36 research outputs found
Smooth matter and source size in microlensing simulations of gravitationally lensed quasars
Several gravitationally lensed quasars are observed with anomalous
magnifications in pairs of images that straddle a critical curve. Simple
theoretical arguments suggest that the magnification of these images should be
approximately equivalent, whereas one image is observed to be significantly
demagnified. Microlensing provides a possible explanation for this discrepancy.
There are two key parameters when modelling this effect. The first, the
fraction of smooth matter in the lens at the image positions, has been explored
by Schechter and Wambsganss (2002). They have shown that the anomalous flux
ratio observed in the lensed quasar MG 0414+0534 is a priori a factor of 5 more
likely if the assumed smooth matter content in the lens model is increased from
0% to 93%. The second parameter, the size of the emission region, is explored
in this paper, and shown to be more significant. We find that the broadening of
the magnification probability distributions due to smooth matter content is
washed out for source sizes that are predicted by standard models for quasars.
We apply our model to the anomalous lensed quasar MG 0414+0534, and find a 95%
upper limit of 2.62 x 10^(16) h^(-1/2) (M/Msun)^(1/2) cm on the radius of the
I-band emission region. The smooth matter percentage in the lens is
unconstrained.Comment: 6 pages, 6 figures. To be published in MNRA
Microlensing Constraints on Broad Absorption and Emission Line Flows in the Quasar H1413+117
We present new integral field spectroscopy of the gravitationally lensed
broad absorption line (BAL) quasar H1413+117, covering the ultraviolet to
visible rest-frame spectral range. We observe strong microlensing signatures in
lensed image D, and we use this microlensing to simultaneously constrain both
the broad emission and broad absorption line gas. By modeling the lens system
over the range of probable lensing galaxy redshifts and using on a new argument
based on the wavelength-independence of the broad line lensing magnifications,
we determine that there is no significant broad line emission from smaller than
~20 light days. We also perform spectral decomposition to derive the intrinsic
broad emission line (BEL) and continuum spectrum, subject to BAL absorption. We
also reconstruct the intrinsic BAL absorption profile, whose features allow us
to constrain outflow kinematics in the context of a disk-wind model. We find a
very sharp, blueshifted onset of absorption of 1,500 km/s in both C IV and N V
that may correspond to an inner edge of a disk-wind's radial outflow. The lower
ionization Si IV and Al III have higher-velocity absorption onsets, consistent
with a decreasing ionization parameter with radius in an accelerating outflow.
There is evidence of strong absorption in the BEL component which indicates a
high covering factor for absorption over two orders of magnitude in outflow
radius.Comment: 29 pages, 8 figure
The masses of Local Group dwarf spheroidal galaxies: The death of the universal mass profile
We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside
within halos that share a common, universal mass profile as has been derived
for dSphs of the Galaxy. By folding in kinematic information for 25 Andromeda
dSphs, more than doubling the previous sample size, we find that a singular
mass profile can not be found to fit all the observations well. Further, the
best-fit dark matter density profile measured for solely the Milky Way dSphs is
marginally discrepant (at just beyond the 1 sigma level) with that of the
Andromeda dSphs, where a profile with lower maximum circular velocity, and
hence mass, is preferred. The agreement is significantly better when three
extreme Andromeda outliers, And XIX, XXI and XXV, all of which have large
half-light radii (>600pc) and low velocity dispersions (sigma_v < 5km/s) are
omitted from the sample. We argue that the unusual properties of these outliers
are likely caused by tidal interactions with the host galaxy.Comment: ApJ in press, 16 pages, 7 figures. Updated to address referee
comment
A kinematic study of the Andromeda dwarf spheroidal system
We present a homogeneous kinematic analysis of red giant branch stars within
18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the
Keck I LRIS and Keck II DEIMOS spectrographs. Based on their g-i colors (taken
with the CFHT MegaCam imager), physical positions on the sky, and radial
velocities, we assign probabilities of dSph membership to each observed star.
