arXiv subjects

Michael Romano

Publications and source records attributed to Michael Romano.

At least 19 recordsLinked to original sources

arXiv2026

Tracing Lyman alpha escape in the CRISTAL-02 galaxy at z~5.3

We investigate the mechanisms regulating Lyman-alpha (Ly$\alpha$) escape in the star-forming galaxy CRISTAL-02 at z~5.3. The galaxy has clumpy morphology, suggestive that it may be interacting with other system(s). Two clumps (A and B, hereafter) are suggested as a site for intense star-formation or potential AGN candidates. We investigate how the local gas, dust, and feedback shape the escape of Ly$\alpha$ photons around these clumps. Using VLT/MUSE and JWST/NIRSpec IFU observations, complemented by NIRCam UV imaging, we constructed spatially matched emission-line maps. We derived flux, line-ratio, and extinction maps, together with spatially resolved Ly$\alpha$ escape fractions and ionizing photon production efficiencies. We find that Ly$\alpha$ is significantly more extended than H$\alpha$ and UV, reaching ~33 kpc and preferentially extending along the cold molecular gas outflow traced by [C II] emission. Clumps A and B show contrasting Ly$\alpha$ properties: Clump A has lower dust attenuation and enhanced Ly$\alpha$/H$\alpha$ ratios and escape fraction, whereas Clump B is brighter in H$\alpha$ and UV but has suppressed Ly-$\alpha$ despite a higher ionizing photon production efficiency. These results indicate that Ly$\alpha$ escape is strongly influenced by the local H I geometry, dust, and outflows and cannot be explained by ionizing photon production alone. The observed Ly$\alpha$ morphology and zELDA radiative transfer modeling favor an outflow-driven escape scenario, while the available data cannot uniquely distinguish between AGN and star formation-driven feedback.

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arXiv2026

Breathing Fire: Hot Dust in the Big Three Dragons at z = 7.15

We present new Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 ($\lambda_\mathrm{obs} = 0.45\,\mathrm{mm}$) and 4 ($\lambda_\mathrm{obs} = 2.2\,\mathrm{mm}$) observations towards the Big Three Dragons, a pair of merging Lyman-break galaxies (LBGs) at $z=7.15$. The system was previously detected in ALMA Bands 6, 7 and 8 ($\lambda_\mathrm{obs} = 0.73 - 1.32\,\mathrm{mm}$), which, combined with our new observations, allows us to robustly constrain its dust temperature and obscured SFR. The unresolved Band 4 observations yield a $3.5\sigma$ detection, and the $0.4''$ Band 9 observations detect the Eastern and Western LBGs at $3.7$ and $3.5\sigma$, respectively. Through modified blackbody fitting, we infer a global dust temperature of $T_d = 78_{-23}^{+35}\,\mathrm{K}$ for the system, which implies a high IR luminosity of $\log(L_\mathrm{IR}/L_\odot) = 12.32_{-0.41}^{+0.43}$. This makes the Big Three Dragons one of the most IR-luminous systems known at $z>7$, with a total $\mathrm{SFR}_\mathrm{UV+IR} = 267_{-153}^{+418}\,M_\odot\,\mathrm{yr}^{-1}$ that is almost completely obscured ($f_\mathrm{obs} = 0.94_{-0.09}^{+0.04}$). Using resolved ALMA observations in Bands 6, 8 and 9, we confirm both LBGs have hot dust temperatures ($T_d \approx 67 - 84\,\mathrm{K}$) and correspondingly high obscured fractions ($f_\mathrm{obs} \approx 0.88 -0.95$). We find the Western LBG to fall $\sim1\,\mathrm{dex}$ above the canonical IRX-$\beta_\mathrm{UV}$ relation, suggesting patchy dust obscuration. The compact Eastern component, on the other hand, is consistent with a Calzetti- or SMC-like dust screen within the uncertainties. Together with the similarly hot dust temperature recently reported for the $z=8.31$ galaxy MACS0416-Y1, our results suggest a non-negligible fraction of star formation at the bright end of the UV luminosity function is highly dust-obscured, even at $z\gtrsim7$.

