3,709 research outputs found
Observing the End of Cold Flow Accretion using Halo Absorption Systems
We use cosmological SPH simulations to study the cool, accreted gas in two
Milky Way-size galaxies through cosmic time to z=0. We find that gas from
mergers and cold flow accretion results in significant amounts of cool gas in
galaxy halos. This cool circum-galactic component drops precipitously once the
galaxies cross the critical mass to form stable shocks, Mvir = Msh ~ 10^12
Msun. Before reaching Msh, the galaxies experience cold mode accretion (T<10^5
K) and show moderately high covering fractions in accreted gas: f_c ~ 30-50%
for R10^16 cm^-2. These values are considerably
lower than observed covering fractions, suggesting that outflowing gas (not
included here) is important in simulating galaxies with realistic gaseous
halos. Within ~500 Myr of crossing the Msh threshold, each galaxy transitions
to hot mode gas accretion, and f_c drops to ~5%. The sharp transition in
covering fraction is primarily a function of halo mass, not redshift. This
signature should be detectable in absorption system studies that target
galaxies of varying host mass, and may provide a direct observational tracer of
the transition from cold flow accretion to hot mode accretion in galaxies.Comment: 6 pages, 2 figures. Minor changes to match published version (results
unchanged
Health utility reporting in Chronic Rhinosinusitis patients
Objectives: Direct comparison of different diseases allows clinicians and researchers to place the burden of symptoms and impact on quality of life of each condition in context. Generic health-related quality of life assessment tools allow such analysis, limited data is available for British patients with Chronic rhinosinusitis. Design: As part of a larger feasibility study, patients underwent baseline assessment using the SNOT-22, SF-12 and EQ-5D-5L tools. Data was analysed using Microsoft excel and algorithms available for the analysis of the later 2 tools. We plotted EQ-5D-5L VAS and utility scores and SF-12 MCS and PCS scores separately against SNOT-22 scores and quantified associations using bivariate ordinary least squares regression analysis. Setting: Patients were prospectively recruited from 6 UK outpatient clinics. Participants: Adult patients with chronic rhinosinusitis without nasal polyps (CRSsNPs). Main Outcome measures: Baseline SNOT-22, SF-12 and EQ-5D-5L scores. Results: Fifty-two adults were recruited with a mean age of 55 years, 51% were male. The mean SNOT-22 score was 43.82. Mental and physical component scores of the SF-12 were 46.53 and 46 respectively. Mean index score computed form the EQ-5D-5L was 0.75. Worse (higher) SNOT-22 scores were associated with lower EQ-5D-5L VAS and utility scores and SF-12 MCS and PCS scores. Conclusion: The EQ-5D-5L suggests that British CRSsNPs patients are negatively impacted with regards to quality of life. We found the SF-12 to be less sensitive and conclude that the EQ-5D-5L tool is a quick and accessible method for assessing QOL in order it can be compared with other disease states
Molecular Gas in Intermediate Redshift ULIRGs
We report on the results of observations in the CO(1-0) transition of a
complete sample of Southern, intermediate redshift (z = 0.2 - 0.5)
Ultra-Luminous Infra-Red Galaxies using the Mopra 22m telescope. The eleven
ULIRGs with L_FIR > 10^12.5 L_Sun south of Dec = -12 deg were observed with
integration times that varied between 5 and 24 hours. Four marginal detections
were obtained for individual targets in the sample. The "stacked" spectrum of
the entire sample yields a high significance, 10{\sigma} detection of the
CO(1-0) transition at an average redshift of z = 0.38. The tightest correlation
of L_FIR and L_CO for published low redshift ULIRG samples (z < 0.2) is
obtained after normalisation of both these measures to a fixed dust
temperature. With this normalisation the relationship is linear. The
distribution of dust-to-molecular hydrogen gas mass displays a systematic
increase in dust-to-gas mass with galaxy luminosity for low redshift samples
but this ratio declines dramatically for intermediate redshift ULIRGs down to
values comparable to that of the Small Magellanic Cloud. The upper envelope to
the distribution of ULIRG molecular mass as function of look-back time
demonstrates a dramatic rise by almost an order of magnitude from the current
epoch out to 5 Gyr. This increase in maximum ULIRG gas mass with look-back time
is even more rapid than that of the star formation rate density.Comment: 7 pages, 5 figures, accepted for publication by MNRA
Large scale outflows from z ~ 0.7 starburst galaxies identified via ultra-strong MgII quasar absorption lines
(Abridged) Star formation-driven outflows are a critical phenomenon in
theoretical treatments of galaxy evolution, despite the limited ability of
observations to trace them across cosmological timescales. If the strongest
MgII absorption-line systems detected in the spectra of background quasars
arise in such outflows, "ultra-strong" MgII (USMgII) absorbers would identify
significant numbers of galactic winds over a huge baseline in cosmic time, in a
manner independent of the luminous properties of the galaxy. To this end, we
present the first detailed imaging and spectroscopic study of the fields of two
USMgII absorber systems culled from a statistical absorber catalog, with the
goal of understanding the physical processes leading to the large velocity
spreads that define such systems. Each field contains two bright emission-line
galaxies at similar redshift (dv < 300 km/s) to that of the absorption.
Lower-limits on their instantaneous star formation rates (SFR) from the
observed OII and Hb line fluxes, and stellar masses from spectral template
fitting indicate specific SFRs among the highest for their masses at z~0.7.
