Physical Properties of 15 Quasars at z 6.5 Mazzucchelli, C.; Bañados, E.; Venemans, B. P. ...
The Astrophysical journal,
11/2017, Letnik:
849, Številka:
2
Journal Article
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Quasars are galaxies hosting accreting supermassive black holes; due to their brightness, they are unique probes of the early universe. To date, only a few quasars have been reported at (<800 Myr ...after the big bang). In this work, we present six additional quasars discovered using the Pan-STARRS1 survey. We use a sample of 15 quasars to perform a homogeneous and comprehensive analysis of this highest-redshift quasar population. We report four main results: (1) the majority of quasars show large blueshifts of the broad C iv λ1549 emission line compared to the systemic redshift of the quasars, with a median value ∼3× higher than a quasar sample at ; (2) we estimate the quasars' black hole masses ( (0.3-5) × 109 M ) via modeling of the Mg ii λ2798 emission line and rest-frame UV continuum and find that quasars at high redshift accrete their material (with ) at a rate comparable to a luminosity-matched sample at lower redshift, albeit with significant scatter (0.4 dex); (3) we recover no evolution of the Fe ii/Mg ii abundance ratio with cosmic time; and (4) we derive near-zone sizes and, together with measurements for quasars from recent work, confirm a shallow evolution of the decreasing quasar near-zone sizes with redshift. Finally, we present new millimeter observations of the C ii 158 m emission line and underlying dust continuum from NOEMA for four quasars and provide new accurate redshifts and C ii/infrared luminosity estimates. The analysis presented here shows the large range of properties of the most distant quasars.
ABSTRACT Luminous quasars at can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far, these studies ...have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare, and therefore, wide-field surveys are required to identify them, and multiwavelength data are required to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for the quasars presented in Bañados et al. (2014) using the Pan-STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range that satisfy our selection criteria. Of these quasars, 77 have been discovered with PS1, and 63 of them are newly identified in this paper. We present the composite spectra of the PS1 distant quasar sample. This sample spans a factor of ∼20 in luminosity and shows a variety of emission line properties. The number of quasars at presented in this work almost doubles the previously known quasars at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.
We present a multiline survey of the interstellar medium (ISM) in two
z
> 6 quasar host galaxies, PJ231−20 (
z
= 6.59) and PJ308−21 (
z
= 6.23), and their two companion galaxies. Observations were ...carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: NII
205 μm
, CI
369 μm
, CO (
J
up
= 7, 10, 15, 16), H
2
O 3
12
− 2
21
, 3
21
− 3
12
, 3
03
− 2
12
, and the OH
163 μm
doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA CII
158 μm
observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the CII
158 μm
and CI
369 μm
emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high-
J
CO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities for
J
up
≤ 7, while the
J
up
≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The
J
up
> 10 lines are undetected in the other galaxies in our study. The H
2
O 3
21
− 3
12
line detection in the same quasar places this object on the
L
H
2
O
−
L
TIR
relation found for low-
z
sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H
2
O SLED and of the H
2
O-to-OH
163 μm
ratio point to PDR contributions with high volume and column density (
n
H
∼ 0.8 × 10
5
cm
−3
,
N
H
= 10
24
cm
−2
) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.
While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting z > 6 ...quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first gigayear of the Universe from an observational point of view. We report the Chandra discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close (≈5 kpc) galaxy pair at z = 6.515. One of the members is an optically classified type-1 QSO, PSO167–13. The companion galaxy was first detected as a C II emitter by Atacama large millimeter array (ALMA). An X-ray source is significantly (P = 0.9996) detected by Chandra in the 2–5 keV band, with < 1.14 net counts in the 0.5–2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167–13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of NH > 2 × 1024 cm−2 and NH > 6 × 1023 cm−2 at 68% and 90% confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at z > 6.
We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202−0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. ...We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Ly emitters ("LAE 1" and "LAE 2"), and an additional companion discovered in this work "LAE 3" just 5″ to the north of the QSO. We find that QSO BR1202−0725 exhibits a large Ly halo, covering 55 pkpc on-sky at surface-brightness levels of SB ≥ 1 × 10−17 erg s−1 cm−2 arcsec−2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Ly halo. The QSO's halo exhibits high velocity widths (∼1000 km s−1) but the gas motion is to some extent kinematically coupled with the previously observed C ii bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Ly emission, rather, its profile is more consistent with being part of the QSO's extended Ly halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure FLy (LAE 3) = 0.24 0.03 × 10−16 erg s−1 cm−2, corresponding to SFRLy 5.0 0.5 M yr−1. The velocity width is Δv(LAE 3) 400 km s−1, and the equivalent width is EW0( , consistent with star formation being the primary driver of Ly emission. We also note a coherent absorption feature at ∼−400 km s−1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.
