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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Central star formation in double-peak, gas-rich radio galaxies

The respective contributions of gas accretion, galaxy interactions, and mergers to the mass assembly of galaxies, as well as the evolution of their molecular gas and star-formation activity are still not fully understood. In a recent work, a large sample of double-peak (DP) emission-line galaxies have been identified from the SDSS. While the two peaks could represent two kinematic components, they may be linked to the large bulges that their host galaxies tend to have. Star-forming DP galaxies display a central star-formation enhancement and have been discussed as compatible with a sequence of recent minor mergers. In order to probe merger-induced star-formation mechanisms, we conducted observations of the molecular-gas content of 35 star-forming DP galaxies in the upper part of the main sequence (MS) of star formation (SF) with the IRAM 30 m telescope. Including similar galaxies 0.3 dex above the MS and with existing molecular-gas observations from the literature, we finally obtained a sample of 52 such galaxies. We succeeded in fitting the same kinematic parameters to the optical ionised- and molecular-gas emission lines for ten (19%) galaxies. We find a central star-formation enhancement resulting most likely from a galaxy merger or galaxy interaction, which is indicated by an excess of gas extinction found in the centre. This SF is traced by radio continuum emissions at 150 MHz, 1.4 GHz, and 3 GHz, all three of which are linearly correlated in log with the CO luminosity with the same slope. The 52 DP galaxies are found to have a significantly larger amount of molecular gas and longer depletion times, and hence a lower star-formation efficiency, than the expected values at their distance of the MS. The large bulges in these galaxies might be stabilising the gas, hence reducing the SF efficiency. This is consistent with a scenario of minor mergers increasing the mass of bulges and driving gas to the centre. We also excluded the inwards-directed gas migration and central star-formation enhancement as the origin of a bar morphology. Hence, these 52 DP galaxies could be the result of recent minor mergers that funnelled molecular gas towards their centre, triggering SF, but with moderate efficiency.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Gamma ray bursts from extragalactic sources

The properties of gamma ray bursts of classical type are found to be explicable in terms of high speed collisions between stars. A model is proposed in which the frequency of such collisions can be calculated. The model is then applied to the nuclei of galaxies in general on the basis that galaxies, or at least some fraction of them, originate in the expulsion of stars from creation centers. Evidence that low level activity of this kind is also taking place at the center of our own Galaxy is discussed. The implications for galactic evolution are discussed and a negative view of black holes is taken.

Hoyle, Fred↗
NASA NTRS2013

Reflection-dominated Nuclear X-Ray Emission in the Early-Type Galaxy ESO 565 G019

We present the discovery of a reflection-dominated active galactic nucleus (AGN) in the early-type radio-quietgalaxy ESO 565G019 with Suzaku and SwiftBurst Alert Telescope. The source X-ray spectrum below 10 keVis characteristic of other Compton-thick (CT) AGNs, clearly showing an inverted continuum and prodigiousfluorescence iron emission above 3 keV. A Compton shoulder to the neutral Fe K line also appears to be present.There is evidence for long-term hard X-ray flux variability that we associate with changes in the intrinsic AGNpower law. More of such reflection-dominated AGNs should be uncovered in the near future with the increasedsensitivity of ongoing and new hard X-ray surveys. ESO 565G019 is hosted in an early-type galaxy whosemorphology has been variously classified as either type E or type S0. Only about 20 bona fide CT-AGNs have been identified in the local universe so far, and all exist in host galaxies with late Hubble types (S0 or later). CT columns of nuclear obscuring gas are uncommon in early-type galaxies in the local universe, so confirmation of the exact morphological class of ESO 565G019 is important. Infrared photometry also shows the presence of largequantities of cool dust in the host, indicative of significant ongoing star formation. ESO 565G019 may be the firstidentified local example of minor-merger-driven CT-AGN growth in an early-type host, or may be the result ofinteraction with its neighboring galaxy ESO 565G018 in a wide pair.

comparison↗
DOE OSTI2021

The Physics of the Coronal-line Region for Galaxies in Mapping Galaxies at Apache Point Observatory

