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Lyman-alpha-emitting galaxies (LAEs) are typically young, low-mass, star-forming galaxies with little extinction from interstellar dust. Their low dust attenuation allows their Ly α emission to shine brightly in spectroscopic and photometric observations, providing an observational window into the high-redshift Universe. Narrowband surveys reveal large, uniform samples of LAEs at specific redshifts that probe large-scale structure and the temporal evolution of galaxy properties. The One-hundred-deg ^2 DECam Imaging in Narrowbands (ODIN) utilizes three custom-made narrowband filters on the Dark Energy Camera (DECam) to discover LAEs at three equally spaced periods in cosmological history. In this paper, we introduce the hybrid-weighted double-broadband continuum estimation technique, which yields improved estimation of Ly α equivalent widths. Using this method, we discover 6032, 5691, and 4066 LAE candidates at z = 2.4, 3.1, and 4.5 in the extended COSMOS field (∼9 deg ^2 ). We find that [O ii ] emitters are a minimal contaminant in our LAE samples, but that interloping Green Pea–like [O iii ] emitters are important for our redshift 4.5 sample. We introduce an innovative method for identifying [O ii ] and [O iii ] emitters via a combination of narrowband excess and galaxy colors, enabling their study as separate classes of objects. We present scaled median stacked spectral energy distributions for each galaxy sample, revealing the overall success of our selection methods. We also calculate rest-frame Ly α equivalent widths for our LAE samples and find that the EW distributions are best fit by exponential functions with scale lengths of w _0 = 53 ± 1, 65 ± 1, and 59 ± 1 Å, respectively.

We test whether Lyα emitters (LAEs) and Lyman-break galaxies (LBGs) can be good tracers of high- z large-scale structures, using the Horizon Run 5 cosmological hydrodynamical simulation. We identify LAEs using the Ly α emission line luminosity and its equivalent width, and LBGs using the broadband magnitudes at z ∼ 2.4, 3.1, and 4.5. We first compare the spatial distributions of LAEs, LBGs, all galaxies, and dark matter around the filamentary structures defined by dark matter. The comparison shows that both LAEs and LBGs are more concentrated toward the dark matter filaments than dark matter. We also find an empirical fitting formula for the vertical density profile of filaments as a binomial power-law relation of the distance to the filaments. We then compare the spatial distributions of the samples around the filaments defined by themselves. LAEs and LBGs are again more concentrated toward their filaments than dark matter. We also find the overall consistency between filamentary structures defined by LAEs, LBGs, and dark matter, with the median spatial offsets that are smaller than the mean separation of the sample. These results support the idea that the LAEs and LBGs could be good tracers of large-scale structures of dark matter at high redshifts.

We study the global kinematics of the Perseus galaxy cluster (A426) at redshift z = 0.017 using a large sample of galaxies from our new MMT/Hectospec spectroscopic observation for this cluster. The sample includes 1447 galaxies with measured redshifts within 60′ from the cluster center (1148 from this MMT/Hectospec program and 299 from the literature). The resulting spectroscopic completeness is 67% at r -band apparent magnitude r _Petro,0 ≤ 18.0 within 60′ from the cluster center. To identify cluster member galaxies in this sample, we develop a new open-source Python package, CausticSNUpy. This code implements the algorithm of the caustic technique and yields 418 member galaxies within 60′ of the cluster. We study the cluster using this sample of member galaxies. The cluster shows no significant signal of global rotation. A statistical test shows that the cluster does not have a noticeable substructure within 30′. We find two central regions where the X-ray-emitting intracluster medium and galaxies show significant velocity differences (>7 σ ). On a large scale, however, the overall morphology and kinematics between the intracluster medium and galaxies agree well. Our results suggest that the Perseus cluster is a relaxed system and has not experienced a recent merger.

We study the formation and evolution of dark galaxies using the IllustrisTNG cosmological hydrodynamical simulation. We first identify dark galaxies with stellar-to-total mass ratios, M _* / M _tot , smaller than 10 ^−4 , which differ from luminous galaxies with M _* / M _tot ≥ 10 ^−4 . We then select the galaxies with a dark matter halo mass of ∼10 ^9 h ^−1 M _⊙ for mass completeness and compare their physical properties with those of luminous galaxies. We find that, at the present epoch ( z = 0), dark galaxies are predominantly located in void regions without star-forming gas. We also find that dark galaxies tend to have larger sizes and higher spin parameters than luminous galaxies. In the early universe, dark and luminous galaxies show small differences in the distributions of spin and local environment estimates, and the difference between the two samples becomes more significant as they evolve. Our results suggest that, unlike luminous galaxies, dark galaxies tend to be initially formed in less dense regions and could not form stars because of heating from cosmic reionization and few interactions and mergers with other systems containing stars. This study based on numerical simulations can provide important hints for validating dark galaxy candidates in observations and for constraining galaxy formation models.

