The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED):
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.
Showing posts with label Feedback. Show all posts
Showing posts with label Feedback. Show all posts
Sunday, March 10, 2013
HST/COS observations of a new population of associated QSO absorbers. (arXiv:1302.5510v1 [astro-ph.CO])
HST/COS observations of a new population of associated QSO absorbers. (arXiv:1302.5510v1 [astro-ph.CO]):
(Abridged) We present a sample of new population of associated absorbers,
detected through Ne VIII \lambda\lambda 770,780 absorption, in HST/COS spectra
of intermediate redshift (0.45 < z < 1.21) quasars (QSOs). Our sample comprised
of total 12 associated Ne VIII systems detected towards 8 lines of sight (none
of them are radio bright). The incidence rate of these absorbers is found to be
40%. Majority of the Ne VIII systems at small ejection velocities (v_ej) show
complete coverage of the background source, but systems with higher v_ej show
lower covering fractions (i.e. f_c < 0.8) and systematically higher values of
N(Ne VIII). We detect Mg X \lambda\lambda 609,624 absorption in 7 out of the 8
Ne VIII systems where the expected wavelength range is cover by our spectra and
is free of any strong blending. We report the detections of Na IX
\lambda\lambda 681,694 absorption, for the first time, in three highest
ejection velocity (e.g. v_ej > 7,000 km/s) systems in our sample. All these
systems show very high N(Ne VIII) (i.e. > 10^{15.6} cm^{-2}), high ionization
parameter (i.e. log U > 0.5), high metallicity (i.e. Z > Z_{\odot}), and
ionization potential dependent f_c values. The observed column density ratios
of different ions are reproduced by multiphase photoionization (PI) and/or
collisional ionization (CI) equilibrium models. While solar abundance ratios
are adequate in CIE, enhancement of Na relative to Mg is required in PI models
to explain our observations.
(Abridged) We present a sample of new population of associated absorbers,
detected through Ne VIII \lambda\lambda 770,780 absorption, in HST/COS spectra
of intermediate redshift (0.45 < z < 1.21) quasars (QSOs). Our sample comprised
of total 12 associated Ne VIII systems detected towards 8 lines of sight (none
of them are radio bright). The incidence rate of these absorbers is found to be
40%. Majority of the Ne VIII systems at small ejection velocities (v_ej) show
complete coverage of the background source, but systems with higher v_ej show
lower covering fractions (i.e. f_c < 0.8) and systematically higher values of
N(Ne VIII). We detect Mg X \lambda\lambda 609,624 absorption in 7 out of the 8
Ne VIII systems where the expected wavelength range is cover by our spectra and
is free of any strong blending. We report the detections of Na IX
\lambda\lambda 681,694 absorption, for the first time, in three highest
ejection velocity (e.g. v_ej > 7,000 km/s) systems in our sample. All these
systems show very high N(Ne VIII) (i.e. > 10^{15.6} cm^{-2}), high ionization
parameter (i.e. log U > 0.5), high metallicity (i.e. Z > Z_{\odot}), and
ionization potential dependent f_c values. The observed column density ratios
of different ions are reproduced by multiphase photoionization (PI) and/or
collisional ionization (CI) equilibrium models. While solar abundance ratios
are adequate in CIE, enhancement of Na relative to Mg is required in PI models
to explain our observations.
Saturday, March 9, 2013
Can AGN feedback-driven star formation explain the size evolution of massive galaxies?. (arXiv:1302.4998v1 [astro-ph.GA])
Can AGN feedback-driven star formation explain the size evolution of massive galaxies?. (arXiv:1302.4998v1 [astro-ph.GA]):
Observations indicate that massive galaxies at z~2 are more compact than
galaxies of comparable mass at z~0, with effective radii evolving by a factor
of ~3-5. This implies that galaxies grow significantly in size but relatively
little in mass over the past ~10 Gyr. Two main physical models have been
proposed in order to explain the observed evolution of massive galaxies:
"mergers" and "puffing-up" scenarios. Here we introduce another possibility,
and discuss the potential role of the central active galactic nucleus (AGN)
feedback on the evolution of its host galaxy. We consider triggering of star
formation, due to AGN feedback, with radiation pressure on dusty gas as the
driving feedback mechanism. In this picture, stars are formed in the
feedback-driven outflow at increasingly larger radii and build up the outer
regions of the host galaxy. The resulting increase in size and stellar mass can
be compared with the observed growth of massive galaxies. Star formation in the
host galaxy is likely obscured due to dust extinction and reddening. We suggest
a number of observational predictions of our model, and discuss possible
implications for AGN feedback-driven star formation.
