arXiv subjects

Yoshinobu Fudamoto

Publications and source records attributed to Yoshinobu Fudamoto.

104 records · Page 6Linked to original sources

arXiv2022

Identification of Large Equivalent Width Dusty Galaxies at 4 $<$ z $<$ 6 from Sub-mm Colours

Infrared (IR), sub-millimetre (sub-mm) and millimetre (mm) databases contain a huge quantity of high quality data. However, a large part of these data are photometric, and are thought not to be useful to derive a quantitative information on the nebular emission of galaxies. The aim of this project is first to identify galaxies at z > 4-6, and in the epoch of reionization from their sub-mm colours. We also aim at showing that the colours can be used to try and derive physical constraints from photometric bands, when accounting for the contribution from the IR fine structure lines to these photometric bands. We model the flux of IR fine structure lines with CLOUDY, and add them to the dust continuum emission with CIGALE. Including or not emission lines in the simulated spectral energy distribution (SED) modifies the broad band emission and colours. The introduction of the lines allows to identify strong star forming galaxies at z > 4 - 6 from the log10 (PSW_250um/PMW_350um) versus log10 (LABOCA_870um/PLW_500um) colour-colour diagramme. By comparing the relevant models to each observed galaxy colour, we are able to roughly estimate the fluxes of the lines, and the associated nebular parameters. This method allows to identify a double sequence in a plot built from the ionization parameter and the gas metallicity. The HII and photodissociation region (PDR) fine structure lines are an essential part of the SEDs. It is important to add them when modelling the spectra, especially at z > 4 - 6 where their equivalent widths can be large. Conversely, we show that we can extract some information on strong IR fine structure lines and on the physical parameters related to the nebular emission from IR colour-colour diagrams.

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arXiv2022

The ALMA REBELS Survey: The Dust-obscured Cosmic Star Formation Rate Density at Redshift 7

Cosmic dust is an essential component shaping both the evolution of galaxies and their observational signatures. How quickly dust builds up in the early Universe remains an open question that requires deep observations at (sub-)millimeter wavelengths to resolve. Here we use Atacama Large Millimeter Array observations of 45 galaxies from the Reionization Era Bright Emission Line Survey (REBELS) and its pilot programs, designed to target [CII] and dust emission in UV-selected galaxies at $z\sim7$, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation $f_\mathrm{obs} = \mathrm{SFR}_\mathrm{IR} / \mathrm{SFR}_\mathrm{UV + IR}$ depends on stellar mass, similar to what is observed at lower redshift, and ranges from $f_\mathrm{obs} \approx 0.3 - 0.6$ for galaxies with $\log_{10}\left(M_\star / M_\odot\right) = 9.4 - 10.4$. We further adopt the $z\sim7$ stellar mass function from the literature to extract the obscured cosmic star formation rate density (SFRD) from the REBELS survey. Our results suggest only a modest decrease in the SFRD between $3\lesssim z \lesssim 7$, with dust-obscured star formation still contributing $\sim30\%$ at $z\sim7$. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization.

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arXiv2022

The ALMA REBELS Survey: Dust Continuum Detections at z > 6.5

We report 18 dust continuum detections ($\geq 3.3σ$) at $\sim88{\rm μm}$ and $158{\rm μm}$ out of 49 ultraviolet(UV)-bright galaxies ($M_{\rm UV} < -21.3$ mag) at $z>6.5$, observed by the Cycle-7 ALMA Large Program, REBELS and its pilot programs. This has more than tripled the number of dust continuum detections known at $z>6.5$. Out of these 18 detections, 12 are reported for the first time as part of REBELS. In addition, 15 of the dust continuum detected galaxies also show a [CII]$_{\rm 158{\rm μm}}$ emission line, providing us with accurate redshifts. We anticipate more line emission detections from six targets (including three continuum detected targets) where observations are still ongoing. The dust continuum detected sources in our sample tend to have a redder UV spectral slope than the ones without a dust continuum detection. We estimate that all of the sources have an infrared (IR) luminosity ($L_{\rm IR}$) in a range of $3-8 \times 10^{11} L_\odot$, except for one with $L_{\rm IR} = 1.5^{+0.8}_{-0.5} \times 10^{12}\,L_{\odot}$. Their fraction of obscured star formation is significant at $\gtrsim 50\%$. Some of the dust continuum detected galaxies show spatial offsets ($\sim 0.5-1.5''$) between the rest-UV and far-IR emission peaks. These separations appear to have an increasing trend against an indicator that suggests spatially decoupled phases of obscured and unobscured star formation. REBELS offers the best available statistical constraints on obscured star formation in UV-bright, massive galaxies at $z > 6.5$.

