Star-planet interactions and selection effects from planet detection methods. (arXiv:1303.0307v1 [astro-ph.SR]):
Planets may have effects on their host stars by tidal or magnetic
interaction. Such star-planet interactions are thought to enhance the activity
level of the host star. However, stellar activity also affects the sensitivity
of planet detection methods. Samples of planet-hosting stars which are
investigated for such star-planet interactions are therefore subject to strong
selection effects which need to be taken into account.
RKS Note: Discusses X-ray implications
Showing posts with label HasRKSNote. Show all posts
Showing posts with label HasRKSNote. Show all posts
Sunday, March 10, 2013
Sunday, February 17, 2013
X-ray C-M relation: theory and observation. (arXiv:1301.7476v1 [astro-ph.CO])
X-ray C-M relation: theory and observation. (arXiv:1301.7476v1 [astro-ph.CO]):
[Abridged] Since fifteen years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
this relation has been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
By analyzing a total of 52 objects, simulated each time with different
physical recipes for the baryonic component, as well as 60 synthetic X-ray
images, we aim at determining if these discrepancies are real or artificial. In
particular, we investigate how the simulated concentration-mass relation
depends i) on the radial range used to derive the concentration, ii) on the
presence of baryons in the simulations, and on the prescription used to
reproduce the gas. Finally, we evaluate iii) how the results differ when
adopting an X-ray approach for the analysis and iv) how the selection functions
based on X-ray luminosity, temperature, and SZ-signal can impact the results.
All effects studied go in the direction of explaining the discrepancy between
observations and simulations, but they contribute at different levels: while
the fitting radial range and the baryonic component play only a minor role, the
X-ray approach and selection function have profound repercussion on the
results.
RKS Note: Important paper comparing simulated clusters with observed ones, especially in regard to extracting cosmological parameters.
[Abridged] Since fifteen years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
this relation has been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
By analyzing a total of 52 objects, simulated each time with different
physical recipes for the baryonic component, as well as 60 synthetic X-ray
images, we aim at determining if these discrepancies are real or artificial. In
particular, we investigate how the simulated concentration-mass relation
depends i) on the radial range used to derive the concentration, ii) on the
presence of baryons in the simulations, and on the prescription used to
reproduce the gas. Finally, we evaluate iii) how the results differ when
adopting an X-ray approach for the analysis and iv) how the selection functions
based on X-ray luminosity, temperature, and SZ-signal can impact the results.
All effects studied go in the direction of explaining the discrepancy between
observations and simulations, but they contribute at different levels: while
the fitting radial range and the baryonic component play only a minor role, the
X-ray approach and selection function have profound repercussion on the
results.
RKS Note: Important paper comparing simulated clusters with observed ones, especially in regard to extracting cosmological parameters.
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO])
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO]):
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
Saturday, December 1, 2012
Identification of members in the central and outer regions of galaxy clusters. (arXiv:1211.3669v1 [astro-ph.CO])
Identification of members in the central and outer regions of galaxy clusters. (arXiv:1211.3669v1 [astro-ph.CO]):
The caustic technique measures the mass of galaxy clusters in both their
virial and infall regions and, as a byproduct, yields the list of cluster
galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h
extracted from a cosmological N-body simulation of a LambdaCDM universe to test
the ability of the caustic technique to identify the cluster galaxy members. We
identify the true three-dimensional members as the gravitationally bound
galaxies. The caustic technique uses the caustic location in the redshift
diagram to separate the cluster members from the interlopers. We apply the
technique to mock catalogues containing 1000 galaxies in the field of view of
12 Mpc/h on a side at the cluster location. On average, this sample size
roughly corresponds to 180 real galaxy members within 3r200, similar to recent
redshift surveys of cluster regions. The caustic technique yields a
completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within
3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to
fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of
the members of a galaxy cluster provides such large completeness and small
contamination at these large radii. The caustic technique assumes spherical
symmetry and the asphericity of the cluster is responsible for most of the
spread of the completeness and the contamination. By applying the technique to
an approximately spherical system obtained by stacking the individual clusters,
the spreads decrease by at least a factor of two. We finally estimate the
cluster mass within 3r200 after removing the interlopers: for individual
clusters, the mass estimated with the virial theorem is unbiased and within 30
per cent of the actual mass; this spread decreases to less than 10 per cent for
the spherically symmetric stacked cluster.
