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At least 1,063 records · Page 59
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DOE OSTI2020

Cosmic Reionization On Computers: The Galaxy-Halo Connection between $5 \leq z \leq10$

We explore the connection between the stellar component of galaxies and their host halos during the epoch of reionization (5 ≤ z ≤ 10) using the CROC (Cosmic Reionization on Computers) simulations. We compare simulated galaxies with observations and find that CROC underpredicts the abundance of luminous galaxies when compared to observed UV luminosity functions, and analogously the most massive galaxies when compared to observed stellar mass functions. We can trace the deficit of star formation to high redshifts, where the slope of the star formation rate to stellar mass relation is consistent with observations, but the normalization is systematically low. This results in a star formation rate density and stellar mass density that are systematically offset from observations. However, the less luminous or lower stellar mass objects have luminosities and stellar masses that agree fairly well with observational data. We explore the stellar-to-halo mass ratio (SHMR), a key quantity that is difficult to measure at high redshifts and that models do not consistently predict. In CROC, the SHMR decreases with redshift, a trend opposite to some abundance-matching studies. These discrepancies uncover where future effort should be focused in order to improve the fidelity of modeling cosmic reionization. We also compare the CROC galaxy bias with observational measurements using Lyman-break galaxy samples, finding reasonable consistency.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Binary–Host Connection: Astrophysics of Gravitational-Wave Binaries from Host Galaxy Properties

Gravitational waves from the merger of binary neutron stars (BNSs) are accompanied by electromagnetic counterparts, making it possible to identify the associated host galaxy. In this work, we explore how properties of the hosts relate to the astrophysical processes leading to the mergers. It is thought that the BNS merger rate within a galaxy at a given epoch depends primarily on the galaxy's star formation history, as well as the underlying merger time-delay distribution of the binary systems. The stellar history of a galaxy, meanwhile, depends on the cosmological evolution of the galaxy through time, and is tied to the growth of structure in the universe. We study the hosts of BNS mergers in the context of structure formation by populating the UniverseMachine simulations with gravitational wave (GW) events, based on a simple time-delay model. We find that different time-delay distributions predict different properties of the associated host galaxies, including the distributions of stellar mass, star formation rate, halo mass, and local and large-scale clustering of hosts. Moreover, BNSs merging today with short delay times occur preferentially in hosts with high star formation rates, while those with long delay times live in dense regions within massive halos that have low star formation. Here, we show that with ${ \mathcal O }(10)$ events from current GW detector networks, it is possible to make preliminary distinctions between formation channels which trace stellar mass, halo mass, or star formation rate. We also find that strategies to follow-up GW events with electromagnetic telescopes can be significantly optimized using the clustering properties of their hosts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

WALLABY Pre-pilot Survey: The Effects of Tidal Interaction on Radial Distribution of Color in Galaxies of the Eridanus Supergroup

We study the tidal interaction of galaxies in the Eridanus supergroup, using H i data from the pre-pilot survey of the Widefield ASKAP L-band Legacy All-sky Blind surveY. We obtain optical photometric measurements and quantify the strength of tidal perturbation using a tidal parameter S sum . For low-mass galaxies of M * ≲ 10 9 M ⊙ , we find a dependence of decreasing H i to optical disk size ratio with increasing S sum , but no dependence of H i spectral line asymmetry with S sum . This is consistent with the behavior expected under tidal stripping. We confirm that the color profile shape and color gradient depend on the stellar mass, but there is an additional correlation of low-mass galaxies having their color gradients within 2R 50 increasing with higher S sum . For these low-mass galaxies, the dependence of color gradients on S sum is driven by the color becoming progressively redder in the inner disk when tidal perturbations are stronger. For high-mass galaxies, there is no dependence of color gradients on S sum , and we find a marginal reddening throughout the disks with increasing S sum . Our result highlights tidal interaction as an important environmental effect in producing the faint end of the star formation suppressed sequence in galaxy groups.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The DESI One-Percent Survey: Constructing Galaxy–Halo Connections for ELGs and LRGs Using Auto and Cross Correlations

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at z ~ 1. We measure the auto and cross correlation functions of ELGs and LRGs at 0.8 < z ≤ 1.0 from the DESI One-Percent survey. Following Gao et al., we construct the galaxy–halo connections for ELGs and LRGs simultaneously. With the stellar–halo mass relation for the whole galaxy population (i.e., normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability P sat of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent P sat model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at r p > 0.1 Mpc h –1 . We can also reproduce the auto correlations of ELGs at r p > 0.3 Mpc h –1 (s > 1 Mpc h –1 ) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of 0.8 < z ≤ 1.6, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions for ELGs, which can be used to produce ELG mocks in coarse simulations without resolving subhalos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