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arXiv2022

Bridging Optical and Far-Infrared Emission-Line Diagrams of Galaxies from Local to the Epoch of Reionization: Characteristic High [O III] 88 $\mathrm{μm}$/SFR at $z > 6$

We present photoionization modeling of galaxy populations at $z\sim0$, $2$, and $> 6$ to bridge optical and far-infrared (FIR) emission-line diagrams. We collect galaxies with measurements of optical and/or FIR ([O III] 88 $\mathrm{μm}$ and [C II] 158 $\mathrm{μm}$) emission line fluxes and plot them on the [O III]$\lambda5007/\mathrm{Hβ}$--[N II]$\lambda6585/\mathrm{Hα}$ (BPT) and L([O III]88)/SFR--L([C II]158)/SFR diagrams, where SFR is the star-formation rate and L([O III]88) and L([C II]158) are the FIR line luminosities. We aim to explain the galaxy distributions on the two diagrams with photoionization models that employ three nebular parameters: the ionization parameter $U$, hydrogen density $n_\text{H}$, and gaseous metallicity $Z_\text{gas}$. Our models successfully reproduce the nebular parameters of local galaxies, and then predict the distributions of the $z\sim0$, $2$, and $> 6$ galaxies on the diagrams. The predicted distributions illustrate the redshift evolution on all the diagrams; e.g., [O III]$/\mathrm{Hβ}$ and [O III]88/[C II]158 ratios continuously decrease from $z > 6$ to $0$. Specifically, the $z > 6$ galaxies exhibit $\sim\!0.5$ dex higher $U$ than low-redshift galaxies at a given $Z_\text{gas}$ and show predicted flat distributions on the BPT diagram at $\log{\mathrm{[O III]/Hβ}} = 0.5$-$0.8$. We find that some of the $z > 6$ galaxies exhibit high L([O III]88)/SFR ratios. To explain these high ratios, our photoionization models require a low stellar-to-gaseous metallicity ratio or bursty/increasing star-formation history at $z > 6$. The James Webb Space Telescope will test the predictions and scenarios for the $z > 6$ galaxies proposed by our photoionization modeling.

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arXiv2022

Possible Systematic Rotation in the Mature Stellar Population of a $z=9.1$ Galaxy

We present new observations with the Atacama Large Millimeter/submillimeter Array for a gravitationally-lensed galaxy at $z=9.1$, MACS1149-JD1. [O III] 88-$μ$m emission is detected at 10$σ$ with a spatial resolution of $\sim0.3$ kpc in the source plane, enabling the most distant morpho-kinematic study of a galaxy. The [O III] emission is distributed smoothly without any resolved clumps and shows a clear velocity gradient with $ΔV_{\rm obs}/2σ_{\rm tot}=0.84\pm0.23$, where $ΔV_{\rm obs}$ is the observed maximum velocity difference and $σ_{\rm tot}$ is the velocity dispersion measured in the spatially-integrated line profile, suggesting a rotating system. Assuming a geometrically thin self-gravitating rotation disk model, we obtain $V_{\rm rot}/σ_V=0.67_{-0.26}^{+0.73}$, where $V_{\rm rot}$ and $σ_V$ are the rotation velocity and velocity dispersion, respectively, still consistent with rotation. The resulting disk mass of $0.65_{-0.40}^{+1.37}\times10^{9}$ M$_\odot$ is consistent with being associated with the stellar mass identified with a 300 Myr-old stellar population independently indicated by a Balmer break in the spectral energy distribution. We conclude that the most of the dynamical mass is associated with the previously-identified mature stellar population that formed at $z\sim15$.

