The diffuse ultraviolet background radiation has been mapped over most of the sky with 2\arcmin \ resolution using data from the \textit{GALEX} survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the \textit{Planck} survey. We use only high Galactic latitude ($|b| > 60^{\circ} $) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range $0.02 \leq z \leq 0.72$, which we further subdivide into four redshift bins. In analysing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with $z<0.3$. We then stacked these $z<0.3$ clusters to find a statistically significant excess of $12 \pm 2.3$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ Å$^{-1}$ \ over the median of $\sim 380$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ Å$^{-1}$ \ measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of $\sim 1$ Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.
We present the first observations of diffuse radiation in the far ultraviolet (1000 -- 1150 Å) from the Large Magellanic Cloud based on observations made with the {\it Far Ultraviolet Spectroscopic Explorer}. The fraction of the total radiation in the field emitted as diffuse radiation is typically 5 -- 20\% with a high of 45\% near N70 where there are few exciting stars, indicating that much of the emission is not due to nearby stars. Much less light is scattered in the far ultraviolet than at longer wavelengths with the stellar radiation going into heating the interstellar dust.
CONTEXT: The Virgo direction has been observed at many wavelengths in the recent years, in particular in the ultraviolet with GALEX. The far ultraviolet (FUV) diffuse light detected by GALEX bears interesting information on the large scale distribution of Galactic dust, owing to the GALEX FUV band sensitivity and resolution. AIMS: We aim to characterise the ultraviolet large scale distribution of diffuse emission in the Virgo direction. A map of this emission may become useful for various studies by identifying regions where dust affects observations by either scattering light or absorbing rad…
We have used Voyager and Galex observations to map the diffuse Galactic light near the Galactic equator. We find that most of the observations are relatively faint with surface brightnesses of less than 5,000 photon units. This is important because many ultraviolet telescopes have not observed at low Galactic latitudes because of the fear of a bright diffuse emission. Our data are consistent with emission from interstellar dust grains with albedo ($a$) of 0.2 -- 0.3 and phase function ($g$) $ < 0.7$ at 1100 Å; $0.2 < a < 0.5; g < 0.8$ at 1500 Å; and $0.4 < a < 0.6; g < 0.4$ at 2300 Å.
I report on progress in my ongoing work with Professor Jayant Murthy concerning the origin and nature of the diffuse ultraviolet background radiation over the sky. We have obtained and are reducing a vast trove of Voyager ultraviolet spectrometer observations of the diffuse background shortward of Lyman alpha, including for the first time measurements made from the outermost regions of the solar system, where noise from solar-system scattered (and then grating-scattered) solar Lyman alpha is lowest. Also, we have obtained and are investigating the complete set of GALEX observations of the diff…
Recent availability of high quality infrared (IR) data for diffuse regions in the Galaxy and external galaxies have added to our understanding of interstellar dust. A comparison of ultraviolet (UV) and IR observations may be used to estimate absorption, scattering and thermal emission from interstellar dust. In this paper, we report IR and UV observations for selective diffuse sources in the Galaxy. Using archival mid-infrared (MIR) and far-infrared (FIR) observations from Spitzer Space Telescope, we look for counterparts of diffuse far-ultraviolet (FUV) sources observed by the Voyager, Far Ul…
Using over a million and a half extragalactic spectra we study the properties of the mysterious Diffuse Interstellar Bands (DIBs) in the Milky Way. These data provide us with an unprecedented sampling of the skies at high Galactic-latitude and low dust-column-density. We present our method, study the correlation of the equivalent width of 8 DIBs with dust extinction and with a few atomic species, and the distribution of four DIBs - 5780.6A, 5797.1A, 6204.3A, and 6613.6A - over nearly 15000 squared degrees. As previously found, DIBs strengths correlate with extinction and therefore inevitably w…