How Population III Supernovae Determined the Properties of the First Galaxies

Abstract Massive Population III stars can die as energetic supernovae that enrich the early Universe with metals and determine the properties of the first galaxies. With masses of about 10 9 M ⊙ atz≳ 10, these galaxies are believed to be the ancestors of the Milky Way. This paper investigates the impact of Population III supernova remnants (SNRs) from both Salpeter-like and top-heavy initial mass functions (IMFs) on the formation of first galaxies with high-resolution radiation-hydrodynamical simulations with theENZOcode. Our findings indicate that SNRs from a top-heavy Population III IMF produce more metals, leading to more efficient gas cooling and earlier Population II star formation in the first galaxies. From a few hundred to a few thousand Population II stars can form in the central regions of these galaxies. These stars have metallicities of 10 −3 –10 −2 ,Z ⊙ , greater than those of extremely metal-poor (EMP) stars. Their mass function follows a power-law distribution with dN ( M * ) / dM * ∝ M * α , whereM * is stellar mass, andα= 2.66–5.83 and is steeper for a top-heavy IMF. We thus find that EMP stars were not typical of most primitive galaxies.

Astronomy & Astrophysics↗
DOE OSTI2026

Dwarf Galaxies at Cosmic Noon: New JWST Constraints on Satellite Models and Subhalo Tidal Evolution

The advent of JWST has revolutionized the study of faint satellite galaxies at z ≳ 1, enabling statistical constraints on galaxy evolution and the galaxy–halo connection in a previously unexplored mass and redshift regime. We compare satellite abundances at 1 < z < 3.5 from recent JWST observations with predictions from cosmological dark-matter-only zoom-in simulations. We identify and quantify several sources of biases that can impact theoretical satellite counts, finding that assumptions about subhalo tidal evolution introduce the largest uncertainty in predictions for the satellite mass function. Using a flexible galaxy disruption model, we explore a range of disruption scenarios, spanning hydrodynamically motivated and idealized prescriptions, to bracket plausible physical outcomes. We show that varying galaxy durability can change the predicted satellite mass functions by a factor of ∼3.5. The JWST data and our fiducial model are consistent within 1σ–2σ across the full redshift (1 < z < 3.5) and stellar mass (M⋆ > 10 7 M ⊙ ) range probed. We find evidence that subhalos are at least as long-lived as predicted by hydrodynamic simulations. Our framework will enable robust constraints on the tidal evolution of subhalos with future observations. This work presents the first direct comparison between cosmological models and observations of the high-redshift satellite population in this low-mass regime. These results showcase JWST’s emerging power to test structure formation in the first half of the Universe in a new domain and to constrain the physical processes driving the evolution of low-mass galaxies across cosmic time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Galactic Rain: Cool Gas Inflows in Red Geyser Galaxies and Their Connection to Active Galactic Nuclei Activity and Interactions

Red geysers are a population of massive (logM/M ⊙ ~ 10.5), quiescent galaxies with large-scale but weak, bisymmetric ionized gas outflows, interpreted as signatures of ongoing, low-level active galactic nucleus (AGN) feedback. We investigate the kinematics and prevalence of cool (T ∼ 100–1000 K) neutral gas traced by Na I D absorption, and its connection to galaxy environment and AGN activity. Using 140 red geyser galaxies from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (or MaNGA), we measure spatially resolved velocities and dispersions via double-Gaussian fits to the Na I D doublet. We find that ∼70% of the cool gas is inflowing, with a median velocity of ∼47 km s −1 (∼10% of the expected freefall velocity), and that it also exhibits kinematically ordered motions with σ NaD /σ* ∼ 0.4. Additionally, the Na I D absorption is more prevalent in red geysers than in a matched control sample, with a higher detection fraction (63% versus 40%) and reservoir areas ∼1.6 times larger. Acceleration (∼1 Myr) and accretion (∼20 Myr) timescales indicate that the Na I D-absorbing clouds are likely young and short-lived. Another intriguing result is that radio-detected red geysers (30% of the sample) show inflowing gas reservoirs ∼7 times larger than in non-radio systems. Similarly, galaxies subject to environmental effects host inflowing gas reservoirs ∼2.7 times larger than isolated red geysers. We take this as evidence that galaxy environments play a key role in replenishing the cool gas reservoirs of red geysers, fueling central AGN activity, sustaining radio emission, and regulating long-term quiescence. These findings reveal that quiescent systems are governed by cycles of inflow, feedback, and regulation.

