1,836 research outputs found
Two-Face(s): ionized and neutral gas winds in the local Universe
We present a comprehensive study of the Na I 5890, 5895 (Na I D)
resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample
to look for neutral gas outflows in the local galaxies. Individual galaxy
spectra are stacked in bins of M and SFR to investigate the dependence
of galactic wind occurrence and velocity as a function of the galaxy position
in the SFR- plane. In massive galaxies at the high SFR tail we find
evidence of a significant blue-shifted Na I D absorption, which we interpret as
evidence of neutral outflowing gas. The occurrence of the blue-shifted
absorption is observed at the same significance for purely SF galaxies, AGN and
composite systems at fixed SFR. In all classes of objects the blue-shift is the
largest and the Na I D equivalent width the smallest for face-on galaxies while
the absorption feature is at the systemic velocity for edge-on systems. This
indicates that the neutral outflow is mostly perpendicular or biconical with
respect to the galactic disk. We also compare the kinematics of the neutral gas
with the ionized gas phase as traced by the [OIII]5007, H,
[NII] and [NII] emission lines. Differently for the
neutral gas phase, all the emission lines show evidence of perturbed kinematics
only in galaxies with a significant level of nuclear activity and, they are
independent from the disk inclination. In conclusion, we find that, in the
local Universe, galactic winds show two faces which are related to two
different ejection mechanisms, namely the neutral outflowing gas phase related
to the SF activity along the galaxy disk and the ionized phase related to the
AGN feedback. In both the neutral and ionized gas phases, the observed wind
velocities suggest that the outflowing gas remains bound to the galaxy with no
definitive effect on the gas reservoir.Comment: Accepted to A&A, 13 pages, 9 figure
Properties of the integrated spectrum of serendipitous 2XMM catalogue sources
Our analysis is aimed at characterizing the properties of the integrated
spectrum of active galactic nuclei (AGNs) such as the ubiquity of the Fe
K{\alpha} emission in AGNs and the dependence of the spectral parameters on the
X-ray luminosity and redshift. We selected 2646 point sources from the 2XMM
catalogue at high galactic latitude (|BII| > 25 degrees) and with the sum of
EPIC-PN and EPIC-MOS 0.2-12 keV counts greater than 1000. Redshifts were
obtained for 916 sources from the NED. The final sample consists of 507 AGN.
Individual source spectra have been summed in the observed frame to compute the
integrated spectra in different redshift and luminosity bins over the range
0<z<5. Detailed analysis of these spectra has been performed. We find that the
narrow Fe K{\alpha} line at 6.4 keV is significantly detected up to z=1. The
line equivalent width decreases with increasing X-ray luminosity in the 2-10
keV band (''IT effect''). The anti-correlation is characterized by the relation
log(EWFe) = (1.66 +/- 0.09) + (-0.43 +/- 0.07) log(LX,44), where EWFe is the
rest frame equivalent width of the neutral iron K{\alpha} line in eV and LX,44
is the 2-10 keV X-ray luminosity in units of 10^{44} erg s^{-1}. The equivalent
width is nearly independent of redshift up to z ~ 0.8 with an average value of
101+/-40 (rms dispersion) eV in the luminosity range 43.5<= logLX <= 44.5. Our
analysis also confirmed the hardening of the spectral indices at low
luminosities implying a dependence of obscuration on luminosity. We confirm
that the neutral narrow Fe K{\alpha} line is an almost ubiquitous feature of
AGNs. We find compelling evidence for the ''IT effect'' over a redshift
interval larger than probed in any previous study. We detect no evolution of
the average rest frame equivalent width of the Fe K{\alpha} line with redshift.Comment: 10 pages, 7 figures, 2 Tables. A&A in pres
The clustering properties of radio-selected AGN and star-forming galaxies up to redshifts z~3
We present the clustering properties of a complete sample of 968 radio
sources detected at 1.4 GHz by the VLA-COSMOS survey with radio fluxes brighter
than 0.15 mJy. 92% have redshift determinations from the Laigle et al. (2016)
catalogue. Based on their radio-luminosity, these objects have been divided
into two populations of 644 AGN and 247 star-forming galaxies. By fixing the
slope of the auto-correlation function to gamma=2, we find
