45 research outputs found
An X-ray/SDSS sample (II): outflowing gas plasma properties
Galaxy-scale outflows are nowadays observed in many active galactic nuclei
(AGNs); however, their characterisation in terms of (multi-) phase nature,
amount of flowing material, effects on the host galaxy, is still unsettled. In
particular, ionized gas mass outflow rate and related energetics are still
affected by many sources of uncertainties. In this respect, outflowing gas
plasma conditions, being largely unknown, play a crucial role.
Taking advantage of the spectroscopic analysis results we obtained studying
the X-ray/SDSS sample of 563 AGNs at z presented in our companion paper,
we analyse stacked spectra and sub-samples of sources with high signal-to-noise
temperature- and density-sensitive emission lines to derive the plasma
properties of the outflowing ionized gas component. For these sources, we also
study in detail various diagnostic diagrams to infer information about
outflowing gas ionization mechanisms. We derive, for the first time, median
values for electron temperature and density of outflowing gas from medium-size
samples ( targets) and stacked spectra of AGNs. Evidences of shock
excitation are found for outflowing gas.
We measure electron temperatures of the order of K and
densities of cm for faint and moderately luminous AGNs
(intrinsic X-ray luminosity in the 2-10 keV band). We
caution that the usually assumed electron density ( cm) in
ejected material might result in relevant overestimates of flow mass rates and
energetics and, as a consequence, of the effects of AGN-driven outflows on the
host galaxy.Comment: 16 pages, 10 figures. Accepted for publication in A&
An X-ray/SDSS sample. I. Multi-phase outflow incidence and dependence on AGN luminosity
Aims: The connection between the growth of super-massive black holes (SMBHs) and the evolution of their host galaxies is nowadays well established, although the underlying mechanisms explaining their mutual relations are still debated. Multi-phase fast, massive outflows have been postulated to play a crucial role in this process. The aim of this work is to constrain the nature and the fraction of outflowing gas in active galactic nuclei (AGNs) as well as the nuclear conditions possibly at the origin of such phenomena. Methods: We present a large spectroscopic sample of X-ray detected SDSS AGNs at z Results: We derive the incidence of ionized ( 40%) and atomic (42 to 1046 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained by studying high-z QSOs. Conclusions: We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (MBH), [O III], and X-ray luminosity. We show a well-defined positive trend between outflow velocity and LX, for the first time, over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at MBH> 108M☉ the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionized phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: first, an initial stage characterized by X-ray/optical obscured AGNs, in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components and, second, a later stage associated with unobscured AGNs, in which the line of sight has been cleaned and the cold components have been heated or exhausted
X-ray redshifts for obscured AGN: a case study in the J1030 deep field
We present a procedure to constrain the redshifts of obscured ( cm) Active Galactic Nuclei (AGN) based on low-count statistics
X-ray spectra, which can be adopted when photometric and/or spectroscopic
redshifts are unavailable or difficult to obtain. We selected a sample of 54
obscured AGN candidates on the basis of their X-ray hardness ratio, ,
in the Chandra deep field (479 ks, 335 arcmin) around the QSO
SDSS J1030+0524. The sample has a median value of net counts in the
0.5-7 keV energy band. We estimate reliable X-ray redshift solutions taking
advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV
K emission line, the 7.1 keV Fe absorption edge and the
photoelectric absorption cut-off. The significance of such features is
investigated through spectral simulations, and the derived X-ray redshift
solutions are then compared with photometric redshifts. Both photometric and
X-ray redshifts are derived for 33 sources. When multiple solutions are derived
by any method, we find that combining the redshift solutions of the two
techniques improves the rms by a factor of two. Using our redshift estimates
(), we derived absorbing column densities in the
range cm and absorption-corrected, 2-10 keV
rest-frame luminosities between and erg s, with
median values of cm and erg s, respectively. Our results suggest that
the adopted procedure can be applied to current and future X-ray surveys, for
sources detected only in the X-rays or that have uncertain photometric or
single-line spectroscopic redshifts.Comment: 22 pages, 18 figure
Testing the paradigm: First spectroscopic evidence of a quasar-galaxy Mpc-scale association at cosmic dawn
State-of-the-art models of massive black hole formation postulate that quasars at z > 6 reside in extreme peaks of the cosmic density structure in the early universe. Even so, direct observational evidence of these overdensities is elusive, especially on large scales ( 6b1 Mpc) as the spectroscopic follow-up of z > 6 galaxies is observationally expensive. Here we present Keck/DEIMOS optical and IRAM/NOEMA millimeter spectroscopy of a z \u303 6 Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous z = 6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a z > 6 quasar. The Keck observations suggest a z \u303 6.3 dropout identification of the galaxy. The NOEMA 1.2 mm spectrum shows a 3.5\u3c3 line that, if interpreted as [C II], would place the galaxy at z = 6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured [C II] luminosity is 3
