Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “interstellar medium”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The diffuse gamma-ray flux associated with sub-PEV/PEV neutrinos from starburst galaxies

One attractive scenario for the excess of sub-PeV/PeV neutrinos recently reported by IceCube is that they are produced by cosmic rays in starburst galaxies colliding with the dense interstellar medium. These proton-proton (pp) collisions also produce high-energy gamma rays, which finally contribute to the diffuse high-energy gamma-ray background. We calculate the diffuse gamma-ray flux with a semi-analytic approach and consider that the very high energy gamma rays will be absorbed in the galaxies and converted into electron-positron pairs, which then lose almost all of their energy through synchrotron radiation in the strong magnetic fields in the starburst region. Since the synchrotron emission goes into energies below GeV, this synchrotron loss reduces the diffuse high-energy gamma-ray flux by a factor of about two, thus leaving more room for other sources to contribute to the gamma-ray background. For an E{sub ν}{sup −2} neutrino spectrum, we find that the diffuse gamma-ray flux contributes about 20% of the observed diffuse gamma-ray background in the 100 GeV range. However, for a steeper neutrino spectrum, this synchrotron loss effect is less important, since the energy fraction in absorbed gamma rays becomes lower.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Plasma flows in the heliosheath along the Voyager 1 and 2 trajectories due to effects of the 11 yr solar cycle

We investigate the role of the 11 yr solar cycle variations in the solar wind (SW) parameters on the flows in the heliosheath using a new three-dimensional time-dependent model of the interaction between the SW and the interstellar medium. For boundary conditions in the model we use realistic time and the latitudinal dependence of the SW parameters obtained from SOHO/SWAN and interplanetary scintillation data for the last two solar cycles (1990-2011). This data set generally agrees with the in situ Ulysses measurements from 1991 to 2009. For the first ∼30 AU of the heliosheath the time-dependent model predicts constant radial flow speeds at Voyager 2 (V2), which is consistent with observations and different from the steady models that show a radial speed decrease of 30%. The model shows that V2 was immersed in SW with speeds of 500-550 km s{sup –1} upstream of the termination shock before 2009 and in wind with upstream speeds of 450-500 km s{sup –1} after 2009. The model also predicts that the radial velocity along the Voyager 1 (V1) trajectory is constant across the heliosheath, contrary to observations. This difference in observations implies that additional effects may be responsible for the different flows at V1 and V2. The model predicts meridional flows (VN) higher than those observed because of the strong bluntness of the heliosphere shape in the N direction in the model. The modeled tangential velocity component (VT) at V2 is smaller than observed. Both VN and VT essentially depend on the shape of the heliopause.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

OH{sup +} in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He

The rate constants required to model the OH{sup +} observations in different regions of the interstellar medium have been determined using state of the art quantum methods. First, state-to-state rate constants for the H{sub 2}(v = 0, J = 0, 1) + O{sup +}({sup 4} S) → H + OH{sup +}(X {sup 3}Σ{sup –}, v', N) reaction have been obtained using a quantum wave packet method. The calculations have been compared with time-independent results to assess the accuracy of reaction probabilities at collision energies of about 1 meV. The good agreement between the simulations and the existing experimental cross sections in the 0.01-1 eV energy range shows the quality of the results. The calculated state-to-state rate constants have been fitted to an analytical form. Second, the Einstein coefficients of OH{sup +} have been obtained for all astronomically significant rovibrational bands involving the X {sup 3}Σ{sup –} and/or A {sup 3}Π electronic states. For this purpose, the potential energy curves and electric dipole transition moments for seven electronic states of OH{sup +} are calculated with ab initio methods at the highest level, including spin-orbit terms, and the rovibrational levels have been calculated including the empirical spin-rotation and spin-spin terms. Third, the state-to-state rate constants for inelastic collisions between He and OH{sup +}(X {sup 3}Σ{sup –}) have been calculated using a time-independent close coupling method on a new potential energy surface. All these rates have been implemented in detailed chemical and radiative transfer models. Applications of these models to various astronomical sources show that inelastic collisions dominate the excitation of the rotational levels of OH{sup +}. In the models considered, the excitation resulting from the chemical formation of OH{sup +} increases the line fluxes by about 10% or less depending on the density of the gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

