Galactic Extinction Research Articles

ABSTRACT Robust measurements of cosmological parameters from galaxy surveys rely on our understanding of systematic effects that impact the observed galaxy density field. In this paper, we present, validate, and implement the idea of adopting the systematics mitigation method of artificial neural networks for modelling the relationship between the target galaxy density field and various observational realities including but not limited to Galactic extinction, seeing, and stellar density. Our method by construction allows a wide class of models and alleviates overtraining by performing k-fold cross-validation and dimensionality reduction via backward feature elimination. By permuting the choice of the training, validation, and test sets, we construct a selection mask for the entire footprint. We apply our method on the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Emission Line Galaxies (ELGs) selection from the Dark Energy Camera Legacy Survey (DECaLS) Data Release 7 and show that the spurious large-scale contamination due to imaging systematics can be significantly reduced by up-weighting the observed galaxy density using the selection mask from the neural network and that our method is more effective than the conventional linear and quadratic polynomial functions. We perform extensive analyses on simulated mock data sets with and without systematic effects. Our analyses indicate that our methodology is more robust to overfitting compared to the conventional methods. This method can be utilized in the catalogue generation of future spectroscopic galaxy surveys such as eBOSS and Dark Energy Spectroscopic Instrument (DESI) to better mitigate observational systematics.

Abstract The sight line toward the luminous blue hypergiant Cyg OB2-12 is widely used to study interstellar dust on account of its large extinction (A V ≃ 10 mag) and the fact that this extinction appears to be dominated by dust typical of the diffuse interstellar medium. We present a new analysis of archival Infrared Space Observatory Short Wavelength Spectrometer and Spitzer IRS observations of Cyg OB2-12 using a model of the emission from the star and its stellar wind to determine the total extinction A λ from 2.4 to 37 μm. In addition to the prominent 9.7 and 18 μm silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons, including the first identification of the 7.7 μm feature in absorption. The 3.3 μm aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 μm aliphatic hydrocarbon features are observed with relative strengths that are consistent with observations of these features on sight lines toward the Galactic center. We identify and characterize more than 60 spectral lines in this wavelength range, which may be useful in constraining models of the star and its stellar wind. Based on this analysis, we present an extinction curve that extrapolates smoothly to determinations of the mean Galactic extinction curve at shorter wavelengths and to dust opacities inferred from emission at longer wavelengths, providing a new constraint on models of interstellar dust in the mid-infrared.

Abstract We present the earliest observations of the short Gamma‐Ray Burst, GRB 160927A, by the D50 telescope from the Ondřejov Observatory. The 50‐cm robotic telescope reacted to the alert of GRB 160927A and started obtaining unfiltered images 40 s after the trigger with a total exposure of 7,230 s. The magnitude obtained by D50 reached 22.4 ± 0.3 mag not corrected for the galactic foreground extinction of 0.2 mag. We obtained the temporal decay index with α = 0.93 ± 0.03 and the spectral slope with β = 0.68 ± 0.2.

Abstract We present a narrow Hα-band imaging survey of 357 low surface brightness galaxies (LSBGs) that are selected from the spring sky region of the 40% Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) H i Survey. All the Hα images are obtained from the 2.16 m telescope, operated by the Xinglong Observatory of the National Astronomical Observatories, Chinese Academy of Sciences. We provide the Hα fluxes and derive the global star formation rates (SFRs) of LSBGs after the Galactic extinction, internal extinction, and [N ii] contamination correction. Compared to normal star-forming galaxies, LSBGs have a similar distribution in the H i surface density (ΣH i ), but their SFRs and star formation surface density (ΣSFR) are much lower. Our results show that the gas-rich LSBGs selected from the ALFALFA survey obviously deviate from the Kennicutt–Schmidt law, in the relation between the star formation surface density (ΣSFR) and the gas surface density (Σgas). However, they follow the extended Schmidt law well when taking the stellar mass of the galaxy into consideration.

