134 research outputs found
Simulations of momentum feedback by black hole winds
The observed super-massive black hole (SMBH) mass -- galaxy velocity
dispersion () correlation may be established when
winds/outflows from the SMBH drive gas out of the potential wells of classical
bulges. Here we present numerical simulations of this process in a static
isothermal potential. Simple spherically symmetric models of SMBH feedback at
the Eddington luminosity can successfully explain the and
nuclear cluster mass correlations, as well as why larger
bulges host SMBHs while smaller ones host nuclear star clusters. However these
models do not specify how SMBHs feed on infalling gas whilst simultaneously
producing feedback that drives gas out of the galaxy.
More complex models with rotation and/or anisotropic feedback allow SMBHs to
feed via a disc or regions not exposed to SMBH winds, but in these more
realistic cases it is not clear why a robust relation
should be established. In fact, some of the model predictions contradict
observations. For example, an isotropic SMBH wind impacting on a disc (rather
than a shell) of aspect ratio requires the SMBH mass to be larger
by a factor , which is opposite to what is observed. We conclude that
understanding how a SMBH feeds is as important a piece of the puzzle as
understanding how its feedback affects its host galaxy.
Finally, we note that in aspherical cases the SMBH outflows induce
differential motions in the bulge. This may pump turbulence that is known to
hinder star formation in star forming regions. SMBH feedback thus may not only
drive gas out of the bulge but also reduce the fraction of gas turned into
stars.Comment: 17 pages, to appear in MNRA
Forming supermassive black holes by accreting dark and baryon matter
Given a large-scale mixture of self-interacting dark matter (SIDM) particles
and baryon matter distributed in the early Universe, we advance here a
two-phase accretion scenario for forming supermassive black holes (SMBHs) with
masses around at high redshifts z (\gsim 6). The first
phase is conceived to involve a rapid quasi-spherical and quasi-steady Bondi
accretion of mainly SIDM particles embedded with baryon matter onto seed black
holes (BHs) created at redshifts z\lsim 30 by the first generation of massive
Population III stars; this earlier phase rapidly gives birth to significantly
enlarged seed BH masses of $M_{\hbox{\tiny BH},t_1}\backsimeq 1.4\times 10^6\
M_\odot \sigma_0/(1\hbox{cm}^2\hbox{g}^{-1})(C_s/30\hbox{km s}^{-1})^4z\sim 20-15\sigma_0C_sM_{\hbox{\tiny BH}}\sim 10^9 M_\odotz\sim 6z$ for
sub-Eddington mean accretion rates. We intend to account for the reported
detections of a few SMBHs at early epochs, e.g., SDSS 1148+5251 and so forth,
without necessarily resorting to either super-Eddington baryon accretion or
very frequent BH merging processes. Only extremely massive dark SIDM halos
associated with rare peaks of density fluctuations in the early Universe may
harbour such early SMBHs or quasars. Observational consequences are discussed.Comment: 7 pages, 2 figures. accepted by MNRA
The correlation of black hole mass with metallicity index of host spheroid
We investigate the correlation between the mass of the supermassive black
holes (SMBHs) and metal abundance, using existing data sets. The SMBH mass
is well correlated with integrated stellar feature of Mgb. For 28
galaxies, the best-fit -Mgb relation has a small scatter, which is an
equivalent level with other well-known relation, such as a correlation between
the stellar velocity dispersion and the mass. An averaged iron index
also positively correlates with $M_{bh}$, but the best-fit $M_{bh}$-
relation has a larger scatter. The difference comes from the synthesis and
evolution mechanisms, and may be important for the SMBH and star formation
history in the host spheroid.Comment: 6 pages, 4 figures, 1 table
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Impact of the Adipokine Adiponectin and the Hepatokine Fetuin-A on the Development of Type 2 Diabetes: Prospective Cohort- and Cross-Sectional Phenotyping Studies
Background: Among adipokines and hepatokines, adiponectin and fetuin-A were consistently found to predict the incidence of type 2 diabetes, both by regulating insulin sensitivity. Objective: To determine to what extent circulating adiponectin and fetuin-A are independently associated with incident type 2 diabetes in humans, and the major mechanisms involved. Methods: Relationships with incident diabetes were tested in two cohort studies: within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study (628 cases) and the Nurses' Health Study (NHS; 470 cases). Relationships with body fat compartments, insulin sensitivity and insulin secretion were studied in the Tübingen Lifestyle Intervention Program (TULIP; N = 358). Results: Circulating adiponectin and fetuin-A, independently of several confounders and of each other, associated with risk of diabetes in EPIC-Potsdam (RR for 1 SD: adiponectin: 0.45 [95% CI 0.37–0.54], fetuin-A: 1.18 [1.05–1.32]) and the NHS (0.51 [0.42–0.62], 1.35 [1.16–1.58]). Obesity measures considerably attenuated the association of adiponectin, but not of fetuin-A. Subjects with low adiponectin and concomitantly high fetuin-A had the highest risk. Whereas both proteins were independently (both p<1.8×10−7) associated with insulin sensitivity, circulating fetuin-A (r = −0.37, p = 0.0004), but not adiponectin, associated with insulin secretion in subjects with impaired glucose tolerance. Conclusions: We provide novel information that adiponectin and fetuin-A independently of each other associate with the diabetes risk. Furthermore, we suggest that they are involved in the development of type 2 diabetes via different mechanisms, possibly by mediating effects of their source tissues, expanded adipose tissue and nonalcoholic fatty liver
