arXiv subjects

M. Dessauges-Zavadsky

Publications and source records attributed to M. Dessauges-Zavadsky.

At least 55 records · Page 3Linked to original sources

arXiv2021

The ALPINE-ALMA [CII] survey: The contribution of major mergers to the galaxy mass assembly at z~5

Galaxy mergers are thought to be one of the main mechanisms of the mass assembly of galaxies. Recently, many works have suggested a possible increase in the fraction of major mergers in the early Universe, reviving the debate on which processes (e.g., cold accretion, star formation, mergers) most contribute to the mass build-up of galaxies through cosmic time. To estimate the importance of major mergers in this context, we make use of the new data collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE), which observed the [CII] 158 $μ$m emission line from a sample of 75 main-sequence star-forming galaxies at 4.4 < z < 5.9. We used, for the first time, the morpho-kinematic information provided by the [CII] emission to obtain the fraction of major mergers ($f_{MM}$) at z~5. By adopting different prescriptions for the merger timescales ($T_{MM}$), we converted this fraction into the merger rate per galaxy ($R_{MM}$) and per volume ($Γ_{MM}$). We then combined our results with those at lower redshifts from the literature, computing the cosmic evolution of the merger fraction. This is described by a rapid increase from z~0 to higher redshifts, a peak at z~3, and a slow decrease towards earlier epochs. Depending on the timescale prescription used, this fraction translates into a merger rate ranging between ~0.1 and ~4.0 Gyr$^{-1}$ at z~5. Finally, we compare the specific star formation and star-formation rate density with the analogous quantities from major mergers. Our new ALPINE data reveal the presence of a significant merging activity in the early Universe. However, whether this population of mergers can provide a relevant contribution to the galaxy mass assembly at these redshifts and through the cosmic epochs is strongly dependent on the assumption of the merger timescale.

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arXiv2021

The ALPINE-ALMA [CII] survey: Dust mass budget in the early Universe

The dust content of normal galaxies and the dust mass density (DMD) at high-z (z>4) are unconstrained given the source confusion and the sensitivity limitations of previous observations. The ALMA Large Program to INvestigate [CII] at Early Times (ALPINE), which targeted 118 UV-selected star-forming galaxies at 4.4<z<5.9, provides a new opportunity to tackle this issue for the first time with a statistically robust dataset. We have exploited the rest-frame far-infrared (FIR) fluxes of the 23 continuum individually detected galaxies and stacks of continuum images to measure the dust content of the 118 UV-selected ALPINE galaxies. We have focused on the dust scaling relations and, by comparing them with predictions from chemical evolution models, we have probed the evolutionary stage of UV-selected galaxies at high-z. By using the observed correlation between the UV-luminosity and the dust mass, we have estimated the DMD of UV-selected galaxies at z~5, weighting the galaxies by means of the UV-luminosity function (UVLF). The derived DMD has been compared with the value we have estimated from the 10 ALPINE far-IR continuum blindly detected galaxies at the redshift of the ALPINE targets. The comparison of the observed dust scaling relations with chemical evolution models suggests that ALPINE galaxies are not likely progenitors of disc galaxies, but of intermediate and low mass proto-spheroids, resulting in present-day bulges of spiral or elliptical galaxies. Interestingly, this conclusion is in line with the independent morphological analysis, that shows that the majority (~70\%) of the dust-continuum detected galaxies have a disturbed morphology. The DMD obtained at z~5 from UV-selected sources is ~30% of the value obtained from blind far-IR selected sources, showing that the UV-selection misses the most dust-rich, UV-obscured galaxies.