Note: Describes how well cluster masses can be derived from optical measurements, useful to know as a comparison to X-ray approaches
The caustic technique measures the mass of galaxy clusters in both their
virial and infall regions and, as a byproduct, yields the list of cluster
galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h
extracted from a cosmological N-body simulation of a LambdaCDM universe to test
the ability of the caustic technique to identify the cluster galaxy members. We
identify the true three-dimensional members as the gravitationally bound
galaxies. The caustic technique uses the caustic location in the redshift
diagram to separate the cluster members from the interlopers. We apply the
technique to mock catalogues containing 1000 galaxies in the field of view of
12 Mpc/h on a side at the cluster location. On average, this sample size
roughly corresponds to 180 real galaxy members within 3r200, similar to recent
redshift surveys of cluster regions. The caustic technique yields a
completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within
3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to
fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of
the members of a galaxy cluster provides such large completeness and small
contamination at these large radii. The caustic technique assumes spherical
symmetry and the asphericity of the cluster is responsible for most of the
spread of the completeness and the contamination. By applying the technique to
an approximately spherical system obtained by stacking the individual clusters,
the spreads decrease by at least a factor of two. We finally estimate the
cluster mass within 3r200 after removing the interlopers: for individual
clusters, the mass estimated with the virial theorem is unbiased and within 30
per cent of the actual mass; this spread decreases to less than 10 per cent for
the spherically symmetric stacked cluster.
Note: Describes how well cluster masses can be derived from optical measurements, useful to know as a comparison to X-ray approaches
A comparative study of statistical models for nuclear equation of state of stellar matter. (arXiv:1211.5990v1 [nucl-th])
A comparative study of statistical models for nuclear equation of state of stellar matter. (arXiv:1211.5990v1 [nucl-th]):
We compare three different statistical models for the equation of state (EOS)
of stellar matter at subnuclear densities and temperatures (0.5-10 MeV)
expected to occur during the collapse of massive stars and supernova
explosions. The models introduce the distributions of various nuclear species
in nuclear statistical equilibrium, but use somewhat different nuclear physics
inputs. It is demonstrated that the basic thermodynamical quantities of stellar
matter under these conditions are similar, except in the region of high
densities and low temperatures. We demonstrate that mass and isotopic
distributions have considerable differences related to the different
assumptions of the models on properties of nuclei at these stellar conditions.
Overall, the three models give similar trends, but the details reflect the
uncertainties related to the modelling of medium effects, such as the
temperature and density dependence of surface and bulk energies of heavy
nuclei, and the nuclear shell structure effects. In order to establish a
relationship between nuclear physics inputs for astrophysical calculations and
the experimental data obtained from intermediate-energy nuclear reactions, we
also discuss the similarities and differences of the conditions reached during
supernova explosions and heavy-ion collisions.
Note: One of the few EOS papers to consider what the impact of variable EOS would have on other areas of astrophysics, as opposed to pure nuclear physics issues.
We compare three different statistical models for the equation of state (EOS)
of stellar matter at subnuclear densities and temperatures (0.5-10 MeV)
expected to occur during the collapse of massive stars and supernova
explosions. The models introduce the distributions of various nuclear species
in nuclear statistical equilibrium, but use somewhat different nuclear physics
inputs. It is demonstrated that the basic thermodynamical quantities of stellar
matter under these conditions are similar, except in the region of high
densities and low temperatures. We demonstrate that mass and isotopic
distributions have considerable differences related to the different
assumptions of the models on properties of nuclei at these stellar conditions.
Overall, the three models give similar trends, but the details reflect the
uncertainties related to the modelling of medium effects, such as the
temperature and density dependence of surface and bulk energies of heavy
nuclei, and the nuclear shell structure effects. In order to establish a
relationship between nuclear physics inputs for astrophysical calculations and
the experimental data obtained from intermediate-energy nuclear reactions, we
also discuss the similarities and differences of the conditions reached during
supernova explosions and heavy-ion collisions.
