Abstract
We use Atacama Large Millimeter/submillimeter Array CO (2–1) observations of six low-redshift Palomar-Green quasars to study the distribution and kinematics of the molecular gas of their ...host galaxies at kiloparsec-scale resolution. While the molecular gas content, molecular gas fraction, and star formation rates are similar to those of nearby massive, star-forming galaxies, the quasar host galaxies possess exceptionally compact, disky molecular gas distributions with a median half-light radius of 1.8 kpc and molecular gas mass surface densities ≳22
M
⊙
pc
−2
. While the overall velocity field of the molecular gas is dominated by regular rotation out to large radii, with ratio of rotation velocity to velocity dispersion ≳9, the nuclear region displays substantial kinematic complexity associated with small-scale substructure in the gas distribution. A tilted-ring analysis reveals that the kinematic and photometric position angles are misaligned on average by ∼ 34° ± 26° and provides evidence of kinematic twisting. These observations provide tantalizing clues to the detailed physical conditions of the circumnuclear environments of actively accreting supermassive black holes.
We report Atacama Large Millimeter/submillimeter Array observations of CO(8-7), (9-8), , and and NOrthern Extended Millimeter Array observations of CO(5-4), (6-5), (12-11), and (13-12) toward the z = ...6.003 quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at z = 6.003, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature Tkin = 228 K, molecular gas density ) = 4.75, and CO column density ; although, a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies, starburst galaxies, and high-redshift submillimeter galaxies, J2310+1855 exhibits higher CO excitation at (J ≥ 8), like other high-redshift quasars. The high CO excitation, together with the enhanced , , and ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic-rays, and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.
We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and C ii 158 m fine structure line emission toward a far-infrared-luminous quasar, ULAS ...J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of ∼0 3, and resolve both the dust continuum and the C ii line emission on a few kiloparsec scales. The C ii line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the C ii-emitting gas. The combined data confirm the C ii velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the C ii velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 55 km s−1 at a radius of 3.2 kpc with an inclination angle of 34°. We measure the dynamical mass within the 3.2 kpc region to be . This yields a black-hole and host galaxy mass ratio of , which is about times higher than that of the present-day / ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.
We present Karl G. Jansky Very Large Array observations of the CO (2−1) line emission toward three far-infrared luminous quasars at z ∼ 6: SDSS J231038.88+185519.7 and SDSS J012958.51−003539.7 with ...∼0 6 resolution and SDSS J205406.42−000514.8 with ∼2 1 resolution. All three sources are detected in the CO (2−1) line emission-one source is marginally resolved, and the other two appear as point sources. Measurements of the CO (2−1) line emission allow us to calculate the molecular gas mass even without a CO excitation model. The inferred molecular gas masses are (0.8-4.3) × 1010 M . The widths and redshifts derived from the CO (2−1) line are consistent with previous CO (6−5) and C ii measurements. We also report continuum measurements using Herschel for SDSS J231038.88+185519.7 and SDSS J012958.51−003539.7, and for SDSS J231038.88+185519.7 data obtained at ∼140 and ∼300 GHz using the Atacama Large Millimeter/submillimeter Array. In the case of SDSS J231038.88+185519.7, we present a detailed analysis of the spectral energy distribution and derive the dust temperature (∼40 K), the dust mass (∼109 M ), the far-infrared luminosity (8-1000 m; ∼1013 L ), and the star formation rate (2400-2700 M yr−1). Finally, an analysis of the photodissociation regions associated with the three high-redshift quasars indicates that the interstellar medium in these sources has similar properties to local starburst galaxies.
Observing the interstellar medium (ISM) in the z 6 quasar host galaxies is essential for understanding the coevolution between supermassive black holes and their hosts. To probe the gas physical ...conditions and search for imprints of active galactic nuclei (AGNs) on the ISM, we report ALMA observations of the N ii122 m and O i146 m lines and the underlying continuum from the z = 6.003 quasar SDSS J231038.88+185519.7. Together with previous C ii158 m and O iii88 m observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-z systems, this object exhibits a C ii158 m/O i146 m ratio comparable to the lowest values found in local (ultra)luminous infrared galaxies, suggesting a "warmer" and "denser" gas component compared to typical local systems. The O iii88 m/O i146 m ratio is lower than that of other local and high-z systems, indicating a smaller ionized gas fraction in this quasar. The O iii88 m/N ii122 m ratio is comparable to that of local systems and suggests a metallicity of Z/Z = 1.5-2.1. Based on the N ii122 m detection, we estimate that 17% of the C ii158 m emission is associated with ionized gas. The N ii122 m line shows a "flux deficit" comparable to local systems. The O i146 m line, with an O i146 m/FIR ratio >2× than expected from the local relation, indicates no O i146 m deficit. The low C ii158 m/O i146 m ratio, together with the high O i146 m/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating of the ISM.
