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The influence of diffuse scattered light
摘要： All telescopes and instruments are to some degree affected by scattered light. It is possible to estimate the amount of such scattered light, and even correct for it, with a radially extended point spread function (PSF). The outer parts of the PSF have only rarely been determined, since they are faint and therefore difficult to measure. A mostly complete overview of existing properties and measurements of radially extended PSFs is presented, to both show their similarities and to indicate how bright extended objects can be used to measure the faintest regions. The importance of the far wings of the PSF and their possible temporal variations are demonstrated in three edge-on galaxy models. The same study is applied to the first edge-on galaxy where earlier observations reveal a halo, NGC 5907. All PSFs were collected in two diagrams, after they were offset or normalized, when that was possible. Surface-brightness structures of edge-on galaxies were modelled and analysed to study scattered-light haloes that result when there is an exponential disc. The models were convolved with both a lower-limit PSF and a more average PSF. The PSF of the observed data could be used in the case of NGC 5907. The comparison of the PSFs demonstrates a lower-limit r?2 power-law decline at larger radii. The analysis of the galaxy models shows that the outer parts of the PSF also are important to correctly model and analyse observations and, in particular, fainter regions. The reassessed analysis of the earlier measurements of NGC 5907 reveals an explanation for the faint halo in scattered light, within the quoted level of accuracy.
关键词： telescopes,galaxies: individual: NGC 5907,methods: observational,galaxies: halos,methods: data analysis,galaxies: structure
更新于2025-09-23 15:22:29
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Enhanced characteristics of fused silica fibers using laser polishing
摘要： We present a measurement of the mean density pro?le of Ca ii gas around galaxies out to ～200 kpc, traced by Fraunhofer’s H & K absorption lines. The measurement is based on cross-correlating the positions of about one million foreground galaxies at z ～ 0.1 and the ?ux decrements induced in the spectra of about 105 background quasars from the Sloan Digital Sky Survey. This technique allows us to trace the total amount of Ca ii absorption induced by the circumgalactic medium, including absorbers too weak to be detected in individual spectra. We can statistically measure Ca ii rest equivalent widths down to several m?, corresponding to column densities of about 5 × 1010 cm?2. We ?nd that the Ca ii column density distribution follows NCa ii ～ r ?1.4 and the mean Ca ii mass in the halo within 200 kpc is ～5 × 103 M(cid:4), averaged over the foreground galaxy sample with median mass ～1010.3 M(cid:4). This is about an order-of-magnitude larger than the Ca ii mass in the interstellar medium of the Milky Way, suggesting that more than 90% of Ca ii in the universe is in the circum- and inter-galactic environments. Our measurements indicate that the amount of Ca ii in halos is larger for galaxies with higher stellar mass and higher star formation rate. For edge-on galaxies we ?nd Ca ii to be more concentrated along the minor axis, i.e., in the polar direction. This suggests that bipolar out?ows induced by star formation must have played a signi?cant role in producing Ca ii in galaxy halos.
关键词： quasars: absorption lines,galaxies: halos,galaxies: evolution,intergalactic medium
更新于2025-09-11 14:15:04