C{sub 60} in photodissociation regions

Recent studies have confirmed the presence of buckminsterfullerene (C{sub 60}) in different interstellar and circumstellar environments. However, several aspects regarding C{sub 60} in space are not yet well understood, such as the formation and excitation processes, and the connection between C{sub 60} and other carbonaceous compounds in the interstellar medium, in particular polycyclic aromatic hydrocarbons (PAHs). In this paper, we study several photodissociation regions (PDRs) where C{sub 60} and PAHs are detected and the local physical conditions are reasonably well constrained to provide observational insights into these questions. C{sub 60} is found to emit in PDRs where the dust is cool (T{sub d} = 20-40 K) and even in PDRs with cool stars. These results exclude the possibility for C{sub 60} to be locked in grains at thermal equilibrium in these environments. We observe that PAH and C{sub 60} emission are spatially uncorrelated and that C{sub 60} is present in PDRs where the physical conditions (in terms of radiation field and hydrogen density) allow for full dehydrogenation of PAHs, with the exception of Ced 201. We also find trends indicative of an increase in C{sub 60} abundance within individual PDRs, but these trends are not universal. These results support models where the dehydrogenation of carbonaceous species is the first step toward C{sub 60} formation. However, this is not the only parameter involved and C{sub 60} formation is likely affected by shocks and PDR age.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Pinpointing the knee of cosmic rays with diffuse PeV γ-rays and neutrinos

The origin of the knee in the cosmic ray spectrum remains to be an unsolved fundamental problem. There are various kinds of models that predict different break positions and the compositions of the knee. In this work, we suggest the use of diffuse γ-rays and neutrinos as probes to test these models. Based on several typical types of composition models, the diffuse γ-ray and neutrino spectra are calculated and show distinctive cutoff behaviors at energies from tens of TeV to multi-PeV. The expected flux will be observable by the newly upgraded Tibet-ASγ+MD (muon detector) experiment as well as more sensitive future projects, such as LHAASO and HiSCORE. By comparing the neutrino spectrum with the recent observations by the IceCube experiment, we find that the diffuse neutrinos from interactions between the cosmic rays and the interstellar medium may not be responsible to the majority of the IceCube events. Future measurements of the neutrinos may be able to identify the Galactic diffuse component and shed further light on the problem of the knee of cosmic rays.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The structure, dynamics, and star formation rate of the Orion nebula cluster

The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues to the conditions during the star formation event and the processes that regulated it. We analyze the Orion Nebula Cluster (ONC), utilizing the latest censuses of its stellar content and membership estimates over a large wavelength range. We determine the center of mass of the ONC and study the radial dependence of angular substructure. The core appears rounder and smoother than the outskirts, which is consistent with a higher degree of dynamical processing. At larger distances, the departure from circular symmetry is mostly driven by the elongation of the system, with very little additional substructure, indicating a somewhat evolved spatial morphology or an expanding halo. We determine the mass density profile of the cluster, which is well fitted by a power law that is slightly steeper than a singular isothermal sphere. Together with the interstellar medium density, which is estimated from average stellar extinction, the mass content of the ONC is insufficient by a factor ∼1.8 to reproduce the observed velocity dispersion from virialized motions, in agreement with previous assessments that the ONC is moderately supervirial. This may indicate recent gas dispersal. Based on the latest estimates for the age spread in the system and our density profiles, we find that at the half-mass radius, 90% of the stellar population formed within ∼5-8 free-fall times (t {sub ff}). This implies a star formation efficiency per t {sub ff} of ε{sub ff} ∼ 0.04-0.07 (i.e., relatively slow and inefficient star formation rates during star cluster formation).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

An HST/COS observation of broad Lyα emission and associated absorption lines of the BL Lacertae object H 2356-309