We describe the survey design and science goals for One-hundred-deg ^2 DECam Imaging in Narrowbands (ODIN), a NOIRLab survey using the Dark Energy Camera (DECam) to obtain deep (AB ∼ 25.7) narrowband images over an unprecedented area of sky. The three custom-built narrowband filters, N 419, N 501, and N 673, have central wavelengths of 419, 501, and 673 nm and respective FWHM of 7.5, 7.6, and 10.0 nm, corresponding to Ly α at z = 2.4, 3.1, and 4.5 and cosmic times of 2.8, 2.1, and 1.4 Gyr, respectively. When combined with even deeper, public broadband data from the Hyper Suprime-Cam, DECam, and in the future, the Legacy Survey of Space and Time, the ODIN narrowband images will enable the selection of over 100,000 Ly α -emitting (LAE) galaxies at these epochs. ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the deep narrowband images enable detection of highly extended Ly α blobs (LABs). Primary science goals include measuring the clustering strength and dark matter halo connection of LAEs, LABs, and protoclusters, and their respective relationship to filaments in the cosmic web. The three epochs allow for the redshift evolution of these properties to be determined during the period known as Cosmic Noon, where star formation was at its peak. The narrowband filter wavelengths are designed to enable interloper rejection and further scientific studies by revealing [O ii ] and [O iii ] at z = 0.34, Ly α and He ii 1640 at z = 3.1, and Lyman continuum plus Ly α at z = 4.5. Ancillary science includes similar studies of the lower-redshift emission-line galaxy samples and investigations of nearby star-forming galaxies resolved into numerous [O iii ] and [S ii ] emitting regions.

We search for quasi-stellar objects (QSOs) in a wide area of the south ecliptic pole (SEP) field, which has been and will continue to be intensively explored through various space missions. For this purpose, we obtain deep broadband optical images of the SEP field covering an area of ∼14.5 × 14.5 deg ^2 with the Korea Microlensing Telescope Network (KMTNet). The 5 σ detection limits for point sources in the BVRI bands are estimated to be ∼22.59, 22.60, 22.98, and 21.85 mag, respectively. Utilizing data from the Wide-field Infrared Survey Explorer, unobscured QSO candidates are selected among the optically pointlike sources using mid-infrared (MIR) and optical–MIR colors. To refine our selection further and eliminate any contamination not adequately removed by the color-based selection, we perform spectral energy distribution fitting with archival photometric data ranging from optical to MIR. As a result, we identify a total of 2383 unobscured QSO candidates in the SEP field. We also apply a similar method to the north ecliptic pole field using Pan-STARRS data and obtain a similar result of identifying 2427 candidates. The differential number count per area of our QSO candidates is in good agreement with those measured from spectroscopically confirmed ones in other fields. Finally, we compare the results with the literature and discuss how this work will impact future studies, especially upcoming space missions.

We present bolometric luminosity ( L _bol ) and black hole (BH) mass ( M _BH ) estimators based on mid-infrared (MIR) continuum luminosity (hereafter, L _MIR ) that are measured from infrared (IR) photometric data. The L _MIR -based estimators are relatively immune from dust extinction effects, hence they can be used for dust-obscured quasars. To derive the L _bol and M _BH estimators, we use unobscured quasars selected from the Sloan Digital Sky Survey (SDSS) quasar catalog, which have wide ranges of L _bol (10 ^44.62 –10 ^46.16 erg s ^−1 ) and M _BH (10 ^7.14 –10 ^9.69 M _⊙ ). We find empirical relations between (i) continuum luminosity at 5100 Å (hereafter, L5100) and L _MIR ; (ii) L _bol and L _MIR . Using these relations, we derive the L _MIR -based L _bol and M _BH estimators. We find that our estimators allow the determination of L _bol and M _BH at an accuracy of ∼0.2 dex against the fiducial estimates based on the optical properties of the unobscured quasars. We apply the L _MIR -based estimators to SDSS quasars at z ≲ 0.5 including obscured ones. The ratios of L _bol from the L _MIR -based estimators to those from the optical luminosity-based estimators become larger with the amount of the dust extinction, and a non-negligible fraction (∼15%) of the SDSS quasars exhibits ratios greater than 1.5. This result suggests that dust extinction can significantly affect physical parameter derivations even for SDSS quasars, and that dust extinction needs to be carefully taken into account when deriving quasar properties.

