241 research outputs found
The Effect of Mass Ratio on the Morphology and Time-scales of Disc Galaxy Mergers
The majority of galaxy mergers are expected to be minor mergers. The
observational signatures of minor mergers are not well understood, thus there
exist few constraints on the minor merger rate. This paper seeks to address
this gap in our understanding by determining if and when minor mergers exhibit
disturbed morphologies and how they differ from the morphology of major
mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy
mergers. With the resulting g-band images, we determine how the time-scale for
identifying galaxy mergers via projected separation and quantitative morphology
(the Gini coefficient G, asymmetry A, and the second-order moment of the
brightest 20% of the light M20) depends on the merger mass ratio, relative
orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1
baryonic mass ratio mergers as 1:1 mergers, with observability time-scales ~
0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios
between 4:1 and 1:1 (assuming local disc galaxy gas-fractions). Asymmetry
time-scales for moderate gas-fraction major disc mergers are ~ 0.2-0.4 Gyr, and
less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative
orientations and orbits have little effect on the time-scales for morphological
disturbances. Observational studies of close pairs often select major mergers
by choosing paired galaxies with similar luminosities and/or stellar masses.
Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs)
are sensitive to galaxy mergers of different mass ratios. By comparing the
frequency of mergers selected by different techniques, one may place empirical
constraints on the major and minor galaxy merger rates.Comment: 16 pages; resubmitted to MNRA
The effect of galaxy mass ratio on merger--driven starbursts
We employ numerical simulations of galaxy mergers to explore the effect of
galaxy mass ratio on merger--driven starbursts. Our numerical simulations
include radiative cooling of gas, star formation, and stellar feedback to
follow the interaction and merger of four disk galaxies. The galaxy models span
a factor of 23 in total mass and are designed to be representative of typical
galaxies in the local Universe. We find that the merger--driven star formation
is a strong function of merger mass ratio, with very little, if any, induced
star formation for large mass ratio mergers. We define a burst efficiency that
is useful to characterize the merger--driven star formation and test that it is
insensitive to uncertainties in the feedback parameterization. In accord with
previous work we find that the burst efficiency depends on the structure of the
primary galaxy. In particular, the presence of a massive stellar bulge
stabilizes the disk and suppresses merger--driven star formation for large mass
ratio mergers. Direct, co--planar merging orbits produce the largest tidal
disturbance and yield that most intense burst of star formation. Contrary to
naive expectations, a more compact distribution of gas or an increased gas
fraction both decrease the burst efficiency. Owing to the efficient feedback
model and the newer version of SPH employed here, the burst efficiencies of the
mergers presented here are smaller than in previous studies.Comment: 26 pages, 21 figures, submitted to MNRA
The Effect of Gas Fraction on the Morphology and Time-scales of Disc Galaxy Mergers
Gas-rich galaxy mergers are more easily identified by their disturbed
morphologies than mergers with less gas. Because the typical gas fraction of
galaxy mergers is expected to increase with redshift, the under-counting of low
gas-fraction mergers may bias morphological estimates of the evolution of
galaxy merger rate. To understand the magnitude of this bias, we explore the
effect of gas fraction on the morphologies of a series of simulated disc galaxy
mergers. With the resulting g-band images, we determine how the time-scale for
identifying major and minor galaxy mergers via close projected pairs and
quantitative morphology (the Gini coefficient G, the second-order moment of the
brightest 20% of the light M20, and asymmetry A) depends on baryonic gas
fraction f(gas). Strong asymmetries last significantly longer in high
gas-fraction mergers of all mass ratios, with time-scales ranging from >= 300
Myr for f(gas) ~ 20% to >= 1 Gyr for f(gas) ~ 50%. Therefore the strong
evolution with redshift observed in the fraction of asymmetric galaxies may
reflect evolution in the gas properties of galaxies rather than the global
galaxy merger rate. On the other hand, the time-scale for identifying a galaxy
merger via G-M20 is weakly dependent on gas-fraction (~ 200-400 Myr),
consistent with the weak evolution observed for G-M20 mergers.Comment: 15 pages; resubmitted to MNRA
Simulations of Dust in Interacting Galaxies I: Dust Attenuation
A new Monte-Carlo radiative-transfer code, Sunrise, is used in conjunction
with hydrodynamic simulations of major galaxy mergers to calculate the effects
of dust in such systems. The simulations are in good agreement with
observations of dust absorption in starburst galaxies, and the dust has a
profound effect on their appearance. The dust attenuation increases with
luminosity such that at peak luminosities ~90% of the bolometric luminosity is
absorbed by dust. In general, the detailed appearance of the merging event
depends on the stage of the merger and the geometry of the encounter. The
fraction of bolometric energy absorbed by the dust, however, is a robust
quantity that can be predicted from the intrinsic properties bolometric
luminosity, baryonic mass, star-formation rate, and metallicity of the system.