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arXiv2020

The ALPINE-ALMA [C II] Survey: [C II]158micron Emission Line Luminosity Functions at $z \sim 4-6$

We present the [CII]158$μ$m line luminosity functions (LFs) at $z\sim4-6$ using the ALMA observations of 118 sources, which are selected to have UV luminosity $M_{1500A}<-20.2$ and optical spectroscopic redshifts in COSMOS and ECDF-S. Of the 118 targets, 75 have significant [CII] detections and 43 are upper limits. This is by far the largest sample of [CII] detections which allows us to set constraints to the volume density of [CII] emitters at $z\sim4-6$. But because this is a UV-selected sample, we are missing [CII]-bright but UV-faint sources making our constraints strict lower limits. Our derived LFs are statistically consistent with the $z\sim0$ [CII] LF at $10^{8.25} - 10^{9.75}L_\odot$. We compare our results with the upper limits of the [CII] LF derived from serendipitous sources in the ALPINE maps (Loiacono et al. 2020). We also infer the [CII] LFs based on published far-IR and CO LFs at $z\sim4-6$. Combining our robust lower limits with these additional estimates, we set further constraints to the true number density of [CII] emitters at $z\sim 4 - 6$. These additional LF estimates are largely above our LF at $L_{[CII]}>10^9L_{\odot}$, suggesting that UV-faint but [CII]-bright sources likely make a significant contributions to the [CII] emitter volume density. When we include all the LF estimates, we find that available model predictions underestimate the number densities of [CII] emitters at $z\sim4-6$. Finally, we set a constraint on the molecular gas mass density at $z\sim4-6$, with $ρ_{mol} \sim (2-7)\times10^7M_\odot$\,Mpc$^{-3}$. This is broadly consistent with previous studies.

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arXiv2020

The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured star formation at z~4.4-5.8

We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at a redshift of ~4.4-5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158μm obtained with the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [CII] at Early times (ALPINE). We study the connection between the ultraviolet (UV) spectral slope ($β$), stellar mass (M_*), and infrared excess (IRX=L_IR/L_UV). Twenty-three galaxies are individually detected in the continuum at >3.5 sigma significance. We perform a stacking analysis using both detections and nondetections to study the average dust attenuation properties at z~4.4-5.8. The individual detections and stacks show that the IRX-$β$ relation at z~5 is consistent with a steeper dust attenuation curve than typically found at lower redshifts (z<4). The attenuation curve is similar to or even steeper than that of the extinction curve of the Small Magellanic Cloud (SMC). This systematic change of the IRX-$β$ relation as a function of redshift suggests an evolution of dust attenuation properties at z>4. Similarly, we find that our galaxies have lower IRX values, up to 1dex on average, at a fixed mass compared to previously studied IRX-M_* relations at z<4, albeit with significant scatter. This implies a lower obscured fraction of star formation than at lower redshifts. Our results suggest that dust properties of UV-selected star forming galaxies at z>4 are characterised by (i) a steeper attenuation curve than at z<4, and (ii) a rapidly decreasing dust obscured fraction of star formation as a function of redshift. Nevertheless, even among this UV-selected sample, massive galaxies (log M_*/$M_\odot$>10) at z~5-6 already exhibit an obscured fraction of star formation of ~45%, indicating a rapid build-up of dust during the epoch of reionization.

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arXiv2020

The ALPINE-ALMA [CII] Survey: The nature, luminosity function and star formation history of dusty galaxies up to z~6

We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7, as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE) in COSMOS and ECDFS. These sources have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z=6. We have looked for counterparts in all the available multi-wavelength and photometric redshift catalogues, and in deeper near- and mid-IR source lists and maps, to identify optically dark sources with no matches in the public catalogues. Our ALMA blind survey allows us to push further the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint-end of the infrared LF, showing little evolution from z=2.5 to z=6, and a flat slope up to the highest redshifts. The SFRD obtained by integrating the luminosity function remains almost constant between z=2 and 6, and significantly higher than the optical/UV derivations, showing an important contribution of dusty galaxies and obscured star formation up to high-z. About 14 per cent of the ALPINE serendipitous continuum sources are optically+near-IR dark (six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [CII] emitters at z=5). The six HST and near-IR dark galaxies with mid-IR counterpart contribute for about 17 per cent of the total SFRD at z=5 and dominate the high-mass end of the stellar mass function at z>3.

