arXiv subjects

Jennifer K. S. Friske

Publications and source records attributed to Jennifer K. S. Friske.

5 recordsLinked to original sources

arXiv2026

The impact of hot mode accretion and angular momentum conservation on metallicity gradients of galactic discs

The hot circumgalactic medium (CGM) of a galaxy inevitably rotates more slowly than the cold gas in the disc it surrounds, due to a higher pressure support against gravity. If it accretes vertically onto the disc, angular momentum conservation leads to radial flows, advection of metals inwards and the steepening of a metallicity gradient. The observed gradient hence carries information on the kinematics of the accreting gas. Previous models built on this premise parametrised the angular momentum mismatch as a simple function of radius, constant in time, rather than derived from the properties of the CGM itself. Here, we present a semi-analytic chemical evolution model of a galaxy with a cosmologically motivated evolution, a self-consistent and time-evolving potential and an isothermal rotating CGM. The model includes inside-out formation and the radial flows induced both by the deepening of the potential well (acting on gas and stars) and by accretion, following their combined effect on the gas-phase metallicity gradient over cosmic time. We use a Bayesian framework to fit simultaneously the structural properties and metallicity gradient of a galaxy, inferring both the required inside-out growth and the CGM temperature needed to drive the required radial flows and abundance gradient. Fitting our model to the Milky Way, we find a mild preference for a subvirial corona ($T_\mathrm{CGM}/T_{200}=0.82^{+0.44}_{-0.38}$), in mild tension with observations, and we discuss possible resolutions. The predicted CGM rotation velocity lies between ~100-160 km/s at the present time and is substantially lower at earlier epochs. We further recover an evolution of the gradient over the past ~8Gyr consistent with observations. Our approach is not restricted to the Milky Way and can be directly applied to external galaxies, offering a new handle to constrain hot mode accretion onto galactic discs.

astro-ph.GA↗

arXiv2025

The JWST Galactic Center Survey -- A White Paper

The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of the most well-studied regions in astrophysics. Due to its proximity, we can study the center of our Galaxy on scales down to a few hundred AU, a hundred times better than in similar Local Group galaxies and thousands of times better than in the nearest active galaxies. The Galactic Center (GC) is therefore of outstanding astrophysical interest. However, in spite of intense observational work over the past decades, there are still fundamental things unknown about the GC. JWST has the unique capability to provide us with the necessary, game-changing data. In this White Paper, we advocate for a JWST NIRCam survey that aims at solving central questions, that we have identified as a community: i) the 3D structure and kinematics of gas and stars; ii) ancient star formation and its relation with the overall history of the Milky Way, as well as recent star formation and its implications for the overall energetics of our galaxy's nucleus; and iii) the (non-)universality of star formation and the stellar initial mass function. We advocate for a large-area, multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy in the form of a Treasury GO JWST Large Program that is open to the community. We describe how this survey will derive the physical and kinematic properties of ~10,000,000 stars, how this will solve the key unknowns and provide a valuable resource for the community with long-lasting legacy value.

astro-ph.GA↗

arXiv2023

The Prince and the Pauper: Evidence for the early high-redshift formation of the Galactic $α$-poor disc population

