Browsing by Author "Valenzuela-Navarro, A."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Observed kinematics of the Milky Way nuclear stellar disk region
    (2024) Zoccali, M.; Rojas-Arriagada, A.; Valenti, E.; Ramos, R. Contreras; Valenzuela-Navarro, A.; Salvo-Guajardo, C.
    Context. The nuclear region of the Milky Way, within approximately -1 degrees < l < +1 degrees and -0.3 degrees < b < +0.3 degrees (i.e., |l|< 150 pc, |b|< 45 pc), is believed to host a nuclear stellar disk, co-spatial with the gaseous central molecular zone. Previous kinematical studies detected faster rotation for the stars belonging to the nuclear stellar disk, compared to the surrounding regions. Aims. We analyze the rotation velocity of stars at the nuclear stellar disk, and compare them with its analog in a few control fields just outside this region. We limit our analysis to stars in the red clump of the color magnitude diagram, in order to be able to relate their mean de-reddened luminosity with distance along the line of sight. Methods. We used a proper motion catalog, obtained from point spread function photometry on VISTA variables in the V & iacute;a L & aacute;ctea images, to construct maps of the transverse velocity for these stars. We complemented our analysis with radial velocities from the 17th data release of the APOGEE survey. Results. We find that the main difference between the nuclear stellar disk region and its surroundings is that at the former we see only stars moving eastward, which we believe are located in front of the Galactic center. On the contrary, in every other direction, we see the brightest red clump stars moving eastward, and the faintest ones moving westward, as expected for a rotating disk. We interpret these observations as being produced by the central molecular zone, hiding stars behind itself. What we observe is compatible with being produced by just the absence of the component at the back, without requiring the presence of a cold, fast rotating disk. This component is also not clearly detected in the newest release of the APOGEE catalog. In other words, we find no clear signature of the nuclear stellar disk as a distinct kinematical component. Conclusions. This work highlights the need for nearby control fields when attempting to characterize the properties of the nuclear stellar disk, as the different systematics affecting this region, compared to nearby ones, might introduce spurious results. Deep, wide field and high resolution photometry of the inner 4 deg of the Milky Way is needed in order to understand the structure and kinematics of this very unique region of our Galaxy.
  • Thumbnail Image
    Item
    VVV catalog of ab-type RR Lyrae in the inner Galactic bulge
    (2024) Zoccali, Manuela; Quezada, C.; Contreras Ramos, R.; Valenti, E.; Valenzuela-Navarro, A.; Olivares Carvajal, J.; Rojas Arriagada, A.; Minniti, J.H.; Gran, F.; De Leo, M.
    Context. Observational evidence has accumulated in recent years, showing that the Galactic bulge includes two populations, a metal-poor one and a metal-rich one, which in addition to having different metallicities show different alpha over iron abundances, spatial distribution, and kinematics. While the metal-rich, barred component has been fairly well characterized, the metal-poor, spheroidal component has been more elusive and harder to describe. RR Lyrae variables are clean tracers of the old bulge component, and they are, on average, more metal-poor than red clump stars. Aims. In the present paper, we provide a new catalog of 16488 ab-type RR Lyrae variables in the bulge region within |l|≲10° and |b|≲2.8°, extracted from multi-epoch Point Spread Function photometry performed on VISTA Variable in the Vía Láctea survey data. We used the catalog to constrain the shape of the old, metal-poor, bulge stellar population. Methods. The identification of ab-type RR Lyrae among a large sample of candidate variables of different types has been performed via a combination of a Random Forest classifier and visual inspection. We optimized this process in such a way to extract a clean catalog with high purity, although for this reason its completeness, close to the midplane, is lower compared to a few other near-infrared catalogs covering the same region of the sky. Results. We used the present catalog to derive the shape of their distribution around the Galactic center, resulting in an elongated spheroid with projected axis ratio of b/a∼0.7 and an inclination angle of φ∼20 degrees. We discuss how observational biases, such as errors on the distances and a nonuniform sampling in longitude, affect both the present measurements and previous ones, especially those based on red clump stars. Because the latter have not been taken into account before, we refrain from a quantitative comparison between these shape parameters and those derived for the main Galactic bar. Nonetheless, qualitatively, taking into account observational biases would lower the estimated ellipticity of the bar derived from red clump stars, and hence reduce the difference with the present results. Conclusions. We publish a high-purity RRab sample for future studies of the oldest Galactic bulge population, close to the midplane. We explore different choices for the period-luminosity-metallicity relation, highlighting how some of them introduce spurious trends of distance with either the period or the metallicity, or both. We provide evidence that they trace a structure that is less elongated than the main bar, though we also highlight some biases of these kind of studies not discussed before.