The fundamental nature and extent of the coronal-line region (CLR), which may serve as a vital tracer for active galactic nucleus (AGN) activity, remain unresolved. Previous studies suggest that the CLR is produced by AGNdriven outflows and occupies a distinct region between the broad-line region and the narrow-line region, which places it tens to hundreds of parsecs from the galactic center. Here, we investigate 10 coronal line (CL; ionization potential ≳100 eV) emitting galaxies from the Sloan Digital Sky Survey IV Mapping Galaxies at Apache Point Observatory (MaNGA) catalog with emission from one or more CLs detected at ≥5$σ$ above the continuum in at least 10 spaxels—the largest such MaNGA catalog. We find that the CLR is far more extended, reaching out to 1.3–23 kpc from the galactic center. We crossmatch our sample of 10 CL galaxies with the largest existing MaNGA AGN catalog and identify seven in it; two of the remaining three are galaxy mergers and the final one is an AGN candidate. Further, we measure the average CLR electron temperatures as ranging between 12,331 and 22,530 K, slightly above the typical threshold for pure AGN photoionization (~20,000 K) and indicative of shocks (e.g., merger induced or from supernova remnants) in the CLR. In conclusion, we reason that ionizing photons emitted by the central continuum source (i.e., AGN photoionization) primarily generate the CLs, and that energetic shocks are an additional ionization mechanism that likely produce the most extended CLRs we measure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

H i -rich but low star formation galaxies in MaNGA: physical properties and comparison to control samples

ABSTRACT Gas-rich galaxies are typically star forming. We make use of H i-MaNGA, a programme of H i follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey of the Sloan Digital Sky Surveys, to construct a sample of unusual neutral hydrogen (H i, 21 cm)-rich galaxies that have low star formation rates (SFRs), using infrared colour from the Wide-field Infrared Survey Explorer as a proxy for specific SFR. Out of a set of 1575 MaNGA galaxies with H i-MaNGA detections, we find that 83 (5 per cent) meet our selection criteria to be H i rich with low SFR. We construct two stellar mass-matched control samples: H i-rich galaxies with typical SFR (high SF control) and H i-poor galaxies with low SFR (low H i control). We investigate the properties of each of these samples, comparing physical parameters such as ionization state maps, stellar and ionized gas velocity and dispersion, environment measures, metallicity, and morphology to search for the reasons why these unusual H i-rich galaxies are not forming stars. We find evidence for recent external accretion of gas in some galaxies (via high counter-rotating fractions), along with some evidence for active galactic nucleus (AGN) feedback (from a high central low-ionization emission-line region and/or red geyser fraction), and bar quenching (via an enhanced strong bar fraction). Some galaxies in the sample are consistent with simply having their H i in a high angular momentum, large-radius, low-density disc. We conclude that no single physical process can explain all H i-rich, low-SFR galaxies.

Astronomy & Astrophysics↗
NASA NTRS2014

First Hard X-Ray Detection of the Non-Thermal Emission Around the Arches Cluster: Morphology and Spectral Studies With NuSTAR

The Arches cluster is a young, densely packed massive star cluster in our Galaxy that shows a high level of star formation activity. The nature of the extended non-thermal X-ray emission around the cluster remains unclear. The observed bright Fe K(alpha) line emission at 6.4 keV from material that is neutral or in a low ionization state can be produced either by X-ray photoionization or by cosmic-ray particle bombardment or both. In this paper, we report on the first detection of the extended emission around the Arches cluster above 10 keV with the NuSTAR mission, and present results on its morphology and spectrum. The spatial distribution of the hard X-ray emission is found to be consistent with the broad region around the cluster where the 6.4 keV line is observed. The interpretation of the hard X-ray emission within the context of the X-ray reflection model puts a strong constraint on the luminosity of the possible illuminating hard X-ray source. The properties of the observed emission are also in broad agreement with the low-energy cosmic-ray proton excitation scenario. Key words: cosmic rays - Galaxy: center - ISM: general - X-rays: individual (Arches cluster)

Arches cluster↗
NASA NTRS1988

Far-infrared emission in single and binary galaxies

The properties of the far-IR emission from a sample of optically selected isolated galaxies is studied using data obtained by the Infrared Astronomical Satellite (IRAS). This set of galaxies is used as a standard of comparison representing galaxies whose far-IR properties have been little influenced by interaction with their surroundings. An optically selected sample of isolated binary galaxies is then considered. For the binary galaxies, no extreme highly luminous IR emitters are found, reaffirming the rarity of these objects. However, the occurrence of some low-level enhancement of infrared activity is substantiated by the comparison of far-IR emission in single galaxies and those found to have nearby companions. This effect may be influenced by the occurrence of a few instances of more luminous galaxies. Indeed, many galaxies that show evidence for interaction, i.e., distortion, tails, etc., do not show enhanced IR emission.