Observations indicate that massive galaxies at z~2 are more compact than
galaxies of comparable mass at z~0, with effective radii evolving by a factor
of ~3-5. This implies that galaxies grow significantly in size but relatively
little in mass over the past ~10 Gyr. Two main physical models have been
proposed in order to explain the observed evolution of massive galaxies:
"mergers" and "puffing-up" scenarios. Here we introduce another possibility,
and discuss the potential role of the central active galactic nucleus (AGN)
feedback on the evolution of its host galaxy. We consider triggering of star
formation, due to AGN feedback, with radiation pressure on dusty gas as the
driving feedback mechanism. In this picture, stars are formed in the
feedback-driven outflow at increasingly larger radii and build up the outer
regions of the host galaxy. The resulting increase in size and stellar mass can
be compared with the observed growth of massive galaxies. Star formation in the
host galaxy is likely obscured due to dust extinction and reddening. We suggest
a number of observational predictions of our model, and discuss possible
implications for AGN feedback-driven star formation.
Monday, February 25, 2013
A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO])
A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO]):
Modelling AGN feedback in numerical simulations is both technically and
theoretically challenging, with numerous approaches having been published in
the literature. We present a study of five distinct approaches to modelling AGN
feedback within gravitohydrodynamic simulations of major mergers of Milky
Way-sized galaxies. To constrain differences to only be between AGN feedback
models, all simulations start from the same initial conditions and use the same
star formation algorithm. Most AGN feedback algorithms have five key aspects:
black hole accretion rate, energy feedback rate and method, particle accretion
algorithm, black hole advection algorithm, and black hole merger algorithm. All
models follow different accretion histories, with accretion rates that differ
by up to three orders of magnitude at any given time. We consider models with
either thermal or kinetic feedback, with the associated energy deposited
locally around the black hole. Each feedback algorithm modifies the gas
properties near the black hole to different extents. The particle accretion
algorithms usually (but not always) maintain good agreement between the mass
accreted by \dot{M} dt and the mass of gas particles removed from the
simulation. The black hole advection algorithms dampen inappropriate dragging
of the black holes by two-body interactions. Advecting the black hole a limited
distance based upon local mass distributions has many desirably properties. The
black holes merge when given criteria are met, and we find a range of merger
times for different criteria. Using the M_{BH}-\sigma relation as a diagnostic
of the remnants yields three models that lie within the one-sigma scatter of
the observed relation and two that fall below it. The wide variation in
accretion behaviours of the models reinforces the fact that there remains much
to be learnt about the evolution of galactic nuclei. (abridged)
Modelling AGN feedback in numerical simulations is both technically and
theoretically challenging, with numerous approaches having been published in
the literature. We present a study of five distinct approaches to modelling AGN
feedback within gravitohydrodynamic simulations of major mergers of Milky
Way-sized galaxies. To constrain differences to only be between AGN feedback
models, all simulations start from the same initial conditions and use the same
star formation algorithm. Most AGN feedback algorithms have five key aspects:
black hole accretion rate, energy feedback rate and method, particle accretion
algorithm, black hole advection algorithm, and black hole merger algorithm. All
models follow different accretion histories, with accretion rates that differ
by up to three orders of magnitude at any given time. We consider models with
either thermal or kinetic feedback, with the associated energy deposited
locally around the black hole. Each feedback algorithm modifies the gas
properties near the black hole to different extents. The particle accretion
algorithms usually (but not always) maintain good agreement between the mass
accreted by \dot{M} dt and the mass of gas particles removed from the
simulation. The black hole advection algorithms dampen inappropriate dragging
of the black holes by two-body interactions. Advecting the black hole a limited
distance based upon local mass distributions has many desirably properties. The
black holes merge when given criteria are met, and we find a range of merger
times for different criteria. Using the M_{BH}-\sigma relation as a diagnostic
of the remnants yields three models that lie within the one-sigma scatter of
the observed relation and two that fall below it. The wide variation in