We investigate the variation in the mid-infrared spectral energy distributions of 373 low-redshift ( z < 0.4) star-forming galaxies, which reflects a variety of polycyclic aromatic hydrocarbon (PAH) emission features. The relative strength of PAH emission is parameterized as q _PAH , which is defined as the mass fraction of PAH particles in the total dust mass. With the aid of continuous mid-infrared photometric data points covering 7–24 μ m and far-infrared flux densities, q _PAH values are derived through spectral energy distribution fitting. The correlation between q _PAH and other physical properties of galaxies, i.e., gas-phase metallicity ( $12+\mathrm{log}({\rm{O}}/{\rm{H}})$ ), stellar mass, and specific star-formation rate (sSFR) are explored. As in previous studies, q _PAH values of galaxies with high metallicity are found to be higher than those with low metallicity. The strength of PAH emission is also positively correlated with the stellar mass and negatively correlated with the sSFR. The correlation between q _PAH and each parameter still exists even after the other two parameters are fixed. In addition to the PAH strength, the application of metallicity-dependent gas-to-dust mass ratio appears to work well to estimate gas mass that matches the observed relationship between molecular gas and physical parameters. The result obtained will be used to calibrate the observed PAH luminosity-total infrared luminosity relation, based on the variation of MIR-FIR SED, which is used in the estimation of hidden star formation.

Context. To understand the formation, evolution, and present-day properties of the cosmic web we need to study it at low and high redshifts. Aims. We trace the cosmic web at redshifts that range from 1.0 ⩽ z ⩽ 1.8 by using the quasar (QSO) data from the SDSS DR7 QSO catalogue. Methods. We apply a friend-of-friend algorithm to the quasar and random catalogues to determine systems at a series of linking length and analyse richness and sizes of these systems. Results. At the linking lengths l ⩽ 30 h-1 Mpc, the number of quasar systems is larger than the number of systems detected in random catalogues, and the systems themselves have smaller diameters than random systems. The diameters of quasar systems are comparable to the sizes of poor galaxy superclusters in the local Universe. The richest quasar systems have four members. The mean space density of quasar systems, ≈10-7 (h-1 Mpc)-3, is close to the mean space density of local rich superclusters. At intermediate linking lengths (40 ⩽ l ⩽ 70 h-1 Mpc), the richness and length of quasar systems are similar to those derived from random catalogues. Quasar system diameters are similar to the sizes of rich superclusters and supercluster chains in the local Universe. The percolating system, which penetrate the whole sample volume appears in a quasar sample at a smaller linking length than in random samples (85 h-1 Mpc). At the linking length 70 h-1 Mpc, the richest systems of quasars have diameters exceeding 500 h-1 Mpc. Quasar luminosities in systems are not correlated with the system richness. Conclusions. Quasar system catalogues in our web pages and at the Strasbourg Astronomical Data Center (CDS) serve as a database for searching superclusters of galaxies and for tracing the cosmic web at high redshifts. [ABSTRACT FROM AUTHOR]

The effect of massive neutrinos on the evolution of early-type galaxies in size and stellar mass is explored by tracing the merging history of galaxy progenitors with the help of robust semi-analytic prescriptions. We show that as the presence of massive neutrinos plays a role in enhancing the mean merger rate per halo as well as the merger-driven increment in halo mass, the high-z progenitors of a massive descendant galactic halo evolve more rapidly in mass-normalized size for a ⋀MDM (⋀ cold dark matter + massive neutrinos) model than for the ⋀CDM (⋀ cold dark matter) case. We provide a physical reason for why the halo mass growth rate and the merger rate are higher in a ⋀MDM cosmology and conclude that if the presence and the role of massive neutrinos are properly taken into account, then it may explain the anomalous compactness of the high-z massive ETGs compared with local giant ellipticals with similar stellar masses. [ABSTRACT FROM AUTHOR]