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arXiv2022

The ALMA REBELS Survey: Specific Star-Formation Rates in the Reionization Era

We present specific star-formation rates for 40 UV-bright galaxies at $z\sim7-8$ observed as part of the Reionization Era Bright Emission Line Survey (REBELS) ALMA large program. The sSFRs are derived using improved measures of SFR and stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [CII]-based spectroscopic redshifts. For each source in the sample, we derive stellar masses from SED fitting and total SFRs from calibrations of the UV and FIR emission. The median sSFR is $18_{-5}^{+7}$ Gyr$^{-1}$, significantly larger than literature measurements lacking constraints in the FIR. The increase in sSFR reflects the larger obscured SFRs we derive from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly-dependent on the assumed star formation history (SFH) in reionization-era galaxies. When large sSFR galaxies are modeled with non-parametric SFHs, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The [CII] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses that are easily able to accommodate the dominant old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties in the derived parameters, we find that the sSFR increases rapidly toward higher redshifts for massive galaxies ($9.6<\log(\rm M_*/M_{\odot})<9.8$), with a power law that goes as $(1+z)^{1.7\pm0.3}$, broadly consistent with expectations from the evolving baryon accretion rates.

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arXiv2022

IR SED and Dust Masses of Sub-solar Metallicity Galaxies at z~2.3

We present results from ALMA 1.2mm continuum observations of a sample of 27 star-forming galaxies at z=2.1-2.5 from the MOSFIRE Deep Evolution Field (MOSDEF) survey. These galaxies have gas-phase metallicity and star-formation rate measurements from Hb, [OIII], Ha, and [NII]. Using stacks of Spitzer, Herschel, and ALMA photometry (rest-frame ~ 8-400$μ$m), we examine the IR SED of high-redshift subsolar metallicity (~0.5 $Z_{\odot}$) LIRGs. We find that the data agree well with an average SED template of higher luminosity local low-metallicity dwarf galaxies (reduced $χ^2$ of 1.8). When compared with the commonly used templates for solar-metallicity local galaxies or high-redshift LIRGs and ULIRGs, even in the most favorable case (with reduced $χ^2$ of 2.8), the templates are rejected at >98% confidence level. The broader and hotter IR SED of both the local dwarfs and high-redshift subsolar metallicity galaxies may result from different grain properties, a clumpy dust geometry, or a harder/more intense ionizing radiation field that heats the dust to higher temperatures. The obscured SFR indicated by the FIR emission of the subsolar metallicity galaxies is only ~ 60% of the total SFR, which is considerably lower than that of the local LIRGs with ~ 96-97% obscured fractions. Due to the evolving IR SED shape, the local LIRG templates fit to mid-IR data can overestimate the Rayleigh-Jeans tail measurements at z~2 by a factor of 2-20, and these templates underestimate IR luminosities if fit to the observed ALMA fluxes by >0.4dex. At a given stellar mass or metallicity, dust masses at z~2.3 are an order of magnitude higher than those at z~0. Given the predicted molecular gas mass fractions, the observed z~2.3 dust-to-stellar mass ratios suggest lower dust-to-molecular gas masses than in local galaxies at the same metallicity.

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arXiv2022

A Search for H-Dropout Lyman Break Galaxies at z~12-16

We present two bright galaxy candidates at z~12-13 identified in our H-dropout Lyman break selection with 2.3 deg2 near-infrared deep imaging data. These galaxy candidates, selected after careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 um, a flat continuum at 2-5 um, and non-detections at <1.2 um in the available photometric datasets, all of which are consistent with z>12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4sigma [OIII]88um line at z=13.27, in agreement with its photometric redshift estimate. The number density of the z~12-13 candidates is comparable to that of bright z~10 galaxies, and is consistent with a recently proposed double power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z~4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z~10-13. Combined with recent studies reporting similarly bright galaxies at z~9-11 and mature stellar populations at z~6-9, our results indicate the existence of a number of star-forming galaxies at z>10, which will be detected with upcoming space missions such as James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS.

