392 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
New XMM-Newton observation of the Phoenix cluster: properties of the cool core
(Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton
observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine
with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from
the core region to search for the signature of cold gas, and constrain the mass
deposition rate in the cooling flow which is thought to be responsible of the
massive star formation episode observed in the BCG. We find an average mass
deposition rate of /yr in the temperature range 0.3-3.0 keV from MOS data. A
temperature-resolved analysis shows that a significant amount of gas is
deposited only above 1.8 keV, while upper limits of the order of hundreds of
/yr can be put in the 0.3-1.8 keV temperature range. From pn data we
obtain /yr, and the
upper limits from the temperature-resolved analysis are typically a factor of 3
lower than MOS data. In the RGS spectrum, no line emission from ionization
states below Fe XXIII is seen above , and the amount of gas cooling
below keV has a best-fit value
/yr. In addition, our analysis of the FIR SED of the BCG based on
Herschel data provides /yr, significantly lower
than previous estimates by a factor 1.5. Current data are able to firmly
identify substantial amount of cooling gas only above 1.8 keV in the core of
the Phoenix cluster. While MOS data analysis is consistent with values as high
as within , pn data provide
yr at c.l. at temperature below 1.8 keV. At present, this
discrepancy cannot be explained on the basis of known calibration uncertainties
or other sources of statistical noise.Comment: A&A in press, typos corrected, revised text according to published
versio
Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries
The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic compass for orientation, but whether their magnetic direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic compass direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic compass to memorize the magnetic direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.publishedVersio
Glass eels (Anguilla anguilla) have a magnetic compass linked to the tidal cycle
The European eel (Anguilla anguilla) has one of the longest migrations in the animal kingdom. It crosses the Atlantic Ocean twice during its life history, migrating between the spawning area in the Sargasso Sea and Europe, where it is widely distributed. The leptocephalus larvae drift with the Gulf Stream and other currents for more than a year and metamorphose into glass eels when they arrive on the continental shelf and move toward coastal areas. The mechanisms underlying glass eel orientation toward the coast and into freshwater systems are poorly known. However, anguillid eels, including the glass eel life stage, have a geomagnetic sense, suggesting the possibility that they use Earth’s magnetic field to orient toward the coast. To test this hypothesis, we used a unique combination of laboratory tests and in situ behavioral observations conducted in a drifting circular arena. Most (98%) of the glass eels tested in the sea exhibited a preferred orientation that was related to the tidal cycle. Seventy-one percent of the same eels showed the same orientation during ebb tide when tested in the laboratory under a manipulated simulated magnetic field in the absence of any other cue. These results demonstrate that glass eels use a magnetic compass for orientation and suggest that this magnetic orientation system is linked to a circatidal rhythm.publishedVersio
Herschel Far-IR counterparts of SDSS galaxies: Analysis of commonly used Star Formation Rate estimates
We study a hundred of galaxies from the spectroscopic Sloan Digital Sky
Survey with individual detections in the Far-Infrared Herschel PACS bands (100
or 160 m) and in the GALEX Far-UltraViolet band up to z0.4 in the
COSMOS and Lockman Hole fields. The galaxies are divided into 4 spectral and 4
morphological types. For the star forming and unclassifiable galaxies we
calculate dust extinctions from the UV slope, the H/H ratio and
the ratio. There is a tight correlation between the
dust extinction and both and metallicity. We calculate
SFR and compare it with other SFR estimates (H, UV, SDSS)
finding a very good agreement between them with smaller dispersions than
typical SFR uncertainties. We study the effect of mass and metallicity, finding
that it is only significant at high masses for SFR. For the AGN and
composite galaxies we find a tight correlation between SFR and L
(0.29), while the dispersion in the SFR - L relation is
larger (0.57). The galaxies follow the prescriptions of the
Fundamental Plane in the M-Z-SFR space.Comment: 24 pages, 23 figures, accepted for publication in MNRA
The MAGNUM survey: Positive feedback in the nuclear region of NGC 5643 suggested by MUSE
We study the ionization and kinematics of the ionized gas in the nuclear
region of the barred Seyfert 2 galaxy NGC~5643 using MUSE integral field
observations in the framework of the MAGNUM (Measuring Active Galactic Nuclei
Under MUSE Microscope) survey. The data were used to identify regions with
different ionization conditions and to map the gas density and the dust
extinction. We find evidence for a double sided ionization cone, possibly
collimated by a dusty structure surrounding the nucleus. At the center of the
ionization cone, outflowing ionized gas is revealed as a blueshifted,
asymmetric wing of the [OIII] emission line, up to projected velocity
v(10)~-450 km/s. The outflow is also seen as a diffuse, low luminosity radio
and X-ray jet, with similar extension. The outflowing material points in the
direction of two clumps characterized by prominent line emission with spectra
typical of HII regions, located at the edge of the dust lane of the bar. We
propose that the star formation in the clumps is due to `positive feedback'
induced by gas compression by the nuclear outflow, providing the first
candidate for outflow induced star formation in a Seyfert-like radio quiet AGN.
