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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The Rise and Fall of Star Formation Histories of Blue Galaxies at Redshifts 0.2 < z < 1.4

Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitor, each with their own unique star formation history (SFH). We use the approach recently developed by Pacifici et al. to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range O.2 < z < 1:4 from the All-Wavelength Extended Groth Strip International Survey (AEGIS). This consists in the Bayesian analysis of the observed galaxy spectral ' energy distributions with a comprehensive library of synthetic spectra assembled using state-of-the-art models of star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We constrain the SFH of each galaxy in our sample by comparing the observed fluxes in the B, R,l and K(sub s) bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFH on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs wIdely used to interpret observed galaxy spectral energy distributions is not appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

Pacifici, Camilla↗
NASA NTRS1984

Ultraviolet observations of starburst and mini-Seyfert galactic nuclei

The high excitation emission line galaxies NGC 1667, NGC 5135, and IC 5135 show activity which, while similar to that of Seyfert 2 galaxies, is 1-2 orders of magnitude smaller. The line and continuum emission is in all three cases more extended than would correspond to a point source. In addition to showing such Seyfert-like characteristics as broad, low contrast wings in the Lyman-alpha profiles and unusual strengths in the emission lines of such high ionization species as He II, NGC 5135 and IC 5135 show starburst characteristics in their UV spectra, with P Cygni profiles that furnish direct evidence of the presence of very massive and hot O stars in their nuclei. It is suggested that they may be galaxies undergoing the transition from the starburst stage to the mini-Seyfert stage.

Thuan, T. X.↗
NASA NTRS2002

Hubble Space Telescope Imaging of the Circumnuclear Environments of the CfA Seyfert Galaxies: Nuclear Spirals and Fueling

We present archival Hubble Space Telescope (HST) images of the nuclear regions of 43 of the 46 Seyfert galaxies found in the volume limited,spectroscopically complete CfA Redshift Survey sample. Using an improved method of image contrast enhancement, we created detailed high-quality " structure maps " that allow us to study the distributions of dust, star clusters, and emission-line gas in the circumnuclear regions (100-1000 pc scales) and in the associated host galaxy. Essentially all of these Seyfert galaxies have circumnuclear dust structures with morphologies ranging from grand-design two-armed spirals to chaotic dusty disks. In most Seyfert galaxies there is a clear physical connection between the nuclear dust spirals on hundreds of parsec scales and large-scale bars and spiral arms in the host galaxies proper. These connections are particularly striking in the interacting and barred galaxies. Such structures are predicted by numerical simulations of gas flows in barred and interacting galaxies and may be related to the fueling of active galactic nuclei by matter inflow from the host galaxy disks. We see no significant differences in the circumnuclear dust morphologies of Seyfert 1s and 2s, and very few Seyfert 2 nuclei are obscured by large-scale dust structures in the host galaxies. If Sevfert 2s are obscured Sevfert Is, then the obscuration must occur on smaller scales than those probed by HST.

Pogge, Richard W.↗
NASA NTRS2016

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

We obtain total galaxy X-ray luminosities, LX, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the +/-1σ scatter of the Mineo et al. LX-star formation rate (SFR) correlation or have higher LX than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. LX-stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme LX values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high LX values can be observed due to strong XRB variability.

X-rays: binaries↗
NASA NTRS1994

Ultraluminous starbursts in major mergers

We use numerical simulation to investigate the triggering of starbursts in merging disk galaxies. The properties of the merger-driven starbursts are sensitive to the structure of the progenitor galaxies; specifically, to the amount of material in a dense central bulge. Galaxies without bulges develop bars shortly after their first close passage, driving significant gas inflow and subsequent starbursts in the centers of the galaxies. These starbursts significantly deplete the star-forming gas, so that only relatively weak starbursts arise during the final merger. By contrast, models of galaxies with central bulges show that a bulge acts to stabilize the galaxies against inflow and starbursts until the galaxies actually merge. At this time, strong dissipation leads to the formation of a massive central gas mass and an ensuing star-formation rate two orders of magnitude greater than that in our isolated disk models. These starbursts are very short in duration, typically approximately 50 Myr, suggesting that the rarity of ultraluminous infrared galaxies is a result of their being in a very short evolutionary phase, rather than special and rare formation conditions. The fact that these mergers display many of the properties of ultraluminous infrared galaxies--tidal features, double nuclei, massive compact gas concentrations, and extreme levels of starburst activity--suggets that merger-driven starbursts can explain the emission from many ultraluminous infrared galaxies without an active nucleus.

