Wide-field Infrared Survey Explorer Color Research Articles

The Baryonic Tully–Fisher Relation. I. WISE/Spitzer Photometry

We present Wide-field Infrared Survey Explorer (WISE) W1 photometry of the Spitzer Photometry and Accurate Rotation Curves sample. The baseline of near-IR fluxes is established for use by stellar mass models, a key component to the baryonic Tully–Fisher relation and other kinematic galaxies scaling relations. We focus this paper on determination of the characteristics of the W1 fluxes compared to IRAC 3.6 μm fluxes, internal accuracy limitations from photometric techniques, external accuracy by comparison to other work in the literature and the range of W1 to IRAC 3.6 μm colors. We outline the behavior of SDSS g, W1 and IRAC 3.6 colors with respect to underlying spectral energy distribution features. We also note a previously unknown correlation between WISE colors and the central surface brightness, probably related to the low metallicity of low-surface-brightness dwarfs.

Recognizing Blazars Using Radio Morphology from the VLA Sky Survey

Blazars are radio-loud active galactic nuclei whose jets have a very small angle to our line of sight. Observationally, the radio emissions are mostly compact or compact-core with a one-sided jet. With 2.″5 resolution at 3 GHz, the Very Large Array Sky Survey (VLASS) enables us to resolve the structure of some blazar candidates in the sky north of decl. −40°. We introduce an algorithm to classify radio sources as either blazar-like or non-blazar-like based on their morphology in the VLASS images. We apply our algorithm to three existing catalogs, including one of the known blazars (Roma-BzCAT) and two blazar candidates identified by Wide-field Infrared Survey Explorer colors and radio emission (WIBRaLS, KDEBLLACS). We show that in all three catalogs, there are objects with morphologies inconsistent with being blazars. Considering all the catalogs, more than 12% of the candidates are unlikely to be blazars, based on this analysis. Notably, we show that 3% of the Roma-BzCAT confirmed blazars could be a misclassification based on their VLASS morphology. The resulting table with all sources and their radio morphological classification is available online.

An Excess of Active Galactic Nuclei Triggered by Galaxy Mergers in MaNGA Galaxies of Stellar Mass ∼1011 M ⊙

To facilitate new studies of galaxy-merger-driven fueling of active galactic nuclei (AGNs), we present a catalog of 387 AGNs that we have identified in the final population of over 10,000 z < 0.15 galaxies observed by the Sloan Digital Sky Survey-IV (SDSS-IV) integral field spectroscopy survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). We selected the AGNs via mid-infrared Wide-field Infrared Survey Explorer colors, Swift/Burst Alert Telescope ultra-hard X-ray detections, NRAO Very Large Array Sky Survey and Faint Images of the Radio Sky at Twenty centimeters radio observations, and broad emission lines in SDSS spectra. By combining the MaNGA AGN catalog with a new SDSS catalog of galaxy mergers that were identified based on a suite of hydrodynamical simulations of merging galaxies, we study the link between galaxy mergers and nuclear activity for AGNs above a limiting bolometric luminosity of 1044.4 erg s−1. We find an excess of AGNs in mergers, relative to nonmergers, for galaxies with stellar mass ∼1011 M ⊙, where the AGN excess is somewhat stronger in major mergers than in minor mergers. Further, when we combine minor and major mergers and sort by merger stage, we find that the highest AGN excess occurs in post-coalescence mergers in the highest-mass galaxies. However, we find no evidence of a correlation between galaxy mergers and AGN luminosity or accretion rate. In summary, while galaxy mergers overall do appear to trigger or enhance AGN activity more than nonmergers, they do not seem to induce higher levels of accretion or higher luminosities. We provide the MaNGA AGN Catalog and the MaNGA Galaxy Merger Catalog for the community here.

