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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

The first quiescent galaxies in TNG300

We identify the first quiescent galaxies in TNG300, the largest volume of the IllustrisTNG cosmological simulation suite, and explore their quenching processes and time evolution to z = 0. We find that the first quiescent galaxies with stellar masses M_* > 3 × 10^10 M_⊙ and specific star formation rates sSFR < 10^−11 yr^−1 emerge at z ∼ 4.2 in TNG300. Suppression of star formation in these galaxies begins with a thermal mode of active galactic nucleus feedback at z ∼ 6, and a kinetic feedback mode acts in each galaxy by z ∼ 4.7 to complete the quenching process, which occurs on a time-scale of ∼0.35 Gyr. Surprisingly, we find that the majority of these galaxies are not the main progenitors of their z = 0 descendants; instead, four of the five galaxies fall into more massive galaxies in subsequent mergers at a range of redshifts 2.5 < z < 0.2. By z = 0, these descendants are the centres of galaxy clusters with average stellar masses of 8 × 10^11 M_⊙. We make predictions for the first quenched galaxies to be located by the JWST.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2019

The Lyα Luminosity Function and Cosmic Reionization at z ~ 7.0: A Tale of Two LAGER Fields

We present the largest-ever sample of 79 Lyα emitters (LAEs) at z ~ 7.0 selected in the COSMOS and CDFS fields of the LAGER project (the Lyman Alpha Galaxies in the Epoch of Reionization). Our newly amassed ultradeep narrowband exposure and deeper/wider broadband images have more than doubled the number of LAEs in COSMOS, and we have selected 30 LAEs in the second field CDFS. We detect two large-scale LAE-overdense regions in the COSMOS that are likely protoclusters at the highest redshift to date. We perform injection and recovery simulations to derive the sample incompleteness. We show that significant incompleteness comes from blending with foreground sources, which, however, has not been corrected in LAE luminosity functions (LFs) in the literature. The bright-end bump in the Lyα LF in COSMOS is confirmed with six (two newly selected) luminous LAEs (LLyα > 1043.3 erg s−1). Interestingly, the bump is absent in CDFS, in which only one luminous LAE is detected. Meanwhile, the faint-end LFs from the two fields agree well with each other. The six luminous LAEs in COSMOS coincide with two LAE-overdense regions, while such regions are not seen in CDFS. The bright-end LF bump could be attributed to ionized bubbles in a patchy reionization. It appears associated with cosmic overdensities and thus supports an inside-out reionization topology at z ~ 7.0, i.e., the high-density peaks were ionized earlier compared to the voids. An average neutral hydrogen fraction of xH I ~ 0.2–0.4 is derived at z ~ 7.0 based on the cosmic evolution of the Lyα LF.

cosmology: observations↗
DOE OSTI2020

Forecasting [C II ] Line-intensity Mapping Measurements between the End of Reionization and the Epoch of Galaxy Assembly

We combine recent simulation work on the SFR–[C II ] correlation at high redshift with empirical modeling of the galaxy–halo connection (via UniverseMachine) to forecast [C ii] auto power spectra from z ~ 4 to z ~ 8. We compare these to sensitivities realistically expected from various instruments expected to come online in the next decade. If the predictions of our model are correct, [C II ] should be detectable up to z ~ 6 in this generation of surveys, but detecting [C II ] past the end of reionization will require a generational leap in line-intensity survey capabilities.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

Shaping the Dust Mass-Star-Formation Rate Relation

There is a remarkably tight relation between the observationally inferred dust masses and star-formation rates (SFRs) of Sloan Digital Sky Survey galaxies, M dust ∝ SFR 1.11(exp). Here we extend the M dust-SFR relation to the high end and show that it bends over at very large SFRs (i.e., dust masses are lower than predicted for a given SFR). We identify several distinct evolutionary processes in the diagram: (1) a star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the cause of the bend-over of the relation. A high dust-formation efficiency, a bottom-light initial mass function, and negligible supernova shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent star-forming phase in which the subsequent parallel decline in dust mass and SFR gives rise to the M dust-SFR relation, through astration and dust destruction. The dust-to-gas ratio is approximately constant along the relation. We show that the power-law slope of the M dust-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (i.e., ~0.9) in simple chemical evolution models. (3) A quenching phase which causes star formation to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original M dust-SFR relation. (4) At very high redshifts, a population of galaxies located significantly below the local relation is predicted.

