220 research outputs found
Gamma-ray burst contributions to constraining the evolution of dark energy
We explore the gamma-ray bursts' (GRBs') contributions in constraining the
dark energy equation of state (EOS) at high () and at middle
redshifts () and estimate how many GRBs are needed to get
substantial constraints at high redshifts. We estimate the constraints with
mock GRBs and mock type Ia supernovae (SNe Ia) for comparisons. When
constraining the dark energy EOS in a certain redshift range, we allow the dark
energy EOS parameter to vary only in that redshift bin and fix EOS parameters
elsewhere to -1. We find that it is difficult to constrain the dark energy EOS
beyond the redshifts of SNe Ia with GRBs unless some new luminosity relations
for GRBs with smaller scatters are discovered. However, at middle redshifts,
GRBs have comparable contributions with SNe Ia in constraining the dark energy
EOS.Comment: 3 pages, 5 figures. Published in Astronomy and Astrophysics.
Corrected referenc
HI study of the warped spiral galaxy NGC5055: a disk/dark matter halo offset?
We present a study of the HI distribution and dynamics of the nearby spiral
galaxy NGC5055 based on observations with the Westerbork Synthesis Radio
Telescope. The gaseous disk of NGC5055 extends out to about 40 kpc, equal to
3.5 R_25, and shows a pronounced warp that starts at the end of the bright
optical disk (R_25= 11.6 kpc). This very extended warp has large-scale
symmetry, which along with the rotation period of its outer parts (~1.5 Gyr at
40 kpc), suggests a long-lived phenomenon. The rotation curve rises steeply in
the central parts up to the maximum velocity (v_max ~ 206 km/s). Beyond the
bright stellar disk (R_25), it shows a decline of about 25 km/s and then
remains flat out to the last measured point. The standard analysis with
luminous and dark matter components shows the dynamical importance of the disk.
The best fit to the rotation curve is obtained with a ``maximum disk''. Less
satisfactory fits with lighter disks help to set a firm lower limit of 1.4 to
the mass-to-light ratio in F band of the disk. Such a ``minimum disk''
contributes about 60% of the observed maximum rotational velocity. NGC5055
shows remarkable overall regularity and symmetry. A mild lopsidedness is
noticeable, however, both in the distribution and kinematics of the gas. The
tilted ring analysis of the velocity field led us to adopt different values for
the kinematical centre and for the systemic velocity for the inner and the
outer parts of the system. This has produced a remarkable result: the
kinematical and geometrical asymmetries disappear, both at the same time. These
results point at two different dynamical regimes: an inner region dominated by
the stellar disk and an outer one, dominated by a dark matter halo offset with
respect to the disk.Comment: Accepted for publication in A&A. Minor correction
Accurate Determination of the Mass Distribution in Spiral Galaxies: II. Testing the Shape of Dark Halos
New high resolution CFHT Fabry-Perot data, combined with published VLA 21 cm
observations are used to determine the mass distribution of NGC 3109 and IC
2574. The multi-wavelength rotation curves allow to test with confidence
different dark halo functional forms from the pseudo-isothermal sphere to some
popular halo distributions motivated by N-body simulations. It appears that
density distribution with an inner logarithmic slope <= -1 are very hard to
reconcile with rotation curves of late type spirals. Modified Newtonian
Dynamics (MOND) is also considered as a potential solution to missing mass and
tested the same way. The new higher resolution data show that MOND can
reproduce in details the rotation curve of IC 2574 but confirm its difficulty
to fit the kinematics of NGC 3109.Comment: 28 pages, accepted by AJ. New HI profile increases the compatibility
of NGC 3109 rotation curve with MON
A High-Resolution Study of the HI Content of Local Group Dwarf Irregular Galaxy WLM
Dwarf irregular galaxies are unique laboratories for studying the interaction
between stars and the interstellar medium in low mass environments. We present
the highest spatial resolution observations to date of the neutral hydrogen
content of the Local Group dwarf irregular galaxy WLM. We find that WLM's
neutral hydrogen distribution is typical for a galaxy of its type and size and
derive an HI mass of 6.3e7 Msun for WLM. In addition, we derive an HI extent
for WLM of 30 arcmin, which is much less than the 45 arcmin extent found by
Huchtmeier, Seiradakis, and Materne (1981). We show that the broken ring of
