The ALMA-ALPINE [CII] survey is aimed at characterizing the properties of a sample of normal star-forming galaxies (SFGs). The ALMA Large Program to INvestigate (ALPINE) features 118 galaxies observed in the [CII]-158 μ m line and far infrared (FIR) continuum emission during the period of rapid mass assembly, right after the end of the HI reionization, at redshifts of 4 < z < 6. We present the survey science goals, the observational strategy, and the sample selection of the 118 galaxies observed with ALMA, with an average beam minor axis of about 0.85″, or ∼5 kpc at the median redshift of the survey. The properties of the sample are described, including spectroscopic redshifts derived from the UV-rest frame, stellar masses, and star-formation rates obtained from a spectral energy distribution (SED) fitting. The observed properties derived from the ALMA data are presented and discussed in terms of the overall detection rate in [CII] and FIR continuum, with the observed signal-to-noise distribution. The sample is representative of the SFG population in the main sequence at these redshifts. The overall detection rate in [CII] is 64% for a signal-to-noise ratio (S/N) threshold larger than 3.5 corresponding to a 95% purity (40% detection rate for S / N > 5). Based on a visual inspection of the [CII] data cubes together with the large wealth of ancillary data, we find a surprisingly wide range of galaxy types, including 40% that are mergers, 20% extended and dispersion-dominated, 13% compact, and 11% rotating discs, with the remaining 16% too faint to be classified. This diversity indicates that a wide array of physical processes must be at work at this epoch, first and foremost, those of galaxy mergers. This paper sets a reference sample for the gas distribution in normal SFGs at 4 < z < 6, a key epoch in galaxy assembly, which is ideally suited for studies with future facilities, such as the James Webb Space Telescope (JWST) and the Extremely Large Telescopes (ELTs).
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The ALPINE-ALMA [CII] survey: Circumgalactic medium pollution and gas mixing by tidal stripping in a merging system at z ∼ 4.57
We present ALMA observations of a merging system at z ∼ 4.57, observed as a part of the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey. Combining ALMA [CII]158 μ m and far-infrared continuum data with multi-wavelength ancillary data, we find that the system is composed of two massive ( M ⋆ ≳ 10 10 M ⊙ ) star-forming galaxies experiencing a major merger (stellar mass ratio r mass ≳ 0.9) at close spatial (∼13 kpc; projected) and velocity (Δ v < 300 km s −1 ) separations, and two additional faint narrow [CII]-emitting satellites. The overall system belongs to a larger scale protocluster environment and is coincident to one of its overdensity peaks. Additionally, ALMA reveals the presence of [CII] emission arising from a circumgalactic gas structure, extending up to a diameter-scale of ∼30 kpc. Our morpho-spectral decomposition analysis shows that about 50% of the total flux resides between the individual galaxy components, in a metal-enriched gaseous envelope characterised by a disturbed morphology and complex kinematics. Similarly to observations of shock-excited [CII] emitted from tidal tails in local groups, our results can be interpreted as a possible signature of interstellar gas stripped by strong gravitational interactions, with a possible contribution from material ejected by galactic outflows and emission triggered by star formation in small faint satellites. Our findings suggest that mergers could be an efficient mechanism of gas mixing in the circumgalactic medium around high- z galaxies, and thus play a key role in the galaxy baryon cycle at early epochs.
