Keywords

The rich information on (sub)millimeter dust continuum emission from distant galaxies in the public Atacama Large Millimeter/submillimeter Array (ALMA) archive is contained in thousands of inhomogeneous observations from individual PI-led programs. To increase the usability of these data for studies deepening our understanding of galaxy evolution, we have developed automated mining pipelines for the ALMA archive in the COSMOS field (A3COSMOS) that efficiently exploit the available information for large numbers of galaxies across cosmic time and keep the data products in sync with the increasing public ALMA archive: (a) a dedicated ALMA continuum imaging pipeline, (b) two complementary photometry pipelines for both blind source extraction and prior source fitting, (c) a counterpart association pipeline utilizing the multiwavelength data available (including quality assessment based on machine-learning techniques), (d) an assessment of potential (sub)millimeter line contribution to the measured ALMA continuum, and (e) extensive simulations to provide statistical corrections to biases and uncertainties in the ALMA continuum measurements. Application of these tools yields photometry catalogs with ∼1000 (sub)millimeter detections (spurious fraction ∼8%–12%) from over 1500 individual ALMA continuum images. Combined with ancillary photometric and redshift catalogs and the above quality assessments, we provide robust information on redshift, stellar mass, and star formation rate for ∼700 galaxies at redshifts 0.5–6 in the COSMOS field (with undetermined selection function). The ALMA photometric measurements and galaxy properties are released publicly within our blind extraction, prior fitting, and galaxy property catalogs, plus the images. These products will be updated on a regular basis in the future.

We analyze the multifrequency radio spectral properties of 41 6 GHz-detected Atacama Large Millimeter/submillimeter Array (ALMA)-identified, submillimeter galaxies (SMGs), observed at 610 MHz, 1.4 GHz, and 6 GHz with the Giant Metrewave Radio Telescope and the Very Large Array. Combining high-resolution (∼05) 6 GHz radio and ALMA 870 μm imaging (tracing rest frame ∼20 GHz, and ∼250 μm dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio q_IR, measuring $\langle {q}_{\mathrm{IR}}\rangle =2.20\pm 0.06$ for our sample. We show that the high-frequency radio sizes of SMGs are ∼1.9 ± 0.4× (∼2–3 kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on ∼10 kpc scales at 1.4 GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample shows evidence of a spectral break, with a median $\langle {\alpha }_{610\,\mathrm{GHz}}^{1.4\,\mathrm{GHz}}\rangle =-0.60\pm 0.06$, but $\langle {\alpha }_{1.4\,\mathrm{GHz}}^{6\,\mathrm{GHz}}\rangle =-1.06\pm 0.04$—a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields (B ∼ 35 μG) and young ages (t_SB ∼ 40–80 Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts, and we are observing these systems roughly halfway through their current episode of star formation, this implies starburst durations of ≲100 Myr, in reasonable agreement with estimates derived via gas depletion timescales.

We present the first high-resolution map of the cold molecular gas distribution as traced by CO(2−1) emission with ALMA in a long ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intracluster medium and is one of the nearest jellyfish galaxies with a long multiphase and multicomponent tail. We have mapped the full extent of the tail at 1'' (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total, about 10⁹ M_⊙ of molecular gas was detected with ALMA. From comparison with previous APEX observations, we also infer the presence of a substantial extended molecular component in the tail. The ALMA CO features are found predominantly at the heads of numerous small-scale (∼1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also large-scale (∼8 kpc) superfireballs and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite the stellar tails. The new data help to shed light on the origin of the molecular tail; CO filaments oriented in the direction of the tail are likely young molecular features formed in situ, whereas large CO features tilted with respect to the tail may have originated from dense gas complexes that were gradually pushed away from the disk.

We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at z = 2.49 using 04 resolution CO (4–3) data taken with ALMA. Eleven Hα emitters (HAEs) are detected in CO (4–3), including six HAEs that were previously detected in CO (3–2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of log (M_cl/M_⊙) = 13.4–13.6, suggesting that the protocluster would evolve into a Virgo-like cluster (>10¹⁴ M_⊙). We compare the CO line widths and the CO luminosities with other (proto)clusters (n_gal = 91) and general field (n_gal = 80) galaxies from other studies. The 4C 23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by ≈50% compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples.

