Wide-field Infrared Survey Explorer W1 Research Articles

A Closer Look at Dwarf Galaxies Exhibiting Mid-infrared Variability: Active Galactic Nuclei Confirmation and Comparison With Nonvariable Dwarf Galaxies

Detecting active black holes in dwarf galaxies has proven to be a challenge due to their small size and weak electromagnetic signatures. Mid-infrared variability has emerged as a promising tool that can be used to detect active low-mass black holes in dwarf galaxies. We analyzed 10.4 yr of photometry from the AllWISE/NEOWISE multiepoch catalogs, identifying 25 objects with active galactic nuclei (AGN)-like variability. Independent confirmation of AGN activity was found in 68% of these objects using optical and near-infrared diagnostics. Notably, we discover a near-infrared coronal line [S ix] λ 1.252 μm in J1205, the galaxy with the lowest stellar mass (log M * = 7.5 M ⊙) and low metallicity (12 + log(O/H) = 7.46) in our sample. Additionally, we find broad Paα potentially from the broad-line region in two targets, and their implied black hole masses are consistent with black hole-stellar mass relations. Comparing nonvariable galaxies with similar stellar masses and Wide-field Infrared Survey Explorer W1 − W2 colors, we find no clear trends between variability and large-scale galaxy properties. However, we find that AGN activity likely causes redder W1 − W2 colors in variable targets, while for the nonvariable galaxies, the contribution stems from strong star formation activity. A high incidence of optical broad lines was also observed in variable targets. Our results suggest that mid-infrared variability is an effective method for detecting AGN activity in low-mass galaxies and can help uncover a larger sample of active low-mass (<106 M ⊙) black holes in the Universe.

Measurement of the evolving galaxy luminosity and mass function using clustering-based redshift inference

ABSTRACT We develop a framework for using clustering-based redshift inference (cluster-$z$ ) to measure the evolving galaxy luminosity function (GLF) and galaxy stellar mass function (GSMF) using Wide-field Infrared Survey Explorer W1 (3.4 μm) mid-infrared photometry and positions. We use multiple reference sets from the Galaxy And Mass Assembly survey, Sloan Digital Sky Survey and Baryon Oscillation Spectroscopic Survey. Combining the resulting cluster-$z$ s allows us to enlarge the study area, and by accounting for the specific properties of each reference set, making best use of each reference set to produce the best overall result. Thus we are able to measure the GLF and GSMF over ∼7500 deg2 of the Northern Galactic Cap up to $z$ &amp;lt; 0.6. Our method can easily be adapted for new studies with fainter magnitudes, which pose difficulties for the derivation of photo-$z$ s. With better statistics in future surveys this technique is a strong candidate for studies with new emerging data from, e.g. the Vera C Rubin Observatory, the Euclid mission or the Nancy Grace Roman Space Telescope.

A New Wide-field Infrared Survey Explorer Calibration of Stellar Mass

We derive new empirical scaling relations between Wide-field Infrared Survey Explorer (WISE) mid-IR (MIR) galaxy photometry and well-determined stellar masses from spectral energy distribution modeling of a suite of optical–infrared photometry provided by the Data Release 4 (DR4) Catalog of the GAMA-KiDS-VIKING survey of the southern G23 field. The MIR source extraction and characterization are drawn from the WISE Extended Source Catalogue and the archival ALLWISE catalog, combining both resolved and compact galaxies in the G23 sample to a redshift of 0.15. Three scaling relations are derived: W1 3.4 μm luminosity versus stellar mass, and WISE W1–W2, W1–W3 colors versus mass-to-light ratio (M/L, sensitive to a variety of galaxy types from passive to star-forming). For each galaxy in the sample, we then derive the combined stellar mass from these scaling relations, producing M ⋆ estimates with better than ∼25%–30% accuracy for galaxies with >109 M ⊙ and <40%–50% for lower-luminosity dwarf galaxies. We also provide simple prescriptions for rest-frame corrections and estimating stellar masses using only the W1 flux and the W1–W2 color, making stellar masses more accessible to users of the WISE data. Given a redshift or distance, these new scaling relations will enable stellar mass estimates for any galaxy in the sky detected by WISE with high fidelity across a range of M/L ratios.