Gaia17bpp: A Giant Star with the Deepest and Longest Known Dimming Event

We report the serendipitous discovery of Gaia17bpp/2MASS J19372316+1759029, a binary star with a deep single large-amplitude dimming event of ∼4.5 mag that lasted over 6.5 yr. Using the optical-to-IR spectral energy distribution (SED), we constrain the primary star to be a cool giant M0III star with effective temperature T eff = 3850 K and radius R = 58 R ⊙. Based on the SED fitting, we obtained a bimodal posterior distribution of primary stellar masses with a stronger preference for a 1.5 M ⊙ mass star. Within the last 66 yr of photometric coverage, no other significant dimming events of this depth and duration were identified in the optical light curves. Using a Gaussian process, we fit a generalized Gaussian distribution to the optical and IR light curves and conclude that the dimming event exhibits moderate asymmetries from optical to IR. At the minimum of the dimming event, the Wide-field Infrared Survey Explorer color (W1–W2) differed by ∼0.2 mag relative to the primary star color outside the dimming event. The ingress and egress colors show a shallow reddening profile. We suggest that the main culprit of the dimming event is likely due to the presence of a large, optically thick disk transiting the primary giant star. By fitting a monochromatic transit model of an oblate disk transiting a star, we found good agreement with a slow-moving (0.005 km s−1) disk with a ∼1.4 au radius. We propose that Gaia17bpp belongs to a rare binary star population similar to the ϵ Aurigae system, which consists of a secondary star enshrouded by an optically thick debris disk.

Revisiting X-Ray-bright Optically Normal Galaxies with the Chandra Source Catalog

X-ray bright optically normal galaxies (XBONGs) are galaxies with X-ray luminosities consistent with those of active galactic nuclei (AGNs) but no evidence of AGN optical emission lines. Crossmatching the Chandra Source Catalog version 2 with the Sloan Digital Sky Survey sample of spectroscopically classified galaxies, we have identified 817 XBONG candidates with L X > 1042 erg s−1 and X-ray to optical flux ratio F XO > 0.1. Comparisons with Wide-field Infrared Survey Explorer colors and near-IR, optical, UV, and radio luminosities show that the loci of XBONGs are in-between those of control samples of normal galaxies and quasars and are consistent with low-luminosity quasars. We find that 43% of the XBONG sample have X-ray colors suggesting N H > 1022 cm−2, double the fraction in the QSO sample, suggesting that a large fraction of XBONG are highly obscured AGNs. However, ∼50% of the XBONGs are not obscured and have X-ray colors harder than those of normal galaxies. Some of these XBONGs have spatially extended X-ray emission. These characteristics suggest that they may be unidentified galaxy groups and clusters. Using the X-ray luminosity functions of QSOs, galaxies, groups and clusters, we estimate the approximate fraction of extended XBONGs to be <20%. We also assess the approximate fraction of XBONGs whose AGN signatures are diluted by stellar light of host galaxies to be ∼30%, based on their redshift and deviation from the extrapolation of the QSO L X–L r relation.

The Chandra Source Catalog Normal Galaxy Sample

We present the extensive and well-characterized Chandra X-ray Galaxy Catalog (CGC) of 8547 galaxy candidates in the redshift range z ∼ 0.04–0.7, optical luminosity 1010–1011 Lr ⊙, and X-ray luminosity (0.5–7 keV) L X = 2 × 1040–2 × 1043 erg s−1. We estimate a ∼5% false-match fraction and contamination by quasi-stellar objects (QSOs). The CGC was extracted from the Chandra Source Catalog version 2 (CSC2) by cross-correlating with optical and IR all-sky survey data, including the Sloan Digital Sky Survey, Pan-STARRS, DESI Legacy, and Wide-field Infrared Survey Explorer (WISE). Our selection makes use of two main criteria that we have tested on the subsample with optical spectroscopical identification. (1) A joint selection based on X-ray luminosity (L X) and X-ray-to-optical flux ratio (F XO), which recovers 63% of the spectroscopically classified galaxies with a small contamination fraction (7%), which is a significant improvement over methods using L X or F XO alone (<50% recovery). (2) A joint W1–W2 (W12) WISE color and L X selection that proves effective in excluding QSOs and improves our selection by recovering 72% of the spectroscopically classified galaxies and reducing the contamination fraction (4%). Of the CGC, 24% was selected by means of optical spectroscopy; 30% on the basis of L X, F XO, and W12; and 46% by using either the L X–F XO or the L X–W12 selection criteria. We have individually examined the data for galaxies with z < 0.1, which may include more than one CSC2 X-ray source, leading to the exclusion of 110 local galaxies. Our catalog also includes near-IR and UV data and galaxy morphological types.