Note: One of the few EOS papers to consider what the impact of variable EOS would have on other areas of astrophysics, as opposed to pure nuclear physics issues.
Feedback from High-Mass X-Ray Binaries on the High Redshift Intergalactic Medium : Model Spectra. (arXiv:1211.5854v1 [astro-ph.CO])
Feedback from High-Mass X-Ray Binaries on the High Redshift Intergalactic Medium : Model Spectra. (arXiv:1211.5854v1 [astro-ph.CO]):
Massive stars at redshifts z > 6 are predicted to have played a pivotal role
in cosmological reionization as luminous sources of ultra-violet (UV) photons.
However, the remnants of these massive stars could be equally important as
X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the
absorption cross section of neutral hydrogen decreases sharply with photon
energy (proportional to the inverse cube), X-rays can escape more freely than
UV photons from the star-forming regions in which they are produced, allowing
HMXBs to make a potentially significant contribution to the ionizing X-ray
background during reionization. In this paper, we explore the ionizing power of
HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar
population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB
Cygnus X-1 as our template, we propose a composite HMXB spectral energy
distribution consisting of black-body and power-law components, whose
contributions depend on the accretion state of the system. We determine the
time-dependent ionizing power of a combined population of UV-luminous stars and
X-ray luminous HMXBs, and deduce fitting formulae for the boost in the
population's ionizing power arising from HMXBs; these fits allow for simple
implementation of HMXB feedback in numerical simulations. Based on this
analysis, we estimate the contribution of high redshift HMXBs to the
present-day soft X-ray background, and we show that it is a factor of ~100-1000
smaller than the observed limit. Finally, we discuss the implications of our
results for the role of HMXBs in reionization and in high redshift galaxy
formation.
Note: An interesting concept to consider feedback from non-SMBHs
Massive stars at redshifts z > 6 are predicted to have played a pivotal role
in cosmological reionization as luminous sources of ultra-violet (UV) photons.
However, the remnants of these massive stars could be equally important as
X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the
absorption cross section of neutral hydrogen decreases sharply with photon
energy (proportional to the inverse cube), X-rays can escape more freely than
UV photons from the star-forming regions in which they are produced, allowing
HMXBs to make a potentially significant contribution to the ionizing X-ray
background during reionization. In this paper, we explore the ionizing power of
HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar
population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB
Cygnus X-1 as our template, we propose a composite HMXB spectral energy
distribution consisting of black-body and power-law components, whose
contributions depend on the accretion state of the system. We determine the
time-dependent ionizing power of a combined population of UV-luminous stars and
X-ray luminous HMXBs, and deduce fitting formulae for the boost in the
population's ionizing power arising from HMXBs; these fits allow for simple
implementation of HMXB feedback in numerical simulations. Based on this
analysis, we estimate the contribution of high redshift HMXBs to the
present-day soft X-ray background, and we show that it is a factor of ~100-1000
smaller than the observed limit. Finally, we discuss the implications of our
results for the role of HMXBs in reionization and in high redshift galaxy
formation.
Note: An interesting concept to consider feedback from non-SMBHs
Friday, October 5, 2012
A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc])
A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc]):
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.
Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.
Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.
Monday, September 10, 2012
The first massive black holes. (arXiv:1209.1195v1 [astro-ph.CO])
The first massive black holes. (arXiv:1209.1195v1 [astro-ph.CO]):
I briefly outline recent theoretical developments on the formation of the
first massive black holes (MBHs) that may grow into the population of MBHs
powering quasars and inhabiting galactic centers today. I also touch upon
possible observational tests that may give insights on what the properties of
the first MBHs were.
Note: Brief but clear exposition on the relevant issues.
I briefly outline recent theoretical developments on the formation of the
first massive black holes (MBHs) that may grow into the population of MBHs
powering quasars and inhabiting galactic centers today. I also touch upon
possible observational tests that may give insights on what the properties of
the first MBHs were.
Note: Brief but clear exposition on the relevant issues.