Galaxy and Mass Assembly (GAMA)

Aims. We investigate how different mid-infrared (mid-IR) properties of galaxies are correlated with the environment in which the galaxies are located. For this purpose, we first study the dependence of galaxy clustering on the absolute magnitude at 3.4 μm and redshift. Then, we look into the environmental dependence of mid-IR luminosities and the galaxy properties derived from these luminosities. We also explore how various IR galaxy luminosity selections influence the galaxy clustering measurements. Methods. We used a set of W1 (3.4 μm) absolute magnitude (MW1) selected samples from the Galaxy and Mass Assembly (GAMA) survey matched with mid-IR properties from the Wide-field Infrared Survey Explorer (WISE) in the redshift range 0.07 ≤ z &lt; 0.43. We computed the galaxy two-point correlation function (2pCF) and compared the clustering lengths between subsamples binned in MW1 and in redshift. We also measured the marked correlation function (MCF), in which the galaxies are weighted by marks when measuring clustering statistics, using the luminosities in the WISE W1 to W4 (3.4 to 22 μm) bands as marks. Additionally, we compared the measurements of MCFs with different estimates of stellar mass and star formation rate (SFR) used as marks. Finally, we checked how different selections applied to the sample affect the clustering measurements. Results. We show strong clustering dependence on the W1 absolute magnitude: galaxies brighter in the W1 band are more strongly clustered than their fainter counterparts. We also observe a lack of significant redshift dependence of clustering in the redshift range 0.07 ≤ z &lt; 0.43. We show that although the W1 and W2 bands are direct indicators of stellar mass, a galaxy sample selected based on W1 or W2 bands does not perfectly show the clustering behaviour of a stellar mass-selected sample. The proxy relation between W3 and W4 bands and SFR is similar. We also demonstrate the influence of estimation techniques of stellar mass and SFR on the clustering measurements.

Measurement of AGN dust extinction based on the near-infrared flux variability of WISE data

ABSTRACT We present the measurement of the line-of-sight extinction of the dusty torus for a large number of obscured active galactic nuclei (AGNs) based on the reddening of the colour of the variable flux component in near-infrared (NIR) wavelengths. We collected long-term monitoring data by Wide-field Infrared Survey Explorer (WISE) for 513 local AGNs catalogued by the Swift/BAT AGN Spectroscopic Survey (BASS) and found that the multi-epoch NIR flux data in two different bands (WISE W1 and W2) are tightly correlated for more than 90 per cent of the targets. The flux variation gradient (FVG) in the W1 and W2 bands was derived by applying linear regression analysis, and we reported that those for unobscured AGNs fall in a relatively narrow range, whereas those for obscured AGNs are distributed in a redder and broader range. The AGN’s line-of-sight dust extinction (AV) is calculated using the amount of the reddening in the FVG and is compared with the neutral hydrogen column density (NH) of the BASS catalogue. We found that the NH/AV ratios of obscured AGNs are greater than those of the Galactic diffuse interstellar medium (ISM) and are distributed with a large scatter by at most two orders of magnitude. Furthermore, we found that the lower envelope of the NH/AV of obscured AGNs is comparable to the Galactic diffuse ISM. These properties of the NH/AV can be explained by increase in the NH attributed to the dust-free gas clouds covering the line of sight in the broad-line region.

Kinematics and multiband period–luminosity–metallicity relation of RR Lyrae stars via statistical parallax

