36 research outputs found
International support for the Arab uprisings: Understanding sympathetic collective action using theories of social dominance and social identity
Inspired by the popular Arab protests against oppressive regimes that began in 2010, people around the world protested in sympathy with the Arab peoples. The present research draws on two major theories of intergroup relations to develop an initial integrative model of sympathetic collective action. We incorporate social dominance theoryâs (SDT) concept of (rejectionist) legitimizing myths with the solidarity and emotional mediation concept of the social identity model of collective action (SIMCA) to understand motivations for sympathetic collective action among bystanders. Using data from 12 nations (N = 1,480), we tested three models: (a) SIMCA (i.e., solidarity, anger, and efficacy), (b) a social dominance theory model of collective action (i.e., social dominance orientation and ideologies concerning Arab competence), and (c) an integrated model of sympathetic collective action combining both theories. Results find the greatest support for an integrated model of collective action. Discussion focuses on theoretical pluralism and suggestions for future research
Hydrogen and Metal Line Absorption Around Low-Redshift Galaxies in Cosmological Hydrodynamic Simulations
We study the physical conditions of the circum-galactic medium (CGM) around
z=0.25 galaxies as traced by HI and metal line absorption, using cosmological
hydrodynamic simulations that include galactic outflows. Using lines of sight
targeted at impact parameters from 10 kpc to 1 Mpc around galaxies with halo
masses from 10^11-10^13 M_solar, we study the physical conditions and their
variation with impact parameter b and line-of-sight velocity delta v in the CGM
as traced by HI, MgII, SiIV, CIV, OVI, and NeVIII absorbers. All ions show a
strong excess of absorption near galaxies compared to random lines of sight.
The excess continues beyond 1 Mpc, reflecting the correlation of metal
absorption with large-scale structure. Absorption is particularly enhanced
within about v<300 km/sec and roughly 300 kpc of galaxies (with distances
somewhat larger for the highest ion), approximately delineating the CGM; this
range contains the majority of global metal absorption. Low ions like MgII and
SiIV predominantly arise in denser gas closer to galaxies and drop more rapidly
with b, while high ions OVI and NeVIII trace more diffusely distributed gas
with a comparatively flat radial profile; CIV is intermediate. All ions
predominantly trace T~10^4-4.5 K photo-ionised gas at all b, but when hot CGM
gas is present (mostly in larger halos), we see strong collisionally-ionised
OVI and NeVIII at b <= 100 kpc. Larger halo masses generally produce more
absorption, though overall the trends are not as strong as that with impact
parameter. These findings arise using our favoured outflow scalings as expected
for momentum-driven winds; with no winds, the CGM gas remains mostly
unenriched, while our outflow model with a constant velocity and mass loading
factor produce hotter, more widely dispersed metals.Comment: 26 pages, 15 figures, published in MNRAS. Updates to citations from
previous versio
How to distinguish starbursts and quiescently star-forming galaxies: The `bimodal' submillimetre galaxy population as a case study
In recent work (arXiv:1101.0002) we have suggested that the high-redshift (z
~ 2-4) bright submillimetre galaxy (SMG) population is heterogeneous, with
major mergers contributing both at early stages, where quiescently star-forming
discs are blended into one submm source (`galaxy-pair SMGs'), and late stages,
where mutual tidal torques drive gas inflows and cause strong starbursts. Here
we combine hydrodynamic simulations of major mergers with 3-D dust radiative
transfer calculations to determine observational diagnostics that can
distinguish between quiescently star-forming SMGs and starburst SMGs via
integrated data alone. We fit the far-IR SEDs of the simulated galaxies with
the optically thin single-temperature modified blackbody, the full form of the
single-temperature modified blackbody, and a power-law temperature-distribution
model. The effective dust temperature, T_dust, and power-law index of the dust
emissivity in the far-IR, \beta, derived can significantly depend on the
fitting form used, and the intrinsic \beta\ of the dust is not recovered.