Haynes, Martha P.↗
NASA NTRS2017

NuSTAR Observations of WISE J1036+0449, A Galaxy at Z Approx. 1 Obscured by Hot Dust

Hot dust-obscured galaxies (hot DOGs), selected from Wide-Field Infrared Survey Explorer's all-sky infrared survey, host some of the most powerful active galactic nuclei known and may represent an important stage in the evolution of galaxies. Most known hot DOGs are located at z > 1.5, due in part to a strong bias against identifying them at lower redshift related to the selection criteria. We present a new selection method that identifies 153 hot DOG candidates at z approx. 1, where they are significantly brighter and easier to study. We validate this approach by measuring a redshift z = 1.009 and finding a spectral energy distribution similar to that of higher-redshift hot DOGs for one of these objects, WISE J1036+0449 (L(BOL) approx. = 8 x 10(exp 46) erg/s). We find evidence of a broadened component in Mg II, which would imply a black hole mass of M(BH) approx. = 2 x 10(exp 8) Stellar Mass and an Eddington ratio of lambda(Edd) approx. = 2.7. WISE J1036+0449 is the first hot DOG detected by the Nuclear Spectroscopic Telescope Array, and observations show that the source is heavily obscured, with a column density of N(H) approx. = (2-15) x 10(exp 23)/sq cm. The source has an intrinsic 2-10 keV luminosity of approx. 6 x 10(exp 44) erg/s, a value significantly lower than that expected from the mid-infrared X-ray correlation. We also find that other hot DOGs observed by X-ray facilities show a similar deficiency of X-ray flux. We discuss the origin of the X-ray weakness and the absorption properties of hot DOGs. Hot DOGs at z < or approx. 1 could be excellent laboratories to probe the characteristics of the accretion flow and of the X-ray emitting plasma at extreme values of the Eddington ratio.

galaxies↗
DOE OSTI2024

A VLBA-uGMRT search for candidate binary black holes: study of six X-shaped radio galaxies with double-peaked emission lines

ABSTRACT Identifying methods to discover dual active galactic nucleus (AGN) has proven to be challenging. Several indirect tracers have been explored in the literature, including X/S-shaped radio morphologies and double-peaked (DP) emission lines in the optical spectra. However, the detection rates of confirmed dual AGN candidates from the individual methods remain extremely small. We search for binary black holes (BBH) in a sample of six sources that exhibit both X-shaped radio morphology and DP emission lines using the Very Long Baseline Array (VLBA). Three out of the six sources show dual VLBA compact components, making them strong candidates for BBH sources. In addition, we present deep uGMRT images revealing the exquisite details of the X-shaped wings in three sources. We present a detailed precession modeling analysis of these sources. The black hole separations estimated from the simplistic geodetic precession model are incompatible with those estimated from emission line offsets and the VLBA separations. However, precession induced by a non-coplanar secondary black hole is a feasible mechanism for explaining the observed X-shaped radio morphologies and the black hole separations estimated from other methods. The black hole separations estimated from the double-peaked emission lines agree well with the VLBA compact component separations. Future multifrequency VLBA observations will be critical in ruling out or confirming the BBH scenario in the three galaxies with dual component detections.

Sebastian, Biny (ORCID:0000000184286525)↗
NASA NTRS2003

Chandra Observations of Point Sources in A2255

In our search for "hidden" active galactic nuclei (AGNs), we present results from a Chandra observation of the nearby cluster A2255. Eight cluster galaxies are associated with pointlike X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with AGNs with no optical signatures of nuclear activity, with a further two being potential AGNs. Of the potential AGNs, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray-detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies, five are associated with luminous (massive) galaxies, and the remaining three lie in much lower luminosity systems. We note that the use of X-ray-to-optical flux ratios for classification of X-ray sources is often misleading and strengthens the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.

Davis, David S.↗
NASA NTRS1987

The effects of interactions on spiral galaxies. II - Disk star-formation rates

H-alpha emission-line and IRAS far-IR observations of interacting spiral and irregular galaxies are here used to assess the influence of interactions on their global star-formation rates. Two samples of interacting galaxies were observed: a complete sample of close pairs, and an Arp atlas sample of peculiar systems. When compared to a control sample of single galaxies, both samples of interacting systems exhibit systematically higher levels of H-alpha and infrared emission on average, and a larger dispersion in emission properties. Emission levels in the very active system are much more strongly correlated with the properties of the interaction than with the internal properties of the galaxies themselves. Strong disk emission is almost always accompanied by unusually strong nuclear activity. Simple star-formation burst models can reproduce the observed H-alpha equivalent widths and broadband colors of most of the galaxies. The bursts are relatively short (few times 10 million yr) and rarely involve more than 1-2 percent of a galaxy's total mass.

