We present the Swimmy (Subaru WIde-field Machine-learning anoMalY) survey program, a deep-learning-based search for unique sources using multicolored (grizy) imaging data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). This program aims to detect unexpected, novel, and rare populations and phenomena, by utilizing the deep imaging data acquired from the wide-field coverage of the HSC-SSP. This article, as the first paper in the Swimmy series, describes an anomaly detection technique to select unique populations as "outliers"from the data-set. The model was tested with known extreme emission-line galaxies (XELGs) and quasars, which consequently confirmed that the proposed method successfully selected ∼60%-70% of the quasars and 60% of the XELGs without labeled training data. In reference to the spectral information of local galaxies at z = 0.05-0.2 obtained from the Sloan Digital Sky Survey, we investigated the physical properties of the selected anomalies and compared them based on the significance of their outlier values. The results revealed that XELGs constitute notable fractions of the most anomalous galaxies, and certain galaxies manifest unique morphological features. In summary, deep anomaly detection is an effective tool that can search rare objects, and, ultimately, unknown unknowns with large data-sets. Further development of the proposed model and selection process can promote the practical applications required to achieve specific scientific goals.

<title>ABSTRACT</title>
Subaru Strategic Program with the Hyper-Suprime Cam (HSC-SSP) has proven to be successful with its extremely wide area coverage in past years. Taking advantages of this feature, we report initial results from exploration and research of expansive over- and underdense structures at z = 0.3–1 based on the second Public Data Release where optical 5-band photometric data for ∼ eight million sources with i &amp;lt; 23 mag are available over ∼360 deg2. We not only confirm known superclusters but also find candidates of titanic over- and underdense regions out to z = 1. The mock data analysis suggests that the density peaks would involve one or more massive dark matter haloes (&amp;gt;1014 M⊙) of the redshift, and the density troughs tend to be empty of massive haloes over &amp;gt;10 comoving Mpc. Besides, the density peaks and troughs at z ≲ 0.6 are in part identified as positive and negative weak lensing signals respectively, in mean tangential shear profiles, showing a good agreement with those inferred from the full-sky weak lensing simulation. The coming extensive spectroscopic surveys will be able to resolve these colossal structures in 3D space. The number density information over the entire survey field is available as grid-point data on the website of the HSC-SSP data release (https://hsc.mtk.nao.ac.jp/ssp/data-release/).

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 [N II]λ6584 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 (log M∗/M◦ < 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 (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.

We perform the weak lensing mass mapping analysis to identify troughs, which are defined as local minima in the mass map. Since weak lensing probes the projected matter distribution along the line of sight, these troughs can be produced by single or multiple voids projected along the line of sight. To scrutinize the origins of the weak lensing troughs, we systematically investigate the line-of-sight structure of troughs selected from the latest Subaru Hyper Suprime-Cam (HSC) Year 3 weak lensing data covering 433.48 deg2. From a curved sky mass map constructed with the HSC data, we identify 15 troughs with the signal-to-noise ratio higher than 5.7 and address their line-of-sight density structure utilizing redshift distributions of two galaxy samples, photometric luminous red galaxies observed by HSC and spectroscopic galaxies detected by Baryon Oscillation Spectroscopic Survey. While most weak lensing signals due to the troughs are explained by multiple voids aligned along the line of sight, we find that two of the 15 troughs potentially originate from single voids at redshift ∼0.3. The single void interpretation appears to be consistent with our three-dimensional mass mapping analysis. We argue that single voids can indeed reproduce observed weak lensing signals at the troughs if these voids are not spherical but are highly elongated along the line-of-sight direction.

This paper presents the results of 475h 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 supergalactic scale. This result suggests a high frequency of extended gas reservoirs, comprising at least 30 percent of our CO-selected sample. An environmental study of the candidates is carried out based on Nth 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 eight 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 potential sources of the intracluster medium seen in low redshift Virgo- or Coma-like galaxy clusters.