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- Award ID(s):
- 1908422
- NSF-PAR ID:
- 10286665
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 643
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A7
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Dragonfly galaxy (MRC 0152-209), the most infrared-luminous radio galaxy at redshift
z ∼ 2, is a merger system containing a powerful radio source and large displacements of gas. We present kiloparsec-resolution data from the Atacama Large Millimeter/submillimeter Array and the Very Large Array of carbon monoxide (6−5), dust, and synchrotron continuum, combined with Keck integral field spectroscopy. We find that the Dragonfly consists of two galaxies with rotating disks that are in the early phase of merging. The radio jet originates from the northern galaxy and brightens when it hits the disk of the southern galaxy. The Dragonfly galaxy therefore likely appears as a powerful radio galaxy because its flux is boosted into the regime of high-z radio galaxies by the jet–disk interaction. We also find a molecular outflow of (1100 ± 550)M ⊙yr−1associated with the radio host galaxy, but not with the radio hot spot or southern galaxy, which is the galaxy that hosts the bulk of the star formation. Gravitational effects of the merger drive a slower and longer-lived mass displacement at a rate of (170 ± 40)M ⊙yr−1, but this tidal debris contains at least as much molecular gas mass as the much faster outflow, namelyM H2= (3 ± 1) × 109(α CO/0.8)M ⊙. This suggests that both the active-galactic-nucleus-driven outflow and mass transfer due to tidal effects are important in the evolution of the Dragonfly system. The Keck data show Lyα emission spread across 100 kpc, and Civ and Heii emission across 35 kpc, confirming the presence of a metal-rich and extended circumgalactic medium previously detected in CO(1–0). -
Of the almost 40 star-forming galaxies at z≳ 5 (not counting quasi-stellar objects) observed in [{{C}} {{II}}] to date, nearly half are either very faint in [{{C}} {{II}}] or not detected at all, and fall well below expectations based on locally derived relations between star formation rate and [{{C}} {{II}}] luminosity. This has raised questions as to how reliable [{{C}} {{II}}] is as a tracer of star formation activity at these epochs and how factors such as metallicity might affect the [{{C}} {{II}}] emission. Combining cosmological zoom simulations of galaxies with SÍGAME (SImulator of GAlaxy Millimeter/submillimeter Emission), we modeled the multiphased interstellar medium (ISM) and its emission in [{{C}} {{II}}], as well as in [O I] and [O III], from 30 main-sequence galaxies at z≃ 6 with star formation rates ˜3-23 {M}⊙ {yr}}-1, stellar masses ˜ (0.7{--}8)× {10}9 {M}⊙ , and metallicities ˜ (0.1{--}0.4)× {Z}⊙ . The simulations are able to reproduce the aforementioned [{{C}} {{II}}] faintness of some normal star-forming galaxy sources at z≥slant 5. In terms of [O I] and [O III], very few observations are available at z≳ 5, but our simulations match two of the three existing z≳ 5 detections of [O III] and are furthermore roughly consistent with the [O I] and [O III] luminosity relations with star formation rate observed for local starburst galaxies. We find that the [{{C}} {{II}}] emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ˜66% and ˜27%, respectively. The molecular gas, which constitutes only ˜ 10 % of the total gas mass, is thus a more efficient emitter of [{{C}} {{II}}] than the ionized gas, which makes up ˜85% of the total gas mass. A principal component analysis shows that the [{{C}} {{II}}] luminosity correlates with the star formation activity of a galaxy as well as its average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their [{{C}} {{II}}] faintness, and we suggest that these factors may also be responsible for the [{{C}} {{II}}]-faint normal galaxies observed at these early epochs.more » « less
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Abstract We report new observations toward the hyperluminous dusty starbursting major merger ADFS-27 ( z = 5.655), using the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). We detect CO ( J = 2 → 1), CO ( J = 8 → 7), CO ( J = 9 → 8), CO ( J = 10 → 9), and H 2 O (3 12 → 2 21 ) emission, and a P Cygni−shaped OH + (1 1 → 0 1 ) absorption/emission feature. We also tentatively detect H 2 O (3 21 → 3 12 ) and OH + (1 2 → 0 1 ) emission and CH + ( J = 1 → 0) absorption. We find a total cold molecular mass of M gas = (2.1 ± 0.2) × 10 11 ( α CO /1.0) M ⊙ . We also find that the excitation of the star-forming gas is overall moderate for a z > 5 dusty starburst, which is consistent with its moderate dust temperature. A high-density, high kinetic temperature gas component embedded in the gas reservoir is required to fully explain the CO line ladder. This component is likely associated with the “maximum starburst” nuclei in the two merging galaxies, which are separated by only 140 ± 13 km s −1 along the line of sight and 9.0 kpc in projection. The kinematic structure of both components is consistent with galaxy disks, but this interpretation remains limited by the spatial resolution of the current data. The OH + features are only detected toward the northern component, which is also the one that is more enshrouded in dust and thus remains undetected up to 1.6 μ m even in our sensitive new Hubble Space Telescope Wide Field Camera 3 imaging. The absorption component of the OH + line is blueshifted and peaks near the CO and continuum emission peak, while the emission is redshifted and peaks offset by 1.7 kpc from the CO and continuum emission peak, suggesting that the gas is associated with a massive molecular outflow from the intensely star-forming nucleus that supplies 125 M ⊙ yr −1 of enriched gas to its halo.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/0004-6361/202038284
