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At least 1,405 records · Page 78
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DOE OSTI2016

The possible detection of a binary companion to a type Ibn supernova progenitor

We present late-time observations of the site of the Type Ibn supernova (SN) 2006jc, acquired with the Hubble Space Telescope Advanced Camera for Surveys. A faint blue source is recovered at the SN position, with brightness m{sub F435W}=26.76±0.20, m{sub F555W}=26.60±0.23 and m{sub F625W}=26.32±0.19 mag, although there is no detection in a contemporaneous narrow-band Hα image. The spectral energy distribution of the late-time source is well-fit by a stellar-like spectrum (log T{sub eff}>3.7 and log L/L{sub ⊙}>4), subject to only a small degree of reddening—consistent with that estimated for SN 2006jc itself at early-times. The lack of further outbursts after the explosion of SN 2006jc suggests that the precursor outburst originated from the progenitor. The possibility of the source being a compact host cluster is ruled out on the basis of the source’s faintness; however, the possibility that the late-time source may be an unresolved light echo originating in a shell or sphere of pre-SN dust (within a radius 1 pc) is also discussed. Irrespective of the nature of the late-time source, these observations rule out a luminous blue variable as a companion to the progenitor of SN 2006jc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The panchromatic hubble andromeda treasury. XVII. Examining obscured star formation with synthetic ultraviolet flux maps in M31

We present synthetic far- and near-ultraviolet (FUV and NUV) maps of M31, both with and without dust reddening. These maps were constructed from spatially resolved star formation histories (SFHs) derived from optical Hubble Space Telescope imaging of resolved stars, taken as part of the Panchromatic Hubble Andromeda Treasury program. We use stellar population synthesis modeling to generate synthetic UV maps with a spatial resolution of ∼100 pc (∼24 arcsec), projected. When reddening is included, these maps reproduce all of the main morphological features in the GALEX imaging, including rings and large star-forming complexes. The predicted UV flux also agrees well with the observed flux, with median ratios between the modeled and observed flux of log{sub 10}(f{sub FUV}{sup syn}/f{sub FUV}{sup obs})=0.03±0.24 and log{sub 10}(f{sub NUV}{sup syn}/f{sub NUV}{sup obs})=−0.03±0.16 in the FUV and NUV, respectively. This agreement is particularly impressive given that we used only optical photometry to construct these UV maps. Having verified the synthetic reddened maps, we use the dust-free maps to examine properties of obscured flux and star formation. We compare our dust-free and reddened maps of FUV flux with the observed GALEX FUV flux and FUV + 24 μm flux to examine the fraction of obscured flux. We find that the maps of synthetic flux require that ∼90% of the FUV flux in M31 is obscured by dust, while the GALEX -based methods suggest that ∼70% of the FUV flux is absorbed by dust. This 30% increase in the estimate of the obscured flux is driven by significant differences between the dust-free synthetic FUV flux and that derived when correcting the observed FUV flux for dust absorption with 24 μm emission observations. The difference is further illustrated when we compare the SFRs derived from the FUV + 24 μm flux with the 100 Myr average SFR from the CMD-based SFHs. We find that the 24 μm corrected FUV flux underestimates the SFR by a factor of 2.3–2.5, depending on the chosen calibration. This discrepancy could be reduced by allowing for variability in the weight applied to the 24 μm data, as has been recently suggested in the literature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Isophote shapes of early-type galaxies in massive clusters at z ∼ 1 and 0