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arXiv2026

The ALPINE-CRISTAL-JWST Survey: Gas-phase abundance gradients of main sequence star-forming galaxies and their kinematics at $4 < z < 6$

We present gas-phase radial metallicity profiles for 20 main-sequence galaxies at $4 0.05{\rm dexkpc^{-1}}$ at $1\sigma$, and none have a significant negative gradient. We investigated the correlation between the metallicity gradients and the intrinsic gas velocity dispersion $\sigma_0$ as well as the $V_{\rm rot}/\sigma_0$ ratio of the disks. Combining our sample with mass-matched literature samples at $3<z<7$, we found a negative shallow correlation between $V_{\rm rot}/\sigma_0$ and the metallicity gradients, but no strong relationships with $\sigma_0$. As $V_{\rm rot}/\sigma_0$ increases towards later cosmic times, the observed negative trend with $V_{\rm rot}/\sigma_0$ is consistent with the overall cosmic evolution of metallicity gradients from high to low redshifts. This suggests that disk maturity plays a crucial role in shaping the radial metallicity gradients. [Abridged abstract]

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arXiv2026

The ALPINE-CRISTAL-JWST Survey: Chemical Abundance Comparison Between the ISM and CGM of Main-Sequence Galaxies at z=4-6

Gaseous halos around galaxies play an important role in galaxy evolution. The exchange of metals from the interstellar medium (ISM) to the circumgalactic medium (CGM) are caused by the formation, feedback, and/or merging history of galaxies. We study the variation in chemical composition between the ISM ($\lesssim3\,$kpc) and CGM ($\sim5-10\,$kpc) for a sample of $M_{\star}>10^{9.5}\,M_{\odot}$ main-sequence galaxies at $4<z<6$ with both JWST and ALMA observations. Using JWST/NIRSpec integral field spectroscopy, we derive the optical line ratios from the ISM and the CGM for our sample focusing on the typical optical lines used for metallicity studies. Our comparison shows that the ISM and the CGM have similar chemical abundances. This indicates that the CGM of these typical $4<z<6$ galaxies is enriched to the level of their ISM in the early universe. Using statistical tests, we find that some of the line ratios show marginal differences between the ISM and CGM. Combined with \texttt{Cloudy} modeling, our results suggest that a difference in ionization level (higher for the ISM) is the dominant reason for the observed ratio difference of oxygen line ratios. There is also indication of a deficit in the nitrogen abundance with respect to oxygen in the CGM, which suggests a delay in redistribution of secondary nitrogen. Finally, an enhanced $F_{[\rm CII]\rm 158\mu m}/F_{\rm H\alpha}$ ratio is observed in the CGM, suggesting that feedback and/or mergers play a key role in metal mixing.

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arXiv2025

The molecular diversity of the ISM in galaxies across cosmic time

Submillimetre molecular lines (e.g., CO, HCN, SiO) provide a uniquely powerful view of the physical and chemical processes that govern star formation (SF) and galaxy evolution. Yet, our current picture of the molecular universe beyond the Milky Way remains strikingly incomplete: broad chemical inventories exist for only a handful of galaxies, typically more extreme than the Milky Way, constrained by sensitivity limits and narrow survey strategies. In the 2040s, surveying galaxies with multi-species, multi-transitions observations across diverse galactic environments will be crucial to establish effective chemical diagnostics of the various ISM processes from the early universe to $z=0$. Extragalactic astrochemistry provides a uniquely sensitive probe of the physical processes shaping galaxies, allowing us to understand, species by species, how gas responds to its local environment and how galaxies grow, transform, and recycle matter over cosmic time.

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arXiv2025

The ALPINE-CRISTAL-JWST Survey: Stellar and nebular dust attenuation of main-sequence galaxies at z~4-6