Sunday, August 12, 2012
Miscentring in Galaxy Clusters: Dark Matter to Brightest Cluster Galaxy Offsets in 10,000 SDSS Clusters. (arXiv:1208.1766v1 [astro-ph.CO])
Miscentring in Galaxy Clusters: Dark Matter to Brightest Cluster Galaxy Offsets in 10,000 SDSS Clusters. (arXiv:1208.1766v1 [astro-ph.CO]):
We characterise the typical offset between the Dark Matter (DM) projected
centre and the Brightest Cluster Galaxy (BCG) in 10,000 SDSS clusters. To place
constraints on the centre of DM, we use an automated strong-lensing analysis,
mass-modelling technique which is based on the well-tested assumption that
light traces mass. The cluster galaxies are modelled with a steep power-law,
and the DM component is obtained by smoothing the galaxy distribution fitting a
low-order 2D polynomial (via spline interpolation), while probing a whole range
of polynomial degrees and galaxy power laws. We find that the offsets between
the BCG and the peak of the smoothed light map representing the DM, \Delta, are
distributed equally around zero with no preferred direction, and are well
described by a log-normal distribution with <log_{10}(\Delta [h^{-1}
Mpc])>=-1.895^{+0.003}_{-0.004}, and \sigma=0.501\pm0.004 (95% confidence
levels), or <log_{10}(\Delta [\arcsec])>=0.564\pm0.005, and
\sigma=0.475\pm0.007. Some of the offsets originate in prior misidentifications
of the BCG or other bright cluster members by the cluster finding algorithm,
whose level we make an additional effort to assess, finding that ~10% of the
clusters in the probed catalogue are likely to be misidentified, contributing
to higher-end offsets in general agreement with previous studies. Our results
constitute the first statistically-significant high-resolution distributions of
DM-to-BCG offsets obtained in an observational analysis, and importantly show
that there exists such a typical non-zero offset in the probed catalogue. The
offsets show a weak positive correlation with redshift, so that higher
separations are generally found for higher-z clusters in agreement with the
hierarchical growth of structure, which in turn could help characterise the
merger, relaxation and evolution history of clusters, in future studies.
[ABRIDGED]
RKS Note: Could this be even better done with eROSITA data?
We characterise the typical offset between the Dark Matter (DM) projected
centre and the Brightest Cluster Galaxy (BCG) in 10,000 SDSS clusters. To place
constraints on the centre of DM, we use an automated strong-lensing analysis,
mass-modelling technique which is based on the well-tested assumption that
light traces mass. The cluster galaxies are modelled with a steep power-law,
and the DM component is obtained by smoothing the galaxy distribution fitting a
low-order 2D polynomial (via spline interpolation), while probing a whole range
of polynomial degrees and galaxy power laws. We find that the offsets between
the BCG and the peak of the smoothed light map representing the DM, \Delta, are
distributed equally around zero with no preferred direction, and are well
described by a log-normal distribution with <log_{10}(\Delta [h^{-1}
Mpc])>=-1.895^{+0.003}_{-0.004}, and \sigma=0.501\pm0.004 (95% confidence
levels), or <log_{10}(\Delta [\arcsec])>=0.564\pm0.005, and
\sigma=0.475\pm0.007. Some of the offsets originate in prior misidentifications
of the BCG or other bright cluster members by the cluster finding algorithm,
whose level we make an additional effort to assess, finding that ~10% of the
clusters in the probed catalogue are likely to be misidentified, contributing
to higher-end offsets in general agreement with previous studies. Our results
constitute the first statistically-significant high-resolution distributions of
DM-to-BCG offsets obtained in an observational analysis, and importantly show
that there exists such a typical non-zero offset in the probed catalogue. The
offsets show a weak positive correlation with redshift, so that higher
separations are generally found for higher-z clusters in agreement with the
hierarchical growth of structure, which in turn could help characterise the
merger, relaxation and evolution history of clusters, in future studies.
[ABRIDGED]
RKS Note: Could this be even better done with eROSITA data?