We report the measurement of rest-frame UV size and morphology of Hα-emission-selected star-forming galaxies (HAEs) in four protoclusters at z ∼ 2 (PKS 1138-262, USS 1558-003, PHz G237.0+42.5, and CC 2.2) using archival Hubble Space Telescope Advanced Camera Survey (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 a typical half-light radius of ∼2.5 kpc. At fixed stellar mass, there is no significant difference between HAEs in the protocluster and in the 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 the Sérsic index and nonparametric morphologies, HAE morphologies in both environments at z ∼ 2 in rest-frame UV are consistent with disk-like star-forming galaxies, although we also find 29% ± 4% HAEs showing disturbed morphologies. The fraction of disturbed galaxies is higher in the protocluster environment, with 39% ± 8% protocluster HAEs showing disturbed morphologies, compared to 26% ± 4% 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.

We present the first results from GALAXY CRUISE, a community (or citizen) science project based on data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). The current paradigm of galaxy evolution suggests that galaxies grow hierarchically via mergers, but our observational understanding of the role of mergers is still limited. The data from HSC-SSP are ideally suited to improve our understanding with improved identifications of interacting galaxies thanks to the superb depth and image quality of HSC-SSP. We launched a community science project, GALAXY CRUISE, in 2019 and have collected over two million independent classifications of 20686 galaxies at z < 0.2. We first characterize the accuracy of the participants’ classifications and demonstrate that it surpasses previous studies based on shallower imaging data. We then investigate various aspects of interacting galaxies in detail. We show that there is a clear sign of enhanced activities of super-massive black holes and star formation in interacting galaxies compared to those in isolated galaxies. The enhancement seems particularly strong for galaxies undergoing violent mergers. We also show that the mass growth rate inferred from our results is roughly consistent with the observed evolution of the stellar mass function. The second season of GALAXY CRUISE is currently underway and we conclude with future prospects. We make the morphological classification catalog used in this paper publicly available at the GALAXY CRUISE website, which will be particularly useful for machine-learning applications.

ABSTRACT

We use multi-object near-infrared 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 [N ii]λ6584, we confirm the cluster membership of 39 of our targets (i.e. 93 per cent success rate), and measure their star formation rates (SFR), gas-phase oxygen abundances, and effective radius. We parametrize the environment where our targets reside 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 (0.06 ± 0.03 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 starbursty submillimetre galaxies 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 seven 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.

Abstract

We present new Atacama Large Millimeter/submillimeter Array (ALMA) results obtained from spatially resolved CO J = 2–1 line (0.″4 resolution) and 870 μm continuum (0.″2 resolution) observations of cluster galaxies in XMMXCS J2215.9-1738 at z = 1.46. Our sample comprises 17 galaxies within ∼0.5 Mpc (0.6R₂₀₀) 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 μm 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 ± 1.4. 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 &lt; r &lt; R_e,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,870μm &lt; r &lt; R_e,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 μm radii of star-forming members and the Hubble Space Telescope/1.6 μm radii of passive members in a mass–size distribution, which suggests a transition from star-forming to passive members within ∼0.5 Gyr. In addition, no clear differences in the KS relation nor in the sizes are found between galaxies with and without a close companion.

Abstract

This paper presents a thousand passive spiral galaxy samples at z = 0.01–0.3 based on a combined analysis of the Third Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP PDR3) and the GALEX–SDSS–WISE Legacy Catalog (GSWLC-2). Among 54871 gri galaxy cutouts taken from the HSC-SSP PDR3 over 1072 deg2, we conducted a search with deep-learning morphological classification for candidates of passive spirals below the star-forming main sequence derived by ultraviolet to mid-infrared spectral energy distribution fitting in the GSWLC-2. We then classified the candidates into 1100 passive spirals and 1141 secondary samples based on visual inspections. Most of the latter cases are considered to be passive ringed S0 or pseudo-ringed galaxies. The remaining secondary samples have ambiguous morphologies, including two peculiar objects with diamond-shaped stellar wings. The selected passive spirals have a similar distribution to the general quiescent galaxies on the EWHδ–Dn4000 diagram and concentration indices. Moreover, we detected an enhanced passive fraction of spiral galaxies in X-ray clusters. Passive spirals in galaxy clusters are preferentially located in the midterm or late infall phase on the phase–space diagram, supporting the ram pressure scenario, which has been widely advocated in previous studies. The source catalog and gri-composite images are available on the HSC-SSP PDR3 website 〈https://hsc.mtk.nao.ac.jp/ssp/data-release/〉. Future updates, including integration with a citizen science project dedicated to the HSC data, will achieve more effective and comprehensive classifications.