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arXiv2020

The ALPINE-ALMA [CII] Survey: CGM 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 micron and far-infrared continuum data with multi-wavelength ancillary data we find that the system is composed of two massive (Mstar >~ 10^10 Msun) star-forming galaxies experiencing a major merger (stellar mass ratio r_mass ~ 0.9) at close spatial (~13 kpc; projected) and velocity (delta_v < 300 km/s) 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. ALMA reveals also 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 characterized 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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arXiv2020

The ALPINE-ALMA [CII] Survey: data processing, catalogs, and statistical source properties

The ALPINE-ALMA large program targets the [CII] 158 $μ$m line and the far-infrared continuum in 118 spectroscopically confirmed star-forming galaxies between z=4.4 and z=5.9. It represents the first large [CII] statistical sample built in this redshift range. We present details of the data processing and the construction of the catalogs. We detected 23 of our targets in the continuum. To derive accurate infrared luminosities and obscured star formation rates, we measured the conversion factor from the ALMA 158 $μ$m rest-frame dust continuum luminosity to the total infrared luminosity (L$_{\rm IR}$) after constraining the dust spectral energy distribution by stacking a photometric sample similar to ALPINE in ancillary single-dish far-infrared data. We found that our continuum detections have a median L$_{\rm IR}$ of 4.4$\times 10^{11}$ L$_\odot$. We also detected 57 additional continuum sources in our ALMA pointings. They are at lower redshift than the ALPINE targets, with a mean photometric redshift of 2.5$\pm$0.2. We measured the 850 $μ$m number counts between 0.35 and 3.5 mJy, improving the current interferometric constraints in this flux density range. We found a slope break in the number counts around 3 mJy with a shallower slope below this value. More than 40 % of the cosmic infrared background is emitted by sources brighter than 0.35 mJy. Finally, we detected the [CII] line in 75 of our targets. Their median [CII] luminosity is 4.8$\times$10$^8$ L$_\odot$ and their median full width at half maximum is 252 km/s. After measuring the mean obscured SFR in various [CII] luminosity bins by stacking ALPINE continuum data, we find a good agreement between our data and the local and predicted SFR-L$_{\rm [CII]}$ relations of De Looze et al. (2014) and Lagache et al. (2018).

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arXiv2020

The ALPINE-ALMA [CII] Survey: Obscured Star Formation Rate Density and Main Sequence of star-forming galaxies at z>4

Star formation rate (SFR) measurements at z>4 have relied mostly on rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on IRX-$β$ relation are highly uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4<z<5.9. We use stacks of continuum images to measure average infrared (IR) luminosities taking into account both detected and undetected sources. Based on these measurements, we measure the position of the main sequence of star-forming galaxies and the specific SFR (sSFR) at $z\sim4.5$ and $z\sim5.5$. We find that the main sequence and sSFR do not evolve significantly between $z\sim4.5$ and $z\sim5.5$, as opposed to lower redshifts. We develop a method to derive the obscured SFR density (SFRD) using the stellar masses or FUV-magnitudes as a proxy of FIR fluxes measured on the stacks and combining them with the galaxy stellar mass functions and FUV luminosity functions from the literature. We obtain consistent results independent of the chosen proxy. We find that the obscured fraction of SFRD is decreasing with increasing redshift but even at $z\sim5.5$ it constitutes around 61\% of the total SFRD.

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arXiv2020

The ALPINE-ALMA [CII] survey: Small Lya-[CII] velocity offsets in main-sequence galaxies at 4.4 < z < 6

The Lya line in the UV and the [CII] line in the FIR are widely used tools to identify galaxies and to obtain insights into ISM properties in the early Universe. By combining data obtained with ALMA in band 7 at ~ 320 GHz as part of the ALMA Large Program to INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from DEIMOS at Keck, VIMOS and FORS2 at the VLT, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 < z < 6 in which we detect both the Lya line and the [CII]. We used [CII], observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we find that 90% of the selected objects have Lya-[CII] velocity offsets in the range 0 < Dv_Lya-[CII] < 400 km/s, in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower z. We observe ISM-[CII] offsets in the range -500 < Dv_ISM-[CII] < 0 km/s, in line with values at all redshifts. We find significant anticorrelations between Dv_Lya-[CII] and the Lya rest-frame equivalent width EW0(Lya) (or equivalently, the Lya escape fraction f_esc(Lya)). According to available models for the radiative transfer of Lya photons, the escape of Lya photons would be favored in galaxies with high outflow velocities, in agreement with our observations. The uniform shell model would also predict that the Lya escape in galaxies with slow outflows (0 < v_out < 300 km/s) is mainly determined by the neutral hydrogen column density (NHI), while the alternative model by Steidel+10 would favor a combination of NHI and covering fraction as driver of the Lya escape. We suggest that the observed increase in Lya escape that is observed between z~2 and z~6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction. [abridged]

