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Tadayuki Kodama

Publications and source records attributed to Tadayuki Kodama.

At least 55 records · Page 3Linked to original sources
arXiv2023

Enhanced star formation and metallicity deficit in the USS 1558-003 forming protocluster at z=2.53

We use K-band multi-object near-infrared spectroscopy with Keck/MOSFIRE to search for environmental imprints on the gas properties of 27 narrow-band selected H$α$ emitters (HAEs) across the three major clumps of the assembling USS1558--003 protocluster at $z=2.53$. We target the H$α$ and [NII]$λ$6584 emission lines to obtain star-formation rates (SFR) and gas-phase oxygen abundances for our sources, confirming the membership of 23 objects. HAEs belonging to this protocluster display enhanced SFRs with respect to the main sequence of star formation at the same cosmic epoch. This effect is more prominent for low-mass galaxies ($\mathrm{\log M_*/M_\odot<10.0}$), which may be experiencing a vigorous phase of mass assembly shortly after they were formed. We compute the individual and stacked gas-phase metallicities for our sources finding a metallicity deficit for low-mass objects when compared against the field mass-metallicity relation and the massive Spiderweb protocluster at $z=2.16$. These results suggest that HAEs within USS1558--003 may be less evolved than those in the Spiderweb protocluster. Finally, we explore the gas metallicity - gas fraction relation for a small sample of five galaxies with CO(3-2) molecular gas information. Assuming our objects are in equilibrium, we obtain a relatively wide range of mass loading factors ($\mathrm{λ=0.5-2}$) matching field samples at the cosmic noon but in contrast with our previous results in the Spiderweb protocluster. We speculate that these discrepancies between protoclusters may be (partly) driven by differences in their current dynamical and mass assembly stages, hinting at the co-evolution of protoclusters and their galaxy populations at $2<z<3$.

astro-ph.GA↗
arXiv2023

Spatial extent of molecular gas, dust, and stars in massive galaxies at z=2-2.5 determined with ALMA and JWST

We present the results of 0.6"-resolution observations of CO J=3-2 line emission in 10 massive star-forming galaxies at z=2.2-2.5 with the Atacama Large Millimeter/submillimeter Array (ALMA). We compare the spatial extent of molecular gas with those of dust and stars, traced by the 870 $μ$m and 4.4 $μ$m continuum emissions, respectively. The average effective radius of the CO emission is 1.75$\pm$0.34 kpc, which is about 60 percent larger than that of the 870 $μ$m emission and is comparable with that of the 4.4 $μ$m emission. Utilizing the best-fit parametric models, we derive the radial gradients of the specific star-formation rate (sSFR), gas depletion timescale, and gas-mass fraction within the observed galaxies. We find a more intense star-formation activity with a higher sSFR and a shorter depletion timescale in the inner region than in the outer region. The central starburst may be the primary process for massive galaxies to build up a core. Furthermore, the gas-mass fraction is high, independent of the galactocentric radius in the observed galaxies, suggesting that the galaxies have not begun to quench star formation. Given the shorter gas depletion timescale in the center compared to the outer region, quenching is expected to occur in the center first and then propagate outward. We may be witnessing the observed galaxies in the formation phase of a core prior to the forthcoming phase of star formation propagating outward.

astro-ph.GA↗
arXiv2023

An enhanced abundance of bright galaxies in protocluster candidates at z~3-5

We present a protocluster search covering $z\sim3$ to $z\sim5$ based on the combination of the Hyper SuprimeCam Subaru Strategic Programme and the CFHT Large Area $U$-band Deep Survey. We identify about 30 protocluster candidates per unit redshift over the $\sim25\,\mathrm{deg^2}$ area of the Deep/Ultra-Deep layer. Protocluster candidates are selected as regions with a significantly enhanced surface density of dropout galaxies. With this large sample, we characterise the properties of their individual member galaxies. We compare the number counts of dropout galaxies in protocluster candidates with that of coeval field galaxies. Rest-frame UV bright galaxies are over-abundant in protocluster candidates, a trend seen across the full redshift range studied. We do not find evidence for their spatial distribution within protocluster candidates to be distinct from their fainter counterparts, nor for their UV colour to be different from that of field galaxies with the same brightness. Cosmological simulations predict this bright-end excess, with the main cause being a richer population of massive galaxies, with only a minor contribution from an enhancement in star formation activity (and therefore UV emission) at fixed mass. $U$-to-$K$ SED modelling of our observed samples supports this interpretation. This environmental differentiation in number counts is already in place at $z\sim5$, with no significant redshift dependence over the range in lookback times probed. These observational results and model predictions suggest that the cosmic clock is ahead in high-density environments.

