Abstract
Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The ...number of astronomical objects identified at
z
> 6 has increased dramatically over the last few years, but previously only three radio-loud (
R
2500
=
f
ν
,5 GHz
/
f
ν
,2500 Å
> 10) sources had been reported at
z
> 6, with the most distant being a quasar at
z
= 6.18. Here we present the discovery and characterization of PSO J172.3556+18.7734, a radio-loud quasar at
z
= 6.823. This source has an Mg
ii
-based black hole mass of ∼3 × 10
8
M
⊙
and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the
z
≳ 6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasar’s radio spectrum between 1.4 and 3.0 GHz is steep (
α
= −1.31). Assuming the measured radio slope and extrapolating to rest-frame 5 GHz, the quasar has a radio-loudness parameter
R
2500
∼ 90. A second steep radio source (
α
= −0.83) of comparable brightness to the quasar is only 23.″1 away (∼120 kpc at
z
= 6.82; projection probability <2%), but shows no optical or near-infrared counterpart. Further follow-up is required to establish whether these two sources are physically associated.
Abstract
The identification of bright quasars at
z
≳ 6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within ...the first billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6 <
z
< 6.5 and UV magnitudes −24.5 <
M
1450
< −28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have independently been discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, 10 broad absorption line quasars, and 5 objects with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate at
z
= 6.23, a likely gravitationally lensed quasar at
z
= 6.41, and a
z
= 5.84 quasar in the outskirts of the nearby (
D
∼ 3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the C
ii
and underlying emission, implying a star formation rate <30–70
M
⊙
yr
−1
. A significant fraction of the quasars presented here lies at the foundation of the first measurement of the
z
∼ 6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). These quasars will enable further studies of the high-redshift quasar population with current and future facilities.
Abstract We present observations using the Northern Extended Millimetre Array (NOEMA) of CO and H 2 O emission lines and the underlying dust continuum in two quasars at z ∼ 6, i.e., P215−16 at z = ...5.78 and J1429+5447 at z = 6.18. Notably, among all published CO spectral line energy distributions (SLEDs) of quasars at z ∼ 6, the two systems reveal the highest and the lowest CO levels of excitation, respectively. Our radiative transfer modeling of the CO SLED of P215−16 suggests that the molecular gas heated by active galactic nuclei could be a plausible origin for the high CO excitation. For J1429+5447, we obtain the first well-sampled CO SLED (from transitions from 2−1 to 10−9) of a radio-loud quasar at z ≳ 6. Analysis of the CO SLED suggests that a component from a single photodissociation region could explain the CO excitation in the radio-loud quasar J1429+5447. This work highlights the utility of the CO SLED in uncovering the properties of the interstellar medium in these young quasar–starburst systems at the highest redshift. The diversity of the CO SLEDs reveals the complexities in gas conditions and excitation mechanisms at their early evolutionary stage.
We report new Northern Extended Millimeter Array observations of the C ii158 μm, N ii205 μm, and O i146 μm atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a z = 6.42 ...quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged C ii158 μm and dust continuum emission have similar extensions (up to $\theta ={2.51}_{-0.25}^{+0.46}\ \mathrm{arcsec}$, corresponding to $r={9.8}_{-2.1}^{+3.3}\ \mathrm{kpc}$, accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest C ii158 μm-emitting reservoir known at these epochs. Moreover, if the C ii158 μm emission is examined only along its NE–SW axis, a significant excess (>5.8σ) of C ii158 μm emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad C ii158 μm line wings that were reported in previous studies. We also report the first detection of the O i146 μm and (tentatively) N ii205 μm emission lines in J1148+5251. Using FSL ratios of the C ii158 μm, N ii205 μm, O i146 μm, and previously measured C i369 μm emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (103.5–4.5 G0), a high gas density (n ≃ 103.5–4.5 cm−3), and an H i column density of 1023 cm−2 reproduce the observed FSL ratios well.
Molecular gas in z ∼ 6 quasar host galaxies Decarli, Roberto; Pensabene, Antonio; Venemans, Bram ...