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arXiv2020

The KMOS Lens-Amplified Spectroscopic Survey (KLASS): Kinematics and clumpiness of low-mass galaxies at cosmic noon

We present results from the KMOS Lens-Amplified Spectroscopic Survey (KLASS), an ESO Very Large Telescope (VLT) large program using gravitational lensing to study the spatially resolved kinematics of 44 star-forming galaxies at 0.6 1), we find a weak increase or flat trend. We investigate the relation between the rest-frame UV clumpiness of galaxies and their global kinematic properties. We find no clear trend between the clumpiness and the velocity dispersion and $\upsilon_{rot}/σ_0$. This could suggest that the kinematic properties of galaxies evolve after the clumps formed in the galaxy disk or that the clumps can form in different physical conditions.

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arXiv2020

The ALPINE-ALMA [CII] survey. Little to no evolution in the [CII]-SFR relation over the last 13 Gyr

The [CII] 158 micron line is one of the strongest IR emission lines, which has been shown to trace the star-formation rate (SFR) of galaxies in the nearby Universe and up to $z \sim 2$. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at $4.4 < z< 5.9$, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature we examine the relation between the [CII] luminosity and the SFR over the entire redshift range from $z \sim 4-8$. ALPINE galaxies, which are both detected in [CII] and dust continuum, show a good agreement with the local L([CII])-SFR relation. Galaxies undetected in the continuum with ALMA are found to be over-luminous in [CII], when the UV SFR is used. After accounting for dust-obscured star formation, by an amount SFR(IR)$\approx$SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L([CII])-SFR relation comparable to the local one. When [CII] non-detections are taken into account, the slope may be marginally steeper at high-z, although this is still somewhat uncertain. When compared in a homogeneous manner, the $z>6 $ [CII] measurements (detections and upper limits) do not behave very differently from the $z \sim 4-6$ data. We find a weak dependence of L([CII])/SFR on the Lyman-alpha equivalent width. Finally, we find that the ratio L([CII])/LIR $\sim (1-3) \times 10^{-3}$ for the ALPINE sources, comparable to that of "normal" galaxies at lower redshift. Our analysis, which includes the largest sample ($\sim 150$ galaxies) of [CII] measurements at $z>4$ available so far, suggests no or little evolution of the L([CII])-SFR relation over the last 13 Gyr of cosmic time.

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arXiv2020

The ALPINE-ALMA [CII] Survey: Size of Individual Star-Forming Galaxies at z=4-6 and their Extended Halo Structure

We present the physical extent of [CII] 158um line-emitting gas from 46 star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate CII at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [CII] line (r_e,[CII]) for individual galaxies and compare them with the rest-frame ultra-violet (UV) continuum (r_e,UV) from Hubble Space Telescope images. The effective radius r_e,[CII] exceeds r_e,UV by factors of ~2-3 and the ratio of r_e,[CII]/r_e,UV increases as a function of M_star. We do not find strong evidence that [CII] line, the rest-frame UV, and FIR continuum are always displaced over ~ 1-kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [CII] component over 10-kpc scales detected at 4.1$σ$-10.9$σ$ beyond the size of rest-frame UV and far-infrared (FIR) continuum. One object has tentative rotating features up to ~10-kpc, where the 3D model fit shows the rotating [CII]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [CII] line structure have high star-formation rate (SFR), stellar mass (M_star), low Lya equivalent-width, and more blue-shifted (red-shifted) rest-frame UV metal absorption (Lya line), as compared to galaxies without such extended [CII] structures. Although we cannot rule out the possibility that a selection bias towards luminous objects may be responsible for such trends, the star-formation driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [CII] line structures are ubiquitous to high-z star-forming galaxies.