The Growth of Massive Black Holes in Galaxy Merger Simulations with Feedback by Radiation Pressure
We study the growth of massive black holes (BH) in galaxies using smoothed
particle hydrodynamic simulations of major galaxy mergers with new
implementations of BH accretion and feedback. The effect of BH accretion on gas
in its host galaxy is modeled by depositing momentum at a rate ~ tau L/c into
the ambient gas, where L is the luminosity produced by accretion onto the BH
and tau is the wavelength-averaged optical depth of the galactic nucleus to the
AGN's radiation (a free parameter of our model). The accretion rate onto the BH
is relatively independent of our subgrid accretion model and is instead
determined by the BH's dynamical impact on its host galaxy: BH accretion is
thus self-regulated rather than `supply limited.' We show that the final BH
mass and total stellar mass formed during a merger are more robust predictions
of the simulations than the time dependence of the star formation rate or BH
accretion rate. In particular, the latter depend on the assumed interstellar
medium physics, which determines when and where the gas fragments to form star
clusters; this in turn affects the fuel available for further star formation
and BH growth. Simulations over a factor of ~ 30 in galaxy mass are consistent
with the observed M_BH-sigma relation for a mean optical depth of tau ~ 25.
This requires that most BH growth occur when the galactic nucleus is optically
thick to far-infrared radiation, consistent with the hypothesized connection
between ultra-luminous infrared galaxies and quasars. We find tentative
evidence for a shallower M_BH-sigma relation in the lowest mass galaxies, sigma
< 100 km/s. Our results demonstrate that feedback-regulated BH growth and
consistency with the observed M_BH-sigma relation do not require that BH
feedback terminate star formation in massive galaxies or unbind large
quantities of cold gas.Comment: 21 pages, 17 figures, submitted MNRA
Serum Neurofilament Light Trajectories and Their Relation to Subclinical Radiological Disease Activity in Relapsing Multiple Sclerosis Patients in the APLIOS Trial
Introduction: Several studies have described prognostic value of serum neurofilament light chain (sNfL) at the group level in relapsing multiple sclerosis (RMS) patients. Here, we aimed to explore the temporal association between sNfL and development of subclinical disease activity as assessed by magnetic resonance imaging (MRI) at the group level and evaluate the potential of sNfL as a biomarker for capturing subclinical disease activity in individual RMS patients. Methods: In the 12-week APLIOS study, patients (N = 284) received subcutaneous ofatumumab 20 mg. Frequent sNfL sampling (14 time points over 12 weeks) and monthly MRI scans enabled key analyses including assessment of the group-level temporal relationship of sNfL levels with on-study subclinical development of gadolinium-enhancing (Gd +)T1 lesions. Prognostic value of baseline sNfL ("high" vs. "low") level for subsequent on-study clinical relapse or Gd + T1 activity was assessed. Individual patient-level development of on-study Gd + T1 lesions wascompared across three predictors: baseline Gd + T1 lesion number, baseline sNfL ("high" vs. "low"), and time-matched sNfL. Results: In patients developing Gd + T1 lesions at week 4 (absent at baseline), sNfL levels increased during the month preceding the week-4 MRI scan and then gradually decreased back to baseline. High versus low baseline sNfL conferred increased risk of subsequent on-study clinical relapse or Gd + T1 activity (HR, 2.81; p < 0.0001) in the overall population and, notably, also in the patients without baseline Gd + T1 lesions (HR, 2.48; p = 0.0213). Individual patient trajectories revealed a marked difference in Gd + T1 lesions between patients with the ten highest vs. lowest baseline sNfL levels (119 vs. 19 lesions). Prognostic value of baseline or time-matched sNfL for on-study Gd + T1 lesions was comparable to that of the number of baseline MRI Gd + T1 lesions. Conclusions: sNfL measurement may have utility in capturing and monitoring subclinical disease activity in RMS patients. sNfL assessments could complement regular MRI scans and may provide an alternative when MRI assessment is not feasible. ClinicalTrials.gov: NCT03560739. Classification of Evidence: This study provides class I evidence that serum neurofilament light may be used as a biomarker for monitoring subclinical disease activity in relapsing multiple sclerosis patients, as shown by its elevation in the weeks preceding the development of new gadolinium-enhancing T1 lesion activity
Episodic activities of supermassive black holes at redshift : driven by mergers?