Characterizing dust attenuation is crucial for revealing the intrinsic physical properties of galaxies. We present an analysis of dust attenuation in 18 spectroscopically confirmed star-forming main-sequence galaxies at $z = 4.4-5.7$ observed with JWST/NIRSpec IFU and NIRCam, selected from the ALPINE and CRISTAL ALMA large programs. We fit the emission line fluxes from NIRSpec and the broad-band photometry from NIRCam with Prospector, using both spatially integrated emission and $\sim0.6$ kpc pixel-by-pixel measurements. We derive the stellar-to-nebular dust attenuation ratio ($f=E(B-V)_{\mathrm{star}}/E(B-V)_{\mathrm{neb}}$) from the SED fits and the Balmer decrement with H$\alpha$ and H$\beta$. Although individual galaxies show large scatter, the best-fit value is $f = 0.51^{+0.04}_{-0.03}$, slightly higher than that measured for local starburst galaxies. We find weak correlations of $f$ with galaxy properties, increasing with higher specific star-formation rates, younger stellar ages, and more recent star-formation. For the range of $E(B-V)_{\mathrm{star}} = 0.009-0.15$ mag for in our sample, assuming $f = 1$ (often adopted in high-redshift studies) instead of $f = 0.51$ underestimate line luminosities and ionizing photon production efficiency $\xi_\text{ion}$ by $\sim3-36\%$ and $\sim4-46\%$, respectively. We also find that the total stellar masses estimated from spatially-integrated SED fits with a delayed-$\tau$ star-formation histories are systematically smaller than the sum of pixel-by-pixel SED fits, with a median offset of $\sim 0.26$ dex, likely because the integrated fits are biased toward luminous young stellar populations.

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arXiv2025

The slope and scatter of the star forming main sequence at z~5 : reconciling observations with simulations

Galaxies exhibit a tight correlation between their star-formation rate and stellar mass over a wide redshift range known as the star-forming main sequence (SFMS). With JWST, we can now investigate the SFMS at high redshifts down to masses of $\sim10^6$ M$_{\odot}$, using sensitive star-formation rate tracers such as H$\alpha$ emission -- which allow us to probe the variability in star formation histories. We present inferences of the SFMS based on 316 H$\alpha$-selected galaxies at $z\sim4$-$5$ with $\log(\rm M_\star/M_\odot) = 6.4$ -$10.6$. These galaxies were identified behind the Abell 2744 lensing cluster with NIRCam grism spectroscopy from the ``All the Little Things'' (ALT) survey. At face value, our data suggest a shallow slope of the SFMS (SFR $\propto \mathrm{M}_\star^\alpha$, with $\alpha=0.45$). After correcting for the H$\alpha$-flux limited nature of our survey using a Bayesian framework, the slope steepens to $\alpha = 0.59^{+0.10}_{-0.09}$, whereas current data on their own are inconclusive on the mass dependence of the scatter. These slopes differ significantly from the slope of $\approx1$ expected from the observed evolution of the galaxy stellar mass function and from simulations. When fixing the slope to $\alpha=1$, we find evidence for a decreasing intrinsic scatter with stellar mass (from $\approx 0.5$ dex at M$_\star=10^8$ M$_\odot$ to $0.4$ dex at M$_\star=10^{10}$ M$_\odot$). This tension might be explained by a (combination of) luminosity-dependent SFR(H$\alpha$) calibration, a population of (mini)-quenched low-mass galaxies, or underestimated dust attenuation in high-mass galaxies. Future deep observations across facilities can quantify these processes, enabling better insights into the variability of star formation histories.

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arXiv2025

The ALPINE-CRISTAL-JWST Survey: The Fast Metal Enrichment of Massive Galaxies at z~5

We present the stellar mass-metallicity relation (MZR) and mass-metallicity-star formation relation ("fundamental metallicity relation"; FMR) of 18 massive (log(M/Msun) = 9.5 - 11) main-sequence galaxies at z~5 from the ALPINE-CRISTAL-JWST sample. This sample complements recent studies by JWST at up to two orders of magnitude lower stellar masses. The metallicities are derived using strong optical lines, and verified by temperature-based oxygen abundance measurements for five galaxies for which faint auroral lines are detected. We find that the metal abundance evolves, on average, from 40% to 60% solar between z~5 and cosmic noon (z~2) at the massive end of the MZR, suggesting already significant metal enrichment at early times. The FMR at z=5 exhibits a 5x larger scatter (preferentially to lower metallicities) compared the local FMR relation. This scatter can be explained by a bursty star formation and the direct build-up of metals in early galaxies as well as differences in age and outflow efficiencies. Capitalizing on all available samples, we find that the observed MZR and FMR over three orders of stellar mass is generally in good agreement with results from cosmological simulation, although some underestimate the metal enrichment at low stellar masses. This may be due to too efficient metal-rich outflows. We show that the ALPINE-CRISTAL-JWST galaxies likely joined the current FMR at z~10 and will evolve into massive (log(M/Msun)~11.4) galaxies with super-solar metallicities by z=0.

