ABSTRACT We present Atacama Large Millimeter Array (ALMA) detections of atomic carbon line and dust continuum emission in two UV-luminous galaxies at redshift 6. The far-infrared (far-IR) ...luminosities of these galaxies are substantially lower than similar starbursts at later cosmic epochs, indicating an evolution in the dust properties with redshift, in agreement with the evolution seen in ultraviolet (UV) attenuation by dust. The C ii to FIR ratios are found to be higher than at low redshift showing that C ii should be readily detectable by ALMA within the reionization epoch. One of the two galaxies shows a complex merger nature with the less massive component dominating the UV emission and the more massive component dominating the FIR line and continuum. Using the interstellar atomic carbon line to derive the systemic redshifts we investigate the velocity of Ly emission emerging from high-z galaxies. In contrast to previous work, we find no evidence for decreasing Ly velocity shifts at high-redshift. We observe an increase in velocity shifts from to , consistent with the effects of increased intergalactic medium absorption.
Abstract
We present a reanalysis of the Event Horizon Telescope 228 GHz observations of M87. We apply traditional hybrid mapping techniques to the publicly available
network-calibrated
data. We ...explore the impact on the final image of different starting models, including the following: a point source, a disk, an annulus, a Gaussian, and an asymmetric double Gaussian. The images converge to an extended source with a size ∼44
μ
as. Starting with the annulus and disk models leads to images with the lowest noise, smallest off-source artifacts, and better closure residuals. The source appears as a ring, or edge-brightened disk, with higher surface brightness in the southern half, consistent with previous results. Starting with the other models leads to a surface brightness distribution with a similar size, and an internal depression, but not as clearly ringlike. A consideration of visibility amplitudes versus UV-distance argues for a roughly circularly symmetric structure of ∼50
μ
as scale, with a sharp edge, based on a prominent minimum in the UV-distribution, and the amplitude of the secondary peak in the UV-plot is more consistent with an annular model than a flat disk model. With further processing, we find a possible modest extension from the ring toward the southwest, in a direction consistent with the southern limb of the jet seen on 3mm VLBI images on a factor of few larger scales. However, this extension appears along the direction of one of the principle sidelobes of the synthesized beam, and hence requires testing with better UV-coverage.
Detecting neutral hydrogen (H i) via the 21 cm line emission from the intergalactic medium at z≳6 has been identified as one of the most promising probes of the epoch of cosmic reionization-a major ...phase transition of the Universe. However, these studies face severe challenges imposed by the bright foreground emission from cosmic objects. Current techniques require precise instrumental calibration to separate the weak H i line signal from the foreground continuum emission. We propose to mitigate this calibration requirement by using measurements of the interferometric bispectrum phase. The bispectrum phase is unaffected by antenna-based direction-independent calibration errors and hence for a compact array it depends on the sky brightness distribution only (subject to the usual thermal-like noise). We show that the bispectrum phase of the foreground synchrotron continuum has a characteristically smooth spectrum relative to the cosmological line signal. The two can be separated effectively by exploiting this spectral difference using Fourier techniques, while eliminating the need for precise antenna-based calibration of phases introduced by the instrument, and the ionosphere, inherent in existing approaches. Using fiducial models for continuum foregrounds, and for the cosmological H i signal, we show the latter should be detectable in bispectrum phase spectra, with reasonable significance at |k_{∥}|≳0.5h Mpc^{-1}, using existing instruments. Our approach will also benefit other H i intensity mapping experiments that face similar challenges, such as those measuring baryon acoustic oscillations (BAO).
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.
The Kinematics of z ≳ 6 Quasar Host Galaxies Neeleman, Marcel; Novak, Mladen; Venemans, Bram P. ...
The Astrophysical journal,
04/2021, Letnik:
911, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We explore the kinematics of 27
z
≳ 6 quasar host galaxies observed in C
ii
158
μ
m (C
ii
) emission with the Atacama Large Millimeter/submillimeter Array at a resolution of ≈025. We find ...that nine of the galaxies show disturbed C
ii
emission, due to either a close companion galaxy or a recent merger. Ten galaxies have smooth velocity gradients consistent with the emission arising from a gaseous disk. The remaining eight quasar host galaxies show no velocity gradient, suggesting that the gas in these systems is dispersion dominated. All galaxies show high velocity dispersions with a mean of 129 ± 10 km s
−1
. To provide an estimate of the dynamical mass within twice the half-light radius of the quasar host galaxy, we model the kinematics of the C
ii
emission line using our publicly available kinematic fitting code,
qubefit
. This results in a mean dynamical mass of 5.0 ± 0.8( ± 3.5) × 10
10
M
⊙
. Comparison between the dynamical mass and the mass of the supermassive black hole reveals that the sample falls above the locally derived bulge mass–black hole mass relation at 2.4
σ
significance. This result is robust even if we account for the large systematic uncertainties. Using several different estimators for the molecular mass, we estimate a gas mass fraction of >10%, indicating that gas makes up a large fraction of the baryonic mass of
z
≳ 6 quasar host galaxies. Finally, we speculate that the large variety in C
ii
kinematics is an indication that gas accretion onto
z
≳ 6 supermassive black holes is not caused by a single precipitating factor.
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.
ABSTRACT We present CO(1-0) observations obtained at the Karl G. Jansky Very Large Array for 14 galaxies with existing CO(3-2) measurements, including 11 galaxies that contain active galactic nuclei ...(AGNs) and three submillimeter galaxies (SMGs). We combine this sample with an additional 15 galaxies from the literature that have both CO(1-0) and CO(3-2) measurements in order to evaluate differences in CO excitation between SMGs and AGN host galaxies, to measure the effects of CO excitation on the derived molecular gas properties of these populations, and to look for correlations between the molecular gas excitation and other physical parameters. With our expanded sample of CO(3-2)/CO(1-0) line ratio measurements, we do not find a statistically significant difference in the mean line ratio between SMGs and AGN host galaxies as can be found in the literature; we instead find for AGN host galaxies and for SMGs (or for both populations combined). We also do not measure a statistically significant difference between the distributions of the line ratios for these populations at the p = 0.05 level, although this result is less robust. We find no excitation dependence on the index or offset of the integrated Schmidt-Kennicutt relation for the two CO lines, and we obtain indices consistent with N = 1 for the various subpopulations. However, including low-z "normal" galaxies increases our best-fit Schmidt-Kennicutt index to . While we do not reproduce correlations between the CO line width and luminosity, we do reproduce correlations between CO excitation and star-formation efficiency.
We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at z = 0.46-3.60, observed as part of the ALMA Spectroscopic ...Survey in the Hubble Ultra Deep Field (ASPECS). Combined with Very Large Array follow-up observations, we detect a total of 34 CO transitions with J = 1 up to 8 (and an additional 21 upper limits, up to J = 10) and 6 and transitions (and 12 upper limits). The CO(2-1) and CO(3-2)-selected galaxies, at and 2.5, respectively, exhibit a range in excitation in their mid-J = 4, 5 and high-J = 7, 8 lines, on average lower than ( -brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at . We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at z < 2 and z ≥ 2, finding and , respectively. From the models, we infer that the galaxies at z ≥ 2 have intrinsically higher excitation than those at z < 2. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of , comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities (≥104 cm−3), consistent with the low-J CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at z ≥ 2 compared to previous ASPECS measurements.
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