Dissecting Photometric Redshift for Active Galactic Nucleus Using XMM- and Chandra-COSMOS Samples

In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy σ_(Δz/(1+z(spec))~0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg^2 of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Δz > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H_(AB) = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band

Numerical modelling of drawbeads for forming of aluminium alloys

The drawbeads in stamping tools are usually designed based on experience from the forming of steel. However, aluminium alloys display different forming behaviour to steels, which is not reflected in the drawbead design for tools used for stamping aluminium. This paper presents experimental results from different semi-circular drawbead geometries commonly encountered in automotive dies and compares them to those obtained from Stoughton's analytical drawbead model and the 2D plane strain drawbead model set up using LS-DYNA. The study was conducted on lubricated NG5754 strips. The results presented are in terms of drawbead restraining force versus strip displacement, as a function of drawbead depth. The FE drawbead model agrees well with the experiments whereas the analytical model overpredicted the drawbead forces

The Megamaser Cosmology Project: IV. A Direct Measurement of the Hubble Constant from UGC 3789

In Papers I and II from the Megamaser Cosmology Project (MCP), we reported initial observations of water masers in an accretion disk of a supermassive black hole at the center of the galaxy UGC 3789, which gave an angular-diameter distance to the galaxy and an estimate of Ho with 16% uncertainty. We have since conducted more VLBI observations of the spatial-velocity structure of these water masers, as well as continued monitoring of its spectrum to better measure maser accelerations. These more extensive observations, combined with improved modeling of the masers in the accretion disk of the central supermassive black hole, confirm our previous results, but with signifcantly improved accuracy. We find Ho = 68.9 +/- 7.1 km/s/Mpc; this estimate of Ho is independent of other methods and is accurate to +/-10%, including sources of systematic error. This places UGC 3789 at a distance of 49.6 +/- 5.1 Mpc, with a central supermassive black hole of (1.16 +/- 0.12) x 10^7 Msun.Comment: to appear in Ap

The Quasar-LBG Two-point Angular Cross-correlation Function at z ~ 4 in the COSMOS Field

In order to investigate the origin of quasars, we estimate the bias factor for low-luminosity quasars at high redshift for the first time. In this study, we use the two-point angular cross-correlation function (CCF) for both low-luminosity quasars at $-24<M_{\rm 1450}<-22$ and Lyman-break galaxies (LBGs). Our sample consists of both 25 low-luminosity quasars (16 objects are spectroscopically confirmed low-luminosity quasars) in the redshift range $3.1<z<4.5$ and 835 color-selected LBGs with $z^{\prime}_{\rm LBG}<25.0$ at $z\sim4$ in the COSMOS field. We have made our analysis for the following two quasar samples; (1) the spectroscopic sample (the 16 quasars confirmed by spectroscopy), and (2) the total sample (the 25 quasars including 9 quasars with photometric redshifts). The bias factor for low-luminosity quasars at $z\sim4$ is derived by utilizing the quasar-LBG CCF and the LBG auto-correlation function. We then obtain the $86\%$ upper limits of the bias factors for low-luminosity quasars, that are 5.63 and 10.50 for the total and the spectroscopic samples, respectively. These bias factors correspond to the typical dark matter halo masses, log $(M_{\rm DM}/(h^{-1}M_{\odot}))=$$12.7$ and $13.5$, respectively. This result is not inconsistent with the predicted bias for quasars which is estimated by the major merger models.Comment: 13 pages, 9 figures, Accepted for publication in Ap

Rest-UV Absorption Lines as Metallicity Estimator: the Metal Content of Star-Forming Galaxies at z~5

We measure a relation between the depth of four prominent rest-UV absorption complexes and metallicity for local galaxies and verify it up to z~3. We then apply this relation to a sample of 224 galaxies at 3.5 = 4.8) in COSMOS, for which unique UV spectra from DEIMOS and accurate stellar masses from SPLASH are available. The average galaxy population at z~5 and log(M/Msun) > 9 is characterized by 0.3-0.4 dex (in units of 12+log(O/H)) lower metallicities than at z~2, but comparable to z~3.5. We find galaxies with weak/no Ly-alpha emission to have metallicities comparable to z~2 galaxies and therefore may represent an evolved sub-population of z~5 galaxies. We find a correlation between metallicity and dust in good agreement with local galaxies and an inverse trend between metallicity and star-formation rate (SFR) consistent with observations at z~2. The relation between stellar mass and metallicity (MZ relation) is similar to z~3.5, however, there are indications of it being slightly shallower, in particular for the young, Ly-alpha emitting galaxies. We show that, within a "bathtub" approach, a shallower MZ relation is expected in the case of a fast (exponential) build-up of stellar mass with an e-folding time of 100-200 Myr. Due to this fast evolution, the process of dust production and metal enrichment as a function of mass could be more stochastic in the first billion years of galaxy formation compared to later times.Comment: 20 pages, 13 figures, 4 tables; Submitted to Ap

Novel organic photovoltaic polymer blends: A rapid, 3-dimensional morphology analysis using backscattered electron imaging in the scanning electron microscope

Finding the optimal morphology of novel organic photovoltaic (OPV) polymer blends is a major obstacle slowing the development of more efficient OPV devices. With a focus on accelerating the systematic morphology optimisation process, we demonstrate a technique offering rapid high-resolution, 3-dimensional blend morphology analysis in the scanning electron microscope. This backscattered electron imaging technique is used to investigate the morphological features and lengthscales defining the promising PffBT4T-2OD:PC70BM blend system and show how its photovoltaic performance is related to the nature of its phase separation. Low-voltage backscattered electron imaging can be used to probe for structure and domain stacking through the thickness of the film, as well as imaging surface morphology with highly competitive spatial resolution. For reference, we compare our results with equivalent images of the widely studied P3HT:PC60BM blend system. Our results also demonstrate that backscattered electron imaging offers significant advantages over conventional cross-sectional imaging techniques, and show that it enables a fast, systematic approach to control 3-dimensional active layer morphology in polymer:fullerene blends