ABSTRACT

The redshift of z ∼ 1.5 is the transition epoch of protoclusters (PCs) from the star-forming phase into the quenching phase, and hence an appropriate era to investigate the build up of the quenched population. We define a ‘core’ as the most massive halo in a given PC, where environmental effects are likely to work most effectively, and search for cores at 1 &amp;lt; z &amp;lt; 1.5. We use a photometric redshift catalogue of a wide (effective area of ${\sim}22.2\, \mathrm{deg}^{2}$) and deep ($i\sim 26.8\, \mathrm{mag}$) optical survey with Subaru Hyper-Suprime Cam. Regarding galaxies with log (M*/M⊙) &amp;gt; 11.3 as the central galaxies of PC cores, we estimate their average halo mass by clustering analysis and find it to be log (Mh/M⊙) ∼ 13.7. An expected mass growth by the IllustrisTNG simulation and the observed overdensities around them suggest that the PC cores we find are progenitors of present-day clusters. Classifying our galaxy sample into red and blue galaxies, we calculate the stellar mass function (SMF) and the red galaxy fraction. The SMFs in the PC cores are more-top heavy than field, implying early high-mass galaxy formation and disruption of low-mass galaxies. We also find that the red fraction increases with stellar mass, consistent with stellar mass dependent environmental quenching recently found at z &amp;gt; 1. Interestingly, although the cores with red and blue centrals have similar halo masses, only those with red centrals show a significant red fraction excess compared to the field, suggesting a conformity effect. Some observational features of PC cores may imply that the conformity is caused by assembly bias.

This paper reports detections of Hα emission and stellar continuum out to approximately 30 physical kiloparsecs, and Hα directionality in the outskirts of Hα-emitting galaxies (Hα emitters) at $z$ = 0.4. This research adopts narrow-band selected Hα emitters at $z$ = 0.4 from the emission-line object catalog by Hayashi et al. (2020, PASJ, 72, 86), which is based on data in the Deep and Ultradeep layers of the Hyper Suprime-Cam Subaru Strategic Program. Deep narrow- and broad-band images of 8625 Hα emitters across 16.8 deg2 enable us to construct deep composite emission-line and continuum images. The stacked images show diffuse Hα emission (down to ∼5 × 10-20 erg s-1 cm-2 arcsec-2) and stellar continuum (down to ∼5 × 10-22 erg s-1 cm-2 Å-1 arcsec-2), extending beyond 10 kpc at stellar masses >109 $M⊙$, parts of which may originate from stellar halos. Those radial profiles are broadly consistent with each other. In addition, we obtain a dependence of the Hα emission on the position angle because relatively higher Hα equivalent width has been detected along the minor-axis towards galaxy disks. While the Hα directionality could be attributed to biconical outflows, further research with hydrodynamic simulations is highly demanded to pin down the exact cause.

In a protocluster USS1558-003 at z = 2.53, galaxies in the dense cores show systematically elevated star-forming activity compared to 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 1.1 mm observations with the Atacama Large Millimeter/submillimeter Array. We detect interstellar dust continuum emission from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from the 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 ∗ ∼ 1010 M o˙ where we see the enhanced star-forming activity), suggesting that such large gas masses can sustain their high star-forming activity. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at a 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 activity 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 in which 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 activity, but without changing the star formation law.

This study investigates the role of large-scale environments on the fraction of spiral galaxies at z = 0.3-0.6 sliced to three redshift bins of Δz = 0.1. Here, we sample 276220 massive galaxies in a limited stellar mass of 5 × 1010 solar mass (∼M∗) over 360 deg2, as obtained from the Second Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). By combining projected two-dimensional density information (Shimakawa et al. 2021, MNRAS, 503, 3896) and the CAMIRA cluster catalog (Oguri et al. 2018, PASJ, 70, S20), we investigate the spiral fraction across large-scale overdensities and in the vicinity of red sequence clusters. We adopt transfer learning to reduce the cost of labeling spiral galaxies significantly and then perform stacking analysis across the entire field to overcome the limitations of sample size. Here we employ a morphological classification catalog by the Galaxy Zoo Hubble (Willett et al., 2017, MNRAS, 464, 4176) to train the deep learning model. Based on 74103 sources classified as spirals, we find moderate morphology-density relations on a 10 comoving Mpc scale, thanks to the wide-field coverage of HSC-SSP. Clear deficits of spiral galaxies have also been confirmed, in and around 1136 red sequence clusters. Furthermore, we verify whether there is a large-scale environmental dependence on rest-frame u - r colors of spiral galaxies; such a tendency was not observed in our sample.