We report the first detection obtained with the Atacama Large Millimeter/submillimeter Array of the [N ii] 122 μm line emission from a galaxy group BRI 1202−0725 at z = 4.69 consisting of a quasi-stellar object (QSO) and a submillimeter-bright galaxy (SMG). Combining this with a detection of [N ii] 205 μm line in both galaxies, we constrain the electron densities of the ionized gas based on the line ratio of [N ii] 122/205. The derived electron densities are ${26}_{-11}^{+12}$ and ${134}_{-39}^{+50}$ cm⁻³ for the SMG and the QSO, respectively. The electron density of the SMG is similar to that of the Galactic Plane and to the average of the local spirals. However, higher electron densities (by up to a factor of three) could be possible for systematic uncertainties of the line flux estimates. The electron density of the QSO is comparable to high-z star-forming galaxies at z = 1.5–2.3, obtained using rest-frame optical lines and with the lower limits suggested from stacking analysis on lensed starbursts at z = 1–3.6 using the same tracer of [N ii]. Our results suggest a large scatter of electron densities in global scale at fixed star formation rates for extreme starbursts. The success of the [N ii] 122 μm and 205 μm detections at z = 4.69 demonstrates the power of future systematic surveys of extreme starbursts at z > 4 for probing the interstellar medium conditions and the effects on surrounding environments.

Recent interferometric observations have shown bright HCN emission from the ν₂ = 1 vibrational state arising in buried nuclear regions of galaxies, indicating an efficient pumping of the ν₂ = 1 state through the absorption of 14 μm continuum photons. We modeled the continuum and HCN vibrational line emission in these regions, characterized by high column densities of dust and high luminosities, using a spherically symmetric approach, simulating both a central heating source (active galactic nucleus, AGN) and a compact nuclear starburst (SB). We find that when the H₂ columns become very high, N_H2 ≳ 10²⁵ cm⁻², trapping of continuum photons within the nuclear region dramatically enhances the dust temperature (T_dust) in the inner regions, even though the predicted spectral energy distribution as seen from the outside becomes relatively cold. The models thus predict a bright continuum at millimeter wavelengths for a luminosity surface brightness (averaged over the model source) of ∼10⁸ L_⊙ pc⁻². This greenhouse effect significantly enhances the mean mid-infrared intensity within the dusty volume, populating the ν₂ = 1 state to the extent that the HCN vibrational lines become optically thick. AGN models yield higher T_dust in the inner regions and higher peak (sub)millimeter continuum brightness than SB models, but similar HCN vibrational J = 3–2 and 4–3 emission owing to both optical depth effects and a moderate impact of high T_dust on these low-J lines. The observed HCN vibrational emission in several galaxies can be accounted for with an HCN abundance of ∼10⁻⁶ (relative to H₂) and luminosity surface brightness in the range (0.5–2) × 10⁸ L_⊙ pc⁻², predicting a far-infrared photosphere with T_dust ∼ 80–150 K, in agreement with the values inferred from far-infrared molecular absorption.

The Atacama Large Millimeter/submillimeter Array (ALMA) SPECtroscopic Survey in the Hubble Ultra Deep Field (HUDF) is an ALMA large program that obtained a frequency scan in the 3 mm band to detect emission lines from the molecular gas in distant galaxies. Here we present our search strategy for emission lines and continuum sources in the HUDF. We compare several line search algorithms used in the literature, and critically account for the line widths of the emission line candidates when assessing significance. We identify 16 emission lines at high fidelity in our search. Comparing these sources to multiwavelength data we find that all sources have optical/infrared counterparts. Our search also recovers candidates of lower significance that can be used statistically to derive, e.g., the CO luminosity function. We apply the same detection algorithm to obtain a sample of six 3 mm continuum sources. All of these are also detected in the 1.2 mm continuum with optical/near-infrared counterparts. We use the continuum sources to compute 3 mm number counts in the sub-millijansky regime, and find them to be higher by an order of magnitude than expected for synchrotron-dominated sources. However, the number counts are consistent with those derived at shorter wavelengths (0.85–1.3 mm) once extrapolating to 3 mm with a dust emissivity index of β = 1.5, dust temperature of 35 K, and an average redshift of z = 2.5. These results represent the best constraints to date on the faint end of the 3 mm number counts.