Context. The presence of [$α$/Fe]-[Fe/H] bi-modality in the Milky Way disc has animated the Galactic archaeology community since more than two decades. Aims. Our goal is to investigate the chemical, temporal, and kinematical structure of the Galactic discs using abundances, kinematics, and ages derived self-consistently with the new Bayesian framework SAPP. Methods. We employ the public Gaia-ESO spectra, as well as Gaia EDR3 astrometry and photometry. Stellar parameters and chemical abundances are determined for 13 426 stars using NLTE models of synthetic spectra. Ages are derived for a sub-sample of 2 898 stars, including subgiants and main-sequence stars. The sample probes a large range of Galactocentric radii, $\sim$ 3 to 12 kpc, and extends out of the disc plane to $\pm$ 2 kpc. Results. Our new data confirm the known bi-modality in the [Fe/H] - [$α$/Fe] space, which is often viewed as the manifestation of the chemical thin and thick discs. The over-densities significantly overlap in metallicity, age, and kinematics, and none of these is a sufficient criterion for distinguishing between the two disc populations. Different from previous studies, we find that the $α$-poor disc population has a very extended [Fe/H] distribution and contains $\sim$ 20$\%$ old stars with ages of up to $\sim$ 11 Gyr. Conclusions. Our results suggest that the Galactic thin disc was in place early, at look-back times corresponding to redshifts z $\sim$ 2 or more. At ages $\sim$ 9 to 11 Gyr, the two disc structures shared a period of co-evolution. Our data can be understood within the clumpy disc formation scenario that does not require a pre-existing thick disc to initiate a formation of the thin disc. We anticipate that a similar evolution can be realised in cosmological simulations of galaxy formation.

astro-ph.GA↗

arXiv2023

On the likelihoods of finding very metal-poor (and old) stars in the Milky Way's disc, bulge, and halo

Recent observational studies have uncovered a small number of very metal-poor stars with cold kinematics in the Galactic disc and bulge. However, their origins remain enigmatic. We select a total of 138 Milky Way (MW) analogs from the TNG50 cosmological simulation based on their $z=0$ properties: disky morphology, stellar mass, and local environment. In order to make more predictive statements for the MW, we further limit the spatial volume coverage of stellar populations in galaxies to that targeted by the upcoming 4MOST high-resolution survey of the Galactic disc and bulge. We find that across all galaxies, $\sim$20 per cent of very metal-poor (${\rm [Fe/H]} < -2$) stars belong to the disk, with some analogs reaching 30 per cent. About 50$\pm$10 per cent of the VMP disc stars are, on average, older than 12.5 Gyr and $\sim$70$\pm$10 per cent come from accreted satellites. A large fraction of the VMP stars belong to the halo ($\sim$70) and have a median age of 12 Gyr. Our results with the TNG50 cosmological simulation confirm earlier findings with simulations of fewer individual galaxies, and suggest that the stellar disc of the Milky Way is very likely to host significant amounts of very- and extremely-metal-poor stars that, although mostly of ex situ origin, can also form in situ, reinforcing the idea of the existence of a primordial Galactic disc.

astro-ph.GA↗

arXiv2020

Resonance sweeping by a decelerating Galactic bar

We provide the first quantitative evidence for the deceleration of the Galactic bar from local stellar kinematics in agreement with dynamical friction by a typical dark matter halo. The kinematic response of the stellar disk to a decelerating bar is studied using secular perturbation theory and test particle simulations. We show that the velocity distribution at any point in the disk affected by a naturally slowing bar is qualitatively different from that perturbed by a steadily rotating bar with the same current pattern speed $Ω_{\rm p}$ and amplitude. When the bar slows down, its resonances sweep through phase space, trapping and dragging along a portion of previously free orbits. This enhances occupation on resonances, but also changes the distribution of stars within the resonance. Due to the accumulation of orbits near the boundary of the resonance, the decelerating bar model reproduces with its corotation resonance the offset and strength of the Hercules stream in the local $v_R$-$v_φ$ plane and the double-peaked structure of mean $v_R$ in the $L_z$-$φ$ plane. At resonances other than the corotation, resonant dragging by a slowing bar is associated with a continuing increase in radial action, leading to multiple resonance ridges in the action plane as identified in the Gaia data. This work shows models using a constant bar pattern speed likely lead to qualitatively wrong conclusions. Most importantly we provide a quantitative estimate of the current slowing rate of the bar $dΩ_{\rm p}/dt = (-4.5 \pm 1.4)~{\rm km} {\rm s}^{-1} {\rm kpc}^{-1} {\rm Gyr}^{-1}$ with additional systematic uncertainty arising from unmodeled impacts of e.g. spiral arms.

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