high column density neutral hydrogen surrounding the center of WLM is likely
the result of star formation propagating out from the center of the galaxy. The
young stars and Ha emission in this galaxy are mostly correlated with the high
column density neutral hydrogen. The gap in the central ring is the result of
star formation in that region using up, blowing out, or ionizing all of the
neutral hydrogen. Like many late-type galaxies, WLM's velocity field is
asymmetric with the approaching (northern) side appearing to be warped and a
steeper velocity gradient for the approaching side than for the receding side
in the inner region of the galaxy. We derive a dynamical mass for WLM of 2.16e9
Msun.Comment: 38 pages, 15 figures, 5 tables, accepted by AJ, high resolution
version at http://www.astro.wisc.edu/~kepley/kepley_wlm.p
Dual targeting of ptp1b and aldose reductase with marine drug phosphoeleganin: A promising strategy for treatment of type 2 diabetes
An in-depth study on the inhibitory mechanism on protein tyrosine phosphatase 1B (PTP1B) and aldose reductase (AR) enzymes, including analysis of the insulin signalling pathway, of phosphoeleganin, a marine-derived phosphorylated polyketide, was achieved. Phosphoeleganin was demonstrated to inhibit both enzymes, acting respectively as a pure non-competitive inhibitor of PTP1B and a mixed-type inhibitor of AR. In addition, in silico docking analyses to evaluate the interaction mode of phosphoeleganin with both enzymes were performed. Interestingly, this study showed that phosphoeleganin is the first example of a dual inhibitor polyketide extracted from a marine invertebrate, and it could be used as a versatile scaffold structure for the synthesis of new designed multiple ligands
Star--forming galaxies at intermediate redshifts: morphology, ages and sizes
We present the analysis of the deepest near-UV image obtained with HST using
the WFPC2(F300W) as part of the parallel observations of the Ultra Deep Field
campaign. The U-band 10sigma limiting magnitude measured over 0.2 arcsec square
is m(AB)=27.5 which is 0.5 magnitudes deeper than that in the HDF-North. We
matched the U-band catalog with those in the ACS images taken during the GOODS
observations of the CDF-South and obtained photometric-z for 306 matched
objects. We find that the UV-selected galaxies span all the major morphological
types at 0.2<z_phot<1.2. However, disks are more common at lower redshifts,
0.2<z_phot<0.8. Higher-z objects (0.7<z_phot<1.2) are on average bluer than
lower-z and have spectral type typical of starbursts. Their morphologies are
compact, peculiar or low surface brightness galaxies. The average half-light
radius (rest-frame 1200--1800 A) of the UV-selected galaxies at 0.66<z_
phot<1.5 is 0.26 +- 0.01 arcsec (2.07 +- 0.08 kpc). The UV-selected galaxies
are on average fainter (M_B=-18.43+-0.13) than Lyman Break Galaxies
(M_B=-23+-1). Our sample includes early-type galaxies that are presumably
massive and forming stars only in their cores, as well as starburst-type
systems that are more similar to the LBGs, although much less luminous. This
implies that even the starbursts in our sample are either much less massive
than LBGs or are forming stars at a much lower rate or both. The low surface
brightness galaxies have no overlap with the LBGs and form an interesting new
class of their own.Comment: 22 pages, 15 figures. Astronomical Journal Accepte
Extra-planar gas in the spiral galaxy NGC 4559
We present 21-cm line observations of the spiral galaxy NGC 4559, made with
the Westerbork Synthesis Radio Telescope. We have used them to study the HI
distribution and kinematics, the relative amount and distribution of luminous
and dark matter in this galaxy and, in particular, the presence of extra-planar
gas. Our data do reveal the presence of such a component, in the form of a
thick disk, with a mass of 5.9 x 10^8 Mo (one tenth of the total HI mass) and a
mean rotation velocity 25-50 km/s lower than that of the thin disk. The
extra-planar gas may be the result of galactic fountains but accretion from the
IGM cannot be ruled out. With this study we confirm that lagging, thick HI
layers are likely to be common in spiral galaxies.Comment: 17 pages, 10 figures. Accepted for publication in A&
HST Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution
The optical expansion parallax of NGC 6543 has been detected and measured
using two epochs of HST images separated by a time baseline of only three
years. We have utilized three separate methods of deriving the angular
expansion of bright fiducials, the results of which are in excellent agreement.
