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.
ABSTRACT
We present an extensive ALMA spectroscopic follow-up programme of the $z\, {=}\, 4.3$ structure SPT2349–56, one of the most actively star-forming protocluster cores known, to identify ...additional members using their C ii 158 μm and CO(4–3) lines. In addition to robustly detecting the 14 previously published galaxies in this structure, we identify a further 15 associated galaxies at $z\, {=}\, 4.3$, resolving 55$\, {\pm }\,$5 per cent of the 870 μm flux density at 0.5 arcsec resolution compared to 21 arcsec single-dish data. These galaxies are distributed into a central core containing 23 galaxies extending out to 300 kpc in diameter, and a northern extension, offset from the core by 400 kpc, containing three galaxies. We discovered three additional galaxies in a red Herschel-SPIRE source 1.5 Mpc from the main structure, suggesting the existence of many other sources at the same redshift as SPT2349–56 that are not yet detected in the limited coverage of our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9$\pm 5)\, {\times }\, 10^{12}$ M⊙, while the two offset galaxy groups are about 30 and 60 per cent less massive and show significant velocity offsets from the central group. We calculate the C ii and far-infrared number counts, and find evidence for a break in the C ii luminosity function. We estimate the average SFR density within the region of SPT2349–56 containing single-dish emission (a proper diameter of 720 kpc), assuming spherical symmetry, to be roughly 4$\, {\times }\, 10^4$ M⊙ yr−1 Mpc−3; this may be an order of magnitude greater than the most extreme examples seen in simulations.
Galactic outflows of molecular gas are a common occurrence in galaxies and may represent a mechanism by which galaxies self-regulate their growth, redistributing gas that could otherwise have formed ...stars. We previously presented the first survey of molecular outflows at z > 4 toward a sample of massive, dusty galaxies. Here we characterize the physical properties of the molecular outflows discovered in our survey. Using low-redshift outflows as a training set, we find agreement at the factor of 2 level between several outflow rate estimates. We find molecular outflow rates of 150-800 yr−1 and infer mass loading factors just below unity. Among the high-redshift sources, the molecular mass loading factor shows no strong correlations with any other measured quantity. The outflow energetics are consistent with expectations for momentum-driven winds with star formation as the driving source, with no need for energy-conserving phases. There is no evidence for active galactic nucleus activity in our sample, and while we cannot rule out deeply buried active galactic nuclei, their presence is not required to explain the outflow energetics, in contrast to nearby obscured galaxies with fast outflows. The fraction of the outflowing gas that will escape into the circumgalactic medium (CGM), though highly uncertain, may be as high as 50%. This nevertheless constitutes only a small fraction of the total cool CGM mass based on a comparison to z ∼ 2-3 quasar absorption line studies, but could represent 10% of the CGM metal mass. Our survey offers the first statistical characterization of molecular outflow properties in the very early universe.
Using the NSF's Karl G. Jansky Very Large Array (VLA), we report six detections of CO(J = 1 → 0) emission and one upper limit in z = 2-3 galaxies originally detected in higher-J CO emission in the ...Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). From the CO(J = 1 → 0) line strengths, we measure total cold molecular gas masses of Mgas = (2.4-11.6) × 1010 ( CO/3.6)M . We also measure a median CO(J = 3 → 2) to CO(J = 1 → 0) line brightness temperature ratio of r31 = 0.84 0.26, and a CO(J = 7 → 6) to CO(J = 1 → 0) ratio range of r71 < 0.05 to r71 = 0.17. These results suggest that CO(J = 3 → 2) selected galaxies may have a higher CO line excitation on average than CO(J = 1 → 0) selected galaxies, based on the limited, currently available samples from the ASPECS and VLA CO Luminosity Density at High Redshift (COLDz) surveys. This implies that previous estimates of the cosmic density of cold gas in galaxies based on CO(J = 3 → 2) measurements should be revised down by a factor of 2 on average based on assumptions regarding CO excitation alone. This correction further improves the agreement between the best currently existing constraints on the cold gas density evolution across cosmic history from line scan surveys, and the implied characteristic gas depletion times.
We present a study of six far-infrared fine structure lines in the z = 4.225 lensed dusty star-forming galaxy SPT 0418−47 to probe the physical conditions of its interstellar medium (ISM). In ...particular, we report Atacama Pathfinder EXperiment (APEX) detections of the OI 145 μm and OIII 88 μm lines and Atacama Compact Array (ACA) detections of the NII 122 and 205 μm lines. The OI 145 μm/CII 158 μm line ratio is ∼5× higher compared to the average of local galaxies. We interpret this as evidence that the ISM is dominated by photo-dissociation regions with high gas densities. The line ratios, and in particular those of OIII 88 μm and NII 122 μm imply that the ISM in SPT 0418−47 is already chemically enriched to nearly solar metallicity. While the strong gravitational amplification was required to detect these lines with APEX, larger samples can be observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and should allow observers to determine if the dense, solar metallicity ISM is common among these highly star-forming galaxies.
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.
