113 research outputs found
The Physical Properties and Cosmic Environments of Quasars in the First Gyr of the Universe
Luminous quasars at redshift z >6, i.e. <1 Gyr after the Big Bang, are formidable probes of
the early universe, at the edge of the Epoch of Reionization. These sources are predicted
to be found in high–density peaks of the dark matter distribution at that time, surrounded
by overdensities of galaxies. In this thesis, we present a search for and study of the most
distant quasars, from the properties of their innermost regions, to those of their host galaxies
and of their Mpc–scale environments. We search for the highest redshift quasars in the
Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1, PS1), discovering
six new objects at z >6.5. Using optical/near–infrared spectroscopic data, we perform a homogeneous
analysis of the properties of 15 quasars at z> 6.5. In short : 1) The majority of z >6.5
show large blueshifts of the broad CIV 1549 Ã… emission line, suggesting the presence of strong
winds/outflows; 2) They already host supermassive black holes (M_BH = 0.3 - 5 x 10^9 M_sun) in their
centers, which are accreting at a rate comparable to a luminosity–matched sample at z =1-3)
No evolution of the Fe II/MgII abundance ratio with cosmic time is observed; 4) The sizes of
their surrounding ionized bubbles weakly decrease with redshift. We present new millimeter
observations of the dust continuum and of the [CII] 158 mm emission line (one of the main
coolant of the intergalactic medium) in the host galaxies of four quasars, providing new accurate
redshifts and [CII]/infrared luminosities. We study the Mpc–scale environment of a z =5.7
quasar, via observations with broad– and narrow–band filters. We recover no overdensities
of galaxies. Among the potential explanations for these findings, are that the ionizing radiation
from the quasar prevents galaxy formation, the sources in the fields are dust–obscured,
or quasars do not live in the most massive dark matter halos. Finally, we report sensitive
optical/near–infrared follow–up observations of gas–rich companion galaxies to four quasars
at z >6, firstly detected with the Atacama Large Millimeter Array (ALMA).With the exception
of one source, we detect no emission from the stellar population of these galaxies. Our limits on
their stellar masses (< 10^10 M_sun) and unobscured star formation rates (<few M_sun yr^1) suggest
that the companions are highly dust obscured and/or harboring a modest stellar content. In
synthesis, in this thesis we show the large range of parameters of the most distant quasars, and
the variety of their environments, with the aim of shading light on massive galaxy and black
hole formation in the first Gyr of the universe
A powerful radio-loud quasar at the end of cosmic reionization
We present the discovery of the radio-loud quasar PSO J352.4034-15.3373 at
z=5.84 pm 0.02. This quasar is the radio brightest source known, by an order of
magnitude, at z~6 with a flux density in the range of 8-100 mJy from 3GHz to
230MHz and a radio loudness parameter R>~1000. This source provides an
unprecedented opportunity to study powerful jets and radio-mode feedback at the
highest redshifts, and presents the first real chance to probe deep into the
neutral intergalactic medium by detecting 21 cm absorption at the end of cosmic
reionization.Comment: ApJL accepted on May 8, 2018. See the companion paper by Momjian et
a
Mapping the Lyman-Alpha Emission Around a z~6.6 QSO with MUSE: Extended Emission and a Companion at Close Separation
We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large
Telescope (VLT) to search for extended Lyman-Alpha emission around the z~6.6
QSO J0305-3150. After carefully subtracting the point-spread-function, we reach
a nominal 5-sigma surface brightness limit of SB = 1.9x10
erg/s/cm/arcsec over a 1 arcsec aperture, collapsing 5 wavelength
slices centered at the expected location of the redshifted Lyman-Alpha emission
(i.e. at 9256 Ang.). Current data suggest the presence (5-sigma, accounting for
systematics) of a Lyman-Alpha nebula that extends for 9 kpc around the QSO.
