The cosmic X-ray background: abundance and evolution of hidden black holes. (arXiv:1304.3665v1 [astro-ph.CO]):
The growth of supermassive black holes across cosmic time leaves a radiative
imprint recorded in the X-ray background (XRB). The XRB spectral shape suggests
that a large population of distant, hidden nuclei must exist, which are now
being revealed at higher and higher redshifts by the deepest surveys performed
by Chandra and XMM.
Our current understanding of the XRB emission in terms of AGN population
synthesis models is here reviewed, and the evolutionary path of nuclear
accretion and obscuration, as emerging from the major X-ray surveys, is
investigated. The role of galaxy merging versus secular processes in triggering
nuclear activity is also discussed in the framework of recent galaxy/black hole
co-evolutionary scenarios. Finally, the limits of current instrumentation in
the detection of the most obscured and distant black holes are discussed and
some possible directions to overcome these limits are presented.
Showing posts with label SMBHGrowth. Show all posts
Showing posts with label SMBHGrowth. Show all posts
Saturday, April 27, 2013
Sunday, March 10, 2013
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction. (arXiv:1302.6253v1 [astro-ph.CO])
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction. (arXiv:1302.6253v1 [astro-ph.CO]):
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.
Saturday, February 23, 2013
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO])
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO]):
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
Sunday, February 17, 2013
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO])
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO]):
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
Monday, February 11, 2013
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.
The Evolution of Active Galactic Nuclei in Warm Dark Matter Cosmology. (arXiv:1302.2000v1 [astro-ph.CO])
The Evolution of Active Galactic Nuclei in Warm Dark Matter Cosmology. (arXiv:1302.2000v1 [astro-ph.CO]):
Recent measurements of the abundance of AGN with low-luminosities (L_X< 10^44
erg/s in the 2-10 keV energy band) at high redshifts z>4 provide a serious
challenge for Cold Dark Matter (CDM) models based on interaction-driven fueling
of AGN. Using a semi-analytic model of galaxy formation we investigate how such
observations fit in a Warm Dark Matter (WDM) scenario of galaxy formation, and
compare the results with those obtained in the standard CDM scenario with
different efficiencies for the stellar feedback. Taking on our previous
exploration of galaxy formation in WDM cosmology, we assume as a reference case
a spectrum which is suppressed - compared to the standard CDM case - below a
cut-off scale ~ 0.2$ Mpc corresponding (for thermal relic WDM particles) to a
mass m_X=0.75 keV. We run our fiducial semi-analytic model with such a WDM
spectrum to derive AGN luminosity functions from z~6 to the present over a wide
range of luminosities (10^43< L_X/erg/s < 10^46 in the 2-10 keV X-ray band), to
compare with recent observations and with the results in the CDM case. When
compared with the standard CDM case, the luminosity distributions we obtain
assuming a WDM spectrum are characterized by a similar behaviour at low
redshift, and by a flatter slope at faint magnitudes for z>3, which provide an
excellent fit to present observations. We discuss how such a result compares
with CDM models with maximized feedback efficiency, and how future deep AGN
surveys will allow for a better discrimination between feedback and
cosmological effects on the evolution of AGN in interaction-driven models for
AGN fueling.
Recent measurements of the abundance of AGN with low-luminosities (L_X< 10^44
erg/s in the 2-10 keV energy band) at high redshifts z>4 provide a serious
challenge for Cold Dark Matter (CDM) models based on interaction-driven fueling
of AGN. Using a semi-analytic model of galaxy formation we investigate how such
observations fit in a Warm Dark Matter (WDM) scenario of galaxy formation, and
compare the results with those obtained in the standard CDM scenario with
different efficiencies for the stellar feedback. Taking on our previous
exploration of galaxy formation in WDM cosmology, we assume as a reference case
a spectrum which is suppressed - compared to the standard CDM case - below a
cut-off scale ~ 0.2$ Mpc corresponding (for thermal relic WDM particles) to a
mass m_X=0.75 keV. We run our fiducial semi-analytic model with such a WDM
spectrum to derive AGN luminosity functions from z~6 to the present over a wide
range of luminosities (10^43< L_X/erg/s < 10^46 in the 2-10 keV X-ray band), to
compare with recent observations and with the results in the CDM case. When
compared with the standard CDM case, the luminosity distributions we obtain
assuming a WDM spectrum are characterized by a similar behaviour at low
redshift, and by a flatter slope at faint magnitudes for z>3, which provide an
excellent fit to present observations. We discuss how such a result compares
with CDM models with maximized feedback efficiency, and how future deep AGN
surveys will allow for a better discrimination between feedback and
cosmological effects on the evolution of AGN in interaction-driven models for
AGN fueling.
