated red giant branch, with a prominent red clump at K s = 13.35 ± 0.05, and J − K s = 1.30 ± 0.05. We present the cluster RR Lyrae positions, magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with age > 10 Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, < P >= 0.540 days, and argue that this is a relatively metal-poor cluster with [F e/H] = −1.5 ± 0.4 dex. The mean extinction and reddening for arXiv:1703.02033v1 [astro-ph.GA] 6 Mar 2017 2 this cluster are A Ks = 0.38 ± 0.02, and E(J − K s ) = 0.72 ± 0.02 mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is (m − M ) 0 = 14.38 ± 0.03 mag, implying a distance D = 7.5 ± 0.2 kpc, and a Galactocentric distance R G = 4.3 kpc.

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Mapping the outer bulge with RRab stars from the VVV Survey

Cited by 58 publications

References 51 publications

Discovery of Rr Lyrae Stars in the Nuclear Bulge of the Milky Way

Discovery of Rr Lyrae Stars in the Nuclear Bulge of the Milky Way

The Gaia-ESO Survey: Exploring the complex nature and origins of the Galactic bulge populations

FSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars

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