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arXiv2025

The ALPINE-CRISTAL-JWST Survey: NIRSpec IFU Data Processing and Spatially-resolved Views of Chemical Enrichment in Normal Galaxies at z=4-6

We present a statistical study of spatially resolved chemical enrichment in 18 main-sequence galaxies at $z=4$--6, observed with \jwst/NIRSpec IFU as part of the ALPINE-CRISTAL-\jwst\ survey. Performing an optimized reduction and calibration procedure, including local background subtraction, light-leakage masking, stripe removal, and astrometry refinement, we achieve robust emission-line mapping on kiloparsec scales. Although line-ratio distributions vary across galaxies in our sample, we generally find mild central enhancements in [O\,\textsc{iii}]/H$\beta$, [O\,\textsc{ii}]/[O\,\textsc{iii}], [S\,\textsc{ii}]$_{6732}$/[S\,\textsc{ii}]$_{6718}$, H$\alpha$/H$\beta$, and $L_{\rm H\alpha}/L_{\rm UV}$, consistent with elevated electron density, dust obscuration, and bursty star formation accompanied by reduced metallicity and ionization parameter. These features point to inside-out growth fueled by recent inflows of pristine gas. Nevertheless, the median metallicity gradient is nearly flat over a few kpc scale, $\Delta \log({\rm O/H}) = 0.02 \pm 0.01$ dex kpc$^{-1}$, implying efficient chemical mixing through inflows, outflows, and mergers. From pixel-by-pixel stellar and emission-line characterizations, we further investigate the resolved Fundamental Metallicity Relation (rFMR). Metallicity is described by a fundamental plane with stellar mass and SFR surface densities, but with a stronger dependence on $\Sigma_{\rm SFR}$ than seen in local galaxies. Our results indicate that the regulatory processes linking star formation, gas flows, and metal enrichment were already vigorous $\sim$1 Gyr after the Big Bang, producing the nearly flat metallicity gradient and a stronger coupling between star formation and metallicity than observed in evolved systems in the local universe.

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arXiv2025

ALMA reveals diverse dust-to-gas mass ratios and quenching modes in old quiescent galaxies

Recent discoveries of dust and molecular gas in quiescent galaxies (QGs) up to $z\sim3$ challenge the long-standing view that the interstellar medium depletes rapidly once star formation ceases, raising key questions of whether dust and gas co-evolve in QGs, and how their depletion links to stellar aging. We present deep Atacama Large Millimeter/submillimeter Array (ALMA) Band~6 continuum and CO(3--2) observations of 17 QGs at $z\sim0.4$ in the COSMOS field. Using the dust-to-molecular gas mass ratio ($\delta_{\rm DGR}$) as a key diagnostic, we trace post-quenching evolution of the cold interstellar medium. Our study triples the number of QGs with direct $\delta_{\rm DGR}$ estimates, constraining 12 systems with stellar population ages of $\sim$5--10 Gyr. For the first time, we show that $\delta_{\rm DGR}$ in QGs ranges from $\sim8\times$ below to $\sim2.5\times$ above the canonical value of $\delta_{\rm DGR}\sim1/100$. Despite uniformly low molecular gas fractions (median $f_{\rm H_2}=M_{\rm H_2}/M_{\star}\sim4.1\%$), QGs follow diverse evolutionary paths: about half exhibit rapid ($\sim700$ Myr) exponential dust decline with age, while the rest show mild decline over $\gtrsim$2 Gyr, maintaining elevated $\delta_{\rm DGR}\gtrsim1/100$. Our results support simulations predictions of dust and molecular gas evolving independently post-quenching, without a preferred quenching mode. This challenges the use of dust continuum as a $\rm H_2$ tracer, implying that quenching cannot be robustly linked to interstellar medium conditions when relying solely on dust or gas.