We present an enhanced version of the multiwavelength spectral modeling code MAGPHYS that allows the estimation of galaxy photometric redshift and physical properties (e.g., stellar mass, star formation rate, dust attenuation) simultaneously, together with robust characterization of their uncertainties. The self-consistent modeling over ultraviolet to radio wavelengths in MAGPHYS+photo-z is unique compared to standard photometric redshift codes. The broader wavelength consideration is particularly useful for breaking certain degeneracies in color versus redshift for dusty galaxies with limited observer-frame ultraviolet and optical data (or upper limits). We demonstrate the success of the code in estimating redshifts and physical properties for over 4000 infrared-detected galaxies at 0.4 < z < 6.0 in the COSMOS field with robust spectroscopic redshifts. We achieve high photo-z precision (${\sigma }_{{\rm{\Delta }}z/(1+{z}_{\mathrm{spec}})}\lesssim 0.04$), high accuracy (i.e., minimal offset biases; median(Δz/(1 + z_spec)) ≲ 0.02), and low catastrophic failure rates (η ≃ 4%) over all redshifts. Interestingly, we find that a weak 2175 Å absorption feature in the attenuation curve models is required to remove a subtle systematic z_phot offset (${z}_{\mathrm{phot}}\mbox{--}{z}_{\mathrm{spec}}\simeq -0.03$) that occurs when this feature is not included. As expected, the accuracy of derived physical properties in MAGPHYS+photo-z decreases strongly as redshift uncertainty increases. The all-in-one treatment of uncertainties afforded with this code is beneficial for accurately interpreting physical properties of galaxies in large photometric data sets. Finally, we emphasize that MAGPHYS+photo-z is not intended to replace existing photo-z codes, but rather offers flexibility to robustly interpret physical properties when spectroscopic redshifts are unavailable. The MAGPHYS+photo-z code is publicly available online.

We report the Atacama Large Millimeter/submillimeter Array observations of the metal-rich host galaxy of superluminous supernova (SLSN) PTF10tpz, a barred spiral galaxy at z = 0.03994. We find the CO(1–0) emission to be confined within the bar of the galaxy. The distribution and kinematics of molecular gas in the host galaxy resemble gas flows along two lanes running from the tips of the bar toward the galaxy center. These gas lanes end in a gaseous structure in the inner region of the galaxy, likely associated with an inner Lindblad resonance. The interaction between the large-scale gas flows in the bar and the gas in the inner region plausibly leads to the formation of massive molecular clouds and consequently massive clusters. This in turn can result in formation of massive stars, and thus the likely progenitor of the SLSN in a young, massive cluster. This picture is consistent with SLSN PTF10tpz being located near the intersection regions of the gas lanes and the inner structure. It is also supported by the high molecular gas surface densities that we find in the vicinity of the SLSN, surface densities that are comparable with those in interacting galaxies or starburst regions in nearby galaxies. Our findings therefore suggest in situ formation of massive stars due to the internal dynamics of the host galaxy and also lend support to high densities being favorable conditions for formation of SLSN progenitors.

We report on ≈035 (≈2kpc) resolution observations of the [C ii] and dust continuum emission from five z > 6 quasar host–companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter Array. The [C ii] emission is resolved in all galaxies, with physical extents of 3.2–5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger [C ii] deficits in the center of the galaxies. However, the measured [C ii] deficits are fully consistent with those found at lower redshifts. Four of the galaxies show [C ii] velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (∼80−200 km s⁻¹) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high-redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which ranges between (0.3 − >5.4) × 10¹⁰ M_⊙. For the three closest-separation galaxy pairs, we observe dust and [C ii] emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the [C ii] and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.