Tuesday, February 5, 2013
High redshift blazars. (arXiv:1302.0011v1 [astro-ph.CO])
High redshift blazars. (arXiv:1302.0011v1 [astro-ph.CO]):
Blazars are sources whose jet is pointing to us. Since their jets are
relativistic, the flux is greatly amplified in the direction of motion, making
blazars the most powerful persistent objects in the Universe. This is true at
all frequencies, but especially where their spectrum peaks. Although the
spectrum of moderate powerful sources peaks in the ~GeV range, extremely
powerful sources at high redshifts peak in the ~MeV band. This implies that the
hard X-ray band is the optimal one to find powerful blazars beyond a redshift
of ~4. First indications strongly suggest that powerful high-z blazars harbor
the most massive and active early black holes, exceeding a billion solar
masses. Since for each detected blazars there must exist hundreds of similar,
but misaligned, sources, the search for high-z blazars is becoming competitive
with the search of early massive black holes using radio-quiet quasars. Finding
how the two populations of black holes (one in jetted sources, the other in
radio-quiet objects) evolve in redshift will shed light on the growth of the
most massive black holes and possibly on the feedback between the central
engine and the rest of the host galaxy.
Blazars are sources whose jet is pointing to us. Since their jets are
relativistic, the flux is greatly amplified in the direction of motion, making
blazars the most powerful persistent objects in the Universe. This is true at
all frequencies, but especially where their spectrum peaks. Although the
spectrum of moderate powerful sources peaks in the ~GeV range, extremely
powerful sources at high redshifts peak in the ~MeV band. This implies that the
hard X-ray band is the optimal one to find powerful blazars beyond a redshift
of ~4. First indications strongly suggest that powerful high-z blazars harbor
the most massive and active early black holes, exceeding a billion solar
masses. Since for each detected blazars there must exist hundreds of similar,
but misaligned, sources, the search for high-z blazars is becoming competitive
with the search of early massive black holes using radio-quiet quasars. Finding
how the two populations of black holes (one in jetted sources, the other in
radio-quiet objects) evolve in redshift will shed light on the growth of the
most massive black holes and possibly on the feedback between the central
engine and the rest of the host galaxy.
Thursday, January 31, 2013
A black-hole mass measurement from molecular gas kinematics in NGC4526. (arXiv:1301.7184v1 [astro-ph.CO])
A black-hole mass measurement from molecular gas kinematics in NGC4526. (arXiv:1301.7184v1 [astro-ph.CO]):
The masses of the supermassive black-holes found in galaxy bulges are
correlated with a multitude of galaxy properties, leading to suggestions that
galaxies and black-holes may evolve together. The number of reliably measured
black-hole masses is small, and the number of methods for measuring them is
limited, holding back attempts to understand this co-evolution. Directly
measuring black-hole masses is currently possible with stellar kinematics (in
early-type galaxies), ionised-gas kinematics (in some spiral and early-type
galaxies) and in rare objects which have central maser emission. Here we report
that by modelling the effect of a black-hole on the kinematics of molecular gas
it is possible to fit interferometric observations of CO emission and thereby
accurately estimate black hole masses. We study the dynamics of the gas in the
early-type galaxy NGC4526, and obtain a best fit which requires the presence of
a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit).
With next generation mm-interferometers (e.g. ALMA) these observations could be
reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing
time. The use of molecular gas as a kinematic tracer should thus allow one to
estimate black-hole masses in hundreds of galaxies in the local universe, many
more than accessible with current techniques.
The masses of the supermassive black-holes found in galaxy bulges are
correlated with a multitude of galaxy properties, leading to suggestions that
galaxies and black-holes may evolve together. The number of reliably measured
black-hole masses is small, and the number of methods for measuring them is
limited, holding back attempts to understand this co-evolution. Directly
measuring black-hole masses is currently possible with stellar kinematics (in
early-type galaxies), ionised-gas kinematics (in some spiral and early-type
galaxies) and in rare objects which have central maser emission. Here we report
that by modelling the effect of a black-hole on the kinematics of molecular gas
it is possible to fit interferometric observations of CO emission and thereby
accurately estimate black hole masses. We study the dynamics of the gas in the
early-type galaxy NGC4526, and obtain a best fit which requires the presence of
a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit).
