SAO: Weekly Science Updates 2018

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What Powers the Most Luminous Galaxies?

Post by bystander » Fri Jul 06, 2018 3:10 pm

What Powers the Most Luminous Galaxies?
SAO Weekly Science Update | 2018 Jul 06
Galaxy-galaxy interactions have long been known to influence galaxy evolution. They are commonplace events, and a large majority of galaxies show signs of interactions, including tidal tails or other morphological distortions. The most dramatic collisions trigger the galaxies to light up, especially in the infrared, and they are some of the most luminous objects in the sky. Their brightness allows them to be studied at cosmological distances, helping astronomers reconstruct activity in the early universe.

Two processes in particular are responsible for the enhanced radiation: bursts of star formation or the fueling of the supermassive black hole at a galaxy’s core (an active galactic nuclei - AGN). Although in principle these two processes are quite different and should be readily distinguishable (AGN, for example, produce much hotter ultraviolet and X-ray radiation), in practice the discriminating features can be faint and/or obscured by dust in the galaxies. Astronomers therefore often use the shape of the galaxy’s entire emission profile from the ultraviolet to the far infrared (its spectral energy distribution - SED), to diagnose what is going on. The dust that absorbs much of the radiation also re-radiates it at the longer infrared wavelengths and computer codes can model and unravel the numerous physical effects. ...

The astronomers find that the AGN contribution in their sample of galaxies reaches as high as ninety percent of the total luminosity; in other cases it falls below twenty percent and is possibly negligible. The team makes efforts to relate the magnitude of the AGN contribution to the merger stage of the system (from beginning to coalescing stages), but their modest sample size limited the generality of the conclusions. They are expanding their analysis to several hundred other mergers in order to strengthen the conclusions.

The AGN Luminosity Fraction in Merging Galaxies - Jeremy Dietrich et al
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Gravitational Microlens Detection from Spitzer

Post by bystander » Fri Jul 13, 2018 5:10 pm

Gravitational Microlens Detection from Spitzer
SAO Weekly Science Update | 2018 Jul 13
su201828.jpg
Hubble Space Telescope images of a microlens system. The image on the left was
taken 3.7 years after an observed microlensing event; the one on the right was taken
8.9 years later after the moving foreground (lensing) source had changed position.
The lens and source components (A and B) are clearly resolved in the later image.
(Image Credit: NASA/Hubble)

The path of light from a star as it passes by a massive body, like an exoplanet, will be bent and an observer looking towards the star will see its image distorted. Like an object seen through the stem of a wineglass, the stellar image could even be deformed into two bright peaks. That mass could influence light in this way was first confirmed in 1919, but some of the more subtle effects have only been detected in the past twenty-five years. In one such process, microlensing, a flash of light is produced when the path of a moving cosmic body (perhaps otherwise unknown) passes fortuitously in front of a star and briefly increases the intensity of its light.

The Spitzer Space Telescope circles the Sun in an Earth-trailing orbit, and it is currently 1.66 astronomical units away from Earth (one AU is the average distance of the Earth form the Sun). Scientists had predicted that if it ever became possible to observe a microlensing flash from two well-separated vantage points, a parallax measurement (the apparent angular difference between the positions of the star as seen from the two separated sites) would determine the distance of the dark object. In fact, since 2014 Spitzer has been used successfully to measure the parallax for hundreds of microlensing events. In all these cases, Spitzer was used after ground-based observations had first identified a microlensing event underway. ...

OGLE-2017-BLG-1130: The First Binary Gravitational Microlens Detected From Spitzer Only - Tianshu Wang et al
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Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor