Browsing by Subject "diffuse radiation"

Sort by: Order: Results:

Now showing items 1-5 of 5
  • Mattila, K.; Väisänen, P.; Lehtinen, K.; von Appen-Schnur, G.; Leinert, Ch. (2017)
    In a project aimed at measuring the optical extragalactic background light (EBL), we are using the shadow of a dark cloud. We have performed, with the ESO VLT/FORS, spectrophotometry of the surface brightness towards the high-galactic-latitude dark cloud Lynds 1642. A spectrum representing the difference between the opaque core of the cloud and several unobscured positions around the cloud was presented in Paper I. The topic of this paper is the separation of the scattered starlight from the dark cloud itself which is the only remaining foreground component in this difference. While the scattered starlight spectrum has the characteristic Fraunhofer lines and the discontinuity at 400 nm, typical of integrated light of galaxies, the EBL spectrum is a smooth one without these features. As template for the scattered starlight, we make use of the spectra at two semitransparent positions. The resulting EBL intensity at 400 nm is I-EBL = 2.9 +/- 1.1 10(-9) erg cm(-2) s(-1) sr(-1) angstrom(-1) or 11.6 +/- 4.4 nW m(-2) sr(-1), which represents a 2.6 sigma detection; the scaling uncertainty is +20 per cent/-16 per cent. At 520 nm, we have set a 2 sigma upper limit of I-EBL
  • Mattila, K.; Lehtinen, K.; Väisänen, P.; von Appen-Schnur, G.; Leinert, Ch. (2017)
    We present the method and observations for the measurement of the Extragalactic Background Light (EBL) utilizing the shadowing effect of a dark cloud. We measure the surface brightness difference between the opaque cloud core and its unobscured surroundings. In the difference the large atmospheric and Zodiacal light components are eliminated and the only remaining foreground component is the scattered starlight from the cloud itself. Although much smaller, its separation is the key problem in the method. For its separation we use spectroscopy. While the scattered starlight has the characteristic Fraunhofer lines and 400 nm discontinuity, the EBL spectrum is smooth and without these features. Medium resolution spectrophotometry at lambda = 380-580 nm was performed with VLT/FORS at ESO of the surface brightness in and around the high-galactic-latitude dark cloud Lynds 1642. Besides the spectrum for the core with AV greater than or similar to 15 mag, further spectra were obtained for intermediate-opacity cloud positions. They are used as proxy for the spectrum of the impinging starlight spectrum and to facilitate the separation of the scattered starlight (cf. Paper II; Mattila et al.). Our spectra reach a precision of less than or similar to 0.5 x 10(-9) erg cm(-2) s(-1) sr(-1) angstrom(-1) as required to measure an EBL intensity in range of similar to 1 to a few times 10(-9) erg cm(-2) s(-1) sr(-1) angstrom(-1). Because all surface brightness components are measured using the same equipment, the method does not require unusually high absolute calibration accuracy, a condition that has been a problem for some previous EBL projects.
  • Planck Collaboration; Akrami, Y.; Keihanen, E.; Kiiveri, K.; Kurki-Suonio, H.; Lindholm, V.; Savelainen, M.; Suur-Uski, A. -S.; Valiviita, J. (2020)
    We present full-sky maps of the cosmic microwave background (CMB) and polarized synchrotron and thermal dust emission, derived from the third set of Planck frequency maps. These products have significantly lower contamination from instrumental systematic effects than previous versions. The methodologies used to derive these maps follow closely those described in earlier papers, adopting four methods (Commander, NILC, SEVEM, and SMICA) to extract the CMB component, as well as three methods (Commander, GNILC, and SMICA) to extract astrophysical components. Our revised CMB temperature maps agree with corresponding products in the Planck 2015 delivery, whereas the polarization maps exhibit significantly lower large-scale power, reflecting the improved data processing described in companion papers; however, the noise properties of the resulting data products are complicated, and the best available end-to-end simulations exhibit relative biases with respect to the data at the few percent level. Using these maps, we are for the first time able to fit the spectral index of thermal dust independently over 3 degrees regions. We derive a conservative estimate of the mean spectral index of polarized thermal dust emission of beta (d)=1.55 +/- 0.05, where the uncertainty marginalizes both over all known systematic uncertainties and different estimation techniques. For polarized synchrotron emission, we find a mean spectral index of beta (s)=-3.1 +/- 0.1, consistent with previously reported measurements. We note that the current data processing does not allow for construction of unbiased single-bolometer maps, and this limits our ability to extract CO emission and correlated components. The foreground results for intensity derived in this paper therefore do not supersede corresponding Planck 2015 products. For polarization the new results supersede the corresponding 2015 products in all respects.
  • Cappelluti, N.; Arendt, R.; Kashlinsky, A.; Li, Y.; Hasinger, G.; Helgason, K.; Urry, M.; Natarajan, P.; Finoguenov, A. (2017)
    We present new measurements of the large-scale clustering component of the cross-power spectra of the source-subtracted Spitzer-IRAC cosmic infrared background and Chandra-ACIS cosmic X-ray background surface brightness fluctuations Our investigation uses data from the Chandra Deep Field South, Hubble Deep Field North, Extended Groth Strip/AEGIS field, and UDS/SXDF surveys, comprising 1160 Spitzer hours and similar to 12 Ms of Chandra data collected over a total area of 0.3 deg(2). We report the first (> 5 sigma) detection of a cross-power signal on large angular scales > 20" between [0.5-2] keV and the 3.6 and 4.5 mu m bands, at similar to 5 sigma and 6.3 sigma significance, respectively. The correlation with harder X-ray bands is marginally significant. Comparing the new observations with existing models for the contribution of the known unmasked source population at z <7, we find an excess of about an order of magnitude at 5 sigma confidence. We discuss possible interpretations for the origin of this excess in terms of the contribution from accreting early black holes (BHs), including both direct collapse BHs and primordial BHs, as well as from scattering in the interstellar medium and intra-halo light.
  • Kashlinsky, A.; Arendt, R. G.; Cappelluti, N.; Finoguenov, A.; Hasinger, G.; Helgason, K.; Merloni, A. (2019)
    The source-subtracted cosmic infrared background (CIB) fluctuations uncovered in deep Spitzer data cannot be explained by known galaxy populations and appear strongly coherent with unresolved cosmic X-ray background (CXB). This suggests that the source-subtracted CIB contains emissions from significantly abundant accreting black holes (BHs). We show that theoretically such populations would have the angular power spectrum that is largely independent of the epochs occupied by these sources, provided they are at z greater than or similar to 4, offering an important test of the origin of the new populations. Using the current measurements we reconstruct the underlying soft X-ray CXB from the new sources and show that its fluctuations, while consistent with a high-z origin, have an amplitude that cannot be reached in direct measurements with the foreseeable X-ray space missions. This necessitates application of the methods developed by the authors to future IR and X-ray data sets, which must cover large areas of the sky in order to measure the signal with high precision. The LIBRAE project within ESA's Euclid mission will probe source-subtracted CIB over similar to one-half of the sky at three near-IR bands, and its cross-power with unresolved CXB can be measured then from the concurrent eROSITA mission covering the same areas of the sky. We discuss the required methodology for this measurement and evaluate its projected signal-to-noise ratio to show the unique potential of this experimental configuration to accurately probe the CXB from the new BH sources and help identify their epochs.