Analyzing the halo and galaxy catalogs from the Millennium Simulations at redshifts z = 0, 0.5, 1, we determine the alignment profiles of cluster galaxies by measuring the average alignments between the major axes of the pseudo inertia tensors from all satellites within a cluster's virial radius and from only those satellites within some smaller radius as a function of the top-hat scale difference. The alignment profiles quantify how well the satellite galaxies retain the memory of the external tidal fields after merging into their host clusters and how fast they lose the initial alignment tendency as the cluster's relaxation proceeds. It is found that the alignment profile drops faster at higher redshifts and on smaller mass scales. This result is consistent with the picture that the faster merging of the satellites and earlier onset of the nonlinear effect inside clusters tend to break the preferential alignments of the satellites with the external tidal fields. Modeling the alignment profile of cluster galaxies as a power law of the density correlation coefficient that is independent of the power spectrum normalization (σ8) and demonstrating that the density correlation coefficient varies sensitively with the density parameter (Ωm) and neutrino mass fraction (fv), we suggest that the alignment profile of cluster galaxies might be useful for breaking the Ωm-σ8 and fv-σ8 degeneracies. [ABSTRACT FROM AUTHOR]

We study the effect of massive neutrinos on the formation and evolution of the first filaments containing the first star-forming halos of mass M ~ l06 M⊙ at z ~ 20. With the help of the extended Press-Schechter formalism, we evaluate analytically the merging rates of the first star-forming halos into zero-dimensional larger halos and one-dimensional first filaments. It is shown that as the neutrino mass fraction fv increases, the halo-to-filament merging rate increases while the halo-to-halo merging decreases sharply. For fv ≤ 0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales, while for fv ≥ 0.07 it exceeds 0.1 at the characteristic filament mass scale of 109 M⊙. The distribution of the redshifts at which the first filaments ultimately collapse along their longest axes is derived and found to have a sharp maximum at z ~ 8. We also investigate the formation and evolution of second-generation filaments which contain the first galaxies of mass 109 M⊙ at z = 8. A similar trend is found: for fv ≥ 0.07 the rate of clustering of the first galaxies into second-generation filaments exceeds 0.3 at the characteristic mass scale of ~1011 M⊙. The longest-axis collapse of these second-generation filaments is found to occur at z ~ 3. The implications of our results on the formation of massive high-z galaxies and the early metal enrichment of the intergalactic medium by supernova-driven outflows, and the possibility of constraining the neutrino mass from the mass distribution of the high-z central black holes, are discussed. [ABSTRACT FROM AUTHOR]

In our recent report, observational evidence supports that the rotational direction of a galaxy tends to be coherent with the average motion of its nearby neighbors within 1 Mpc. We extend the investigation to neighbors at farther distances in order to examine if such dynamical coherence is found even in large scales. The Calar Alto Legacy Integral Field Area (CALIFA) survey data and the NASA-Sloan Atlas (NSA) catalog are used. From the composite map of velocity distribution of “neighbor” galaxies within 15 Mpc from the CALIFA galaxies, the composite radial profiles of the luminosity-weighted mean velocity of neighbors are derived. These profiles show unexpectedly strong evidence of the dynamical coherence between the rotation of the CALIFA galaxies and the average line-of-sight motion of their neighbors within several-megaparsec distances. Such a signal is particularly strong when the neighbors are limited to red ones: the luminosity-weighted mean velocity at 1 < D ≤ 6 Mpc is as large as 30.6 ± 10.9 km s−1 (2.8σ significance to random spin-axis uncertainty) for central rotation (R ≤ Re). In the comparison of several subsamples, the dynamical coherence tends to be marginally stronger for the diffuse or kinematically well-aligned CALIFA galaxies. For this mysterious coherence in large scales, we cautiously suggest a scenario in which it results from a possible relationship between the long-term motion of a large-scale structure and the rotations of galaxies in it. [ABSTRACT FROM AUTHOR]

