Revealing the X-ray source in IRAS 13224-3809 through flux-dependent reverberation lags. (arXiv:1301.1924v1 [astro-ph.HE]):
IRAS 13224-3809 was observed in 2011 for 500 ks with the XMM-Newton
observatory. We detect highly significant X-ray lags between soft (0.3 - 1 keV)
and hard (1.2 - 5 keV) energies. The hard band lags the soft at low frequencies
(i.e. hard lag), while the opposite (i.e. soft lag) is observed at high
frequencies. In this paper, we study the lag during flaring and quiescent
periods. We find that the frequency and absolute amplitude of the soft lag is
different during high-flux and low-flux periods. During the low flux intervals,
the soft lag is detected at higher frequencies and with smaller amplitude.
Assuming that the soft lag is associated with the light travel time between
primary and reprocessed emission, this behaviour suggests that the X-ray source
is more compact during low-flux intervals, and irradiates smaller radii of the
accretion disc (likely because of light bending effects). We continue with an
investigation of the lag dependence on energy, and find that isolating the
low-flux periods reveals a strong lag signature at the Fe K line energy,
similar to results found using 1.3 Ms of data on another well known Narrow-Line
Seyfert I galaxy, 1H0707-495.
Monday, January 14, 2013
Bulk motion measurements in clusters of galaxies with ATHENA-like missions. (arXiv:1301.1852v1 [astro-ph.CO])
Bulk motion measurements in clusters of galaxies with ATHENA-like missions. (arXiv:1301.1852v1 [astro-ph.CO]):
The hierarchical formation of clusters of galaxies by accretion of material
releases gravitational energy which dissipates into the intracluster gas. The
process heats the material and generates gas turbulence and bulk motions and
thus kinetic pressure. Mapping the velocity fields of the moving subunits would
enable a new diagnostics tool for cluster formation studies and unbiased X-ray
mass estimates. The required spatially resolved high resolution spectroscopy is
not currently available. I demonstrate here the feasibility of detecting and
mapping the velocities of the bulk motions using the Doppler shift of the Fe
XXV K alpha line with the proposed ATHENA satellite.
The hierarchical formation of clusters of galaxies by accretion of material
releases gravitational energy which dissipates into the intracluster gas. The
process heats the material and generates gas turbulence and bulk motions and
thus kinetic pressure. Mapping the velocity fields of the moving subunits would
enable a new diagnostics tool for cluster formation studies and unbiased X-ray
mass estimates. The required spatially resolved high resolution spectroscopy is
not currently available. I demonstrate here the feasibility of detecting and
mapping the velocities of the bulk motions using the Doppler shift of the Fe
XXV K alpha line with the proposed ATHENA satellite.
The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra. (arXiv:1301.1847v1 [astro-ph.SR])
The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra. (arXiv:1301.1847v1 [astro-ph.SR]):
We analyze the high-resolution X-ray spectrum of the supergiant O-star delta
Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model,
and we examine its variability. The O-supergiant delta Ori was observed in the
wavelength range 5-175 Angstrom by the X-ray detector HRC-S in combination with
the grating LETG aboard Chandra. We studied the He-like ions in combination
with the UV-radiation field to determine local plasma temperatures and to
establish the distance of the X-ray emitting ions to the stellar surface. We
measured individual lines by means of Gaussian profiles, folded through the
response matrix, to obtain wavelengths, line fluxes, half widths at half
maximum (HWHM) and line shifts to characterize the plasma. We consider
multitemperature models in collisional ionization equilibrium (CIE) to
determine temperatures, emission measures, and abundances. Analysis of the
He-like triplets extended to N VI and C V implies ionization stratification
with the hottest plasma to be found within a few stellar radii 3R* (Mg XI) and
the coolest farther out, far beyond the acceleration zone, up to 49R* (N VI)
and 75R* (C V). The observed temperatures cover a range from about 0.1 to 0.7
keV, i.e., 1-8 MK. The X-ray luminosity L is about 1.5 x 10e+32 erg/s in the
range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km/s
have been determined.
We analyze the high-resolution X-ray spectrum of the supergiant O-star delta
Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model,
and we examine its variability. The O-supergiant delta Ori was observed in the
wavelength range 5-175 Angstrom by the X-ray detector HRC-S in combination with
the grating LETG aboard Chandra. We studied the He-like ions in combination
with the UV-radiation field to determine local plasma temperatures and to
establish the distance of the X-ray emitting ions to the stellar surface. We
measured individual lines by means of Gaussian profiles, folded through the
response matrix, to obtain wavelengths, line fluxes, half widths at half
maximum (HWHM) and line shifts to characterize the plasma. We consider
multitemperature models in collisional ionization equilibrium (CIE) to
determine temperatures, emission measures, and abundances. Analysis of the
He-like triplets extended to N VI and C V implies ionization stratification
with the hottest plasma to be found within a few stellar radii 3R* (Mg XI) and
the coolest farther out, far beyond the acceleration zone, up to 49R* (N VI)
and 75R* (C V). The observed temperatures cover a range from about 0.1 to 0.7
keV, i.e., 1-8 MK. The X-ray luminosity L is about 1.5 x 10e+32 erg/s in the
range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km/s
have been determined.