We compare the isophote shape parameter a{sub 4} of early-type galaxies (ETGs) between z ∼ 1 and 0 as a proxy for dynamics to investigate the epoch at which the dynamical properties of ETGs are established, using cluster ETG samples with stellar masses of log(M{sub ∗}/M{sub ⊙})⩾10.5 which have spectroscopic redshifts. We have 130 ETGs from the Hubble Space Telescope Cluster Supernova Survey for z ∼ 1 and 355 ETGs from the Sloan Digital Sky Survey for z ∼ 0. We have developed an isophote shape analysis method, which can be used for high-redshift galaxies and has been carefully compared with published results. We have applied the same method for both the z ∼ 1 and 0 samples. We find similar dependence of the a{sub 4} parameter on the mass and size at z ∼ 1 and 0; the main population of ETGs changes from disky to boxy at a critical stellar mass of log(M{sub ∗}/M{sub ⊙})∼11.5 with the massive end dominated by boxy. The disky ETG fraction decreases with increasing stellar mass both at z ∼ 1 and 0, and is consistent between these redshifts in all stellar mass bins when the Eddington bias is taken into account. Although uncertainties are large, the results suggest that the isophote shapes and probably dynamical properties of ETGs in massive clusters are already in place at z > 1 and do not significantly evolve in z < 1, despite significant size evolution in the same galaxy population. The constant disky fraction favors less violent processes than mergers as the main cause of the size and morphological evolution of intermediate mass ETGs in z < 1.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

SCExAO and GPI Y JH band photometry and integral field spectroscopy of the young brown dwarf companion to HD 1160

Here, we present high signal-to-noise ratio, precise Y JH photometry and Y band (0.957–1.120 μm) spectroscopy of HD 1160 B, a young substellar companion discovered from the Gemini NICI Planet Finding Campaign using the Subaru Coronagraphic Extreme Adaptive Optics instrument and the Gemini Planet Imager. HD 1160 B has typical mid-M dwarf-like infrared colors and a spectral type of M5.5${}_{-0.5}^{+1.0}$, where the blue edge of our Y band spectrum rules out earlier spectral types. Atmospheric modeling suggests HD 1160 B has an effective temperature of 3000–3100 K, a surface gravity of log g = 4–4.5, a radius of 1.55 ± 0.10 R J, and a luminosity of log L/L ⊙ = –2.76 ± 0.05. Neither the primary's Hertzspring–Russell diagram position nor atmospheric modeling of HD 1160 B show evidence for a subsolar metallicity. Interpretation of the HD 1160 B spectroscopy depends on which stellar system components are used to estimate the age. Considering HD 1160 A, B and C jointly, we derive an age of 80–125 Myr, implying that HD 1160 B straddles the hydrogen-burning limit (70–90 M J ). If we consider HD 1160 A alone, younger ages (20–125 Myr) and a brown dwarf-like mass (35–90 M J ) are possible. Interferometric measurements of the primary, a precise Gaia parallax, and moderate-resolution spectroscopy can better constrain the system's age and how HD 1160 B fits within the context of (sub)stellar evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Toward understanding the B[e] phenomenon. VI. Nature and spectral variations of HD 85567

We report the results of high-resolution (R ∼ 80,000) spectroscopic observations of the emission-line object HD 85567, which has been classified as an FS CMa type object or a pre-main-sequence star. The main goal is to put more constraints on the object’s fundamental parameters, as well as on its nature and evolutionary state. Absorption lines in the spectrum of HD 85567 were found to be similar to those of mid-B-type dwarfs and correspond to the following fundamental parameters: T{sub eff} = 15,000 ± 500 K, vsin i=31±3 km s{sup −1}, and log g∼4.0. The interstellar extinction, A{sub V} = 0.50 ± 0.02 mag, was measured using the strengths of some diffuse interstellar bands. We also obtained UBV(RI){sub c} images of a 10′ × 10′ region around the object. Photometry of projectionally close stars was used to derive an interstellar extinction law in this direction and resulted in a distance of 1300 ± 100 pc to the object and a luminosity of log L/L{sub ⊙} = 3.3 ± 0.2. We found no significant radial velocity variations of the absorption lines in the spectra of HD 85567 obtained during two-month-long periods of time in 2012 and 2015. Our analysis of the spectroscopic and photometric data available for the star led us to a conclusion that it cannot be a pre-main-sequence Herbig Ae/Be star. We argue that the circumstellar gas and dust were produced during the object’s evolution as most likely a binary system, which contains an undetected secondary component and is unlikely to be a merger product.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log–log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2–3 relative to clouds of comparable mass. We identify the two primary sources of scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10{sup 22} cm{sup −2}, accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as an active galactic nucleus and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The VMC Survey. XXII. Hierarchical Star Formation in the 30 Doradus-N158–N159–N160 Star-forming Complex

