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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  |$M_\odot$|⁠ , 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. [ABSTRACT FROM AUTHOR]

We study the angular correlation function of star-forming galaxies and properties of their host dark matter halos at z > 1 using the Hyper-Suprime Cam (HSC) Subaru Stragetic Program (SSP) survey. We use [O  ii ] emitters identified using two narrow-band (NB) filters, NB816 and NB921 , in the Deep/UltraDeep layers, which respectively cover large angular areas of 16.3 deg2 and 16.9 deg2. Our sample contains 8302 and 9578 [O  ii ] emitters at z = 1.19 (NB816) and z = 1.47 (NB921), respectively. We detect a strong clustering signal over a wide angular range, |$0{_{.}^{\circ}} 001$| < θ < 1 °, with bias |$b=1.61^{+0.13}_{-0.11}$| (z = 1.19) and |$b=2.09^{+0.17}_{-0.15}$| (z = 1.47). We also find a clear deviation of the correlation from a simple power-law form. To interpret the measured clustering signal, we adopt a halo occupation distribution (HOD) model that is constructed to explain the spatial distribution of galaxies selected by star formation rate. The observed correlation function and number density are simultaneously explained by the best-fitting HOD model. From the constrained HOD model, the average mass of halos hosting the [O  ii ] emitters is derived to be |$\log {M_{\rm eff}/(h^{-1}\, {M}_{\odot })}=12.70^{+0.09}_{-0.07}$| and |$12.61^{+0.09}_{-0.05}$| at z = 1.19 and 1.47, respectively, which will become halos with the present-day mass M ∼ 1.5 × 1013  h −1  M ⊙. The satellite fraction of the [O  ii ] emitter sample is found to be f sat ∼ 0.15. All these values are consistent with previous studies of similar samples, but we obtain tighter constraints even in a larger parameter space due to the larger sample size from the HSC. The results obtained for host halos of [O  ii ] emitters in this paper enable the construction of mock galaxy catalogs and the systematic forecast study of cosmological constraints from upcoming emission line galaxy surveys such as the Subaru Prime Focus Spectrograph survey. [ABSTRACT FROM AUTHOR]

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 < 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 (>1014 M⊙) of the redshift, and the density troughs tend to be empty of massive haloes over >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/). [ABSTRACT FROM AUTHOR]

To determine the dominant sources for cosmic reionization, the evolution history of the global ionizing fraction, and the topology of the ionized regions, we have conducted a deep imaging survey using four narrow-band (NB) and one intermediate-band (IB) filters on the Subaru/Hyper Suprime-Cam (HSC), called Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). The central wavelengths and full-widths-at-half-maximum of the CHORUS filters are, respectively, 386.2 nm and 5.5 nm for NB387 , 526.0 nm and 7.9 nm for NB527 , 717.1 nm and 11.1 nm for NB718 , 946.2 nm and 33.0 nm for IB945 , and 971.2 nm and 11.2 nm for NB973. This combination, including NB921 (921.5 nm and 13.5 nm) from the Subaru Strategic Program with HSC (HSC SSP), is carefully designed, as if they were playing a chorus, to observe multiple spectral features simultaneously, such as Lyman continuum, Lyα, C  iv , and He  ii for |$z$| = 2–7. The observing field is the same as that of the deepest footprint of the HSC SSP in the COSMOS field and its effective area is about 1.6 deg2. We present an overview of the CHORUS project, which includes descriptions of the filter design philosophy, observations and data reduction, multiband photometric catalogs, assessments of the imaging quality, measurements of the number counts, and example use cases for the data. All the imaging data, photometric catalogs, masked pixel images, data of limiting magnitudes and point spread functions, results of completeness simulations, and source number counts are publicly available through the HSC SSP database. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is M gas = (4.8 ± 0.3) × 109  M ⊙, placing it on the sequence of normal star-forming galaxies in an M gas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies. [ABSTRACT FROM AUTHOR]