ABSTRACT This paper presents results from photometric and statistical-parallax analysis of a sample of 850 field RR Lyrae (RRL) variables. The photometric and spectroscopic data for our sample of RRLs are obtained from (1) our new spectroscopic observations (for 448 RRLs) carried out with the Southern African Large Telescope; (2) our photometric observations using the 1.0-m telescope of the South African Astronomical Observatory, and (3) literature. These are combined with accurate proper motion data from the second data release of the Gaia mission (DR2). This study primarily determines the velocity distribution of solar neighbourhood RRLs, and it also calibrates the zero-points of the RRLs’ visual V-band luminosity–metallicity (LZ or MV–[Fe/H]) relation and their period–luminosity–metallicity (PLZ) relations in the Wide-field Infrared Survey ExplorerW1 and Two-Micron All-Sky Survey Ks bands. We find the bulk velocity of the halo RRLs relative to the Sun to be (U0, V0, W0)Halo =(− 16 ± 7, −219 ± 7, −6 ± 5) km s−1 in the direction of Galactic centre, Galactic rotation, and North Galactic pole, respectively, with velocity-dispersion ellipsoids (σVR, σVϕ, σVθ)Halo = (153 ± 7, 106 ± 4, 101 ± 4) km s−1. The corresponding parameters for the disc component are found to be (U0, V0, W0)Disc = (− 19 ± 5, −46 ± 5, −14 ± 3) km s−1 and (σVR, σVϕ, σVθ)Disc =(49 ± 4, 38 ± 4, 25 ± 3) km s−1. The calibrated PLZ in W1-, Ks-, and V-band LZ relations are $\langle \, M_{W1}\rangle =$ $-0.824+0.124[\mathrm{ Fe/H}]-2.381\log \, P_F$, 〈MKs〉 = $-0.804+0.101[\mathrm{ Fe/H}]-2.33\log \, P_F$, and $\langle \, M_V\rangle =1.041+0.232[\mathrm{ Fe/H}]$, respectively. The calibrated PLZ and LZ relations are used to estimate the Galactic Centre distance and the distance modulus of the Large Magellanic Cloud (LMC), which are found to be 7.99 ± 0.49 kpc and 18.46 ± 0.09 mag, respectively. All our results are in excellent agreement with available literature based on statistical-parallax analysis, but are considerably more accurate and precise. Moreover, the zero-points of our calibrated PLZ and LZ relations are quite consistent with current results found by other techniques and yield an LMC distance modulus that is within 0.04 mag of the current most precise estimate.

Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries

Abstract We present Spitzer 3.6 and 4.5 μm follow-up of 170 candidate extremely cool brown dwarfs newly discovered via the combination of Wide-field Infrared Survey Explorer (WISE) and NEOWISE imaging at 3–5 μm. CatWISE, a joint analysis of archival WISE and NEOWISE data, has improved upon the motion measurements of AllWISE by leveraging a &gt;10× time baseline enhancement, from 0.5 yr (AllWISE) to 6.5 yr (CatWISE). As a result, CatWISE motion selection has yielded a large sample of previously unrecognized brown dwarf candidates, many of which have archival detections exclusively in the WISE 4.6 μm (W2) channel, suggesting that they could be both exceptionally cold and nearby. Where these objects go undetected in WISE W1 (3.4 μm), Spitzer can provide critically informative detections at 3.6 μm. Of our motion-confirmed discoveries, 17 have a best-fit Spitzer [3.6]–[4.5] color most consistent with spectral type Y. It is likely that CWISEP J144606.62–231717.8 (μ ≈ 1.″3 yr−1) is the reddest, and therefore potentially coldest, member of our sample with a very uncertain [3.6]–[4.5] color of 3.71 ± 0.44 mag. We also highlight our highest proper-motion discovery, WISEA J153429.75–104303.3, with μ ≈ 2.″7 yr−1. Given that the prior list of confirmed and presumed Y dwarfs consists of just 27 objects, the Spitzer follow-up presented in this work has substantially expanded the sample of identified Y dwarfs. Our new discoveries thus represent significant progress toward understanding the bottom of the substellar mass function, investigating the diversity of the Y dwarf population, and selecting optimal brown dwarf targets for James Webb Space Telescope spectroscopy.