This emission is displaced and redshifted by 155 km/s with respect to the
location of the QSO host galaxy traced by the [CII] emission line. The total
luminosity is L = 3.0x10 erg/s. Our analysis suggests that this emission
is unlikely to rise from optically thick clouds illuminated by the ionizing
radiation of the QSO. It is more plausible that the Lyman-Alpha emission is due
to fluorescence of the highly ionized optically thin gas. This scenario implies
a high hydrogen volume density of n ~ 6 cm. In addition, we detect a
Lyman-Alpha emitter (LAE) in the immediate vicinity of the QSO: i.e., with a
projected separation of 12.5 kpc and a line-of-sight velocity difference of 560
km/s. The luminosity of the LAE is L = 2.1x10 erg/s and its inferred
star-formation-rate is SFR ~ 1.3 M/yr. The probability of finding such
a close LAE is one order of magnitude above the expectations based on the
QSO-galaxy cross-correlation function. This discovery is in agreement with a
scenario where dissipative interactions favour the rapid build-up of
super-massive black holes at early Cosmic times.Comment: 17 pages, 15 figures. Accepted for publication in Ap
Copious Amounts of Dust and Gas in a z=7.5 Quasar Host Galaxy
We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at
z=7.54 and report detections of copious amounts of dust and [CII] emission in
the interstellar medium (ISM) of its host galaxy. At this redshift, the age of
the universe is 690 Myr, about 10% younger than the redshift of the previous
quasar record holder. Yet, the ISM of this new quasar host galaxy is
significantly enriched by metals, as evidenced by the detection of the [CII]
158micron cooling line and the underlying far-infrared (FIR) dust continuum
emission. To the first order, the FIR properties of this quasar host are
similar to those found at a slightly lower redshift (z~6), making this source
by far the FIR-brightest galaxy known at z>7.5. The [CII] emission is spatially
unresolved, with an upper limit on the diameter of 7 kpc. Together with the
measured FWHM of the [CII] line, this yields a dynamical mass of the host of
<1.5x10^11 M_sun. Using standard assumptions about the dust temperature and
emissivity, the NOEMA measurements give a dust mass of (0.6-4.3)x10^8 M_sun.
The brightness of the [CII] luminosity, together with the high dust mass, imply
active ongoing star formation in the quasar host. Using [CII]-SFR scaling
relations, we derive star formation rates of 85-545 M_sun/yr in the host,
consistent with the values derived from the dust continuum. Indeed, an episode
of such past high star formation is needed to explain the presence of ~10^8
M_sun of dust implied by the observations.Comment: 8 pages, 4 figures. Published in ApJ Letter
A metal-poor damped Ly-alpha system at redshift 6.4
We identify a strong Ly-alpha damping wing profile in the spectrum of the
quasar P183+05 at z=6.4386. Given the detection of several narrow metal
absorption lines at z=6.40392, the most likely explanation for the absorption
profile is that it is due to a damped Ly-alpha system. However, in order to
match the data a contribution of an intergalactic medium 5-38% neutral or
additional weaker absorbers near the quasar is also required. The absorption
system presented here is the most distant damped Ly-alpha system currently
known. We estimate an HI column density (cm),
metallicity ([O/H]), and relative chemical abundances of a
system consistent with a low-mass galaxy during the first Gyr of the universe.
This object is among the most metal-poor damped Ly-alpha systems known and,
even though it is observed only ~850 Myr after the big bang, its relative
abundances do not show signatures of chemical enrichment by Population III
stars.Comment: Updated to match published versio
Ly Halos Around Quasars
We present deep MUSE observations of five quasars within the first Gyr of the
Universe (), four of which display extended Ly halos. After
PSF-subtraction, we reveal halos surrounding two quasars for the first time, as
well as confirming the presence of two more halos for which tentative
detections exist in long-slit spectroscopic observations and narrow-band
imaging. The four Ly halos presented here are diverse in morphology and
size, they each display spatial asymmetry, and none are centred on the position
of the quasar. Spectra of the diffuse halos demonstrate that none are
dramatically offset in velocity from the systemic redshift of the quasars
( v kms), however each halo shows a broad Ly
line, with a velocity width of order kms. Total Ly
luminosities range between erg s and erg s, reaching maximum radial extents of pkpc
from the quasar positions. We find larger sizes and higher Ly
luminosities than previous literature results at this redshift, but find no
correlation between the quasar properties and the Ly halo, suggesting
that the detected emission is most closely related to the physical properties
of the circum-galactic mediumComment: 19 pages, Accepted for publication in Ap
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