We present our discovery of observational evidence for the coherence between galaxy rotation and the average line-of-sight motion of neighbors. We use the Calar Alto Legacy Integral Field Area (CALIFA) survey data analyzed with the Python CALIFA STARLIGHT Synthesis Organizer platform, and the NASA-Sloan Atlas catalog. After estimating the projected angular momentum vectors of 445 CALIFA galaxies, we build composite maps of their neighbor galaxies on the parameter space of line-of-sight velocity versus projected distance. The composite radial profiles of the luminosity-weighted mean velocity of neighbors show striking evidence for dynamical coherence between the rotational direction of the CALIFA galaxies and the average moving direction of their neighbor galaxies. The signal of such dynamical coherence is significant for the neighbors within 800 kpc from the CALIFA galaxies, for which the luminosity-weighted mean velocity is as large as 61.7 ± 17.6 km s−1 (3.5σ significance to the bootstrap uncertainty) when the angular momentum is measured at Re < R ≤ 2Re of each CALIFA galaxy. In the comparison of the subsamples, we find that faint, blue, or kinematically misaligned galaxies show stronger coherence with neighbor motions than bright, red, or kinematically well-aligned galaxies do. Our results indicate that (1) the rotation of a galaxy (particularly at its outskirt) is significantly influenced by interactions with its neighbors up to 800 kpc, (2) the coherence is particularly strong between faint galaxies and bright neighbors, and (3) galaxy interactions often cause internal kinematic misalignment or possibly even kinematically distinct cores. [ABSTRACT FROM AUTHOR]

We study the rotational motion of the galaxy cluster A2107 at redshift z = 0.04 and its connection to nearby large-scale structures using a large amount of spectroscopic redshift data. By combining 978 new redshifts from the MMT/Hectospec observations with data in the literature, we construct a large sample of 1968 galaxies with measured redshifts at clustercentric radius R < 60′. Our sample has high (80%) and spatially uniform completeness at r-band apparent magnitude . We first apply the caustic method to the sample and identify 285 member galaxies of A2107 at R < 60′. Then the rotation amplitude and the position angle of the rotation axis are measured. We find that the member galaxies show strong global rotation at R < 20′ (vrot/σv ∼ 0.6) with a significance of >3.8σ, which is confirmed by two independent methods. The rotation becomes weaker in outer regions. There are at least five filamentary structures that are connected to the cluster and that consist of known galaxy groups. These structures are smoothly connected to the cluster, which seem to be inducing the global rotation of the cluster through inflow of galaxies. [ABSTRACT FROM AUTHOR]

We present the results from an extensive spectroscopic survey of the central region of the nearby galaxy cluster Abell 2199 (A2199) at z = 0.03. By combining 775 new redshifts from the MMT/Hectospec observations with the data in the literature, we construct a large sample of 1624 galaxies with measured redshifts at , which results in high spectroscopic completeness at (77%). We use these data to study the kinematics and clustering of galaxies, focusing on the comparison with those of the intracluster medium (ICM) from Suzaku X-ray observations. We identify 406 member galaxies of A2199 at using the caustic technique. The velocity dispersion profile of cluster members appears smoothly connected to the stellar velocity dispersion profile of the cD galaxy. The luminosity function is well fitted with a Schechter function at . The radial velocities of cluster galaxies generally agree well with those of the ICM, but there are some regions where the velocity difference between the two is about a few hundred kilometers per second. The cluster galaxies show a hint of global rotation at with , but the ICM in the same region does not show such rotation. We apply a friends-of-friends algorithm to the cluster galaxy sample at and identify 32 group candidates, and examine the spatial correlation between the galaxy groups and X-ray emission. This extensive survey in the central region of A2199 provides an important basis for future studies of interplay among the galaxies, the ICM, and the dark matter in the cluster. [ABSTRACT FROM AUTHOR]

We study the dependence of the number density and properties of quasars on the background galaxy density using the currently largest spectroscopic data sets of quasars and galaxies. We construct a galaxy number density field smoothed over the variable smoothing scale of between approximately 10 and 20 h−1 Mpc over the redshift range 0.46 < z < 0.59 using the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS galaxies. The quasar sample is prepared from the SDSS-I/II DR7. We examine the correlation of incidence of quasars with the large-scale background density and the dependence of quasar properties such as bolometric luminosity, black hole mass, and Eddington ratio on the large-scale density. We find a monotonic correlation between the quasar number density and large-scale galaxy number density, which is fitted well with a power-law relation, . We detect weak dependences of quasar properties on the large-scale density such as a positive correlation between black hole mass and density, and a negative correlation between luminosity and density. We discuss the possibility of using quasars as a tracer of large-scale structures at high redshifts, which may be useful for studies of the growth of structures in the high-redshift universe. [ABSTRACT FROM AUTHOR]