We study the hierarchical stellar structures in a ∼1.5 deg{sup 2} area covering the 30 Doradus-N158–N159–N160 star-forming complex with the VISTA Survey of Magellanic Clouds. Based on the young upper main-sequence stars, we find that the surface densities cover a wide range of values, from log(Σ⋅pc{sup 2}) ≲ −2.0 to log(Σ⋅pc{sup 2}) ≳ 0.0. Their distributions are highly non-uniform, showing groups that frequently have subgroups inside. The sizes of the stellar groups do not exhibit characteristic values, and range continuously from several parsecs to more than 100 pc; the cumulative size distribution can be well described by a single power law, with the power-law index indicating a projected fractal dimension D{sub 2} = 1.6 ± 0.3. We suggest that the phenomena revealed here support a scenario of hierarchical star formation. Comparisons with other star-forming regions and galaxies are also discussed.

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DOE OSTI2017

The NuSTAR Serendipitous Survey: The 40-month Catalog and the Properties of the Distant High-energy X-Ray Source Population

We present the first full catalog and science results for the Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey. The catalog incorporates data taken during the first 40 months of NuSTAR operation, which provide ≈20 Ms of effective exposure time over 331 fields, with an areal coverage of 13 deg{sup 2}, and 497 sources detected in total over the 3–24 keV energy range. There are 276 sources with spectroscopic redshifts and classifications, largely resulting from our extensive campaign of ground-based spectroscopic follow-up. We characterize the overall sample in terms of the X-ray, optical, and infrared source properties. The sample is primarily composed of active galactic nuclei (AGNs), detected over a large range in redshift from z = 0.002 to 3.4 (median of 〈z〉=0.56), but also includes 16 spectroscopically confirmed Galactic sources. There is a large range in X-ray flux, from log(f{sub 3−24keV}/erg s{sup −1} cm{sup −2})≈−14 to −11, and in rest-frame 10–40 keV luminosity, from log(L{sub 10−40keV}/erg s{sup −1})≈39 to 46, with a median of 44.1. Approximately 79% of the NuSTAR sources have lower-energy (<10 keV) X-ray counterparts from XMM-Newton, Chandra, and Swift XRT. The mid-infrared (MIR) analysis, using WISE all-sky survey data, shows that MIR AGN color selections miss a large fraction of the NuSTAR-selected AGN population, from ≈15% at the highest luminosities (L{sub X}>10{sup 44} erg s{sup −1}) to ≈80% at the lowest luminosities (L{sub X}<10{sup 43} erg s{sup −1}). Our optical spectroscopic analysis finds that the observed fraction of optically obscured AGNs (i.e., the type 2 fraction) is F{sub Type2}=53{sub −15}{sup +14}%, for a well-defined subset of the 8–24 keV selected sample. This is higher, albeit at a low significance level, than the type 2 fraction measured for redshift- and luminosity-matched AGNs selected by <10 keV X-ray missions.

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DOE OSTI2017

Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment

The grain growth process in the Caltech water–ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (i) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μ m, (ii) the major axis length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (i.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ∼0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Constraints on the Evolution of the Galaxy Stellar Mass Function. I. Role of Star Formation, Mergers, and Stellar Stripping

