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The Merian survey is mapping ∼ 850 deg2 of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-m Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 (λ c  = 7080 Å, Δλ = 275 Å) and N540 (λ c  = 5400 Å, Δλ = 210 Å). The central wavelengths and filter widths of N708 and N540 were designed to detect the |$\rm H\alpha$| and |$\rm [OIII]$| emission lines of galaxies in the mass range |$8\lt \rm \log M_*/M_\odot \lt 9$| by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of ∼ 85 000 star-forming dwarf galaxies with a photometric redshift accuracy of σΔ z /(1 + z) ∼ 0.01 and an outlier fraction of |$\eta =2.8~{{\ \rm per\ cent}}$| over the redshift range 0.058 < z < 0.10. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing S/N ∼32 within r < 0.5 Mpc and lensing S/N ∼90 within r < 1.0 Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies. [ABSTRACT FROM AUTHOR]

We propose that observations of supermassive galaxies contain cosmological statistical constraining power similar to conventional cluster cosmology, and we provide promising indications that the associated systematic errors are comparably easier to control. We consider a fiducial spectroscopic and stellar mass complete sample of galaxies drawn from the Dark Energy Spectroscopic Instrument (DESI) and forecast how constraints on Ωm–σ8 from this sample will compare with those from number counts of clusters based on richness λ. At fixed number density, we find that massive galaxies offer similar constraints to galaxy clusters. However, a mass-complete galaxy sample from DESI has the potential to probe lower halo masses than standard optical cluster samples (which are typically limited to λ ≳ 20 and M halo ≳ 1013.5 M⊙  h −1); additionally, it is straightforward to cleanly measure projected galaxy clustering w p for such a DESI sample, which we show can substantially improve the constraining power on Ωm. We also compare the constraining power of M *-limited samples to those from larger but mass-incomplete samples [e.g. the DESI Bright Galaxy Survey (BGS) sample]; relative to a lower number density M *-limited samples, we find that a BGS-like sample improves statistical constraints by 60 per cent for Ωm and 40 per cent for σ8, but this uses small-scale information that will be harder to model for BGS. Our initial assessment of the systematics associated with supermassive galaxy cosmology yields promising results. The proposed samples have a ∼10 per cent satellite fraction, but we show that cosmological constraints may be robust to the impact of satellites. These findings motivate future work to realize the potential of supermassive galaxies to probe lower halo masses than richness-based clusters and to potentially avoid persistent systematics associated with optical cluster finding. [ABSTRACT FROM AUTHOR]

We compare stellar mass surface density, metallicity, age, and line-of-sight velocity dispersion profiles in massive (⁠|$M_*\ge 10^{10.5}\, \mathrm{M_\odot }$|⁠) present-day early-type galaxies (ETGs) from the MaNGA survey with simulated galaxies from the TNG100 simulation of the IllustrisTNG suite. We find an excellent agreement between the stellar mass surface density profiles of MaNGA and TNG100 ETGs, both in shape and normalization. Moreover, TNG100 reproduces the shapes of the profiles of stellar metallicity and age, as well as the normalization of velocity dispersion distributions of MaNGA ETGs. We generally also find good agreement when comparing the stellar profiles of central and satellite galaxies between MaNGA and TNG100. An exception is the velocity dispersion profiles of very massive (⁠|$M_*\gtrsim 10^{11.5}\, \mathrm{M_\odot }$|⁠) central galaxies, which, on average, are significantly higher in TNG100 than in MaNGA (⁠|$\approx 50\, \mathrm{km\, s^{-1}}$|⁠). We study the radial profiles of in situ and ex situ stars in TNG100 and discuss the extent to which each population contributes to the observed MaNGA profiles. Our analysis lends significant support to the idea that high-mass (⁠|$M_*\gtrsim 10^{11}\, \mathrm{M_\odot }$|⁠) ETGs in the present-day Universe are the result of a merger-driven evolution marked by major mergers that tend to homogenize the stellar populations of the progenitors in the merger remnant. [ABSTRACT FROM AUTHOR]