Weak spectral features in BL Lacertae objects (BL Lacs) often provide a unique opportunity to probe the inner region of this rare type of active galactic nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph observation of the BL Lac H 2356-309. A weak Lyα emission line was detected. This is the fourth detection of a weak Lyα emission feature in the ultraviolet (UV) band in the so-called high-energy peaked BL Lacs, after Stocke et al. Assuming the line-emitting gas is located in the broad line region (BLR) and the ionizing source is the off-axis jet emission, we constrain the Lorentz factor (Γ) of the relativistic jet to be ≥8.1 with a maximum viewing angle of 3.°6. The derived Γ is somewhat larger than previous measurements of Γ ≈ 3-5, implying a covering factor of ∼3% of the line-emitting gas. Alternatively, the BLR clouds could be optically thin, in which case we constrain the BLR warm gas to be ∼10{sup –5} M {sub ☉}. We also detected two H I and one O VI absorption lines that are within |Δv| < 150 km s{sup –1} of the BL Lac object. The O VI and one of the H I absorbers likely coexist due to their nearly identical velocities. We discuss several ionization models and find a photoionization model where the ionizing photon source is the BL Lac object that can fit the observed ion column densities with reasonable physical parameters. This absorber can either be located in the interstellar medium of the host galaxy or in the BLR.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Mixing between high velocity clouds and the galactic halo

In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed two- and three-dimensional simulations of cloud-interstellar medium interactions. Our simulations track the hydrodynamics and time-dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A far-infrared spectral sequence of galaxies: trends and models

We present a framework for the interpretation of the far-infrared spectra of galaxies in which we have expanded the model parameters compared with previous work by varying the ionization parameter U, column density N(H), and gas density at the cloud face n(H{sup +}) for a central starburst or active galactic nucleus (AGN). We compare these models carried out with the Cloudy spectral synthesis code to trends in line-to-total far-infrared luminosity ratios, far-infrared fine-structure line ratios, IRAS colors, and OH and H{sub 2}O column densities found in the well-studied sample of 10 nearby galaxies from the IRAS Bright Galaxy Sample with infrared luminosities greater than 10{sup 10} L {sub ☉} and IRAS 60 μm fluxes equal to or greater than that of the nearby ultraluminous infrared galaxy (ULIRG) Arp 220. We find that the spectral sequence extending from normal starburst-type emission-line-dominated spectra to ULIRG-type absorption-dominated spectra with significant absorption from excited levels can be best explained by simultaneously increasing the hydrogen column density, from as low as 10{sup 21} cm{sup –2} to as high as 10{sup 24.8} cm{sup –2} or greater, and the ionization parameter, from as low as 10{sup –4} to as high as 1. The starburst models best reproduce most of the sequence, while AGN models are somewhat better able to produce the high OH and H{sub 2}O column densities in Arp 220. Our results suggest that the molecular interstellar medium in ULIRG-like, molecular-absorption-dominated systems is located close to and at least partially obscures the source of power throughout much of the far-infrared, which must be taken into account in order to properly interpret diagnostics of both their sources of power and of feedback.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Scaling relations for galaxies prior to reionization

The first galaxies in the universe are the building blocks of all observed galaxies. We present scaling relations for galaxies forming at redshifts z ≥ 15 when reionization is just beginning. We utilize the 'Rarepeak' cosmological radiation hydrodynamics simulation that captures the complete star formation history in over 3300 galaxies, starting with massive Population III stars that form in dark matter halos as small as ∼10{sup 6} M {sub ☉}. We make various correlations between the bulk halo quantities, such as virial, gas, and stellar masses and metallicities and their respective accretion rates, quantifying a variety of properties of the first galaxies up to halo masses of 10{sup 9} M {sub ☉}. Galaxy formation is not solely relegated to atomic cooling halos with virial temperatures greater than 10{sup 4} K, where we find a dichotomy in galaxy properties between halos above and below this critical mass scale. Halos below the atomic cooling limit have a stellar mass-halo mass relationship log M {sub *} ≅ 3.5 + 1.3log (M {sub vir}/10{sup 7} M {sub ☉}). We find a non-monotonic relationship between metallicity and halo mass for the smallest galaxies. Their initial star formation events enrich the interstellar medium and subsequent star formation to a median of 10{sup –2} Z {sub ☉} and 10{sup –1.5} Z {sub ☉}, respectively, in halos of total mass 10{sup 7} M {sub ☉}, which is then diluted by metal-poor inflows well beyond Population III pre-enrichment levels of 10{sup –3.5} Z {sub ☉}. The scaling relations presented here can be employed in models of reionization, galaxy formation, and chemical evolution in order to consider these galaxies forming prior to reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Observation and modeling of geocoronal charge exchange X-ray emission during solar wind gusts

Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar wind ions such as O{sup 7{sup +}} collide with neutral gas, including the Earth's tenuous outer atmosphere (exosphere or geocorona) and hydrogen and helium from the local interstellar medium drifting through the heliosphere. This geocoronal and heliospheric emission comprises a significant and varying fraction of the soft X-ray background (SXRB) and is seen in every X-ray observation, with the intensity dependent on solar wind conditions and observation geometry. Under the right conditions, geocoronal emission can increase the apparent SXRB by roughly an order of magnitude for an hour or more. In this work, we study a dozen occasions when the near-Earth solar wind flux was exceptionally high. These gusts of wind lead to abrupt changes in SWCX X-ray emission around Earth, which may or may not be seen by X-ray observatories depending on their line of sight. Using detailed three-dimensional magnetohydrodynamical simulations of the solar wind's interaction with the Earth's magnetosphere, and element abundances and ionization states measured by ACE, we model the time-dependent brightness of major geocoronal SWCX emission lines during those gusts and compare with changes in the X-ray background measured by the Chandra X-ray Observatory. We find reasonably good agreement between model and observation, with measured geocoronal line brightnesses averaged over 1 hr of up to 136 photons s{sup –1} cm{sup –2} sr{sup –1} in the O VII Kα triplet around 564 eV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The Vela pulsar with an active fallback disk

Fallback disks are expected to form around young neutron stars. The presence of these disks can be revealed by their blackbody spectrum in the infrared, optical, and UV bands. We present a re-reduction of the archival optical and infrared data of the Vela pulsar, together with the existing infrared and UV spectrum of Vela, and model their unpulsed components with the blackbody spectrum of a supernova debris disk. We invoke the quiescent disk solution of Sunyaev and Shakura for the description of the disk in the propeller stage and find the inner radius of the disk to be inside the light cylinder radius. We perform a high-resolution X-ray analysis with XMM-Newton and find a narrow absorption feature at 0.57 keV that can be interpreted as the K {sub α} line of He-like oxygen (O VII). The strength of the line indicates an element over-abundance in our line of sight exceeding the amounts that would be expected from interstellar medium. The spectral feature may originate from the pulsar wind nebula and may be partly caused by the reprocessed X-ray radiation by the fallback disk. We discuss the lower-than-three braking index of Vela as partially due to the contribution of the propeller torques. Our results suggest that the pulsar mechanism can work simultaneously with the propeller processes and that the debris disks can survive the radiation pressure for at least ∼10{sup 4} yr. As Vela is a relatively close object, and a prototypical pulsar, the presence of a disk, if confirmed, may indicate the ubiquity of debris disks around young neutron stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A far-infrared spectroscopic survey of intermediate redshift (ultra) luminous infrared galaxies

We present Herschel far-IR photometry and spectroscopy as well as ground-based CO observations of an intermediate redshift (0.21 ≤ z ≤ 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (L {sub IR} > 10{sup 11.5} L {sub ☉}). With these measurements, we trace the dust continuum, far-IR atomic line emission, in particular [C II] 157.7 μm, as well as the molecular gas of z ∼ 0.3 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have L {sub C} {sub II}/L {sub FIR} ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-z star-forming galaxies. Using our sample to bridge local and high-z [C II] observations, we find that the majority of galaxies at all redshifts and all luminosities follow an L {sub C} {sub II}–L {sub FIR} relation with a slope of unity, from which local ULIRGs and high- z active-galactic-nucleus-dominated sources are clear outliers. We also confirm that the strong anti-correlation between the L {sub C} {sub II}/L {sub FIR} ratio and the far-IR color L {sub 60}/L {sub 100} observed in the local universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower L {sub C} {sub II}/L {sub FIR} at any epoch. Intermediate redshift ULIRGs are also characterized by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high L {sub C} {sub II}/L {sub FIR} ratios, the moderate star formation efficiencies (L {sub IR}/L{sub CO}{sup ′} or L {sub IR}/M{sub H{sub 2}}), and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star-forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z > 1 is already significant by z ∼ 0.3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA imaging of gas and dust in a galaxy protocluster at redshift 5.3: [C II] emission in 'typical' galaxies and dusty starbursts ≈1 billion years after the big bang

