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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Smooth H i Low Column Density Outskirts in Nearby Galaxies

The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) represents the interface between galaxies and the intergalactic medium, i.e., where galaxies are believed to get their supply of gas to fuel future episodes of star formation. Photoionization models predict a break in the radial profiles of H i at a column density of ∼5 × 10{sup 19} cm{sup −2} due to the lack of self-shielding against extragalactic ionizing photons. To investigate the prevalence of such breaks in galactic disks and to characterize what determines the potential edge of the H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i emission that would otherwise be undetected using conventional moment map analysis, we line up individual profiles to the same reference velocity and average them azimuthally to derive stacked radial profiles. To do so, we use model velocity fields created from a simple extrapolation of the rotation curves to align the profiles in velocity at radii beyond the extent probed with the sensitivity of traditional integrated H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Optical Detection of Star Formation in a Cold Dust Cloud in the Counterjet Direction of Centaurus A

We have identified a set of optical emission-line features 700″ (12 kpc) to the southwest of the nucleus of Centaurus A, roughly opposite to the radio jet and well-known optical emission filaments associated with the northern radio structure. This location is roughly along the axis of the southwestern radio lobes, although there is no coherent jet at this radius. We use integral-field optical spectroscopy to trace the ratios of strong emission lines, showing changes in excitation across the region, and significant local reddening. The emission regions are spatially associated with far-infrared emission peaks in one of two cold dust clouds identified using Herschel and Spitzer data, and there may be a mismatch between the low temperature of the dust and the expected heating effect of young stars. The strong emission lines have ratios consistent with photoionization in normal H ii regions, requiring only modest numbers of OB stars; these stars and their cooler accompanying populations must be largely obscured along our line of sight. These data fit with a picture of fairly ordinary formation of clusters in a large giant molecular cloud, or network of such clouds. The location, projected near the radio-source axis and within the radius where a starburst wind has been inferred on the other side of the galaxy, raises the question of whether this star-forming episode was enhanced or indeed triggered by an outflow from the central parts of Centaurus A. However, the level of star formation is normal for the associated cold-gas mass and column density, and optical emission-line ratios and line widths limit the role of shocks on the gas, so any interaction with an outflow, associated either with the radio source or star formation in the gas-rich disk of Centaurus A, can at most have compressed the gas weakly. We speculate that the presence of similar star-forming regions on both sides of the galaxy, contrasted with the difference in the character of the emission-line clouds, reflects the presence of a collimated radio jet to the northeast and perhaps anisotropic escape of ionizing radiation from the AGN as well. In this view, the star formation on the southwestern side of Cen A could be enhanced indirectly via compression by a broad outflow (whether originated by a starburst or AGN), distinct from the radio jet and lobes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Coronal Line Spectrum of the Iron Nova V3666 Ophiuchi

Optical and infrared spectroscopy are presented for the classical nova V3666 Ophiuchi (Nova Ophiuchi 2018 No.3) from 11 months after its outburst. At that epoch, V3666 Oph displayed an [Fe x] λ0.6375 emission line stronger than Hα and nearly a factor of 3 larger, relative to Hα, than in any nova observed previously. The [Fe x] feature, with an equivalent width exceeding 1300 Å, was enormously strong relative to the continuum emission as well. V3666 Oph also reached a state of high excitation for an Fe ii type nova, displaying coronal lines of [Fe xi], [S ix], and [Ar x], and permitted features that can be identified with the C vi (8–7), (9–8), and (10–9) transitions. In addition to [Fe x] and [Fe xi], V3666 Oph also displayed bright lines of [Fe vii], indicating that the prominent iron features were not confined to a single or narrow range of ionization states. Modeling the emission line spectrum of V3666 Oph with the photoionization code Cloudy indicated that the bulk of the emission line gas was matter-bounded, severely reducing the amount of low ionization gas and resulting in coronal lines that were very strong in comparison to lines such as H i and He i, and the familiar low excitation forbidden lines of nitrogen and oxygen. Such matter-bounded regions are observationally rare in novae since they are both faint and short-lived, offering a plausible explanation for why [Fe x] λ0.6375 had not be seen at this strength previously.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

A Lyα Transit Left Undetected: the Environment and Atmospheric Behavior of K2-25b

