136 research outputs found
The galaxy environment of a QSO at z ~ 5.7
High-redshift quasars are believed to reside in massive halos in the early
universe and should therefore be located in fields with overdensities of
galaxies, which are thought to evolve into galaxy clusters seen in the local
universe. However, despite many efforts, the relationship between galaxy
overdensities and z~6 quasars is ambiguous. This can possibly be attributed to
the difficulty of finding galaxies with accurate redshifts in the vicinity of
z~6 quasars. So far, overdensity searches around z~6 quasars have been based on
studies of Lyman break galaxies (LBGs), which probe a redshift range of Delta z
~ 1. This range is large enough to select galaxies that may not be physically
related to the quasar. We use deep narrow- and broadband imaging to study the
environment of the z=5.72 quasar ULAS J0203+0012. The redshift range probed by
our narrow-band selection of Lyman alpha emitters (LAEs) is Delta z ~ 0.1,
which is significantly narrower than the LBG searches. This is the first time
that LAEs were searched for near a z~6 quasar, in an effort to provide clues
about the environments of quasars at the end of the epoch of reionization. We
find no enhancement of LAEs in the surroundings of ULAS J0203+0012 in
comparison with blank fields. We explore different explanations and
interpretations for this non-detection of a galaxy overdensity, including that
(1) the strong ionization from the quasar may prevent galaxy formation in its
immediate vicinity and (2) high-redshift quasars may not reside in the center
of the most massive dark matter halos.Comment: text updated to match published versio
400 pc Imaging of a Massive Quasar Host Galaxy at a Redshift of 6.6
We report high spatial resolution (~0.076", 410pc) Atacama Large
Millimeter/submillimeter Array imaging of the dust continuum and the ionized
carbon line [CII] in a luminous quasar host galaxy at z=6.6, 800 million years
after the big bang. Based on previous studies, this galaxy hosts a ~1x10^9
M_sun black hole and has a star-formation rate of ~1500 M_sun/yr. The
unprecedented high resolution of the observations reveals a complex morphology
of gas within 3kpc of the accreting central black hole. The gas has a high
velocity dispersion with little ordered motion along the line of sight, as
would be expected from gas accretion that has yet to settle in a disk. In
addition, we find the presence of [CII] cavities in the gas distribution (with
diameters of ~0.5kpc), offset from the central black hole. This unique
distribution and kinematics cannot be explained by a simple model. Plausible
scenarios are that the gas is located in a truncated or warped disk, or the
holes are created by interactions with nearby galaxies or due to energy
injection into the gas. In the latter case, the energy required to form the
cavities must originate from the central active galactic nucleus, as the
required energy far exceeds the energy output expected from supernovae. This
energy input into the gas, however, does not inhibit the high rate of
star-formation. Both star-formation and black hole activity could have been
triggered by interactions with satellite galaxies; our data reveal three
additional companions detected in [CII] emission around the quasar.Comment: Published in ApJ Letter
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
Spatially resolved molecular interstellar medium in a quasar host galaxy
We present high spatial resolution (0.4", 2.2kpc) observations of the
CO(6-5), CO(7-6) and [CI] lines and dust continuum emission from the
interstellar medium in the host galaxy of the quasar J03053150 at .
These, together with archival [CII] data at comparable spatial resolution,
enable studies of the spatial distribution and kinematics between the ISM in
different phases. When comparing the radial profiles of CO, [CII] and the dust
continuum, we find that the CO and dust continuum exhibit similar spatial
distributions, both of which are less extended than the [CII], indicating that
the CO and dust continuum are tracing the same gas component, while the [CII]
is tracing a more extended one. In addition, we derive the radial profiles of
the [CII]/CO, [CII]/far-infrared (FIR), CO/FIR, and dust continuum ratios. We find a decreasing ratio with radius, possibly indicating a decrease of dust optical
depth with increasing radius. We also detect some of the ISM lines and
continuum emission in the companion galaxies previously discovered in the field
around J03053150. Through comparing the line-to-line and line-to-FIR ratios,
we find no significant differences between the quasar and its companion
galaxies.Comment: 12 pages, 6 figures, accepted for publication in Ap
The CGM and IGM at z5: metal budget and physical connection
We present further results of a survey for absorption line systems in the
spectra of four high redshift quasars (5.79 z 6.13)
obtained with the ESO Very Large Telescope X-Shooter. We identify 36
and 7 systems with a 5
significance. The highest redshift and absorbers
identified in this work are at z = 5.80738 0.00017 and z = 5.77495
0.00038, respectively. We compute the comoving mass density of
() and find that it evolves from
= 4.3 10 at = 5.05
to = 1.4 10 at =
5.66. We also measure = 1.6
10 at = 4.77 and =
3.4 10 at = 5.66. We classify our
absorber population by the presence of associated
and/or systems and compute their velocity width
(v). We find that all systems with
v > 200 kms have associated
systems. We investigate two such systems, separated by 550 physical kpc along a
line of sight, and find it likely that they are both tracing a multi-phase
medium where hot and cold gas is mixing at the interface between the CGM and
IGM. We further discuss the \textrm{MgII} systems presented in a previous work
and we identify 5 , 10 , 12 , 1
, 7 and 1 associated transitions.