accretion behaviours of the models reinforces the fact that there remains much
to be learnt about the evolution of galactic nuclei. (abridged)
Sunday, February 17, 2013
On the Star Formation-AGN Connection at $z \lesssim 0.3$. (arXiv:1302.2631v1 [astro-ph.CO])
On the Star Formation-AGN Connection at $z \lesssim 0.3$. (arXiv:1302.2631v1 [astro-ph.CO]):
Using the spectra of a sample of $\sim$28,000 nearby obscured active galaxies
from Data Release 7 of the Sloan Digital Sky Survey (SDSS), we probe the
connection between AGN activity and star formation over a range of radial
scales in the host galaxy. We use the extinction-corrected luminosity of the
[OIII] 5007 \AA\ line as a proxy of intrinsic AGN power and supermassive black
hole (SMBH) accretion rate. The star formation rates (SFRs) are taken from the
MPA-JHU value-added catalog and are measured through the 3$^{\prime\prime}$
SDSS aperture. We construct matched samples of galaxies covering a range in
redshifts. With increasing redshift, the projected aperture size encompasses
increasing amounts of the host galaxy. This allows us to trace the radial
distribution of star-formation as a function of AGN luminosity. We find that
the star formation becomes more centrally concentrated with increasing AGN
luminosity and Eddington ratio. This implies that such circumnuclear star
formation is associated with AGN activity, and that it increasingly dominates
over omnipresent disk star formation at higher AGN luminosities, placing
critical constraints on theoretical models that link host galaxy star formation
and SMBH fueling. We parametrize this relationship and find that the star
formation on radial scales ${body}lt;$1.7 kpc, when including a constant disk
component, has a sub-linear dependence on SMBH accretion rate: $SFR \propto
\dot{M}^{0.36}$, suggesting that angular momentum transfer through the disk
limits accretion efficiency rather than the supply from stellar mass loss.
Using the spectra of a sample of $\sim$28,000 nearby obscured active galaxies
from Data Release 7 of the Sloan Digital Sky Survey (SDSS), we probe the
connection between AGN activity and star formation over a range of radial
scales in the host galaxy. We use the extinction-corrected luminosity of the
[OIII] 5007 \AA\ line as a proxy of intrinsic AGN power and supermassive black
hole (SMBH) accretion rate. The star formation rates (SFRs) are taken from the
MPA-JHU value-added catalog and are measured through the 3$^{\prime\prime}$
SDSS aperture. We construct matched samples of galaxies covering a range in
redshifts. With increasing redshift, the projected aperture size encompasses
increasing amounts of the host galaxy. This allows us to trace the radial
distribution of star-formation as a function of AGN luminosity. We find that
the star formation becomes more centrally concentrated with increasing AGN
luminosity and Eddington ratio. This implies that such circumnuclear star
formation is associated with AGN activity, and that it increasingly dominates
over omnipresent disk star formation at higher AGN luminosities, placing
critical constraints on theoretical models that link host galaxy star formation
and SMBH fueling. We parametrize this relationship and find that the star
formation on radial scales ${body}lt;$1.7 kpc, when including a constant disk
component, has a sub-linear dependence on SMBH accretion rate: $SFR \propto
\dot{M}^{0.36}$, suggesting that angular momentum transfer through the disk
limits accretion efficiency rather than the supply from stellar mass loss.
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO])
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO]):
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO])
Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO]):
In order to understand the mutual influence between active galactic nuclei
(AGN) and star formation during the evolution of galaxies, we investigate 142
galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic
Evolution Survey) field. All of our data are obtained from archive, X-ray point
source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m
point source catalog from Spitzer-MIPS observation. Although the IRAC colors of
our samples indicate the existence of star formation, the ratio of rest frame
2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN
predominates the spectral energy distribution (SED). We identify obscured AGN
in these 70{\mu}m luminous galaxies as characterized by a larger hardness
ratio. The higher X-ray obscuration fraction indicates an extra contribution
from the star formation in the host galaxy in addition to the usual AGN dusty
torus. If AGN feedback occurs in their host galaxies, the star formation must
be quenched and dust in host galaxy will be dispersed. However, our temperature
fitting shows there is no significant dust temperature enhancement in
far-infrared wavelength, suggesting the thermal radiative feedback is absent
from the AGN to the galaxy.