Abstract A primary aim of the (NuSTAR) mission is to find and characterize heavily obscured Active Galactic Nuclei (AGNs). Based on mid-infrared photometry from the Wide-Field Infrared Survey Explorer (WISE) and optical photometry from the Sloan Digital Sky Surveys, we have selected a large population of luminous obscured AGNs (i.e., “obscured quasars”). Here we report NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy from the Southern African Large Telescope and W. M. Keck Observatory. Optical diagnostics confirm that all four targets are AGNs. With NuSTAR hard X-ray observations, three of the four objects are undetected, while the fourth has a marginal detection. We confirm that these objects have observed hard X-ray (10–40 keV) luminosities at or below ∼1043 erg s−1. We compare X-ray and IR luminosities to obtain estimates of the hydrogen column densities (N H) based on the suppression of the hard X-ray emission. We estimate N H of these quasars to be at or larger than 1025 cm−2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys, and they do not contribute significantly to the cosmic X-ray background. From the optical Balmer decrements, we found that our three extreme obscured targets lie in highly reddened host environments. This galactic extinction cannot adequately explain the more obscured AGNs, but it may imply a different scale of obscuration in the galaxy.

We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet (FUV) and near ultraviolet (NUV), respectively. These stars exceed their expected values by 5σ with respect to over one million ultraviolet stars in the log g vs. Teff diagram. Galactic extinction is corrected with a 3D dust map. In order to limit the Lutz-Kelker bias to an insignificant level, we select stars with relative uncertainties in luminosity less than 40% and trigonometric parallaxes less than 20%. We cross-identified our sample with the catalogs of RR Lyr stars and possible white dwarf main-sequence binaries, and find they compose ∼62% and ∼16% of our sample in the FUV and NUV, respectively. This catalog provides a unique sample to study stellar activity, spectrally unresolved compact main-sequence binaries and variable stars.

We describe the selection of the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-domain Field (TDF), a ≳14′ diameter field located within JWST’s northern continuous viewing zone (CVZ) and centered at (R.A., decl.)J2000 = (17:22:47.896, +65:49:21.54). We demonstrate that this is the only region in the sky where JWST can observe a clean (i.e., free of bright foreground stars and with low Galactic foreground extinction) extragalactic deep survey field of this size at arbitrary cadence or at arbitrary orientation, and without a penalty in terms of a raised zodiacal background. This will crucially enable a wide range of new and exciting time-domain science, including high-redshift transient searches and monitoring (e.g., SNe), variability studies from active galactic nuclei (AGNs) to brown dwarf atmospheres, as well as proper motions of possibly extreme scattered Kuiper Belt and Inner Oort Cloud Objects, and of nearby Galactic brown dwarfs, low-mass stars, and ultracool white dwarfs. A JWST/NIRCam+NIRISS GTO program will provide an initial 0.8–5.0 μm spectrophotometric characterization to ∼ 28.8 ± 0.3 mag of four orthogonal “spokes” within this field. The multi-wavelength (radio through X-ray) context of the field is in hand (ground-based near–UV-visible–near-IR), in progress (VLA 3 GHz, VLBA 5 GHz, HST UV-visible, Chandra X-ray, and IRAM 30 m 1.3 and 2 mm), or scheduled (JCMT 850 μm). We welcome and encourage ground- and space-based follow-up of the initial GTO observations and ancillary data, to realize its potential as an ideal JWST time-domain community field.

Abstract We have compiled the first all-sky mid-infrared variable-star catalog based on Wide-field Infrared Survey Explorer five-year survey data. Requiring more than 100 detections for a given object, 50,282 carefully and robustly selected periodic variables are discovered, of which 34,769 (69%) are new. Most are located in the Galactic plane and near the equatorial poles. A method to classify variables based on their mid-infrared light curves is established using known variable types in the General Catalog of Variable Stars. Careful classification of the new variables results in a tally of 21,427 new EW-type eclipsing binaries, 5654 EA-type eclipsing binaries, 1312 Cepheids, and 1231 RR Lyrae. By comparison with known variables available in the literature, we estimate that the misclassification rate is 5% and 10% for short- and long-period variables, respectively. A detailed comparison of the types, periods, and amplitudes with variables in the Catalina catalog shows that the independently obtained classifications parameters are in excellent agreement. This enlarged sample of variable stars will not only be helpful to study Galactic structure and extinction properties, but can also be used to constrain stellar evolution theory and provide potential candidates for the James Webb Space Telescope.

