7 research outputs found
Asymmetric Drift of Andromeda Analogs in the IllustrisTNG Simulation
We analyze the kinematics as a function of stellar age for Andromeda (M31)
mass analogs from the IllustrisTNG cosmological simulation. We divide the star
particles into four age groups: less than 1 Gyr, 1 to 5 Gyr, 5 to 10 Gyr, and
greater 10 Gyr, and compare the kinematics of these groups to that of the
neutral gas cells. We calculate rotation curves for the stellar and gaseous
components of each analog from 2 kpc to 20 kpc from the center of mass. We find
that the lag, or asymmetric drift (AD), between the gas rotation curve and the
stellar rotation curve on average increases with stellar age. This finding is
consistent with observational measurements of AD in the disk of the Andromeda
galaxy. When the M31 analogs are separated into groups based on merger history,
we find that there is a difference in the AD of the analogs that have had a 4:1
merger the last 4 Gyr, 8 Gyr, or 12 Gyr compared to analogs that have not
experienced a 4:1 merger in the same time frame. The subset of analogs that
have had a 4:1 merger within the last 4 Gyr are also similar to AD measurements
of stars in the disk of M31, providing evidence that M31 may in fact have
recently merged with a galaxy nearly one fourth of its mass. Further work using
high resolution zoom in simulations is required to explore the contribution of
internal heating to AD.Comment: 14 pages, 11 figures, accepted to MNRAS for publication July 20, 202
Resolved SPLASH Chemodynamics in Andromeda's PHAT Stellar Halo and Disk: On the Nature of the Inner Halo Along the Major Axis
Stellar kinematics and metallicity are key to exploring formation scenarios
for galactic disks and halos. In this work, we characterized the relationship
between kinematics and photometric metallicity along the line-of-sight to M31's
disk. We combined optical HST/ACS photometry from the Panchromatic Hubble
Andromeda Treasury (PHAT) survey with Keck/DEIMOS spectra from the
Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH)
survey. The resulting sample of 3536 individual red giant branch stars spans
4-19 projected kpc, making it a useful probe of both the disk and inner halo.
We separated these stars into disk and halo populations by modeling the
line-of-sight velocity distributions as a function of position across the disk
region, where 70.9% stars have a high likelihood of belonging to the disk and
17.1% to the halo. Although stellar halos are typically thought to be
metal-poor, the kinematically identified halo contains a significant population
of stars (29.4%) with disk-like metallicity ([Fe/H]).
This metal-rich halo population lags the gaseous disk to a similar extent as
the rest of the halo, indicating that it does not correspond to a canonical
thick disk. Its properties are inconsistent with those of tidal debris
originating from the Giant Stellar Stream merger event. Moreover, the halo is
chemically distinct from the phase-mixed component previously identified along
the minor axis (i.e., away from the disk), implying contributions from
different formation channels. These metal-rich halo stars provide direct
chemodynamical evidence in favor of the previously suggested "kicked-up'' disk
population in M31's inner stellar halo.Comment: Submitted to AJ. Conclusions on page 20. 18 figures, 2 tables, 4
appendice
Sleep-amount differentially affects fear-processing neural circuitry in pediatric anxiety: A preliminary fMRI investigation
Insufficient sleep, as well as the incidence of anxiety disorders, both peak during adolescence. While both conditions present perturbations in fear-processing-related neurocircuitry, it is unknown whether these neurofunctional alterations directly link anxiety and compromised sleep in adolescents. Fourteen anxious adolescents (AAs) and 19 healthy adolescents (HAs) were compared on a measure of sleep amount and neural responses to negatively valenced faces during fMRI. Group differences in neural response to negative faces emerged in the dorsal anterior cingulate cortex (dACC) and the hippocampus. In both regions, correlation of sleep amount with BOLD activation was positive in AAs, but negative in HAs. Follow-up psychophysiological interaction (PPI) analyses indicated positive connectivity between dACC and dorsomedial prefrontal cortex, and between hippocampus and insula. This connectivity was correlated negatively with sleep amount in AAs, but positively in HAs. In conclusion, the presence of clinical anxiety modulated the effects of sleep-amount on neural reactivity to negative faces differently among this group of adolescents, which may contribute to different clinical significance and outcomes of sleep disturbances in healthy adolescents and patients with anxiety disorders
Astro2020 Science White Paper: Construction of an L* Galaxy: the Transformative Power of Wide Fields for Revealing the Past, Present and Future of the Great Andromeda System
Submitted as a science white paper to the Astro2020 Decadal SurveyThe Great Andromeda Galaxy (M31) is the nexus of the near-far galaxy evolution connection and a principal data point for near-field cosmology. Due to its proximity (780 kpc), M31 can be resolved into individual stars like the Milky Way (MW). Unlike the MW, we have the advantage of a global view of M31, enabling M31 to be observed with techniques that also apply to more distant galaxies. Moreover, recent evidence suggests that M31 may have survived a major merger within the last several Gyr, shaping the morphology of its stellar halo and triggering a starburst, while leaving the stellar disk largely intact. The MW and M31 thus provide complementary opportunities for in-depth studies of the disks, halos, and satellites of L* galaxies. Our understanding of the M31 system will be transformed in the 2020s if they include wide field facilities for both photometry (HST-like sensitivity and resolution) and spectroscopy (10-m class telescope, >1 sq. deg. field, highly multiplexed, R~ 3000 to 6000). We focus here on the power of these facilities to constrain the past, present, and future merger history of M31, via chemo-dynamical analyses and star formation histories of phase-mixed stars accreted at early times, as well as stars in surviving tidal debris features, M31's extended disk, and intact satellite galaxies that will eventually be tidally incorporated into the halo. This will yield an unprecedented view of the hierarchical formation of the M31 system and the subhalos that built it into the L* galaxy we observe today