Astronomy and astrophysics (Berlin),
06/2022, Letnik:
662
Journal Article
Recenzirano
Odprti dostop
We investigate the molecular gas content of
z
∼ 6 quasar host galaxies using the Institut de Radioastronomie Millimétrique Northern Extended Millimeter Array. We targeted the 3 mm dust continuum, ...and the line emission from CO(6–5), CO(7–6), and C
I
2−1
in ten infrared–luminous quasars that have been previously studied in their 1 mm dust continuum and C
II
line emission. We detected CO(7–6) at various degrees of significance in all the targeted sources, thus doubling the number of such detections in
z
∼ 6 quasars. The 3 mm to 1 mm flux density ratios are consistent with a modified black body spectrum with a dust temperature
T
dust
∼ 47 K and an optical depth
τ
ν
= 0.2 at the C
II
frequency. Our study provides us with four independent ways to estimate the molecular gas mass,
M
H2
, in the targeted quasars. This allows us to set constraints on various parameters used in the derivation of molecular gas mass estimates, such as the mass per luminosity ratios
α
CO
and
α
CII
, the gas-to-dust mass ratio
δ
g/d
, and the carbon abundance C/H
2
. Leveraging either on the dust, CO, C
I
, or C
II
emission yields mass estimates of the entire sample in the range
M
H2
∼ 10
10
–10
11
M
⊙
. We compared the observed luminosities of dust, C
II
, C
I
, and CO(7–6) with predictions from photo-dissociation and X-ray dominated regions. We find that the former provide better model fits to our data, assuming that the bulk of the emission arises from dense (
n
H
> 10
4
cm
−3
) clouds with a column density
N
H
∼ 10
23
cm
−2
, exposed to a radiation field with an intensity of
G
0
∼ 10
3
(in Habing units). Our analysis reiterates the presence of massive reservoirs of molecular gas fueling star formation and nuclear accretion in
z
∼ 6 quasar host galaxies. It also highlights the power of combined 3 mm and 1 mm observations for quantitative studies of the dense gas content in massive galaxies at cosmic dawn.
Characterizing the physical conditions (density, temperature, ionization state, metallicity, etc) of the interstellar medium is critical to improving our understanding of the formation and evolution ...of galaxies. In this work, we present a multi-line study of the interstellar medium in the host galaxy of a quasar at
z
≈ 6.4, that is, when the universe was 840 Myr old. This galaxy is one of the most active and massive objects emerging from the dark ages and therefore represents a benchmark for models of the early formation of massive galaxies. We used the Atacama Large Millimeter Array to target an ensemble of tracers of ionized, neutral, and molecular gas, namely the following fine-structure lines: O
III
88 μm, N
II
122 μm, C
II
158 μm, and C
I
370 μm – as well as the rotational transitions of CO(7–6), CO(15–14), CO(16–15), and CO(19–18); OH 163.1 μm and 163.4 μm; along with H
2
O 3(0,3)–2(1,2), 3(3,1)–4(0,4), 3(3,1)–3(2,2), 4(0,4)–3(1,3), and 4(3,2)–4(2,3). All the targeted fine-structure lines were detected, along with half of the targeted molecular transitions. By combining the associated line luminosities with the constraints on the dust temperature from the underlying continuum emission and predictions from photoionization models of the interstellar medium, we find that the ionized phase accounts for about one-third of the total gaseous mass budget and is responsible for half of the total C
II
emission. This phase is characterized by a high density (
n
∼ 180 cm
−3
) that typical of HII regions. The spectral energy distribution of the photoionizing radiation is comparable to that emitted by B-type stars. Star formation also appears to be driving the excitation of the molecular medium. We find marginal evidence for outflow-related shocks in the dense molecular phase, but not in other gas phases. This study showcases the power of multi-line investigations in unveiling the properties of the star-forming medium in galaxies at cosmic dawn.