astro-ph.GA↗
arXiv2023

COALAS II. Extended molecular gas reservoirs are common in a distant, forming galaxy cluster

This paper presents the results of 475 hours of interferometric observations with the Australia Telescope Compact Array towards the Spiderweb protocluster at \(z=2.16\). We search for large, extended molecular gas reservoirs among 46 previously detected CO(1-0) emitters, employing a customised method we developed. Based on the CO emission images and position-velocity diagrams, as well as the ranking of sources using a binary weighting of six different criteria, we have identified 14 robust and 7 tentative candidates that exhibit large extended molecular gas reservoirs. These extended reservoirs are defined as having sizes greater than 40 kpc or super-galactic scale. This result suggests a high frequency of extended gas reservoirs, comprising at least \(30 \%\) of our CO-selected sample. An environmental study of the candidates is carried out based on N-th nearest neighbour and we find that the large molecular gas reservoirs tend to exist in denser regions. The spatial distribution of our candidates is mainly centred on the core region of the Spiderweb protocluster. The performance and adaptability of our method are discussed. We found 13 (potentially) extended gas reservoirs located in nine galaxy (proto)clusters from the literature. We noticed that large extended molecular gas reservoirs surrounding (normal) star-forming galaxies in protoclusters are rare. This may be attributable to the lack of observations low-J CO transitions and the lack of quantitative analyses of molecular gas morphologies. The large gas reservoirs in the Spiderweb protocluster are a potential source of the intracluster medium seen in low redshift Virgo- or Coma-like galaxy clusters.

astro-ph.GA↗
arXiv2023

Environmental impacts on the rest-frame UV size and morphology ofstar-forming galaxies at $z\sim2$

We report the measurement of rest-frame UV size and morphology of H$α$-emission-selected star-forming galaxies (HAEs) in four protoclusters at z $\sim$ 2 (PKS 1138-262, USS 1558-003, PHz G237.0+42.5, and CC 2.2) using archival Hubble Space Telescope Advanced Camera Surveys (HST/ACS) F814W data. We compare the measurement of 122 HAEs in protoclusters detected by HST/ACS to a coeval comparison field sample of 436 HAEs. We find the size distributions of protocluster and field HAEs are similar with typical half-light radius of $\sim$ 2.5 kpc. At fixed stellar mass, there is no significant difference between HAE in protocluster and in field, which is also supported by stacking analyses. This result suggests that the environment does not significantly affect the size of galaxies during the star-forming phase at this epoch. Based on Sérsic index and non-parametric morphologies, HAE morphologies in both environments at $z\sim2$ in rest-frame UV are consistent with disk-like star-forming galaxies, although we also find $29\% \pm 4\%$ HAEs have peculiar or disturbed morphologies. The fraction of disturbed galaxies is higher in protocluster environment, with $39 \pm 8 \%$ protocluster HAEs showing disturbed morphologies, compared to $26\pm4\%$ in the comparison field. The apparent disturbed morphologies are correlated with higher star-formation activity and may be caused by either in situ giant clumps or mergers.

astro-ph.GA↗
arXiv2023

A Multi-Wavelength Investigation of Dust and Stellar Mass Distributions in Galaxies: Insights from High-Resolution JWST Imaging

We study the morphological properties of mid-infrared selected galaxies at $1.0<z<1.7$ in the SMACS J0723.3-7327 cluster field, to investigate the mechanisms of galaxy mass assembly and structural formation at cosmic noon. We develop a new algorithm to decompose the dust and stellar components of individual galaxies by utilizing high-resolution images in the MIRI F770W and NIRCam F200W bands. Our analysis reveals that a significant number of galaxies with stellar masses between ${\rm 10^{9.5}<M_*/M_\odot<10^{10.5}}$ exhibit dust cores that are relatively more compact compared to their stellar cores. Specifically, within this mass range, the non-parametric method indicates that the dust cores are, on average, 1.23 ($\pm0.05$) times more compact than the stellar cores, when evaluated with flux concentration of the two components within a fixed radius. Similarly, the parametric method yields an average compactness ratio of 1.27 ($\pm0.06$). Notably, the most massive galaxy ($\rm{M_* \sim 10^{10.9}\,M_\odot}$) in our sample demonstrates a comparable level of compactness between its stellar core and dust, with a dust-to-stellar ratio of 0.86 (0.89) as derived from non-parametric (parametric) method. The observed compactness of the dust component is potentially attributed to the presence of a (rapidly growing) massive bulge, in some cases associated with elevated star formation. Expanding the sample size through a joint analysis of multiple Cycle~1 deep-imaging programs can help to confirm the inferred picture. Our pilot study highlights that MIRI offers an efficient approach to studying the structural formation of galaxies from cosmic noon to the modern universe.