The 1931 MW7.8 Fuyun earthquake occurred around the Altai mountains, an intracontinental deformation belt with limited active strain-rate accumulation. To explore whether seismic activity in this ...deformation belt was affected by stress interaction among different active faults, we calculate the Coulomb failure stress change (ΔCFS) induced by the Fuyun earthquake due to coseismic deformation of the elastic crust and postseismic viscoelastic relaxation of the lower crust and upper mantle. Numerical results show that the total ΔCFS at a 10-km depth produced by the Fuyun earthquake attains approximately 0.015–0.134 bar near the epicenter, and just before the occurrence of the 2003 MW7.2 Chuya earthquake, which distances about 400 km away from the Fuyun earthquake. Among the increased ΔCFS, viscoelastic relaxation from 1931 to 2003 contributes to approximately 0.014–0.131 bar, accounting for >90% of the total ΔCFS. More importantly, we find that for the recorded seismicity in the region with a radius of about 270 km to the Fuyun earthquake from 1970 to 2018, the percentage of earthquakes that fall in positive lobes of ΔCFS resolved on the NNW-SSE Fuyun strike-slip fault, on the NWW-SEE Irtysh strike-slip fault, and on the NW-SE Kurti reverse fault is up to 67.22%–91.36%. Therefore, the predicted ΔCFS suggests that the impact of the 1931 MW7.8 Fuyun earthquake on seismic activity around the Altai mountains is still significant as to hasten occurrence of the 2003 MW7.2 Chuya earthquake at a relatively far distance and to trigger its aftershocks in the near-field even after several decades of the mainshock.
Abstract
The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a ...submillimeter wavelength continuum survey of 54
z
∼ 6 quasars using the Submillimeter Common-User Bolometre Array-2 on the James Clerk Maxwell Telescope to study the environments around
z
∼ 6 quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5
σ
detections in 450 or 850
μ
m maps. Their far-IR luminosities are (2.2–6.4) × 10
12
L
⊙
, and their star formation rates are ∼400–1200
M
⊙
yr
−1
. We also calculated the SMGs’ differential and cumulative number counts in a combined area of ∼620 arcmin
2
. To a 4
σ
detection (at ∼5.5 mJy), SMGs’ overdensity is
0.68
−
0.19
+
0.21
(±0.19), exceeding the blank-field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at ∼5.5 mJy) of
δ
SMG
∼ 1.5–5.4. The combined area of these 13 quasars exceeds the blank-field counts with the overdensity to 5.5 mJy of
δ
SMG
∼
2.46
−
0.55
+
0.64
(±0.25) in the regions of ∼150 arcmin
2
. However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Ly
α
emitters and Lyman break galaxies on a similar scale. Our survey presents the first systematic study of the environment of quasars at
z
∼ 6. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch.
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.
The carrier multiplication phenomenon involves hot carriers, which gain kinetic energy while accelerating to equilibrium with the established avalanching electric fields, and is typically explained ...via the local avalanche model. This work presents two vertical Ge-on-Si avalanche photodetectors fabricated in a separate absorption, charge, and multiplication configuration. Uniformity in materials, doping densities, and device dimensions is maintained, except for the multiplication width, which is used as a control parameter to manipulate avalanching fields under identical electric biasing and illumination schemes. Nonlocal carrier multiplication model is implemented during analysis of the extracted current-voltage signatures under small and large reverse biasing arrangements. For such an APD characterized by thinner multiplication region ( W m = 0.1 μm), reduced linear and Geiger-mode multiplication regimes are perceived to be at play, outperforming the device having thicker multiplication region in almost all related figures of merit, e.g ., responsivity (22.58 A/W), photo-to-dark current ratio (~10 5 ), normalized photo-to-dark current ratio (2.5×10 9 W −1 ), specific detectivity (7.45×10 12 Jones), and noise equivalent power (~2.42×10 −15 W/√Hz). The enhanced performance characteristics are due to excessively strong avalanching fields, reduced thermal charge density, and negligible dead space compared to its counterpart characterized by thicker multiplication width.
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