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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 [C II] survey: the luminosity function of serendipitous [C II] line emitters at $z\sim 5$

We present the first [CII] 158 $μ$m luminosity function (LF) at $z\sim 5$ from a sample of serendipitous lines detected in the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). A search performed over the 118 ALPINE pointings revealed several serendipitous lines. Based on their fidelity, we selected 14 lines for the final catalog. According to the redshift of their counterparts, we identified 8 out of 14 detections as [CII] lines at $z\sim 5$, and two as CO transitions at lower redshifts. The remaining 4 lines have an elusive identification in the available catalogs and we considered them as [CII] candidates. We used the 8 confirmed [CII] and the 4 [CII] candidates to build one of the first [CII] LFs at $z\sim 5$. We found that 11 out of these 12 sources have a redshift very similar to that of the ALPINE target in the same pointing, suggesting the presence of overdensities around the targets. Therefore, we split the sample in two (a "clustered" and "field" sub-sample) according to their redshift separation and built two separate LFs. Our estimates suggest that there could be an evolution of the [CII] LF between $z \sim 5$ and $z \sim 0$. By converting the [CII] luminosity to star formation rate we evaluated the cosmic star formation rate density (SFRD) at $z\sim 5$. The clustered sample results in a SFRD $\sim 10$ times higher than previous measurements from UV-selected galaxies. On the other hand, from the field sample (likely representing the average galaxy population) we derived a SFRD $\sim 1.6$ higher compared to current estimates from UV surveys but compatible within the errors. Because of the large uncertainties, observations of larger samples are necessary to better constrain the SFRD at $z\sim 5$. This study represents one of the first efforts aimed at characterizing the demography of [CII] emitters at $z\sim 5$ using a mm-selection of galaxies.

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arXiv2020

ALMA Characterises the Dust Temperature of z ~ 5.5 Star-Forming Galaxies

The infrared spectral energy distributions (SEDs) of main-sequence galaxies in the early universe (z > 4) is currently unconstrained as infrared continuum observations are time consuming and not feasible for large samples. We present Atacama Large Millimetre Array (ALMA) Band 8 observations of four main-sequence galaxies at z ~ 5.5 to study their infrared SED shape in detail. Our continuum data (rest-frame 110$\rm μm$, close to the peak of infrared emission) allows us to constrain luminosity weighted dust temperatures and total infrared luminosities. With data at longer wavelengths, we measure for the first time the emissivity index at these redshifts to provide more robust estimates of molecular gas masses based on dust continuum. The Band 8 observations of three out of four galaxies can only be reconciled with optically thin emission redward of rest-frame 100$\rm μm$. The derived dust peak temperatures at z ~ 5.5 (38$\pm$8K) are elevated compared to average local galaxies, however, 5-10K below what would be predicted from an extrapolation of the trend at $z<4$. This behaviour can be explained by decreasing dust abundance (or density) towards high redshifts, which would cause the infrared SED at the peak to be more optically thin, making hot dust more visible to the external observer. From the 850$\rm μm$ dust continuum, we derive molecular gas masses between $10^{10}$ and $10^{11}\,{\rm M_{\odot}}$ and gas fractions (gas over total mass) of 30-80% (gas depletion times of 100-220Myrs). All in all, our results provide a first measured benchmark SED to interpret future millimetre observations of normal, main-sequence galaxies in the early Universe.

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arXiv2019

A$^3$COSMOS: The Dust Attenuation of Star-Forming Galaxies at $z=2.5-4.0$ from the COSMOS-ALMA Archive

We present an analysis of the dust attenuation of star forming galaxies at $z=2.5-4.0$ through the relationship between the UV spectral slope ($β$), stellar mass ($M_{\ast}$) and the infrared excess (IRX$=L_{\rm{IR}}/L_{\rm{UV}}$) based on far-infrared continuum observations from the Atacama Large Millimeter/sub-millimeter Array (ALMA). Our study exploits the full ALMA archive over the COSMOS field processed by the A$^3$COSMOS team, which includes an unprecedented sample of $\sim1500$ galaxies at $z\sim3$ as primary or secondary targets in ALMA band 6 or 7 observations with a median continuum sensitivity of 126 $\rm{μJy/beam}$ (1$σ$). The detection rate is highly mass dependent, decreasing drastically below $\log (M_{\ast}/M_{\odot})=10.5$. The detected galaxies show that the IRX-$β$ relationship of massive ($\log M_{\ast}/M_{\odot} > 10$) main sequence galaxies at $z=2.5-4.0$ is consistent with that of local galaxies, while starbursts are generally offset by $\sim0.5\,{\rm dex}$ to larger IRX values. At the low mass end, we derive upper limits on the infrared luminosities through stacking of the ALMA data. The combined IRX-$M_{\ast}$ relation at $\rm{log\,(M_{\ast}/M_{\odot})>9}$ exhibits a significantly steeper slope than reported in previous studies at similar redshifts, implying little dust obscuration at $\log M_{\ast}/M_{\odot}<10$. However, our results are consistent with early measurements at $z\sim5.5$, indicating a potential redshift evolution between $z\sim2$ and $z\sim6$. Deeper observations targeting low mass galaxies will be required to confirm this finding.