We report a detailed CO(1−0) survey of a galaxy protocluster field at <italic>z</italic> = 2.16, based on 475 h of observations with the Australia Telescope Compact Array. We constructed a large mosaic of 13 individual pointings, covering an area of 21 arcmin² and ±6500 km s⁻¹ range in velocity. We obtained a robust sample of 46 CO(1−0) detections spanning <italic>z</italic> = 2.09 − 2.22, constituting the largest sample of molecular gas measurements in protoclusters to date. The CO emitters show an overdensity at <italic>z</italic> = 2.12 − 2.21, suggesting a galaxy super-protocluster or a protocluster connected to large-scale filaments of ∼120 cMpc in size. We find that 90% of CO emitters have distances &gt;0.′5−4′ to the center galaxy, indicating that small area surveys would miss the majority of gas reservoirs in similar structures. Half of the CO emitters have velocities larger than escape velocities, which appears gravitationally unbound to the cluster core. These unbound sources are barely found within the <italic>R</italic>₂₀₀ radius around the center, which is consistent with a picture in which the cluster core is collapsed while outer regions are still in formation. Compared to other protoclusters, this structure contains a relatively higher number of CO emitters with relatively narrow line widths and high luminosities, indicating galaxy mergers. We used these CO emitters to place the first constraint on the CO luminosity function and molecular gas density in an overdense environment. The amplitude of the CO luminosity function is 1.6 ± 0.5 orders of magnitude higher than that observed for field galaxy samples at <italic>z</italic> ∼ 2, and one order of magnitude higher than predictions for galaxy protoclusters from semi-analytical SHARK models. We derive a high molecular gas density of 0.6 − 1.3 × 10⁹ <italic>M</italic>_⊙ cMpc⁻³ for this structure, which is consistent with predictions for cold gas density of massive structures from hydro-dynamical DIANOGA simulations.

<title>Abstract</title>
We have conducted a comprehensive survey of emission-line galaxies at z ≲ 1.6 based on narrow-band (NB) imaging data taken with Hyper Suprime-Cam (HSC) on the Subaru telescope. In this paper, we update the catalogs of Hα, [O iii], and [O ii] emission-line galaxies using the data from the second Public Data Release (PDR2) of the Subaru Strategic Program (SSP) of the HSC and Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) survey along with the spectroscopic redshifts for 2019 emission-line galaxies selected with the PDR1 data. The wider effective coverage of NB816 and NB921, 16.3 deg2 and 16.9 deg2, respectively, are available in the Deep and UltraDeep layers of HSC-SSP from the PDR2. The CHORUS survey provides us with data with additional three NBs (NB527, NB718, and NB973) in the COSMOS field in the UltraDeep layer (1.37 deg2). The five NB datasets allow us to investigate the star-forming galaxies presenting emission-lines at 14 specific redshifts ranging from z ∼ 1.6 down to z ∼ 0.05. We revisit the distribution of large-scale structures and luminosity functions (LFs) for the emission-line galaxies with the large samples of 75377 emission-line galaxies selected. The redshift revolution of LFs shows that the star formation rate densities (SFRDs) decreases monotonically from z ∼ 1.6, which is consistent with the cosmic SFRD known to-date. Our samples of emission-line galaxies covering a sufficiently large survey volume are useful to investigate the evolution of star-forming galaxies since the cosmic noon in a wide range of environments including galaxy clusters, filaments, and voids.