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arXiv2025

The ALPINE-CRISTAL-JWST Survey: Revealing Less Massive Black Holes in High-Redshift Galaxies

We present a systematic search for broad-line active galactic nuclei (AGNs) in the ALPINE-CRISTAL-JWST sample of 18 star-forming galaxies ($M_\star>10^{9.5}~M_{\odot}$) at redshifts $z=4.4-5.7$. Using JWST/NIRSpec IFU, we identify 7 AGN candidates through the detection of broad \Ha\ emission lines from 33 aperture spectra centred on photometric peaks. These candidates include one highly robust AGN detection with FWHM $\sim$ 2800 \kms\ and six showing broad components with FWHM $\sim 600-1600$ \kms, with two in a merger system. We highlight that only broad-line detection is effective since these candidates uniformly lie within narrow emission-line ratio diagnostic diagrams where star-forming galaxies and AGNs overlap. The broad-line AGN fraction ranges from 5.9\% to 33\%, depending on the robustness of the candidates. Assuming that the majority are AGNs, the relatively high AGN fraction is likely due to targeting high-mass galaxies, where simulations demonstrate that broad-line detection is more feasible. Their black hole masses range from $10^6$ to $10^{7.5}~M_{\odot}$ with $0.1 \lesssim L_{\rm bol}/L_{\rm Edd}\lesssim 1$. Counter to previous JWST studies at high redshift that found overmassive black holes relative to their host galaxies, our candidates lie close to or below the local $M_{\rm BH}-M_\star$ scaling relations, thus demonstrating the effect of selection biases. This study provides new insights into AGN-host galaxy co-evolution at high redshift by identifying faint broad-line AGNs in galaxy samples, highlighting the importance of considering mass-dependent selection biases and the likelihood of a large population of AGNs being undermassive and just now being tapped by JWST.

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arXiv2025

Origins of Carbon Dust in a JWST-Observed Primeval Galaxy at $z\sim$6.7

JADES-GS-z6-0, a high-redshift galaxy ($z \sim 6.7$) recently observed as part of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES), exhibits a distinct bump in its rest-frame ultraviolet (UV) spectrum indicative of a large quantity of hydrocarbon grains, a sign of rapid metal and dust enrichment in its interstellar medium (ISM). This galaxy serves as an ideal case for examining rapid dust formation processes in the early universe. We investigated diverse dust production channels from a possible maximal formation redshift of $z_{\rm form} \approx 17$, enabling dust contributions from asymptotic giant branch (AGB) stars over the longest possible timescale. Our model simultaneously reproduces key spectral features of JADES-GS-z6-0 such as its Balmer decrement, UV slope, and UV bump. The match is obtained by adopting a star-formation history in which a burst at $\sim 600$~Myr accounts for approximately 30\% of the galaxy's final stellar mass. Our findings indicate two pathways for the formation of hydrocarbon grains, such as polycyclic aromatic hydrocarbons (PAHs): (1) efficient dust accretion within the ISM, necessitating a low depletion of metals into dust grains from Type II supernovae ($\approx 10$\%), or (2) dust production predominantly by Type II supernovae, requiring a high depletion fraction ($\approx 73$\%) without dust accretion. We further demonstrate that PAHs are unlikely to originate solely from AGB stars or from shattering of large grains in the ISM. The evolution of the UV slope with redshift points to a complex and bursty star formation history for galaxies observed by JADES.

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arXiv2024

The ALPINE-ALMA [C II] survey: Characterisation of Spatial Offsets in Main-Sequence Galaxies at $z \sim$ 4-6

Galaxy morphology is shaped by stellar activity, feedback, gas and dust properties, and interactions with surroundings, and can therefore provide insight into these processes. In this paper, we study the spatial offsets between stellar and interstellar medium emission in a sample of 54 main-sequence star-forming galaxies at $z\sim4-6$ observed with the Atacama Large Millimeter/submillimeter Array (ALMA) and drawn from the ALMA Large Program to INvestigate C$^+$ at Early times (ALPINE). We find no significant spatial offset for the majority ($\sim$ 70 percent) of galaxies in the sample among any combination of [C II], far-infrared continuum, optical, and ultraviolet emission. However, a fraction of the sample ($\sim$ 30 percent) shows offsets larger than the median by more than 3$\sigma$ significance (compared to the uncertainty on the offsets), especially between [C II] and ultraviolet emission. We find that these significant offsets are of the order of $\sim$0.5-0.7 arcsec, corresponding to $\sim$3.5-4.5 kiloparsecs. The offsets could be caused by a complex dust geometry, strong feedback from stars and active galactic nuclei, large-scale gas inflow and outflow, or a combination of these phenomena. However, our current analysis does not definitively constrain the origin. Future, higher resolution ALMA and JWST observations may help resolve the ambiguity. Regardless, since there exist at least some galaxies that display such large offsets, galaxy models and spectral energy distribution fitting codes cannot assume co-spatial emission in all main-sequence galaxies, and must take into account that the observed emission across wavelengths may be spatially segregated.