Abstract This paper describes the second data release (DR2) of the Beijing–Arizona Sky Survey (BASS). BASS is an imaging survey covering a 5400 deg2 footprint in the g and r bands using the 2.3 m Bok telescope. DR2 includes the observations through 2017 July obtained by BASS and by the Mayall z-band Legacy Survey (MzLS), which used the 4 m Mayall telescope to observe the same footprint. BASS and MzLS have completed 72% and 76% of their observations. The two surveys will be served for the spectroscopic targeting of the upcoming Dark Energy Spectroscopic Instrument. Both BASS and MzLS data are reduced by the same pipeline. We have updated the basic data reduction and photometric calibrations in DR2. In particular, source detections are performed on stacked images, and photometric measurements are co-added from single-epoch images based on these sources. The median 5σ point-source depths after Galactic extinction corrections are 24.05, 23.61, and 23.10 mag for the g, r, and z bands, respectively. The DR2 data products include stacked images, co-added catalogs, and single-epoch images and catalogs. The BASS website (http://batc.bao.ac.cn/BASS/) provides detailed information and links to download the data.

Abstract The ultraviolet (UV) extinction feature at 2175 Å is ubiquitously observed in the Galaxy but is rarely detected at high redshifts. Here we report the spectroscopic detection of the 2175 Å bump on the sightline to the γ-ray burst (GRB) afterglow GRB 180325A at z = 2.2486, the only unambiguous detection over the past 10 years of GRB follow-up, at four different epochs with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT)/X-shooter. Additional photometric observations of the afterglow are obtained with the Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We construct the near-infrared to X-ray spectral energy distributions (SEDs) at four spectroscopic epochs. The SEDs are well described by a single power law and an extinction law with R V ≈ 4.4, A V ≈ 1.5, and the 2175 Å extinction feature. The bump strength and extinction curve are shallower than the average Galactic extinction curve. We determine a metallicity of [Zn/H] > −0.98 from the VLT/X-shooter spectrum. We detect strong neutral carbon associated with the GRB with equivalent width of W r(λ 1656) = 0.85 ± 0.05. We also detect optical emission lines from the host galaxy. Based on the Hα emission-line flux, the derived dust-corrected star formation rate is ∼46 ± 4 M ⊙ yr−1 and the predicted stellar mass is log M */M ⊙ ∼ 9.3 ± 0.4, suggesting that the host galaxy is among the main-sequence star-forming galaxies.

The X-ray spectra of many active galactic nuclei (AGNs) show a soft X-ray excess below 1–2 keV on top of the extrapolated high-energy power law. The origin of this component is uncertain. It could be a signature of relativistically blurred, ionized reflection or the high-energy tail of thermal Comptonization in a warm (kT ~ 1 keV), optically thick (τ ≃ 10–20) corona producing the optical/UV to soft X-ray emission. The purpose of the present paper is to test the warm corona model on a statistically significant sample of unabsorbed, radio-quiet AGNs with XMM-Newton archival data, providing simultaneous optical/UV and X-ray coverage. The sample has 22 objects and 100 observations. We use two thermal Comptonization components to fit the broadband spectra, one for the warm corona emission and one for the high-energy continuum. In the optical/UV, we also include the reddening, the small blue bump, and the Galactic extinction. In the X-rays, we include a warm absorber and a neutral reflection. The model gives a good fit (reduced χ2 < 1.5) to more than 90% of the sample. We find the temperature of the warm corona to be uniformly distributed in the 0.1–1 keV range, while the optical depth is in the range ~10–40. These values are consistent with a warm corona covering a large fraction of a quasi-passive accretion disk, i.e., that mostly reprocesses the warm corona emission. The disk intrinsic emission represents no more than 20% of the disk total emission. According to this interpretation, most of the accretion power would be released in the upper layers of the accretion flow.

The Frontier Fields are a director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combine the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters - Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370 - were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and pre-existing ancillary data. These clusters have been targeted by the HST ACS/WFC and WFC3/IR with coordinated parallels of adjacent blank fields for over 840 HST orbits. The Spitzer Space Telescope has dedicated > 1000 hours of director's discretionary time to obtain IRAC 3.6 and 4.5 micron imaging to ~26.5, 26.0 ABmag 5-sigma point-source depths in the six cluster and six parallel Frontier Fields. The Frontier Field parallel fields are the second-deepest observations thus far by HST with ~29th ABmag 5-sigma point source depths in seven optical - near-infrared bandpasses. Galaxies behind the Frontier Field cluster lenses experience typical magnification factors of a few, with small regions near the critical curves magnified by factors 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ~30-33 magnitudes over very small volumes. Early studies of the Frontier Fields have probed galaxies fainter than any seen before during the epoch of reionization 6 < z < 10, mapped out the cluster dark matter to unprecedented resolution, and followed lensed transient events.