In order to understand the mutual influence between active galactic nuclei
(AGN) and star formation during the evolution of galaxies, we investigate 142
galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic
Evolution Survey) field. All of our data are obtained from archive, X-ray point
source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m
point source catalog from Spitzer-MIPS observation. Although the IRAC colors of
our samples indicate the existence of star formation, the ratio of rest frame
2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN
predominates the spectral energy distribution (SED). We identify obscured AGN
in these 70{\mu}m luminous galaxies as characterized by a larger hardness
ratio. The higher X-ray obscuration fraction indicates an extra contribution
from the star formation in the host galaxy in addition to the usual AGN dusty
torus. If AGN feedback occurs in their host galaxies, the star formation must
be quenched and dust in host galaxy will be dispersed. However, our temperature
fitting shows there is no significant dust temperature enhancement in
far-infrared wavelength, suggesting the thermal radiative feedback is absent
from the AGN to the galaxy.
Observational constraints on the powering mechanism of transient relativistic jets. (arXiv:1301.6771v1 [astro-ph.HE])
Observational constraints on the powering mechanism of transient relativistic jets. (arXiv:1301.6771v1 [astro-ph.HE]):
We revisit the paradigm of the dependency of jet power on black hole spin in
accreting black hole systems. In a previous paper we showed that the luminosity
of compact jets continuously launched due to accretion onto black holes in
X-ray binaries (analogous to those that dominate the kinetic feedback from AGN)
do not appear to correlate with reported black hole spin measurements. It is
therefore unclear whether extraction of the black hole spin energy is the main
driver powering compact jets from accreting black holes. Occasionally, black
hole X-ray binaries produce discrete, transient (ballistic) jets for a brief
time over accretion state changes. Here, we quantify the dependence of the
power of these transient jets (adopting two methods to infer the jet power) on
black hole spin, making use of all the available data in the current
literature, which includes 12 BHs with both measured spin parameters and radio
flares over the state transition. In several sources, regular, well-sampled
radio monitoring has shown that the peak radio flux differs dramatically
depending on the outburst (up to a factor of 1000) whereas the total power
required to energise the flare may only differ by a factor ~< 4 between
outbursts. The peak flux is determined by the total energy in the flare and the
time over which it is radiated (which can vary considerably between outbursts).
Using a Bayesian fitting routine we rule out a statistically significant
positive correlation between transient jet power measured using these methods,
and current estimates of black hole spin. Even when selecting subsamples of the
data that disregard some methods of black hole spin measurement or jet power
measurement, no correlation is found in all cases.
We revisit the paradigm of the dependency of jet power on black hole spin in
accreting black hole systems. In a previous paper we showed that the luminosity
of compact jets continuously launched due to accretion onto black holes in
X-ray binaries (analogous to those that dominate the kinetic feedback from AGN)
do not appear to correlate with reported black hole spin measurements. It is
therefore unclear whether extraction of the black hole spin energy is the main
driver powering compact jets from accreting black holes. Occasionally, black
hole X-ray binaries produce discrete, transient (ballistic) jets for a brief
time over accretion state changes. Here, we quantify the dependence of the
power of these transient jets (adopting two methods to infer the jet power) on
black hole spin, making use of all the available data in the current
literature, which includes 12 BHs with both measured spin parameters and radio
flares over the state transition. In several sources, regular, well-sampled
radio monitoring has shown that the peak radio flux differs dramatically
depending on the outburst (up to a factor of 1000) whereas the total power
required to energise the flare may only differ by a factor ~< 4 between
outbursts. The peak flux is determined by the total energy in the flare and the
time over which it is radiated (which can vary considerably between outbursts).
Using a Bayesian fitting routine we rule out a statistically significant
positive correlation between transient jet power measured using these methods,
and current estimates of black hole spin. Even when selecting subsamples of the
data that disregard some methods of black hole spin measurement or jet power
measurement, no correlation is found in all cases.