Kennicutt, Robert C., Jr.↗
NASA NTRS1993

Deep, wide-field, multi-band imaging of z approximately equal to 0.4 clusters and their environs

The existence of an excess population of blue galaxies in the cores of distant, rich clusters of galaxies, commonly referred to as the 'Butcher-Oemler' effect is now well established. Spectroscopy of clusters at z = 0.2-0.4 has confirmed that the luminous blue populations comprise as much as 20 percent of these clusters. This fraction is much higher that the 2 percent blue fraction found for nearby rich clusters, such as Coma, indicating that rapid galaxy evolution has occurred on a relatively short time scale. Spectroscopy has also shown that the 'blue' galaxies can basically be divided into three classes: 'starburst' galaxies with large (O II) equivalent widths, 'post-starburst' E+A galaxies (i.e. galaxies with strong Balmer lines shortward of 4000A but elliptical-like colors, and normal spiral/irregulars. Unfortunately, it is difficult to obtain enough spectra of individual galaxies in these intermediate redshift clusters to say anything statistically meaningful. Thus, limited information is available about the relative numbers of these three classes of 'blue' galaxies and the associated E/SO population in these intermediate redshift clusters. More statistically meaningful results can be derived from deep imaging of these clusters. However, the best published data to date (e.g. MacLaren et al. 1988; Dressler & Gunn 1992) are limited to the cluster cores and do not sample the galaxy luminosity functions very deeply at the bluest wavelengths. Furthermore, only limited spectro-energy distribution data is available below 4000A in the observed cluster rest frame providing limited sensitivity to 'recent' star formation activity. To improve this situation, we are currently obtaining deep, wide-field UBRI images of all known rich clusters at z approx. equals 0.4. Our main objective is to obtain the necessary color information to distinguish between the E+SO, 'E+A', and spiral/irregular galaxy populations throughout the cluster/supercluster complex. At this redshift, UBRI correspond to rest-frame 2500A/UVR bandpasses. The rest-frame UVR system provides a powerful 'blue' galaxy discriminate given the expected color distribution. Moreover, since 'hot' stars peak near 2500A, that bandpass is a powerful probe of recent star formation activity in all classes of galaxies. In particular, it is sensitive to ellipticals with 'UV excess' populations (MacLaren et al. 1988).

Silva, David R.↗
DOE OSTI2023

The Demographics, Stellar Populations, and Star Formation Histories of Fast Radio Burst Host Galaxies: Implications for the Progenitors

We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈10 9.9 M ⊙ , mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M ⊙ yr -1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Nuclear star formation on 100 parsec scales: 10" resolution radio continuum, HI and CO observations

A program of radio line and continuum studies of star formation in nearby spiral galaxies is reported. The objective is a search for hot gas and peculiar dynamics in spiral nuclei with 10" to 30" angular resolution. Vigorous star formation is found to be a common phenomenon in the inner kpc of spirals. Arcsecond resolution observations of radio continuum emission at 6 and 2 cm were used to separate the thermal and nonthermal radio components. It was found that thermal and nonthermal emission are well mixed even on sizescales of 10 pc. To understand the reason for the increased level of star formation activity in spiral nuclei, HI and CO emission in these galaxies is studied. The CO transition was detected in M51, M82, NGC 253, NGC 6946 and IC 342 with T sub a approx. 0.5 to 2.0 K, at 20" angular resolution. The dynamics and spatial distribution of nuclear gas are being studied using VLA HI maps with 30" synthesized beams. Evidence for noncircular motions in HI was found in the nucleus of IC 342.