We report interferometric imaging of [C II]({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) and OH({sup 2}Π{sub 1/2} J = 3/2→1/2) emission toward the center of the galaxy protocluster associated with the z = 5.3 submillimeter galaxy (SMG) AzTEC-3, using the Atacama Large (sub)Millimeter Array (ALMA). We detect strong [C II], OH, and rest-frame 157.7 μm continuum emission toward the SMG. The [C II]({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of 9.7 × 10{sup 10} M {sub ☉}, and a star formation rate (SFR) surface density of Σ{sub SFR} = 530 M {sub ☉} yr{sup –1} kpc{sup –2}. This suggests that AzTEC-3 forms stars at Σ{sub SFR} approaching the Eddington limit for radiation pressure supported disks. We find that the OH emission is slightly blueshifted relative to the [C II] line, which may indicate a molecular outflow associated with the peak phase of the starburst. We also detect and dynamically resolve [C II]({sup 2} P {sub 3/2}→{sup 2} P {sub 1/2}) emission over a scale of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs in the protocluster at ∼95 kpc projected distance from the SMG. These galaxies are not detected in the continuum, suggesting far-infrared SFRs of <18-54 M {sub ☉} yr{sup –1}, consistent with a UV-based estimate of 22 M {sub ☉} yr{sup –1}. The spectral energy distribution of these galaxies is inconsistent with nearby spiral and starburst galaxies, but resembles those of dwarf galaxies. This is consistent with expectations for young starbursts without significant older stellar populations. This suggests that these galaxies are significantly metal-enriched, but not heavily dust-obscured, 'normal' star-forming galaxies at z > 5, showing that ALMA can detect the interstellar medium in 'typical' galaxies in the very early universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA observations of the host galaxy of GRB 090423 at z = 8.23: deep limits on obscured star formation 630 million years after the big bang

We present rest-frame far-infrared (FIR) and optical observations of the host galaxy of GRB 090423 at z = 8.23 from the Atacama Large Millimeter Array (ALMA) and the Spitzer Space Telescope, respectively. The host remains undetected to 3σ limits of F {sub ν}(222 GHz) ≲ 33 μJy and F {sub ν}(3.6 μm) ≲ 81 nJy. The FIR limit is about 20 times fainter than the luminosity of the local ULIRG Arp 220 and comparable to the local starburst M 82. Comparing this with model spectral energy distributions, we place a limit on the infrared (IR) luminosity of L {sub IR}(8-1000 μm) ≲ 3 × 10{sup 10} L {sub ☉}, corresponding to a limit on the obscured star formation rate of SFR{sub IR}≲5 M {sub ☉} yr{sup –1}. For comparison, the limit on the unobscured star formation rate from Hubble Space Telescope rest-frame ultraviolet (UV) observations is SFR{sub UV} ≲ 1 M {sub ☉} yr{sup –1}. We also place a limit on the host galaxy stellar mass of M {sub *} ≲ 5 × 10{sup 7} M {sub ☉} (for a stellar population age of 100 Myr and constant star formation rate). Finally, we compare our millimeter observations to those of field galaxies at z ≳ 4 (Lyman break galaxies, Lyα emitters, and submillimeter galaxies) and find that our limit on the FIR luminosity is the most constraining to date, although the field galaxies have much larger rest-frame UV/optical luminosities than the host of GRB 090423 by virtue of their selection techniques. We conclude that GRB host galaxies at z ≳ 4, especially those with measured interstellar medium metallicities from afterglow spectroscopy, are an attractive sample for future ALMA studies of high redshift obscured star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The Lyα reference sample. I. Survey outline and first results for Markarian 259