Mid-IR Variability and Dust Reverberation Mapping of Low-z Quasars. I. Data, Methods, and Basic Results

Abstract The continued operation of the Wide-field Infrared Survey Explorer (WISE), combined with several ground-based optical transient surveys (e.g., CRTS, ASAS-SN, and PTF), offers an unprecedented opportunity to explore the dust structures in luminous active galactic nuclei (AGNs). We use these data for a mid-IR dust reverberation mapping (RM) study of 87 archetypal Palomar–Green quasars at z ≲ 0.5. To cope with various contaminations of the photometry data and the sparse time sampling of the light curves, procedures to combine these data sets and retrieve the dust RM signals have been developed. We find that ∼70% of the sample (with a completeness correction up to 95%) has convincing mid-IR time lags in the WISE W1 (∼3.4 μm) and W2 (∼4.5 μm) bands, and they are proportional to the square root of the AGN luminosity. Combined with previous K-band (∼2.2 μm) RM results in the literature, the inferred dust emission size ratios are R K : R W 1 : R W 2 = 0.6 : 1 : 1.2 . Under simple assumptions, we put preliminary constraints on the projected dust surface density at these bands and reveal the possibly different torus structures among hot-dust-deficient, warm-dust-deficient, and normal quasars from the reverberation signals. With multi-epoch Spitzer data and later WISE photometry, we also explore AGN IR variability at 10–24 μm over a 5 yr timescale. Except for blazars and flat-spectrum radio sources, the majority of AGNs have typical variation amplitudes at 24 μm of no more than 10% of that in the W1 band, indicating that the dust reverberation signals damp out quickly at longer wavelengths. In particular, steep-spectrum radio quasars also lack strong 24 μm variability, consistent with the unification picture of radio-loud AGNs.

A Flaring AGN in a ULIRG Candidate in Stripe 82

Abstract We report the discovery of a mid-infrared variable AGN that is hosted by an ultraluminous infrared galaxy (ULIRG) in the Sloan Stripe 82 field. WISE J030654.88+010833.6 is a red, extended galaxy, which we estimate to be at a photometric redshift of 0.28 ≤ z ≤ 0.31, based on its optical and near-infrared spectral energy distribution (SED). The factor of two variability over 8 yr seen in the Wide-field Infrared Survey Explorer (WISE) 3.4 and 4.6 μm wavelength channels is not clearly correlated with optical variability in archival data. Based on our estimation of the physical parameters of the host galaxy, J030654.88+010833.6 is possibly a composite AGN/starburst ULIRG in a phase where high star formation ∼70 M ⊙ yr−1 is occurring. Our estimate of the black hole mass to stellar mass ratio also appears to be consistent with that of broad line AGN in the local universe. The long-term variability of J030654.88+010833.6 as seen in the WISE W1 and W2 light curves is likely due to variations in the accretion rate, with the energy being reprocessed by dust in the vicinity of the AGN.

On the origin of the dramatic spectral variability of WPVS 007

We report the discovery of large-amplitude mid-infrared variabilities (MIR; $\sim 0.3$ mag) in the Wide-field Infrared Survey Explorer W1 and W2 bands of the low-luminosity narrow-line Seyfert 1 galaxy WPVS 007, which exhibits prominent and varying broad-absorption lines (BALs) with blueshifted velocity up to $\rm \sim 14000\ km\ s^{-1}$. The observed significant MIR variability, the UV to optical color variabilities in the Swift bands that deviate from the predictions of pure dust attenuation models, and the fact that Swift light curves can be well fitted by the stochastic AGN variability model suggest that its observed flux variabilities in UV-optical-MIR bands should be intrinsic, rather than owing to variable dust extinction. Furthermore, the variations of BAL features (i.e., trough strength and maximum velocity) and continuum luminosity are concordant. Therefore, we propose that the BAL variability observed in WPVS 007 is likely induced by the intrinsic ionizing continuum variation, alternative to the rotating-torus model proposed in a previous work. The BAL gas in WPVS 007 might be in the low-ionization state as traced by its weak N V BAL feature; as the ionizing continuum strengthens, the Ci IV and Si IV column densities also increase, resulting in stronger BALs and the emergence of high-velocity components of the outflow. The outflow launch radius might be as small as $\sim 8 \times 10^{-4}$ pc under the assumption of being radiatively driven, but a large-scale origin (e.g., torus) cannot be fully excluded because of the unknown effects from additional factors, e.g., the magnetic field.