This paper presents fitting formulae, valid over a wide range of masses and
metallicities, from which the absorbed fraction of luminosity (and consequently
also the infrared dust luminosity) can be predicted. The attenuation of the
luminosity at specific wavelengths can also be predicted, albeit with a larger
scatter due to the variation with viewing angle. These formulae for dust
attenuation appear to be valid for both isolated and interacting galaxies, are
consistent with earlier studies, and would be suitable for inclusion in
theoretical models, e.g. semi-analytic models of galaxy formation.Comment: 12 pages, 10 figures, submitted to Ap
Evolution of the Stellar Mass Tully-Fisher Relation in Disk Galaxy Merger Simulations
There is a large observational scatter toward low velocities in the stellar
mass Tully-Fisher relation if disturbed and compact objects are included.
However, this scatter can be eliminated if one replaces rotation velocity with
, a quantity that includes a velocity dispersion term added in
quadrature with the rotation velocity. In this work we use a large suite of
hydrodynamic N-body galaxy merger simulations to explore a possible mechanism
for creating the observed relations. Using mock observations of the
simulations, we test for the presence of observational effects and explore the
relationship between and intrinsic properties of the
galaxies. We find that galaxy mergers can explain the scatter in the TF as well
as the tight -stellar mass relation. Furthermore, is correlated with the total central mass of a galaxy, including
contributions due to dark matter.Comment: ApJ accepte
Longitudinal Study of Recurrent Metastatic Melanoma Cell Lines Underscores the Individuality of Cancer Biology.
Recurrent metastatic melanoma provides a unique opportunity to analyze disease evolution in metastatic cancer. Here, we followed up eight patients with an unusually prolonged history of metastatic melanoma, who developed a total of 26 recurrences over several years. Cell lines derived from each metastasis were analyzed by comparative genomic hybridization and global transcript analysis. We observed that conserved, patient-specific characteristics remain stable in recurrent metastatic melanoma even after years and several recurrences. Differences among individual patients exceeded within-patient lesion variability, both at the DNA copy number (P<0.001) and RNA gene expression level (P<0.001). Conserved patient-specific traits included expression of several cancer/testis antigens and the c-kit proto-oncogene throughout multiple recurrences. Interestingly, subsequent recurrences of different patients did not display consistent or convergent changes toward a more aggressive disease phenotype. Finally, sequential recurrences of the same patient did not descend progressively from each other, as irreversible mutations such as homozygous deletions were frequently not inherited from previous metastases. This study suggests that the late evolution of metastatic melanoma, which markedly turns an indolent disease into a lethal phase, is prone to preserve case-specific traits over multiple recurrences and occurs through a series of random events that do not follow a consistent stepwise process.Journal of Investigative Dermatology advance online publication, 2 January 2014; doi:10.1038/jid.2013.495
Genome-wide association study identifies Sjögrenâs risk loci with functional implications in immune and glandular cells
Sjögrenâs disease is a complex autoimmune disease with twelve established susceptibility loci. This genome-wide association study (GWAS) identifies ten novel genome-wide significant (GWS) regions in Sjögrenâs cases of European ancestry: CD247, NAB1, PTTG1-MIR146A, PRDM1-ATG5, TNFAIP3, XKR6, MAPT-CRHR1, RPTOR-CHMP6-BAIAP6, TYK2, SYNGR1. Polygenic risk scores yield predictability (AUROCâ=â0.71) and relative risk of 12.08. Interrogation of bioinformatics databases refine the associations, define local regulatory networks of GWS SNPs from the 95% credible set, and expand the implicated gene list to >40. Many GWS SNPs are eQTLs for genes within topologically associated domains in immune cells and/or eQTLs in the main target tissue, salivary glands.Research reported in this publication was supported by the National Institutes of Health (NIH): R01AR073855 (C.J.L.), R01AR065953 (C.J.L.), R01AR074310 (A.D.F.), P50AR060804 (K.L.S.), R01AR050782 (K.L.S), R01DE018209 (K.L.S.), R33AR076803 (I.A.), R21AR079089 (I.A.); NIDCR Sjögrenâs Syndrome Clinic and Salivary Disorders Unit were supported by NIDCR Division of Intramural Research at the National Institutes of Health funds - Z01-DE000704 (B.W.); Birmingham NIHR Biomedical Research Centre (S.J.B.); Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germanyâs Excellence Strategy â EXC 2155 â Projektnummer 390874280 (T.W.); Research Council of Norway (Oslo, Norway) â Grant 240421 (TR.R.), 316120 (M.W-H.); Western Norway Regional Health Authority (Helse Vest) â 911807, 912043 (R.O.); Swedish Research Council for Medicine and Health (L.R., G.N., M.W-H.); Swedish Rheumatism Association (L.R., G.N., M.W-H.); King Gustav Vâs 80-year Foundation (G.N.); Swedish Society of Medicine (L.R., G.N., M.W-H.); Swedish Cancer Society (E.B.); Sjögrenâs Syndrome Foundation (K.L.S.); Phileona Foundation (K.L.S.). The Stockholm County Council (M.W-H.); The Swedish Twin Registry is managed through the Swedish Research Council - Grant 2017-000641. The French ASSESS (Atteinte SystĂ©mique et Evolution des patients atteints de Syndrome de Sjögren primitive) was sponsored by Assistance Publique-HĂŽpitaux de Paris (Ministry of Health, PHRC 2006 P060228) and the French society of Rheumatology (X.M.).publishedVersio