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
A Two-Phase Low-velocity Outflow in the Seyfert 1 Galaxy Ark~564. (arXiv:1301.6138v1 [astro-ph.HE])
A Two-Phase Low-velocity Outflow in the Seyfert 1 Galaxy Ark~564. (arXiv:1301.6138v1 [astro-ph.HE]):
The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy
transmission gratings for 250 ks. We present the high resolution X-ray spectrum
that shows several associated absorption lines. The photoionization model
requires two warm absorbers with two different ionization states
(logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities
(~100 km s^-1) and relatively low line of sight column densities (logNH=20.94
and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII,
OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase
produces lines at lower energies (OVI & OVII). The pressure--temperature
equilibrium curve for the Ark 564 absorber does not have the typical "S" shape,
even if the metallicity is super-solar; as a result the two warm-absorber
phases do not appear to be in pressure balance. This suggests that the
continuum incident on the absorbing gas is perhaps different from the observed
continuum. We also estimated the mass outflow rate and the associated kinetic
energy and find it to be at most 0.006% of the bolometric luminosity of
Ark~564. Thus it is highly unlikely that these outflows provide significant
feedback required by the galaxy formation models.
The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy
transmission gratings for 250 ks. We present the high resolution X-ray spectrum
that shows several associated absorption lines. The photoionization model
requires two warm absorbers with two different ionization states
(logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities
(~100 km s^-1) and relatively low line of sight column densities (logNH=20.94
and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII,
OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase
produces lines at lower energies (OVI & OVII). The pressure--temperature
equilibrium curve for the Ark 564 absorber does not have the typical "S" shape,
even if the metallicity is super-solar; as a result the two warm-absorber
phases do not appear to be in pressure balance. This suggests that the
continuum incident on the absorbing gas is perhaps different from the observed
continuum. We also estimated the mass outflow rate and the associated kinetic
energy and find it to be at most 0.006% of the bolometric luminosity of
Ark~564. Thus it is highly unlikely that these outflows provide significant
feedback required by the galaxy formation models.
Discovery of Relativistic Outflow in the Seyfert Galaxy Ark 564. (arXiv:1301.6139v1 [astro-ph.HE])
Discovery of Relativistic Outflow in the Seyfert Galaxy Ark 564. (arXiv:1301.6139v1 [astro-ph.HE]):
We present Chandra high energy transmission grating spectra of the
narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption
lines which are well modeled with low velocity outflow components usually
observed in Seyfert galaxies (Gupta et al. 2013). There are, however, some
residual absorption lines which are not accounted for by low-velocity outflows.
Here we present identifications of the strongest lines as K{\alpha} transitions
of OVII(two lines) and OVI at outflow velocities of ~0.1c. These lines are
detected at 6.9{\sigma}, 6.2{\sigma}, and 4.7{\sigma} respectively and cannot
be due to chance statistical fluctuations. Photoionization models with
ultra-high velocity components improves the spectral fit significantly,
providing further support for the presence of relativistic outflow in this
source. Without knowing the location of the absorber, its mass and energy
outflow rates cannot be well constrained; we find E$\dot{E}(outflow)/L_{bo}$
ranging from < 0.001% to 60% using different assumptions. This is the first
time that absorption lines with ultra-high velocities are unambiguously
detected in the soft X-ray band. The presence of outflows with relativistic
velocities in AGNs with Seyfert-type luminosities is hard to understand and
provides valuable constraints to models of AGN outflows.
We present Chandra high energy transmission grating spectra of the
narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption
lines which are well modeled with low velocity outflow components usually
observed in Seyfert galaxies (Gupta et al. 2013). There are, however, some
residual absorption lines which are not accounted for by low-velocity outflows.
Here we present identifications of the strongest lines as K{\alpha} transitions
of OVII(two lines) and OVI at outflow velocities of ~0.1c. These lines are
detected at 6.9{\sigma}, 6.2{\sigma}, and 4.7{\sigma} respectively and cannot
be due to chance statistical fluctuations. Photoionization models with
ultra-high velocity components improves the spectral fit significantly,
providing further support for the presence of relativistic outflow in this
source. Without knowing the location of the absorber, its mass and energy
outflow rates cannot be well constrained; we find E$\dot{E}(outflow)/L_{bo}$
ranging from < 0.001% to 60% using different assumptions. This is the first
time that absorption lines with ultra-high velocities are unambiguously
detected in the soft X-ray band. The presence of outflows with relativistic
velocities in AGNs with Seyfert-type luminosities is hard to understand and
provides valuable constraints to models of AGN outflows.