K2-25b is a Neptune-sized exoplanet (3.45R {sub ⊕}) that orbits its M4.5 host with a period of 3.48 days. Due to its membership in the Hyades Cluster, the system has a known age (727 ± 75 Myr). K2-25b’s youth and its similarities with Gl 436b suggested that K2-25b could be undergoing strong atmospheric escape. We observed two transits of K2-25b at Lyα using HST/STIS in order to search for escaping neutral hydrogen. We were unable to detect an exospheric signature, but placed an upper limit of (R {sub p}/R {sub ⋆})∣{sub Ly α} < 0.56 at 95% confidence by fitting the light curve of the Lyα red wing, or < 1.20 in the blue wing. We reconstructed the intrinsic Lyα profile of K2-25 to determine its Lyα flux, and analyzed XMM-Newton observations to determined its X-ray flux. Based on the total X-ray and extreme ultraviolet irradiation of the planet (8763 ± 1049 erg s{sup −1} cm{sup −2}), we estimated the maximum energy-limited mass-loss rate of K2-25b to be 10.6{sub −6.13}{sup +15.2}×10{sup 10} g s{sup −1} (0.56M {sub ⊕} per 1 Gyr), five times larger than the similarly estimated mass-loss rate of Gl 436b (2.2 × 10{sup 10} g s{sup −1}). The photoionization time is about 3 hr, significantly shorter than Gl 436b’s 14 hr. A nondetection of a Lyα transit could suggest K2-25b is not significantly losing its atmosphere, or factors of the system are resulting in the mass loss being unobservable (e.g., atmosphere composition or the system’s large high-energy flux). Further observations could provide more stringent constraints.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

On the formation of molecular clumps in QSO outflows

We study the origin of the cold molecular clumps in quasar outflows, recently detected in CO and HCN emission. We first describe the physical properties of such radiation-driven outflows and show that a transition from a momentum- to an energy-driven flow must occur at a radial distance of R≈0.25 kpc. During this transition, the shell of swept-up material fragments due to Rayleigh–Taylor instabilities, but these clumps contain little mass and are likely to be rapidly ablated by the hot gas in which they are immersed. We then explore an alternative scenario in which clumps form from thermal instabilities at R≳1 kpc, possibly containing enough dust to catalyze molecule formation. We investigate this process with 3D two-fluid (gas+dust) numerical simulations of a kpc{sup 3} patch of the outflow, including atomic and dust cooling, thermal conduction, dust sputtering, and photoionization from the QSO radiation field. In all cases, dust grains are rapidly destroyed in ≈10{sup 4} years; and while some cold clumps form at later times, they are present only as transient features, which disappear as cooling becomes more widespread. In fact, we only find a stable two-phase medium with dense clumps if we artificially enhance the QSO radiation field by a factor of 100. This result, together with the complete destruction of dust grains, renders the interpretation of molecular outflows a very challenging problem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

BOOSTING LY α AND He ii λ 1640 LINE FLUXES FROM POPULATION III GALAXIES: STOCHASTIC IMF SAMPLING AND DEPARTURES FROM CASE-B

We revisit calculations of nebular hydrogen Ly α and He ii λ 1640 line strengths for Population III (Pop III) galaxies, undergoing continuous, and bursts of, star formation. We focus on initial mass functions (IMFs) motivated by recent theoretical studies, which generally span a lower range of stellar masses than earlier works. We also account for case-B departures and the stochastic sampling of the IMF. In agreement with previous work, we find that departures from case-B can enhance the Ly α flux by a factor of a few, but we argue that this enhancement is driven mainly by collisional excitation and ionization, and not due to photoionization from the n = 2 state of atomic hydrogen. The increased sensitivity of the Ly α flux to the high-energy end of the galaxy spectrum makes it more subject to stochastic sampling of the IMF. The latter introduces a dispersion in the predicted nebular line fluxes around the deterministic value by as much as a factor of ∼4. In contrast, the stochastic sampling of the IMF has less impact on the emerging Lyman Werner photon flux. When case-B departures and stochasticity effects are combined, nebular line emission from Pop III galaxies can be up to one order of magnitude brighter than predicted by “standard” calculations that do not include these effects. This enhances the prospects for detection with future facilities such as the James Webb Space Telescope and large, ground-based telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

NEAR-INFRARED SPECTROSCOPY OF NEARBY SEYFERT GALAXIES: IS THERE EVIDENCE FOR SHOCK EXCITATION IN NARROW-LINE REGIONS?