astro-ph.GA↗
arXiv2023

GREX-PLUS Science Book

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a mission candidate for a JAXA's strategic L-class mission to be launched in the 2030s. Its primary sciences are two-fold: galaxy formation and evolution and planetary system formation and evolution. The GREX-PLUS spacecraft will carry a 1.2 m primary mirror aperture telescope cooled down to 50 K. The two science instruments will be onboard: a wide-field camera in the 2-8 $μ$m wavelength band and a high resolution spectrometer with a wavelength resolution of 30,000 in the 10-18 $μ$m band. The GREX-PLUS wide-field camera aims to detect the first generation of galaxies at redshift $z>15$. The GREX-PLUS high resolution spectrometer aims to identify the location of the water ``snow line'' in proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of supermassive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on.

astro-ph.CO↗
arXiv2022

A ~600 pc view of the strongly-lensed, massive main sequence galaxy J0901: a baryon-dominated, thick turbulent rotating disk with a clumpy cold gas ring at z = 2.259

We present a high-resolution kinematic study of the massive main-sequence star-forming galaxy (SFG) SDSS J090122.37+181432.3 (J0901) at z=2.259, using 0.36 arcsec ALMA CO(3-2) and 0.1-0.5 arcsec SINFONI/VLT H-alpha observations. J0901 is a rare, strongly-lensed but otherwise normal massive (log(M_star/M_sun)~11) main sequence SFG, offering a unique opportunity to study a typical massive SFG under the microscope of lensing. Through forward dynamical modeling incorporating lensing deflection, we fit the CO and H-alpha kinematics in the image plane out to about one disk effective radius (R_e ~ 4 kpc) at a ~600pc delensed physical resolution along the kinematic major axis. Our results show high intrinsic dispersions of the cold molecular and warm ionized gas (sig0_mol ~ 40 km/s and sig0_ion ~ 66 km/s) that remain constant out to R_e; a moderately low dark matter fraction (f_DM(R_e) ~ 0.3-0.4) within R_e; and a centrally-peaked Toomre Q-parameter -- agreeing well with the previously established sig0 vs. z, f_DM vs. Sig_baryon, and Q's radial trends using large-sample non-lensed main sequence SFGs. Our data further reveal a high stellar mass concentration within ~1-2 kpc with little molecular gas, and a clumpy molecular gas ring-like structure at R ~ 2-4 kpc, in line with the inside-out quenching scenario. Our further analysis indicates that J0901 had assembled half of its stellar mass only ~400 Myrs before its observed cosmic time, and cold gas ring and dense central stellar component are consistent with signposts of a recent wet compaction event of a highly turbulent disk found in recent simulations.

astro-ph.GA↗
arXiv2022

CO($J$=1-0) mapping survey of 64 galaxies in the Fornax cluster with the ALMA Morita array

We conduct a $^{12}$C$^{16}$O($J$=1-0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the ALMA Morita array in cycle 5. CO emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf, spiral and elliptical galaxies with stellar masses of $M_{\rm star}\sim10^{6.3-11.6}$~M$_\odot$. The achieved beam size and sensitivity are $15''\times8''$ and $\sim12$~mJy~beam$^{-1}$ at the velocity resolution of $\sim10$~km~s$^{-1}$, respectively. We study the cold-gas (molecular- and atomic-gas) properties of 38 subsamples with $M_{\rm star}>10^9$~M$_\odot$ combined with literature HI data. We find that: (1) the low star-formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold-gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas; (2) the atomic-gas fraction is more heavily reduced than the molecular-gas fraction of such galaxies with low SF activity. A comparison between the cold-gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Pre-processes in the group environment would also play a role in reducing cold-gas reservoirs in some Fornax galaxies.

astro-ph.GA↗
arXiv2022

Signs of environmental effects on star-forming galaxies in the Spiderweb protocluster at z=2.16