With next generation mm-interferometers (e.g. ALMA) these observations could be
reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing
time. The use of molecular gas as a kinematic tracer should thus allow one to
estimate black-hole masses in hundreds of galaxies in the local universe, many
more than accessible with current techniques.
Tuesday, January 29, 2013
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data. (arXiv:1301.6162v1 [astro-ph.CO])
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data. (arXiv:1301.6162v1 [astro-ph.CO]):
We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization.
We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization.
Wednesday, January 23, 2013
The relationship between X-ray emission and accretion in X-ray selected AGNs. (arXiv:1212.5693v1 [astro-ph.HE])
The relationship between X-ray emission and accretion in X-ray selected AGNs. (arXiv:1212.5693v1 [astro-ph.HE]):
We study the link between the X-ray emission in radio-quiet AGNs and the
accretion rate on the central Supermassive Black-Hole (SMBH) using a
well-defined and statistically complete sample of 70 type1 AGNs extracted from
the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and
quantify the statistical correlations between the main parameters that
characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray
loudness), and the accretion rate, both absolute and relative to the Eddington
limit (Eddington ratio). Here, we summarize and discuss the main statistical
correlations found and their possible implications on current disk-corona
models.
We study the link between the X-ray emission in radio-quiet AGNs and the
accretion rate on the central Supermassive Black-Hole (SMBH) using a
well-defined and statistically complete sample of 70 type1 AGNs extracted from
the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and
quantify the statistical correlations between the main parameters that
characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray
loudness), and the accretion rate, both absolute and relative to the Eddington
limit (Eddington ratio). Here, we summarize and discuss the main statistical
correlations found and their possible implications on current disk-corona
models.
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO])
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO]):
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Super-Eddington accreting massive black holes as long-lived cosmological standards. (arXiv:1301.4225v1 [astro-ph.CO])
Super-Eddington accreting massive black holes as long-lived cosmological standards. (arXiv:1301.4225v1 [astro-ph.CO]):
Super-Eddington accreting massive black holes (SEAMBHs) reach saturated
luminosities above a certain accretion rate due to photon trapping and
advection in slim accretion disks. We show that these SEAMBHs could provide a
new tool for estimating cosmological distances if they are properly identified
by hard X-ray observations, in particular by the slope of their 2-10 keV
continuum. To verify this idea we obtained black hole mass estimates and X-ray
data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be
the most promising SEAMBH candidates. We demonstrate that the distances derived
by the new method for the objects in the sample get closer to the standard
luminosity distances as the hard X-ray continuum gets steeper. The results
allow us to analyze the requirements for using the method in future samples of
active black holes and to demonstrate that the expected uncertainty, given
large enough samples, can make them into a useful, new cosmological ruler.
Super-Eddington accreting massive black holes (SEAMBHs) reach saturated
luminosities above a certain accretion rate due to photon trapping and
advection in slim accretion disks. We show that these SEAMBHs could provide a
new tool for estimating cosmological distances if they are properly identified
by hard X-ray observations, in particular by the slope of their 2-10 keV
continuum. To verify this idea we obtained black hole mass estimates and X-ray
data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be
the most promising SEAMBH candidates. We demonstrate that the distances derived
by the new method for the objects in the sample get closer to the standard
luminosity distances as the hard X-ray continuum gets steeper. The results
allow us to analyze the requirements for using the method in future samples of
active black holes and to demonstrate that the expected uncertainty, given
large enough samples, can make them into a useful, new cosmological ruler.
