We present a study of the C ii 158 m line and underlying far-infrared (FIR) continuum emission of 27 quasar host galaxies at z ∼ 6, traced by the Atacama Large Millimeter/submillimeter Array at a ...spatial resolution of ∼1 physical kpc. The C ii emission in the bright, central regions of the quasars have sizes of 1.0-4.8 kpc. The dust continuum emission is typically more compact than C ii. We find that 13/27 quasars (approximately one-half) have companion galaxies in the field, at projected separations of 3-90 kpc. The position of dust emission and the Gaia-corrected positions of the central accreting black holes are cospatial (typical offsets 0 1). This suggests that the central black holes are located at the bottom of the gravitational wells of the dark matter halos in which the quasar hosts reside. Some outliers with offsets of ∼500 pc can be linked to disturbed morphologies, most likely due to ongoing or recent mergers. We find no correlation between the central brightness of the FIR emission and the bolometric luminosity of the accreting black hole. The FIR-derived star formation rate densities (SFRDs) in the host galaxies peak at the galaxies' centers, at typical values between 100 and 1000 M yr−1 kpc−2. These values are below the Eddington limit for star formation, but similar to those found in local ultraluminous infrared galaxies. The SFRDs drop toward larger radii by an order of magnitude. Likewise, the C ii/FIR luminosity ratios of the quasar hosts are lowest in their centers (few ×10−4) and increase by a factor of a few toward the galaxies' outskirts, consistent with resolved studies of lower-redshift sources.
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 use Atacama Large Millimeter Array observations of the host galaxy of the quasar ULAS J1342+0928 at z = 7.54, to study the dust continuum and far-infrared lines emitted from its interstellar ...medium (ISM). The Rayleigh-Jeans tail of the dust continuum is well sampled with eight different spectral setups, and from a modified blackbody fit we obtain an emissivity coefficient of β = 1.85 0.3. Assuming a standard dust temperature of 47 K we derive a dust mass of Mdust = 0.35 × 108 M☉ and a star formation rate of . We have >4 detections of the , , and atomic fine structure lines and limits on the , , and emission. We also report multiple limits of CO rotational lines with Jup ≥ 7, as well as a tentative 3.3 detection of the stack of four CO lines (Jup = 11, 10, 8, and 7). We find line deficits that are in agreement with local ultra-luminous infrared galaxies. Comparison of the and lines indicates that the emission arises predominantly from the neutral medium, and we estimate that the photodisassociation regions in J1342+0928 have densities 5 × 104 cm−3. The data suggest that ∼16% of hydrogen is in ionized form and that the H ii regions have high electron densities of ne > 180 cm−3. Our observations favor a low gas-to-dust ratio of <100, and a metallicity of the ISM comparable to the solar value. All the measurements presented here suggest that the host galaxy of J1342+0928 is highly enriched in metal and dust, despite being observed just 680 Myr after the big bang.
ABSTRACT We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly absorbers (DLAs) at low redshift ( ). Our statistical ...sample includes 463 quasars with spectral coverage spanning a total redshift path or an absorption path . Within this survey path, we identify 4 DLAs defined as absorbers with H i column density cm−2, which implies an incidence per absorption length at a median survey path redshift of z = 0.623. While our estimate of is lower than earlier estimates at from H i 21 cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the frequency distribution function , but the observed distribution agrees with previous estimates at . Adopting the shape of , we infer an H i mass density at of . This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z H i 21 cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyr.
Abstract
We present 0.″035 resolution (∼200 pc) imaging of the 158
μ
m C
ii
line and the underlying dust continuum of the
z
= 6.9 quasar J234833.34–305410.0. The 18 hour Atacama Large ...Millimeter/submillimeter Array observations reveal extremely compact emission (diameter ∼1 kpc) that is consistent with a simple, almost face-on, rotation–supported disk with a significant velocity dispersion of ∼160 km s
−1
. The gas mass in just the central 200 pc is ∼4 × 10
9
M
⊙
, about a factor of two higher than that of the central supermassive black hole. Consequently we do not resolve the black hole’s sphere of influence, and find no kinematic signature of the central supermassive black hole. Kinematic modeling of the C
ii
line shows that the dynamical mass at large radii is consistent with the gas mass, leaving little room for a significant mass contribution by stars and/or dark matter. The Toomre–Q parameter is less than unity throughout the disk, and thus is conducive to star formation, consistent with the high-infrared luminosity of the system. The dust in the central region is optically thick, at a temperature >132 K. Using standard scaling relations of dust heating by star formation, this implies an unprecedented high star formation rate density of >10
4
M
⊙
yr
−1
kpc
−2
. Such a high number can still be explained with the Eddington limit for star formation under certain assumptions, but could also imply that the central supermassive black hole contributes to the heating of the dust in the central 200 pc.