The Lyα Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Lyαline of neutral hydrogen. Lyα is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Lyα to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes Hα and Hβ narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Lyα photons are produced (whether or not they escape), we demanded an Hα equivalent width W(Hα) ≥100 Å. The final sample of 14 galaxies covers far-UV (FUV, λ ∼ 1500 Å) luminosities that overlap with those of high-z Lyα emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Lyα images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Lyα. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Lyα filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Lyα emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Lyα emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Lyα line profile and confirms the presence of an outflow. From the integrated photometry we measure an Lyα luminosity of L {sub Lyα}=1.3 × 10{sup 42} erg s{sup –1} an equivalent width W(Lyα) = 45 Å and an FUV absolute magnitude M {sub FUV} = –19.2 (AB). Mrk 259 would hence be detectable in high-z Lyα and LBG surveys. The total Lyα escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The hydrogen-poor superluminous supernova iPTF 13ajg and its host galaxy in absorption and emission

We present imaging and spectroscopy of a hydrogen-poor superluminous supernova (SLSN) discovered by the intermediate Palomar Transient Factory, iPTF 13ajg. At a redshift of z = 0.7403, derived from narrow absorption lines, iPTF 13ajg peaked at an absolute magnitude of M {sub u,} {sub AB} = –22.5, one of the most luminous supernovae to date. The observed bolometric peak luminosity of iPTF 13ajg is 3.2 × 10{sup 44} erg s{sup –1}, while the estimated total radiated energy is 1.3 × 10{sup 51} erg. We detect narrow absorption lines of Mg I, Mg II, and Fe II, associated with the cold interstellar medium in the host galaxy, at two different epochs with X-shooter at the Very Large Telescope. From Voigt profile fitting, we derive the column densities log N(Mg I) =11.94 ± 0.06, log N(Mg II) =14.7 ± 0.3, and log N(Fe II) =14.25 ± 0.10. These column densities, as well as the Mg I and Mg II equivalent widths of a sample of hydrogen-poor SLSNe taken from the literature, are at the low end of those derived for gamma-ray bursts (GRBs) whose progenitors are also thought to be massive stars. This suggests that the environments of hydrogen-poor SLSNe and GRBs are different. From the nondetection of Fe II fine-structure absorption lines, we derive a lower limit on the distance between the supernova and the narrow-line absorbing gas of 50 pc. The neutral gas responsible for the absorption in iPTF 13ajg exhibits a single narrow component with a low velocity width, ΔV = 76 km s{sup –1}, indicating a low-mass host galaxy. No host galaxy emission lines are detected, leading to an upper limit on the unobscured star formation rate (SFR) of SFR{sub [O} {sub II]}<0.07M{sub ⊙}yr{sup −1}. Late-time imaging shows the iPTF 13ajg host galaxy to be faint, with g {sub AB} ≈ 27.0 and R {sub AB} ≥ 26.0 mag, corresponding to M {sub B,} {sub Vega} ≳ –17.7 mag.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

THE EFFECTS OF INITIAL ABUNDANCES ON NITROGEN IN PROTOPLANETARY DISKS

The dominant form of nitrogen provided to most solar system bodies is currently unknown, though available measurements show that the detected nitrogen in solar system rocks and ices is depleted with respect to solar abundances and the interstellar medium. We use a detailed chemical/physical model of the chemical evolution of a protoplanetary disk to explore the evolution and abundance of nitrogen-bearing molecules. Based on this model, we analyze how initial chemical abundances provided as either gas or ice during the early stages of disk formation influence which species become the dominant nitrogen bearers at later stages. We find that a disk with the majority of its initial nitrogen in either atomic or molecular nitrogen is later dominated by atomic and molecular nitrogen as well as NH{sub 3} and HCN ices, where the dominant species varies with disk radius. When nitrogen is initially in gaseous ammonia, it later becomes trapped in ammonia ice except in the outer disk where atomic nitrogen dominates. For a disk with the initial nitrogen in the form of ammonia ice, the nitrogen remains trapped in the ice as NH{sub 3} at later stages. The model in which most of the initial nitrogen is placed in atomic N best matches the ammonia abundances observed in comets. Furthermore, the initial state of nitrogen influences the abundance of N{sub 2}H{sup +}, which has been detected in protoplanetary disks. Strong N{sub 2}H{sup +} emission is found to be indicative of an N{sub 2} abundance greater than n{sub N{sub 2}}/n{sub H{sub 2}}>10{sup −6} in addition to tracing the CO snow line. Our models also indicate that NO is potentially detectable, with lower N gas abundances leading to higher NO abundances.

79 ASTRONOMY AND ASTROPHYSICS↗