Mihos, J. Christopher↗
DOE OSTI2024

Tracing the green valley with entropic thresholding

ABSTRACT The green valley represents the population of galaxies that are transitioning from the actively star-forming blue cloud to the passively evolving red sequence. Studying the properties of the green valley galaxies is crucial for our understanding of the exact mechanisms and processes that drive this transition. The green valley does not have a universally accepted definition. The boundaries of the green valley are often determined by empirical lines that are subjective and vary across studies. We present an unambiguous definition of the green valley in the colour–stellar mass plane using the entropic thresholding. We first divide the galaxy population into the blue cloud and the red sequence based on a colour threshold that minimizes the intraclass variance and maximizes the interclass variance. Our method splits the region between the mean colours of the blue cloud and the red sequence into three parts by maximizing the total entropy of that region. We repeat our analysis in a number of independent stellar mass bins to define the boundaries of the green valley in the colour–mass diagram. Our method provides a robust and natural definition of the green valley.

Pandey, Biswajit (ORCID:000000017876595X)↗
NASA NTRS1993

Everything you ever wanted to know about the ultraviolet spectra of star-forming galaxies but were afraid to ask

We present ultraviolet spectra of 143 star-forming galaxies of different morphological types and activity classes including S0, Sa, Sb, Sc, Sd, irregular, starburst, blue compact, blue compact dwarf, Liner, and Seyfert 2 galaxies. These IUE spectra cover the wavelength range from 1200 to 3200 A and are taken in a large aperture (10 x 20 inch). The ultraviolet spectral energy distributions are shown for a subset of the galaxies, ordered by spectral index, and separated by type for normal galaxies, Liners, starburst galaxies, blue compact (BCG) and blue compact dwarf (BCDG) galaxies, and Seyfert 2 galaxies. The ultraviolet spectra of Liners are, for the most part, indistinguishable from the spectra of normal galaxies. Starburst galaxies have a large range of ultraviolet slope, from blue to red. The star-forming galaxies which are the bluest in the optical (BCG and BCDG), also have the 'bluest' average ultraviolet slope of beta = -1.75 +/- 0.63. Seyfert 2 galaxies are the only galaxies in the sample that consistently have detectable UV emission lines.

Kinney, A. L.↗
NASA NTRS2020

The Next Generation X-Ray Galaxy Survey with eROSITA

eROSITA, launched on 13 July 2019, will be completing the first all-sky survey in the soft and medium X-ray band in nearly three decades. This 4-year survey, finishing in late 2023, will present a rich legacy for the entire astrophysics community and complement upcoming multi-wavelength surveys (with, e.g. the Large Synoptic Survey Telescope and the Dark Energy Survey). Besides the major scientific aim to study active galactic nuclei (AGN) and galaxy clusters, eROSITA will contribute significantly to X-ray studies of normal (i.e. not AGN) galaxies. Starting from multi-wavelength catalogues, we measure star formation rates and stellar masses for 60 212 galaxies constrained to distances of 50–200 Mpc. We chose this distance range to focus on the relatively unexplored volume outside the local Universe, where galaxies will be largely spatially unresolved and probe a range of X-ray luminosities that overlap with the low luminosity and/or highly obscured AGN population. We use the most recent X-ray scaling relations as well as the on-orbit eROSITA instrument performance to predict the X-ray emission from XRBs and diffuse hot gas and to perform both an analytic prediction and an end-to-end simulation using the mission simulation software, SIXTE. We consider potential contributions from hidden AGN and comment on the impact of normal galaxies on the measurement of the faint end of the AGN luminosity function. We predict that the eROSITA 4-year survey, will detect ≳15 000 galaxies (3σ significance) at 50–200 Mpc, which is ~ 100× more normal galaxies than detected in any X-ray survey to date.