We study the connection between the observed star formation rate–stellar mass (SFR–M {sub *}) relation and the evolution of the stellar mass function (SMF) by means of a subhalo abundance matching technique coupled to merger trees extracted from an N-body simulation. Our approach, which considers both galaxy mergers and stellar stripping, is to force the model to match the observed SMF at redshift z>2, and let it evolve down to the present time according to the observed SFR–M {sub *} relation. In this study, we use two different sets of SMFs and two SFR–M {sub *} relations: a simple power law and a relation with a mass-dependent slope. Our analysis shows that the evolution of the SMF is more consistent with an SFR–M {sub *} relation with a mass-dependent slope, in agreement with predictions from other models of galaxy evolution and recent observations. In order to fully and realistically describe the evolution of the SMF, both mergers and stellar stripping must be considered, and we find that both have almost equal effects on the evolution of SMF at the massive end. Taking into account the systematic uncertainties in the observed data, the high-mass end of the SMF obtained by considering stellar stripping results in good agreement with recent observational data from the Sloan Digital Sky Survey. At log M{sub ∗}<11.2, our prediction at z = 0.1 is close to Li and White data, but the high-mass end (log M{sub ∗}>11.2) is in better agreement with D’Souza et al. data which account for more massive galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Energetics and Birth Rates of Supernova Remnants in the Large Magellanic Cloud

Published X-ray emission properties for a sample of 50 supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) are used as input for SNR evolution modeling calculations. The forward shock emission is modeled to obtain the initial explosion energy, age, and circumstellar medium density for each SNR in the sample. The resulting age distribution yields a SNR birthrate of 1/(500 yr) for the LMC. The explosion energy distribution is well fit by a log-normal distribution, with a most-probable explosion energy of 0.5×10{sup 51} erg, with a 1σ dispersion by a factor of 3 in energy. The circumstellar medium density distribution is broader than the explosion energy distribution, with a most-probable density of ∼0.1 cm{sup −3}. The shape of the density distribution can be fit with a log-normal distribution, with incompleteness at high density caused by the shorter evolution times of SNRs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Evolution of Dust-obscured Star Formation and Gas to z = 2.2 from HiZELS

We investigate the far-infrared (far-IR) properties of galaxies selected via deep, narrow-band imaging of the Hα emission line in four redshift slices from z=0.40--2.23 over ∼1 deg{sup 2} as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE far-IR bands, along with 850 μm imaging from SCUBA-2 and Very Large Array 1.4 GHz imaging, to study the evolution of the dust properties of Hα-emitters selected above an evolving characteristic luminosity threshold, 0.2L{sub Hα}{sup ⋆}(z). We investigate the relationship between the dust temperatures, T {sub dust}, and the far-infrared luminosities, L {sub IR}, of our stacked samples, finding that our Hα-selection identifies cold, low-L {sub IR} galaxies (T{sub dust}∼14 K; log[L{sub IR}/L{sub ⊙}]∼9.9) at z = 0.40, and more luminous, warmer systems (T{sub dust}∼34 K; log[L{sub IR}/L{sub ⊙}]∼11.5) at z = 2.23. Using a modified graybody model, we estimate “characteristic sizes” for the dust-emitting regions of Hα-selected galaxies of ∼0.5 kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy interstellar medium structure. Lastly, we use measurements of the dust masses from our far-IR stacking along with metallicity-dependent gas-to-dust ratios (δ{sub GDR}) to measure typical molecular gas masses of ∼1×10{sup 10} M{sub ⊙} for these bright Hα-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of Hα-selected galaxies, we find that typical star-forming galaxies brighter than 0.2L{sub Hα}{sup ⋆}(z) comprise a significant fraction (35 ± 10%) of the total gas content of the universe, consistent with the predictions of the latest state-of-the-art cosmological simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Revisiting the Bulge–Halo Conspiracy. I. Dependence on Galaxy Properties and Halo Mass

