245 research outputs found
Is there any evidence that ionised outflows quench star formation in type 1 quasars at z<1?
The aim of this paper is to test the basic model of negative AGN feedback.
According to this model, once the central black hole accretes at the Eddington
limit and reaches a certain critical mass, AGN driven outflows blow out gas,
suppressing star formation in the host galaxy and self-regulating black hole
growth. We consider a sample of 224 quasars selected from the SDSS at z<1
observed in the infrared band by Herschel. We evaluate the star formation rate
in relation to several outflow signatures traced by the [OIII]4959,5007 and
[OII]3726,3729 emission lines in about half of the sample with high quality
spectra. Most of the quasars show asymmetric and broad wings in [OIII], which
we interpret as outflow signatures. We separate the quasars in two groups,
``weakly'' and ``strongly'' outflowing, using three different criteria. When we
compare the mean star formation rate in five redshift bins in the two groups,
we find that the SFRs are comparable or slightly larger in the strongly
outflowing quasars. We estimate the stellar mass from SED fitting and the
quasars are distributed along the star formation main sequence, although with a
large scatter. The scatter from this relation is uncorrelated with respect to
the kinematic properties of the outflow. Moreover, for quasars dominated in the
infrared by starburst or by AGN emission, we do not find any correlation
between the star formation rate and the velocity of the outflow, a trend
previously reported in the literature for pure starburst galaxies. We conclude
that the basic AGN negative feedback scenario seems not to agree with our
results. Although we use a large sample of quasars, we did not find any
evidence that the star formation rate is suppressed in the presence of AGN
driven outflows on large scale. A possibility is that feedback is effective
over much longer timescales than those of single episodes of quasar activity.Comment: 18 pages, new version that implements the suggestions of the referee
and matches the AA published versio
Widespread {QSO}-driven outflows in the early Universe
We present the stacking analysis of a sample of 48 quasi-stellar objects (QSOs) at 4.5 < z < 7.1 detected by the Atacama Large Millimetre Array (ALMA) in the [CII] lambda 158 mu m emission line to investigate the presence and the properties of massive, cold outflows associated with broad wings in the [CII] profile. The high sensitivity reached through this analysis allows us to reveal very broad [CII] wings tracing the presence of outflows with velocities in excess of 1000 km s(-1). We find that the luminosity of the broad [CII] emission increases with L-AGN, while it does not significantly depend on the star formation rate of the host galaxy, indicating that the central active galactic nucleus (AGN) is the main driving mechanism of the [CII] outflows in these powerful, distant QSOs. From the stack of the ALMA cubes, we derive an average outflow spatial extent of similar to 3.5 kpc. The average atomic neutral mass outflow rate inferred from the stack of the whole sample is (M)over dot(out) similar to 100 M-circle dot yr(-1), while for the most luminous systems it increases to similar to 200 M(circle dot)yr(-1). The associated outflow kinetic power is about 0.1% of LAGN, while the outflow momentum rate is similar to L-AGN/C or lower, suggesting that these outflows are either driven by radiation pressure onto dusty clouds or, alternatively, are driven by the nuclear wind and energy conserving but with low coupling with the interstellar medium. We discuss the implications of the resulting feedback effect on galaxy evolution in the early Universe
Widespread QSO-driven outflows in the early Universe
We present the stacking analysis of a sample of 48 quasi-stellar objects (QSOs) at 4.5 < z < 7.1 detected by the Atacama Large
Millimetre Array (ALMA) in the [CII] \u3bb158 \ub5m emission line to investigate the presence and the properties of massive, cold outflows
associated with broad wings in the [CII] profile. The high sensitivity reached through this analysis allows us to reveal very broad
[CII] wings tracing the presence of outflows with velocities in excess of 1000 km s 121. We find that the luminosity of the broad [CII]
emission increases with LAGN, while it does not significantly depend on the star formation rate of the host galaxy, indicating that the
central active galactic nucleus (AGN) is the main driving mechanism of the [CII] outflows in these powerful, distant QSOs. From
the stack of the ALMA cubes, we derive an average outflow spatial extent of 3c3.5 kpc. The average atomic neutral mass outflow rate
inferred from the stack of the whole sample is M\u2d9out 3c 100 M yr 121, while for the most luminous systems it increases to 3c200 M yr 121.