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arXiv2023

Dust survival in harsh environments -- Is photo-evaporation an important destruction mechanism?

Aims. We investigate the role of photo-evaporation of dust exposed to the radiation field from hot young stars and planetary nebulae (PNe) as a possible destruction mechanism of dust grains in the interstellar medium (ISM). Methods. We estimate photo-evaporation induced by the feedback of individual or clustered young stars, of PNe and in the presence of a variable radiation field scaled with the interstellar radiation field. For PNe we investigate dust photo-evaporation of both dust grains already present in the ISM as well as those formed in the last phases of the evolution of thermally pulsing asymptotic giant branch (TP-AGB) stars. We include dust photo-evaporation rate in models of dust evolution in galaxies for different assumptions of the dust growth scenario, dust-to-gas ratios, star formation histories, and initial mass functions of the stars. Results. For all the cases considered, we find that both photo-evaporation from young stars and from PNe are negligible with respect to other dust removal processes such as destruction from supernovae shocks, astration and possibly outflow. Grains are stable against photo-evaporation if they are exposed to a radiation field which is up to 10^7 times the interstellar radiation field. Conclusions. Dust grains of size >= 0.01 microns are not efficiently destroyed by photo-evaporation also in the presence of a strong radiation field.

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arXiv2023

Star-formation driven outflows in local dwarf galaxies as revealed from [CII] observations by Herschel

We characterize the physical properties of star-formation driven outflows in a sample of 29 local dwarf galaxies drawn from the Dwarf Galaxy Survey. We make use of Herschel/PACS archival data to search for atomic outflow signatures in the wings of individual [CII] 158 um spectra and in their stacked line profile. We find a clear excess of emission in the high-velocity tails of 11 sources which can be explained with an additional broad component in the modeling of their spectra. The remaining objects are likely hosts of weaker outflows that can still be detected in the average stacked spectrum. In both cases, we estimate the atomic mass outflow rates which result to be comparable with the star-formation rates of the galaxies, implying mass-loading factors of the order of unity. Outflow velocities in all the 11 galaxies with individual detection are larger than (or compatible with) the escape velocities of their dark matter halos, with an average fraction of 40% of gas escaping into the intergalactic medium (IGM). Depletion timescales due to outflows are lower than those due to gas consumption by star formation in most of our sources, ranging from hundred million to a few billion years. Our outflows are mostly consistent with momentum-driven winds generated by the radiation pressure of young stellar populations on dust grains, although the energy-driven scenario is not excluded if considering a coupling efficiency up to 20% between the energy injected by supernova (SN) and the interstellar medium. Our results suggest that galactic outflows can regulate the star formation history of dwarf galaxies as they are able to enrich with metals the circumgalactic medium of these sources, bringing on average a non-negligible amount of gas into the IGM. Our findings are suitable for tuning chemical evolution models attempting to describe the physical processes shaping the evolution of dwarf galaxies.

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arXiv2023

In pursuit of giants: II. Evolution of dusty quiescent galaxies over the last six billion years from the hCOSMOS survey

Quantifying changes in galaxies' interstellar medium (ISM) abundance after quenching star formation is an important aspect of galaxy evolution, but it is poorly constrained beyond the local universe. We characterise the dust-related properties in 548 quiescent galaxies observed at $0.1<z<0.6$ as part of the hCOSMOS spectroscopic survey. This is the largest sample of quiescent galaxies at intermediate redshifts, for which the co-evolution of dust, metals and stars have been estimated. We reveal the complex relations between the key markers of galaxies' dust life-cycles, such as specific dust mass ($M_{\rm dust}$/$M_{\rm \star}$), with gas-metallicity ($Z_{\rm gas}$), time since quenching ($t_{\rm quench}$), stellar age and size. We find morphology to be important factor of a large scatter ($\sim2$ orders of magnitude) in $M_{\rm dust}/M_{\rm \star}$. Through modelling the star formation histories of our objects, we derive a broad dynamical range of post-quenching timescales ($60\:\rm Myr<t_{\rm quench}<3.2\:\rm Gyr$). We find that $M_{\rm dust}/M_{\rm \star}$ is the highest in recently quenched systems ($t_{\rm quench}<500$ Myr), but its further evolution is non-monotonic as a consequence of diverse pathways for prolonged dust formation, or removal on various timescales. Our data are well reproduced by the SIMBA cosmological simulation and chemical models that include dust growth in the ISM. While this process is prevalent in dusty quiescent galaxies, $\sim15\%$ of objects show signs of external dust acquisition, most likely via minor mergers. Our results strongly suggest that prolonged dust production on a timescale $0.5-1\:\rm Gyr$ since quenching may be common in dusty quiescent galaxies at intermediate redshifts, even if their gas reservoirs are heavily exhausted (i.e., cold gas fraction $<1-5\%$).