One of the important unsettled problems regarding active galactic nuclei (AGNs) is the major ionization mechanism of gas clouds in AGN narrow-line regions (NLRs). In order to investigate this issue, we present our J -band spectroscopic observations of a sample of 26 nearby Seyfert galaxies. In our study, we use the flux ratio of the following two forbidden emission lines, [Fe ii]1.257 μ m and [P ii]1.188 μ m, because it is known that this ratio is sensitive to the ionization mechanism. We obtain the [Fe ii]/[P ii] flux ratio or its lower limit for 19 objects. In addition to our data, we compile this flux ratio (or its lower limit) for 23 nearby Seyfert galaxies from the literature. Based on the collected data, we find that three Seyfert galaxies show very large lower limits of the [Fe ii]/[P ii] flux ratios (≳10): NGC 2782, NGC 5005, and Mrk 463. It is thus suggested that the contribution of the fast shock in the gas excitation is significantly large for them. However, more than half of the Seyfert galaxies in our sample show moderate [Fe ii]/[P ii] flux ratios (∼2), which is consistent with pure photoionization by power-law ionizing continuum emission. We also find that the [Fe ii]/[P ii] flux ratio shows no clear correlation with the radio loudness, suggesting that the radio jet is not the primary origin of shocks in NLRs of Seyfert galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

AN ANALYTIC MODEL OF DUSTY, STRATIFIED, SPHERICAL H ii REGIONS

We study analytically the effect of radiation pressure (associated with photoionization processes and with dust absorption) on spherical, hydrostatic H ii regions. We consider two basic equations, one for the hydrostatic balance between the radiation-pressure components and the gas pressure, and another for the balance among the recombination rate, the dust absorption, and the ionizing photon rate. Based on appropriate mathematical approximations, we find a simple analytic solution for the density stratification of the nebula, which is defined by specifying the radius of the external boundary, the cross section of dust absorption, and the luminosity of the central star. We compare the analytic solution with numerical integrations of the model equations of Draine, and find a wide range of the physical parameters for which the analytic solution is accurate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The cosmic evolution of the metallicity distribution of ionized gas traced by Lyman limit systems

We present the first results from our KODIAQ Z survey aimed at determining the metallicity distribution and physical properties of the z≳2 partial and full Lyman limit systems (pLLSs and LLSs; 16.2⩽logN{sub HI}<19), which are probed of the interface regions between the intergalactic medium (IGM) and galaxies. We study 31 H i-selected pLLSs and LLSs at 2.3<z<3.3 observed with Keck/HIRES in absorption against background QSOs. We compare the column densities of metal ions to H i and use photoionization models to assess the metallicity. The metallicity distribution of the pLLSs/LLSs at 2.3<z<3.3 is consistent with a unimodal distribution peaking at [X/H]≃−2. The metallicity distribution of these absorbers therefore evolves markedly with z since at z≲1 it is bimodal with peaks at [X/H]≃−1.8 and −0.3. There is a substantial fraction (25%–41%) of pLLSs/LLSs with metallicities well below those of damped Lyα absorbers (DLAs) at any studied z from z≲1 to z∼2–4, implying reservoirs of metal-poor, cool, dense gas in the IGM/galaxy interface at all z. However, the gas probed by pLLSs and LLSs is rarely pristine, with a fraction of 3%–18% for pLLSs/LLSs with [X/H]⩽−3. We find C/α enhancement in several pLLSs and LLSs in the metallicity range −2≲[X/H]≲−0.5, where C/α is 2–5 times larger than observed in Galactic metal-poor stars or high-redshift DLAs at similar metallicities. This is likely caused by preferential ejection of carbon from metal-poor galaxies into their surroundings.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Multiwavelength study of the star formation in the S237 H ii region

