Sep. 28 |
Drummond Fielding |
The impact of star formation driven galactic winds on the circumgalactic medium
I will present a series of idealized three-dimensional hydrodynamic
simulations that we use to study the dynamics and thermal structure of
the circumgalactic medium (CGM). Our simulations quantify the role of
cooling, galactic winds driven by stellar feedback, and cosmological
accretion of gas in setting the properties of the CGM in dark matter
halos ranging from 1011-1012 M⊙.
As in calculations without stellar feedback, we find that above a
critical halo mass of 1011.5 M⊙, halo gas is
supported by thermal pressure created in the virial shock. The thermal
properties of the halo gas at small radii (near any central galaxy) are
regulated by feedback triggered when tcool/ tff ≲ 10
in the hot halo gas. Below the critical halo mass, however, there is no
thermally supported halo and self-regulation at tcool/ tff~10
does not apply. Instead, the halo gas properties are determined by the
interaction between the cosmological inflow of gas and the outgoing
galactic winds. The halo gas is not in hydrostatic equilibrium, but
is supported against gravity by bulk flows (turbulence and coherent
inflow/outflow), and its phase structure depends on both the energy
per unit mass and the mass-loading factor of the galaxy outflows. The
properties of our idealized simulations can account for some of the
properties of the multiphase halo gas inferred from HST-COS observations,
including the presence of significant mass at a wide range of temperatures,
and the characteristic OVI column densities and kinematics. I will also
briefly mention a related project in which we adopt a similar idealized
approach applied to the launching of galactic winds by supernovae with
the goal of self-consistently determining how the wind velocity and
mass-loading scale with host galaxy properties. |
Oct. 5 |
Yan-Fei Jiang |
Understanding AGN Accretion Disks based on 3D Global Radiation MHD Simulations with Realistic Opacity
Although AGN unification model is very successful to explain many observational properties of AGN, little progress has
been made to understand the physical properties of the inner accretion disks, where most of the photons are emitted.
The standard thin disk model, which has been widely used to model the accretion disks, causes a lot of puzzles for AGN disks
theoretically and cannot easily explain recent micro-lensing observations and timing analysis of quasars.
I will first point out that the iron opacity bump can significant change the structures and properties of AGN accretion disks
compared to case with dominated electron scattering opacity. Then I will show a series of global 3D radiation MHD simulations
for AGNs for a wide range of accretion rates. The iron opacity bump increases the disk thickness and drive strong outflow from the disk.
I will also discuss implications of these simulations for understanding AGNs and their interactions with the host galaxies. |
Oct. 12 |
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Oct. 19 |
Daniel Masters |
The redshift evolution of strong
emission line ratios reflects a link between N/O ratio and galaxy stellar mass
The offset of high redshift star-forming
galaxies in the classical [OIII]/H-β vs. [NII]/H-α BPT diagnostic
diagram in comparison with the local star-forming galaxy sequence is now
well established. The physical origin of the shift is the subject of some
debate, with potentially important implications for metallicity estimation
at all redshifts. I will present results from an investigation of the BPT
shift using a sample of ~100,000 star-forming galaxies from SDSS DR12.
This sample (which includes numerous high-redshift "analogs") lets us
determine how galaxy physical properties - in particular, star formation
rate density, ionization parameter, N/O ratio, and stellar mass - drive
position in key emission line diagnostic diagrams. I will present evidence
that a relation between the nitrogen-to-oxygen (N/O) ratio and galaxy
stellar mass underlies the observed BPT offset, and is more fundamental
than the well-studied relation between N/O and O/H. The relation between
N/O ratio and stellar mass induces a mass-dependence in the BPT diagram,
such that the BPT shift observed in high redshift galaxies reflects the
evolution of the mass-metallicity (MZ) relation. I will discuss implications
of this result for metallicity measurements based on strong lines at high
redshift, as well as for the proposed fundamental metallicity relation (FMR)
between metallicity, star-formation rate, and stellar mass. |
Oct. 26 |
Greg Salvesen |
Rethinking Black Hole Accretion Disks
I am a new postdoc at UCSB and in this talk I will highlight some of
my previous work on accretion disks around black holes, which exhibit
some amazing phenomena. Black hole X-ray binaries showcase complicated
cycles of dramatic brightening and dimming accompanied by observable
changes in the accretion disk spectrum. This disk evolution is often
attributed to the migration of the inner disk edge, but can alternatively
be explained by changes to the disk atmosphere. Properly understanding
the observed disk spectrum also has important consequences for black hole
spin measurements. I'll also discuss results from zoomed-in (shearing box)
accretion disk simulations showing that the properties and behavior of
the disk become particularly interesting in the presence of a strong
magnetic field. |
Nov. 2 |
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Nov. 9 |
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Nov. 16 |
Joseph Burchett |
Large-scale environment and the CGM: the hidden variables of
galaxy transformation?
While the environments in which galaxies live have long been
known to correlate with their star formation activity and morphology,
the mechanisms inducing these effects, particularly at low environmental
densities, are not well understood. I will present results leveraging
the HST/COS archive, SDSS, and my own observational campaign showing
that properties of the circumgalactic medium (CGM) strongly correlate
with galaxy environment across a wide range of densities, from voids to
clusters. Because these effects are evident on scales of even moderately
populated groups, the implications are quite profound: Environmental
processes are first detectable in the galaxies' halo gas, well before
effects arise in their stellar or neutral gas components. In turn, UV
absorption line spectroscopy provides detailed thermal, chemical, and
kinematic information about this intervening medium and offers key
insight to the previously 'hidden variables' driving such phenomena as
quenching and galactic conformity.
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Nov. 23 |
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Nov. 30 |
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Dec 7 |
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