Dust scattering is the main source of diffuse emission in the far-ultraviolet (FUV). For several locations in the Large Magellanic Cloud (LMC), Far Ultraviolet Spectroscopic Explorer (FUSE) satellite has observed diffuse radiation in the FUV with intensities ranging from 1000 - 3 X 10^5 photon units and diffuse fraction between 5% - 20% at 1100 °A. Here, we compare the FUV diffuse emission with the mid-infrared (MIR) and far-infrared (FIR) diffuse emission observed by the Spitzer Space Telescope and the AKARI satellite for the same locations. The intensity ratios in the different MIR and FIR b…
The ultraviolet and optical background forms a baseline for any observation of the sky. It includes emission lines and scattered light from the atmosphere; resonant scattering from the Lyman lines of interplanetary hydrogen and the scattering of sunlight from Solar System dust (zodiacal light); scattering of starlight from interstellar dust (DGL) with emission from molecular hydrogen fluorescence or from line emission in selected areas; and an extragalactic component seen most easily at high Galactic latitudes. We will discuss the different components of the diffuse radiation field in the UV a…
The Far-Ultraviolet Extragalactic Legacy (FUEL) Survey: Hubble Far-UV Images and Catalogs of the Extragalactic Legacy Fields
University of California, Riverside（加州大学河滨分校）；California Institute of Technology（加州理工学院）；Universidad Complutense de Madrid（马德里康普顿斯大学）；University of Western Australia（西澳大学）；Stockholm University（斯德哥尔摩大学）；University of California at Santa Cruz（加州大学圣克鲁兹分校）；Clemson University（克莱姆森大学）
We present a map of the diffuse ultraviolet cosmic background in two wavelength bands (FUV: 1530 Å; NUV: 2310 Å) over almost 75% of the sky using archival data from the GALEX mission. Most of the diffuse flux is due to dust-scattered starlight and follows a cosecant law with slopes of 545 photons cm-2 s-1 sr-1 Å-1 and 433 photons cm-2 s-1 sr-1 Å-1 in the FUV and NUV bands, respectively. There is a strong correlation with the 100 μm IRAS flux with an average UV/IR ratio of 300 photons cm-2 s-1 sr-1 Å-1 (MJy sr-1)-1 in the FUV band and 220 photons cm-2 s-1 sr-1 Å-1 (MJy sr-1)-1 in the NUV but wi…
We present images from the Solar Blind Channel on HST that resolve hundreds of far ultraviolet (FUV) emitting stars in two ~1 kpc$^2$ interarm regions of the grand-design spiral M101. The luminosity functions of these stars are compared with predicted distributions from simple star formation histories, and are best reproduced when the star formation rate has declined recently (past 10-50 Myr). This pattern is consistent with stars forming within spiral arms and then streaming into the interarm regions. We measure the diffuse FUV surface brightness after subtracting all of the detected stars, c…
We have used data from the Galaxy Evolution Explorer to study the different components of the diffuse ultraviolet background in the region between the Galactic latitudes 70-80 degree. We find an offset at zero dust column density (E(B - V) = 0) of $240 \pm 18$ photon units in the FUV (1539A) and $394 \pm 37$ photon units in the NUV (2316A). This is approximately half of the total observed radiation with the remainder divided between an extragalactic component of $114 \pm 18$ photon units in the FUV and $194 \pm 37$ photon units in the NUV and starlight scattered by Galactic dust at high latitu…
The diffuse cosmic background radiation in the GALEX far ultraviolet (FUV, 1300 Å - 1700 Å) is deduced to originate only partially in the dust-scattered radiation of FUV-emitting stars: the source of a substantial fraction of the FUV background radiation remains a mystery. The radiation is remarkably uniform at both far northern and far southern Galactic latitudes, and it increases toward lower Galactic latitudes at all Galactic longitudes. We examine speculation that it might be due to interaction of the dark matter with the nuclei of the interstellar medium but we are unable to point to a pl…
We present an all sky map of the diffuse Galactic far ultraviolet (1344-1786 Angstroms) background using GALEX data, covering 65% of the sky with 11.79 arcmin square pixels. We investigate the dependence of the background on Galactic coordinates, finding that a standard cosecant model of intensity is not a valid fit. Furthermore, we compare our map to Galactic all sky maps of 100 micron emission, N_HI column, and H-alpha intensity. We measure a consistent low level FUV intensity at zero-points for other Galactic quantities, indicating a 300 CU non-scattered isotropic component to the diffuse F…
