51 research outputs found
Radio Observations Reveal Unusual Circumstellar Environments for Some Type Ibc Supernova Progenitors
We present extensive radio observations of the nearby Type Ibc supernovae
2004cc, 2004dk, and 2004gq spanning 8-1900 days after explosion. Using a
dynamical model developed for synchrotron emission from a slightly decelerated
shockwave, we estimate the velocity and energy of the fastest ejecta and the
density profile of the circumstellar medium. The shockwaves of all three
supernovae are characterized by non-relativistic velocities of v ~ (0.1-25)c
and associated energies of E ~ (2-10) * 1e47 erg, in line with the expectations
for a typical homologous explosion. Smooth circumstellar density profiles are
indicated by the early radio data and we estimate the progenitor mass loss
rates to be ~ (0.6-13) * 1e-5 M_sun/yr (wind velocity 10^3 km/s). These
estimates approach the saturation limit (~1e-4 M_sun/yr) for line-driven winds
from Wolf-Rayet stars, the favored progenitors of SNe Ibc including those
associated with long-duration GRBs. Intriguingly, at later epochs all three
supernovae show evidence for abrupt radio variability that we attribute to
large density modulations (factor of ~3-6) at circumstellar radii of r ~ (1-50)
* 1e16 cm. If due to variable mass loss, these modulations are associated with
progenitor activity on a timescale of ~ 10-100 years before explosion. We
consider these results in the context of variable mass loss mechanisms
including wind clumping, metallicity-independent continuum-driven ejections,
and binary-induced modulations. It may also be possible that the SN shockwaves
are dynamically interacting with wind termination shocks, however, this
requires the environment to be highly pressurized and/or the progenitor to be
rapidly rotating prior to explosion. The proximity of the density modulations
to the explosion sites may suggest a synchronization between unusual progenitor
mass loss and the SN explosion, reminiscent of Type IIn supernovae. [ABRIDGED]Comment: 23 pages, 8 figures, 5 tables, accepted to Ap
Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies
Advances in instrumentation have recently extended detailed measurements of gas kinematics to large samples of high-redshift galaxies. Relative to most nearby, thin disc galaxies, in which gas rotation accurately traces the gravitational potential, the interstellar medium (ISM) of z âł 1 galaxies is typically more dynamic and exhibits elevated turbulence. If not properly modelled, these effects can strongly bias dynamical mass measurements. We use high-resolution FIRE-2 cosmological zoom-in simulations to analyse the physical effects that must be considered to correctly infer dynamical masses from gas kinematics. Our analysis covers a range of galaxy properties from low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (Mâ > 10ÂčÂč Mâ at z = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile v_Ï(r) of the cool (â 10^(3.5) < T <10^(4.5) Kâ ) gas and compare it to the circular velocity v_c = âGM_(enc)/râ . In the simulated galaxies, the gas rotation traces the circular velocity at intermediate radii, but the two quantities diverge significantly in the centre and in the outer disc. Our simulations appear to over-predict observed rotational velocities in the centres of massive galaxies (likely from a lack of black hole feedback), so we focus on larger radii. Gradients in the turbulent pressure at these radii can provide additional radial support and bias dynamical mass measurements low by up to 40 per cent. In both the interior and exterior, the gasâ motion can be significantly non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the accuracy of commonly used analytic models for pressure gradients (or âasymmetric driftâ) in the ISM of high-redshift galaxies
The diverse evolutionary paths of simulated high-z massive, compact galaxies to z=0
Massive quiescent galaxies have much smaller physical sizes at high redshift
than today. The strong evolution of galaxy size may be caused by progenitor
bias, major and minor mergers, adiabatic expansion, and/or renewed star
formation, but it is difficult to test these theories observationally. Herein,
we select a sample of 35 massive, compact galaxies (
M, M/kpc) at in the
cosmological hydrodynamical simulation Illustris and trace them forward to
to uncover their evolution and identify their descendants. By , the
original factor of 3 difference in stellar mass spreads to a factor of 20. The
dark matter halo masses similarly spread from a factor of 5 to 40. The
galaxies' evolutionary paths are diverse: about half acquire an ex-situ
envelope and are the core of a more massive descendant, a third survive
undisturbed and gain very little mass, 15% are consumed in a merger with a more
massive galaxy, and a small remainder are thoroughly mixed by major mergers.
