A Study of the Effect of Bulges on Bar Formation in Disk galaxies

We use N-body simulations of bar formation in isolated galaxies to study the effect of bulge mass and bulge concentration on bar formation. Bars are global disk instabilities that evolve by transferring angular momentum from the inner to outer disks and to the dark matter halo. It is well known that a massive spherical component such as halo in a disk galaxy can make it bar stable. In this study we explore the effect of another spherical component, the bulge, on bar formation in disk galaxies. In our models we vary both the bulge mass and concentration. We have used two sets of models, one that has a dense bulge and high surface density disk. The second model has a less concentrated bulge and a lighter disk. In both models we vary the bulge to disk mass fraction from 0 to 0.7. Simulations of both the models show that there is an upper cutoff in bulge to disk mass ratio M b /M d above which bars cannot form; the cutoff is smaller for denser bulges( M b /M d = 0.2) compared to less denser ones (M b /M d = 0.5). We define a new criteria for bar formation in terms of bulge to disk radial force ratio (F b /F d ) at the disk scale lengths above which bars cannot form. We find that if F b /F d > 0.35, a disk is stable and a bar cannot form. Our results indicate that early type disk galaxies can still form strong bars in spite of having massive bulges.Comment: Accepted at MNRAS,12 pages, 19 figure

Testing a theoretical prediction for bar formation in galaxies with bulges

Earlier studies have shown that massive bulges impede bar formation in disk galaxies. Recent N-body simulations have derived a bar formation criterion that depends on the radial bulge force in a galaxy disk. We use those simulations to show that bars can form only when the force constant FB < 0.13, where FB depends on the ratio of the bulge force to the total force of the galaxy at twice the disk scale length 2R d . In this article, we test this theoretical prediction using observational data obtained from the literature. Our sample consists of 63 barred galaxies with a wide range of Hubble classes from the S 4 G catalogue for which bulge, disk and bar decomposition has been done. We find that 92 % of our sample galaxies satisfy the condition FB < 0.13 for bar formation in galaxies and hence agree with the bar formation criterion given by the simulations.Comment: 7 pages, 5 figures, accepted for publication in A&

Modelling Dark Matter Halo Spin using Observations and Simulations: application to UGC 5288

Dark matter (DM) halo properties are extensively studied in cosmological simulations but are very challenging to estimate from observations. The DM halo density profile of observed galaxies is modelled using multiple probes that trace the dark matter potential. However, the angular momentum distribution of DM halos is still a subject of debate. In this study we investigate a method for estimating the halo spin and halo concentration of low surface brightness (LSB), gas-rich dwarf barred galaxy UGC 5288, by forward modelling disk properties derived from observations - stellar and gas surface densities, disk scale length, HI rotation curve, bar length and bar ellipticity. We combine semi-analytical techniques, N-body/SPH and cosmological simulations to model the DM halo of UGC 5288 with both a cuspy Hernquist profile and a flat-core pseudo-isothermal profile. We find that the best match with observations is a pseudo-isothermal halo model with a core radius of $r_{c} = 0.23$ kpc, and halo spin of $\lambda$= 0.08 at the virial radius. Although our findings are consistent with previous core radius estimates of the halo density profile of UGC 5288, as well as with the halo spin profiles of similar mass analogues of UGC5288 in the high-resolution cosmological-magneto-hydrodynamical simulation TNG50, there still remain some uncertainties as we are limited in our knowledge of the formation history of the galaxy. Additionally, we find that the inner halo spin ($r< 10$ kpc) in barred galaxies is different from the unbarred ones, and the halo spin shows weak correlations with bar properties.Comment: 29 pages including Appendix, 28 figures, accepted in MNRAS, comments are welcome from the communit

Design and Implementation of Solar Charge Controller for Photovoltaic Systems

The paper presents a design of solar charge controller for PV energy system. A voltage regulator circuit, an Over-charging Protection circuit and an Over-discharging Protection circuit design are proposed in this paper. The voltage regulator circuit modulates the voltage variation at the output of solar panel and fed it to the Charging Controller circuit. The Over-charging controller circuit prevents overcharging of battery and helps to increase lifespan of battery. The Over-discharging circuit protects the battery by restricting flow of current from battery to PV panel. The entire model is implemented in hardware and results are observed and analyzed to examine the capability of the Solar Charge Controlle