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

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

A New Infrared Criterion for Selecting Active Galactic Nuclei to Lower Luminosities

We present a spectroscopic and photometric analysis of a sample of 416,288 galaxies from the Sloan Digital Sky Survey (SDSS) matched to mid-infrared (mid-IR) data from the Wide-field Infrared Survey Explorer (WISE). By using a new spectroscopic fitting package, GELATO (Galaxy/AGN Emission Line Analysis TOol), we are able to retrieve emission line fluxes and uncertainties for SDSS spectra and robustly determine the presence of broad lines and outflowing components, enabling us to investigate WISE color space as a function of optical spectroscopic properties. In addition, we pursue spectral energy distribution template fitting to assess the relative active galactic nucleus (AGN) contribution and nuclear obscuration to compare to existing mid-IR selection criteria with WISE. We present a selection criterion in mid-IR color space to select AGNs with an ∼80% accuracy and a completeness of ∼16%. This is the first mid-IR color selection defined by solely using the distribution of Type I and Type II optical spectroscopic AGNs in WISE mid-IR color space. Our selection is an improvement of ∼50% in the completeness of targeting spectroscopic AGNs with WISE down to an SDSS r < 17.77 mag. In addition, our new criterion targets a less-luminous population of AGNs, with on average lower [O iii] luminosities by ∼30% ( > 0.1 dex) compared to typical WISE color–color selections. With upcoming large photometric surveys without corresponding spectroscopy, our method presents a way to select larger populations of AGNs at lower AGN luminosities and higher nuclear obscuration levels than traditional mid-IR color selections.

Classifying Blazar Candidates from the 3FGL Unassociated Catalog into BL Lacertae Objects and Flat Spectrum Radio Quasars Using Swift and WISE Data

Abstract We utilize machine-learning methods to distinguish BL Lacertae (BL Lac) objects from flat spectrum radio quasars (FSRQs) within a sample of likely X-ray blazar counterparts to Fermi 3FGL unassociated gamma-ray sources. From our previous work, we have extracted 84 sources that were classified as ≥99% likely to be blazars. We then utilize Swift-XRT, Fermi, and The Wide-field Infrared Survey Explorer (WISE) data together to distinguish the specific type of blazar, FSRQs, or BL Lac objects. Various X-ray and gamma-ray parameters can be used to differentiate between these subclasses. These are also known to occupy different parameter space on the WISE color–color diagram. Using all these data together would provide more robust results for the classified sources. We utilized a random forest classifier to calculate the probability for each blazar to be associated with a BL Lac object or an FSRQ. Based on P bll, which is the probability for each source to be a BL Lac object, we placed our sources into five different categories based on this value as follows: P bll ≥ 99%: highly likely BL Lac object, P bll ≥ 90%: likely BL Lac object, P bll ≤ 1%: highly likely FSRQ, P bll ≤ 10%: likely FSRQ, and 90% &lt; P bll &lt; 10%: ambiguous. Our results categorize the 84 blazar candidates as 50 likely BL Lac objects and the other 34 as being ambiguous. A small subset of these sources have been listed as associated sources in the most recent Fermi catalog, 4FGL, and in these cases our results are in agreement on the classification.

Galaxy and Mass Assembly (GAMA): A WISE Study of the Activity of Emission-line Systems in G23

Abstract We present a detailed study of emission-line systems in the Galaxy And Mass Assembly (GAMA) G23 region, making use of Wide-field Infrared Survey Explorer (WISE) photometry that includes carefully measured resolved sources. After applying several cuts to the initial catalog of ∼41,000 galaxies, we extract a sample of 9809 galaxies. We then compare the spectral diagnostic Baldwin, Philips &amp; Terlevich (BPT) classification of 1154 emission-line galaxies (38% resolved in W1) to their location in the WISE color–color diagram, leading to the creation of a new zone for mid-infrared “warm” galaxies located 2σ above the star-forming sequence, below the standard WISE active galactic nucleus (AGN) region. We find that the BPT and WISE diagrams agree on the classification for 85% and 8% of the galaxies as non-AGN (star-forming = SF) and AGN, respectively, and disagree on ∼7% of the entire classified sample. Thirty-nine percent of the AGNs (all types) are broad-line systems for which the [N ii] and [Hα] fluxes can barely be disentangled, giving in most cases spurious [N ii]/[Hα] flux ratios. However, several optical AGNs appear to be completely consistent with SF in WISE. We argue that these could be low-power AGNs, or systems whose hosts dominate the IR emission. Alternatively, given the sometimes high [O iii] luminosity in these galaxies, the emission lines may be generated by shocks coming from super-winds associated with SF rather than AGN activity. Based on our findings, we have created a new diagnostic: [W1 – W2] versus [N ii]/[Hα], which has the virtue of separating SF from AGNs and high-excitation sources. It classifies 3 to ∼5 times more galaxies than the classic BPT.