Turner, Jean L.↗
DOE OSTI2023

Decoding NGC 7252 as a blue elliptical galaxy

Elliptical galaxies with blue optical colours and significant star formation are hypothesised to be major merger remnants of gas-rich spiral galaxies or normal elliptical galaxies with a sudden burst of star formation. We present here a scenario in which blue elliptical galaxies identified in shallow imaging surveys may fail to recover faint features that are indicative of past merger activity using a nearby major merger remnant. Based on deep optical imaging data of the post-merger galaxy, NGC 7252, we demonstrate that the galaxy can appear as an elliptical galaxy if it is observed at higher redshifts. The main body and the low surface brightness merger features found at the outskirts of the galaxy are blue in the optical g – r colour map. We argue that the higher-redshift blue elliptical galaxies discovered in surveys as shallow as the SDSS or DECaLS may be advanced mergers whose defining tidal features fall below the detection limits of the surveys. This should be taken into consideration during the morphological classification of these systems in future and ongoing surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

$\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$: Studying Quenching in Intermediate- z Galaxies—Gas, $\scriptsize\mathrm{{Angu\overrightarrow{L}ar}}$ Momentum, and Evolution

We describe the Studying Quenching in Intermediate-z Galaxies: Gas, $\scriptsize\mathrm{\rm{angu}}\overrightarrow{L}{\rm{ar}}$ momentum, and Evolution ($\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$) survey of intermediate-redshift post-starburst galaxies. We leverage the large sky coverage of the Sloan Digital Sky Survey to select ~1300 recently quenched galaxies at 0.5 < z ≤ 0.9 based on their unique spectral shapes. These bright, intermediate-redshift galaxies are ideal laboratories to study the physics responsible for the rapid quenching of star formation: they are distant enough to be useful analogs for high-redshift quenching galaxies, but low enough redshift that multiwavelength follow-up observations are feasible with modest telescope investments. We use the Prospector code to infer the stellar population properties and nonparametric star formation histories (SFHs) of all galaxies in the sample. We find that $\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$ galaxies are both very massive (M * ~ 10 11.25 M ⊙ ) and quenched, with inferred star formation rates ≲1 M ⊙ yr -1 , more than an order of magnitude below the star-forming main sequence. The best-fit SFHs confirm that these galaxies recently quenched a major burst of star formation: >75% of $\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$ galaxies formed at least a quarter of their total stellar mass in the recent burst, which ended just ~200 Myr before observation. We find that $\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$ galaxies are on average younger and more burst-dominated than most other z ≲ 1 post-starburst galaxy samples. This large sample of bright post-starburst galaxies at intermediate redshift opens a wide range of studies into the quenching process. In particular, the full $\scriptsize\mathrm{{SQuIGG\overrightarrow{L}E}}$ survey will investigate the molecular gas reservoirs, morphologies, kinematics, resolved stellar populations, active galactic nucleus incidence, and infrared properties of this unique sample of galaxies in order to place definitive constraints on the quenching process.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Evidence for Black Holes in Green Peas from WISE Colors and Variability

We explore the presence of active galactic nuclei (AGNs)/black holes in Green Pea galaxies (GPs), motivated by the presence of high-ionization emission lines such as He ii and [Ne iii] in their optical spectra. In order to identify AGN candidates, we used mid-infrared (MIR) photometric observations from the all-sky Wide-field Infrared Survey Explorer (WISE) mission for a sample of 1004 GPs. Considering only >5σ detections with no contamination from neighboring sources in AllWISE, we select 31 GPs out of 134 as candidate AGNs based on a stringent three-band WISE color diagnostic. Using multi-epoch photometry in W1 and W2 bands based on time-resolved unWISE coadd images, we find two sources exhibiting variability in both the WISE bands among 112 GPs with W1 ≤16 mag and no contamination from neighboring sources in unWISE. These two variable sources were selected as AGNs by the WISE three-band color diagnostic as well. Compared to variable AGN fractions observed among low-mass galaxy samples in previous studies, we find a higher fraction (~1.8%) of MIR variable sources among GPs, which demonstrates the uniqueness and importance of studying these extreme objects. Through this work, we demonstrate that MIR diagnostics are promising tools to select AGNs that may be missed by other selection techniques (including optical emission-line ratios and X-ray emission) in star formation-dominated, low-mass, low-metallicity galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

The space telescope scientific instruments

The paper describes the space telescope with a 2.4 m aperture to be launched at 500 km altitude in late 1983. Four axial-bay and one radial-bay scientific instrument, a wide-field and planetary camera, a faint-object camera, a faint-object spectrograph, and a high-speed photometer are to be installed to conduct the initial observations. The axial instruments are constrained to envelopes with dimensions 0.9 x 0.9 x 2.2 m and their masses cannot exceed 317 kg. The observatory will also be equipped with fine-guidance sensors and a microprocessor. The design concepts of the instruments are outlined and some of the astronomical capabilities including studies of distant and local galaxies, physical properties of quasars, interrelations between quasars and active galactic nuclei are mentioned.

Leckrone, D. S.↗