Shaping↗
DOE OSTI2021

Quiescent galaxies in a virialized cluster at redshift 2: evidence for accelerated size growth

ABSTRACT We present an analysis of the galaxy population in XLSSC 122, an X-ray-selected, virialized cluster at redshift z = 1.98. We utilize Hubble Space Telescope (HST)Wide Field Camera 3 (WFC3) photometry to characterize the activity and morphology of spectroscopically confirmed cluster members. The quiescent fraction is found to be $88^{+4}_{-20}$ per cent within 0.5r500, significantly enhanced over the field value of $20^{+2}_{-2}$ per cent at z ∼ 2. We find an excess of ‘bulge-like’ quiescent cluster members with Sérsic index n > 2 relative to the field. These galaxies are found to be larger than their field counterparts at 99.6 per cent confidence, being on average $63^{+31}_{-24}$ per cent larger at a fixed mass of $M_\star = 5\times 10^{10} \, \mathrm{M}_\odot$. This suggests that these cluster member galaxies have experienced an accelerated size evolution relative to the field at z > 2. We discuss minor mergers as a possible mechanism underlying this disproportionate size growth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The SOUX AGN sample: SDSS– XMM-Newton optical, ultraviolet, and X-ray selected active galactic nuclei spanning a wide range of parameter space – sample definition

Abstract We assemble a sample of 696 type 1 active galactic nuclei (AGN) up to a redshift of z = 2.5, all of which have an SDSS spectrum containing at least one broad emission line (H α, H β, or Mg ii) and an XMM-Newton X-ray spectrum containing at least 250 counts in addition to simultaneous optical/ultraviolet photometry from the XMM Optical Monitor. Our sample includes quasars and narrow-line Seyfert 1s: thus our AGN span a wide range in luminosity, black hole mass, and accretion rate. We determine single-epoch black hole mass relations for the three emission lines and find that they provide broadly consistent mass estimates whether the continuum or emission line luminosity is used as the proxy for the broad emission line region radius. We explore variations of the UV/X-ray energy index αox with the UV continuum luminosity and with black hole mass and accretion rate, and make comparisons to the physical quasar spectral energy distribution model qsosed. The majority of the AGN in our sample lie in a region of parameter space with 0.02 < L/LEdd < 2 as defined by this model, with narrow-line type 1 AGN offset to lower masses and higher accretion rates than typical broad-line quasars. We find differences in the dependence of αox on UV luminosity between both narrow/broad-line and radio-loud/quiet subsets of AGN: αox has a slightly weaker dependence on UV luminosity for broad-line AGN and radio-loud AGN have systematically harder αox.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Nuclear activity and the environments of nearby radio galaxies

Much of our present understanding of galaxy evolution over a large redshift range is based on the study of samples selected on the basis of non-thermal radio emission. It is therefore necessary to understand the relationship between radio source activity and the host galaxy. Recent observations suggest that there is a connection between radio galaxy (RG) activity and radio galaxy evolution. For example, high-redshift RGs (z approx. greater than 0.7) show evidence for significant populations of young stars, and have optical continuum morphologies nearly always aligned with the radio axis (McCarthy et al. 1987; Chambers et al. 1987). This phenomenon is generally attributed to radio jet induced star formation (DeYoung 1989), but the lack of high S/N spectra of the galaxy continua, and recent detections of polarized light in a few objects make it hard to rule out other processes such as scattering or synchrotron radiation. A detailed study of the continuum light in the distant RGs is difficult as they are optically very faint. However, nearby RGs (z approx. less than 0.1) have bluer B-V colors than radio-quiet ellipticals, presumably due to the presence of young stellar populations (Smith and Heckman 1989) and several have extended UV continuum emitting regions along their radio axes (van Bruegel et al. 1985a, b, di Serego Alighieri et al. 1989), reminiscent of the alignment effect seen in the high redshift RGs. We have almost completed a continuum imaging survey of nearby (and therefore optically brighter), powerful RGs to study any possible relationships between the optical continuum light and radio source activity. In particular we are interested in (1) whether these lower redshift RGs shown any evidence of the alignment effect (in their rest-frame UV light) that is seen in the distant RGs, and (2) the effects that the radio source has on the environment of the host galaxy.