Variants at multiple loci implicated in both innate and adaptive immune responses are associated with Sjögrenâs syndrome
Sjögrenâs syndrome is a common autoimmune disease (~0.7% of European Americans) typically presenting as keratoconjunctivitis sicca and xerostomia. In addition to strong association within the HLA region at 6p21 (Pmeta=7.65Ă10â114), we establish associations with IRF5-TNPO3 (Pmeta=2.73Ă10â19), STAT4 (Pmeta=6.80Ă10â15), IL12A (Pmeta =1.17Ă10â10), FAM167A-BLK (Pmeta=4.97Ă10â10), DDX6-CXCR5 (Pmeta=1.10Ă10â8), and TNIP1 (Pmeta=3.30Ă10â8). Suggestive associations with Pmeta<5Ă10â5 were observed with 29 regions including TNFAIP3, PTTG1, PRDM1, DGKQ, FCGR2A, IRAK1BP1, ITSN2, and PHIP amongst others. These results highlight the importance of genes involved in both innate and adaptive immunity in Sjögrenâs syndrome
A Genome-Wide Association Study of Diabetic Kidney Disease in Subjects With Type 2 Diabetes
dentification of sequence variants robustly associated with predisposition to diabetic kidney disease (DKD) has the potential to provide insights into the pathophysiological mechanisms responsible. We conducted a genome-wide association study (GWAS) of DKD in type 2 diabetes (T2D) using eight complementary dichotomous and quantitative DKD phenotypes: the principal dichotomous analysis involved 5,717 T2D subjects, 3,345 with DKD. Promising association signals were evaluated in up to 26,827 subjects with T2D (12,710 with DKD). A combined T1D+T2D GWAS was performed using complementary data available for subjects with T1D, which, with replication samples, involved up to 40,340 subjects with diabetes (18,582 with DKD). Analysis of specific DKD phenotypes identified a novel signal near GABRR1 (rs9942471, P = 4.5 x 10(-8)) associated with microalbuminuria in European T2D case subjects. However, no replication of this signal was observed in Asian subjects with T2D or in the equivalent T1D analysis. There was only limited support, in this substantially enlarged analysis, for association at previously reported DKD signals, except for those at UMOD and PRKAG2, both associated with estimated glomerular filtration rate. We conclude that, despite challenges in addressing phenotypic heterogeneity, access to increased sample sizes will continue to provide more robust inference regarding risk variant discovery for DKD.Peer reviewe
Safety of procuring research tissue during a clinically indicated kidney biopsy from patients with lupus: data from the Accelerating Medicines Partnership RA/SLE Network
Objectives In lupus nephritis the pathological diagnosis from tissue retrieved during kidney biopsy drives treatment and management. Despite recent approval of new drugs, complete remission rates remain well under aspirational levels, necessitating identification of new therapeutic targets by greater dissection of the pathways to tissue inflammation and injury. This study assessed the safety of kidney biopsies in patients with SLE enrolled in the Accelerating Medicines Partnership, a consortium formed to molecularly deconstruct nephritis.Methods 475 patients with SLE across 15 clinical sites in the USA consented to obtain tissue for research purposes during a clinically indicated kidney biopsy. Adverse events (AEs) were documented for 30 days following the procedure and were determined to be related or unrelated by all site investigators. Serious AEs were defined according to the National Institutes of Health reporting guidelines.Results 34 patients (7.2%) experienced a procedure-related AE: 30 with haematoma, 2 with jets, 1 with pain and 1 with an arteriovenous fistula. Eighteen (3.8%) experienced a serious AE requiring hospitalisation; four patients (0.8%) required a blood transfusion related to the kidney biopsy. At one site where the number of cores retrieved during the biopsy was recorded, the mean was 3.4 for those who experienced a related AE (n=9) and 3.07 for those who did not experience any AE (n=140). All related AEs resolved.Conclusions Procurement of research tissue should be considered feasible, accompanied by a complication risk likely no greater than that incurred for standard clinical purposes. In the quest for targeted treatments personalised based on molecular findings, enhanced diagnostics beyond histology will likely be required
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