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 make use of sensitive (9.3
μ
Jy beam
−1
rms) 1.2 mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra-Deep Field ...(ASPECS) large program to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range
z
= 1.5–10 (to ∼7–28
M
⊙
yr
−1
at 4
σ
over the entire range). We find that the fraction of ALMA-detected galaxies in our
z
= 1.5–10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 10
9.0
M
⊙
to
% at >10
10
M
⊙
. Moreover, on stacking all 1253 low-mass (<10
9.25
M
⊙
) galaxies over the ASPECS footprint, we find a mean continuum flux of −0.1 ± 0.4
μ
Jy beam
−1
, implying a hard upper limit on the obscured star formation rate of <0.6
M
⊙
yr
−1
(4
σ
) in a typical low-mass galaxy. The correlation between the infrared excess (IRX) of UV-selected galaxies (
L
IR
/
L
UV
) and the UV-continuum slope is also seen in our ASPECS data and shows consistency with a Calzetti-like relation at >
and an SMC-like relation at lower masses. Using stellar mass and
β
measurements for
z
∼ 2 galaxies over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we derive a new empirical relation between
β
and stellar mass and then use this correlation to show that our IRX–
β
and IRX–stellar mass relations are consistent with each other. We then use these constraints to express the IRX as a bivariate function of
β
and stellar mass. Finally, we present updated estimates of star formation rate density determinations at
z
> 3, leveraging present improvements in the measured IRX and recent probes of ultraluminous far-IR galaxies at
z
> 2.
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 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.
We present a "super-deblended" far-infrared (FIR) to (sub)millimeter photometric catalog in the Cosmic Evolution Survey (COSMOS), prepared with the method recently developed by Liu et al., with key ...adaptations. We obtain point-spread function fitting photometry at fixed prior positions including 88,008 galaxies detected in VLA 1.4, 3 GHz, and/or MIPS 24 m images. By adding a specifically carved mass-selected sample (with an evolving stellar mass limit), a highly complete prior sample of 194,428 galaxies is achieved for deblending FIR/(sub)mm images. We performed "active" removal of nonrelevant priors at FIR/(sub)mm bands using spectral energy distribution fitting and redshift information. In order to cope with the shallower COSMOS data, we subtract from the maps the flux of faint nonfitted priors and explicitly account for the uncertainty of this step. The resulting photometry (including data from Spitzer, Herschel, SCUBA2, AzTEC, MAMBO, and NSF's Karl G. Jansky Very Large Array at 3 and 1.4 GHz) displays well-behaved quasi-Gaussian uncertainties calibrated from Monte Carlo simulations and tailored to observables (crowding, residual maps). Comparison to ALMA photometry for hundreds of sources provides a remarkable validation of the technique. We detect 11,220 galaxies over the 100-1200 m range extending to zphot ∼ 7. We conservatively selected a sample of 85 z > 4 high-redshift candidates significantly detected in the FIR/(sub)mm, often with secure radio and/or Spitzer/IRAC counterparts. This provides a chance to investigate the first generation of vigorous starburst galaxies (SFRs ∼ 1000 M yr−1). The photometric and value-added catalogs are publicly released.
We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate (SFR)-stellar mass (M*) relation, called the main sequence (MS) of star-forming galaxies , for ...star-forming and all galaxies out to . We measure the MS using mean stacks of 3 GHz radio-continuum images to derive average SFRs for ∼ 200,000 mass-selected galaxies at z > 0.3 in the COSMOS field. We describe the MS relation by adopting a new model that incorporates a linear relation at low stellar mass (log(M*/M ) < 10) and a flattening at high stellar mass that becomes more prominent at low redshift (z < 1.5). We find that the SFR density peaks at 1.5 < z < 2, and at each epoch there is a characteristic stellar mass (M* = 1-4 × 1010M ) that contributes the most to the overall SFR density. This characteristic mass increases with redshift, at least to z ∼ 2.5. We find no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy number density at 0.3 < z < 3, nor for galaxies in X-ray groups at z ∼ 0.75. We confirm that massive bulge-dominated galaxies have lower SFRs than disk-dominated galaxies at a fixed stellar mass at z < 1.2. As a consequence, the increase in bulge-dominated galaxies in the local star-forming population leads to a flattening of the MS at high stellar masses. This indicates that "mass quenching" is linked with changes in the morphological composition of galaxies at a fixed stellar mass.
We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift ...evolution of (H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ∼2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to ∼90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at z = 1.0-3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H2 conversion factor, we constrain the evolution of the cosmic molecular gas density (H2): this cosmic gas density peaks at z ∼ 1.5 and drops by a factor of to the value measured locally. The observed evolution in (H2), therefore, closely matches the evolution of the cosmic star formation rate density SFR. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of (H2) and SFR leaves only little room for a significant evolution of the average star formation efficiency in galaxies since z ∼ 3 (85% of cosmic history).
In a multiwavelength survey of 13 quasars at 5.8 z 6.5, which were preselected to be potentially young, we find five objects with extremely small proximity zone sizes that may imply UV-luminous ...quasar lifetimes of 100,000 yr. Proximity zones are regions of enhanced transmitted flux in the vicinity of quasars that are sensitive to the quasars' lifetimes because the intergalactic gas has a finite response time to their radiation. We combine submillimeter observations from the Atacama Large Millimetre Array and the NOrthern Extended Millimeter Array, as well as deep optical and near-infrared spectra from the medium-resolution spectrograph on the Very Large Telescope and on the Keck telescopes, in order to identify and characterize these new young quasars, which provide valuable clues about the accretion behavior of supermassive black holes in the early universe and pose challenges on current black hole formation models to explain the rapid formation of billion-solar-mass black holes. We measure the quasars' systemic redshifts, black hole masses, Eddington ratios, emission-line luminosities, and star formation rates of their host galaxies. Combined with previous results, we estimate the fraction of young objects within the high-redshift quasar population at large to be 5% fyoung 10%. One of the young objects, PSO J158-14, shows a very bright dust continuum flux (Fcont = 3.46 0.02 mJy), indicating a highly starbursting host galaxy with a star formation rate of approximately 1420 M yr−1.
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.
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