Sunday, January 20, 2013
Chaotic cold accretion onto black holes. (arXiv:1301.3130v1 [astro-ph.CO])
Chaotic cold accretion onto black holes. (arXiv:1301.3130v1 [astro-ph.CO]):
Using 3D AMR simulations, linking the 50 kpc to the sub-pc scales over the
course of 40 Myr, we systematically relax the classic Bondi assumptions in a
typical galaxy hosting a SMBH. In the realistic scenario, where the hot gas is
cooling, while heated and stirred on large scales, the accretion rate is
boosted up to two orders of magnitude compared with the Bondi prediction. The
cause is the nonlinear growth of thermal instabilities, leading to the
condensation of cold clouds and filaments when t_cool/t_ff < 10. Subsonic
turbulence of just over 100 km/s (M > 0.2) induces the formation of thermal
instabilities, even in the absence of heating, while in the transonic regime
turbulent dissipation inhibits their growth (t_turb/t_cool < 1). When heating
restores global thermodynamic balance, the formation of the multiphase medium
is violent, and the mode of accretion is fully cold and chaotic. The recurrent
collisions, shearing and tidal motions between clouds, filaments and the
central torus cause a significant reduction of angular momentum, boosting
accretion. On sub-pc scales the clouds are channelled to the very centre via a
funnel. A good approximation to the accretion rate is the cooling rate, which
can be used as subgrid model, physically reproducing the boost factor of 100
required by cosmological simulations, while accounting for fluctuations.
Chaotic cold accretion may be common in many systems, such as hot galactic
halos, groups, and clusters, generating high-velocity clouds and strong
variations of the AGN luminosity, jet orientation, and spin. In this mode, the
black hole can quickly react to the state of the entire host galaxy, leading to
efficient self-regulated feedback and the symbiotic Magorrian relation. During
phases of overheating, the hot mode becomes the single channel of accretion
(with a different cuspy temperature profile), though strongly suppressed by
turbulence.
Using 3D AMR simulations, linking the 50 kpc to the sub-pc scales over the
course of 40 Myr, we systematically relax the classic Bondi assumptions in a
typical galaxy hosting a SMBH. In the realistic scenario, where the hot gas is
cooling, while heated and stirred on large scales, the accretion rate is
boosted up to two orders of magnitude compared with the Bondi prediction. The
cause is the nonlinear growth of thermal instabilities, leading to the
condensation of cold clouds and filaments when t_cool/t_ff < 10. Subsonic
turbulence of just over 100 km/s (M > 0.2) induces the formation of thermal
instabilities, even in the absence of heating, while in the transonic regime
turbulent dissipation inhibits their growth (t_turb/t_cool < 1). When heating
restores global thermodynamic balance, the formation of the multiphase medium
is violent, and the mode of accretion is fully cold and chaotic. The recurrent
collisions, shearing and tidal motions between clouds, filaments and the
central torus cause a significant reduction of angular momentum, boosting
accretion. On sub-pc scales the clouds are channelled to the very centre via a
funnel. A good approximation to the accretion rate is the cooling rate, which
can be used as subgrid model, physically reproducing the boost factor of 100
required by cosmological simulations, while accounting for fluctuations.
Chaotic cold accretion may be common in many systems, such as hot galactic
halos, groups, and clusters, generating high-velocity clouds and strong
variations of the AGN luminosity, jet orientation, and spin. In this mode, the
black hole can quickly react to the state of the entire host galaxy, leading to
efficient self-regulated feedback and the symbiotic Magorrian relation. During
phases of overheating, the hot mode becomes the single channel of accretion
(with a different cuspy temperature profile), though strongly suppressed by
turbulence.
The largest mid-infrared atlas of active galactic nuclei at sub-arcsecond spatial scales. (arXiv:1301.3680v1 [astro-ph.CO])
The largest mid-infrared atlas of active galactic nuclei at sub-arcsecond spatial scales. (arXiv:1301.3680v1 [astro-ph.CO]):
We present the largest mid-infrared atlas of active galactic nuclei at
sub-arcsecond spatial scales containing 249 objects. It comprises all
ground-based HR MIR observations performed to date. This catalog includes a
large number of new observations. The photometry in multiple filters allows for
characterizing the properties of the dust emission for most objects. Because of
its size and characteristics, this sample is very well-suited for AGN
unification studies. In particular, we discuss the enlarged MIR--X-ray
correlation which extends over six orders of magnitude in luminosity and
potentially probes different physical mechanisms. Finally, tests for intrinsic
differences between the AGN types are presented and we discuss dependencies of
MIR--X-ray properties with respect to fundamental AGN parameters such as
accretion rate and the column density and covering factor of obscuring
material.
We present the largest mid-infrared atlas of active galactic nuclei at
sub-arcsecond spatial scales containing 249 objects. It comprises all
ground-based HR MIR observations performed to date. This catalog includes a
large number of new observations. The photometry in multiple filters allows for
characterizing the properties of the dust emission for most objects. Because of
its size and characteristics, this sample is very well-suited for AGN
unification studies. In particular, we discuss the enlarged MIR--X-ray
correlation which extends over six orders of magnitude in luminosity and
potentially probes different physical mechanisms. Finally, tests for intrinsic
differences between the AGN types are presented and we discuss dependencies of
MIR--X-ray properties with respect to fundamental AGN parameters such as
accretion rate and the column density and covering factor of obscuring
material.