We present a detailed multiwavelength study of observations from X-ray, near-infrared, and centimeter wavelengths to probe the star formation processes in the S237 region. Multiwavelength images trace an almost sphere-like shell morphology of the region, which is filled with the 0.5–2 keV X-ray emission. The region contains two distinct environments—a bell-shaped cavity-like structure containing the peak of 1.4 GHz emission at center, and elongated filamentary features without any radio detection at edges of the sphere-like shell—where Herschel clumps are detected. Using the 1.4 GHz continuum and {sup 12}CO line data, the S237 region is found to be excited by a radio spectral type of B0.5V star and is associated with an expanding H ii region. The photoionized gas appears to be responsible for the origin of the bell-shaped structure. The majority of molecular gas is distributed toward a massive Herschel clump (M{sub clump} ∼ 260 M{sub ⊙}), which contains the filamentary features and has a noticeable velocity gradient. The photometric analysis traces the clusters of young stellar objects (YSOs) mainly toward the bell-shaped structure and the filamentary features. Considering the lower dynamical age of the H ii region (i.e., 0.2–0.8 Myr), these clusters are unlikely to be formed by the expansion of the H ii region. Our results also show the existence of a cluster of YSOs and a massive clump at the intersection of filamentary features, indicating that the collisions of these features may have triggered cluster formation, similar to those found in the Serpens South region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Mass–metallicity relation for local analogs of high-redshift galaxies: implications for the evolution of the mass–metallicity relations

We revisit the evolution of the mass–metallicity relation of low- and high-redshift galaxies by using a sample of local analogs of high-redshift galaxies. These analogs share the same location of the UV-selected star-forming galaxies at z∼2 on the [O iii]λ5007/Hβ versus [N ii]λ6584/Hα nebular emission-line diagnostic (or BPT) diagram. Their physical properties closely resemble those in z∼2 UV-selected star-forming galaxies being characterized, in particular, by high ionization parameters (logq≈7.9) and high electron densities (n{sub e}≈100 cm{sup −3}). With the full set of well-detected rest-frame optical diagnostic lines, we measure the gas-phase oxygen abundance in the SDSS galaxies and these local analogs using the empirical relations and the photoionization models. We find that the metallicity difference between the SDSS galaxies and our local analogs in the 8.5<log(M{sub ∗}/M{sub ⊙})<9.0 stellar mass bin varies from −0.09 to 0.39 dex, depending on strong-line metallicity measurement methods. Due to this discrepancy, the evolution of mass–metallicity should be used to compare with the cosmological simulations with caution. We use the [S ii]/Hα and [O i]/Hα BPT diagram to reduce the potential AGN and shock contamination in our local analogs. We find that the AGN/shock influences are negligible on the metallicity estimation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

X-Ray Reflection and an Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143

Thermonuclear X-ray bursts from accreting neutron stars power brief but strong irradiation of their surroundings, providing a unique way to study accretion physics. We analyze MAXI /Gas Slit Camera and Swift /XRT spectra of a day-long flash observed from IGR J17062-6143 in 2015. It is a rare case of recurring bursts at a low accretion luminosity of 0.15% Eddington. Spectra from MAXI , Chandra , and NuSTAR observations taken between the 2015 burst and the previous one in 2012 are used to determine the accretion column. We find it to be consistent with the burst ignition column of 5×10{sup 10} g cm{sup −2}, which indicates that it is likely powered by burning in a deep helium layer. The burst flux is observed for over a day, and decays as a straight power law: F ∝ t {sup −1.15}. The burst and persistent spectra are well described by thermal emission from the neutron star, Comptonization of this emission in a hot optically thin medium surrounding the star, and reflection off the photoionized accretion disk. At the burst peak, the Comptonized component disappears, when the burst may dissipate the Comptonizing gas, and it returns in the burst tail. The reflection signal suggests that the inner disk is truncated at ∼10{sup 2} gravitational radii before the burst, but may move closer to the star during the burst. At the end of the burst, the flux drops below the burst cooling trend for 2 days, before returning to the pre-burst level.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Thermal Disk Winds in X-Ray Binaries: Realistic Heating and Cooling Rates Give Rise to Slow, but Massive, Outflows

A number of X-ray binaries exhibit clear evidence for the presence of disk winds in the high/soft state. A promising driving mechanism for these outflows is mass loss driven by the thermal expansion of X-ray heated material in the outer disk atmosphere. Higginbottom and Proga recently demonstrated that the properties of thermally driven winds depend critically on the shape of the thermal equilibrium curve, since this determines the thermal stability of the irradiated material. For a given spectral energy distribution, the thermal equilibrium curve depends on an exact balance between the various heating and cooling mechanisms at work. Most previous work on thermally driven disk winds relied on an analytical approximation to these rates. Here, we use the photoionization code cloudy to generate realistic heating and cooling rates which we then use in a 2.5D hydrodynamic model computed in ZEUS to simulate thermal winds in a typical black hole X-ray binary. We find that these heating and cooling rates produce a significantly more complex thermal equilibrium curve, with dramatically different stability properties. The resulting flow, calculated in the optically thin limit, is qualitatively different from flows calculated using approximate analytical rates. Specifically, our thermal disk wind is much denser and slower, with a mass-loss rate that is a factor of two higher and characteristic velocities that are a factor of three lower. The low velocity of the flow—v{sub max}≃200 km s{sup −1}—may be difficult to reconcile with observations. However, the high mass-loss rate—15 × the accretion rate—is promising, since it has the potential to destabilize the disk. Thermally driven disk winds may therefore provide a mechanism for state changes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Relativistic Jet-accretion Flow–wind Connection in Mrk 231

