skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Exploring Asymmetric Substructures of the Outer Disk Based on the Conjugate Angle of the Radial Action
Abstract We use the conjugate angle of radial action (θR), the best representation of the orbital phase, to explore the “midplane,” “north branch,” “south branch,” and “Monoceros area” disk structures that were previously revealed in the LAMOST K giants. The former three substructures, identified by their 3D kinematical distributions, have been shown to be projections of the phase space spiral (resulting from nonequilibrium phase mixing). In this work, we find that all of these substructures associated with the phase spiral show high aggregation in conjugate angle phase space, indicating that the clumping in conjugate angle space is a feature of ongoing, incomplete phase mixing. We do not find theZ–VZphase spiral located in the “Monoceros area,” but we do find a very highly concentrated substructure in the quadrant of conjugate angle space with the orbital phase from the apocenter to the guiding radius. The existence of the clump in conjugate angle space provides a complementary way to connect the “Monoceros area” with the direct response to a perturbation from a significant gravitationally interactive event. Using test particle simulations, we show that these features are analogous to disturbances caused by the impact of the last passage of the Sagittarius dwarf spheroidal galaxy.  more » « less
Award ID(s):
1908653
PAR ID:
10470480
Author(s) / Creator(s):
; ; ; ; ; ; ;
Publisher / Repository:
Institute of Physics
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
956
Issue:
1
ISSN:
0004-637X
Page Range / eLocation ID:
13
Subject(s) / Keyword(s):
galaxy kinematics galaxy anticenters
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Monthly Notices of the Royal Astronomical Society: Letters)
    ABSTRACT Gaia Data Release 2 revealed that the Milky Way contains significant indications of departures from equilibrium in the form of asymmetric features in the phase space density of stars in the Solar neighbourhood. One such feature is the z–vz phase spiral, interpreted as the response of the disc to the influence of a perturbation perpendicular to the disc plane, which could be external (e.g. a satellite) or internal (e.g. the bar or spiral arms). In this work, we use Gaia Data Release 3 to dissect the phase spiral by dividing the local data set into groups with similar azimuthal actions, Jϕ, and conjugate angles, θϕ, which selects stars on similar orbits and at similar orbital phases, thus having experienced similar perturbations in the past. These divisions allow us to explore areas of the Galactic disc larger than the surveyed region. The separation improves the clarity of the z–vz phase spiral and exposes changes to its morphology across the different action-angle groups. In particular, we discover a transition to two armed ‘breathing spirals’ in the inner Milky Way. We conclude that the local data contain signatures of not one, but multiple perturbations with the prospect to use their distinct properties to infer the properties of the interactions that caused them. 
    more » « less
  2. ; ; ; ; ; (, The Astrophysical Journal)
    Abstract Signatures of vertical disequilibrium have been observed across the Milky Way’s (MW’s) disk. These signatures manifest locally as unmixed phase spirals inz–vzspace (“snails-in-phase”), and globally as nonzero meanzandvz, wrapping around the disk into physical spirals in thex–yplane (“snails-in-space”). We explore the connection between these local and global spirals through the example of a satellite perturbing a test-particle MW-like disk. We anticipate our results to broadly apply to any vertical perturbation. Using az–vzasymmetry metric, we demonstrate that in test-particle simulations: (a) multiple local phase-spiral morphologies appear when stars are binned by azimuthal actionJϕ, excited by a single event (in our case, a satellite disk crossing); (b) these distinct phase spirals are traced back to distinct disk locations; and (c) they are excited at distinct times. Thus, local phase spirals offer a global view of the MW’s perturbation history from multiple perspectives. Using a toy model for a Sagittarius (Sgr)–like satellite crossing the disk, we show that the full interaction takes place on timescales comparable to orbital periods of disk stars withinR≲ 10 kpc. Hence such perturbations have widespread influence, which peaks in distinct regions of the disk at different times. This leads us to examine the ongoing MW–Sgr interaction. While Sgr has not yet crossed the disk (currently,zSgr≈ −6 kpc,vz,Sgr≈ 210 km s−1), we demonstrate that the peak of the impact has already passed. Sgr’s pull over the past 150 Myr creates a globalvzsignature with amplitude ∝MSgr, which might be detectable in future spectroscopic surveys. 
    more » « less
  3. ; ; ; ; ; (, The Astrophysical Journal)
    Abstract We construct a sample of nearly 30,000 main-sequence stars with 4500 K < Teff < 5000 K and stellar ages estimated by the chromospheric activity−age relation. This sample is used to determine the age distribution in theR–Zplane of the Galaxy, whereRis the projected Galactocentric distance in the disk midplane andZis the height above the disk midplane. As ∣Z∣ increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases asRincreases, which is called a flare. A mild flare fromR ∼ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures inZ–υZphase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last ∼1.0 Gyr. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal)
    Abstract We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098Z⊙) and low stellar masses (104.7–107.6M⊙). Taking deep medium/high-resolution (R∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hαemission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hαflux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (vrot) of 5–23 km s−1smaller than the velocity dispersions (σ0) of 17–31 km s−1, indicating dispersion-dominated (vrot/σ0= 0.29–0.80 < 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions offgas≃ 0.9–1.0. Comparing our results with other Hαkinematics studies, we find thatvrot/σ0decreases andfgasincreases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z(z∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations atz∼ 7. 
    more » « less
  5. ; ; ; ; (, Weather and Forecasting)
    Abstract Polarimetric radar data from the WSR-88D network are used to examine the evolution of various polarimetric precursor signatures to tornado dissipation within a sample of 36 supercell storms. These signatures include an increase in bulk hook echo median raindrop size, a decrease in midlevel differential radar reflectivity factor (ZDR) column area, a decrease in the magnitude of theZDRarc, an increase in the area of low-level large hail, and a decrease in the orientation angle of the vector separating low-levelZDRand specific differential phase (KDP) maxima. Only supercells that produced “long-duration” tornadoes (with at least four consecutive volumes of WSR-88D data) are investigated, so that signatures can be sufficiently tracked in time, and novel algorithms are used to isolate each storm-scale process. During the time leading up to tornado dissipation, we find that hook echo median drop size (D0) and medianZDRremain relatively constant, but hook echo medianKDPand estimated number concentration (NT) increase. TheZDRarc maximum magnitude andZDR–KDPseparation orientation angles are observed to decrease in most dissipation cases. Neither the area of large hail nor theZDRcolumn area exhibit strong signals leading up to tornado dissipation. Finally, combinations of storm-scale behaviors and TVS behaviors occur most frequently just prior to tornado dissipation, but also are common 15–20 min prior to dissipation. The results from this study provide evidence that nowcasting tornado dissipation using dual-polarization radar may be possible when combined with TVS monitoring, subject to important caveats. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email