We use multi-object near-infrared (NIR) spectroscopy with VLT/KMOS to investigate the role of the environment in the evolution of the ionized gas properties of narrow-band selected H$α$ emitters (HAEs) in the Spiderweb protocluster at $z=2.16$. Based on rest-frame optical emission lines, H$α$ and [NII]$λ$6584, we confirm the cluster membership of 39 of our targets (i.e. 93% success rate), and measure their star-formation rates (SFR), gas-phase oxygen abundances and effective radius. We parametrize the environment where our targets reside by using local and global density indicators based on previous samples of spectroscopic and narrow-band cluster members. We find that star-forming galaxies embedded in the Spiderweb protocluster display SFRs compatible with those of the main sequence and morphologies comparable to those of late-type galaxies at $z=2.2$ in the field. We also report a mild gas-phase metallicity enhancement ($0.6\pm0.3$ dex) at intermediate stellar masses. Furthermore, we identify two UVJ-selected quiescent galaxies with residual H$α$-based star formation and find signs of extreme dust obscuration in a small sample of SMGs based on their FIR and H$α$ emission. Interestingly, the spatial distribution of these objects differs from the rest of HAEs, avoiding the protocluster core. Finally, we explore the gas fraction-gas metallicity diagram for 7 galaxies with molecular gas masses measured by ATCA using CO(1-0). In the context of the gas-regulator model, our objects are consistent with relatively low mass-loading factors, suggesting lower outflow activity than field samples at the cosmic noon and thus, hinting at the onset of environmental effects in this massive protocluster.

astro-ph.GA↗
arXiv2022

Revealing impacts of stellar mass and environment on galaxy quenching

Galaxy quenching is a critical step in galaxy evolution. In this work, we present a statistical study of galaxy quenching in 17 cluster candidates at 0.5<z<1.0 in the COSMOS field. We selected cluster members with a wide range of stellar mass and environment to study their mass and environment dependence. Member galaxies are classified into star-forming, quiescent and recently-quenched galaxies (RQG) using the rest-frame UVJ diagram. We further separated fast and slow quenching RQGs by model evolutionary tracks on the UVJ diagram. We defined the quenching efficiency as the ratio of RQGs over star-forming galaxies and the quenching stage as the ratio of RQGs over quiescent galaxies to quantify the quenching processes. We found quenching efficiency is enhanced by both higher stellar mass and denser environment. Massive or dense environment galaxies quench earlier. Slow quenching is more dominant for massive galaxies and at lower redshifts, but no clear dependence on the environment is found. Our results suggest that low-mass galaxies in dense environments are likely quenched through a short-timescale process such as ram pressure stripping, while massive galaxies in a sparse environment are mostly quenched by a longer-timescale process. Using the line strength of H$δ$ and [OII], we confirmed that our UVJ method to select RQGs agrees with high S/N DEIMOS spectra. However, we caution that the visibility time (duration of a galaxy's stay in the RQG region on the UVJ diagram) may also depend on mass or environment. The method introduced in this work can be applied to RQG candidates for future statistical RQG spectroscopic surveys. The systematic spectroscopic RQG study will disentangle the degeneracy between visibility time and quenching properties.

astro-ph.GA↗
arXiv2022

Low star-formation activity and low gas content of quiescent galaxies at $z=$ 3.5-4.0 constrained with ALMA

The discovery in deep near-infrared surveys of a population of massive quiescent galaxies at $z>3$ has given rise to the question of how they came to be quenched so early in the history of the Universe. Measuring their molecular gas properties can distinguish between physical processes where they stop forming stars due to a lack of fuel versus those where star-formation efficiency is reduced and the gas is retained. We conducted Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of four quiescent galaxies at $z=$ 3.5-4.0 found by the Fourstar Galaxy Evolution Survey (ZFOURGE) and a serendipitous optically dark galaxy at $z=3.71$. We aim to investigate the presence of dust-obscured star-formation and their gas content by observing the dust continuum emission at Band-7 and the atomic carbon [C I]($^3P_1$-$^3P_0$) line at 492.16 GHz. Among the four quiescent galaxies, only one source is detected in the dust continuum at $λ_{\rm obs} = 870 {\rm μm}$. The sub-mm observations confirm their passive nature, and all of them are located more than four times below the main sequence of star-forming galaxies at $z=3.7$. None of the targets are detected in [C I], constraining their gas mass fractions to be $<$ 20%. These gas mass fractions are more than three times lower than the scaling relation for star-forming galaxies at $z=3.7$. These results support scenarios where massive galaxies at $z=$ 3.5-4.0 quench by consuming/expelling all the gas rather than by reducing the efficiency of the conversion of their gas into stars.