Surveys↗
NASA NTRS1976

Accretion by galaxy clusters and the relationship between X-ray luminosity and velocity dispersion

A relationship between X-ray luminosity and cluster velocity dispersion is derived, which improves on the results of Solinger and Tucker (1972) in several important respects, and a simple model for primordial gas accretion by a cluster of galaxies is described. It is argued that the accreted gas may be causally related to the occurrence of a central active radio or giant cD or galaxy in X-ray clusters. Accretion and subsequent dissipation lead to a decrease with time in the amount of hot gas and in the X-ray luminosity as well as to an increase in mass of the dominant central galaxy.

Silk, J.↗
NASA NTRS2011

What Turns Galaxies Off? the Different Morphologies of Star-Forming and Quiescent Galaxies Since z Approximates 2 from CANDELS

We use HST/WFC3 imaging from the CANDELS multicyc1e treasury survey, in conjunction with the Sloan Digital Sky Survey, to explore the evolution of galactic structure for galaxies with stellar masses > 3 x 10(exp 10) Solar Mass from Z= 2.2 to the present epoch, a time span of 10 Gyr. We explore the relationship between rest-frame optical color, stellar mass, star formation activity and the structural parameters of galaxies as determined from parametric fits to the surface brightness profiles of galaxies. We confirm the dramatic evolution from z= 2.2 to the present day in the number density of non-star-forming galaxies above 3 x 10(exp 10) Solar Mass reported by other authors. We find that the vast majority of these quiescent systems have concentrated light profiles, as parameterized by the Sersic index, and the population of concentrated galaxies grows similarly rapidly. We examine the joint distribution of star formation activity, Sersic index, stellar mass, mass divided by radius (a proxy for velocity dispersion), and stellar surface density. Quiescence correlates poorly with stellar mass at all z < 2.2 (given the approx < 0.2 dex scatter between halo mass and stellar mass at z approximates 0 inferred by More et al, this argues against halo mass being the only factor determining quiescence). Quiescence correlates better with Sersic index, 'velocity dispersion' and stellar surface density, where Sersic index correlates the best (increasingly so at lower redshift). Yet, there is significant scatter between quiescence and galaxy structure: while the vast majority of quiescent galaxies have prominent bulges, many of them have significant disks, and a number of bulge-dominated galaxies have significant star formation. Noting the rarity of quiescent galaxies without prominent bulges, we argue that a prominent bulge (and, perhaps by association, a supermassive black hole) is a necessary but not sufficient condition for quenching star formation on galactic scales over the last 10 Gyr; such a result is qualitatively consistent with the expectations of the AGN feedback paradigm.

Bell, Eric F.↗
NASA NTRS1990

CO aperture synthesis of NGC 4038/39 (ARP 244)

High-resolution CO observations of the merging galaxies NGC 4038/39 (the 'Antennae') have been made with the Owens Valley Millimeter Wave Interferometer. Three concentrations of CO emission were detected. In addition to masses of a few x 100 million solar masses at each nucleus, approximately 1.2 x 10 to the 9th solar masses of molecular gas was discovered in a 32 arcsec x 22 arcsec region where the two galaxies overlap. Within this region are four distinct clumps. These coincide with H-alpha, 10 microns, and radio continuum peaks, suggesting that they are extremely active sites of star formation. The galaxy interaction appears to have concentrated gas at the nuclei of NGC 4038 and NGC 4039 and to have engendered enhanced star formation activity in the region where their disks overlap. From estimates of the SFR in this overlap region, it is suggested that the gas will be completely depleted in 240 million yr.

