The VVV Survey Reveals Classical Cepheids Tracing a Young and Thin Stellar Disk Across the Galaxy’s Bulge

Abstract

Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy's evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years. A Ks,T 1 has > 3σ positive deviation from A Ks ,B . b Known ionozed hydrogen bubble close to the Cepheid. d Elevated diffuse mid-infrared emission around the Cepheid at 8-and 24-µm GLIMPSE images. e Extended bright object close to the Cepheid in 8-and 24-µm GLIMPSE images. y Young stellar object(s) close to the Cepheid.

The central spheroids of Milky Way mass-sized galaxies

“…These stars are formed in situ, and have high metallicity and low α-element enhancements; they formed from heavily recycled material. It would of great interest to measure the chemical abundances of the cepheids stars that have been detected in the bulge of the MW (Dékány et al 2015).…”

“…Interestingly, most of them are part of the bulge component (i.e., they belong to the most gravitationallybound stellar populations). Recent discoveries of cepheids in the bulge of the MW indicates the existence of young stars in the bulge (Dékány et al 2015). A census of these young populations would be of utmost importance to set constraints on the formation of the MW and large spirals in general.…”

“…Recent observations have reported the existence of very old stars traced by RR Lyrae populations , as well as young stars (Dékány et al 2015), within the bulge region.…”

The Galaxy in Context: Structural, Kinematic, and Integrated Properties

“…The structure of the inner Galactic disk between the NSD and R ∼ 2 kpc is not well-known due to heavy extinction and crowding. Observations of maser stars and vvv Cepheids indicate a barred disk of young stars (Habing et al 2006;Dékány et al 2015). The cold kinematics of young bar stars has likely been seen in apogee LOS velocity histograms .…”

“…Large numbers of RR Lyrae stars found in the ogle and vvv bulge surveys have shown that the most metal-poor ([Fe/H] = −1.0 ± 0.2), old population does not participate in the b/p-bulge (Dékány et al 2013;Pietrukowicz et al 2015), consistent with the argos result that only stars with [Fe/H] > ∼ − 0.5 participate in the split red clump (Ness et al 2012). The RR Lyrae stars show no significant rotation (Kunder et al 2016).…”