This paper is the second in a series presenting the results of our deep H α-line survey towards protoclusters at |$z$| > 2, based on narrow-band imaging with the Subaru Telescope. This work investigates massive galaxies in a protocluster region associated with a radio galaxy (PKS 1138 − 262), the Spiderweb galaxy, at |$z$| = 2.2. Our 0.5 mag deeper narrow-band imaging than previous surveys collects a total of 68 H α emitters (HAE). Here, 17 out of the 68 are newly discovered protocluster members. First, a very high characteristic stellar mass of M |$_\star ^\ast = 10^{11.73}$| M⊙is measured from a Schechter function fit to the mass distribution of HAEs. Together with the Chandra X-ray data, we find that four out of six massive HAEs (M⋆> 1011M⊙) show bright X-ray emission, suggesting that they host active galactic nuclei (AGNs). Their mass estimates, therefore, would be affected by the nuclear emission from AGNs. Notably, the X-ray-detected HAEs are likely positioned near the boundary between star-forming and quiescent populations in the rest-frame UVJ plane. Moreover, our deep narrow-band data succeed in probing the bright H α (+ [N ii ]) line nebula of the Spiderweb galaxy extending over ∼100 physical kpc. These results suggest that the massive galaxies in the Spiderweb protocluster are on the way to becoming the bright red sequence objects seen in local galaxy clusters, where AGNs might play an essential role in their quenching processes, though a more statistical database is needed to build a general picture. [ABSTRACT FROM AUTHOR]

This work presents the results from our near-infrared spectroscopy of narrow-band-selected Hα emitters (HAEs) in two rich overdensities (PKS 1138−262 at z = 2.2 and USS 1558−003 at z = 2.5) with the Multi-Object Infrared Camera and Spectrograph on the Subaru telescope. These protoclusters are promising candidates for the most massive class of galaxy clusters seen today (Paper I). The confirmed HAEs in the protoclusters at z > 2 show high excitation levels as characterized by much higher [O iii]/Hβ or [O iii]/Hα line ratios than those of general galaxies at low-z. Such a high excitation level may not only be driven by high specific star formation rates and lower gaseous metallicities, but also be contributed by some other effects. We investigate the environmental dependence of gaseous metallicities by comparing the HAEs in the protoclustrers with those in the general field at similar redshifts. We find that the gaseous metallicities of protocluster galaxies are more chemically enriched than those of field galaxies at a given stellar mass in the range of M⋆ ≲ 1011 M⊙. This can be attributed to many processes, such as intrinsic (or nature) effects, external (or nurture) effects, and/or some systematic sampling effects. The intrinsic (nature) effect leads to the advanced stage of ‘downsizing’ galaxy evolution in protoclusters. On the other hand, the external (nurture) effects include the recycling of chemically enriched gas due to the higher pressure of intergalactic medium and/or stripping of outer gas in the reservoir in protoclusters. We also find that the offset of the mass–metallicity relation in dense environment becomes larger at higher redshifts. This can be naturally understood by the fact that the inflow/outflow rates in star-forming galaxies are much higher at higher redshifts. Therefore, the environmental dependence of such ‘feeding’ and ‘feedback’ mechanisms in galaxy formation is probably playing major roles in producing the offset of the mass–metallicity relation for the protocluster galaxies at z > 2. [ABSTRACT FROM AUTHOR]

We investigate the relationship between Hα and [O ii](λ3727) emission in faint star-forming galaxies at z = 1.47 with dust uncorrected star formation rates (SFRs) down to 1.4 M⊙ yr−1, using data in two narrow bands from wide-field camera/United Kingdom Infrared Telescope and Subaru prime focus camera/Subaru. A stacking analysis allows us to investigate Hα emission flux from bright [O ii] emitters as well as faint ones for which Hα is not individually detected, and to compare them with a large sample of local galaxies. We find that there is a clear, positive correlation between the average Hα and [O ii] luminosities for [O ii] emitters at z = 1.47, with its slope being consistent with the local relation. [O ii] emitters at z = 1.47 have lower mean observed ratios of Hα/[O ii] suggesting a small but systematic offset (at 2.8σ significance) towards lower values of dust attenuation, AHα ∼ 0.35, than local galaxies. This confirms that [O ii] selection tends to pick up galaxies which are significantly less dusty on average than Hα-selected ones, with the difference being higher at z = 1.47 than at z = 0. The discrepancy of the observed line ratios between [O ii] emitters at z = 1.47 and the local galaxies may in part be due to the samples having different metallicities. However, we demonstrate that metallicity is unlikely to be the main cause. Therefore, it is important to take into account that the relations for the dust correction which are derived using Hα emitter samples, and frequently used in many studies of high-z galaxies, may overestimate the intrinsic SFRs of [O ii]-selected galaxies, and that surveys of [O ii] emission galaxies are likely to miss dusty populations. [ABSTRACT FROM PUBLISHER]