We report cosmic ray ionization rates towards ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between 2 and 10 individual rotational lines of OH$^+$ have been detected in its (0,0) and (1,0) $A^3Π-X^3Σ^-$ electronic band system. This allows constraining of OH$^+$ column densities towards different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the pri…
We report the discovery of diffuse far-infrared and far-ultraviolet emission projected near the interacting pair NGC4435/4438, in the Virgo cluster. This feature spatially coincides with a well known low surface-brightness optical plume, usually interpreted as tidal debris. If extragalactic, this stream would represent not only one of the clearest examples of intracluster dust, but also a rare case of intracluster molecular hydrogen and large-scale intracluster star formation. However, the ultraviolet, far-infrared, HI and CO emission as well as the dynamics of this feature are extremely unusu…
Ultraviolet observations from low Earth orbit (LEO) have to deal with a foreground comprised of airglow and zodiacal light which depend on the look direction and on the date and time of the observation. We have used all-sky observations from the GALEX spacecraft to find that the airglow may be divided into a baseline dependent on the sun angle and a component dependent only on the time from local midnight. The zodiacal light is observable only in the near ultraviolet band (2321 Å) of GALEX and is proportional to the zodiacal light in the visible but with a color of 0.65 indicating that the dus…
We measure NUV aperture magnitudes from {\sl GALEX} images for 258 ultra-diffuse galaxy (UDG) candidates drawn from the initial SMUDGes survey of $\sim 300$ square degrees surrounding, and including, the Coma galaxy cluster. For the vast majority, 242 of them, we present flux upper limits due either to a lack of significant flux in the aperture or confusion with other objects projected within the aperture. These limits often place interesting constraints on the UDG candidates, indicating that they are non-star forming or quiescent. In particular, we identify field, quiescent UDG candidates, wh…
We present a study of diffuse extragalactic radio emission at $1.75\,$GHz from part of the ELAIS-S1 field using the Australia Telescope Compact Array. The resulting mosaic is $2.46\,$deg$^2$, with a roughly constant noise region of $0.61\,$deg$^2$ used for analysis. The image has a beam size of $150 \times60\,$arcsec and instrumental $\langleσ_{\rm n}\rangle= (52\pm5)\, μ$Jy beam$^{-1}$. Using point-source models from the ATLAS survey, we subtract the discrete emission in this field for $S \ge 150\, μ$Jy beam$^{-1}$. Comparison of the source-subtracted probability distribution, or \pd, with th…
We have studied small scale (2 arcmin) spatial variation of the diffuse UV radiation using a set of 11 GALEX deep observations in the constellation of Draco. We find a good correlation between the observed UV background and the IR 100 micron flux, indicating that the dominant contributor of the diffuse background in the field is the scattered starlight from the interstellar dust grains. We also find strong evidence of additional emission in the FUV band which is absent in the NUV band. This is most likely due to Lyman band emission from molecular hydrogen in a ridge of dust running through the…
The diffuse far-ultraviolet (FUV) background has received considerable attention from astronomers since the 1970's. The initial impetus came from the hope of detecting UV radiation from the hot intergalactic medium. The central importance of the FUV background to the physics (heating and ionization) of the diffuse atomic phases motivated the next generation of experiments. The consensus view is that the diffuse FUV emission at high latitudes has three components: stellar FUV reflected by dust grains (diffuse Galactic light or DGL), FUV from other galaxies and the intergalactic medium (extra-ga…
The past decade has seen an explosion of discoveries and new insights into the diffuse gas within galaxies, galaxy clusters, and the filaments composing the Cosmic Web. A new decade will bring fresh opportunities to further this progress towards developing a comprehensive view of the composition, thermal state, and physical processes of diffuse gas in the Universe. Ultraviolet (UV) spectroscopy, probing diffuse 10^4-10^6 K gas at high spectral resolution, is uniquely poised to (1) witness environmental galaxy quenching processes in action, such as strangulation and tidal- and ram-pressure stri…
We present a multi-wavelength correlation study of diffuse ultraviolet radiation using GALEX observations towards the Aquila Rift. Apart from airglow and zodiacal emissions, we find a diffuse background of 1300 - 3700 \photu\ in the far-ultraviolet (FUV: 1350 - 1750 Å) band and 1300 - 2800 \photu\ in the near-ultraviolet (NUV: 1750 - 2850 Å) band. The observed diffuse UV emissions are saturated with total as well as neutral hydrogen column density in the region due to high optical depth in UV ($τ$: 0.91-23.38). Higher values of FUV/NUV ratio in the region, greater than the threshold value of 0…
The Spitzer Data Fusion - A Far-Ultraviolet to Far-Infrared Multi-Wavelength Database in Spitzer Extragalactic Survey Fields
Inter-University Institute for Data Intensive Astronomy (IDIA), Department of Astronomy, University of Cape Town（开普敦大学数据密集型天文学校际研究所）；University of the Western Cape（西开普大学）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文台）
We present the first detection of diffuse dust in the intra-cluster medium of the Virgo cluster out to $\sim$0.4 virial radii, and study the radial variation of its properties on a radial scale of the virial radius. Analysing near-UV - $i$ colours for a sample of $\sim12000$ background galaxies with redshifts $0.02 < z < 0.8$, we find significant colour reddening and relate it to variation in $E(B-V)$ values. The $E(B-V)$ mean profile shows a dust component characterised by an average reddening $E(B-V)\sim0.042 \pm 0.004$ mag within 1.5 degrees ($\sim0.3\, r_{vir}$) from the cluster centre. As…
Argonium has recently been detected as a ubiquitous molecule in our Galaxy. Model calculations indicate that its abundance peaks at molecular fractions in the range of 1E-4 to 1E-3 and that the observed column densities require high values of the cosmic ray ionization rate. Therefore, this molecular cation may serve as an excellent tracer of the very diffuse interstellar medium (ISM), as well as an indicator of the cosmic ray ionization rate. We attempted to detect ArH+ in extragalactic sources to evaluate its diagnostic power as a tracer of the almost purely atomic ISM in distant galaxies. We…
We present the general properties of the far-ultraviolet (FUV; 1370-1720A) continuum background over most of the sky, obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation instrument (SPEAR, also known as FIMS), flown aboard the STSAT-1 satellite mission. We find that the diffuse FUV continuum intensity is well correlated with N_{HI}, 100 $μ$m, and H-alpha intensities but anti-correlated with soft X-ray. The correlation of the diffuse background with the direct stellar flux is weaker than the correlation with other parameters. The continuum spectra are relatively flat…
A large number of interstellar absorption features at ~ 4000Å -- 1.8 μm, known as the "diffuse interstellar bands" (DIBs), remains unidentified. Most recent works relate them to large polycyclic aromatic hydrocarbon (PAH) molecules or ultrasmall carbonaceous grains which are also thought to be responsible for the 2175 Å extinction bump and/or the far ultraviolet (UV) extinction rise at $λ^{-1} > 5.9\ μm^{-1}$. Therefore, one might expect some relation between the UV extinction and DIBs. Such a relationship, if established, could put important constraints on the carrier of DIBs. Over the past f…
Many ultra-diffuse galaxies (UDGs) have been discovered in the Coma cluster, and there is evidence that some, notably Dragonfly 44, have Milky Way-like dynamical masses despite dwarf-like stellar masses. We used X-ray, UV, and optical data to investigate the star formation and nuclear activity in the Coma UDGs, and we obtained deep UV and X-ray data (Swift and XMM-Newton) for Dragonfly 44 to search for low-level star formation, hot circumgalactic gas, and the integrated emission from X-ray binaries. Among the Coma UDGs, we find UV luminosities consistent with quiescence but NUV$-r$ colors indi…