r_0=11.7^{+1.0}_{-1.1} Mpc for the clustering length of the whole sample, while
r_0=11.2^{+2.5}_{-3.3} Mpc and r_0=7.8^{+1.6}_{-2.1} Mpc (r_0=6.8^{+1.4}_{-1.8}
Mpc if we restrict our analysis to z<0.9) are respectively obtained for AGN and
star-forming galaxies. These values correspond to minimum masses for dark
matter haloes of M_min=10^[13.6^{+0.3}_{-0.6}] M_sun for radio-selected AGN and
M_min=10^[13.1^{+0.4}_{-1.6}] M_sun for radio-emitting star-forming galaxies
(M_min=10^[12.7^{+0.7}_{-2.2}] M_sun for z<0.9). Comparisons with previous
works imply an independence of the clustering properties of the AGN population
with respect to both radio luminosity and redshift. We also investigate the
relationship between dark and luminous matter in both populations. We obtain
/M_halo/M_halo<~10^{-2.4} in the case of
star-forming galaxies. Furthermore, if we restrict to z<~0.9 star-forming
galaxies, we derive /M_halo<~10^{-2.1}, result which clearly indicates the
cosmic process of stellar build-up as one moves towards the more local
universe. Comparisons between the observed space density of radio-selected AGN
and that of dark matter haloes shows that about one in two haloes is associated
with a black hole in its radio-active phase. This suggests that the
radio-active phase is a recurrent phenomenon.Comment: 11 pages, 7 figures, minor changes to match published version on
MNRA
Rest-frame stacking of 2XMM catalog sources : Properties of the Fe Kalpha line
The aim of this work is to characterize the average Fe K emission properties
of active galactic nuclei (AGNs) in the source rest-frame. We selected a sample
of 248 AGNs from the 2XMM catalog, covering a wide redshift range 0 < z < 5 and
with the EPIC-PN net 2-10 keV rest-frame counts >=200 and power law photon
indices in the range 1.5-2.2. We employed two fully independent rest-frame
stacking procedures to compute the mean Fe K profile. The counting statistics
for the integrated spectrum is comparable to the one available for the best
studied local Seyferts. To identify the artifacts possibly introduced by the
stacking procedure, we have carried out simulations. We report that the average
Fe K line profile in our sample is best represented by a combination of a
narrow and a broad line. The equivalent widths of the narrow and broad
(parametrized with a diskline) components are ~30 eV and ~100 eV, respectively.
We also discuss the results of more complex fits and the implications of the
adopted continuum modeling on the broad line parameters and its detection
significance.Comment: 13 pages, 13 figures, Accepted for publication in A&
Molecular outflow and feedback in the obscured quasar XID2028 revealed by ALMA
We imaged, with ALMA and ARGOS/LUCI, the molecular gas and dust and stellar continuum in XID2028, which is an obscured quasi-stellar object (QSO) at z = 1.593, where the presence of a massive outflow in the ionised gas component traced by the [OIII]5007 emission has been resolved up to 10 kpc. This target represents a unique test case to study QSO feedback in action at the peak epoch of AGN-galaxy co-evolution. The QSO was detected in the CO(5 â 4) transition and in the 1.3 mm continuum at ~30 and ~20Ï significance, respectively; both emissions are confined in the central (<2 kpc) radius area. Our analysis suggests the presence of a fast rotating molecular disc (v ~ 400 km s^(â1)) on very compact scales well inside the galaxy extent seen in the rest-frame optical light (~10 kpc, as inferred from the LUCI data). Adding available measurements in additional two CO transitions, CO(2 â 1) and CO(3 â 2), we could derive a total gas mass of ~10^(10) Mâ, thanks to a critical assessment of CO excitation and the comparison with the RayleighâJeans continuum estimate. This translates into a very low gas fraction (<5%) and depletion timescales of 40â75 Myr, reinforcing the result of atypical gas consumption conditions in XID2028, possibly because of feedback effects on the host galaxy. Finally, we also detect the presence of high velocity CO gas at ~5Ï, which we interpret as a signature of galaxy-scale molecular outflow that is spatially coincident with the ionised gas outflow. XID2028 therefore represents a unique case in which the measurement of total outflowing mass, of ~500â800 Mâ yr^(â1) including the molecular and atomic components in both the ionised and neutral phases, was attempted for a high-z QSO
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