Monday, February 11, 2013
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
Thursday, January 31, 2013
Ultra-fast outflows (aka UFOs) from AGNs and QSOs. (arXiv:1301.7199v1 [astro-ph.HE])
Ultra-fast outflows (aka UFOs) from AGNs and QSOs. (arXiv:1301.7199v1 [astro-ph.HE]):
During the last decade, strong observational evidence has been accumulated
for the existence of massive, high velocity winds/outflows (aka Ultra Fast
Outflows, UFOs) in nearby AGNs and in more distant quasars. Here we briefly
review some of the most recent developments in this field and discuss the
relevance of UFOs for both understanding the physics of accretion disk winds in
AGNs, and for quantifying the global amount of AGN feedback on the surrounding
medium.
During the last decade, strong observational evidence has been accumulated
for the existence of massive, high velocity winds/outflows (aka Ultra Fast
Outflows, UFOs) in nearby AGNs and in more distant quasars. Here we briefly
review some of the most recent developments in this field and discuss the
relevance of UFOs for both understanding the physics of accretion disk winds in
AGNs, and for quantifying the global amount of AGN feedback on the surrounding
medium.
Wednesday, January 23, 2013
Investigation of X-ray cavities in the cooling flow system Abell 1991. (arXiv:1301.2928v1 [astro-ph.CO])
Investigation of X-ray cavities in the cooling flow system Abell 1991. (arXiv:1301.2928v1 [astro-ph.CO]):
We present results based on the systematic analysis of \textit{Chandra}
archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991
with an objective to investigate properties of the X-ray cavities hosted by
this system. The unsharp masked image as well as 2-d $\beta$ model subtracted
residual image of Abell 1991 reveals a pair of X-ray cavities and a region of
excess emission in the central $\sim$12 kpc region. Both the cavities are of
ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray
surface brightness compared to that in the undisturbed regions. Spectral
analysis of X-ray photons extracted from the cavities lead to the temperature
values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and
$1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray
emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial
temperature profile derived for Abell 1991 reveals a positive temperature
gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines
in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec
region of Abell 1991 reveals relatively cooler three different knot like
features that are about 10\arcsec off the X-ray peak of the cluster. Total
power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum,
while the X-ray luminosity within the cooling radius is found to be 6.04
$\times 10^{43}$ \lum, comparison of which imply that the mechanical energy
released by the central AGN outburst is sufficient to balance the radiative
loss.
We present results based on the systematic analysis of \textit{Chandra}
archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991
with an objective to investigate properties of the X-ray cavities hosted by
this system. The unsharp masked image as well as 2-d $\beta$ model subtracted
residual image of Abell 1991 reveals a pair of X-ray cavities and a region of
excess emission in the central $\sim$12 kpc region. Both the cavities are of
ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray
surface brightness compared to that in the undisturbed regions. Spectral
analysis of X-ray photons extracted from the cavities lead to the temperature
values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and
$1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray
emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial
temperature profile derived for Abell 1991 reveals a positive temperature
gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines
in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec
region of Abell 1991 reveals relatively cooler three different knot like
features that are about 10\arcsec off the X-ray peak of the cluster. Total
power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum,
while the X-ray luminosity within the cooling radius is found to be 6.04
$\times 10^{43}$ \lum, comparison of which imply that the mechanical energy
released by the central AGN outburst is sufficient to balance the radiative
loss.