A Catalog of 406 AGNs in MaNGA: A Connection between Radio-mode AGNs and Star Formation Quenching

Abstract Accurate active galactic nucleus (AGN) identifications and spatially resolved host galaxy properties are a powerful combination for studies of the role of AGNs and AGN feedback in the coevolution of galaxies and their central supermassive black holes. Here, we present robust identifications of 406 AGNs in the first 6261 galaxies observed by the integral field spectroscopy survey Mapping Nearby Galaxies at Apache Point Observatory. Instead of using optical line flux ratios, which can be difficult to interpret in light of the effects of shocks and metallicity, we identify the AGNs via mid-infrared Wide-field Infrared Survey Explorer colors, Swift/BAT ultrahard X-ray detections, NVSS and FIRST radio observations, and broad emission lines in SDSS spectra. We subdivide the AGNs into radio-quiet and radio-mode AGNs, and examine the correlations of the AGN classes with host galaxy star formation rates and stellar populations. When compared to the radio-quiet AGN host galaxies, we find that the radio-mode AGN host galaxies are preferentially elliptical, lie further beneath the star-forming main sequence (with lower star formation rates at fixed galaxy mass), have older stellar populations, and have more negative stellar age gradients with galactocentric distance (indicating inside-out quenching of star formation). These results establish a connection between radio-mode AGNs and the suppression of star formation.

Galaxy and Mass Assembly (GAMA): Demonstrating the Power of WISE in the Study of Galaxy Groups to z &lt; 0.1

Abstract Combining high-fidelity group characterization from the Galaxy and Mass Assembly survey and source-tailored z &lt; 0.1 photometry from the Wide-Field Infrared Survey Explorer (WISE) survey, we present a comprehensive study of the properties of ungrouped galaxies, compared to 497 galaxy groups (4 ≤ N FoF ≤ 20) as a function of stellar and halo mass. Ungrouped galaxies are largely unimodal in WISE color, the result of being dominated by star-forming, late-type galaxies. Grouped galaxies, however, show a clear bimodality in WISE color, which correlates strongly with stellar mass and morphology. We find evidence for an increasing early-type fraction, in stellar mass bins between 1010 M ⊙ ≲ M stellar ≲ 1011 M ⊙, with increasing halo mass. Using ungrouped, late-type galaxies with star-forming colors (W2−W3 &gt; 3), we define a star-forming main sequence (SFMS), which we use to delineate systems that have moved below the sequence (“quenched” for the purposes of this work). We find that with increasing halo mass, the relative number of late-type systems on the SFMS decreases, with a corresponding increase in early-type, quenched systems at high stellar mass (M stellar &gt; 1010.5 M ⊙), consistent with mass quenching. Group galaxies with masses M stellar &lt; 1010.5 M ⊙ show evidence of quenching consistent with environmentally driven processes. The stellar mass distribution of late-type, quenched galaxies suggests that it may be an intermediate population as systems transition from being star-forming and late-type to the “red sequence.” Finally, we use the projected area of groups on the sky to extract groups that are (relatively) compact for their halo mass. Although these show a marginal increase in their proportion of high-mass and early-type galaxies compared to nominal groups, a clear increase in quenched fraction is not evident.

SDSS-IV eBOSS Spectroscopy of X-Ray and WISE AGNs in Stripe 82X: Overview of the Demographics of X-Ray- and Mid-infrared-selected Active Galactic Nuclei

Abstract We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8 deg2 region of Stripe 82. About half this survey (15.6 deg2) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r ∼ 22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z ∼ 1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z &lt; 0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (L x &gt; 1044 erg s−1), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ∼58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.