This suggests that positive feedback may be a relevant mechanism in shaping the
black hole-host galaxy coevolution.Comment: 9 pages, 7 figures, accepted for publication in A&
Ionised outflows in z 2.4 quasar host galaxies
AGN-driven outflows are invoked by galaxy evolutionary models to quench star
formation and to explain the origin of the relations observed locally between
super massive black holes and their host galaxies. This work aims to detect the
presence of extended ionised outflows in luminous quasars where we expect the
maximum activity both in star formation and in black hole accretion. Currently,
there are only a few studies based on spatially resolved observations of
outflows at high redshift, . We analyse a sample of six luminous () quasars at , observed in H-band using the
near-IR integral field spectrometer SINFONI at VLT. We perform a kinematic
analysis of the [OIII] emission line at . [OIII] has a
complex gas kinematic, with blue-shifted velocities of a few hundreds of km/s
and line widths up to 1500 km/s. Using the spectroastrometric method we infer
size of the ionised outflows of up to 2 kpc. The properties of the
ionised outflows, mass outflow rate, momentum rate and kinetic power, are
correlated with the AGN luminosity. The increase in outflow rate with
increasing AGN luminosity is consistent with the idea that a luminous AGN
pushes away the surrounding gas through fast outflows driven by radiation
pressure, which depends on the emitted luminosity. We derive mass outflow rates
of about 6-700 M/yr for our sample, which are lower than those
observed in molecular outflows. Indeed physical properties of ionised outflows
show dependences on AGN luminosity which are similar to those of molecular
outflows but indicating that the mass of ionised gas is smaller than that of
the molecular one. Alternatively, this discrepancy between ionised and
molecular outflows could be explained with different acceleration mechanisms.Comment: 13 pages, 11 figures; accepted for publication in A&
A Multiwavelength Consensus on the Main Sequence of Star-Forming Galaxies at z~2
We compare various star formation rate (SFR) indicators for star-forming
galaxies at in the COSMOS field. The main focus is on the SFRs from
the far-IR (PACS-Herschel data) with those from the ultraviolet, for galaxies
selected according to the BzK criterion. FIR-selected samples lead to a vastly
different slope of the SFR-stellar mass () relation, compared to that of
the dominant main sequence population as measured from the UV, since the FIR
selection picks predominantly only a minority of outliers. However, there is
overall agreement between the main sequences derived with the two SFR
indicators, when stacking on the PACS maps the BzK-selected galaxies. The
resulting logarithmic slope of the SFR-{} relation is , in
agreement with that derived from the dust-corrected UV-luminosity. Exploiting
deeper 24m-Spitzer data we have characterized a sub-sample of galaxies
with reddening and SFRs poorly constrained, as they are very faint in the
band. The combination of Herschel with Spitzer data have allowed us to largely
break the age/reddening degeneracy for these intriguing sources, by
distinguishing whether a galaxy is very red in B-z because of being heavily
dust reddened, or whether because star formation has been (or is being)
quenched. Finally, we have compared our SFR(UV) to the SFRs derived by stacking
the radio data and to those derived from the H luminosity of a sample
of star-forming galaxies at . The two sets of SFRs are broadly
consistent as they are with the SFRs derived from the UV and by stacking the
corresponding PACS data in various mass bins.Comment: Accepted for publication in MNRA
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