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin. (arXiv:1301.1800v1 [astro-ph.CO])
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin. (arXiv:1301.1800v1 [astro-ph.CO]):
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1. (arXiv:1301.1689v1 [astro-ph.CO])
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1. (arXiv:1301.1689v1 [astro-ph.CO]):
We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion rate
(the rate of supermassive black hole growth scaled relative to the host stellar
mass). Our model is based on measurements indicating that the specific
accretion rate distribution is a universal function across a wide range of host
stellar mass with slope gamma_1=0.65 and an overall normalization that evolves
strongly with redshift. We test several simple assumptions to extend this model
to high specific accretion rates (beyond the measurements) and compare the
predictions for the XLF with the observed data. We find good agreement with a
model that allows for a break in the specific accretion rate distribution at a
point corresponding to the Eddington limit, with a steep power-law tail to
super-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convert between
specific accretion rate and Eddington ratio by assuming a scaling between black
hole mass and host stellar mass with an intrinsic scatter of +/-0.38 dex. Our
results show that samples of low luminosity AGNs are dominated by moderately
massive galaxies (M* ~ 10^{10-11} M_sun) growing with a wide range of accretion
rates -- a consequence of the shape of the galaxy stellar mass function rather
than a preference for AGN activity at a particular stellar mass. The observed
population of the most luminous AGN may be severely skewed to the most extreme
sources with elevated black hole masses relative to their host galaxies and in
rare phases of very rapid accretion.
We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion rate
(the rate of supermassive black hole growth scaled relative to the host stellar
mass). Our model is based on measurements indicating that the specific
accretion rate distribution is a universal function across a wide range of host
stellar mass with slope gamma_1=0.65 and an overall normalization that evolves
strongly with redshift. We test several simple assumptions to extend this model
to high specific accretion rates (beyond the measurements) and compare the
predictions for the XLF with the observed data. We find good agreement with a
model that allows for a break in the specific accretion rate distribution at a
point corresponding to the Eddington limit, with a steep power-law tail to
super-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convert between
specific accretion rate and Eddington ratio by assuming a scaling between black
hole mass and host stellar mass with an intrinsic scatter of +/-0.38 dex. Our
results show that samples of low luminosity AGNs are dominated by moderately
massive galaxies (M* ~ 10^{10-11} M_sun) growing with a wide range of accretion
rates -- a consequence of the shape of the galaxy stellar mass function rather
than a preference for AGN activity at a particular stellar mass. The observed
population of the most luminous AGN may be severely skewed to the most extreme
sources with elevated black hole masses relative to their host galaxies and in
rare phases of very rapid accretion.
Observations of Feedback from Radio-Quiet Quasars: I. Extents and Morphologies of Ionized Gas Nebulae. (arXiv:1301.1677v1 [astro-ph.CO])
Observations of Feedback from Radio-Quiet Quasars: I. Extents and Morphologies of Ionized Gas Nebulae. (arXiv:1301.1677v1 [astro-ph.CO]):
Black hole feedback -- the strong interaction between the energy output of
supermassive black holes and their surrounding environments -- is routinely
invoked to explain the absence of overly luminous galaxies, the black hole vs.
bulge correlations and the similarity of black hole accretion and star
formation histories. Yet direct probes of this process in action are scarce and
limited to small samples of active nuclei. We present Gemini IFU observations
of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ)
quasars at z~0.5. We detect extended ionized gas nebulae via [O III]5007
emission in every case, with a mean diameter of 28 kpc. These nebulae are
nearly perfectly round. The regular morphologies of nebulae around RQ quasars
are in striking contrast with lumpy or elongated nebulae seen around radio
galaxies at low and high redshifts. We present the uniformly measured
size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and
type 2 quasars spanning 6 orders of magnitude in luminosity and confirm the
flat slope of the correlation (R ~ L^{0.25+/-0.02}). We find a universal
behavior of the [O III]/H-beta ratio in our entire RQ quasar sample: it
persists at a constant value (~10) in the central regions, until reaching a
"break" isophotal radius ranging from 4 to 11 kpc where it starts to decrease.
We propose a model of clumpy nebulae in which clouds that produce line emission
transition from being ionization-bounded at small distances from the quasar to
being matter-bounded in the outer parts of the nebula, which qualitatively
explains the observed line ratio and surface brightness profiles. It is
striking that we see such smooth and round large-scale gas nebulosities in this
sample, which are inconsistent with illuminated merger debris and which we
suggest may be the signature of accretion energy from the nucleus reaching gas
at large scales.