It has been suggested for quite a long time that galaxy mergers trigger
activities of supermassive black holes (SMBHs) on the grounds of imaging
observations of individual galaxies. To quantitatively examine this hypothesis,
we calculate quasar luminosity functions (LFs) by manipulating the observed
galaxy LFs () and theoretical merger rates from semi-analytical
formulations. We find that the model reproduces the observed quasar LFs
provided that the mass ratio () of the secondary galaxy to the newly formed
one changes with cosmic time. The results show that the fraction of major
mergers decreases from at to
at . As a consequence, the newly formed SMBHs from major mergers at
may acquire a maximal spin due to the orbital angular momentum of the
merging holes. Subsequently, random accretion led by minor mergers rapidly
drives the SMBHs to spin down. Such an evolutionary trend of the SMBH spins is
consistent with that radiative efficiency of accreting SMBHs strongly declines
with cosmic time, reported by Wang et al. (2009). This suggests that minor
mergers are important in triggering activities of SMBHs at low redshift while
major mergers may dominate at high redshift.Comment: 8 pages, 3 figures, 3 table
Black Hole Mass and Bulge Luminosity for Low-mass Black Holes
We study the scaling between bulge magnitude and central black hole (BH) mass
in galaxies with virial BH masses < 10^6 solar mass. Based on careful image
decomposition of a snapshot Hubble Space Telescope I-band survey, we found that
these BHs are found predominantly in galaxies with pseudobulges. Here we show
that the \mbulge\ relation for the pseudobulges at low mass is significantly
different from classical bulges with BH masses >10^7 solar mass. Specfically,
bulges span a much wider range of bulge luminosity, and on average the
luminosity is larger, at fixed black hole mass. The trend holds both for the
active galaxies from Bentz et al. and the inactive sample of Gultekin et al.
and cannot be explained by differences in stellar populations, as it persists
when we use dynamical bulge masses. Put another way, the ratio between bulge
and BH mass is much larger than for our sample. This is consistent
with recent suggestions that black hole mass does not scale with the
pseudobulge luminosity. The low-mass scaling relations appear to flatten,
consistent with predictions from Volonteri & Natarajan for massive seed BHs.Comment: 5 pages, 1 figure, accepted by ApJ
Supermassive Black Holes in Galactic Bulges
Growing evidence indicate supermassive black holes (SMBHs) in a mass range of
lurking in central stellar bulges of
galaxies.Extensive observations reveal fairly tight power laws of
versus the mean stellar velocity dispersion of the host stellar
bulge.Together with evidence for correlations between and other
properties of host bulges, the dynamic evolution of a bulge and the formation
of a central SMBH should be linked. In this Letter, we reproduce the empirical
power laws based on our recent theoretical analyses (Lou &
Wang; Wang & Lou; Lou, Jiang & Jin) for a self-similar general polytropic
quasi-static dynamic evolution of bulges with self-gravity and spherical
symmetry and present a sensible criterion of forming a central SMBH. The key
result is where and
is a proportional coefficient characteristic of different classes of host
bulges. By fitting and comparing several empirical power
laws, we conclude that SMBHs and galactic bulges grow and evolve in a coeval
manner and most likely there exist several classes of galactic bulge systems in
quasi-static self-similar evolution and that to mix them together can lead to
an unrealistic fitting. Based on our bulge-SMBH model, we provide explanations
for intrinsic scatter in the relation and a unified scenario for the formation
and evolution of SMBHs in different classes of host bulges.Comment: 5 pages, 2 figures, accepted to be published on MNRAS Lette
Extending the M_(bh)-sigma diagram with dense nuclear star clusters
Abridged: Four new nuclear star cluster masses, M_nc, plus seven upper
limits, are provided for galaxies with previously determined black hole masses,
M_bh. Together with a sample of 64 galaxies with direct M_bh measurements, 13
of which additionally now have M_nc measurements rather than only upper limits,
plus an additional 29 dwarf galaxies with available M_nc measurements and
velocity dispersions sigma, an (M_bh + M_nc)-sigma diagram is constructed.
Given that major dry galaxy merger events preserve the M_bh/L ratio, and given
that L ~ sigma^5 for luminous galaxies, it is first noted that the observation
M_bh ~ sigma^5 is consistent with expectations. For the fainter elliptical
galaxies it is known that L ~ sigma^2, and assuming a constant M_nc/L ratio
(Ferrarese et al.), the expectation that M_nc ~ sigma^2 is in broad agreement
with our new observational result that M_nc ~ sigma^{1.57\pm0.24}. This
exponent is however in contrast to the value of ~4 which has been reported
previously and interpreted in terms of a regulating feedback mechanism from
stellar winds.Comment: 6 pages, 2 figures. Submitted 08/08/2011 to MNRAS, first referee
report received 19/01/2012, accepted 10/02/201
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