Long-term radio monitoring of the broad absorption line (BAL) quasar Mrk 231 at 17.6 GHz detected a strong flare in 2015. This triggered four epochs of Very Long Baseline Array (VLBA) observations from 8.4 to 43 GHz as well as three epochs of X-ray observations with NuSTAR and two with XMM over a 15 week period. Two ejected components were detected by the VLBA observations. A conservative lower bound on the apparent speed of the first ejection is attained by assuming that it was ejected when the flare began, v{sub app}>3.15c. Serendipitous far-UV Hubble Space Telescope observations combined with our long-term radio monitoring seem to indicate that episodes of relativistic ejections suppress flux that is emitted at wavelengths shortward of the peak of the far-UV spectral energy distribution, similar to what has been observed in radio-loud quasars. Episodes of strong jet production also seem to suppress the high-ionization BAL wind seen in weak jet states. We found a statistically significant increase (∼25%) of the 3–12 keV flux during the radio flare relative to a quiescent radio state. This is explained by an ultra-fast (∼0.06c) X-ray-absorbing photoionized wind that is significantly detected only in the low-radio state (similar to Galactic black holes). Mrk 231 is becoming more radio loud. We found that the putative parsec-scale radio lobe doubled in brightness in nine years. Furthermore, large flares are more frequent, with three major flares occurring at ∼2 year intervals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

SDSS IV MaNGA: Discovery of an Hα Blob Associated with a Dry Galaxy Pair—Ejected Gas or a “Dark” Galaxy Candidate?

We report the discovery of a mysterious giant Hα blob that is ∼8 kpc away from the main MaNGA target 1-24145, one component of a dry galaxy merger, and has been identified in the first-year SDSS-IV MaNGA data. The size of the Hα blob is ∼3–4 kpc in radius, and the Hα distribution is centrally concentrated. However, there is no optical continuum counterpart in the deep broadband images reaching ∼26.9 mag arcsec{sup −2} in surface brightness. We estimate that the masses of the ionized and cold gases are 3.3×10{sup 5} M{sub ⊙} and <1.3×10{sup 9} M{sub ⊙}, respectively. The emission-line ratios indicate that the Hα blob is photoionized by a combination of massive young stars and AGNs. Furthermore, the ionization line ratio decreases from MaNGA 1-24145 to the Hα blob, suggesting that the primary ionizing source may come from MaNGA 1-24145, likely a low-activity AGN. Possible explanations for this Hα blob include the AGN outflow, the gas remnant being tidally or ram-pressure stripped from MaNGA 1-24145, or an extremely low surface brightness galaxy. However, the stripping scenario is less favored according to galaxy merger simulations and the morphology of the Hα blob. With the current data, we cannot distinguish whether this Hα blob is ejected gas due to a past AGN outburst, or a special category of “ultra-diffuse galaxy” interacting with MaNGA 1-24145 that further induces the gas inflow to fuel the AGN in MaNGA 1-24145.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Implications for Extraterrestrial Hydrocarbon Chemistry: Analysis of Ethylene (C{sub 2}H{sub 4}) and D4-Ethylene (C{sub 2}D{sub 4}) Ices Exposed to Ionizing Radiation via Combined Infrared Spectroscopy and Reflectron Time-of-flight Mass Spectrometry