Abstract The Beijing-Arizona Sky Survey (BASS) is a new wide-field legacy imaging survey in the northern Galactic cap using the 2.3 m Bok telescope. The survey will cover about 5400 deg2 in the g and r bands, and the expected 5σ depths (corrected for the Galactic extinction) in these two bands are g = 24.0 and r = 23.4 mag (AB magnitude). BASS started observations in 2015 January and had completed about 41% of the area as of 2016 July. The first data release contains calibrated images obtained in 2015 and 2016 and their corresponding single-epoch and co-added catalogs. The actual depths of the single-epoch images are g ∼ 23.4 and r ∼ 22.9 mag. The full depths of the three epochs are g ∼ 24.1 and r ∼ 23.5 mag.

The Beijing–Arizona Sky Survey (BASS) is a wide-field two-band photometric survey of the northern Galactic Cap using the 90Prime imager on the 2.3 m Bok telescope at Kitt Peak. It is a four-year collaboration between the National Astronomical Observatory of China and Steward Observatory, the University of Arizona, serving as one of the three imaging surveys to provide photometric input catalogs for target selection of the Dark Energy Spectroscopic Instrument (DESI) project. BASS will take up to 240 dark/gray nights to cover an area of about 5400 deg2 in the g and r bands. The 5σ limiting AB magnitudes for point sources in the two bands, corrected for the Galactic extinction, are 24.0 and 23.4 mag, respectively. BASS, together with other DESI imaging surveys, will provide unique science opportunities that cover a wide range of topics in both Galactic and extragalactic astronomy.

In the infrared and visible wavelength ranges, the extinction cross-sections of small irregular particles are essentially proportional to the corresponding cross-sections for spheres of the same volume, which confirms a previous statement by Mathis. The situation differs for large disordered particles because of the contribution of large surface areas. The differences between irregular particles and homogeneous spheres of the same mass might depend on the material. For example, graphite particles are less sensitive to surface shapes than silicate particles. As a consequence, the successful fit of the average galactic extinction curve by an ensemble of graphite + silicate spherical particles, can also be replaced by a fit using an ensemble of irregular particles, including a smaller amount of silicate. Because the interstellar dust particles are expected to be generally of irregular shapes, the former fit with spherical particles could have overestimated the relative amount of silicate in the interstellar medium (ISM). In the same spirit, we discuss various interpretations of the remarkable stability of the 217.5-nm peak in the ISM extinction.

Abstract V404 Cygni is a well-known candidate for the black hole binary thought to have relativistic jets. It showed extreme outbursts in 2015 June, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission but also synchrotron radiation from the relativistic jets was suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near-infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404 Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404 Cygni. Using the highly polarized field stars, we estimated the color excess for the (B − V) color and the extinction in the V band to be E(B − V) = 1.2 ± 0.2 and 3.0 &amp;lt; A(V) &amp;lt; 3.6, respectively. A tendency for a bluer peak of polarization (λmax &amp;lt; 5500 Å) was commonly seen in the highly polarized field stars, suggesting that the dust grains toward this region are generally smaller than the Galactic average. The corrected spectral energy distribution of V404 Cygni in the near-infrared and optical bands in our results indicated a spectral break between 2.5 × 1014 Hz and 3.7 × 1014 Hz, which might originate in the synchrotron self-absorption.

ABSTRACT We study the integral Galactic extinction and reddening based on the galaxy catalog of the South Galactic Cap u-band Sky Survey (SCUSS), where u-band galaxy number counts and u − r color distribution are used to derive the Galactic extinction and reddening respectively. We compare these independent statistical measurements with the reddening map of Schlegel et al. (SFD) and find that both the extinction and reddening from the number counts and color distribution are in good agreement with the SFD results at low extinction regions ( mag). However, for high extinction regions ( mag), the SFD map overestimates the Galactic reddening systematically, which can be approximated by a linear relation ]. By combining the results from galaxy number counts and color distribution, we find that the shape of the Galactic extinction curve is in good agreement with the standard R V = 3.1 extinction law of O’Donnell.