Stanford, S. A.↗
NASA NTRS1987

Star formation in the Magellanic irregular galaxy NGC 4449

New NIR and FIR maps and J = 1-0 CO spectroscopy of the Magellanic irregular galaxy NGC 4449 are presented. The brighter 150-micron emission is concentrated along the central visual ridge of the galaxy, although there is lower intensity extended emission throughout the visible extent of the object. The maximum FIR emission is coincident, within the uncertainties, with the visual and NIR maxima, identified as the galactic nucleus. It is estimated that the IR luminosity of the 1-kpc-diameter central region in NGC 4449 is comparable to that for a similar-sized region at the center of the Galaxy. A large fraction of the 150-micron emission may arise from warm dust distributed throughout the galaxy and heated by the diffuse radiation field. Active star formation follows the NIR emission in part of the galaxy, but no coincidence is found in another region.

Thronson, Harley A., Jr.↗
NASA NTRS1990

Detection of the 3.3-micron feature in two starburst galaxies

This paper reports the detection of the 3.3-micron emission feature in the center of two external galaxies: IC 694 (interacting with NGC 3690) and NGC 4194 (a merger). This feature has been previously detected in various galactic and extragalactic objects and is thought to be due to very small grains or large molecules that probably belong to the Polycyclic Aromatic Hydrocarbon (PAH) family. Its presence, as well as the IRAS colors, strongly suggest that these galaxies are dominated by starbursts rather than active nuclei. From publishing data and the present observations, the brightness of the feature in different galaxies is studied. A simple model of radiative transfer shows that the 3.3-micron feature brightness of a given galaxy allows the determination of the unreddened surface brightness of the galaxy stellar content. In galaxies with relatively large extinction, the 3.3-micron feature (and the other PAH related features) is therefore a useful spatial indicator of star-formation activity in their centers.

Dennefeld, M.↗
NASA NTRS1990

MS 0129.2 - 2237 - Interacting galaxies at z = 0.11

The X-ray source MS 0129.2 - 2237 is positionally coincident with an interacting system of galaxies. This paper presents the results of a spectroscopic and photometric investigation of the system, which show that a Seyfert 1.5, a Seyfert 2 nucleus or H II region, or a starburst galaxy, a normal galaxy plus possibly another galaxy where star-forming activity is taking place are strongly interacting. The redshift of the system is z = 0.11. The maximum projected diameter of the envelope common to the four spectroscopically distinct objects is about 98 kpc (H0 = 50 km/s M/pc and q0 = 0.5). The isolated environment in which the system lies suggests that these results present evidence of the final stage of the life of a compact group of galaxies where members are merging into an elliptical galaxy.

Maccagni, Dario↗
DOE OSTI2021

Contribution of Secondary Neutrinos from Line-of-sight Cosmic-Ray Interactions to the IceCube Diffuse Astrophysical Flux

In 10 years of observations, the IceCube neutrino observatory has revealed a neutrino sky in tension with previous expectations for neutrino point-source emissions. Astrophysical objects associated with hadronic processes might act as production sites for neutrinos, observed as point sources at Earth. Instead, a nearly isotropic flux of astrophysical neutrinos is observed up to PeV energies, prompting a reassessment of the assumed transport and production physics. This work applies a new physical explanation for neutrino production from populations of active galactic nuclei and starburst galaxies to three years of public IceCube point-source data. Specifically, cosmic rays produced at such sources might interact with extragalactic background light and gas along the line of sight, generating a secondary neutrino flux. Furthermore, this model is tested alongside a number of typical flux weighting schemes, in all cases the all-sky flux contribution being constrained to percent levels of the reported IceCube diffuse astrophysical flux.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

The connection between star formation and supermassive black hole activity in the local Universe

ABSTRACT We study the nuclear (AGN) activity in the local Universe (z < 0.33) and its correlation with the host galaxy properties, derived from a Sloan Digital Sky Survey sample with spectroscopic star-formation rate (SFR) and stellar mass determination. To quantify the level of AGN activity we used the XMM-Newton Serendipitous Source Catalogue. Applying multiwavelength selection criteria (optical BPT-diagrams, X-ray/optical ratio etc), we found that 24 per cent of the detected sources are efficiently-accreting AGN with moderate-to-high X-ray luminosity, twice as likely to be hosted by star-forming galaxies than by quiescent ones. The distribution of the specific Black Hole accretion rate (λsBHAR) shows that nuclear activity in local, non-AGN dominated galaxies peaks at very low accretion rates (−4 ≲ log λsBHAR ≲ −3) in all stellar mass ranges. We observe systematically larger values of λsBHAR for galaxies with active star formation than for quiescent ones, and an increase of the mean λsBHAR with SFR for both star-forming and quiescent galaxies. These finding confirm the decrease in AGN activity with cosmic time and are consistent with a scenario where both star-formation and AGN activity are fuelled by a common gas reservoir.