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arXiv2022

The ALPINE-ALMA [CII] survey: The infrared-radio correlation and AGN fraction of star-forming galaxies at z $\sim$ 4.4-5.9

We present the radio properties of 66 spectroscopically-confirmed normal star-forming galaxies (SFGs) at $4.4<z<5.9$ in the COSMOS field that were [C II] detected in the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C II] at Early times (ALPINE). We separate these galaxies ("CII-detected-all") into lower redshift ("CII-detected-lz", $\langle z\rangle=4.5$) and higher redshift ("CII-detected-hz", $\langle z\rangle=5.6$) sub-samples and stack multi-wavelength imaging for each sub-sample from X-ray to radio bands. A radio signal is detected in the stacked 3 GHz image of CII-detected-all and -lz samples at $\gtrsim3\sigma$. We find that the infrared-radio correlation of our sample, quantified by $q_{\mathrm{TIR}}$, is lower than the local relation for normal SFGs at $\sim$3$\sigma$ significance level, and is instead broadly consistent with that of bright sub-mm galaxies at $2<z<5$. Neither of these samples show evidence of dominant AGN activity in their stacked Spectral Energy Distributions (SEDs), rest-frame UV spectra, or X-ray images. Although we cannot rule out the possible effect of the assumed spectral index and the applied infrared SED templates as at least partially causing these differences, the lower obscured fraction of star formation than at lower redshift can alleviate the tension between our stacked $q_{\mathrm{TIR}}$s and that of local normal SFGs. It is possible that the dust buildup, which primarily governs the IR emission in addition to older stellar populations, has not had enough time to occur fully in these galaxies, whereas the radio emission can respond on a more rapid timescale. Therefore, we might expect a lower $q_{\mathrm{TIR}}$ to be a general property of high-redshift SFGs.

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arXiv2022

The ALPINE-ALMA [CII] survey: dust attenuation curves at z=4.4-5.5

There is now ample evidence that dust is already present in abundance at high z. However, given the faintness of distant galaxies in the optical and the NIR, datasets are still limited and how the dust affects the emerging radiation of galaxies at very high redshift is not yet fully understood. Using the ALPINE survey, our objective is to quantify the dust attenuation properties in galaxies at z=4.4-5.5, and in particular the shape of their attenuation curve. Using the CIGALE code, we model the stellar populations and their interaction with the dust in order to measure some of the physical properties of a subsample of 23 main-sequence ALPINE galaxies. We find that the attenuation curves span a broad range of properties, from curves that are much steeper than the SMC extinction curve, to shallower than the starburst attenuation curve. The shape of the attenuation curves strongly depends on the V-band attenuation. Galaxies with the lowest attenuation also present the steepest curves. The steepness of such curves is probably the consequence of the combination of the intrinsic physical properties of the dust, the relative distribution of stars and dust in the interstellar medium, and the differential reddening. The broad range of attenuation curves found at z~5 shows that no single attenuation curve is appropriate for main sequence galaxies and that assuming a fixed curve can lead to large errors, for instance in the interpretation and use of the IRX-beta diagram, if SED modeling is not feasible. Great caution should be exercised when correcting high redshift galaxies for the presence of dust using the UV slope beta as it can affect the estimation of both SFR and stellar mass even at low V-band attenuation due to the steepness of the attenuation curve. However, when SED modeling can be used, the impact of the choice of the attenuation curve on the SFR and the stellar mass is limited.

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