The galaxies grow in size as well as mass, and only 10% remain compact by
. The majority of the size growth is driven by the acquisition of ex-situ
mass. The most massive galaxies at are the most likely to have compact
progenitors, but this trend possesses significant dispersion which precludes a
direct linkage to compact galaxies at . The compact galaxies' merger rates
are influenced by their environments, so that isolated or satellite
compact galaxies (which are protected from mergers) are the most likely to
survive to the present day.Comment: 19 pages, 10 figures, MNRAS accepted version including 2 new figure
An analysis of the evolving comoving number density of galaxies in hydrodynamical simulations
The cumulative comoving number-density of galaxies as a function of stellar
mass or central velocity dispersion is commonly used to link galaxy populations
across different epochs. By assuming that galaxies preserve their
number-density in time, one can infer the evolution of their properties, such
as masses, sizes, and morphologies. However, this assumption does not hold in
the presence of galaxy mergers or when rank ordering is broken owing to
variable stellar growth rates. We present an analysis of the evolving comoving
number density of galaxy populations found in the Illustris cosmological
hydrodynamical simulation focused on the redshift range . Our
primary results are as follows: 1) The inferred average stellar mass evolution
obtained via a constant comoving number density assumption is systematically
biased compared to the merger tree results at the factor of 2(4) level
when tracking galaxies from redshift out to redshift ; 2) The
median number density evolution for galaxy populations tracked forward in time
is shallower than for galaxy populations tracked backward in time; 3) A similar
evolution in the median number density of tracked galaxy populations is found
regardless of whether number density is assigned via stellar mass, stellar
velocity dispersion, or dark matter halo mass; 4) Explicit tracking reveals a
large diversity in galaxies' assembly histories that cannot be captured by
constant number-density analyses; 5) The significant scatter in galaxy linking
methods is only marginally reduced by considering a number of additional
physical and observable galaxy properties as realized in our simulation. We
provide fits for the forward and backward median evolution in stellar mass and
number density and discuss implications of our analysis for interpreting
multi-epoch galaxy property observations.Comment: 18 pages, 11 figures, submitted to MNRAS, comments welcom
Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies
Advances in instrumentation have recently extended detailed measurements of gas kinematics to large samples of high-redshift galaxies. Relative to most nearby, thin disc galaxies, in which gas rotation accurately traces the gravitational potential, the interstellar medium (ISM) of z âł 1 galaxies is typically more dynamic and exhibits elevated turbulence. If not properly modelled, these effects can strongly bias dynamical mass measurements. We use high-resolution FIRE-2 cosmological zoom-in simulations to analyse the physical effects that must be considered to correctly infer dynamical masses from gas kinematics. Our analysis covers a range of galaxy properties from low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (Mâ > 10ÂčÂč Mâ at z = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile v_Ï(r) of the cool (â 10^(3.5) < T <10^(4.5) Kâ ) gas and compare it to the circular velocity v_c = âGM_(enc)/râ . In the simulated galaxies, the gas rotation traces the circular velocity at intermediate radii, but the two quantities diverge significantly in the centre and in the outer disc. Our simulations appear to over-predict observed rotational velocities in the centres of massive galaxies (likely from a lack of black hole feedback), so we focus on larger radii. Gradients in the turbulent pressure at these radii can provide additional radial support and bias dynamical mass measurements low by up to 40 per cent. In both the interior and exterior, the gasâ motion can be significantly non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the accuracy of commonly used analytic models for pressure gradients (or âasymmetric driftâ) in the ISM of high-redshift galaxies
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