We present a panoramic narrow-band study of Hα emitters in the field of the z = 2.16 proto-cluster around PKS 1138−262 using MOIRCS on the Subaru Telescope. We find 83 Hα emitters down to a star formation rate of SFR (Hα) ∼ 10 M⊙ yr−1 across a ∼ 7 × 7 arcmin2 region centred on the radio galaxy, and identify ∼10-Mpc scale filaments of emitters running across this region. By examining the properties of Hα emitters within the large-scale structure, we find that galaxies in the higher density environments at z = 2.16 tend to have redder colours and higher stellar masses compared to galaxies in more underdense regions. We also find a population of Hα emitters with red colours [(J − Ks) ≳ 1], which are much more frequent in the denser environments and which have apparently very high stellar masses with M* ≳ 1011 M⊙, implying that these cluster galaxies have already formed a large part of their stellar mass before z ∼ 2. Spitzer Space Telescope 24-μm data suggest that many of these red Hα emitters are bright, dusty starbursts (rather than quiescent sources). We also find that the proto-cluster galaxies follow the same correlation between SFR and M* (the ‘main sequence’) of z ∼ 2 field star-forming galaxies, but with an excess of massive galaxies. These very massive star-forming galaxies are not seen in our similar, previous study of z ∼ 1 clusters, suggesting that their star formation activity has been shut off at 1 ≲ z ≲ 2. We infer that the massive red (but active) galaxies in this rich proto-cluster are likely to be the products of environmental effects, and they represent the accelerated galaxy formation and evolution in a biased high-density region in the early Universe. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present a panoramic narrow-band imaging survey of [O ii] emitters in and around the ClG J0218.3−0510 cluster at z= 1.62 with Suprime-Cam on Subaru Telescope. 352 [O ii] emitters were identified on the basis of narrow-band excesses and photometric redshifts. We discovered a huge filamentary structure with some clumps traced by [O ii] emitters and found that the ClG J0218.3−0510 cluster is embedded in an even larger superstructure than the one reported previously. 31 [O ii] emitters were spectroscopically confirmed with the detection of Hα and/or [O iii] emission lines by Fibre Multi Object Spectrograph observations. In the high-density regions such as cluster core and clumps, star-forming [O ii] emitters show a high overdensity by a factor of more than 10 compared to the field region. Interestingly, the relative fraction of [O ii] emitters in photo- z selected sample does not depend significantly on the local density. Although the star formation activity is very high even in the cluster core, some massive quiescent galaxies also exist at the same time. Furthermore, the properties of the individual [O ii] emitters, such as star formation rates (SFRs), stellar masses and specific SFRs, do not show a significant dependence on the local density, either. Such a lack of environmental dependence is consistent with our earlier result by Hayashi et al. on a z= 1.5 cluster and its surrounding region. The fact that the star-forming activity of galaxies in the cluster core is as high as that in the field at z∼ 1.6 may suggest that the star-forming galaxies are probably just in a transition phase from a starburst mode to a quiescent mode, and are thus showing comparable level of star formation rates to those in lower density environments. We may be witnessing the start of the reversal of the local SFR-density relation due to the 'biased' galaxy formation and evolution in high-density regions at this high redshift, beyond which massive galaxies would be forming vigorously in a more biased way in protocluster cores. [ABSTRACT FROM AUTHOR]

