790 research outputs found
Highly-mass-loaded hot galactic winds are unstable to cool filament formation
When cool clouds are ram-pressure accelerated by a hot supersonic galactic
wind, some of the clouds may be shredded by hydrodynamical instabilities and
incorporated into the hot flow. Recent one-dimensional steady-state
calculations show how cool cloud entrainment directly affects the bulk
thermodynamics, kinematics, and observational characteristics of the hot gas.
In particular, mass-loading decelerates the hot flow and changes its entropy.
Here, we investigate the stability of planar and spherical mass-loaded hot
supersonic flows using both perturbation analysis and three-dimensional
time-dependent radiative hydrodynamical simulations. We show that mass-loading
is stable over a broad range of parameters and that the 1D time-steady analytic
solutions exactly reproduce the 3D time-dependent calculations, provided that
the flow does not decelerate sufficiently to become subsonic. For higher values
of the mass-loading, the flow develops a sonic point and becomes thermally
unstable, rapidly cooling and forming elongated dense cometary filaments. We
explore the mass-loading parameters required to reach a sonic point and the
radiative formation of these filaments. For certain approximations, we can
derive simple analytic criteria. In general a mass-loading rate similar to the
initial mass outflow rate is required. In this sense, the destruction of small
cool clouds by a hot flow may ultimately spontaneously generate fast cool
filaments, as observed in starburst superwinds. Lastly, we find that the
kinematics of filaments is sensitive to the slope of the mass-loading function.
Filaments move faster than the surrounding wind if mass-loading is over long
distances whereas filaments move slower than their surroundings if mass-loading
is abrupt.Comment: 12 pages, 15 figures, submitted to MNRAS (21 July 2023
CloudFlex: A Flexible Parametric Model for the Small-Scale Structure of the Circumgalactic Medium
We present CloudFlex, a new open-source tool for predicting the
absorption-line signatures of cool gas in galaxy halos with complex small-scale
structure. Motivated by analyses of cool material in hydrodynamical simulations
of turbulent, multiphase media, we model individual cool gas structures as
assemblies of cloudlets with a power-law distribution of cloudlet mass and relative velocities drawn from a turbulent velocity
field. The user may specify , the lower limit of the cloudlet mass
distribution (), and several other parameters that set the
total mass, size, and velocity distribution of the complex. We then calculate
the MgII 2796 absorption profiles induced by the cloudlets along pencil-beam
lines of sight. We demonstrate that at fixed metallicity, the covering fraction
of sightlines with equivalent widths Ang increases
significantly with decreasing , cool cloudlet number density
(), and cloudlet complex size. We then present a first application,
using this framework to predict the projected distribution around
galaxies. We show that the observed incidences of
Ang sightlines within 10 kpc < < 50 kpc are consistent with our
model over much of parameter space. However, they are underpredicted by models
with and , in
keeping with a picture in which the inner cool circumgalactic medium (CGM) is
dominated by numerous low-mass cloudlets ()
with a volume filling factor . When used to simultaneously model
absorption-line datasets built from multi-sightline and/or spatially-extended
background probes, CloudFlex will enable detailed constraints on the size and
velocity distributions of structures comprising the photoionized CGM.Comment: 22 pages, 7 figures. Submitted to AAS Journals, with minor
modifications. Comments welcome. (1) Co-first authors who made equal
contributions to this wor
Dark Matter and Baryons in the Most X-ray Luminous and Merging Galaxy Cluster RX J1347.5-1145
The galaxy cluster RX J1347-1145 is one of the most X-ray luminous and most
massive clusters known. Its extreme mass makes it a prime target for studying
issues addressing cluster formation and cosmology. In this paper we present new
high-resolution HST/ACS and Chandra X-ray data. The high resolution and
sensitivity of ACS enabled us to detect and quantify several new multiply
imaged sources, we now use a total of eight for the strong lensing analysis.
Combining this information with shape measurements of weak lensing sources in
the central regions of the cluster, we derive a high-resolution,
absolutely-calibrated mass map. This map provides the best available
quantification of the total mass of the central part of the cluster to date. We
compare the reconstructed mass with that inferred from the new Chandra X-ray
data, and conclude that both mass estimates agree extremely well in the
observed region, namely within 400 / h_70 kpc of the cluster center. In
addition we study the major baryonic components (gas and stars) and hence
derive the dark matter distribution in the center of the cluster. We find that
the dark matter and baryons are both centered on the BCG within the
uncertainties (alignment is better than <10 kpc). We measure the corresponding
1-D profiles and find that dark matter distribution is consistent with both NFW
and cored profiles, indicating that a more extended radial analysis is needed
to pinpoint the concentration parameter, and hence the inner slope of the dark
matter profile.Comment: 12 pages, Accepted for publication in ApJ, full-res version
http://www.physics.ucsb.edu/~marusa/RXJ1347.pd
New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
Understanding cosmic reionization requires the identification and
characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble
Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with
the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time,
systematically explored the galaxy population deep into the era when cosmic
microwave background (CMB) data indicates reionization was underway. The UDF12
campaign thus provides the best constraints to date on the abundance,
luminosity distribution, and spectral properties of early star-forming
galaxies. We synthesize the new UDF12 results with the most recent constraints
from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity
densities, reionization histories, and electron scattering optical depth
evolution consistent with the available data. Under reasonable assumptions
about the escape fraction of hydrogen ionizing photons and the intergalactic
medium clumping factor, we find that to fully reionize the universe by redshift
z~6 the population of star-forming galaxies at redshifts z~7-9 likely must
extend in luminosity below the UDF12 limits to absolute UV magnitudes of
M_UV\sim -13 or fainter. Moreover, low levels of star formation extending to
redshifts z~15-25, as suggested by the normal UV colors of z\simeq7-8 galaxies
and the smooth decline in abundance with redshift observed by UDF12 to
z\simeq10, are additionally likely required to reproduce the optical depth to
electron scattering inferred from CMB observations.Comment: Version accepted by ApJ (originally submitted Jan 5, 2013). The UDF12
website can be found at http://udf12.arizona.ed
- …