We report high spatial resolution (∼0 076, 410 pc) Atacama Large Millimeter/submillimeter Array imaging of the dust continuum and the ionized carbon line C ii 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 ∼1 × 109 black hole and has a star formation rate of ∼1500 yr−1. The unprecedented high resolution of the observations reveals a complex morphology of gas within 3 kpc 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 C ii cavities in the gas distribution (with diameters of ∼0.5 kpc), 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 C ii emission around the quasar.
We present a CO and atomic fine-structure line-luminosity function analysis using the ALMA Spectroscopic Survey (ASPECS) in the Hubble Ultra Deep Field. ASPECS consists of two spatially overlapping ...mosaics that cover the entire ALMA 3 mm and 1.2 mm bands. We combine the results of a line-candidate search of the 1.2 mm data cube with those previously obtained from the 3 mm cube. Our analysis shows that ∼80% of the line flux observed at 3 mm arises from CO(2-1) or CO(3-2) emitters at z = 1-3 ("cosmic noon"). At 1.2 mm, more than half of the line flux arises from intermediate-J CO transitions (Jup = 3-6); ∼12% from neutral carbon lines; and <1% from singly ionized carbon, C ii. This implies that future C ii intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2 mm show a decrease in the number density at a given line luminosity (in units of L′) at increasing Jup and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal subthermal conditions on average in galaxies up to z ∼ 4. In addition, the comparison of the CO luminosity functions for the same transition at different redshifts reveals that the evolution is not driven by excitation. The cosmic density of molecular gas in galaxies, H2, shows a redshift evolution with an increase from high redshift up to z ∼ 1.5 followed by a factor ∼6 drop down to the present day. This is in qualitative agreement with the evolution of the cosmic star formation rate density, suggesting that the molecular gas depletion time is approximately constant with redshift, after averaging over the star-forming galaxy population.
Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) C
ii
158
μ
m and dust continuum observations of the
z
= 6.79 quasar J0109–3047 at a resolution of 0.″045 (∼300 pc). The dust ...and C
ii
emission are enclosed within a ∼500 pc radius, with the central beam (
r
< 144 pc) accounting for ∼25% (8%) of the total continuum (C
ii
) emission. The far-infrared (FIR) luminosity density increases radially from ∼5 × 10
11
L
⊙
kpc
−2
to a central value of ∼70 × 10
11
L
⊙
kpc
−2
(SFRD ∼50–700
M
⊙
yr
−1
kpc
−2
). The C
ii
kinematics are dispersion dominated with a constant velocity dispersion of 137 ± 6 km s
−1
. The constant dispersion implies that the underlying mass distribution is not centrally peaked, consistent with the expectations of a flat gas mass profile. The lack of an upturn in velocity dispersion within the central beam is inconsistent with a black hole mass greater than
M
BH
< 6.5 × 10
8
M
⊙
(2
σ
level), unless highly fine-tuned changes in the interstellar medium properties conspire to produce a decrease of the gas mass in the central beam comparable to the black hole mass. Our observations therefore imply either that (a) the black hole is less massive than previously measured, or (b) the central peak of the FIR and C
ii
emission are not tracing the location of the black hole, as suggested by the tentative offset between the near-infrared position of the quasar and the ALMA continuum emission.
We present a survey for metal absorption systems traced by neutral oxygen over 3.2 < z < 6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we ...detect 74 O i absorbers, of which 57 are separated from the background QSO by more than 5000 km s−1. We use a maximum likelihood approach to fit the distribution of O i λ1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W1302 > 0.05 , of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7-4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ∼ 6 than at lower redshifts. Absorption from highly ionized metals traced by C iv is also weaker in higher-redshift O i systems, supporting this picture. The evolution of O i absorbers implies that metal-enriched circumgalactic gas at z ∼ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.
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