astro-ph.GA↗
arXiv2022

High-resolution ALMA study of CO (2-1) line and dust continuum emissions in cluster galaxies at z = 1.46

We present new Atacama Large Millimeter/submillimeter Array (ALMA) results obtained from spatially resolved CO $J$=2-1 line ($0.4''$ resolution) and 870 $μ$m continuum ($0.2''$ resolution) observations of cluster galaxies in XMMXCS J2215.9-1738 at $z=1.46$. Our sample comprises 17 galaxies within $\sim0.5$ Mpc ($0.6R_{200}$) of the cluster center, all of which have previously been detected in the CO $J$=2-1 line at a lower resolution. The effective radii of both the CO $J$=2-1 line and 870 $μ$m dust continuum emissions are robustly measured for nine galaxies by modeling the visibilities. We find that the CO $J$=2-1 line emission in all of the nine galaxies is more extended than the dust continuum emission by a factor of $2.8\pm1.4$. We investigate the spatially resolved Kennicutt-Schmidt (KS) relation in two regions within the interstellar medium of the galaxies. The relation for our sample reveals that the central region ($0<r<R_{e,{\rm 870μm}}$) of galaxies tends to have a shorter gas depletion timescale, i.e., a higher star formation efficiency, compared to the extended region ($R_{e,{\rm 870μm}}<r<R_{e,{\rm CO}}$). Overall, our result suggests that star formation activities are concentrated inside the extended gas reservoir, possibly resulting in the formation of a bulge structure. We find consistency between the ALMA 870 $μ$m radii of star-forming members and the Hubble Space Telescope/1.6 $μ$m radii of passive members in a mass-size distribution, which suggests a transition from star-forming to passive members within $\sim0.5$ Gyr. In addition, no clear differences in the KS relation nor in the sizes are found between galaxies with and without a close companion.

astro-ph.GA↗
arXiv2022

Star Formation Properties of Sloan Digital Sky Survey BOSS Void Galaxies in the Hyper Suprime-Cam Survey

We utilize the Hyper Suprime-Cam (HSC) Wide Survey to explore the properties of galaxies located in the voids identified from the Baryon Oscillation Spectroscopic Survey (BOSS) up to z~0.7. The HSC reaches i~25, allowing us to characterize the void galaxies down to 10$^{9.2}$ solar mass. We find that the revised void galaxy densities, when including faint galaxies in voids defined by bright galaxies, are still underdense compared to the mean density from the entire field. In addition, we classify galaxies into star-forming, quiescent, and green valley populations, and find that void galaxies tend to have slightly higher fractions of star-forming galaxies under the mass and redshift control, although the significance of this result is only moderate (2$σ$). However, when we focus on the star-forming population, the distribution of the specific star formation rate (sSFR) of void galaxies shows little difference from that of the control galaxies. Similarly, the median sSFR of star-forming void galaxies is also in good agreement with that of the star-forming control galaxies. Moreover, the effective green valley fraction of void galaxies, defined as the number of green valley galaxies over the number of nonquiescent galaxies, is comparable to that of the control ones, supporting the suggestion that void and control galaxies evolve under similar physical processes and quenching frequencies. Our results thus favor a scenario of the galaxy assembly bias.

astro-ph.GA↗
arXiv2022

FOREVER22: galaxy formation in protocluster regions

We present results from a new cosmological hydrodynamics simulation campaign of protocluster (PC) regions, FOREVER22: FORmation and EVolution of galaxies in Extremely-overdense Regions motivated by SSA22. The simulations cover a wide range of cosmological scales using three different zoom set-ups in a parent volume of $(714.2~\rm cMpc)^{3}$: PCR (Proto-Cluster Region; $V= (28.6~{\rm cMpc})^{3} $, SPH particle mass, $m_{\rm{SPH}} = 4.1 \times 10^{6}~\rm M_{\odot}$ and final redshift, $z_{\rm end}=2.0$), BCG (Brightest proto-Cluster Galaxy; $V \sim (10~{\rm cMpc})^{3} $, $m_{\rm SPH} = 5.0\times10^{5}~\rm M_{\odot}$ and $z_{\rm end}=4.0$ ), and First ( $V \sim (3~{\rm cMpc})^{3} $, $m_{\rm SPH} = 7.9 \times 10^{3}~\rm M_{\odot}$ and $z_{\rm end}=9.5$) runs, that allow to focus on different aspects of galaxy formation. In the PCR runs, we follow 10 PCs, each harbouring 1 - 4 SMBHs with $M_{\rm BH} \ge 10^{9}~\rm M_{\odot}$. One of the PC cores shows a spatially close arrangement of seven starburst galaxies with ${\rm SFR} \gtrsim 100~\rm M_{\odot}~yr^{-1}$ each, that are dust-obscured and would appear as submillimeter galaxies with flux $\gtrsim 1~$ mJy at $1.1~ \rm mm$ in observations. The BCG runs show that the total SFRs of haloes hosting BCGs are affected by AGN feedback, but exceed $1000~\rm M_{\odot}~yr^{-1}$ at $z \lesssim 6$. The First runs resolve mini-haloes hosting population (Pop) III stars and we show that, in PC regions, the dominant stellar population changes from Pop III to Pop II at $z \gtrsim 20$, and the first galaxies with ${\rm SFR} \gtrsim 18~\rm M_{\odot}~yr^{-1}$ form at $z \sim 10$. These can be prime targets for future observations with the James Webb Space Telescope. Our simulations successfully reproduce the global star formation activities in observed PCs and suggest that PCs can kickstart cosmic reionization.