Moghni, Arian [Univ. of California, Santa Cruz, CA↗
DOE OSTI2026

Impact of Cosmic Filaments on Galaxy Morphological Evolution and Predictions of Early Cosmic Web Structure for Roman

We leverage the IllustrisTNG cosmological simulations to test how the large-scale cosmic web shapes galaxy morphology and to forecast the early cosmic web structure that the Nancy Grace Roman Space Telescope will reveal. In the hydrodynamic TNG50 and N-body TNG50-Dark runs, we reconstruct the cosmic web at redshifts z = 0, 0.5, 1, 2, 3, and 4 with the Monte Carlo Physarum Machine density estimator and the DisPerSE structure identification framework. We confirm that dark matter halos start out predominantly prolate (elongated), and their shapes are aligned with their nearest filaments; prolate galaxies retain strong shape alignment with their outer halos to later times. At z ≥ 1, the fraction of prolate (spheroidal) halos increases (decreases) toward lower stellar mass, higher redshift, and lower filament density. At z < 1, more spheroidal (oblate) stellar structures preferentially reside in higher-density (lower-density) filaments. We also find that higher-density filaments favor extended rotationally supported disks, whereas lower-density filaments more often host smaller dispersion-supported systems. Then, generating mock galaxy samples from TNG100 and TNG50, we predict the early cosmic web accessible to Roman. We find that the spectroscopic emission-line depth planned for the High-Latitude Wide-Area Survey (HLWAS) yields a highly incomplete galaxy sample that does not accurately trace the z = 1 cosmic web. A survey ≥2.5× deeper over a few square degrees would enable a proper reconstruction and reveal qualitatively correct filament–galaxy morphology relationships. Nevertheless, the planned HLWAS Deep field should still identify most galaxy overdensities; targeted deeper spectroscopy of these regions would efficiently and adequately map the early filamentary structure.

Hasan, Farhanul [Space Telescope Science Institute↗
DOE OSTI2025

Monopole Fluctuations in Galaxy Surveys

Galaxy clustering provides a powerful way to probe cosmology. This requires understanding of the background mean density of galaxy samples, which is estimated from the survey itself by averaging the observed galaxy number density over the angular position. The angle average includes not only the background mean density but also the monopole fluctuation at each redshift. Here for the first time we compute the monopole fluctuations in galaxy surveys and investigate their impact on galaxy clustering. The monopole fluctuations vary as a function of redshift, and it is correlated with other fluctuations, affecting the two-point correlation function measurements. In an idealized all-sky survey, the rms fluctuation at z = 0.5 can be as large as 7% of the two-point correlation function in amplitude at the baryonic acoustic oscillation scale, and it becomes smaller than 1% at z > 2. The monopole fluctuations are unavoidable, but they can be modeled. We discuss its relation to the integral constraint and the implications for the galaxy clustering analysis.

Baryon acoustic oscillations↗
DOE OSTI2022

Using Maximum Circular Velocity in Halo Occupation Distribution Models to Predict Galaxy Clustering

Abstract Standard halo occupation distribution (HOD) models predict how galaxies occupy halos based on a single property, the virial mass, M vir . To incorporate galaxy assembly bias, we consider alternative halo mass proxies to use in the HOD. A promising replacement is maximum circular velocity, V max , which measures the halo’s potential well, and successfully predicts galaxy clustering in subhalo abundance matching models. We fit galaxy clustering measurements from SDSS DR7 with two modified HODs besides the standard M vir -based model: one where V max is used as the halo property that determines galaxy occupation, and the other adopting an adjustable combination of M vir and V max . Except for the reduced volume M r < − 20 threshold sample fit with V max alone, neither change improves the model performance in predicting the projected two-point correlation function, w p . We conclude that switching the primary variable to V max does not significantly improve the HOD model’s ability to fit galaxy clustering.

Mezini, Lorena↗
NASA NTRS1972

Spectral energy distributions of nuclei of peculiar galaxies.

Consideration of galaxies of the types described by Seyfert, Zwicky, Markarian and others. Quasars are discussed in terms of their similarities to the nuclei of peculiar galaxies. The data discussed were obtained almost exclusively with photoelectric spectrometers. Peculiar galaxies have a wide range of properties insofar as their spectra are concerned. Many have very strong emission lines. Sources of continuous radiation, and distance scale problems and selection effects are discussed. Data are presented which are representative of spectrophotometric observational results for 12 Markarian galaxies, 14 Zwicky compact objects, and 16 radio galaxies. The general properties of spectral energy distributions of peculiar galaxies and quasars are discussed.

Oke, J. B.↗
NASA NTRS1973

Radio maps around five spiral and peculiar galaxies.

Areas of from 1 to 2 degrees square around five spiral and peculiar galaxies of apparent brightness between 10.3 and 12.7 mag have been mapped at a wavelength of 13 cm. In this small sample of observations it is found that, on the average, about two, counting the galaxy itself, radio sources of flux strength between 0.1 and 0.4 f.u. are physically associated with each spiral. This result supports the conclusion of De Jong that satellite radio sources are associated with spiral galaxies. If these preliminary results are indicative, then the radio sources associated with spiral galaxies differ from those classically associated with elliptical galaxies by being (1) intrinsically weaker and (2) not as accurately aligned as pairs across the central galaxy.