We present the discovery of PSO J083.8371+11.8482, a weak emission line quasar with extreme star formation rate at z = 6.3401. This quasar was selected from Pan-STARRS1, UHS, and unWISE photometric ...data. Gemini/GNIRS spectroscopy follow-up indicates a Mg ii-based black hole mass of M and an Eddington ratio of , in line with an actively accreting supermassive black hole (SMBH) at z 6. Hubble Space Telescope imaging sets strong constraint on lens boosting, showing no relevant effect on the apparent emission. The quasar is also observed as a pure point source with no additional emission component. The broad-line region (BLR) emission is intrinsically weak and not likely caused by an intervening absorber. We found rest-frame equivalent widths of EW , EW (3 upper limit), and EW . A small proximity zone size ( pMpc) indicates a lifetime of only years from the last quasar phase ignition. ALMA shows extended C ii emission with a mild velocity gradient. The inferred far-infrared luminosity ( ) is one of the highest among all known quasar hosts at z 6. Dust and C ii emissions put a constraint on the star formation rate of SFR = 900- , similar to that of a hyperluminous infrared galaxy. Considering the observed quasar lifetime and BLR formation timescale, the weak-line profile in the quasar spectrum is most likely caused by a BLR that is not yet fully formed rather than by continuum boosting by gravitational lensing or a soft continuum due to super-Eddington accretion.
We present JWST/NIRSpec integral field spectroscopy in the rest-frame optical bands of the system PJ308--21, a quasar at $z=6.2342$ caught as its host galaxy interacts with companion galaxies. We ...detect the spatially extended emission of several emission lines ( and ), which we used to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detected continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with photoionization conditions typical of an Active Galactic Nucleus, the western companion shows minimal dust extinction, low metallicity ($Z and star formation driven photoionization. The eastern companion shows higher extinction and metallicity ($Z compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive dyn it is still rapidly building up by accreting two relatively massive star companion sources. This dataset showcases the power of JWST in exposing the buildup of massive galaxies in the first gigayear of the Universe.
Abstract
We report new Northern Extended Millimeter Array observations of the C
ii
158
μ
m
, N
ii
205
μ
m
, and O
i
146
μ
m
atomic fine structure lines (FSLs) and dust continuum emission of ...J1148+5251, a
z
= 6.42 quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged C
ii
158
μ
m
and dust continuum emission have similar extensions (up to
θ
=
2.51
−
0.25
+
0.46
arcsec
, corresponding to
r
=
9.8
−
2.1
+
3.3
kpc
, accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest C
ii
158
μ
m
-emitting reservoir known at these epochs. Moreover, if the C
ii
158
μ
m
emission is examined only along its NE–SW axis, a significant excess (>5.8
σ
) of C
ii
158
μ
m
emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad C
ii
158
μ
m
line wings that were reported in previous studies. We also report the first detection of the O
i
146
μ
m
and (tentatively) N
ii
205
μ
m
emission lines in J1148+5251. Using FSL ratios of the C
ii
158
μ
m
, N
ii
205
μ
m
, O
i
146
μ
m
, and previously measured C
i
369
μ
m
emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (10
3.5–4.5
G
0
), a high gas density (
n
≃ 10
3.5–4.5
cm
−3
), and an H
i
column density of 10
23
cm
−2
reproduce the observed FSL ratios well.
We report new Northern Extended Millimeter Array observations of the C II158 μm, N II205 μm, and O I146 μm atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a z = 6.42 ...quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged C II158 μm and dust continuum emission have similar extensions (up to $\theta ={2.51}_{-0.25}^{+0.46}\ \mathrm{arcsec}$ , corresponding to $r={9.8}_{-2.1}^{+3.3}\ \mathrm{kpc}$ , accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest C II158 μm-emitting reservoir known at these epochs. Moreover, if the C II158 μm emission is examined only along its NE-SW axis, a significant excess (>5.8σ) of C II158 μm emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad C II158 μm line wings that were reported in previous studies. We also report the first detection of the O I146 μm and (tentatively) N II205 μm emission lines in J1148+5251. Using FSL ratios of the C II158 μm, N II205 μm, O I146 μm, and previously measured C I369 μm emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (103.5-4.5 G 0), a high gas density (n ≃ 103.5-4.5 cm-3), and an H I column density of 1023 cm-2 reproduce the observed FSL ratios well.
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