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

Effects of Inner Halo Angular Momentum on the Peanut/X-shapes of Bars

Cosmological simulations show that dark matter halos surrounding baryonic disks have a wide range of angular momenta, measured by the spin parameter ($\lambda$). In this study, we bring out the importance of inner angular momentum($<$30 kpc), measured in terms of the halo spin parameter, on the secular evolution of the bar using N-body simulations. We have varied the halo spin parameter $\lambda$ from 0 to 0.1 for co-rotating (prograde) spinning halos and one counter-rotating (retrograde) halo spin ($\lambda$=-0.1) with respect to the disk. We report that as the halo spin increases, the buckling is also triggered earlier and is followed by a second buckling phase in high-spin halo models. The timescale for the second buckling is significantly longer than the first buckling. We find that bar strength does not reduce significantly after the buckling in all of our models, which provides new insights about the role of inner halo angular momentum, unlike previous studies. Also, the buckled bar can still transfer significant angular momentum to the halo in the secular evolution phase, but it reduces with increasing halo spin. In the secular evolution phase, the bar strength increases and saturates to nearly equal values for all the models irrespective of halo spin and the sense of rotation with respect to the disk. The final boxy/peanut shape is more pronounced ($\sim$20 $\%$) in high spin halos having higher angular momentum in the inner region compared to non-rotating halos. We explain our results with angular momentum exchanges between the disk and halo.Comment: 14 pages,13 figures, 2 tables; Accepted for publication in Ap

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

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&

Excitation of vertical breathing motion in disc galaxies by tidally-induced spirals in fly-by interactions

It is now clear that the stars in the Solar neighbourhood display large-scale coherent vertical breathing motions. At the same time, Milky Way-like galaxies experience tidal interactions with satellites/companions during their evolution. While these tidal interactions can excite vertical oscillations, it is still not clear whether vertical breathing motions are excited directly by the tidal encounters or are driven by the tidally-induced spirals. We test whether excitation of breathing motions are directly linked to tidal interactions by constructing a set of N-body models (with mass ratio 5:1) of unbound single fly-by interactions with varying orbital configurations. We first reproduce the well-known result that such fly-by interactions can excite strong transient spirals (lasting for ∼2.9−4.2Gyr⁠) in the outer disc of the host galaxy. The generation and strength of the spirals are shown to vary with the orbital parameters (the angle of interaction, and the orbital spin vector). Furthermore, we demonstrate that our fly-by models exhibit coherent breathing motions whose amplitude increases with height. The amplitudes of breathing motions show characteristic modulation along the azimuthal direction with compressing breathing motions coinciding with the peaks of the spirals and expanding breathing motions falling in the inter-arm regions – a signature of a spiral-driven breathing motion. These breathing motions in our models end when the strong tidally-induced spiral arms fade away. Thus, it is the tidally-induced spirals which drive the large-scale breathing motions in our fly-by models, and the dynamical role of the tidal interaction in this context is indirect

Methanolic extract of Phlogacanthus thyrsiflorus Nees leaf induces apoptosis in cancer cells

Phlogacanthus thyrsiflorus Nees is a medicinal herb commonly used in traditional folk medicine, and it is known to possess anticancer activity. Here, we explored the anticancer properties of methanolic extract of P. thyrsiflorus leaves in HeLa and MCF-7 cell lines. We observed nuclear fragmentation as indication of apoptosis in the MPT treated cancer cells using haematoxylin and eosin (H&amp;E) as well as fluorescent dye. DNA from the treated cells showed characteristic laddering of DNA fragments in agarose gel electrophoresis. Cell populations undergoing secondary necrosis following apoptosis could also be detected in FACS by annexin V/propidium iodide (PI) staining. Activated caspase-3 in the treated HeLa cells was detected by polyclonal anti-caspase-3 antibody utilizing immunocytochemistry. Using transmission electron microscopy, sub-cellular changes like rough endoplasmic reticulum, swollen mitochondria, distorted mitochondrial membrane, loss of cristae and matrix were observed in the treated HeLa cells. Extensive plasma membrane blebbing was also observed by scanning electron microscopy. Our findings support that Phlogacanthus thyrsiflorus leaves are natural source of potent anticancer agent

Methanolic extract of Phlogacanthus thyrsiflorus Nees leaf induces apoptosis in cancer cells

153-161Phlogacanthus thyrsiflorus Nees is a medicinal herb commonly used in traditional folk medicine, and it is known to possess anticancer activity. Here, we explored the anticancer properties of methanolic extract of P. thyrsiflorus leaves in HeLa and MCF-7 cell lines. We observed nuclear fragmentation as indication of apoptosis in the MPT treated cancer cells using haematoxylin and eosin (H&amp;E) as well as fluorescent dye. DNA from the treated cells showed characteristic laddering of DNA fragments in agarose gel electrophoresis. Cell populations undergoing secondary necrosis following apoptosis could also be detected in FACS by annexin V/propidium iodide (PI) staining. Activated caspase-3 in the treated HeLa cells was detected by polyclonal anti-caspase-3 antibody utilizing immunocytochemistry. Using transmission electron microscopy, sub-cellular changes like rough endoplasmic reticulum, swollen mitochondria, distorted mitochondrial membrane, loss of cristae and matrix were observed in the treated HeLa cells. Extensive plasma membrane blebbing was also observed by scanning electron microscopy. Our findings support that Phlogacanthus thyrsiflorus leaves are natural source of potent anticancer agent

Growth of disc-like pseudo-bulges in SDSS DR7 since z = 0.1

Cosmological simulations predict more classical bulges than their observational counterpart in the local Universe. Here, we quantify evolution of the bulges since $z=0.1$ using photometric parameters of nearly 39,000 unbarred disc galaxies from SDSS DR7 which are well represented by two components. We adopted a combination of the S\'ersic index and Kormendy relation to separate classical bulges and disc-like pseudo-bulges. We found that the fraction of pseudo-bulges (classical bulges) smoothly increases (decreases) as the Universe gets older. In the history of the Universe, there comes a point ($z \approx 0.016$) when classical bulges and pseudo-bulges become equal in number. The fraction of pseudo-bulges rises with increasing bulge to disc half-light radius ratio until R$_{\rm e}$/R$_{\rm hlr} \approx 0.6$ suggesting concentrated disc is the most favourable place for pseudo-bulge formation. The mean ellipticity of pseudo-bulges is always greater than that of classical bulges and it decreases with decreasing redshift indicating that the bulges tend to be more axisymmetric with evolution. Also, the massive bulges are progressing towards axisymmetry at steeper rate than the low-mass bulges. There is no tight correlation of bulge S\'ersic index evolution with other photometric properties of the galaxy. Using the sample of multi-component fitting of $S^4G$ data and $N-$body galaxy models, we have verified that our results are consistent or even more pronounced with multi-component fitting and high-resolution photometry.Comment: 16 pages, 12 figures, accepted for publication in MNRA