We carry out a systematic investigation of the total mass density profile of massive (log M{sub star}/M{sub ⊙}≳11.3) early-type galaxies and its dependence on galactic properties and host halo mass with the aid of a variety of lensing/dynamical data and large mock galaxy catalogs. The latter are produced via semi-empirical models that, by design, are based on just a few basic input assumptions. Galaxies with measured stellar masses, effective radii, and Sérsic indices, are assigned, via abundance matching relations, host dark matter halos characterized by a typical ΛCDM profile. Our main results are as follows. (1) In line with observational evidence, our semi-empirical models naturally predict that the total, mass-weighted density slope at the effective radius γ′ is not universal, steepening for more compact and/or massive galaxies, but flattening with increasing host halo mass. (2) Models characterized by a Salpeter or variable initial mass function (IMF) and uncontracted dark matter profiles are in good agreement with the data, while a Chabrier IMF and/or adiabatic contractions/expansions of the dark matter halos are highly disfavored. (3) Currently available data on the mass density profiles of very massive galaxies (log M{sub star}/M{sub ⊙}≳12), with M{sub halo}≳3×10{sup 14} M{sub ⊙}, favor instead models with a stellar profile flatter than a Sérsic one in the very inner regions (r ≲ 3–5 kpc), and a cored NFW or Einasto dark matter profile with median halo concentration a factor of ∼2 or ≲1.3, respectively, higher than those typically predicted by N-body numerical simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Grism Lens-Amplified Survey from Space (GLASS). XI. Detection of C iv in Multiple Images of the z = 6.11 Lyα Emitter behind RXC J2248.7–4431

The C iii] and C iv rest-frame UV emission lines are powerful probes of the ionization states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization (z>6), where the most frequently used redshift indicator, Lyα, is attenuated by the high fraction of neutral hydrogen in the intergalactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of C iv λλ1548, 1551 Å in Hubble Space Telescope slitless grism spectroscopy obtained by GLASS of a Lyα emitter at z = 6.11 multiply imaged by the massive foreground galaxy cluster RXC J2248.7–4431. The C iv emission is detected at the 3σ–5σ level in two images of the source, with marginal detection in two other images. We do not detect significant C iii]λλ1907, 1909 Å emission implying an equivalent width EW{sub CIII]}<20 Å (1σ) and C IV/C III>0.7 (2σ). Combined with limits on the rest-frame UV flux from the He ii λ1640 Å emission line and the O iii]λλ1661, 1666 Å doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits, including nebular emission lines, imply a source with a mass of log(M/M {sub ⊙}) ∼ 9, SFR of around 10 M {sub ⊙} yr{sup −1}, and a young stellar population <50 Myr old. The source shows a stronger ionizing radiation field than objects with detected C iv emission at z<2 and adds to the growing sample of low-mass (log(M/M {sub ⊙}) ≲ 9) galaxies at the epoch of reionization with strong radiation fields from star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Disk–Jet Connection in Active Supermassive Black Holes in the Standard Accretion Disk Regime

We study the disk–jet connection in supermassive black holes by investigating the properties of their optical and radio emissions utilizing the SDSS DR7 and the NVSS catalogs. Our sample contains 7017 radio-loud quasars with detection both at 1.4 GHz and SDSS optical spectra. Using this radio-loud quasar sample, we investigate the correlation among the jet power (${P}_{\mathrm{jet}}$), the bolometric disk luminosity (${L}_{\mathrm{disk}}$), and the black hole mass (${M}_{\mathrm{BH}}$) in the standard accretion disk regime. We find that the jet powers correlate with the bolometric disk luminosities as $\mathrm{log}{P}_{\mathrm{jet}}=(0.96\pm 0.012)\mathrm{log}{L}_{\mathrm{disk}}+(0.79\pm 0.55)$. This suggests the jet production efficiency of ${\eta }_{\mathrm{jet}}\simeq {1.1}_{-0.76}^{+2.6}\,\times {10}^{-2}$ assuming the disk radiative efficiency of 0.1, implying low black hole spin parameters and/or low magnetic flux for radio-loud quasars. But it can be also due to the dependence of this efficiency on the geometrical thickness of the accretion flow, which is expected to be small for quasars accreting at the disk Eddington ratios $0.01\lesssim \lambda \lesssim 0.3$. This low jet production efficiency does not significantly increase even if we set the disk radiative efficiency to be 0.3. We also investigate the fundamental plane in our samples among ${P}_{\mathrm{jet}}$, ${L}_{\mathrm{disk}}$, and ${M}_{\mathrm{BH}}$. In conclusion, we could not find a statistically significant fundamental plane for radio-loud quasars in the standard accretion regime.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

