Extragalactic Background Light: a measurement at 400 nm using dark cloud shadow I. Low surface brightness spectrophotometry in the area of Lynds 1642

Abstract

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 $A_V\ge 15$ mag, further spectra were obtained for intermediate-opacity cloud positions. They are used as proxy for the spectrum of the impinging starlight spectrum and facilitate the separation of the scattered starlight (cf. Paper II, Mattila et al. 2017b). Our spectra reach a precision of $\sim 0.5$ $10^{-9}$ erg cm${}^{-2}$s${}^{-1}$sr${}^{-1}$Å${}^{-1}$ as required to measure an EBL intensity in range of $\sim$1 to a few times $10^{-9}$ erg cm${}^{-2}$s${}^{-1}$sr${}^{-1}$Å${}^{-1}$. Because all surface brightness components are measured using the same equipment the method does not require unusually high absolute calibration accuracy, a condition which has been a problem for some previous EBL projects

22 pages, 9 figures, accepted for publication in MNRAS

References in corpus (4)

• The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
• On the Origin of Near-Infrared Extragalactic Background Light Anisotropy
• Extragalactic background Light: a measurement at 400 nm using dark cloud shadow II. Spectroscopic separation of dark cloud's light, and results
• ISO far infrared observations of the high latitude cloud L1642. II. Correlated variations of far-infrared emissivity and temperature of "classical large" dust particles

Cited by in corpus (4)

• Extragalactic background Light: a measurement at 400 nm using dark cloud shadow II. Spectroscopic separation of dark cloud's light, and results
• GAMA/DEVILS: Constraining the cosmic star-formation history from improved measurements of the 0.3-2.2 micron Extragalactic Background Light
• Extragalactic Background Light: Inventory of light throughout the cosmic history
• The isotropic interplanetary dust cloud and near-infrared extragalactic background light observed with COBE/DIRBE