452 research outputs found
A combined spectroscopic and photometric stellar activity study of Epsilon Eridani
We present simultaneous ground-based radial velocity (RV) measurements and
space-based photometric measurements of the young and active K dwarf Epsilon
Eridani. These measurements provide a data set for exploring methods of
identifying and ultimately distinguishing stellar photospheric velocities from
Keplerian motion. We compare three methods we have used in exploring this data
set: Dalmatian, an MCMC spot modeling code that fits photometric and RV
measurements simultaneously; the FF method, which uses photometric
measurements to predict the stellar activity signal in simultaneous RV
measurements; and H analysis. We show that our H measurements
are strongly correlated with photometry from the Microvariability and
Oscillations of STars (MOST) instrument, which led to a promising new method
based solely on the spectroscopic observations. This new method, which we refer
to as the HH method, uses H measurements as input into the FF
model. While the Dalmatian spot modeling analysis and the FF method with
MOST space-based photometry are currently more robust, the HH method only
makes use of one of the thousands of stellar lines in the visible spectrum. By
leveraging additional spectral activity indicators, we believe the HH method
may prove quite useful in disentangling stellar signals
Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
We present the implementation and the first results of cosmic ray (CR)
feedback in the Feedback In Realistic Environments (FIRE) simulations. We
investigate CR feedback in non-cosmological simulations of dwarf, sub-
starburst, and galaxies with different propagation models, including
advection, isotropic and anisotropic diffusion, and streaming along field lines
with different transport coefficients. We simulate CR diffusion and streaming
simultaneously in galaxies with high resolution, using a two moment method. We
forward-model and compare to observations of -ray emission from nearby
and starburst galaxies. We reproduce the -ray observations of dwarf and
galaxies with constant isotropic diffusion coefficient . Advection-only and streaming-only
models produce order-of-magnitude too large -ray luminosities in dwarf
and galaxies. We show that in models that match the -ray
observations, most CRs escape low-gas-density galaxies (e.g.\ dwarfs) before
significant collisional losses, while starburst galaxies are CR proton
calorimeters. While adiabatic losses can be significant, they occur only after
CRs escape galaxies, so they are only of secondary importance for -ray
emissivities. Models where CRs are ``trapped'' in the star-forming disk have
lower star formation efficiency, but these models are ruled out by -ray
observations. For models with constant that match the -ray
observations, CRs form extended halos with scale heights of several kpc to
several tens of kpc.Comment: 31 pages, 26 figures, accepted for publication in MNRA
Radiative Stellar Feedback in Galaxy Formation: Methods and Physics
Radiative feedback (RFB) from stars plays a key role in galaxies, but remains
poorly-understood. We explore this using high-resolution, multi-frequency
radiation-hydrodynamics (RHD) simulations from the Feedback In Realistic
Environments (FIRE) project. We study dwarf through Milky Way masses, and
explore RHD effects including H/He photoionization; photoelectric, Lyman
Werner, Compton, thermal dust heating; single and multiple-scattering radiation
pressure (RP). We also compare fundamentally distinct RHD algorithms: the
ray-based LEBRON (exact when optically-thin) and moments-based M1 (exact when
optically-thick). In all cases, the dominant RFB channels on galaxy scales are
photoionization heating and single-scattering RP. At all masses, most of the
ionizing/FUV luminosity from young stars (~half bolometric) is absorbed. In
dwarfs, the strongest effect is photoionization heating from the meta-galactic
background, suppressing accretion onto galaxies. At MW-mass the meta-galactic
background has negligible effects; but local photoionization and
single-scattering RP both contribute significantly to regulating the galactic
star formation efficiency and lowering central densities. Without some RFB (or
other 'rapid' FB), resolved GMCs turn most of their mass into stars, making
galaxies dominated by hyper-dense, bound clusters. This makes star formation
more violent and 'bursty' when SNe explode in hyper-clustered objects: thus,
including RFB tends to 'smooth out' star formation. IR multiple-scattering is
rare: the majority of photon absorption occurs in 'normal' GMCs with
. These conclusions are robust to the RHD method, but M1 produces
somewhat stronger RFB effects.Comment: 25 pages, 13 figures, submitted to MNRA
Radiative Stellar Feedback in Galaxy Formation: Methods and Physics
Radiative feedback (RFB) from stars plays a key role in galaxies, but remains
poorly-understood. We explore this using high-resolution, multi-frequency
radiation-hydrodynamics (RHD) simulations from the Feedback In Realistic
Environments (FIRE) project. We study ultra-faint dwarf through Milky Way mass
scales, including H+He photo-ionization; photo-electric, Lyman Werner, Compton,
and dust heating; and single+multiple scattering radiation pressure (RP). We
compare distinct numerical algorithms: ray-based LEBRON (exact when
optically-thin) and moments-based M1 (exact when optically-thick). The most
important RFB channels on galaxy scales are photo-ionization heating and
single-scattering RP: in all galaxies, most ionizing/far-UV luminosity (~1/2 of
lifetime-integrated bolometric) is absorbed. In dwarfs, the most important
effect is photo-ionization heating from the UV background suppressing
accretion. In MW-mass galaxies, meta-galactic backgrounds have negligible
effects; but local photo-ionization and single-scattering RP contribute to
regulating the galactic star formation efficiency and lowering central
densities. Without some RFB (or other 'rapid' FB), resolved GMCs convert
too-efficiently into stars, making galaxies dominated by hyper-dense, bound
star clusters. This makes star formation more violent and 'bursty' when SNe
explode in these hyper-clustered objects: thus, including RFB 'smoothes' SFHs.
