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Register a new userMalin 1: A Deeper Look
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Lesa Moore Macquarien University
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Our R-band data show that the optical light from Malin 1 corresponds well with the >2-arcmin extent of the galaxys HI content and continues well beyond previously published V-band optical light radial profiles. Analysis of our image yields improved understanding of the galaxys properties. We measure ellipticity of 0.20 +/- 0.03, implying inclination of 38 +/- 3 degrees, and we trace the radial profile to 77 arcsec. A single dusty spiral arm is also weakly discernable, and is consistent with the rotation direction of the HI and spiral structure of the inner disk. Possible scenarios for the origin of the spiral structure are discussed.
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We investigate the discounting mismatch in actor-critic algorithm implementations from a representation learning perspective. Theoretically, actor-critic algorithms usually have discounting for both actor and critic, i.e., there is a $gamma^t$ term in the actor update for the transition observed at time $t$ in a trajectory and the critic is a discounted value function. Practitioners, however, usually ignore the discounting ($gamma^t$) for the actor while using a discounted critic. We investigate this mismatch in two scenarios. In the first scenario, we consider optimizing an undiscounted objective $(gamma = 1)$ where $gamma^t$ disappears naturally $(1^t = 1)$. We then propose to interpret the discounting in critic in terms of a bias-variance-representation trade-off and provide supporting empirical results. In the second scenario, we consider optimizing a discounted objective ($gamma < 1$) and propose to interpret the omission of the discounting in the actor update from an auxiliary task perspective and provide supporting empirical results.
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Malin 1, being a class of giant low surface galaxies, continues to surprise us even today. The HST/F814W observation has shown that the central region of Malin 1 is more like a normal SB0/a galaxy, while the rest of the disk has the characteristic of a low surface brightness system. The AstroSat/UVIT observations suggest scattered recent star formation activity all over the disk, especially along the spiral arms. The central 9 ($sim 14$ kpc) region, similar to the size of the Milky Ways stellar disk, has a number of far-UV clumps - indicating recent star-formation activity. The high resolution UVIT/F154W image reveals far-UV emission within the bar region ($sim 4$ kpc) - suggesting the presence of hot, young stars in the bar. These young stars from the bar region are perhaps responsible for producing the strong emission lines such as H$alpha$, [OII] seen in the SDSS spectra. Malin 1B, a dwarf early-type galaxy, is interacting with the central region and probably responsible for inducing the recent star-formation activity in this galaxy.
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