FAR-ULTRAVIOLET CONTINUUM EMISSION: APPLYING THIS DIAGNOSTIC TO THE CHROMOSPHERES OF SOLAR-MASS STARS

Context. Star-forming galaxies at high redshift show anomalous values of infrared excess, which can be described only by extremizing the existing relations between the shape of their ultraviolet continuum emission and their infrared-to-ultraviolet luminosity ratio, or by constructing ad hoc models of star formation and dust distribution. Aims. We present an alternative explanation, based on unveiled AGN activity, of the existence of such galaxies. The scenario of a weak AGN lends itself naturally to explain the observed spectral properties of these high-z objects in terms of a continuum slope distribution and not altered infrared excesses. Methods. To this end, we directly compare the infrared-to-ultraviolet properties of high-redshift galaxies to those of known categories of AGN (quasars and Seyferts). We also infer the characteristics of their possible X-ray emission. Results. We find a strong similarity between the spectral shapes and luminosity ratios of AGN with the corresponding properties of such galaxies. In addition, we derive expected X-ray fluxes that are compatible with the energetics from AGN activity. Conclusions. We conclude that a moderate AGN contribution to the UV emission of such high-z objects is a valid alternative to explain their spectral properties. Even the presence of an active nucleus in each source would not violate the expected quasar statistics. Furthermore, we suggest that the observed similarities between anomalous star-forming galaxies and quasars may provide a benchmark for future theoretical and observational studies on the galaxy population in the early Universe.

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Spatially separated continuum sources revealed by microlensing in the gravitationally lensed broad absorption line quasar SDSS J081830.46+060138.0

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936973 ◽

2020 ◽

Vol 633 ◽

pp. A101

Author(s):

D. Hutsemékers ◽

D. Sluse ◽

P. Kumar

Keyword(s):

Absorption Line ◽

Rest Frame ◽

Continuum Emission ◽

Absorption System ◽

Ultraviolet Continuum ◽

Broad Absorption ◽

Extended Source ◽

Broad Absorption Line ◽

Onset Velocity ◽

The Continuum

Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 (J0818+0601) at redshift z ≃ 2.35. We first show that J0818+0601 is actually gravitationally lensed, and not a binary quasar. A strong absorption system detected at z = 1.0065 ± 0.0002 is possibly due to the lensing galaxy. Microlensing is observed in one image and it magnifies the emission lines, the continuum, and the BALs differently. By disentangling the part of the spectrum that is microlensed from the part that is not microlensed, we unveil two sources of continuum that must be spatially separated: a compact one, which is microlensed, and an extended one, which is not microlensed and contributes to two thirds of the total continuum emission. J0818+0601 is the second BAL quasar in which an extended source of rest-frame ultraviolet continuum is found. We also find that the images are differently polarized, suggesting that the two continua might be differently polarized. Our analysis provides constraints on the BAL flow. In particular, we find that the outflow is seen with a nonzero onset velocity, and stratified according to ionization.

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Relations Between FUV Excess and Coronal Soft X-Ray Emission Among Dwarf Stars

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2017.47 ◽

2017 ◽

Vol 34 ◽

Cited By ~ 7

Author(s):

Graeme H. Smith ◽

Mason Hargrave ◽

Elliot Eckholm

Keyword(s):

Active Regions ◽

Continuum Emission ◽

Stellar Rotation ◽

Dwarf Stars ◽

X Ray ◽

Contrast Detection ◽

Chromospheric Emission ◽

Far Ultraviolet

AbstractThe far-ultraviolet magnitudes of late-F, G and early-K dwarfs with (B − V) ⩾ 0.50 as measured by the GALEX satellite are shown to correlate with soft X-ray luminosity. This result indicates that line and continuum emission from stellar active regions make significant contributions to the flux in the GALEX FUV band for late-F, G and K dwarfs. By contrast, detection of a correlation between FUV brightness and soft X-ray luminosity among early-F dwarfs requires subtraction of the photospheric component from the FUV flux. The range in (B − V) among F and G dwarfs over which a correlation between uncorrected FUV magnitude and X-ray luminosity is detected coincides with the range in colour over which coronal and chromospheric emission correlates with stellar rotation.

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