Using this information, the velocity dispersions, central masses and central
densities of the dark matter halos are calculated for these objects, and
compared with the properties of the Milky Way dSph population. We also measure
the average metallicity ([Fe/H]) from the co-added spectra of member stars for
each M31 dSph and find that they are consistent with the trend of decreasing
[Fe/H] with luminosity observed in the Milky Way population. We find that three
of our studied M31 dSphs appear as significant outliers in terms of their
central velocity dispersion, And XIX, XXI and XXV, all of which have large
half-light radii (>700 pc) and low velocity dispersions (sigma_v<5 km/s). In
addition, And XXV has a mass-to-light ratio within its half-light radius of
just [M/L]_{half}=10.3^{+7.0}_{-6.7}, making it consistent with a simple
stellar system with no appreciable dark matter component within its 1 sigma
uncertainties. We suggest that the structure of the dark matter halos of these
outliers have been significantly altered by tides.Comment: 41 pages, 23 figures. Accepted for publication in Ap
The PAndAS Field of Streams: stellar structures in the Milky Way halo toward Andromeda and Triangulum
We reveal the highly structured nature of the Milky Way stellar halo within
the footprint of the PAndAS photometric survey from blue main sequence and main
sequence turn-off stars. We map no fewer than five stellar structures within a
heliocentric range of ~5 to 30 kpc. Some of these are known (the Monoceros
Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three
well-defined stellar structures that could be, at least partly, responsible for
the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In
particular, we trace a new faint stellar stream located at a heliocentric
distance of ~17 kpc. With a surface brightness of \Sigma_V ~ 32-32.5
mag/arcsec^2, it follows an orbit that is almost parallel to the Galactic plane
north of M31 and has so far eluded surveys of the Milky Way halo as these tend
to steer away from regions dominated by the Galactic disk. Investigating our
follow-up spectroscopic observations of PAndAS, we serendipitously uncover a
radial velocity signature from stars that have colors and magnitudes compatible
with the stream. From the velocity of eight likely member stars, we show that
this stellar structure is dynamically cold, with an unresolved velocity
dispersion that is lower than 7.1 km/s at the 90-percent confidence level.
Along with the width of the stream (300-650 pc), its dynamics points to a
dwarf-galaxy-accretion origin. The numerous stellar structures we can map in
the Milky Way stellar halo between 5 and 30 kpc and their varying morphology is
a testament to the complex nature of the stellar halo at these intermediate
distances.Comment: 11 pages, 8 figures, accepted for publication in the ApJ, Figure 3 is
the money plo
The PAndAS field of streams: Stellar structures in the milky way halo toward andromeda and triangulum
We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of 5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of 17 kpc. With a surface brightness of Σ V 32-32.5 mag arcsec-2, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s-1 at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances
Major substructure in the M31 outer halo: the South-West Cloud
We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo ofM31. The South-West Cloud lies at a projected distance of ̃100 kpc from the centre of M31 and extends for at least ̃
The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies
We present a comprehensive analysis of the structural properties and
luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint
of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies
represent the large majority of Andromeda's known satellite dwarf galaxies and
cover a wide range in luminosity ( or ) and surface brightness ( mag/arcsec). We confirm
most previous measurements, but find And XIX to be significantly larger than
before ( pc, ) and cannot
derive parameters for And XXVII as it is likely not a bound stellar system. We
also significantly revise downward the luminosities of And~XV and And~XVI,
which are now or . Finally, we provide the
first detailed analysis of Cas II/And XXX, a fairly faint system
() of typical size ( pc), located in
close proximity to the two bright elliptical dwarf galaxies NGC 147 & 185.
Combined with the set of homogeneous distances published in an earlier
contribution, our analysis dutifully tracks all relevant sources of uncertainty
in the determination of the properties of the dwarf galaxies from the PAndAS
photometric catalogue. We further publish the posterior probability
distribution functions of all the parameters we fit for in the form of MCMC
chains available online; these inputs should be used in any analysis that aims
to remain truthful to the data and properly account for covariance between
parameters.Comment: 30 pages, 39 figures. Accepted for publication in Ap
NGC 147, NGC 185 and CassII: a genetic approach to orbital properties, star formation and tidal debris
NGC147, NGC185 and CassiopeiaII (CassII) have similar positions in the sky,
distances and measured line of sight velocities. This proximity in phase space
suggests that these three satellites of M31 form a subgroup within the Local
Group. Nevertheless, the differences in their star formation history and
interstellar medium, and the recent discovery of a stellar stream in NGC~147,
combined with the lack of tidal features in the other two satellites, are all
indications of complex and diverse interactions between M31 and these three
satellites. We use a genetic algorithm to explore the different orbits that
these satellites can have and select six sets of orbits that could best explain
the observational features of the NGC147, NGC185 and CassII satellites. The
parameters of these orbits are then used as a starting point for N-body
simulations. We present models for which NGC147, NGC185 and CassII are a bound
group for a total time of at least one Gyr but still undergo different
interactions with M31 and as a result NGC147 has a clear stellar stream whereas
the other two satellites have no significant tidal features. This result shows
that it is possible to find solutions that reproduce the contrasting properties
of the satellites and for which NGC147-NGC185-CassII have been gravitationally
bound.Comment: Accepted for publication on MNRAS. 12 pages, 9 figure