Additionally, their 4000A break and Balmer absorption strengths imply they have
undergone recent (~0.01 - 1 Gyr) starbursts. The concomitant presence of two
rare phenomena - starbursts and USMgII absorbers - strongly implies a causal
connection. We consider these data and USMgII absorbers in general in the
context of various popular models, and conclude that galactic outflows are
generally necessary to account for the velocity extent of the absorption. We
favour starburst driven outflows over tidally-stripped gas from a major
interaction which triggered the starburst as the energy source for the majority
of systems. Finally, we discuss the implications of these results and speculate
on the overall contribution of such systems to the global SFR density at z~0.7.Comment: 15 pages, 6 figure, accepted for publication by MNRA
Black Hole growth and AGN obscuration by instability-driven inflows in high-redshift disk galaxies fed by cold streams
Disk galaxies at high redshift have been predicted to maintain high gas
surface densities due to continuous feeding by intense cold streams leading to
violent gravitational instability, transient features and giant clumps.
Gravitational torques between the perturbations drive angular momentum out and
mass in, and the inflow provides the energy for keeping strong turbulence. We
use analytic estimates of the inflow for a self-regulated unstable disk at a
Toomre stability parameter Q~1, and isolated galaxy simulations capable of
resolving the nuclear inflow down to the central parsec. We predict an average
inflow rate ~10 Msun/yr through the disk of a 10^11 Msun galaxy, with
conditions representative of z~2 stream-fed disks. The inflow rate scales with
disk mass and (1+z)^{3/2}. It includes clump migration and inflow of the
smoother component, valid even if clumps disrupt. This inflow grows the bulge,
while only a fraction ~ 10^-3 of it needs to accrete onto a central black hole
(BH), in order to obey the observed BH-bulge relation. A galaxy of 10^11 Msun
at z~2 is expected to host a BH of ~10^8 Msun, accreting on average with
moderate sub-Eddington luminosity L_X ~ 10^42-43 erg/s, accompanied by brighter
episodes when dense clumps coalesce. We note that in rare massive galaxies at
z~6, the same process may feed 10^9 Msun BH at the Eddington rate. High central
gas column densities can severely obscure AGN in high-redshift disks, possibly
hindering their detection in deep X-ray surveys.Comment: ApJL in pres
Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation
Simulations of the formation of late-type spiral galaxies in a cold dark
matter LCDM universe have traditionally failed to yield realistic candidates.
Here we report a new cosmological N-body/SPH simulation of extreme dynamic
range in which a close analog of a Milky Way disk galaxy arises naturally.
Termed Eris, the simulation follows the assembly of a galaxy halo of mass
Mvir=7.9x10^11 Msun with a total of N=18.6 million particles (gas + dark matter
+ stars) within the final virial radius, and a force resolution of 120 pc. It
includes radiative cooling, heating from a cosmic UV field and supernova
explosions, a star formation recipe based on a high gas density threshold
(nSF=5 atoms cm^-3 rather than the canonical nSF=0.1 atoms cm^-3), and neglects
AGN feedback. At the present epoch, the simulated galaxy has an extended
rotationally-supported disk with a radial scale length Rd=2.5 kpc, a gently
falling rotation curve with circular velocity at 2.2 disk scale lenghts of
V2.2=214 km/s, a bulge-to-disk ratio B/D=0.35, and a baryonic mass fraction
that is 30% below the cosmic value. The disk is thin, is forming stars in the
region of the Sigma_SFR - Sigma_HI plane occupied by spiral galaxies, and falls
on the photometric Tully-Fisher and the stellar mass-halo virial mass
relations. Hot (T>3x10^5 K), X-ray luminous halo gas makes only 26% of the
universal baryon fraction and follows a flattened density profile proportional
to r^-1.13 out to r=100 kpc. Eris appears then to be the first cosmological
hydrodynamic simulation in which the galaxy structural properties, the mass
budget in the various components, and the scaling relations between mass and
luminosity are all consistent with a host of observational constraints.
(Abridged)Comment: 12 pages, 7 figures, accepted for publication on the Astrophysical
Journa
Forming Early-Type Galaxies in LambdaCDM Simulations -I. Assembly histories
We present a sample of nine high resolution cosmological simulations in the
mass range of M_vir=7x10^11-4x10^12 M_sun starting from LambdaCDM initial
conditions. Our simulations include primordial radiative cooling,
photoionization, star formation, supernova II feedback, but exclude supernova
driven winds and AGN feedback. The simulated galaxies assemble in two phases,
with the initial growth dominated by compact (r<r_eff) in situ star formation
fueled by cold, low entropy gas streams resulting in a very similar mean
assembly redshift of z_{f,ins}~2.5 for the in situ stellar component in all
galaxies. The late growth is dominated by accretion of old stars formed in
subunits outside the main galaxy (r>r_eff) resulting in an assembly redshift of
z_{f,acc}~0.5-1.5 with much larger scatter. We find a positive correlation
between the fraction of accreted stars and the final mass of our galaxies. We
show that gravitational feedback strongly suppresses late star formation in
massive galaxies contributing to the observed galaxy color bimodality. The
accretion of stellar material is also responsible for the observed size growth
of early-type galaxies. In addition, we find that the dark matter fractions
within the stellar half-mass radii continuously increase towards lower redshift
from about f_DM~0.05 at z~3 to f_DM~0.1-0.3 at z=0. Furthermore, the
logarithmic slope of the total density profile is nearly isothermal at the
present-day (gamma'~1.9-2.2). Finally, the input of gravitational heating
lowers the central dark matter densities in the galaxies, with the effect being
smaller compared to simulations without supernova feedback.Comment: 23 pages, 16 figures, accepted for publication in Ap
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