Sunday, January 20, 2013
AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes. (arXiv:1301.3499v1 [astro-ph.CO])
AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes. (arXiv:1301.3499v1 [astro-ph.CO]):
Recent results based on the analysis of radio galaxies and their hot X-ray
emitting atmospheres suggest that non-radiating particles dominate the energy
budget in the lobes of FRI radio galaxies, in some cases by a factor of more
than 1000, while radiating particles dominate the energy budget in FRII radio
galaxy lobes. This implies a significant difference in the radiative efficiency
of the two morphological classes. To test this hypothesis, we have measured the
kinetic energy flux for a sample of 3C FRII radio sources using a new method
based on the observed parameters of the jet terminal hotspots, and compared the
resulting Q(jet) - L(radio) relation to that obtained for FRI radio galaxies
based on X-ray cavity measurements. Contrary to expectations, we find
approximate agreement between the Q(jet) - L(radio) relations determined
separately for FRI and FRII radio galaxies. This result is ostensibly difficult
to reconcile with the emerging scenario in which the lobes of FRI and FRII
radio galaxies have vastly different energy budgets. However, a combination of
lower density environment, spectral ageing and strong shocks driven by powerful
FRII radio galaxies may reduce the radiative efficiency of these objects
relative to FRIs and couteract, to some extent, the higher radiative efficiency
expected to arise due to the lower fraction of energy in non-radiating
particles. An unexpected corollary is that extrapolating the Q(jet) - L(radio)
relation determined for low power FRI radio galaxies provides a reasonable
approximation for high power sources, despite their apparently different lobe
compositions.
Recent results based on the analysis of radio galaxies and their hot X-ray
emitting atmospheres suggest that non-radiating particles dominate the energy
budget in the lobes of FRI radio galaxies, in some cases by a factor of more
than 1000, while radiating particles dominate the energy budget in FRII radio
galaxy lobes. This implies a significant difference in the radiative efficiency
of the two morphological classes. To test this hypothesis, we have measured the
kinetic energy flux for a sample of 3C FRII radio sources using a new method
based on the observed parameters of the jet terminal hotspots, and compared the
resulting Q(jet) - L(radio) relation to that obtained for FRI radio galaxies
based on X-ray cavity measurements. Contrary to expectations, we find
approximate agreement between the Q(jet) - L(radio) relations determined
separately for FRI and FRII radio galaxies. This result is ostensibly difficult
to reconcile with the emerging scenario in which the lobes of FRI and FRII
radio galaxies have vastly different energy budgets. However, a combination of
lower density environment, spectral ageing and strong shocks driven by powerful
FRII radio galaxies may reduce the radiative efficiency of these objects
relative to FRIs and couteract, to some extent, the higher radiative efficiency
expected to arise due to the lower fraction of energy in non-radiating
particles. An unexpected corollary is that extrapolating the Q(jet) - L(radio)
relation determined for low power FRI radio galaxies provides a reasonable
approximation for high power sources, despite their apparently different lobe
compositions.
The brightest ULIRG:watching the birth of a quasar. (arXiv:1301.3953v1 [astro-ph.CO])
The brightest ULIRG:watching the birth of a quasar. (arXiv:1301.3953v1 [astro-ph.CO]):
The extreme ULIRG F00183-7111 has recently been found to have a radio-loud
AGN with jets in its centre, representing an extreme example of the class of
radio-loud AGNs buried within dusty star-forming galaxies. This source appears
to be a rare example of a ULIRG glimpsed in the (presumably) brief period as it
changes from "quasar mode" to "radio mode" activity. Such transition stages
probably account for many of the high-redshift radio-galaxies and extreme
high-redshift ULIRGs, and so this object at the relatively low redshift of
0.328 offers a rare opportunity to study this class of objects in detail. We
have also detected the CO signal from this galaxy with the ATCA, and here
describe the implications of this detection for future ULIRG studies.
The extreme ULIRG F00183-7111 has recently been found to have a radio-loud
AGN with jets in its centre, representing an extreme example of the class of
radio-loud AGNs buried within dusty star-forming galaxies. This source appears
to be a rare example of a ULIRG glimpsed in the (presumably) brief period as it
changes from "quasar mode" to "radio mode" activity. Such transition stages
probably account for many of the high-redshift radio-galaxies and extreme
high-redshift ULIRGs, and so this object at the relatively low redshift of
0.328 offers a rare opportunity to study this class of objects in detail. We
have also detected the CO signal from this galaxy with the ATCA, and here
describe the implications of this detection for future ULIRG studies.
Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters. (arXiv:1301.3922v1 [astro-ph.CO])
Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters. (arXiv:1301.3922v1 [astro-ph.CO]):
We present results from a ~100 ks Chandra observation of the 2QZ Cluster
1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally
identified as an overdensity of four optically-selected QSOs at z = 2.23 within
a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the
structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting
galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra
observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully
accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of
~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured
AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS),
we find suggestive evidence that the AGN fraction increases with local HAE
galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment
(a factor of ~2 times over the field), and after excluding optically-selected
QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than
C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra
data and Herschel SPIRE observations at 250 um, we respectively estimate mean
SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus
and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV
luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR \sim
(1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2
X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less
X-ray luminous and have Mdot/SFR \sim (0.2-0.4) x10^-3, comparable to z ~ 1-2
star-forming galaxies with similar mean X-ray luminosities. We estimate that a
periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the
star-forming galaxies onto the local MBH/M* relation.
We present results from a ~100 ks Chandra observation of the 2QZ Cluster
1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally
identified as an overdensity of four optically-selected QSOs at z = 2.23 within
a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the
structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting
galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra
observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully
accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of
~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured
AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS),
we find suggestive evidence that the AGN fraction increases with local HAE
galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment
(a factor of ~2 times over the field), and after excluding optically-selected
QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than
C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra
data and Herschel SPIRE observations at 250 um, we respectively estimate mean
SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus
and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV
luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR \sim
(1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2
X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less
X-ray luminous and have Mdot/SFR \sim (0.2-0.4) x10^-3, comparable to z ~ 1-2
star-forming galaxies with similar mean X-ray luminosities. We estimate that a
periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the
star-forming galaxies onto the local MBH/M* relation.
Monday, January 14, 2013
Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO])
Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO]):
We study galaxy super-winds driven in major mergers, using pc-resolution
simulations with detailed models for stellar feedback that can
self-consistently follow the formation/destruction of GMCs and generation of
winds. The models include molecular cooling, star formation at high densities
in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and
radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky
Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in
all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind
mass-loading efficiency (outflow rate divided by SFR) is similar to that in
isolated galaxy counterparts of each merger: it depends more on global galaxy
properties (mass, size, escape velocity) than on the dynamical state of the
merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up
complex morphologies with overlapping, differently-oriented bubbles/shells at a
range of radii. The winds have complex velocity and phase structure, with
material at a range of speeds up to ~1000 km/s, and a mix of molecular,
ionized, and hot gas that depends on galaxy properties and different feedback
mechanisms. These simulations resolve a problem in some 'sub-grid' models,
where simple wind prescriptions can dramatically suppress merger-induced
starbursts. But despite large mass-loading factors (>~10) in the winds, the
peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration
does not act equally, so cold dense gas can still lose angular momentum and
form stars, while blowing out gas that would not have participated in the
starburst in the first place. Considerable wind material is not unbound, and
falls back on the disk at later times post-merger, leading to higher
post-starburst SFRs in the presence of stellar feedback. This may require AGN
feedback to explain galaxy quenching.
We study galaxy super-winds driven in major mergers, using pc-resolution
simulations with detailed models for stellar feedback that can
self-consistently follow the formation/destruction of GMCs and generation of
winds. The models include molecular cooling, star formation at high densities
in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and
radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky
Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in
all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind
mass-loading efficiency (outflow rate divided by SFR) is similar to that in
isolated galaxy counterparts of each merger: it depends more on global galaxy
properties (mass, size, escape velocity) than on the dynamical state of the
merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up
complex morphologies with overlapping, differently-oriented bubbles/shells at a
range of radii. The winds have complex velocity and phase structure, with
material at a range of speeds up to ~1000 km/s, and a mix of molecular,
ionized, and hot gas that depends on galaxy properties and different feedback
mechanisms. These simulations resolve a problem in some 'sub-grid' models,
where simple wind prescriptions can dramatically suppress merger-induced
starbursts. But despite large mass-loading factors (>~10) in the winds, the
peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration
does not act equally, so cold dense gas can still lose angular momentum and
form stars, while blowing out gas that would not have participated in the
starburst in the first place. Considerable wind material is not unbound, and
falls back on the disk at later times post-merger, leading to higher
post-starburst SFRs in the presence of stellar feedback. This may require AGN
feedback to explain galaxy quenching.
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.
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