ABSTRACT We conduct a wide-field narrow-band imaging survey of [O ii] emitters in and around the XMMXCS J2215.9−1738 cluster at z= 1.46 with Subaru/Suprime-Cam. In a 32 × 23 arcmin2 area, we select 380 [O ii] emitting galaxies down to 1.4 × 10−17 erg s−1 cm−2. Among them, 16 [O ii] emitters in the central region of the cluster are confirmed by near-infrared spectroscopy with Subaru/MOIRCS, suggesting that our photometric selection is valid for sample [O ii] emitters at z= 1.46. We find that [O ii] emitters are distributed along filamentary large-scale structures around the cluster, which are among the largest structures of star-forming galaxies ever identified at 1.3 ≲ z≲ 3.0. We define several environments such as cluster core, outskirts, filament and field in order to investigate the environment dependence of star-forming galaxies at z= 1.46. The colour-magnitude diagram of z′− K versus K for the [O ii] emitting galaxies shows that a significantly higher fraction of [O ii] emitters with red z′− K colours is seen in the cluster core than in other environments. It seems that the environment that hosts such red star-forming galaxies shifts from the core region at z= 1.46 to the outskirts of clusters at lower redshifts. A multicolour analysis of the red emitters indicates that these galaxies are more like nearly passively evolving galaxies which host [O ii] emitting active galactic nuclei (AGNs), rather than dust-reddened star-forming [O ii] emitters. We argue therefore that AGN feedback may be one of the critical processes to quench star formation in massive galaxies in high-density regions. The emission line ratios of [O iii]/Hβ and [N ii]/Hα of the [O ii] emitters in the cluster core support the inference that there is a moderate contribution of AGN to the emitters. We also find that the cluster has experienced high star formation activities at rates comparable to that in the field at z= 1.46 in contrast to lower redshift clusters, and that star formation activity in galaxy clusters on average increases with redshift up to z= 1.46. In addition, line ratios of [N ii]/Hα and [O iii]/Hβ indicate that a mass-metallicity relation exists in the cluster at z= 1.46, which is similar to that of star-forming galaxies in the field at z∼ 2. These results all suggest that at z∼ 1.5 star formation activity in the cluster core becomes as high as those in low-density environments and that there is apparently not yet a strong environmental dependence, except for the red emitters. [ABSTRACT FROM AUTHOR]

We present the first wide-field Hα imaging survey around the distant cluster RXJ1716.4+6708 at with a narrow-band filter on MOIRCS/Subaru, which reveals the star formation activities down to a star formation rate (SFR) of without extinction correction. Combining with a wide-field mid-infrared (MIR) imaging survey with the AKARI satellite, we compare in detail the unobscured and obscured star formation activities in the cluster. We find that both Hα emitters and MIR galaxies avoid the cluster central region and their spatial distribution is quite similar. Most of the Hα emitters show blue colours, but we find some Hα emitters on the red sequence. The MIR galaxies tend to be systematically redder than the Hα emitters probably due to heavy dust extinction. Interestingly, the red Hα emitters and the red MIR galaxies (i.e. dusty red galaxies) are most commonly seen in the medium-density environment such as cluster outskirts, groups and filaments, where optical colours of galaxies change. We investigate the amount of hidden star formation by calculating a ratio, SFR(IR)/SFR(Hα), and find that exceeds ∼3 in extreme cases for actively star-forming galaxies with SFR(IR) . It is notable that most of such very dusty galaxies with are also located in the medium-density environment. These findings suggest that dusty star formation is triggered in the infall region of the cluster, implying a probable link between galaxy transition and dusty star formation. We finally calculate the cluster total SFR and find that the cluster total SFR based on Hα alone can be underestimated more than a factor of ∼2 even after 1-mag extinction correction. We suggest that the mass-normalized cluster SFR rapidly declines since following , although the uncertainty is still large. [ABSTRACT FROM AUTHOR]