ALMA CO Clouds and Young Star Complexes in the Interacting Galaxies IC 2163 and NGC 2207

Atacama Large Millimeter Array (ALMA) observations of CO(1-0) emission in the interacting galaxies IC 2163 and NGC 2207 are used to determine the properties of molecular clouds and their association with star-forming regions observed with the Hubble Space Telescope. Half of the CO mass is in 249 clouds, each more massive than 4.0×10{sup 5} M{sub ⊙}. The mass distribution functions for the CO clouds and star complexes in a galactic-scale shock front in IC 2163 both have a slope on a log–log plot of −0.7, similar to what is observed in Milky Way clouds. The molecular cloud mass function is steeper in NGC 2207. The CO distribution in NGC 2207 also includes a nuclear ring, a mini-bar, and a mini-starburst region that dominates the 24 μm, radio, and Hα emission in both galaxies. The ratio of the sum of the masses of star complexes younger than 30 Myr to the associated molecular cloud masses is ∼4%. The maximum age of star complexes in the galactic-scale shock front in IC 2163 is about 200 Myr, the same as the interaction time of the two galaxies, suggesting the destruction of older complexes in the eyelids.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Steep Decay Phase Shaped by the Curvature Effect. I. Flux Evolution

The curvature effect may be responsible for the steep decay phase observed in gamma-ray bursts. To test the curvature effect with observations, the zero time point t {sub 0} adopted to plot the observer time and flux on a logarithmic scale should be appropriately selected. In practice, however, the true t {sub 0} cannot be directly constrained from the data. Thus, we move t {sub 0} to a certain time in the steep decay phase, which can be easily identified. In this situation, we derive an analytical formula to describe the flux evolution of the steep decay phase. The analytical formula reads as F{sub ν}∝(1+ t-tilde {sub obs}/ t-tilde {sub c}){sup −α}, with α( t-tilde {sub obs})=2+∫{sub 0}{sup log(1+ t-tilde {sub o}{sub b}{sub s}/ t-tilde {sub c})} β(τ)d[log(1+τ/ t-tilde {sub c})]/log(1+ t-tilde {sub obs}/ t-tilde {sub c}), where F {sub ν} is the flux observed at frequency ν, t-tilde {sub obs} is the observer time by setting t {sub 0} at a certain time in the steep decay phase, β is the spectral index estimated around ν, and t-tilde {sub c} is the decay timescale of the phase with t-tilde {sub obs}⩾0. We test the analytical formula with the data from numerical calculations. It is found that the analytical formula presents a good estimate of the evolution of the flux shaped by the curvature effect. Our analytical formula can be used to confront the curvature effect with observations and estimate the decay timescale of the steep decay phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Systematic Search for Hidden Type 1 AGNs: Gas Kinematics and Scaling Relations

We search type 1 active galactic nuclei (AGNs) among emission-line galaxies, that are typically classified as type 2 AGNs based on emission line flux ratios if a broad component in the Hα line profile is not properly investigated. Using ∼24,000 type 2 AGNs at z < 0.1, initially selected from Sloan Digital Sky Survey Data Release 7 by Bae and Woo, we identify a sample of 611 type 1 AGNs based on the spectral fitting results and visual inspection. These hidden type 1 AGNs have relatively low luminosity with a mean broad Hα luminosity, log L{sub Hα}=40.73 ±0.32 erg s{sup −1} and low Eddington ratio with a mean log L {sub bol}/L {sub Edd} = −2.04 ± 0.34, while they do follow the black hole mass–stellar velocity dispersion relation defined by the inactive galaxies and the reverberation-mapped type 1 AGNs. We investigate ionized gas outflows based on the [O III] λ5007 kinematics, which show relatively high velocity dispersion and velocity shift, indicating that the line-of-sight velocity and velocity dispersion of the ionized gas in type 1 AGNs is, on average, larger than that of type 2 AGNs.

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