The processing of the hydrocarbon ice, ethylene (C{sub 2}H{sub 4}/C{sub 2}D{sub 4}), via energetic electrons, thus simulating the processes in the track of galactic cosmic-ray particles, was carried out in an ultrahigh vacuum apparatus. The chemical evolution of the ices was monitored online and in situ utilizing Fourier transform infrared spectroscopy (FTIR) and during temperature programmed desorption, via a quadrupole mass spectrometer utilizing electron impact ionization (EI-QMS) and a reflectron time-of-flight mass spectrometer utilizing a photoionization source (PI-ReTOF-MS). Several previous in situ studies of ethylene ice irradiation using FTIR were substantiated with the detection of six products: [CH{sub 4} (CD{sub 4})], acetylene [C{sub 2}H{sub 2} (C{sub 2}D{sub 2})], the ethyl radical [C{sub 2}H{sub 5} (C{sub 2}D{sub 5})], ethane [C{sub 2}H{sub 6} (C{sub 2}D{sub 6})], 1-butene [C{sub 4}H{sub 8} (C{sub 4}D{sub 8})], and n -butane [C{sub 4}H{sub 10} (C{sub 4}D{sub 10})]. Contrary to previous gas phase studies, the PI-ReTOF-MS detected several groups of hydrocarbon with varying degrees of saturation: C{sub n}H{sub 2n+2} (n = 4–10), C{sub n}H{sub 2n} ( n = 2–12, 14, 16), C{sub n}H{sub 2n−2} ( n = 3–12, 14, 16), C{sub n}H{sub 2n−4} (n = 4–12, 14, 16), C{sub n}H{sub 2n−6} (n = 4–10, 12), C{sub n}H{sub 2n−8} ( n = 6–10), and C{sub n}H{sub 2n−10} ( n = 6–10). Multiple laboratory studies have shown the facile production of ethylene from methane, which is a known ice constituent in the interstellar medium. Various astrophysically interesting molecules can be associated with the groups detected here, such as allene/methylacetylene (C{sub 3}H{sub 4}) or 1, 3-butadiene (C{sub 4}H{sub 6}) and its isomers, which have been shown to lead to polycyclic aromatic hydrocarbons. Finally, several hydrocarbon groups detected here are unique to ethylene ice versus ethane ice and may provide understanding of how complex hydrocarbons form in astrophysical environments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Discovery of an Enormous Lyα Nebula in a Massive Galaxy Overdensity at z = 2.3

Enormous Lyα nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys or have targeted known sources such as ultraluminous quasi-stellar objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Lyα absorptions, we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at z=2--3. In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Lyα nebular luminosity of L{sub nebula}=5.1±0.1×10{sup 44} erg s{sup −1}. Above the 2σ surface brightness limit of SB{sub Lyα}=4.8×10{sup −18} erg s{sup −1} cm{sup −2} arcsec{sup −2}, this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C iv λ1549 and He ii λ1640 emission on ≳30 kpc scales. Note that the Lyα, He ii, and C iv emissions all have double-peaked line profiles. Each velocity component has an FWHM of ≈700–1000 km s{sup −1}. We argue that this Lyα nebula could be powered by shocks due to an active galactic nucleus–driven outflow or photoionization by a strongly obscured source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Ringed Dwarf LINER 1 Galaxy Hosting an Intermediate-mass Black Hole with Large-scale Rotation-like Hα Emission

We report the discovery of a 20 kpc sized Hα emission in SDSS J083803.68+540642.0, a ringed dwarf galaxy (M{sub V}=−17.89 mag) hosting an accreting intermediate-mass black hole at z = 0.02957. Analysis of the Hubble Space Telescope images indicates that it is an early-type galaxy with a featureless low-surface brightness disk (μ{sub 0}=20.39 mag arcsec{sup −2} in the V band) and a prominent, relatively red bulge (V − I = 2.03, R{sub e}=0.28 kpc or 0.″48) that accounts for ≈81% of the total light in the I band. A circumgalactic ring of a diameter 16 kpc is also detected, with a disperse shape on its south side. The optical emission lines reveal the nucleus to be a broad-line LINER. Our MMT longslit observation indicates that the kinematics of the extended Hα emission is consistent with a rotational gaseous disk, with a mean blueshifted velocity of 162 km s{sup −1} and mean redshifted velocity of 86 km s{sup −1}. According to our photoionization calculations, the large-scale Hα emission is unlikely to be powered by the central nucleus or by hot evolved (post-AGB) stars interspersed in the old stellar populations, but by in situ star formation; this is vindicated by the line-ratio diagnostic of the extended emission. We propose that both the ring and large-scale Hα-emitting gas are created by the tidal accretion in a collision—and then merger—with a gas-rich galaxy of a comparable mass.

79 ASTRONOMY AND ASTROPHYSICS↗