Dey, Arjun↗
DOE OSTI2021

Mock light-cones and theory friendly catalogues for the CANDELS survey

Here we present mock catalogues created to support the interpretation of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). We extract haloes along past light-cones from the Bolshoi Planck dissipationless N-body simulations and populate these haloes with galaxies using two different independently developed semi-analytic models of galaxy formation and the empirical model UNIVERSEMACHINE. Our mock catalogues have geometries that encompass the footprints of observations associated with the five CANDELS fields. In order to allow field-to-field variance to be explored, we have created eight realizations of each field. In this paper, we present comparisons with observable global galaxy properties, including counts in observed frame bands, luminosity functions, colour–magnitude distributions and colour–colour distributions. We additionally present comparisons with physical galaxy parameters derived from SED fitting for the CANDELS observations, such as stellar masses and star formation rates. We find relatively good agreement between the model predictions and CANDELS observations for luminosity and stellar mass functions. We find poorer agreement for colours and star formation rate distributions. All of the mock light-cones as well as curated ‘theory friendly’ versions of the observational CANDELS catalogues are made available through a web-based data hub.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

A New Framework for Interstellar Medium Emission Line Models: Connecting Multiscale Simulations across Cosmological Volumes

The James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array have detected emission lines from the ionized interstellar medium (ISM) in some of the first galaxies at z ≳ 6. These measurements present an opportunity to better understand galaxy assembly histories and may allow important tests of state-of-the-art galaxy formation simulations. It is challenging, however, to model these lines in their proper cosmological context. In order to meet this challenge, we introduce a novel subgrid line emission modeling framework. The framework uses the high-z zoom-in simulation suite from the Feedback in Realistic Environments (FIRE) collaboration. The line emission signals from H II regions within each simulated FIRE galaxy are modeled using the semianalytic HIIL INES code. A machine learning approach is then used to determine the conditional probability distribution for the line luminosity to stellar-mass ratio from the H II regions around each simulated stellar particle. This conditional probability distribution can then be applied to predict the line luminosities around stellar particles in lower-resolution, yet larger volume cosmological simulations. As an example, we apply this approach to the IllustrisTNG simulations at z = 6. The resulting predictions for the [O II ], [O III ], and Balmer line luminosities as a function of star formation rate agree well with current observations. Our predictions differ, however, from related works in the literature, which lack detailed subgrid ISM models. This highlights the importance of our multiscale simulation modeling framework. Finally, we provide forecasts for future line luminosity function measurements from the JWST and quantify the cosmic variance in such surveys.

(ISM:) H II regions↗
NASA NTRS1982

Evolution of the cluster X-ray luminosity function slope

The results of an X-ray survey of 58 clusters of galaxies at moderate and high redshifts are reported. Using a luminosity-limited subsample of 25 objects, it is found that to a redshift of 0.5 the slope of the luminosity function of distant clusters is independent of redshift and consistent with that of nearby clusters. The time scale for change in the slope must be greater than 9 billion years. The implications of the data for theoretical models are discussed. In particular, Perrenod's models (1980) with high Omega are excluded by the present data.