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arXiv2020

The ALPINE-ALMA [CII] survey: Molecular gas budget in the Early Universe as traced by [CII]

The molecular gas content of normal galaxies at z>4 is poorly constrained, because the commonly used molecular gas tracers become hard to detect. We use the [CII]158um luminosity, recently proposed as a molecular gas tracer, to estimate the molecular gas content in a large sample of main-sequence star-forming galaxies at z=4.4-5.9, with a median stellar mass of 10^9.7 Msun, drawn from the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey. The agreement between molecular gas masses derived from [CII] luminosity, dynamical mass, and rest-frame 850um luminosity, extrapolated from the rest-frame 158um continuum, supports [CII] as a reliable tracer of molecular gas in our sample. We find a continuous decline of the molecular gas depletion timescale from z=0 to z=5.9, which reaches a mean value of (4.6+/-0.8)x10^8 yr at z~5.5, only a factor of 2-3 shorter than in present-day galaxies. This suggests a mild enhancement of star formation efficiency toward high redshifts, unless the molecular gas fraction significantly increases. Our estimates show that the rise in molecular gas fraction as reported previously, flattens off above z~3.7 to achieve a mean value of 63%+/-3 over z=4.4-5.9. This redshift evolution of the gas fraction is in line with the one of the specific star formation rate. We use multi-epoch abundance matching to follow the gas fraction evolution over cosmic time of progenitors of z=0 Milky Way-like galaxies in 10^13 Msun halos and of more massive z=0 galaxies in 10^14 Msun halos. Interestingly, the former progenitors show a monotonic decrease of the gas fraction with cosmic time, while the latter show a constant gas fraction from z=5.9 to z~2 and a decrease at z<2. We discuss three possible effects, namely outflows, halt of gas supplying, and over-efficient star formation, which may jointly contribute to the gas fraction plateau of the latter massive galaxies.

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arXiv2020

The ALPINE-ALMA [CII] Survey: Multi-Wavelength Ancillary Data and Basic Physical Measurements

We present the ancillary data and basic physical measurements for the galaxies in the ALMA Large Program to Investigate C+ at Early Times (ALPINE) survey - the first large multi-wavelength survey which aims at characterizing the gas and dust properties of 118 main-sequence galaxies at redshifts 4.4 < z < 5.9 via the measurement of [CII]-emission at 158 micro-meter (64% at >3.5$σ$) and the surrounding far-infrared (FIR) continuum in conjunction with a wealth of optical and near-infrared data. We outline in detail the spectroscopic data and selection of the galaxies as well as the ground- and space-based imaging products. In addition, we provide several basic measurements including stellar masses, star formation rates (SFR), rest-frame ultra-violet (UV) luminosities, UV continuum slopes ($β$), and absorption line redshifts, as well as H-alpha emission derived from Spitzer colors. We find that the ALPINE sample is representative of the 4 < z < 6 galaxy population selected by photometric methods and only slightly biased towards bluer colors ($Δβ$ ~ 0.2). Using [CII] as tracer of the systemic redshift (confirmed for one galaxy at z=4.5 out of 118 for which we obtained optical [OII]$λ$3727A emission), we confirm red shifted Ly-alpha emission and blue shifted absorption lines similar to findings at lower redshifts. By stacking the rest-frame UV spectra in the [CII] rest-frame we find that the absorption lines in galaxies with high specific SFR are more blue shifted, which could be indicative of stronger winds and outflows.

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arXiv2020

The ALPINE-ALMA [CII] Survey: On the nature of an extremely obscured serendipitous galaxy

We report the serendipitous discovery of a bright galaxy (Gal-A) observed as part of the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). While this galaxy is detected both in line and continuum emission in ALMA Band 7, it is completely dark in UV/optical filters and only presents a marginal detection in the UltraVISTA Ks band. We discuss the nature of the observed ALMA line, i.e. whether the emission comes from [CII] at z~4.6, or from high-J CO transitions at z~2.2. In the first case we find a [CII]-to-FIR luminosity ratio of log(L_[CII]/L_FIR)=-2.5, consistent with the average value for local star-forming galaxies (SFGs); in the second case, instead, the source would lie outside of the empirical relations between L_CO and L_FIR found in the literature. At both redshifts, we derive the star-formation rate (SFR) from the ALMA continuum, and the stellar mass (M*) by using stellar population synthesis models as input for LePHARE spectral energy distribution (SED) fitting. Exploiting our results, we believe that Gal-A is a Main-Sequence (MS), dusty SFG at z=4.6 (i.e. [CII] emitter) with log(SFR/[M/yr])~1.4 and log(M*/M)~9.7. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global star-formation rate density (SFRD) of the Universe at the end of the Reionisation epoch.