It is clear that within the class of ultra-diffuse galaxies (UDGs), there is an extreme range in the richness of their associated globular cluster (GC) systems. Here, we report the structural properties of five UDGs in the Perseus cluster based on deep Subaru/Hyper Suprime-Cam imaging. Three appear GC-poor and two appear GC-rich. One of our sample, PUDG_R24, appears to be undergoing quenching and is expected to fade into the UDG regime within the next ∼0.5 Gyr. We target this sample with Keck Cosmic Web Imager (KCWI) spectroscopy to investigate differences in their dark matter haloes, as expected from their differing GC content. Our spectroscopy measures both recessional velocities, confirming Perseus cluster membership, and stellar velocity dispersions, to measure dynamical masses within their half-light radius. We supplement our data with that from the literature to examine trends in galaxy parameters with GC system richness. We do not find the correlation between GC numbers and UDG phase space positioning expected if GC-rich UDGs environmentally quench at high redshift. We do find GC-rich UDGs to have higher velocity dispersions than GC-poor UDGs on average, resulting in greater dynamical mass within the half-light radius. This agrees with the first order expectation that GC-rich UDGs have higher halo masses than GC-poor UDGs. [ABSTRACT FROM AUTHOR]

The problem of anomaly detection in astronomical surveys is becoming increasingly important as data sets grow in size. We present the results of an unsupervised anomaly detection method using a Wasserstein generative adversarial network (WGAN) on nearly one million optical galaxy images in the Hyper Suprime-Cam (HSC) survey. The WGAN learns to generate realistic HSC-like galaxies that follow the distribution of the data set; anomalous images are defined based on a poor reconstruction by the generator and outlying features learned by the discriminator. We find that the discriminator is more attuned to potentially interesting anomalies compared to the generator, and compared to a simpler autoencoder-based anomaly detection approach, so we use the discriminator-selected images to construct a high-anomaly sample of ∼13 000 objects. We propose a new approach to further characterize these anomalous images: we use a convolutional autoencoder to reduce the dimensionality of the residual differences between the real and WGAN-reconstructed images and perform UMAP clustering on these. We report detected anomalies of interest including galaxy mergers, tidal features, and extreme star-forming galaxies. A follow-up spectroscopic analysis of one of these anomalies is detailed in the Appendix; we find that it is an unusual system most likely to be a metal-poor dwarf galaxy with an extremely blue, higher-metallicity H  ii region. We have released a catalogue with the WGAN anomaly scores; the code and catalogue are available at https://github.com/kstoreyf/anomalies-GAN-HSC ; and our interactive visualization tool for exploring the clustered data is at https://weirdgalaxi.es. [ABSTRACT FROM AUTHOR]

We perform a consistent comparison of the mass and mass profiles of massive (M ⋆ > 1011.4 M⊙) central galaxies at z ∼ 0.4 from deep Hyper Suprime-Cam (HSC) observations and from the Illustris, TNG100, and Ponos simulations. Weak lensing measurements from HSC enable measurements at fixed halo mass and provide constraints on the strength and impact of feedback at different halo mass scales. We compare the stellar mass function (SMF) and the Stellar-to-Halo Mass Relation (SHMR) at various radii and show that the radius at which the comparison is performed is important. In general, Illustris and TNG100 display steeper values of α where |$M_{\star } \propto M_{\rm vir}^{\alpha }$|⁠. These differences are more pronounced for Illustris than for TNG100 and in the inner rather than outer regions of galaxies. Differences in the inner regions may suggest that TNG100 is too efficient at quenching in situ star formation at M vir ≃ 1013 M⊙ but not efficient enough at M vir ≃ 1014 M⊙. The outer stellar masses are in excellent agreement with our observations at M vir ≃ 1013 M⊙, but both Illustris and TNG100 display excess outer mass as M vir ≃ 1014 M⊙ (by ∼0.25 and ∼0.12 dex, respectively). We argue that reducing stellar growth at early times in |$M_\star \sim 10^{9-10} \, \mathrm{M}_{\odot }$| galaxies would help to prevent excess ex-situ growth at this mass scale. The Ponos simulations do not implement AGN feedback and display an excess mass of ∼0.5 dex at r < 30 kpc compared to HSC which is indicative of overcooling and excess star formation in the central regions. The comparison of the inner profiles of Ponos and HSC suggests that the physical scale over which the central AGN limits star formation is r ≲ 20 kpc. Joint comparisons between weak lensing and galaxy stellar profiles are a direct test of whether simulations build and deposit galaxy mass in the correct dark matter haloes and thereby provide powerful constraints on the physics of feedback and galaxy growth. Our galaxy and weak lensing profiles are publicly available to facilitate comparisons with other simulations. [ABSTRACT FROM AUTHOR]