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
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.
A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO])
A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO]):
We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.
We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.
Saturday, December 22, 2012
Measuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts. (arXiv:1212.5076v1 [astro-ph.CO])
Measuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts. (arXiv:1212.5076v1 [astro-ph.CO]):
Data from the AEGIS, COSMOS and ECDFS surveys are combined to infer the bias
and dark matter halo mass of moderate luminosity [LX(2-10 keV) = 42.9 erg s-1]
X-ray AGN at z~1 via their cross-correlation function with galaxies. In
contrast to standard cross-correlation function estimators, we present a method
that requires spectroscopy only for the AGN and uses photometric redshift
probability distribution functions for galaxies to determine the projected
real-space AGN/galaxy cross-correlation function. The estimated dark matter
halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is
~13h-1M_solar, in agreement with previous studies at similar redshift and
luminosity ranges. Removing from the sample the 5 per cent of the AGN
associated with X-ray selected groups results in a reduction by about 0.5 dex
in the inferred AGN dark matter halo mass. The distribution of AGN in dark
matter halo mass is therefore skewed and the bulk of the population lives in
moderate mass haloes. This result favour cold gas accretion as the main channel
of supermassive black hole growth for most X-ray AGN.
Data from the AEGIS, COSMOS and ECDFS surveys are combined to infer the bias
and dark matter halo mass of moderate luminosity [LX(2-10 keV) = 42.9 erg s-1]
X-ray AGN at z~1 via their cross-correlation function with galaxies. In
contrast to standard cross-correlation function estimators, we present a method
that requires spectroscopy only for the AGN and uses photometric redshift
probability distribution functions for galaxies to determine the projected
real-space AGN/galaxy cross-correlation function. The estimated dark matter
halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is
~13h-1M_solar, in agreement with previous studies at similar redshift and
luminosity ranges. Removing from the sample the 5 per cent of the AGN
associated with X-ray selected groups results in a reduction by about 0.5 dex
in the inferred AGN dark matter halo mass. The distribution of AGN in dark
matter halo mass is therefore skewed and the bulk of the population lives in
moderate mass haloes. This result favour cold gas accretion as the main channel
of supermassive black hole growth for most X-ray AGN.
Wednesday, December 19, 2012
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO])
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO]):
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
Monday, December 17, 2012
Cosmological Evolution of Supermassive Black Holes: Mass Functions and Spins. (arXiv:1212.2187v1 [astro-ph.CO])
Cosmological Evolution of Supermassive Black Holes: Mass Functions and Spins. (arXiv:1212.2187v1 [astro-ph.CO]):
We derive the mass function of supermassive black holes (SMBHs) over the
redshift range 0<z<2, using the latest deep luminosity and mass functions of
field galaxies. Applying this mass function, combined with the bolometric
luminosity function of active galactic nuclei (AGNs), into the the continuity
equation of SMBH number density, we explicitly obtain the mass-dependent
cosmological evolution of the radiative efficiency for accretion. We suggest
that the accretion history of SMBHs and their spins evolve in two distinct
regimes: an early phase of prolonged accretion, plausibly driven by major
mergers, during which the black hole spins up, then switching to a period of
random, episodic accretion, governed by minor mergers and internal secular
processes, during which the hole spins down. The transition epoch depends on
mass, mirroring other evidence for "cosmic downsizing" in the AGN population.
We derive the mass function of supermassive black holes (SMBHs) over the
redshift range 0<z<2, using the latest deep luminosity and mass functions of
field galaxies. Applying this mass function, combined with the bolometric
luminosity function of active galactic nuclei (AGNs), into the the continuity
equation of SMBH number density, we explicitly obtain the mass-dependent
cosmological evolution of the radiative efficiency for accretion. We suggest
that the accretion history of SMBHs and their spins evolve in two distinct
regimes: an early phase of prolonged accretion, plausibly driven by major
mergers, during which the black hole spins up, then switching to a period of
random, episodic accretion, governed by minor mergers and internal secular
processes, during which the hole spins down. The transition epoch depends on
mass, mirroring other evidence for "cosmic downsizing" in the AGN population.
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