We combine our angular expansion estimates with spectroscopically obtained
expansion velocities to derive a distance to NGC 6543 of 1001269 pc. The
deduced kinematic age of the inner bright core of the nebula is 1039259
years; however, the kinematic age of the polar caps that surround the core is
larger - perhaps the result of deceleration or earlier mass ejection. The
morphology and expansion patterns of NGC 6543 provide insight into a complex
history of axisymmetric, interacting stellar mass ejections.Comment: Accepted for publication in AJ. 18 pages. 6 figure
Properties of Dark Matter Haloes
An overview is presented of the main properties of dark matter haloes, as we
know them from observations, essentially from rotation curves around spiral and
dwarf galaxies. Detailed rotation curves are now known for more than a thousand
galaxies, revealing that they are not so flat in the outer parts, but rising
for late-types, and falling for early-types. A well established result now is
that most bright galaxies are not dominated by dark matter inside their optical
disks. Only for dwarfs and LSB (Low Surface Brightness galaxies) dark matter
plays a dominant role in the visible regions. The 3D-shape of haloes are
investigated through several methods, that will be discussed: polar rings,
flaring of HI planes, X-ray isophotes.
It is not yet possible with rotation curves to know how far haloes extend,
but tentatives have been made. It will be shown that the dark matter appears to
be coupled to the gas in spirals and dwarfs, suggesting that dark baryons could
play the major role in rotation curves. Theories proposing to replace the
non-baryonic dark matter by a different dynamical or gravity law, such as MOND,
have to take into account the dark baryons, especially since their spatial
distribution is likely to be quite different from the visible matter.Comment: 20 pages, 8 figures, submitted to NewA Reviews, review given at MOND
workshop, Paris, October 200
Does the Milky Way have a Maximal Disk?
The Milky Way is often considered to be the best example of a spiral for
which the dark matter not only dominates the outer kinematics, but also plays a
major dynamical role in the inner galaxy: the Galactic disk is therefore said
to be ``sub-maximal.'' This conclusion is important to the understanding of the
evolution of galaxies and the viability of particular dark matter models. The
Galactic evidence rests on a number of structural and kinematic measurements,
many of which have recently been revised. The new constraints indicate not only
that the Galaxy is a more typical member of its class (Sb-Sc spirals) than
previously thought, but also require a re-examination of the question of
whether or not the Milky Way disk is maximal. By applying to the Milky Way the
same definition of ``maximal disk'' that is applied to external galaxies, it is
shown that the new observational constraints are consistent with a Galactic
maximal disk of reasonable . In particular, the local disk column can be
substantially less than the oft-quoted required \Sigma_{\odot} \approx 100
\msolar pc^{-2} - as low as 40 \msolar pc^{-2} in the extreme case - and
still be maximal, in the sense that the dark halo provides negligible rotation
support in the inner Galaxy. This result has possible implications for any
conclusion that rests on assumptions about the potentials of the Galactic disk
or dark halo, and in particular for the interpretation of microlensing results
along both LMC and bulge lines of sight.Comment: Accepted for publication in The Astrophysical Journal. 23
Latex-generated pages, one (new) table, three figures (two new). A few
additions to the bibliography, an expanded discussion, and slight
quantitative changes, none of which affect the conclusion
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