Quantitative secondary electron imaging for work function extraction at atomic level and layer identification of graphene

Two-dimensional (2D) materials usually have a layer-dependent work function, which require fast and accurate detection for the evaluation of their device performance. A detection technique with high throughput and high spatial resolution has not yet been explored. Using a scanning electron microscope, we have developed and implemented a quantitative analytical technique which allows effective extraction of the work function of graphene. This technique uses the secondary electron contrast and has nanometre-resolved layer information. The measurement of few-layer graphene flakes shows the variation of work function between graphene layers with a precision of less than 10meV. It is expected that this technique will prove extremely useful for researchers in a broad range of fields due to its revolutionary throughput and accuracy

The DEIMOS 10k spectroscopic survey catalog of the COSMOS field

We present a catalog of 10718 objects in the COSMOS field observed through multi-slit spectroscopy with the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope in the wavelength range ~5500-9800A. The catalog contains 6617 objects with high-quality spectra (two or more spectral features), and 1798 objects with a single spectroscopic feature confirmed by the photometric redshift. For 2024 typically faint objects we could not obtain reliable redshifts. The objects have been selected from a variety of input catalogs based on multi-wavelength observations in the field, and thus have a diverse selection function, which enables the study of the diversity in the galaxy population. The magnitude distribution of our objects is peaked at I_AB~23 and K_AB~21, with a secondary peak at K_AB~24. We sample a broad redshift distribution in the range 0<z<6, with one peak at z~1, and another one around z~4. We have identified 13 redshift spikes at z>0.65 with chance probabilities <4xE-4$, some of which are clearly related to protocluster structures of sizes >10 Mpc. An object-to-object comparison with a multitude of other spectroscopic samples in the same field shows that our DEIMOS sample is among the best in terms of fraction of spectroscopic failures and relative redshift accuracy. We have determined the fraction of spectroscopic blends to about 0.8% in our sample. This is likely a lower limit and at any rate well below the most pessimistic expectations. Interestingly, we find evidence for strong lensing of Ly-alpha background emitters within the slits of 12 of our target galaxies, increasing their apparent density by about a factor of 4.Comment: 28 pages, 11 figures and 5 tables. The full catalogue table is available on http://cosmos.astro.caltech.edu. Accepted for publication in the Astrophysical Journa

SDSS IV MaNGA: Dependence of Global and Spatially Resolved SFR-M ∗ Relations on Galaxy Properties

Indexación: Scopus.The galaxy integrated Hα star formation rate-stellar mass relation, or SFR(global)-M ∗(global) relation, is crucial for understanding star formation history and evolution of galaxies. However, many studies have dealt with SFR using unresolved measurements, which makes it difficult to separate out the contamination from other ionizing sources, such as active galactic nuclei and evolved stars. Using the integral field spectroscopic observations from SDSS-IV MaNGA, we spatially disentangle the contribution from different Hα powering sources for ∼1000 galaxies. We find that, when including regions dominated by all ionizing sources in galaxies, the spatially resolved relation between Hα surface density (ΣHα(all)) and stellar mass surface density (Σ∗(all)) progressively turns over at the high Σ∗(all) end for increasing M ∗(global) and/or bulge dominance (bulge-to-total light ratio, B/T). This in turn leads to the flattening of the integrated Hα(global)-M ∗(global) relation in the literature. By contrast, there is no noticeable flattening in both integrated Hα(H ii)-M ∗(H ii) and spatially resolved ΣHα(H ii)-Σ∗(H ii) relations when only regions where star formation dominates the ionization are considered. In other words, the flattening can be attributed to the increasing regions powered by non-star-formation sources, which generally have lower ionizing ability than star formation. An analysis of the fractional contribution of non-star-formation sources to total Hα luminosity of a galaxy suggests a decreasing role of star formation as an ionizing source toward high-mass, high-B/T galaxies and bulge regions. This result indicates that the appearance of the galaxy integrated SFR-M ∗ relation critically depends on their global properties (M ∗(global) and B/T) and relative abundances of various ionizing sources within the galaxies.http://iopscience.iop.org/article/10.3847/1538-4357/aaa9bc/met

Constraints on the faint end of the quasar luminosity function at z~5 in the COSMOS field

We present the result of our low-luminosity quasar survey in the redshift range of 4.5 < z < 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i' < 24 at z~5, that are ~ 3 mag fainter than the SDSS quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z~5 while a low-luminosity type-2 quasar at z~5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z~5, we calculated the 1sigma confidence upper limits of the space density of type-1 quasars. As a result, the 1sigma confidence upper limits on the quasar space density are Phi< 1.33*10^{-7} Mpc^{-3} mag^{-1} for -24.52 < M_{1450} < -23.52 and Phi< 2.88*10^{-7} Mpc^{-3} mag^{-1} for -23.52 < M_{1450} < -22.52. The inferred 1sigma confidence upper limits of the space density are then used to provide constrains on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z~5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M_{1450} ~ -23), being similar to the trend found for quasars with high luminosity (M_{1450}<-26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts.Comment: 8 pages, 9 figures, 1 table, accepted for publication in Ap