Torbaniuk, O. (ORCID:0000000344652564)↗
NASA NTRS2014

The Contribution of z < or Approx. 6 Sources to the Spatial Coherence in the Unresolved Cosmic Near-Infrared and X-Ray Backgrounds

A spatial clustering signal has been established in Spitzer/IRAC measurements of the unresolved cosmic near-infrared background (CIB) out to large angular scales, approx. 1deg. This CIB signal, while significantly exceeding the contribution from the remaining known galaxies, was further found to be coherent at a highly statistically significant level with the unresolved soft cosmic X-ray background (CXB). This measurement probes the unresolved CXB to very faint source levels using deep near-IR source subtraction.We study contributions from extragalactic populations at low to intermediate redshifts to the measured positive cross-power signal of the CIB fluctuations with the CXB. We model the X-ray emission from active galactic nuclei (AGNs), normal galaxies, and hot gas residing in virialized structures, calculating their CXB contribution including their spatial coherence with all infrared emitting counterparts. We use a halo model framework to calculate the auto and cross-power spectra of the unresolved fluctuations based on the latest constraints of the halo occupation distribution and the biasing of AGNs, galaxies, and diffuse emission. At small angular scales (1), the 4.5microns versus 0.5-2 keV coherence can be explained by shot noise from galaxies and AGNs. However, at large angular scales (approx.10), we find that the net contribution from the modeled populations is only able to account for approx. 3% of the measured CIB×CXB cross-power. The discrepancy suggests that the CIB×CXB signal originates from the same unknown source population producing the CIB clustering signal out to approx. 1deg.

unresolved cosmic near infrared background (CIB)↗
NASA NTRS2008

Tracing the Mass-Dependent Star Formation History of Late-Type Galaxies using X-ray Emission: Results from the CHANDRA Deep Fields

We report on the X-ray evolution over the last approx.9 Gyr of cosmic history (i.e., since z = 1.4) of late-type galaxy populations in the Chandra Deep Field-North and Extended Chandra Deep Field-South (CDF-N and E-CDF-S. respectively; jointly CDFs) survey fields. Our late-type galaxy sample consists of 2568 galaxies. which were identified using rest-frame optical colors and HST morphologies. We utilized X-ray stacking analyses to investigate the X-ray emission from these galaxies, emphasizing the contributions from normal galaxies that are not dominated by active galactic nuclei (AGNs). Over this redshift range, we find significant increases (factors of approx. 5-10) in the X-ray-to-optical mean luminosity ratio (L(sub x)/L(sub B)) and the X-ray-to-stellar-mass mean ratio (L(sub x)/M(sub *)) for galaxy populations selected by L(sub B) and M(sub *), respectively. When analyzing galaxy samples selected via SFR, we find that the mean X-ray-to-SFR ratio (L(sub x)/SFR) is consistent with being constant over the entire redshift range for galaxies with SFR = 1-100 Solar Mass/yr, thus demonstrating that X-ray emission can be used as a robust indicator of star-formation activity out to z approx. 1.4. We find that the star-formation activity (as traced by X-ray luminosity) per unit stellar mass in a given redshift bin increases with decreasing stellar mass over the redshift range z = 0.2-1, which is consistent with previous studies of how star-formation activity depends on stellar mass. Finally, we extend our X-ray analyses to Lyman break galaxies at z approx. 3 and estimate that L(sub x)/L(sub B) at z approx. 3 is similar to its value at z = 1.4.

Lehmer, B.D↗