<title>ABSTRACT</title>
We report an automated morphological classification of galaxies into S-wise spirals, Z-wise spirals, and non-spirals using big image data taken from Subaru/Hyper Suprime-Cam (HSC) Survey and a convolutional neural network (CNN)-based deep learning technique. The HSC i-band images are about 36 times deeper than those from the Sloan Digital Sky Survey (SDSS) and have a two times higher spatial resolution, allowing us to identify substructures such as spiral arms and bars in galaxies at z &amp;gt; 0.1. We train CNN classifiers by using HSC images of 1447 S-spirals, 1382 Z-spirals, and 51 650 non-spirals. As the number of images in each class is unbalanced, we augment the data of spiral galaxies by horizontal flipping, rotation, and rescaling of images to make the numbers of three classes similar. The trained CNN models correctly classify 97.5 per cent of the validation data, which is not used for training. We apply the CNNs to HSC images of a half million galaxies with an i-band magnitude of i &amp;lt; 20 over an area of 320 deg2. 37 917 S-spirals and 38 718 Z-spirals are identified, indicating no significant difference between the numbers of two classes. Among a total of 76 635 spiral galaxies, 48 576 are located at z &amp;gt; 0.2, where we are hardly able to identify spiral arms in the SDSS images. Our attempt demonstrates that a combination of the HSC big data and CNNs has a large potential to classify various types of morphology such as bars, mergers, and strongly lensed objects.

<title>Abstract</title>
We present the large-scale structure over a more than 50 comoving Mpc scale at $z \sim 0.9$ where the CL1604 supercluster, which is one of the largest structures ever known at high redshifts, is embedded. The wide-field deep imaging survey by the Subaru Strategic Program with the Hyper Suprime-Cam reveals that the already-known CL1604 supercluster is a mere part of larger-scale structure extending to both the north and the south. We confirm that there are galaxy clusters at three slightly different redshifts in the northern and southern sides of the supercluster by determining the redshifts of 55 red-sequence galaxies and 82 star-forming galaxies in total via follow-up spectroscopy with Subaru/FOCAS and Gemini-N/GMOS. This suggests that the structure known as the CL1604 supercluster is the tip of the iceberg. We investigate the stellar population of the red-sequence galaxies using 4000 Å break and Balmer H$\delta$ absorption lines. Almost all of the red-sequence galaxies brighter than $21.5\:$mag in the z band show an old stellar population of $\gtrsim\! 2\:$Gyr. The comparison of composite spectra of the red-sequence galaxies in the individual clusters show that the galaxies at a similar redshift have a similar stellar population age, even if they are located $\sim\! 50\:$Mpc apart from each other. However, there could be a large variation in the star formation history. Therefore, it is likely that galaxies associated with the large-scale structure on a 50 Mpc scale formed at almost the same time, have assembled into the denser regions, and then have evolved with different star formation history along the hierarchical growth of the cosmic web.

<title>Abstract</title>
At z ∼ 2, star formation activity is thought to be high even in high-density environments such as galaxy clusters and proto-clusters. One of the critical but outstanding issues is if the structural growth of star-forming galaxies can differ depending on their surrounding environments. In order to investigate how galaxies grow their structures and what physical processes are involved in the evolution of galaxies, one requires spatially resolved images of not only stellar components but also star-forming regions within galaxies. We conducted (Adaptive Optics) AO-assisted imaging observations for star-forming galaxies in a dense proto-cluster core at z = 2.53 with IRCS and AO188 mounted on the Subaru Telescope. A combination of AO and narrow-band filters allows us to obtain resolved maps of Hα-emitting regions with an angular resolution of ${0{^{\prime\prime}_{. } }1}$–${0{^{\prime\prime}_{. } }2}$, which corresponds to ∼1 kpc at z ∼ 2.5. Based on stacking analyses, we compare radial profiles of star-forming regions and stellar components and find that the star-forming region of a sub-sample with log (M*/$M_\odot$) ∼ 10–11 is more extended than the stellar component, indicating the inside-out growth of the structure. This trend is similar to the one for star-forming galaxies in general fields at z = 2–2.5 obtained with the same observational technique. Our results suggest that the structural evolution of star-forming galaxies at z = 2–2.5 is mainly driven by internal secular processes irrespective of surrounding environments.