These conclusions are robust to RHD methods, but M1 produces somewhat stronger
effects. Like in previous FIRE simulations, IR multiple-scattering is rare
(negligible in dwarfs, ~10% of RP in massive galaxies): absorption occurs
primarily in 'normal' GMCs with A_v~1.Comment: 28 pages, 14 figures. Updated to match published MNRAS versio
Jet interactions with a giant molecular cloud in the Galactic centre and ejection of hypervelocity stars
The hypervelocity OB stars in the Milky Way Galaxy were ejected from the
central regions some 10-100 million years ago. We argue that these stars, {as
well as many more abundant bound OB stars in the innermost few parsecs,} were
generated by the interactions of an AGN jet from the central black hole with a
dense molecular cloud. Considerations of the associated energy and momentum
injection have broader implications for the possible origin of the Fermi
bubbles and for the enrichment of the intergalactic medium.Comment: 4 pages, 1 figure. Astronomy and Astrophysics Letters, in pres
The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at z=3
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift.Comment: MNRAS Letters accepted (6 pages, 4 figures, 2 tables
FORGE'd in FIRE: Resolving the End of Star Formation and Structure of AGN Accretion Disks from Cosmological Initial Conditions
It has recently become possible to zoom-in from cosmological to sub-pc scales
in galaxy simulations to follow accretion onto supermassive black holes
(SMBHs). However, at some point the approximations used on ISM scales (e.g.
optically-thin cooling and stellar-population-integrated star formation [SF]
and feedback [FB]) break down. We therefore present the first cosmological
radiation-magnetohydrodynamic (RMHD) simulation which self-consistently
combines the FIRE physics (relevant on galactic/ISM scales where SF/FB are
ensemble-averaged) and STARFORGE physics (relevant on small scales where we
track individual (proto)stellar formation and evolution), together with
explicit RMHD (including non-ideal MHD and multi-band M1-RHD) which
self-consistently treats both optically-thick and thin regimes. This allows us
to span scales from ~100 Mpc down to <100 au (~300 Schwarzschild radii) around
a SMBH at a time where it accretes as a bright quasar, in a single simulation.
We show that accretion rates up to can
be sustained into the accretion disk at , with
gravitational torques between stars and gas dominating on sub-kpc scales until
star formation is shut down on sub-pc scales by a combination of optical depth
to cooling and strong magnetic fields. There is an intermediate-scale,
flux-frozen disk which is gravitoturbulent and stabilized by magnetic pressure
sustaining strong turbulence and inflow with persistent spiral modes. In this
paper we focus on how gas gets into the small-scale disk, and how star
formation is efficiently suppressed.Comment: 37 pages, 18 figures. Submitted to The Open Journal of Astrophysics.
Comments welcom
FORGE'd in FIRE II: The Formation of Magnetically-Dominated Quasar Accretion Disks from Cosmological Initial Conditions
In a companion paper, we reported the self-consistent formation of quasar
accretion disks with inflow rates down to
<300 Schwarzschild radii from cosmological
radiation-magneto-thermochemical-hydrodynamical galaxy and star formation
simulations. We see the formation of a well-defined, steady-state accretion
disk which is stable against star formation at sub-pc scales. The disks are
optically thick, with radiative cooling balancing accretion, but with
properties that are distinct from those assumed in most previous accretion disk
models. The pressure is strongly dominated by (primarily toroidal) magnetic
fields, with a plasma even in the disk midplane. They are
qualitatively distinct from magnetically elevated or arrested disks. The disks
are strongly turbulent, with trans-Alfvenic and highly super-sonic turbulence,
and balance this via a cooling time that is short compared to the disk
dynamical time, and can sustain highly super-Eddington accretion rates. Their
surface and 3D densities at gravitational radii are much
lower than in a Shakura-Sunyaev disk, with important implications for their
thermo-chemistry and stability. We show how the magnetic field strengths and
geometries arise from rapid advection of flux with the inflow from much weaker
galaxy-scale fields in these 'flux-frozen' disks, and how this stabilizes the
disk and gives rise to efficient torques. Re-simulating without magnetic fields
produces catastrophic fragmentation with a vastly smaller, lower-
Shakura-Sunyaev-like disk.Comment: 46 pages, 30 figures. Updated to match accepted version from The Open
Journal of Astrophysics. Part of a series with arXiv:2309.13115 . Animations
of the simulations can be viewed at
http://www.tapir.caltech.edu/~phopkins/Site/animations/Movies_zoom.htm
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