The Effect of Self-gravity of Gas on Gas Fueling in Barred Galaxies with a Supermassive Black Hole

In our previous paper, we have shown that a gas disk in the nuclear region of a barred galaxy which contains a central supermassive black hole (SMBH) rapidly evolves into a nuclear gas ring by the effect of an additional inner Lindblad resonance caused by the SMBH. In this paper, we investigate the fate of the gas ring, involving self-gravity of gas, using two-dimensional hydrodynamical simulations. We find that the gas ring becomes gravitationally unstable for a gas surface density of gas above a critical value, and fragments into several gas clumps. Some denser clumps increase their mass via the accretion of the surrounding gas and collisions with other clumps, and finally a very massive gas clump (10^7 M_sun) is formed. Due to the torque from the most massive clump, a part of the gas in the ring loses its angular momentum and falls into the galactic center. As a result, a nuclear gas disk (50 pc) is formed around the SMBH. The accretion rate for $R<50$ pc attains about 1 M_sun/yr for 3.5*10^7 yr. At the final phase of the bar-driven fueling, self-gravity is crucial for the angular momentum transfer of the gas. This is a new mechanism for gas fueling to the vicinity of the SMBH.Comment: 14 pages, 7 figures, AASTeX, submitted to Ap

Interpopulation variation of behavioural and morphological traits that affect downstream displacement of the juvenile white‐spotted charr Salvelinus leucomaenis

Downstream displacement is a riverine phenomenon in which organisms are advected by water flow from their home river section to a downstream area. Water flows that cause downstream displacement can be divided into two types: flood flows (Chapman & Kramer, 1991; Good et al., 2001; Meffe, 1984; Sato, 2006; Weese et al., 2011; Yamada & Wada, 2021) and flows under ordinary river conditions (i.e., ordinary flows; Lechner et al., 2016; Nagel et al., 2021; Thiesmeier & Schuhmacher, 1990). Although flood flows can cause catastrophic downstream displacement (Meffe, 1984; Sato, 2006; Weese et al., 2011), occurrences of such downstream displacement are often trait-dependent in riverine fishes (Blondel et al., 2021; Chapman & Kramer, 1991; Good et al., 2001; Meffe, 1984; Yamada & Wada, 2021). For example, smaller individuals are more likely to be displaced by strong floods from their home river section in populations of the molly Poecilia gillii (Kner 1863) (Chapman & Kramer, 1991) and the Trinidadian guppy Poecilia reticulata Peters 1859 (Blondel et al., 2021). Downstream displacement due to ordinary flows can also remove individuals with vulnerable traits from upstream populations. For example, reduced use of low-current habitats in the stickleback Gasterosteus aculeatus (Linnaeus 1758) is correlated with increased downstream displacement under ordinary flow conditions (Jiang et al., 2015). Thus, downstream displacement can be a general evolutionary pressure that removes individuals with low resistance to flow-driven displacement from their home river reaches (Yamada & Wada, 2021)

Morphological evolution reduces downstream displacement in juvenile landlocked salmon

Severe flooding often leads to downstream displacement of aquatic animals. Despite this, many salmonid populations persist in habitats located upstream of tall barriers, such as artificial check dams and/or natural waterfalls, that completely block fishes from returning to the upstream areas after flooding. The evolution of such populations may be affected by spatial sorting due to differential rates of downstream displacement. This study examined whether a morphological trait (increased body depth) that allows individuals to better maintain their position during flooding has evolved in juvenile amago salmon Oncorhynchus masou ishikawae inhabiting above-barrier habitats in two rivers. In both rivers, juveniles collected at the stations with multiple downstream barriers had deeper bodies than those collected at other stations. Similar differences were found in juveniles reared in a common-garden experiment. Field experiments with natural flooding also indicated that deep bodies help juveniles resist downstream displacement. These results consistently suggest that juveniles in some above-barrier habitats have evolved deep bodies to resist downstream displacement due to flooding. Our study is the first to show the evolutionary outcomes of passive spatial sorting during severe climate events

Shape from shading with interreflections under proximal light source - 3D shape reconstruction of unfolded book surface from a scanner image

We address the problem to recover the 3D shape of an unfolded book surface from the shading information in a scanner image. From a technical point of view, this shape from shading problem in real world environments is characterized by (1) proximal light source, (2) interreflections, (3) moving light source, (4) specular reflection, and (5) nonuniform albedo distribution. Taking all these factors into account, we first formulate the problem based on an iterative nonlinear optimization scheme. Then we introduce piecewise polynomial models of the 3D shape. Image restoration experiments for a real book surface demonstrated that geometric and photometric distortions are almost completely removed by the proposed method</p

The Effect of a Central Supermassive black hole on the Gas Fuelling

When a supermassive black hole exists in the centre of a galaxy, an additional inner Lindblad resonance (ILR) exists inside the usual ILRs. We study gas dynamics in a weakly barred potential with a central supermassive black hole by using 2D numerical simulations, and we investigate the effect of the additional ILR on fuelling gas into nuclear starburst regions or AGNs. Our numerical results show that strong trailing spiral shocks are formed at the resonance region, and the gas in the shock region is rapidly fuelled into a central region and make a nuclear gas ring. As a result, a large amount of gas is concentrated in the nuclear region beyond the ILR in a dynamical time scale.Comment: 7 pages, 14 Postscript figures, LaTeX 2.09, requires mn.sty, to be published in MNRA