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arXiv2017

A New Constraint on Reionization from Evolution of the Ly$α$ Luminosity Function at $z\sim6-7$ Probed by a Deep Census of $z=7.0$ Ly$α$ Emitter Candidates to 0.3 $L^*$

We detect 20 $z=7.0$ Ly$α$ emitter (LAE) candidates to $L({\rm Ly}α) \geq 2 \times 10^{42}$ erg s$^{-1}$ or $0.3$ $L^*_{z=7}$ and in $6.1\times 10^5$ Mpc$^3$ volume in the Subaru Deep Field and the Subaru/XMM-Newton Deep Survey field by 82 and 37 hours of Subaru Suprime-Cam narrowband NB973 and reddest optical $y$-band imaging. We compare their Ly$α$ and UV luminosity functions (LFs) and densities and Ly$α$ equivalent widths (EWs) to those of $z=5.7$, 6.6 and 7.3 LAEs from previous Suprime-Cam surveys. The Ly$α$ LF (density) rapidly declines by a factor of $\times$1.5 (1.9) in $L({\rm Ly}α)$ at $z=5.7-6.6$ (160 Myr), $\times$1.5 (1.6) at $z=6.6-7.0$ (60 Myr) at the faint end and $\times$2.0 (3.8) at $z=7.0-7.3$ (40 Myr). Also, in addition to the systematic decrease in EW at $z=5.7-6.6$ previously found, 2/3 of the $z=7.0$ LAEs detected in the UV continuum exhibit lower EWs than the $z=6.6$ ones. Moreover, while the UV LF and density do not evolve at $z=5.7-6.6$, they modestly decline at $z=6.6-7.0$, implying galaxy evolution contributing to the decline of the Ly$α$ LF. Comparison of the $z=7.0$ Ly$α$ LF to the one predicted by an LAE evolution model further reveals that galaxy evolution alone cannot explain all the decline of Ly$α$ LF. If we attribute the discrepancy to Ly$α$ attenuation by neutral hydrogen, the intergalactic medium transmission of Ly$α$ photons at $z=7.0$ would be $T_{{\rm Ly}α}^{\rm IGM} \leq 0.6-0.7$. It is lower (higher) than $T_{{\rm Ly}α}^{\rm IGM}$ at $z=6.6$ (7.3) derived by previous studies, suggesting rapid increase in neutral fraction at $z > 6$.

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arXiv2017

The Dust Attenuation of Star-forming Galaxies at $z\sim3$ and Beyond: New Insights from ALMA Observations

We present results on the dust attenuation of galaxies at redshift $\sim3-6$ by studying the relationship between the UV spectral slope ($β_{\rm UV}$) and the infrared excess (IRX; $L_{\rm IR}$/$L_{\rm UV}$) using ALMA far-infrared continuum observations. Our study is based on a sample of 67 massive, star-forming galaxies with a median mass of $M_{\ast}\sim 10^{10.7}\,M_{\rm \odot}$ spanning a redshift range $z=2.6-3.7$ (median $z=3.2$) that were observed with ALMA at $λ_{rest}=300\,{\rm μm}$. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX-$β_{\rm UV}$ relationship at $z\sim3$ is mostly consistent with that of local starburst galaxies on average. However, we find evidence for a large dispersion around the mean relationship by up to $\pm0.5$ dex. Nevertheless, the locally calibrated dust correction factors based on the IRX-$β_{\rm UV}$ relation are on average applicable to main-sequence $z\sim3$ galaxies. This does not appear to be the case at even higher redshifts, however. Using public ALMA observations of $z\sim4-6$ galaxies we find evidence for a significant evolution in the IRX-$β_{\rm UV}$ and the IRX-$M_{\ast}$ relations beyond $z\sim3$ toward lower IRX values. We discuss several caveats that could affect these results, including the assumed dust temperature. ALMA observations of larger $z>3$ galaxy samples will be required to confirm this intriguing redshift evolution.

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