We present the molecular gas mass fraction (f(H2)) and star formation efficiency (SFE) of local galaxies on the basis of our new CO(J = 1 - 0) observations with the Nobeyama 45 m radio telescope, combined with the COLDGASS galaxy catalog, as a function of galaxy environment defined as the local number density of galaxies measured with SDSS DR7 spectroscopic data. Our sample covers a wide range in the stellar mass and star formation rate (SFR), and also covers a wide environmental range over two orders of magnitude. This allows us to conduct the first systematic study of environmental dependence of molecular gas properties in galaxies from the lowest-to the highest-density environments in the local universe. We confirm that both f(H2) and SFE have strong positive correlations with the SFR offset from the star-forming main sequence (Delta MS) and, most importantly, we find that these correlations are universal across all environments. Our result demonstrates that star formation activity within individual galaxies is primarily controlled by their molecular gas content, regardless of their global environment. Therefore, we claim that one always needs to be careful about the Delta MS distribution of the sample when investigating the environmental effects on the H-2 gas content in galaxies.

Gas-rich major mergers in high-redshift proto-clusters are important events, perhaps leading to the creation of the slowly rotating remnants seen in the cores of clusters in the present day. Here, we present a deep Jansky Very Large Array observation of CO J = 1-0 emission line in a proto-cluster at z = 2.5, USS1558-003. The target field is an extremely dense region, where 20 H alpha emitters (HAEs) are clustering. We have successfully detected the CO emission line from three HAEs and discovered a close pair of red and blue CO-emitting HAEs. Given their close proximity (similar to 30 kpc), small velocity offset (similar to 300 km s (1)), and similar stellar masses, they could be in the early phase of a gas-rich major merger. For the red HAE, we derive a total infrared luminosity of L-IR = 5.1 x 10(12) L-circle dot using MIPS 24 mu m and radio continuum images. The LIR/L'(CO) ratio is significantly enhanced compared to local spirals and high-redshift disks with a similar CO luminosity, which is indicative of a starburst mode. We find the gas depletion timescale is shorter than that of normal star-forming galaxies regardless of adopted CO-H-2 conversion factors. The identification of such a rare event suggests that gas-rich major mergers frequently take place in proto-clusters at z > 2 and may involve the formation processes of slow rotators seen in local massive clusters.

MAHALO-Subaru (MApping HAlpha and Lines of Oxygen with Subaru) project aims to investigate how the star forming activities in galaxies are propagated as a function of time, mass, and environment. It employs a unique set of narrow-band filters on MOIRCS/Subaru to search for Ha emitters associated to the proto-clusters or in narrow redshift slices in the general field. We have shown not only filamentary/clumpy structures of all the proto-clusters but also very high star formation activities therein especially at z &gt
2. HST images from the CANDELS survey have revealed that nearly half of the Hα emitters in the field at z ̃ 2 have clumpy structures. Among them, "red dusty clumps" are preferentially found at or near the mass center of galaxies. Therefore, they are probably linked to the formation of bulge component. To explore physical states and the mode of star formation of those forming galaxies, we have started Gracias-ALMA project in full coordination with the Mahalo-Subaru project. We will resolve molecular gas contents and dusty star formation within these galaxies, and tell whether clumps are formed by gravitational instability of gas rich disks, and whether bulges are formed by clump migration or through galaxy-galaxy mergers.

MAHALO-Subaru (MApping HAlpha and Lines of Oxygen with Subaru) is our on-going large programme which aims to investigate how the star forming activities in galaxies are propagated as a function of time, mass, and environment. We are targeting 10 clusters and proto-clusters at 0.4&lt
z&lt
2.6, and two general fields (GOODS-N and SXDF-CANDELS) with Suprime-Cam and MOIRCS by utilizing our unique sets of narrow-band filters. The narrow-band imaging can map out star forming galaxies with the redshifted Halpha and/or [OII] emission lines from our targets, and thus providing relatively unbiased views of star forming activities across time and environment. We have almost completed narrow-band imaging of our targets, and found that star forming activity is very high even in the proto-cluster cores (zâ‰1.5), and that the peak of star formation is shifted outwards with time, indicating the inside-out formation of clusters. Moreover, we have identified many red emitters especially in high density regions at z&gt
2, which suggests that the mode of star formation and/or the activation of AGN are dependent on environment, and thus holding the key to the environmental effects at the early stage of cluster galaxies formation and evolution. © 2013 International Astronomical Union.