We present an unbiased deep [O ii] emission survey of a cluster at , the most distant cluster to date with a detection of extended X-ray emission. With wide-field optical and near-infrared cameras (Suprime-Cam and MOIRCS, respectively) on Subaru telescope, we performed deep imaging with a narrow-band filter Å, Å) as well as broad-band filters ( and ). From the photometric catalogues, we have identified 44 [O ii] emitters in the cluster central region of arcmin2 down to a dust-free star formation rate (SFR) of yr−1 (3σ). Interestingly, it is found that there are many [O ii] emitters even in the central high-density region. In fact, the fraction of [O ii] emitters to the cluster members as well as their SFRs and equivalent widths stay almost constant with decreasing cluster-centric distance up to the cluster core. Unlike clusters at lower redshifts where star formation activity is mostly quenched in their central regions, this higher redshift XMMXCS J2215.9−1738 cluster shows its high star formation activity even at its centre, suggesting that we are beginning to enter the formation epoch of some galaxies in the cluster core eventually. Moreover, we find a deficit of galaxies on the red sequence at magnitudes fainter than on the colour–magnitude diagram. This break magnitude is brighter than that of lower redshift clusters, and it is likely that we are seeing the formation phase of more massive red galaxies in the cluster core at . These results may indicate inside-out and down-sizing propagation of star formation activity in the course of cluster evolution. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present multi-wavelength studies of optically defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable us to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers that is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple peaks and single clusters with single peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of merging clusters is categorized into major mergers. The average halo concentration for the merging clusters is ∼70% smaller than that of the single-peak clusters, which agrees well with predictions of numerical simulations. The spatial distribution of subhalos is less centrally concentrated than the mass distribution of the main halo. The fractions of red galaxies in the merging clusters are not higher than those of the single-peak clusters. We find a signature of the merger boost of the ICM from the stacked Planck Sunyaev–Zel'dovich effect and ROSAT X-ray luminosity, but not in optical richness. The stacked X-ray surface brightness distribution, aligned with the main subhalo pairs of low-redshift and massive clusters, shows that the central gas core is elongated along the merger axis, and overall gas distribution is misaligned by ∼60°. The homogeneous, unbiased sample of cluster mergers and multi-wavelength follow-up studies provide a unique opportunity to make a complete picture of merger physics over the whole process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present the results from ALMA CO(3–2) observations of 66 Hα-selected galaxies in three protoclusters around radio galaxies: PKS 1138−262 (⁠|$z$| = 2.16), USS 1558−003 (⁠|$z$| = 2.53), and 4C 23.56 (⁠|$z$| = 2.49). The pointing areas have an overdensity of ∼100 compared to the mean surface number density of galaxies in field environments. We detect the CO emission line in 16 star-forming galaxies, including six previously published galaxies, to measure the molecular gas mass. In the stellar mass range of 10.5 < log (M star/ M ⊙) < 11.0, the protocluster galaxies have larger gas mass fractions and longer gas depletion timescales compared to the scaling relations established for field galaxies. On the other hand, the amounts of molecular gas in more massive galaxies with log (M star/ M ⊙) > 11.0 are comparable in mass to the scaling relation, or smaller. Our results suggest that the environmental effects on gas properties are mass dependent: in high-density environments, gas accretion through cosmic filaments is accelerated in less massive galaxies, while this is suppressed in the most massive system. [ABSTRACT FROM AUTHOR]

As a science verification study of the newly released AKARI/FIS Faint Source Catalog ver. 1, this paper discusses the different levels of dust attenuation toward stellar light and nebular emission lines within local star-forming galaxies at 0.02 < |$z$| < 0.10. By constructing an updated version of the AKARI–SDSS–GALEX matched galaxy catalog (with >2000 sources), we compare the dust attenuation levels toward stellar light (from the L IR/ L UV ratio) and nebular emission lines (from the Hα/Hβ ratio). We find that there is a clear trend that more massive galaxies tend to have higher "extra" attenuation toward nebular regions, while galaxies with higher specific star formation rates tend to have lower extra attenuation. We also confirm these trends by using the WISE mid-infrared photometry with a significantly large sample size of the WISE–SDSS–GALEX galaxies (>50000 sources). Finally, we study how the levels of extra attenuation toward nebular regions change across the SFR – M ⋆ plane. We find that, even at a fixed stellar mass, galaxies located below the main sequence tend to have higher levels of extra attenuation toward nebular regions, suggesting a change in dust geometry within the galaxies across the star-forming main sequence during the course of the star formation quenching process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]