Black hole feedback -- the strong interaction between the energy output of
supermassive black holes and their surrounding environments -- is routinely
invoked to explain the absence of overly luminous galaxies, the black hole vs.
bulge correlations and the similarity of black hole accretion and star
formation histories. Yet direct probes of this process in action are scarce and
limited to small samples of active nuclei. We present Gemini IFU observations
of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ)
quasars at z~0.5. We detect extended ionized gas nebulae via [O III]5007
emission in every case, with a mean diameter of 28 kpc. These nebulae are
nearly perfectly round. The regular morphologies of nebulae around RQ quasars
are in striking contrast with lumpy or elongated nebulae seen around radio
galaxies at low and high redshifts. We present the uniformly measured
size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and
type 2 quasars spanning 6 orders of magnitude in luminosity and confirm the
flat slope of the correlation (R ~ L^{0.25+/-0.02}). We find a universal
behavior of the [O III]/H-beta ratio in our entire RQ quasar sample: it
persists at a constant value (~10) in the central regions, until reaching a
"break" isophotal radius ranging from 4 to 11 kpc where it starts to decrease.
We propose a model of clumpy nebulae in which clouds that produce line emission
transition from being ionization-bounded at small distances from the quasar to
being matter-bounded in the outer parts of the nebula, which qualitatively
explains the observed line ratio and surface brightness profiles. It is
striking that we see such smooth and round large-scale gas nebulosities in this
sample, which are inconsistent with illuminated merger debris and which we
suggest may be the signature of accretion energy from the nucleus reaching gas
at large scales.
The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA])
The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA]):
For early-type galaxies, the ability to sustain a corona of hot, X-ray
emitting gas could have played a key role in quenching their star-formation
history. Yet, it is still unclear what drives the precise amount of hot gas
around these galaxies. By combining photometric and spectroscopic measurements
for the early-type galaxies observed during the Atlas3D integral-field survey
with measurements of their X-ray luminosity based on X-ray data of both low and
high spatial resolution we conclude that the hot-gas content of early-type
galaxies can depend on their dynamical structure. Specifically, whereas slow
rotators generally have X-ray halos with luminosity L_X,gas and temperature T
values that are in line with what is expected if the hot-gas emission is
sustained by the thermalisaton of the kinetic energy carried by the
stellar-mass loss material, fast rotators tend to display L_X,gas values that
fall consistently below the prediction of this model, with similar T values
that do not scale with the stellar kinetic energy as observed in the case of
slow rotators. Considering that fast rotators are likely to be intrinsically
flatter than slow rotators, and that the few L_X,gas-deficient slow rotators
also happen to be relatively flat, the observed L_X,gas deficiency in these
objects would support the hypothesis whereby flatter galaxies have a harder
time in retaining their hot gas. We discuss the implications that a different
hot-gas content could have on the fate of both acquired and internally-produced
gaseous material, considering in particular how the L_X,gas deficiency of fast
rotators would make them more capable to recycle the stellar-mass loss material
into new stars than slow rotators. This is consistent with the finding that
molecular gas and young stars are detected only in fast rotators in the Atlas3D
sample, and that fast rotators tend to dustier than slow rotators. [Abridged]
For early-type galaxies, the ability to sustain a corona of hot, X-ray
emitting gas could have played a key role in quenching their star-formation
history. Yet, it is still unclear what drives the precise amount of hot gas
around these galaxies. By combining photometric and spectroscopic measurements
for the early-type galaxies observed during the Atlas3D integral-field survey
with measurements of their X-ray luminosity based on X-ray data of both low and
high spatial resolution we conclude that the hot-gas content of early-type
galaxies can depend on their dynamical structure. Specifically, whereas slow
rotators generally have X-ray halos with luminosity L_X,gas and temperature T
values that are in line with what is expected if the hot-gas emission is
sustained by the thermalisaton of the kinetic energy carried by the
stellar-mass loss material, fast rotators tend to display L_X,gas values that
fall consistently below the prediction of this model, with similar T values
that do not scale with the stellar kinetic energy as observed in the case of
slow rotators. Considering that fast rotators are likely to be intrinsically
flatter than slow rotators, and that the few L_X,gas-deficient slow rotators
also happen to be relatively flat, the observed L_X,gas deficiency in these
objects would support the hypothesis whereby flatter galaxies have a harder
time in retaining their hot gas. We discuss the implications that a different
hot-gas content could have on the fate of both acquired and internally-produced
gaseous material, considering in particular how the L_X,gas deficiency of fast
rotators would make them more capable to recycle the stellar-mass loss material
into new stars than slow rotators. This is consistent with the finding that
molecular gas and young stars are detected only in fast rotators in the Atlas3D
sample, and that fast rotators tend to dustier than slow rotators. [Abridged]
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