Sunday, July 29, 2012
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events. (arXiv:1207.6401v1 [astro-ph.CO])
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events. (arXiv:1207.6401v1 [astro-ph.CO]):
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of stellar tidal debris can become gravitationally bound to
the black hole and be subsequently accreted, leading to a bright
electromagnetic flare. In the Newtonian limit, this flare will have a light
curve that scales as t^-5/3 if the tidal debris has a flat distribution in
binding energy. We investigate the time dependence of the black-hole mass
accretion rate when tidal disruption occurs close enough the black hole that
relativistic effects are significant. We find that for orbits with pericenters
comparable to the radius of the marginally bound circular orbit, relativistic
effects can double the peak accretion rate and halve the time it takes to reach
this peak accretion rate. The accretion rate depends on both the magnitude of
the black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.
Note: LSST could detect multiple such events -- might provide limits, worth considering.
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of stellar tidal debris can become gravitationally bound to
the black hole and be subsequently accreted, leading to a bright
electromagnetic flare. In the Newtonian limit, this flare will have a light
curve that scales as t^-5/3 if the tidal debris has a flat distribution in
binding energy. We investigate the time dependence of the black-hole mass
accretion rate when tidal disruption occurs close enough the black hole that
relativistic effects are significant. We find that for orbits with pericenters
comparable to the radius of the marginally bound circular orbit, relativistic
effects can double the peak accretion rate and halve the time it takes to reach
this peak accretion rate. The accretion rate depends on both the magnitude of
the black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.
Note: LSST could detect multiple such events -- might provide limits, worth considering.
Thursday, July 26, 2012
An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO])
An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO]):
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......
RKS Note: Background AGN behind a Galaxy Cluster...
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......
RKS Note: Background AGN behind a Galaxy Cluster...
Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266. (arXiv:1207.5799v1 [astro-ph.CO])
Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266. (arXiv:1207.5799v1 [astro-ph.CO]):
We use the SAURON and GMOS integral field spectrographs to observe the active
galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is
relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN
feedback in action. We present maps of the kinematics and line strengths of the
ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and
report on the detection of Sodium D absorption. We use these tracers to explore
the structure of the source, derive the ionised and atomic gas kinematics and
investigate the gas excitation and physical conditions. NGC 1266 contains two
ionised gas components along most lines of sight, tracing the ongoing outflow
and a component closer to the galaxy systemic, the origin of which is unclear.
This gas appears to be disturbed by a nascent AGN jet. We confirm that the
outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic,
molecular and ionised gas and X-ray emitting plasma. The outflow has velocities
up to \pm900 km/s away from the systemic velocity, and is very likely to be
removing significant amounts of cold gas from the galaxy. The LINER-like
line-emission in NGC 1266 is extended, and likely arises from fast shocks
caused by the interaction of the radio jet with the ISM. These shocks have
velocities of up to 800 km/s, which match well with the observed velocity of
the outflow. Sodium D equivalent width profiles are used to set constraints on
the size and orientation of the outflow. The ionised gas morphology correlates
with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission,
supporting the suggestion that an AGN jet is providing the energy required to
drive the outflow.
RKS Note: Introduction has nice two-paragraph description of the feedback problem.
We use the SAURON and GMOS integral field spectrographs to observe the active
galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is
relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN
feedback in action. We present maps of the kinematics and line strengths of the
ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and
report on the detection of Sodium D absorption. We use these tracers to explore
the structure of the source, derive the ionised and atomic gas kinematics and
investigate the gas excitation and physical conditions. NGC 1266 contains two
ionised gas components along most lines of sight, tracing the ongoing outflow
and a component closer to the galaxy systemic, the origin of which is unclear.
This gas appears to be disturbed by a nascent AGN jet. We confirm that the
outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic,
molecular and ionised gas and X-ray emitting plasma. The outflow has velocities
up to \pm900 km/s away from the systemic velocity, and is very likely to be
removing significant amounts of cold gas from the galaxy. The LINER-like
line-emission in NGC 1266 is extended, and likely arises from fast shocks
caused by the interaction of the radio jet with the ISM. These shocks have
velocities of up to 800 km/s, which match well with the observed velocity of
the outflow. Sodium D equivalent width profiles are used to set constraints on
the size and orientation of the outflow. The ionised gas morphology correlates
with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission,
supporting the suggestion that an AGN jet is providing the energy required to
drive the outflow.
RKS Note: Introduction has nice two-paragraph description of the feedback problem.
Subscribe to:
Posts (Atom)