In this work, a CCD-augmented complete angle scatter instrument (CASI) with a visible red laser source was used to measure the BRDF of a commercially available solar cell designed for small ...satellites, simultaneously capturing both in-plane and out-of-plane data with high angular resolution surrounding the specular direction. The measurements exhibited three distinct scatter features: a central specular peak, an offset specular peak, and a diffraction pattern. The two peaks were caused by different material surfaces with slightly different normal directions, and the diffraction pattern arose from periodically-spaced metal conducting bars running in one direction across the solar cell surface. The diffraction pattern measurements were verified in-plane with an original single-pixel CASI detector and then used to inform the creation of a single closed-form BRDF model capable of describing the out-of-plane features. Both specular peaks were modeled using a traditional microfacet formulation, but the offset peak model implemented a rotation of the incident and scatter directions to account for the difference in surface normal direction. The diffraction pattern–which is not typically described with microfacet models–was described based on Fraunhofer diffraction through two rectangular stripes, adjusted in terms of microfacet coordinates. Parameters for the model were chosen manually, based largely on physical material properties when possible, rather than using optimized fitting algorithms. Model results were compared to the measurements by using the same CCD pixel scatter coordinates. Qualitatively, the model successfully replicated the observed features, and quantitatively, the modeled peak values agree with the measurements within an order of magnitude.
UV Star Formation Rates in the Local Universe Salim, Samir; Rich, R. Michael; Charlot, Stéphane ...
The Astrophysical journal. Supplement series,
12/2007, Letnik:
173, Številka:
2
Journal Article
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We measure star formation rates (SFRs) of approximately 50,000 optically selected galaxies in the local universe (z approximately 0.1)--from gas-rich dwarfs to massive ellipticals. We obtain ...dust-corrected SFRs by fitting the GALEX (ultraviolet) and SDSS photometry to a library of dust-attenuated population synthesis models. For star-forming galaxies, our UV-based SFRs compare remarkably well with those from SDSS-measured emission lines (H alpha ). Deviations from perfect agreement are shown to be due to differences in the dust attenuation estimates. In contrast to H alpha measurements, UV provides reliable SFRs for galaxies with weak H alpha , and where H alpha is contaminated with AGN emission (1/2 of the sample). Using full-SED SFRs, we calibrate a simple prescription that uses GALEX far- and near-UV magnitudes to produce dust-corrected SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGNs, (2) those hosting an AGN, and (3) galaxies without Ha emission. We find that the three have distinct star formation histories, with AGNs lying Intermediate between the star-forming and the quiescent galaxies. Star-forming galaxies without an AGN lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. On the other hand, weak AGNs, while also massive, have lower SFRs, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent galaxies via strong and weak AGNs. We confirm that some galaxies with no H alpha show signs of star formation in the UV. We derive a cosmic star formation density at z = 0.1 with significantly smaller total error than previous measurements.
We introduce a new quantity, the mass flux density of galaxies evolving from the blue sequence to the red sequence. We propose a simple technique for constraining this mass flux using the ...volume-corrected number density in the extinction-corrected UV-optical color-magnitude distribution, the stellar age indexes H delta sub(A) and unk(4000), and a simple prescription for spectral evolution using a quenched star formation history. We exploit the excellent separation of red and blue sequences in the NUV - r band Hess function. The final value we measure, rho T = 0.033 m unk yr super(-1) Mpc super(-3), is strictly speaking an upper limit due to the possible contributions of bursting, composite, and extincted galaxies. However, it compares favorably with estimates of the average mass flux that we make based on the red luminosity function evolution derived from the DEEP2 and COMBO-17 surveys, rho R - +0034 M unk yr super(-1) Mpc super(-3). We find that the blue sequence mass has remained roughly constant since z = 1 ( rho B unk 0.01 M unk yr super(-1) Mpc super(-3), but the average on-going star formation of rho SF unk 0.037 M unk yr super(-1) Mpc super(-3) over 0 < z < 1 is balanced by mass flux off the blue sequence. We explore the nature of the galaxies in the transition zone with particular attention to the frequency and impact of active galactic nuclei (AGNs). The AGN fraction peaks in the transition zone. We find circumstantial, albeit weak evidence that the quench rates are higher in higher luminosity AGNs.
Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by ...means of 'feedback' in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.