Arp, H.↗
NASA NTRS1977

Hot gas in clusters of galaxies

Radio and X-ray observations are discussed which seem to favor the presence of a hot intracluster gas in rich clusters of galaxies. On the assumption that the X-rays are produced by thermal bremsstrahlung, a temperature of the order of 100 million K and a density of a few thousandths per cu cm are computed for the intracluster gas. Theories on the origin and dynamics of this gas are reviewed, and the discovery of an iron line in the spectrum of the Perseus cluster is taken as strong evidence for thermal emission from a hot intracluster gas. Effects of and on the intracluster gas are considered, particularly the formation of radio-tail galaxies due to ram pressure on the galaxies in rich clusters, stripping of interstellar gas from the galaxies, and heating of the intracluster gas by the galaxies. It is concluded that the intracluster gas: (1) originated partially in primordial matter that collapsed into the clusters and partially in gas lost from the galaxies, (2) is in static or almost static equilibrium in the clusters, and (3) either is tightly bound or has an equation of state corresponding to a gamma value of less than 5/3.

Lea, S. M.↗
NASA NTRS1979

ESO 103-G35 - A new Seyfert galaxy and possible X-ray source

By means of an objective prism plate, two emission-line galaxies have been identified within the 0.7-sq deg HEAO-A2 error box for the X-ray source H1834-653. Optical spectrophotometric observations are reported for both objects as well as the galaxy NGC 6684, which also lies near the position of H1834-653. These data show that one of the emission-line galaxies, ESO 103-G35, is a Seyfert galaxy with a high-excitation forbidden-line spectrum and weak broad emission wings at H-alpha. Further measurements of this galaxy reveal an infrared excess at wavelengths longer than 2.2 microns. The H-alpha luminosity of ESO 103-G35 is consistent with the X-ray luminosity estimated from the HEAO-A2 data, thus strengthening the likelihood of association of this galaxy with the X-ray emission.

Phillips, M. M.↗
NASA NTRS1980

Galaxy collisions - A preliminary study

Collisions of spherical galaxies were studied in a series of numerical experiments to see what happens when galaxies collide. Each experiment starts with two model galaxies, each consisting of 50,000 stars, moving toward each other along a specified orbit. The series of experiments provides a systematic sampling of the parameter space spanned by the initial orbital energy and the initial angular momentum. Deeply penetrating collisions are emphasized. The collisions reported here scale to relative velocities as great as 500 km/s, well into the range for collisions within clusters of galaxies. It is found that: (1) the galaxies contract momentarily to about half their original sizes shortly after close passage; and (2) the initial galaxies blend into a single dynamical system while they are near each other.

Miller, R. H.↗
NASA NTRS1980

The contribution of young galaxies to the X-ray background

The contribution of young galaxies to the diffuse X-ray background is estimated and two mechanisms by which young galaxies may emit hard X-rays are considered. The first mechanism is direct thermal bremsstrahlung emission from a hot galactic wind powered by supernovae. Estimating mass-loss rates from galaxies by arguments based on metallicity and on the X-ray spectroscopic observations of rich clusters, it is shown that galactic winds may contribute substantially to the background. The second mechanism relies on the decreased metallicity of young galaxies to increase the number of supergiant stars and hence the numbers of hard X-ray binaries. This effect quantitatively explains the relatively large X-ray luminosity of the Magellanic clouds and also indicates that binaries in young galaxies may contribute a significant fraction of the diffuse X-ray background. Both mechanisms require that the epoch of galaxy formation be recent (redshift less than 2-3) in order to account for the observed spectral temperature (45 keV) of the hard X-ray background.

Bookbinder, J.↗
NASA NTRS1980

X-ray studies of quasars and active galaxies with the Einstein Observatory

Preliminary results of the first six months of an X-ray survey of active galaxies and quasars performed with the imaging proportional counter on board the Einstein Observatory are presented. Consideration is given to detections of Seyfert galaxies, N galaxies, BL Lac objects and quasars, and properties of selected representative objects are discussed in detail. The statistical properties, including class averages and correlation coefficients, of the various X-ray active galaxies are calculated in an attempt to determine the relation of X-ray properties to the similarities and differences between the various classes of galaxies. Evidence is obtained for a continuity of high-energy behavior among all active galaxies, and it is noted that they all exhibit flux variability, often on a short time scale. The soft X-ray emission can be explained in terms of the synchrotron self-Compton model, or alternatively by thermal emission from hot gas. A significant correlation is obtained between the X-ray and optical fluxes for all objects considered, indicating that optical quasar counts may be used to infer the contribution of quasars to the diffuse X-ray background.

Ku, W. H.-M.↗
NASA NTRS1981

Radio emission in the directions of cD and related galaxies in poor clusters. III - VLA observations at 20 cm

VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed

Burns, J. O.↗