Discovery of 21 New Changing-look AGNs in the Northern Sky

Abstract The rare case of changing-look (CL) active galactic nuclei (AGNs), with the appearance or disappearance of broad Balmer emission lines within a few years, challenges our understanding of the AGN unified model. We present a sample of 21 new CL AGNs at 0.08 &lt; z &lt; 0.58 , which doubles the number of such objects known to date. These new CL AGNs were discovered in various ways, from (1) repeat spectra in the SDSS, (2) repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and SDSS, and (3) photometric variability and new spectroscopic observations. We use the photometric data from surveys, including the SDSS imaging survey, the Pan-STARRS1, the DESI Legacy imaging survey, the Wide-field Infrared Survey Explorer (WISE), the Catalina Real-time Transient Survey, and the Palomar Transient Factory. The estimated upper limits of the transition timescale of the CL AGNs in this sample spans from 0.9 to 13 years in the rest-frame. The continuum flux in the optical and mid-infrared becomes brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2 mag in the W1 band were detected in 15 CL AGNs during the transition. The optical and mid-infrared variability is not consistent with the scenario of variable obscuration in 10 CL AGNs at more than the 3σ confidence level. We confirm a bluer-when-brighter trend in the optical. However, the mid-infrared WISE colors W1–W2 become redder when the objects become brighter in the W1 band, possibly due to a stronger hot dust contribution in the W2 band when the AGN activity becomes stronger. The physical mechanism of type transition is important for understanding the evolution of AGNs.

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Abstract Through the modeling of near-infrared photometry of star-plus disk systems with the codes bedisk/beray, we successfully describe the Wide-Field Infrared Survey Explorer (WISE) photometric characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC 884, NGC 3766, and NGC 4755, broadly studied in the literature. WISE photometry allows previously known Be stars to be detected and to find new Be candidates which could be confirmed spectroscopically. The location of Be stars in the WISE color–magnitude diagram, separates them in two groups; active (Be stars hosting a developed circumstellar disk) and quiescent objects (Be stars in a diskless phase), and this way, we can explore how often stars are observed in these different stages. The variability observed in most active variable Be stars is compatible with a disk dissipation phase. We find that 50% of Be stars in the studied open clusters are in an active phase. We can interpret this as Be stars having a developed circumstellar disk one-half of the time. The location of Be stars with a developed disk in the color–magnitude diagram require mass loss rates in agreement with values recently reported in the literature. For these objects, we expect to have a tight relation between the equivalent width of the Hα line and the mass of the disk, if the inclination is known. Also, near-infrared photometry of Be stars in stellar clusters has the potential of being useful to test whether there is a preferential viewing angle.

Star Formation Activity Beyond the Outer Arm. I. WISE-selected Candidate Star-forming Regions

Abstract The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at R G ≥ 13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer (WISE) mid-infrared all-sky survey. From their color distribution, we developed a simple identification criterion of star-forming regions in the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at R G ≥ 13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) 12CO survey of the outer Galaxy, of which the survey region is 102.°49 ≤ l ≤ 141.°54, −3.°03 ≤ b ≤ 5.°41, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star formation properties, including star formation rate, star formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.

Galaxy and Mass Assembly (GAMA): Exploring the WISE Web in G12

Abstract We present an analysis of the mid-infrared Wide-field Infrared Survey Explorer (WISE) sources seen within the equatorial GAMA G12 field, located in the North Galactic Cap. Our motivation is to study and characterize the behavior of WISE source populations in anticipation of the deep multiwavelength surveys that will define the next decade, with the principal science goal of mapping the 3D large-scale structures and determining the global physical attributes of the host galaxies. In combination with cosmological redshifts, we identify galaxies from their WISE W1 (3.4 μm) resolved emission, and we also perform a star-galaxy separation using apparent magnitude, colors, and statistical modeling of star counts. The resulting galaxy catalog has ≃590,000 sources in 60 deg2, reaching a W1 5σ depth of 31 μJy. At the faint end, where redshifts are not available, we employ a luminosity function analysis to show that approximately 27% of all WISE extragalactic sources to a limit of 17.5 mag (31 μJy) are at high redshift, . The spatial distribution is investigated using two-point correlation functions and a 3D source density characterization at 5 Mpc and 20 Mpc scales. For angular distributions, we find that brighter and more massive sources are strongly clustered relative to fainter sources with lower mass; likewise, based on WISE colors, spheroidal galaxies have the strongest clustering, while late-type disk galaxies have the lowest clustering amplitudes. In three dimensions, we find a number of distinct groupings, often bridged by filaments and superstructures. Using special visualization tools, we map these structures, exploring how clustering may play a role with stellar mass and galaxy type.