astro-ph.GA↗
arXiv2022

Do blue galaxy-clusters have hot intracluster gas?

We present herein a systematic X-ray analysis of blue galaxy-clusters at $z=0.84$ discovered by the Subaru telescope. The sample consisted of 43 clusters identified by combining red-sequence and blue-cloud surveys, covering a wide range of emitter fractions (i.e., 0.3--0.8). The spatial extent of the over-density region of emitter galaxies was approximately 1~Mpc in radius. The average cluster mass was estimated as $0.6 (<1.5)\times10^{14}~{\rm M_\odot}$ from the stacked weak-lensing measurement. We analyzed the XMM-Newton archival data, and measured the X-ray luminosity of the hot intracluster medium. As a result, diffuse X-ray emission was marginally detected in 14 clusters, yielding an average luminosity of $5\times 10^{42}~{\rm erg\,s^{-1}}$. On the contrary, it was not significant in 29 clusters. The blue clusters were significantly fainter than the red-dominated clusters, and the X-ray luminosity did not show any meaningful correlation either with emitter fraction or richness. The X-ray surface brightness was low, but the amount of gas mass was estimated to be comparable to that observed in the $10^{13-14}~{\rm M_{\odot}}$ cluster. Based on the results, we suggest that the blue clusters are at the early formation stage, and the gas is yet to be compressed and heated up to produce appreciable X-rays. Follow-up spectroscopic measurements are essential to clarify the dynamical status and co-evolution of galaxies and hot gas in the blue clusters.

astro-ph.CO↗
arXiv2021

Environmental dependence of gas properties in a protocluster at z~2.5

In a protocluster USS1558-003 at z=2.53, galaxies in the dense cores show systematically elevated star-forming activities than those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1mm observations with Atacama Large Millimeter/submillimeter Array (ALMA). We detect interstellar dust continuum emissions from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from CO(3-2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at M* ~ 10^{10} M_sun) where we see the enhanced star-forming activities), suggesting that such large gas masses can sustain their high star-forming activities. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activities are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario that the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star-formation activities, but without changing the star formation law.

astro-ph.GA↗
arXiv2021

Third Data Release of the Hyper Suprime-Cam Subaru Strategic Program

The paper presents the third data release of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), a wide-field multi-band imaging survey with the Subaru 8.2m telescope. HSC-SSP has three survey layers (Wide, Deep, and UltraDeep) with different area coverages and depths, designed to address a wide array of astrophysical questions. This third release from HSC-SSP includes data from 278 nights of observing time and covers about 670 square degrees in all five broad-band filters at the full depth ($\sim26$~mag at $5σ$) in the Wide layer. If we include partially observed area, the release covers 1,470 square degrees. The Deep and UltraDeep layers have $\sim80\%$ of the originally planned integration times, and are considered done, as we have slightly changed the observing strategy in order to compensate for various time losses. There are a number of updates in the image processing pipeline. Of particular importance is the change in the sky subtraction algorithm; we subtract the sky on small scales before the detection and measurement stages, which has significantly reduced false detections. Thanks to this and other updates, the overall quality of the processed data has improved since the previous release. However, there are limitations in the data (for example, the pipeline is not optimized for crowded fields), and we encourage the user to check the quality assurance plots as well as a list of known issues before exploiting the data. The data release website is https://hsc-release.mtk.nao.ac.jp/.

astro-ph.IM↗