The associated outflow kinetic power is about 0.1% of LAGN, while the outflow momentum rate is 3cLAGN/c or lower, suggesting that
these outflows are either driven by radiation pressure onto dusty clouds or, alternatively, are driven by the nuclear wind and energy
conserving but with low coupling with the interstellar medium. We discuss the implications of the resulting feedback effect on galaxy
evolution in the early Universe
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow
We present the best sensitivity and angular resolution maps of the molecular
disk and outflow of Mrk 231, as traced by CO observations obtained with
IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We
constrain the physical properties of both the molecular disk and outflow, the
presence of a highly-ionized ultra-fast nuclear wind, and their connection. The
molecular outflow has a size of ~1 kpc, and extends in all directions around
the nucleus, being more prominent along the south-west to north-east direction,
suggesting a wide-angle biconical geometry. The maximum projected velocity of
the outflow is nearly constant out to ~1 kpc, thus implying that the density of
the outflowing material decreases from the nucleus outwards as . This
suggests that either a large part of the gas leaves the flow during its
expansion or that the bulk of the outflow has not yet reached out to ~1 kpc,
thus implying a limit on its age of ~1 Myr. We find and erg s.
Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow
(UFO) with velocity -20000 km s, , and momentum load .We find as predicted for outflows undergoing an energy
conserving expansion. This suggests that most of the UFO kinetic energy is
transferred to mechanical energy of the kpc-scale outflow, strongly supporting
that the energy released during accretion of matter onto super-massive black
holes is the ultimate driver of giant massive outflows. We estimate a momentum
boost . The ratios and agree
with the requirements of the most popular models of AGN feedback.Comment: 16 pages, 17 figures. Accepted for publication in A&
Strongly star-forming rotating disks in a complex merging system at z = 4,7 as revealed by ALMA
We performed a kinematical analysis of the [CII] line emission of the BR
1202-0725 system at z~4,7 using ALMA observations. The most prominent sources
of this system are a quasar and a submillimeter galaxy, separated by a
projected distance of about 24 kpc and characterized by very high SFR, higher
than 1000 Msun/yr. However, the ALMA observations reveal that these galaxies
apparently have undisturbed rotating disks, which is at variance with the
commonly accepted scenario in which strong star formation activity is induced
by a major merger. We also detected faint components which, after spectral
deblending, were spatially resolved from the main QSO and SMG emissions. The
relative velocities and positions of these components are compatible with
orbital motions within the gravitational potentials generated by the QSO host
galaxy and the SMG, suggesting that they are smaller galaxies in interaction or
gas clouds in accretion flows of tidal streams. We did not find any clear
spectral evidence for outflows caused by AGN or stellar feedback. This suggests
that the high star formation rates might be induced by interactions or minor
mergers with these companions, which do not affect the large-scale kinematics
of the disks, however. Our kinematical analysis also indicates that the QSO and
the SMG have similar Mdyn, mostly in the form of molecular gas, and that the
QSO host galaxy and the SMG are seen close to face-on with slightly different
disk inclinations: the QSO host galaxy is seen almost face-on (i~15), while the
SMG is seen at higher inclinations (i~25). Finally, the ratio between the black
hole mass of the QSO, obtained from XShooter spectroscopy, and the Mdyn of the
host galaxy is similar to value found in very massive local galaxies,
suggesting that the evolution of black hole galaxy relations is probably better
studied with dynamical than with stellar host galaxy masses.Comment: Accepted for publication in Astronomy and Astrophysic
The dense molecular gas in the QSO SDSS J231038.88+185519.7 resolved by ALMA
We present ALMA observations of the CO(6-5) and [CII] emission lines and the
sub-millimeter continuum of the quasi-stellar object (QSO) SDSS
J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic
beam that is ten times smaller in angular size, we have achieved ten times
better sensitivity in the CO(6-5) line, and two and half times better
sensitivity in the [CII] line, enabling us to resolve the molecular gas
emission. We obtain a size of the dense molecular gas of kpc, and
of kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is
thermalized, and by adopting a CO--to-- conversion factor , we infer a molecular gas mass of
. Assuming that the
observed CO velocity gradient is due to an inclined rotating disk, we derive a
dynamical mass of , which is a factor of approximately two smaller than the previously
reported estimate based on [CII]. Regarding the central black hole, we provide
a new estimate of the black hole mass based on the C~IV emission line detected
in the X-SHOOTER/VLT spectrum: . We find a molecular gas fraction of ,
where . We derive a ratio
suggesting high gas turbulence, outflows/inflows
and/or complex kinematics due to a merger event. We estimate a global Toomre
parameter , indicating likely cloud fragmentation. We compare,
at the same angular resolution, the CO(6-5) and [CII] distributions, finding
that dense molecular gas is more centrally concentrated with respect to [CII].