A Study of Quasar Selection in the Supernova Fields of the Dark Energy Survey

Abstract We present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid-IR color, a mixture of WISE and DES colors (g − i and ), and a mixture of Vista Hemisphere Survey and DES colors (g − i and i − K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ 2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i &lt; 19.8 mag and i &lt; 22 mag. For the subset of sources with W1 and W2 detections, the color or XDQSOz method combined with variability gives the highest completenesses of &gt;85% for both i-band magnitude limits and efficiencies of &gt;80% to the bright limit and &gt;60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg2 of the DES supernova fields. The catalog includes quasars with redshifts up to z ∼ 4 and brighter than i = 22 mag, although the catalog is not complete up to this magnitude limit.

A WISE CENSUS OF YOUNG STELLAR OBJECTS IN CANIS MAJOR

ABSTRACT With the Wide-field Infrared Survey Explorer (WISE), we searched for young stellar objects (YSOs) in a 100 deg2 region centered on the lightly studied Canis Major star-forming region. Applying stringent magnitude cuts to exclude the majority of extragalactic contaminants, we find 144 Class I candidates and 335 Class II candidates. The sensitivity to Class II candidates is limited by their faintness at the distance to Canis Major (assumed as 1000 pc). More than half the candidates (53%) are found in 16 groups of more than four members, including four groups with more than 25 members each. The ratio of Class II to Class I objects, N II/N I, varies from 0.4 to 8.3 in just the largest four groups. We compare our results to those obtainable with combined Two Micron All Sky Survey and post-cryogenic Spitzer Space Telescope data; the latter approach recovers missing Class II sources. Via a comparison to protostars characterized with the Herschel Space Observatory, we propose new WISE color criteria for flat-spectrum and Class 0 protostars, finding 80 and 7 of these, respectively. The distribution of YSOs in CMa OB1 is consistent with supernova-induced star formation, although the diverse N II/N I ratios are unexpected if this parameter traces age and the YSOs are due to the same supernova. Less massive clouds feature larger N II/N I ratios, suggesting that initial conditions play a role in determining this quantity.

Mid-infrared dust in two nearby radio galaxies, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36)

Most radio galaxies are hosted by giant gas-poor ellipticals, but some contain significant amounts of dust, which is likely to be of external origin. In order to characterize the mid-IR properties of two of the most nearby and brightest merger-remnant radio galaxies of the Southern hemisphere, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36), we used observations with the Wide-field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12 and 22 micron and Spitzer mid-infrared spectra. By applying a resolution-enhancement technique, new WISE images were produced at angular resolutions ranging from 2.6" to 5.5". Global measurements were performed in the four WISE bands, and stellar masses and star-formation rates were estimated using published scaling relations. Two methods were used to uncover the distribution of dust, one relying on two-dimensional fits to the 3.4 micron images to model the starlight, and the other one using a simple scaling and subtraction of the 3.4 micron images to estimate the stellar continuum contribution to the emission in the 12 and 22 micron bands. The two galaxies differ markedly in their mid-IR properties. The 3.4 micron brightness distribution can be well represented by the superposition of two Sersic models in NGC 1316 and by a Sersic model and an exponential disk in NGC 612. The WISE colors of NGC 1316 are typical of those of early-type galaxies; those of NGC 612 are in the range found for star-forming galaxies. From the 22 micron luminosity, we infer a star-formation rate of about 0.7 solar masses per year in NGC 1316 and about 7 solar masses per year in NGC 612. Spitzer spectroscopy shows that the 7.7-to-11.3 micron PAH line ratio is significantly lower in NGC 1316 than in NGC 612. The WISE images reveal resolved emission from dust in the central 1'-2' of the galaxies. (Abridged)