214 research outputs found
Estimating Black Hole Masses in Triaxial Galaxies
Most of the super massive black hole mass estimates based on stellar
kinematics use the assumption that galaxies are axisymmetric oblate spheroids
or spherical. Here we use fully general triaxial orbit-based models to explore
the effect of relaxing the axisymmetric assumption on the previously studied
galaxies M32 and NGC 3379. We find that M32 can only be modeled accurately
using an axisymmetric shape viewed nearly edge-on and our black hole mass
estimate is identical to previous studies. When the observed 5 degrees
kinematical twist is included in our model of NGC 3379, the best shape is
mildly triaxial and we find that our best-fitting black hole mass estimate
doubles with respect to the axisymmetric model. This particular black hole mass
estimate is still within the errors of that of the axisymmetric model and
consistent with the M-sigma relationship. However, this effect may have a
pronounced impact on black hole demography, since roughly a third of the most
massive galaxies are strongly triaxial.Comment: Accepted for publication in MNRAS. 11 pages, 9 figures. PDFlate
The shape of the dark matter halo in the early-type galaxy NGC 2974
We present HI observations of the elliptical galaxy NGC 2974, obtained with
the Very Large Array. These observations reveal that the previously detected HI
disc in this galaxy (Kim et al. 1988) is in fact a ring. By studying the
harmonic expansion of the velocity field along the ring, we constrain the
elongation of the halo and find that the underlying gravitational potential is
consistent with an axisymmetric shape.
We construct mass models of NGC 2974 by combining the HI rotation curve with
the central kinematics of the ionised gas, obtained with the integral-field
spectrograph SAURON. We introduce a new way of correcting the observed
velocities of the ionised gas for asymmetric drift, and hereby disentangle the
random motions of the gas caused by gravitational interaction from those caused
by turbulence. To reproduce the observed flat rotation curve of the HI gas, we
need to include a dark halo in our mass models. A pseudo-isothermal sphere
provides the best model to fit our data, but we also tested an NFW halo and
Modified Newtonian Dynamics (MOND), which fit the data marginally worse.
The mass-to-light ratio M/L_I increases in NGC 2974 from 4.3 (M/L_I)sun at
one effective radius to 8.5 (M/L_I)sun at 5 Re. This increase of M/L already
suggests the presence of dark matter: we find that within 5 Re at least 55 per
cent of the total mass is dark.Comment: 17 pages, 20 figures, accepted by MNRA
Testing Mass Determinations of Supermassive Black Holes via Stellar Kinematics
We investigate the accuracy of mass determinations M_BH of supermassive black
holes in galaxies using dynamical models of the stellar kinematics. We compare
10 of our M_BH measurements, using integral-field OASIS kinematics, to
published values. For a sample of 25 galaxies we confront our new M_BH derived
using two modeling methods on the same OASIS data.Comment: 4 pages, 4 figures, LaTeX. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista and C.C. Popescu, AIP Conf. Ser., in pres
Supermassive black holes from OASIS and SAURON integral-field kinematics
Supermassive black holes are a key element in our understanding of how
galaxies form. Most of the progress in this very active field of research is
based on just ~30 determinations of black hole mass, accumulated over the past
decade. We illustrate how integral-field spectroscopy, and in particular our
OASIS modeling effort, can help improve the current situation.Comment: 4 pages, 2 figures, LaTeX. To appear in the proceedings of IAU
Symposium 245 "Formation and Evolution of Galaxy Bulges", M. Bureau, E.
Athanassoula, and B. Barbuy, ed
Fast and Slow Rotators: The build-up of the Red Sequence
Using the unique dataset obtained within the course of the SAURON project, a
radically new view of the structure, dynamics and stellar populations of
early-type galaxies has emerged. We show that galaxies come in two broad
flavours (slow and fast rotators), depending on whether or not they exhibit
clear large-scale rotation, as indicated via a robust measure of the specific
angular momentum of baryons. This property is also linked with other physical
characteristics of early-type galaxies, such as: the presence of dynamically
decoupled cores, orbital structure and anisotropy, stellar populations and dark
matter content. I here report on the observed link between this baryonic
angular momentum and a mass sequence, and how this uniquely relates to the
building of the red sequence via dissipative/dissipationless mergers and
secular evolution.Comment: 4 pages, 1 figure. To appear in the Proceedings of IAU Symposium 245
"Formation and Evolution of Galaxy Bulges", Eds M. Bureau, E. Athanassoula,
and B. Barbu
RASSF1A and p16 promoter methylation and treatment response in chronic hepatitis C genotype 1b patients treated with pegylated interferon/ribavirin
Prevention of chronic hepatitis C (CHC) and its complications is based on antiviral therapy and early detection of reliable molecular markers in persons under risk. We investigated whether the methylation status of RASSF1A and p16 genes, alone or in combination with host and viral factors, affects the response to therapy with pegylated interferon/ribavirin (PEG-IFN/RBV). Methylation-specific polymerase chain reaction (MSP) was used to determine the methylation status of the target promoter sequences of RASSF1A and p16 in circulating-free DNA from the peripheral blood of 49 patients with CHC genotype 1b. The methylation status of the examined genes did not affect the response to therapy. However, the simultaneous presence of either RASSF1A or p16 methylation and the CC genotype of IL28B was significantly related to a sustained virologic response (P=0.009 and P=0.032, respectively). After Bonferroni correction, only the result concerning the RASSF1A gene remained significant (P<0.0125). Methylation of RASSF1A was associated with the CC genotype of the IL28B gene (P=0.024) and a higher viral load (≥400 000 IU/mL, P=0.009). Our results suggest that combined analysis of RASSF1A gene methylation and IL28B rs12979860 polymorphism could potentially help in the prediction of therapy response in CHC genotype 1b patients
