Ultraviolet to optical diffuse sky emission as seen by the Hubble Space Telescope Faint Object Spectrograph

Abstract

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 0.7µm. 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, and residual emission, in eight photometric bands spanning our spectral coverage. We found that the derived ZL reflectance spectrum is flat in the optical, which indicates major contribution of C-type asteroids to the interplanetary dust (IPD). In addition, the ZL reflectance spectrum has an absorption feature at ∼ 0.3µm. The shape of the DGL spectrum is consistent with those found in earlier measurements and model predictions. While the residual emission contains a contribution from the extragalactic background light, we found that the spectral shape of the residual looks similar to the ZL spectrum. Moreover, its optical intensity is much higher than that measured from beyond the IPD cloud by Pioneer10/11, and also than that of the integrated galaxy light. These findings may indicate the presence of an isotropic ZL component, which is missed in the conventional ZL models.

Looking at cosmic near-infrared background radiation anisotropies

“…Furthermore, stellar dynamical evolution of PBH minihalo may play important cosmogonical role. The PBHs in minihalos will evolve via secular stellar dynamical effects similar to that discussed in Kashlinsky and Rees (1983) and by loss of energy to GW emissions. Stellar evaporation will lead to a core-halo structure with the isothermal core of radius r c and N PBH PBHs evolving on Gyr timescales…”

“…The CIB is the EBL at IR wavelengths, and in this review we focus on the near-IR CIB at 1 to 10 µm. The cosmic optical background (COB, 0.1-1 µm) has similar origins as the CIB, but is restricted to sources at z < ∼ 7 (Bernstein, 2007;Kawara et al, 2017;Mattila et al, 2017a,b). The CXB is the net diffuse emissions from 0.5 to 100 keV, with the soft X-ray CXB referring to the range of [0.5-2] keV.…”

“…Numerous evolution modes and stellar activity in pregalactic Universe have been discussed with varying constituents from quasi-normal stellar populations, massive stars, BHs forming in the course of stellar activity, massive binaries, etc (e.g. Cooray and Yoshida, 2004;Fernandez et al, 2012;Fernandez and Komatsu, 2006;Fernandez et al, 2010;Helgason et al, 2016;Kashlinsky and Rees, 1983;Mirabel et al, 2011;Salvaterra and Ferrara, 2003;Santos et al, 2002).…”

“…For a more thorough review of DCBH we refer the reader to Latif and Ferrara (2016). Finally, in addition to direct collapse, Begelman and Rees (1978); Kashlinsky and Rees (1983) pointed out that massive seeds may also form as a result of star-star runaway collisions in young ultra-dense Nuclear Star Clusters (for modern versions see, e.g. Lupi et al, 2014;Portegies-Zwart and McMillan, 2002).…”

“…The low angular resolution (0.7 • ) of the DIRBE beam did not allow removal of many sources and restricted the probing of the net CIB fluctuation levels at the DIRBE bands from 1.25 to 240 µm. Further development came with deep 2MASS study of higher angular resolution, but ground-based instrument, where Kashlinsky et al (2002); Odenwald et al (2003) developed studies of source-subtracted CIB to isolate CIB fluctuations at 1.1, 1.6, and 2.2 µm from galaxies fainter than m AB ≃20-21. The next significant step was made using the IRAC instrument (Fazio et al, 2004b) onboard Spitzer, where Kashlinsky et al (2005) identified significant source-subtracted CIB fluctuations at 3.6 and 4.5 µm, after subtracting known sources to deeper levels, which exceed the contribution from remaining known galaxies.…”