The splashback radius (R sp) of dark matter haloes has recently been detected using weak gravitational lensing and cross-correlations with galaxies. However, different methods have been used to measure R sp and to assess the significance of its detection. In this paper, we use simulations to study the precision and accuracy to which we can detect the splashback radius with 3D density, 3D subhalo, and weak lensing profiles. We study how well various methods and tracers recover R sp by comparing it with the value measured directly from particle dynamics. We show that estimates of R sp from density and subhalo profiles correspond to different percentiles of the underlying R sp distribution of particle orbits. At low accretion rates, a second caustic appears and can bias results. Finally, we show that upcoming lensing surveys may be able to constrain the R sp–Γdyn relation directly. [ABSTRACT FROM AUTHOR]

We use the UniverseMachine to analyse the source of scatter between the central galaxy mass, the total stellar mass in the halo, and the dark matter halo mass, for massive (M vir > 1013 M⊙) haloes. We also propose a new halo mass estimator, the cen+N mass: the sum of the stellar mass of the central and the N most massive satellites. We show that, when real space positions are perfectly known, the cen+N mass has scatter competitive with that of richness-based estimators. However, in redshift space, using a simple cluster finder, the cen+N mass suffers less from projection effects in the UniverseMachine model. The cen+N mass is therefore a potential candidate to constrain cosmology with upcoming spectroscopic data from DESI. We analyse the scatter in stellar mass at fixed halo mass and show that the total stellar mass in a halo is uncorrelated with secondary halo properties, but that the central stellar mass is a function of both halo mass and halo age. This is because central galaxies in older haloes have had more time to grow via accretion. If the UniverseMachine model is correct, this implies that haloes selected using the centrals stellar mass will be biased old and that accurate galaxy-halo modelling of mass selected samples therefore needs to consider halo age in addition to mass. [ABSTRACT FROM AUTHOR]

Using deep images from the Hyper Suprime-Cam (HSC) survey and taking advantage of its unprecedented weak lensing capabilities, we reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass. Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes. We explain this connection with a phenomenological model that assumes, (1) a tight relation between the halo mass and the total stellar content in the halo, (2) that the fraction of in situ and ex situ mass at r <10 kpc depends on halo mass. This model provides an excellent description of the stellar mass functions (SMFs) of total stellar mass (⁠|$M_{\star }^{\mathrm{max}}$|⁠) and stellar mass within inner 10 kpc (⁠|$M_{\star }^{10}$|⁠) and also reproduces the HSC weak lensing signals of massive galaxies with different stellar mass distributions. The best-fitting model shows that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on |$M_{\star }^{10}$|⁠. Our two-parameter |$M_{\star }^{\mathrm{max}}$| – |$M_{\star }^{10}$| description provides a more accurate picture of the galaxy–halo connection at the high-mass end than the simple stellar–halo mass relation (SHMR) and opens a new window to connect the assembly history of haloes with those of central galaxies. The model also predicts that the ex situ component dominates the mass profiles of galaxies at r < 10 kpc for log  M ⋆ ≥ 11.7. The code used for this paper is available online https://github.com/dr-guangtou/asap [ABSTRACT FROM AUTHOR]

Although photometric redshifts (photo- z 's) are crucial ingredients for current and upcoming large-scale surveys, the high-quality spectroscopic redshifts currently available to train, validate, and test them are substantially non-representative in both magnitude and colour. We investigate the nature and structure of this bias by tracking how objects from a heterogeneous training sample contribute to photo- z predictions as a function of magnitude and colour, and illustrate that the underlying redshift distribution at fixed colour can evolve strongly as a function of magnitude. We then test the robustness of the galaxy–galaxy lensing signal in 120 deg2 of HSC–SSP DR1 data to spectroscopic completeness and photo- z biases, and find that their impacts are sub-dominant to current statistical uncertainties. Our methodology provides a framework to investigate how spectroscopic incompleteness can impact photo- z -based weak lensing predictions in future surveys such as LSST and WFIRST. [ABSTRACT FROM AUTHOR]