The MUSE-Wide Survey: Survey Description and First Data Release
We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the
CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth
of 1 hour and hence targets more extreme and more luminous objects over 10
times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of
MUSE-Wide lies in providing "spectroscopy of everything" without photometric
pre-selection. We describe the data reduction, post-processing and PSF
characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released
with this publication. Using a 3D matched filtering approach we detected 1,602
emission line sources, including 479 Lyman- (Lya) emitting galaxies
with redshifts . We cross-match the emission line
sources to existing photometric catalogs, finding almost complete agreement in
redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high
redshift, we only find ~55% matches to photometric catalogs. We encounter a
higher outlier rate and a systematic offset of z0.2 when
comparing our MUSE redshifts with photometric redshifts. Cross-matching the
emission line sources with X-ray catalogs from the Chandra Deep Field South, we
find 127 matches, including 10 objects with no prior spectroscopic
identification. Stacking X-ray images centered on our Lya emitters yielded no
signal; the Lya population is not dominated by even low luminosity AGN. A total
of 9,205 photometrically selected objects from the CANDELS survey lie in the
MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are
able to determine the spectroscopic redshift of 98% of 772 photometrically
selected galaxies brighter than 24th F775W magnitude. All the data in the first
data release - datacubes, catalogs, extracted spectra, maps - are available on
the website https://musewide.aip.de. [abridged]Comment: 25 pages 15+1 figures. Accepted, A&A. Comments welcom
Extracting science from surveys of our Galaxy
Our knowledge of the Galaxy is being revolutionised by a series of
photometric, spectroscopic and astrometric surveys. Already an enormous body of
data is available from completed surveys, and data of ever increasing quality
and richness will accrue at least until the end of this decade. To extract
science from these surveys we need a class of models that can give probability
density functions in the space of the observables of a survey -- we should not
attempt to "invert" the data from the space of observables into the physical
space of the Galaxy. Currently just one class of model has the required
capability, so-called "torus models". A pilot application of torus models to
understanding the structure of the Galaxy's thin and thick discs has already
produced two significant results: a major revision of our best estimate of the
Sun's velocity with respect to the Local Standard of Rest, and a successful
prediction of the way in which the vertical velocity dispersion in the disc
varies with distance from the Galactic plane.Comment: 13 pages. Invited review to appear in Pramana - journal of physics
(Indian Academy of Sciences
The MUSE-Faint survey. V. Constraining Scalar Field Dark Matter with Antlia B
Aims. We use stellar line-of-sight velocities of Antlia B, a faint dwarf
galaxy in the NGC 3109 association, to derive constraints on the fundamental
properties of scalar field dark matter originally proposed to solve the
small-scale problems faced by cold dark matter models. Methods. We use the
first spectroscopic observations of Antlia B, a distant (d 1.35 Mpc)
faint dwarf (, MM), from
MUSE-Faint - a survey of ultra-faint dwarfs with the Multi Unit Spectroscopic
Explorer. Through measurement of line-of-sight velocities for stars in the
field-of-view, we identify 127 stars as members of Antlia B,
allowing us to model its dark matter density profile with the Jeans modelling
code GravSphere. We implement a model for scalar field dark matter into
GravSphere and use this to place constraints on the self-coupling strength of
this model. Results. We find a virial mass of M and a concentration parameter of
for Antlia B. These results are
consistent with the mass-concentration relations in the literature. We
constrain the characteristic length scale of the repulsive self-interaction
of the scalar field dark matter model to pc (68% confidence level), which translates to a self-coupling
strength of eVcm. The
constraint on the characteristic length scale of the repulsive self-interaction
is inconsistent with the value required to match the observations of cores of
dwarf galaxies in the Local Group, suggesting that the cored density profiles
of those galaxies are not caused by scalar field dark matter.Comment: Accepted for publication in A&A on 21-07-2023. 17 pages, 22 figures,
4 table
The ATLAS3D project - XXVII : Cold gas and the colours and ages of early-type galaxies
Date of Acceptance: 16/12/2013We present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 M⊙, derived from dynamical models) are found to have H I masses up to M(H I)/M* ∼ 0.06 and H2 masses up to M(H2)/M* ∼ 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 M⊙, where such signatures are found in ∼50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour–magnitude diagramsPeer reviewedFinal Accepted Versio
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