We find that the current BH growth rate is similar to that of its host galaxy.Comment: A&A in pres
The assembly of "normal" galaxies at z=7 probed by ALMA
We report new deep ALMA observations aimed at investigating the [CII]158um
line and continuum emission in three spectroscopically confirmed Lyman Break
Galaxies at 6.8<z<7.1, i.e. well within the re-ionization epoch. With Star
Formation Rates of SFR ~ 5-15 Msun/yr these systems are much more
representative of the high-z galaxy population than other systems targeted in
the past by millimeter observations. For the galaxy with the deepest
observation we detect [CII] emission at redshift z=7.107, fully consistent with
the Lyalpha redshift, but spatially offset by 0.7" (4 kpc) from the optical
emission. At the location of the optical emission, tracing both the Lyalpha
line and the far-UV continuum, no [CII] emission is detected in any of the
three galaxies, with 3sigma upper limits significantly lower than the [CII]
emission observed in lower reshift galaxies. These results suggest that
molecular clouds in the central parts of primordial galaxies are rapidly
disrupted by stellar feedback. As a result, [CII] emission mostly arises from
more external accreting/satellite clumps of neutral gas. These findings are in
agreement with recent models of galaxy formation. Thermal far-infrared
continuum is not detected in any of the three galaxies. However, the upper
limits on the infrared-to-UV emission ratio do not exceed those derived in
metal- and dust-poor galaxies.Comment: 15 pages, 9 figures, MNRAS in press, replaced with accepted versio
ALMA hints at the presence of turbulent disk galaxies at z > 5
High-redshift galaxies are expected to be more turbulent than local galaxies
because of their smaller size and higher star formation and thus stronger
feedback from star formation, frequent mergers events, and gravitational
instabilities. However, this scenario has recently been questioned by the
observational evidence of a few galaxies at z~4-5 with a gas velocity
dispersion similar to what is observed in the local population. Our goal is to
determine whether galaxies in the first Gyrs of the Universe have already
formed a dynamically cold rotating disk similar to the local counterparts. We
studied the gas kinematic of 22 main-sequence star-forming galaxies at z > 5
and determined their dynamical state by estimating the ratio of the rotational
velocity and of the gas velocity dispersion. We mined the ALMA archive and
exploited the [CII] and [OIII] observations to perform a kinematic analysis of
the cold and warm gas of z>5 main-sequence galaxies. The gas kinematics of the
high-z galaxies is consistent within the errors with rotating but turbulent
disks. We infer a velocity dispersion that is systematically higher by 4 times
than the local galaxy population and the z~5 dust-obscured galaxies reported in
the literature. The difference between our results and those reported at
similar redshift can be ascribed to the systematic difference in the galaxy
properties in the two samples: the disks of massive dusty galaxies are
dynamically colder than the disks of dust-poor galaxies. The comparison with
the theoretical predictions suggests that the main driver of the velocity
dispersion in high-z galaxies is the gravitational energy that is released by
the transport of mass within the disk. Finally, we stress that future deeper
ALMA high-angular resolution observations are crucial to constrain the
kinematic properties of high-z galaxies and to distinguish rotating disks from
kpc-scale mergers.Comment: 14 pages, 11 figures, 1 tables, accepted for publication in A&
Dust attenuation law in JWST galaxies at z = 7-8
Attenuation curves in galaxies depend on dust chemical composition, content,
and grain size distribution. Such parameters are related to intrinsic galaxy
properties such as metallicity, star formation rate, and stellar age. Due to
the lack of observational constraints at high redshift, dust empirical curves
measured in the local Universe (e.g. Calzetti and SMC curves) have been
employed to describe the dust attenuation at early epochs. We exploit the high
sensitivity and spectral resolution of the JWST to constrain the dust
attenuation curves in high-z galaxies. Our goals are to check whether dust
attenuation curves evolve with redshift and quantify the dependence of the
inferred galaxy properties on the assumed dust attenuation law. We develop a
modified version of the SED fitting code BAGPIPES by including a detailed dust
attenuation curve parametrization. Dust parameters are derived, along with
galaxy properties, from the fit to the data from FUV to mm bands. Once applied
to three star-forming galaxies at z = 7-8, we find that their attenuation
curves differ from local templates. One out of three galaxies shows a
characteristic MW bump, typically associated to the presence of small
carbonaceous dust grains such as PAHs. This is one of the first evidences
suggesting the presence of PAHs in early galaxies. Galaxy properties such as
stellar mass and SFR inferred from SED fitting are strongly affected by the
assumed attenuation curve, though the adopted star formation history also plays
a major role. Our results highlight the importance of accounting for the
potential diversity of dust attenuation laws when analyzing the properties of
galaxies at the EoR, whose dust properties are still poorly understood. The
application of our method to a larger sample of galaxies observed with JWST can
provide us important insights into the properties of dust and galaxies in the
early universe.Comment: 19 pages, 10 figure
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