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arXiv2019

The ALPINE-ALMA [CII] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe

We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 um emission in a large sample of normal star-forming galaxies at 4 < z < 6 from the ALMA Large Program to INvestigate [C II] at Early times (ALPINE) survey. Searching for typical signatures of outflows in the high-velocity tails of the stacked [C II] profile, we observe (i) deviations from a single-component Gaussian model in the combined residuals and (ii) broad emission in the stacked [C II] spectrum, with velocities of |v|<~ 500 km/s. The significance of these features increases when stacking the subset of galaxies with star formation rates (SFRs) higher than the median (SFRmed = 25 Msun/yr), thus confirming their star-formation-driven nature. The estimated mass outflow rates are comparable to the SFRs, yielding mass-loading factors of the order of unity (similarly to local star-forming galaxies), suggesting that star-formation-driven feedback may play a lesser role in quenching galaxies at z > 4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km/s) of the higher-SFR galaxies is extended on physical sizes of ~ 30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs.

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arXiv2019

Towards sub-kpc scale kinematics of molecular and ionized gas of star-forming galaxies at $z\sim1$

We compare the molecular and ionized gas kinematics of two strongly lensed galaxies at $z\sim1$ based on observations from ALMA and MUSE. We derive the CO and [OII] rotation curves and dispersion profiles of these two galaxies. We find a difference between the observed molecular and ionized gas rotation curves for one of the galaxies, the Cosmic Snake, for which we obtain a spatial resolution of few hundred parsecs along the major axis. The rotation curve of the molecular gas is steeper than the rotation curve of the ionized gas. In the second galaxy, A521, the molecular and ionized gas rotation curves are consistent, but the spatial resolution is only of few kpc on the major axis. Using simulations, we investigate the effect of the thickness of the gas disk and effective radius on the observed rotation curves and find that a more extended and thicker disk smooths the curve. We also find that the presence of a strongly inclined thick disk (>1 kpc) can smooth the rotation curve because it degrades the spatial resolution along the line of sight. By building a model using a stellar disk and two gas disks, we reproduce the rotation curves of the Cosmic Snake with a molecular gas disk that is more massive and more radially and vertically concentrated than the ionized gas disk. Finally, we also obtain an intrinsic velocity dispersion in the Cosmic Snake of 18.5+-7 km/s and 19.5+-6 km/s for the molecular and ionized gas, respectively, which is consistent with a molecular disk with a smaller and thinner disk. For A521, the intrinsic velocity dispersion values are 11+-8 km/s and 54+-11 km/s, with a higher value for the ionized gas. This could indicate that the ionized gas disk is thicker and more turbulent in this galaxy. These results highlight the different spatial distribution of the molecular and ionized gas disks at $z\sim1$ and suggest the presence of thick ionized gas disks at this epoch.

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arXiv2019

The ALPINE-ALMA [CII] Survey: A Triple Merger at z~4.56

We report the detection of [CII]158um emission from a system of three closely-separated sources in the COSMOS field at z~4.56, as part of the ALMA Large Program to INvestigate CII at Early times (ALPINE). The two dominant sources are closely associated, both spatially (1.6"~11kpc) and in velocity (~100km/s), while the third source is slightly more distant (2.8"~18kpc, ~300km/s). The second strongest source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed [CII] luminosities, we derive a total log(SFR_[CII]/[Msol/year])=2.8+/-0.2, which may be split into contributions of 59%, 31%, and 10% from the central, east, and west sources, respectively. Comparison of these [CII] detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an on-going major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z~2.5.

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