We aim to compare variations in the full-UV dust extinction curve (912-3000 Angstrom), with the HI/H$_2$/total H content along diffuse Milky Way sightlines, to investigate possible connections between ISM conditions and dust properties. We combine an existing sample of 75 UV extinction curves based on IUE and FUSE data, with atomic and molecular column densities measured through UV absorption. The H$_2$ column density data are based on existing Lyman-Werner absorption band models from earlier work on the extinction curves. Literature values for the HI column density were compiled, and improved…
We have found variations in the diffuse ultraviolet background on the scale about 10 days over the 10 year life of the GALEX mission. These variations are only apparent in the near-ultraviolet band of GALEX and are most likely related to variations in the zodiacal light due to brightness variations of the solar NUV flux. The variations can be as high as 200 photon units in the NUV, amounting to about 15 % of the zodiacal light or < 10 % of the total NUV diffuse radiation. There is no effect on the far-ultraviolet band of GALEX. Further work will require better observations chosen specifically …
A bright UV GALEX image in the direction of a dense high galactic latitude interstellar dust cloud is examined to test (and to reject) the idea that a bright extragalactic UV background radiation field exists. A GALEX "Deep Imaging Survey" image of a second high latitude region (a region almost totally free of dust) shows a similar bright background, which, clearly, cannot be due to starlight scattered from interstellar dust. I speculate that the background is due to dark matter particles interacting with interstellar gas/dust nucleons.
The abundance of polycyclic aromatic hydrocarbons (PAHs) in low- and high-metallicity galaxies has been widely discussed since the time when detailed infrared data for extragalactic objects were first obtained. On the scales of entire galaxies, a smaller PAH abundance in lower-metallicity galaxies is often observed. We study this relationship for star-forming regions in nearby galaxies, for a sample containing more than 200 HII complexes, using spatially-resolved observations from the Herschel Space Observatory and Spitzer Space Telescope. We use a model for the dust emission to estimate the p…
Far-Ultraviolet diffuse emission as a tracer of Galactic extinction at the North Galactic Pole
Tezpur University（特佐普尔大学）；Manipal Academy of Higher Education（马尼帕尔高等教育学院）；Indian Institute of Astrophysics（印度天体物理研究所）；Institute of Astronomy, 48 Pyatnitskaya St., Moscow 119017, Russia（俄罗斯莫斯科彼特尼茨卡亚街48号天文研究所）
We present a theoretical calculation of the influence of ultraviolet radiative pumping on the excitation of the rotational levels of the ground vibrational state for HD molecules under conditions of the cold diffuse interstellar medium (ISM). Two main excitation mechanisms have been taken into account in our analysis: (i) collisions with atoms and molecules and (ii) radiative pumping by the interstellar ultraviolet (UV) radiation field. The calculation of the radiative pumping rate coefficients $Γ_{\rm ij}$ corresponding to Drane's model of the field of interstellar UV radiation, taking into a…
We have used GALEX observations of the North and South Galactic poles to study the diffuse ultraviolet background at locations where the Galactic light is expected to be at a minimum. We find offsets of 230 -- 290 photon units in the FUV (1531 Å) and 480 -- 580 photon units in the NUV (2361 Å). Of this, approximately 120 photon units can be ascribed to dust scattered light and another 110 (190 in the NUV) photon units to extragalactic radiation. The remaining radiation is, as yet, unidentified and amounts to $120 -- 180$ photon units in the FUV and $300 -- 400$ photon units in the NUV. We find…
We present an analysis of the blank sky spectra observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of the zodiacal light (ZL), diffuse Galactic light (DGL), and residual emission. The observations were performed toward 54 fields distributed widely over the sky, with the spectral coverage from 0.2 to 0.7 um. In order to avoid contaminating light from the earthshine, we use the data collected only in orbital nighttime. The observed intensity is decomposed into the ZL, DGL, a…