Abstract
We present measurements of the CO luminosity functions (LFs) and the evolution of the cosmic molecular gas density out to
z
∼ 6 based on an 8.5 arcmin
2
spectral scan survey at 3 mm of the ...iconic Hubble Deep Field North (HDF-N) observed with the NOrthern Extended Millimeter Array (NOEMA). We use matched filtering to search for line emission from galaxies and determine their redshift probability distributions exploiting the extensive multiwavelength data for the HDF-N. We identify the seven highest-fidelity sources as CO emitters at 1 <
z
< 6, including the well-known submillimeter galaxy HDF 850.1 at
z
= 5.18. Four high-fidelity 3 mm continuum sources are found to be radio galaxies at
z
≤ 1, plus HDF 850.1. We constrain the CO LFs in the HDF-N out to
z
∼ 6, including a first measurement of the CO(5–4) LF at 〈
z
〉 = 5.0. The relatively large area and depth of the NOEMA HDF-N survey extends the existing LFs at 1 <
z
< 4 above the knee, yielding a somewhat lower density by 0.15–0.4 dex at the overlap region for the CO(2–1) and CO(3–2) transitions, attributed to cosmic variance. We perform a joint analysis of the CO LFs in the HDF-N and Hubble Ultra Deep Field from ASPECS, finding that they can be well described by a single Schechter function. The evolution of the cosmic molecular gas density from a joint analysis is in good agreement with earlier determinations. This implies that the impact of cosmic field-to-field variance on the measurements is consistent with previous estimates, adding to the challenges for simulations that model galaxies from first principles.
ABSTRACT We present a wide area ( 8 × 8 kpc), sensitive map of CO (2-1) emission around the nearby starburst galaxy M82. Molecular gas extends far beyond the stellar disk, including emission ...associated with the well-known outflow as far as 3 kpc from M82's midplane. Kinematic signatures of the outflow are visible in both the CO and H i emission: both tracers show a minor axis velocity gradient and together they show double peaked profiles, consistent with a hot outflow bounded by a cone made of a mix of atomic and molecular gas. Combining our CO and H i data with observations of the dust continuum, we study the changing properties of the cold outflow as it leaves the disk. While H2 dominates the ISM near the disk, the dominant phase of the cool medium changes as it leaves the galaxy and becomes mostly atomic after about a kpc. Several arguments suggest that regardless of phase, the mass in the cold outflow does not make it far from the disk; the mass flux through surfaces above the disk appears to decline with a projected scale length of 1-2 kpc. The cool material must also end up distributed over a much wider angle than the hot outflow based on the nearly circular isophotes of dust and CO at low intensity and the declining rotation velocities as a function of height from the plane. The minor axis of M82 appears so striking at many wavelengths because the interface between the hot wind cavity and the cool gas produces H , hot dust, polycyclic aromatic hydrocarbon emission, and scattered UV light. We also show the level at which a face-on version of M82 would be detectable as an outflow based on unresolved spectroscopy. Finally, we consider multiple constraints on the CO-to-H2 conversion factor, which must change across the galaxy but appears to be only a factor of 2 lower than the Galactic value in the outflow.
We present spatially resolved (∼50 pc) imaging of molecular gas species in the central kiloparsec of the nearby starburst galaxy NGC 253, based on observations taken with the Atacama Large ...Millimeter/submillimeter Array. A total of 50 molecular lines are detected over a 13 GHz bandwidth imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines. Based on the measured high CO/C{sup 17}O isotopic line ratio (≳350), we show that {sup 12}CO(1-0) has moderate optical depths. A comparison of the HCN and HCO{sup +} with their {sup 13}C-substituted isotopologues shows that the HCN(1-0) and HCO{sup +}(1-0) lines have optical depths at least comparable to CO(1-0). H{sup 13}CN/H{sup 13}CO{sup +} (and H{sup 13}CN/HN{sup 13}C) line ratios provide tighter constraints on dense gas properties in this starburst. SiO has elevated abundances across the nucleus. HNCO has the most distinctive morphology of all the bright lines, with its global luminosity dominated by the outer parts of the central region. The dramatic variation seen in the HNCO/SiO line ratio suggests that some of the chemical signatures of shocked gas are being erased in the presence of dominating central radiation fields (traced by C{sub 2}H and CN). High density molecular gas tracers (including HCN, HCO{sup +}, and CN) are detected at the base of the molecular outflow. We also detect hydrogen β recombination lines that, like their α counterparts, show compact, centrally peaked morphologies, distinct from the molecular gas tracers. A number of sulfur based species are mapped (CS, SO, NS, C{sub 2}S, H{sub 2}CS, and CH{sub 3}SH) and have morphologies similar to SiO.
The conversion factor αCO from the observable CO(1-0) luminosity to the mass of molecular gas is known to vary between isolated galaxies and some mergers, but the underlying reasons are not clearly ...understood. Thus, the value(s) of αCO that are to be adopted remain highly uncertain. To provide better constraints, we applied the large velocity gradient method to a series of hydrodynamical simulations of galaxies and derived the evolution of αCO. We report significant variations of αCO, and identify three distinct regimes: disk galaxies, starbursts, and post-burst phases. We show that estimating the star formation rate over 20Myr smoothes out some of these differences, but still maintains a distinction between disks and starbursts. We find a tighter correlation of αCO with the gas depletion time than with star formation rate, but deviations are induced by the transitions to and from the starburst episodes. We conclude that αCO fluctuates because of both feedback energy and velocity dispersion. Identifying the phase of an interaction by classical means (e.g., morphology or luminosity) could then help to select the relevant conversion factor that is to be used and to obtain more accurate estimates of the molecular masses of galaxies.
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