We compute the respective comoving mass densities in the redshift range 2 to 6,
as allowed by the wavelength coverage.Comment: Accepted for publication in MNRAS 22 pages, 19 figures, 6 table
Extinction curve template for intrinsically reddened quasars
We analyze the near-infrared to UV data of 16 quasars with redshifts ranging
from 0.71 2.13 to investigate dust extinction properties. The
sample presented in this work is obtained from the High Quasar (HAQ)
survey. The quasar candidates were selected from the Sloan Digital Sky Survey
(SDSS) and the UKIRT Infrared Deep Sky Survey (UKIDSS), and follow-up
spectroscopy was carried out at the Nordic Optical Telescope (NOT) and the New
Technology Telescope (NTT). To study dust extinction curves intrinsic to the
quasars, from the HAQ survey we selected 16 cases where the Small Magellanic
Cloud (SMC) law could not provide a good solution to the spectral energy
distributions (SEDs). We derived the extinction curves using Fitzpatrick &
Massa 1986 (FM) law by comparing the observed SEDs to the combined quasar
template from Vanden Berk et al. 2001 and Glikman et al. 2006. The derived
extinction, , ranges from 0.2-1.0 mag. All the individual extinction
curves of our quasars are steeper (-2.7) than that of the SMC, with a
weighted mean value of . We derive an `average quasar extinction
curve' for our sample by fitting SEDs simultaneously by using the weighted mean
values of the FM law parameters and a varying . The entire sample is well
fit with a single best-fit value of . The `average quasar
extinction curve' deviates from the steepest Milky Way and SMC extinction
curves at a confidence level . Such steep extinction curves
suggest a significant population of silicates to produce small dust grains.
Moreover, another possibility could be that the large dust grains may have been
destroyed by the activity of the nearby active galactic nuclei (AGN), resulting
in steep extinction curves.Comment: 8 pages, 4 figures, 1 tabl
Optical and near-IR spectroscopy of candidate red galaxies in two z~2.5 proto-clusters
We present a spectroscopic campaign to follow-up red colour-selected
candidate massive galaxies in two high redshift proto-clusters surrounding
radio galaxies. We observed a total of 57 galaxies in the field of MRC0943-242
(z=2.93) and 33 in the field of PKS1138-262 (z=2.16) with a mix of optical and
near-infrared multi-object spectroscopy.
We confirm two red galaxies in the field of PKS1138-262 at the redshift of
the radio galaxy. Based on an analysis of their spectral energy distributions,
and their derived star formation rates from the H-alpha and 24um flux, one
object belongs to the class of dust-obscured star-forming red galaxies, while
the other is evolved with little ongoing star formation. This result represents
the first red and mainly passively evolving galaxy to be confirmed as companion
galaxies in a z>2 proto-cluster. Both red galaxies in PKS1138-262 are massive,
of the order of 4-6x10^11 M_Sol. They lie along a Colour-Magnitude relation
which implies that they formed the bulk of their stellar population around z=4.
In the MRC0943-242 field we find no red galaxies at the redshift of the radio
galaxy but we do confirm the effectiveness of our JHK_s selection of galaxies
at 2.3<z<3.1, finding that 10 out of 18 (56%) of JHK_s-selected galaxies whose
redshifts could be measured fall within this redshift range. We also
serendipitously identify an interesting foreground structure of 6 galaxies at
z=2.6 in the field of MRC0943-242. This may be a proto-cluster itself, but
complicates any interpretation of the red sequence build-up in MRC0943-242
until more redshifts can be measured.Comment: 17 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
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
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