7 108 L&09, in line with expectations for a galaxy with a star formation rate \u30315 M&09 yr-1, as inferred from the rest-frame UV photometry. Our combined observations place the galaxy at the same redshift as the quasar, thus strengthening the overdensity scenario for this z > 6 quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasar
The web of the Giant: spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524
We report on the spectroscopic confirmation of a large scale structure around
the luminous, z=6.31 QSO SDSS~J1030+0524, that is powered by a billion solar
mass black hole. The structure is populated by at least six members, four Lyman
Break Galaxies (LBGs) and two Lyman Alpha Emitters (LAEs). The four LBGs have
been identified among a sample of 21 i-band dropouts with z{AB}<25.5 selected
up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their
redshifts have been determined through up to 8hr-long multi-object
spectroscopic observations at 8-10m class telescopes. The two LAEs have been
identified in a 6hr VLT/MUSE observation centered on the QSO. The redshifts of
the six galaxies cover the range 6.129-6.355. Assuming that peculiar velocities
are negligible, this range corresponds to radial separations of +/-5 physical
Mpc from the QSO, that is comparable to the projected scale of the observed LBG
distribution on the sky. We conservatively estimate that this structure is
significant at >3.5 sigma level, and that the level of the galaxy overdensity
is at least 1.5-2 within the large volume sampled (~780 physical Mpc^3). The
spectral properties of the six member galaxies (Lyalpha strength and UV
luminosity) are similar to those of field galaxies at similar redshifts. This
is the first spectroscopic identification of a galaxy overdensity around a
super-massive black hole in the first billion years of the Universe. Our
finding lends support to the idea that the most distant and massive black holes
form and grow within massive (>10^{12} Msun) dark matter halos in large scale
structures, and that the absence of earlier detections of such systems was
likely due to observational limitations.Comment: 8 pages including Appendix, 5 figures, accepted as a letter on
Astronomy & Astrophysics. v2: minor changes in Table 1 caption and Figs. 2 &
3 label
X-ray properties and obscured fraction of AGN in the J1030 Chandra field
The 500ks Chandra ACIS-I observation of the field around the quasar
SDSS J1030+0524 is currently the 5th deepest extragalactic X-ray survey. The
rich multi-band coverage of the field allowed for an effective identification
and redshift determination of the X-ray source counterparts: to date a catalog
of 243 extragalactic X-ray sources with either a spectroscopic or photometric
redshift estimate in the range is available over a 355 arcmin
area. Given its depth and the multi-band information, this catalog is an
excellent resource to investigate X-ray spectral properties of distant Active
Galactic Nuclei (AGN) and derive the redshift evolution of their obscuration.
We performed a thorough X-ray spectral analysis for each object in the sample,
measuring its nuclear column density and intrinsic (de-absorbed)
2-10 keV rest-frame luminosity, . Whenever possible, we also used the
presence of the Fe K emission line to improve the photometric redshift
estimates. We measured the fractions of AGN hidden by column densities in
excess of and cm ( and ,
respectively) as a function of and redshift, and corrected for
selection effects to recover the intrinsic obscured fractions. At ,
we found and , respectively, in broad
agreement with the results from other X-ray surveys. No significant variations
with X-ray luminosity were found within the limited luminosity range probed by
our sample (log). When focusing on luminous AGN with
log to maximize the sample completeness up to large
cosmological distances, we did not observe any significant change in
or over the redshift range . Nonetheless, the obscured
fractions we measure are significantly higher than ...Comment: A&A, in pres
LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z2.8 large scale structure
We present the results of a spectroscopic campaign with the Multi-Object
Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope
(LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030
sources with a photometric redshift >=2.7 and optical magnitude
r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven
targets: all of them have z_spec>=2.5, thus probing the reliability of the
Chandra J1030 photometric redshifts. The spectroscopic campaign led to the
serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030
field: the structure contains four X-ray sources (three of which were targeted
in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a
VLT-MUSE spectrum was already available. The X-ray members of the LSS are
hosted in galaxies that are significantly more massive
(log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources
(log(M_*/M_sun)<10). Both observations and simulations show that massive
galaxies, and particularly objects having log(M_*/M_sun)>10, are among the best
tracers of large scale structures and filaments in the cosmic web.
Consequently, our result can explain why X-ray-detected AGN have also been
shown to be efficient tracers of large scale structures.Comment: 16 pages, 9 Figures. Accepted for publication in Astronomy and
Astrophysic