The outcome of upcoming cosmological surveys will depend on the accurate estimates of photometric redshifts. In the framework of the implementation of the photo-z algorithm for Euclid, we are exploring new avenues to improve template-fitting methods. The paper focusses on the prescription of the extinction of source light by dust in the Milky Way. Since Galactic extinction strongly correlates with wavelength and photometry is commonly obtained in broad-band filters, the amount of absorption depends on the source SED, a point often neglected as the SED is not known a-priori. A consequence of this is that the observed E(B-V) (=A_B-A_V) will be different from the E(B-V) used to normalise the absorption law k_lambda (=A_lambda/E(B-V)). Band-pass corrections are required to renormalise the law for a given SED. We assess the band-pass corrections of a range of SEDs and find they vary by up to 20%. We investigate how dust-to-reddening scaling factors depend of the sources used for their calibration. We derive scaling factors from the color excesses of z<0.4 SDSS red galaxies and show that band-pass corrections predict the observed differences. Extinction is then estimated for a range of SEDs and filters relevant to Euclid and other cosmological ground-based surveys. For high extinction line-of-sights (E(B-V)>0.1, ~8% of the Euclid survey), the variations in corrections can be ~0.1mag in the `bluer' optical filters and ~0.04mag in the NIR filters. An inaccurate correction of extinction critically affects photo-z. In particular, for high extinctions and z<0.5, the bias (mean D_z=z_phot-z_real) exceeds 0.2%(1+z), the precision required by weak-lensing analyses. Additional uncertainty on the MW extinction law further reduces the photo-z precision. We propose a new prescription of Galactic absorption for template-fitting algorithms that takes into consideration the dependence of extinction with SED.

Abstract The Lyα escape fraction is a key measure to constrain the neutral state of the intergalactic medium and then to understand how the universe was fully reionized. We combine deep narrowband imaging data from the custom-made filter NB393 and the filter centered at 2.14 μm to examine the Lyα emitters and Hα emitters at the same redshift z = 2.24. The combination of these two populations allows us to determine the Lyα escape fraction at z = 2.24. Over an area of 383 arcmin2 in the Extended Chandra Deep Field South (ECDFS), 124 Lyα emitters are detected down to NB393 = 26.4 mag at the 5σ level, and 56 Hα emitters come from An et al. Of these, four have both Lyα and Hα emissions (LAHAEs). We also collect the Lyα emitters and Hα emitters at z = 2.24 in the COSMOS field from the literature, and increase the number of LAHAEs to 15 in total. About one-third of them are AGNs. We measure the individual/volumetric Lyα escape fraction by comparing the observed Lyα luminosity/luminosity density to the extinction-corrected Hα luminosity/luminosity density. We revisit the extinction correction for Hα emitters using the Galactic extinction law with color excess for nebular emission. We also adopt the Calzetti extinction law together with an identical color excess for stellar and nebular regions to explore how the uncertainties in extinction correction affect the estimate of individual and global Lyα escape fractions. In both cases, an anti-correlation between the Lyα escape fraction and dust attenuation is found among the LAHAEs, suggesting that dust absorption is responsible for the suppression of the escaping Lyα photons. However, the estimated Lyα escape fraction of individual LAHAEs varies by up to ∼3 percentage points between the two methods of extinction correction. We find the global Lyα escape fraction at z = 2.24 to be (3.7 ± 1.4)% in the ECDFS. The variation in the color excess of the extinction causes a discrepancy of ∼1 percentage point in the global Lyα escape fraction.

We present baryon acoustic oscillation (BAO) scale measurements determined from the clustering of 1.2 million massive galaxies with redshifts 0.2 < z < 0.75 distributed over 9300 square degrees, as quantified by their redshift-space correlation function. In order to facilitate these measurements, we define, describe, and motivate the selection function for galaxies in the final data release (DR12) of the SDSS III Baryon Oscillation Spectroscopic Survey (BOSS). This includes the observational footprint, masks for image quality and Galactic extinction, and weights to account for density relationships intrinsic to the imaging and spectroscopic portions of the survey. We simulate the observed systematic trends in mock galaxy samples and demonstrate that they impart no bias on baryon acoustic oscillation (BAO) scale measurements and have a minor impact on the recovered statistical uncertainty. We measure transverse and radial BAO distance measurements in 0.2 < z < 0.5, 0.5 < z < 0.75, and (overlapping) 0.4 < z < 0.6 redshift bins. In each redshift bin, we obtain a precision that is 2.7 per cent or better on the radial distance and 1.6 per cent or better on the transverse distance. The combination of the redshift bins represents 1.8 per cent precision on the radial distance and 1.1 per cent precision on the transverse distance. This paper is part of a set that analyses the final galaxy clustering dataset from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. (2016) to produce the final cosmological constraints from BOSS.