ABSTRACT Bright quasars, observed when the universe was less than one billion years old (z > 5.5), are known to host massive black holes (∼109 M ) and are thought to reside in the center of massive ...dark matter overdensities. In this picture, overdensities of galaxies are expected around high-redshift quasars. However, observations based on the detection of Lyman-break galaxies (LBGs) around these quasars do not offer a clear picture: this may be due to the uncertain redshift constraints of LBGs, which are solely selected through broadband filters. To circumvent such uncertainties, we here perform a search for Lyman-alpha emitting galaxies (LAEs) in the field of the quasar PSO J215.1512-16.0417 at z ∼ 5.73, through narrowband deep imaging with FORS2 at the Very Large Telescope. We study an area of 37 arcmin2, i.e., ∼206 comoving Mpc2 at the redshift of the quasar. We find no evidence of an overdensity of LAEs in the quasar field with respect to blank-field studies. Possible explanations for these findings may be that our survey volume is too small, or that the strong ionizing radiation from the quasar hinders galaxy formation in its immediate proximity. Another possibility is that these quasars are not situated in the dense environments predicted by some simulations.
Bright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old
. How these black holes formed in ...such a short time is the subject of debate, particularly as they lie above the correlation between black-hole mass and galaxy dynamical mass
in the local Universe. What slowed down black-hole growth, leading towards the symbiotic growth observed in the local Universe, and when this process started, has hitherto not been known, although black-hole feedback is a likely driver
. Here we report optical and near-infrared observations of a sample of quasars at redshifts 5.8 ≲ z ≲ 6.6. About half of the quasar spectra reveal broad, blueshifted absorption line troughs, tracing black-hole-driven winds with extreme outflow velocities, up to 17% of the speed of light. The fraction of quasars with such outflow winds at z ≳ 5.8 is ≈2.4 times higher than at z ≈ 2-4. We infer that outflows at z ≳ 5.8 inject large amounts of energy into the interstellar medium and suppress nuclear gas accretion, slowing down black-hole growth. The outflow phase may then mark the beginning of substantial black-hole feedback. The red optical colours of outflow quasars at z ≳ 5.8 indeed suggest that these systems are dusty and may be caught during an initial quenching phase of obscured accretion
.
Massive, quiescent galaxies are already observed at redshift z ∼ 4, i.e., ∼1.5 Gyr after the big bang. Current models predict them to be formed via massive, gas-rich mergers at z > 6. Recent ALMA ...observations of the cool gas and dust in z 6 quasars have discovered C ii- and far-infrared-bright galaxies adjacent to several quasars. In this work, we present sensitive imaging and spectroscopic follow-up observations, with HST/WFC3, Spitzer/IRAC, VLT/MUSE, Magellan/FIRE, and LBT/LUCI-MODS, of ALMA-detected, dust-rich companion galaxies of four quasars at z 6, specifically acquired to probe their stellar content and unobscured star formation rate. Three companion galaxies do not show significant emission in the observed optical/IR wavelength range. The photometric limits suggest that these galaxies are highly dust-enshrouded, with unobscured star formation rates SFRUV < few M yr−1, and a stellar content of M* < 1010 M yr−1. However, the companion to PJ167−13 shows bright rest-frame UV emission (F140W AB = 25.48). Its spectral energy distribution resembles that of a star-forming galaxy with a total SFR ∼ 50 M yr−1 and M* ∼ 9 × 109 M . All the companion sources are consistent with residing on the galaxy main sequence at z ∼ 6. Additional, deeper data from future facilities, such as the James Webb Space Telescope, are needed in order to characterize these gas-rich sources in the first gigayear of cosmic history.
Context.
The discovery of hundreds of quasi-stellar objects (QSOs) in the first gigayear of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH ...formation. In particular, investigations of
z
> 6 QSOs that present notable properties can provide unique information on the physics of fast SMBH growth in the early Universe.
Aims.
We present the results of follow-up observations of the
z
= 6.515 radio-quiet QSO PSO167–13, which is interacting with a close companion galaxy. The PSO167–13 system has recently been proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO.
Methods.
We observed the PSO167–13 system with
Chandra
/ACIS-S (177 ks) and obtained new spectroscopic observations (7.2 h) with
Magellan
/FIRE.
Results.
No significant X-ray emission is detected from the PSO167–13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167–13 (
L
2−10 keV
< 8.3 × 10
43
erg s
−1
) is the lowest available for a
z
> 6 QSO. The ratio between the X-ray and UV luminosity of
α
ox
< −1.95 makes PSO167–13 a strong outlier from the
α
ox
−
L
UV
and
L
X
−
L
bol
relations. In particular, its X-ray emission is more than six times weaker than the expectation based on its UV luminosity. The new
Magellan
/FIRE spectrum of PSO167–13 is strongly affected by unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted.
Conclusions.
The most plausible explanations for the X-ray weakness of PSO167–13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.
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