A small survey of the UV-absorbing gas in 12 low-$z$ galaxy groups has been conducted using the Cosmic Origins Spectrograph (COS) on-board the Hubble Space Telescope (HST). Targets were selected from a large, homogeneously-selected sample of groups found in the Sloan Digital Sky Survey (SDSS). A critical selection criterion excluded sight lines that pass close ($<1.5$ virial radii) to a group galaxy, to ensure absorber association with the group as a whole. Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these $10^{13.5}$ to $10^{14.5} M…
We examine the constraints on final state radiation from Weakly Interacting Massive Particle (WIMP) dark matter candidates annihilating into various standard model final states, as imposed by the measurement of the isotropic diffuse gamma-ray background by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark matter annihilation has contributions from the local Milky Way (MW) as well as from extragalactic dark matter. The signal from the MW is very insensitive to the adopted dark matter profile of the halos, and dominates the signa…
The Extragalactic Background Light (EBL) stands for the mean surface brightness of the sky as we would see it from a representative vantage point in the intergalactic space outside of our Milky Way Galaxy. Averaged over the whole 4 pi solid angle it represents the collective light from all luminous matter radiated throughout the cosmic history. Part of the EBL is resolved into galaxies that, with the increasing detecting power of giant telescopes and sensitive detectors, are seen to deeper and deeper limiting magnitudes. This resolved part is now known to contribute a substantial or even the m…
The contribution of unresolved sources to the diffuse gamma-ray background could produce anisotropies in this emission on small angular scales. Recent studies have considered the angular power spectrum and other anisotropy metrics as tools for identifying contributions to diffuse emission from unresolved source classes, such as extragalactic and Galactic dark matter as well as various astrophysical gamma-ray source populations. We present preliminary results of an anisotropy analysis of the diffuse emission measured by the Fermi-LAT.
The Extragalactic Background Light (EBL) captures the total integrated emission from stars and galaxies throughout the cosmic history. The amplitude of the near-infrared EBL from space absolute photometry observations has been controversial and depends strongly on the modeling and subtraction of the Zodiacal light foreground. We report the first measurement of the diffuse background spectrum at 0.8-1.7 um from the CIBER experiment. The observations were obtained with an absolute spectrometer over two flights in multiple sky fields to enable the subtraction of Zodiacal light, stars, terrestrial…
Diffuse and translucent molecular clouds fill a vast majority of the interstellar space in the galactic disk being thus the most typical objects of the Interstellar Medium (ISM). Recent advances in observational techniques of modern optical and ultraviolet spectroscopy led to detection of many features of atomic and molecular origin in spectra of such clouds. Molecular spectra of heteronuclear diatomic molecules, ie. OH, OH+, CH CH+, CN, NH, CO play an important role in understanding chemistry and physical conditions in environments they do populate. A historical review of astronomical observa…
Extragalactic microlensing through Ultra Diffuse Galaxies
IFCA, Instituto de Física de Cantabria (UC-CSIC)（坎塔布里亚物理研究所（UC-CSIC））；Department of Physics, The University of Hong Kong（香港大学物理系）；The Hong Kong Institute for Astronomy and Astrophysics, The University of Hong Kong（香港大学天体物理与天文研究所）；Department of Theoretical Physics, University of Basque Country UPV/EHU（巴斯克地区大学理论物理系）；Donostia International Physics Center（圣塞巴斯蒂安国际物理中心）；Ikerbasque, Basque Foundation for Science（伊克尔巴斯基，巴斯克科学基金会）
We reanalyze data of near-infrared background taken by Infrared Telescope in Space (IRTS) based on up-to-date observational results of zodiacal light, integrated star light and diffuse Galactic light. We confirm the existence of residual isotropic emission, which is slightly lower but almost the same as previously reported. At wavelengths longer than 2 μm, the result is fairly consistent with the recent observation with AKARI. We also perform the same analysis using a different zodiacal light model by Wright and detected residual isotropic emission that is slightly lower than that based on the…