Interplanetary scintillation studies with the Murchison Wide-field Array – IV. The hosts of sub-arcsecond compact sources at low radio frequencies

Around 10% of bright low-frequency radio sources observed with the Murchison Widefield Array (MWA) show strong Interplanetary Scintillation (IPS) on timescales of a few seconds, implying that almost all their low-frequency radio emission comes from a compact component less than 0.5 arcsec in angular size. Most of these objects are compact steep-spectrum (CSS) or MHz-peaked spectrum (MPS) radio sources. We have used mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) catalogue to search for the host galaxies of 65 strongly-scintillating MWA sources and compare their properties with those of the overall population of bright low-frequency radio sources. We identified WISE mid-infrared counterparts for 91% of the bright sources in a single 900 square degree MWA field, and found that the hosts of the strongly-scintillating sources were typically at least 1 mag fainter in the WISE W1 (3.4 micron) band than the hosts of weakly-scintillating MWA sources of similar radio flux density. This difference arises mainly because the strongly-scintillating sources are more distant. We estimate that strongly-scintillating MWA sources have a median redshift of z ~ 1.5, and that at least 30% of them are likely to lie at z > 2. The recently-developed wide-field IPS technique therefore has the potential to provide a powerful new tool for identifying high-redshift radio galaxies without the need for radio spectral-index selection.

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.

DISCOVERY OF AN L4β CANDIDATE MEMBER OF ARGUS IN THE PLANETARY MASS REGIME: WISE J231921.92+764544.4

ABSTRACT We present the discovery of a young L dwarf, WISE J231921.92+764544.4, identified by comparing the Wide-field Infrared Survey Explorer (WISE) All-Sky Catalog to the Two Micron All Sky Survey (2MASS). A medium-resolution optical spectrum provides a spectral type of L4β, with a photometric distance estimate of 26.1 ± 4.4 pc. The red WISE W1 − W2 color provides additional evidence of youth, while the 2MASS J − K s color does not. WISE J231921.92+764544.4 is a candidate member of the young moving group Argus, with the space motion and position of WISE J231921.92+764544.4 giving a probability of 79% for membership in Argus and a probability of 21% as a field object, based on BANYAN II. WISE J231921.92+764544.4 has a mass of 12.1 ± 0.4 M Jup ?> based on membership in Argus, within the planetary mass regime.

Characterizing AGB stars in Wide-field Infrared Survey Explorer (WISE) bands

Since asymptotic giant branch (AGB) stars are bright and extended infrared objects, most Galactic AGB stars saturate the Wide-field Infrared Survey Explorer (WISE) detectors and therefore the WISE magnitudes that are restored by applying point-spread-function fitting need to be verified. Statistical properties of circumstellar envelopes around AGB stars are discussed on the basis of a WISE AGB catalog verified in this way. We cross-matched an AGB star sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey catalog. Infrared Space Observatory (ISO) spectra of a subsample of WISE AGB stars were also exploited. The dust radiation transfer code DUSTY was used to help predict the magnitudes in the W1 and W2 bands, the two WISE bands most affected by saturation, for calibration purpose, and to provide physical parameters of the AGB sample stars for analysis. DUSTY is verified against the ISO spectra to be a good tool to reproduce the spectral energy distributions of these AGB stars. Systematic magnitude-dependent offsets have been identified in WISE W1 and W2 magnitudes of the saturated AGB stars, and empirical calibration formulas are obtained for them on the basis of 1877 (W1) and 1558 (W2) AGB stars that are successfully fit with DUSTY. According to the calibration formulae, the corrections for W1 at 5 mag and W2 at 4 mag are $-0.383$ and 0.217 mag, respectively. In total, we calibrated the W1/W2 magnitudes of 2390/2021 AGB stars. The model parameters from the DUSTY and the calibrated WISE W1 and W2 magnitudes are used to discuss the behavior of the WISE color-color diagrams of AGB stars. The model parameters also reveal that O-rich AGB stars with opaque circumstellar envelopes are much rarer than opaque C-rich AGB stars toward the anti-Galactic center direction, which we attribute to the metallicity gradient of our Galaxy.