However, for all forms used here, there is a T_dust above which almost all
simulated galaxies are starbursts, so a T_dust cut is very effective at
selecting starbursts. Simulated merger-induced starbursts also have higher
L_IR/M_gas and L_IR/L_FUV than quiescently star-forming galaxies and lie above
the star formation rate-stellar mass relation. These diagnostics can be used to
test our claim that the SMG population is heterogeneous and to observationally
determine what star formation mode dominates a given galaxy population. We
comment on applicability of these diagnostics to ULIRGs that would not be
selected as SMGs. These `hot-dust ULIRGs' are typically starburst galaxies
lower in mass than SMGs, but they can also simply be SMGs observed from a
different viewing angle.Comment: 21 pages, 11 figures. Accepted for publication in MNRAS. Minor
changes to text but otherwise identical to v
Demographics and Physical Properties of Gas Out/Inflows at 0.4 < z < 1.4
We present Keck/LRIS spectra of over 200 galaxies with well-determined
redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet,
low-ionization absorption lines with previously measured masses, luminosities,
colors, and star formation rates to describe the demographics and properties of
galactic flows. Among star-forming galaxies with blue colors, we find a net
blueshift of the FeII absorption greater than 200 km/s (100 km/s) towards 2.5%
(20%) of the galaxies. The fraction of blueshifted spectra does not vary
significantly with stellar mass, color, or luminosity but does decline at
specific star formation rates less than roughly 0.8 Gyr^{-1}. The insensitivity
of the blueshifted fraction to galaxy properties requires collimated outflows
at these redshifts, while the decline in outflow fraction with increasing
blueshift might reflect the angular dependence of the outflow velocity. The low
detection rate of infalling gas, 3 to 6% of the spectra, suggests an origin in
(enriched) streams favorably aligned with our sightline. We find 4 of these 9
infalling streams have projected velocities commensurate with the kinematics of
an extended disk or satellite galaxy. The strength of the MgII absorption
increases with stellar mass, B-band luminosity, and U-B color, trends arising
from a combination of more interstellar absorption at the systemic velocity and
less emission filling in more massive galaxies. Our results provides a new
quantitative understanding of gas flows between galaxies and the circumgalactic
medium over a critical period in galaxy evolution.Comment: Accepted version in 2-column format with embedded figure
Control of embryonic stem cells self-renewal and differentiation via coordinated splicing and translation of YY2
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Understanding the circumgalactic medium is critical for understanding galaxy evolution
Galaxies evolve under the influence of gas flows between their interstellar
medium and their surrounding gaseous halos known as the circumgalactic medium
(CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a
key role in the long cycles of accretion, feedback, and recycling of gas that
drive star formation. In order to fully understand the physical processes at
work within galaxies, it is therefore essential to have a firm understanding of
the composition, structure, kinematics, thermodynamics, and evolution of the
CGM. In this white paper we outline connections between the CGM and galactic
star formation histories, internal kinematics, chemical evolution, quenching,
satellite evolution, dark matter halo occupation, and the reionization of the
larger-scale intergalactic medium in light of the advances that will be made on
these topics in the 2020s. We argue that, in the next decade, fundamental
progress on all of these major issues depends critically on improved empirical
characterization and theoretical understanding of the CGM. In particular, we
discuss how future advances in spatially-resolved CGM observations at high
spectral resolution, broader characterization of the CGM across galaxy mass and
redshift, and expected breakthroughs in cosmological hydrodynamic simulations
will help resolve these major problems in galaxy evolution.Comment: Astro2020 Decadal Science White Pape
Galactic Supernova Remnant Candidates Discovered by THOR
There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of HII regions makes identifying such features challenging. SNRs can, however, be separated from HII regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with HII regions, we exclude radio continuum sources from the WISE Catalog of Galactic HII Regions, which contains all known and candidate H II regions in the Galaxy. We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4deg>l>17.5deg, |b|<1.25deg and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near l=30deg, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4'+/-4.7' versus 11.0'+/-7.8', and have lower integrated flux densities. If the 76 candidates are confirmed as true SNRs, for example using radio polarization measurements or by deriving radio spectral indices, this would more than double the number of known Galactic SNRs in the survey area. This large increase would still, however, leave a discrepancy between the known and expected SNR populations of about a factor of two