We use the UV-optical color magnitude diagram in combination with spectroscopic and photometric measurements derived from the SDSS spectroscopic sample to measure the distribution of galaxies in the ...local universe (z < 0.25) and their physical properties as a function of specific star formation rate (SFR/M unk) and stellar mass (M unk). Throughout this study our emphasis is on the properties of galaxies on and off of a local "star-forming sequence." We discuss how the physical characteristics of galaxies along this sequence are related to scaling relations typically derived for galaxies of different morphological types. We find, among other trends, that our measure of the star formation rate surface density, capital sigma sub(SFR), is nearly constant along this sequence. We discuss this result and implications for galaxies at higher redshift. For the first time, we report on measurements of the local UV luminosity function versus galaxy structural parameters, as well as inclination. We also split our sample Into disk-dominated and bulge-dominated subsamples using the l-band Sersic index and find that disk-dominated galaxies occupy a very tight locus in SFR/M unk vs. M unk space, while bulge-dominated galaxies display a much larger spread of SFR/M unk at fixed stellar mass. A significant fraction of galaxies with SFR/M unk and capital sigma sub(SFR) above those on the "star-forming sequence" are bulge-dominated. We can use our derived distribution functions to ask whether a significant fraction of these galaxies may be experiencing a final episode of star formation (possibly induced by a merger or other burst), soon to be quenched, by determining whether this population can explain the growth rate of the non-star-forming galaxies on the "red sequence." We find that this is a plausible scenario for bulge-dominated galaxies near the characteristic transition mass under reasonable assumptions regarding quenching timescales. Similarly, we use this technique to estimate the rate of mergers/starbursts that take galaxies off of the star-forming sequence and show that the implied merger rates are consistent with local measurements.
Light curve analysis is often used to discern information about satellites in geosynchronous orbits. Solar panels, comprising a large part of the satellite’s body, contribute significantly to these ...light curves. Historically, theoretical bidirectional reflectance distribution functions (BRDFs) have failed to capture key features in the scattered light from solar panels. In recently published work, a new solar cell BRDF was developed by combining specular microfacet and “two-slit” diffraction terms to capture specular and periodic/array scattering, respectively. This BRDF was experimentally motivated and predicted many features of the solar cell scattered irradiance. However, the experiments that informed the BRDF were limited to a single laser wavelength, single beam size, and single solar cell sample. In addition, the BRDF was not physics based and therefore, physical insight into what causes certain features in the scattered irradiance was not evident. In this work, we examine solar cell scattering from first principles and derive a simple physics-based expression for the scattered irradiance. We analyze this expression and physically link terms to important scattering features, e.g., out-of-plane phenomena. In addition, we compare our model with experimental data and find good agreement in the locations and behaviors of these features. Our new model, being more predictive by nature, will allow for greater flexibility and accuracy when modeling reflection from solar cells in both real-world and experimental situations.
Ultraviolet-luminous galaxies (UVLGs) have been identified as intensely star-forming nearby galaxies. A subset of these, the supercompact UVLGs, are believed to be local analogs of high-redshift ...Lyman break galaxies. Here we investigate the radio continuum properties of this important population for the first time. We have observed 42 supercompact UVLGs with the VLA, all of which have extensive coverage in the UV/optical by GALEX and SDSS. Our analysis includes comparison samples of multiwavelength data from the Spitzer First Look Survey and from the SDSS-GALEX matched catalogs. In addition we have Spitzer MIPS data for 24 of our galaxies and find that they fall on the radio-FIR correlation of normal star-forming galaxies. We find that our galaxies have lower radio to UV ratios and lower Balmer decrements than other local galaxies with similar (high) star formation rates. Optical spectra show they have lower unk(4000) and H delta sub(A) indices, higher H beta emission-line equivalent widths, and higher O III5007/H beta emission-line ratios than normal star-forming galaxies. Comparing these results to galaxy spectral evolution models we conclude that supercompact UVLGs are distinguished from normal star-forming galaxies firstly by their high specific star formation rates. Moreover, compared to other types of galaxies with similar star formation rates, they have significantly less dust attenuation. In both regards they are similar to Lyman break galaxies. This suggests that the process that causes star formation in the supercompact UVLGs differs from other local star-forming galaxies, but may be similar to Lyman break galaxies.
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