Henry, J. P.↗
NASA NTRS1987

Narrowband imaging and spectroscopy close to the nucleus of the Seyfert galaxy NGC 7682

Keel's (1985) report of a jet-like optical feature emanating from the nucleus of NGC 7682 is investigated. Deep CCD images of NGC 7682 were taken with narrowband filters centered on the redshifted wavelength of H-alpha + forbidden N II and on a nearby continuum region. The continuum-subtracted line images show no evidence of the jet feature, although numerous H II regions appear clearly, both close to the nucleus and in the extended spiral arm structure. Spectra were taken at various dispersions and position angles, including the supposed position angle of the jet. These data were used to obtain background-subtracted spectra at the precise location of the jet. No excess emission was detected above the background-galaxy contribution. The highest-resolution spectra were used to determine the redshift of the galaxy to high precision.

Brodie, Jean↗
NASA NTRS1988

Fermi acceleration of Lyman-alpha photons by shocks

The repeated scattering of Ly-alpha radiation across a shock front results in a systematic blueshift which may greatly exceed the shock velocity vs and is proportional to cube root of (Nvs), where N is the column density of hydrogen atoms on either side of the shock front. The blueshifting process is similar to the Fermi acceleration of cosmic rays and may be responsible for the blue asymmetric line profiles that have been observed in high-redshift Ly-alpha galaxies. The Ly-alpha line profile in 3C 326.1 is accounted for by a model in which shocks, driven into a population of interstellar clouds by a radio lobe, trigger the formation of ionizing stars and Fermi accelerate the Ly-alpha radiation emitted by H II regions surrounding those stars. Galaxy mergers, particularly between galaxies with low dust content, should produce Ly-alpha lines with strong blue wings.

Neufeld, David A.↗
NASA NTRS2000

Considerations for a Next Generation GRB Observatory

A framework will be described for the planning of a Next Generation Burst Observatory. This Observatory, using Swift as a pathfinder mission, would study early star formation and early galaxy formation at very high redshifts through observations of thousands of GRBS, their afterglows and environments. It is suggested that the international GRB community should begin some initial studies for such an observatory.

Fishman, Gerald J.↗
NASA NTRS2000

Considerations for a Next Generation GRB Observatory

A framework will be described for the planning of a Next Generation Burst Observatory. This Observatory, using Swift as a pathfinder mission, would study early star formation and early galaxy formation at very high redshifts through observations of thousands of GRBs, their afterglows and environments. It is suggested that the international GRB community should begin some initial studies for such an observatory.

Fishman, Gerald J.↗
NASA NTRS2001

Observations of GRBs: Current Research and Planning for a Next Generation GRB Observatory

The basic observed properties of GRBs in the hard x-ray and gamma-ray region will be reviewed, primarily using analyses from BATSE data. Summaries of new BATSE observations that are presented in this symposium and other work in progress are given. Finally, a framework will be described-for the planning of a Next Generation Burst Observatory. This Observatory, using Swift as a pathfinder mission, would study early star formation and early galaxy formation at very high redshifts through observations of thousands of GRBs, their afterglows and environments. It is suggested that the international GRB community should begin some initial studies for such an observatory.

Fishman, Gerald J.↗
NASA NTRS2002

EXIST (Energetic X-ray Imaging Survey Telescope): The Next Large GRB Observatory

Studies have begun on the EXIST (Energetic X-ray Imaging Survey Telescope) Mission. It is planned as a very wide-field, sensitive coded aperture telescope with a sensitive area of the order of 6-8 m^2 and having a positional accuracy for GRBs (Gamma ray bursts) better than one arc-minute. EXIST will use SWIFT as a pathfinder mission; the findings of SWIFT will refine the scientific objectives of EXIST and will help to determine many of its design parameters. It would study early star formation and early galaxy formation at very high redshifts through observations of thousands of GRBs, their afterglows and environments. It is intended that the international GRB community will play as large role in EXIST through direct participation as well as with complementary observational programs, both space-based and ground-based. Some preliminary design features and capabilities of the EXIST Mission will be presented.

Fishman, G. J.↗
NASA NTRS2010

The Herschel-ATLAS: Extragalatic Number Counts from 250 to 500 Microns

Aims.The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 microns when completed, reaching flux limits (50-) from 32 to 145mJy. We here present galaxy number counts obtained for SPIRE observations of the first -14 sq. deg. observed at 250, 350 and 500 m. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100-200mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.

Clements, D. L.↗