We study the faint stellar halo of isolated central galaxies, by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points. The surface brightness profiles in HSC r band are measured for a wide range of galaxy stellar masses (9.2 < log10 M ∗/M⊙ < 11.4) and out to 120 kpc. Failing to account for the stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by ≤15%. Splitting galaxies according to the concentration parameter of their light distributions, we find that the surface brightness profiles of low-concentration galaxies drop faster between 20 and 100 kpc than those of high-concentration galaxies. Albeit the large galaxy-to-galaxy scatter, we find a strong self-similarity of the stellar halo profiles. They show unified forms once the projected distance is scaled by the halo virial radius. The colour of galaxies is redder in the centre and bluer outside, with high-concentration galaxies having redder and more flattened colour profiles. There are indications of a colour minimum, beyond which the colour of the outer stellar halo turns red again. This colour minimum, however, is very sensitive to the completeness in masking satellite galaxies. We also examine the effect of the extended PSF in the measurement of the stellar halo, which is particularly important for low-mass or low-concentration galaxies. The PSF-corrected surface brightness profile can be measured down to ∼31  |$\mathrm{mag}\, \mathrm{arcsec}^{-2}$| at 3σ significance. PSF also slightly flattens the measured colour profiles. [ABSTRACT FROM AUTHOR]

Narrow-line regions excited by active galactic nuclei (AGNs) are important for studying AGN photoionization and feedback. Their strong [O  iii ] lines can be detected with broad-band images, allowing morphological studies of these systems with large-area imaging surveys. We develop a new broad-band imaging technique to reconstruct the images of the [O  iii ] line, using the Subaru Hyper Suprime-Cam (HSC) Survey aided with spectra from the Sloan Digital Sky Survey (SDSS). The technique involves a careful subtraction of the galactic continuum to isolate emission from the [O  iii ]λ5007 and [O  iii ]λ4959 lines. Compared to traditional targeted observations, this technique is more efficient at covering larger samples without dedicated observational resources. We apply this technique to an SDSS spectroscopically selected sample of 300 obscured AGN at redshifts 0.1–0.7, uncovering extended emission-line region candidates with sizes up to tens of kpc. With the largest sample of uniformly derived narrow-line region sizes, we revisit the narrow-line region size–luminosity relation. The area and radii of the [O  iii ] emission-line regions are strongly correlated with the AGN luminosity inferred from the mid-infrared (15 $$\mu$$ m rest frame) with a power-law slope of $$0.62^{+0.05}_{-0.06}\pm 0.10$$ (statistical and systematic errors), consistent with previous spectroscopic findings. We discuss the implications for the physics of AGN emission-line regions and future applications of this technique, which should be useful for current and next-generation imaging surveys to study AGN photoionization and feedback with large statistical samples. [ABSTRACT FROM AUTHOR]

We use ∼100 deg2 of deep (>28.5 mag arcsec−2 in i band), high-quality (median 0.6 arcsec seeing) imaging data from the Hyper Suprime-Cam (HSC) survey to reveal the halo mass dependence of the surface mass density profiles and outer stellar envelopes of massive galaxies. The i -band images from the HSC survey reach ∼4 mag deeper than Sloan Digital Sky Survey and enable us to directly trace stellar mass distributions to 100 kpc without requiring stacking. We conclusively show that, at fixed stellar mass, the stellar profiles of massive galaxies depend on the masses of their dark matter haloes. On average, massive central galaxies with log10(M ⋆, 100 kpc/M⊙)>11.6 in more massive haloes at 0.3 <  z  < 0.5 have shallower inner stellar mass density profiles (within ∼10–20 kpc) and more prominent outer envelopes. These differences translate into a halo mass dependence of the mass–size relation. Central galaxies in haloes with log10(M 200b/M⊙)>14.0 are ∼20 per cent larger in R 50 at fixed M ⋆, 100 kpc. Such dependence is also reflected in the relationship between the stellar mass within 10 and 100 kpc. Comparing to the mass–size relation, the M ⋆, 100 kpc– M ⋆, 10 kpc relation avoids the ambiguity in the definition of size, and can be straightforwardly compared with simulations. Our results demonstrate that, with deep images from HSC, we can quantify the connection between halo mass and the outer stellar halo, which may provide new constraints on the formation and assembly of massive central galaxies. [ABSTRACT FROM AUTHOR]