Cosmic Evolution of Stellar Disk Truncations: From z~1 to the Local Universe

We have conducted the largest systematic search so far for stellar disk truncations in disk-like galaxies at intermediate redshift (z<1.1), using the Great Observatories Origins Deep Survey South (GOODS-S) data from the Hubble Space Telescope - ACS. Focusing on Type II galaxies (i.e. downbending profiles) we explore whether the position of the break in the rest-frame B-band radial surface brightness profile (a direct estimator of the extent of the disk where most of the massive star formation is taking place), evolves with time. The number of galaxies under analysis (238 of a total of 505) is an order of magnitude larger than in previous studies. For the first time, we probe the evolution of the break radius for a given stellar mass (a parameter well suited to address evolutionary studies). Our results suggest that, for a given stellar mass, the radial position of the break has increased with cosmic time by a factor 1.3+/-0.1 between z~1 and z~0. This is in agreement with a moderate inside-out growth of the disk galaxies in the last ~8 Gyr. In the same period of time, the surface brightness level in the rest-frame B-band at which the break takes place has increased by 3.3+/-0.2 mag/arcsec^2 (a decrease in brightness by a factor of 20.9+/-4.2). We have explored the distribution of the scale lengths of the disks in the region inside the break, and how this parameter relates to the break radius. We also present results of the statistical analysis of profiles of artificial galaxies, to assess the reliability of our results.Comment: 22 pages, 14 figures, accepted for publication in ApJ. Figures 1, 3 and 6 have somehow downgraded resolution to match uploading requirement

Over speed detection using Artificial Intelligence

Over speeding is one of the most common traffic violations. Around 41 million people are issued speeding tickets each year in USA i.e one every second. Existing approaches to detect over- speeding are not scalable and require manual efforts. In this project, by the use of computer vision and artificial intelligence, I have tried to detect over speeding and report the violation to the law enforcement officer. It was observed that when predictions are done using YoloV3, we get the best results

A Possible Formation Scenario for Dwarf Spheroidal Galaxies - II: A Parameter Study

Dwarf spheroidal (dSph) galaxies are considered the basic building blocks of the galaxy formation process in the LCDM (Lambda Cold Dark Matter) hierarchical cosmological model. These galaxies are believed to be the most dark matter (DM) dominated systems known, have the lowest stellar content, and are poor in gas. Many theories attempt to explain the formation of dSph galaxies resorting to the fact that these galaxies are mainly found orbiting large galaxies or invoking other mechanisms of interactions. Here we show the full set of simulation as an extension of our fiducial model, where we study the formation of classical dSph galaxies in isolation by dissolving star clusters within the DM halo of the dwarf galaxy. In our parameter survey we adopt cored and cusped DM halo profiles and consider different numbers of dissolving star clusters. We investigate the dependency of observable quantities with different masses and scale-lengths of the DM halo and different star formation efficiencies (SFE). We find that our proposed scenario explains many features of the classical dSph galaxies of the Milky Way, like their morphology and their dynamics. We see trends how the surface brightness and the scale-length of the luminous component vary with the parameters of our simulations. We also identify how irregularities in their shape, i.e. clumpiness and ellipticity vary in our simulations. In velocity space, we identify the parameters leading to flat velocity dispersions curves. We recognize kinematically cold substructures in velocity space, named fossil remnants and stemming from our unique initial conditions, which alter the expected results. These streaming motions are considered as a key feature for future observation with high resolution to validate our scenario.Comment: 23 pages, 9 figures, 4 Tables, accepted for publication in MNRA

GALAXY DYNAMICS IN CLUSTERS

We use high resolution simulations to study the formation and distribution of galaxies within a cluster which forms hierarchically. We follow both dark matter and baryonic gas which is subject to thermal pressure, shocks and radiative cooling. Galaxy formation is identified with the dissipative collapse of the gas into cold, compact knots. We examine two extreme representations of galaxies during subsequent cluster evolution --- one purely gaseous and the other purely stellar. The results are quite sensitive to this choice. Gas-galaxies merge efficiently with a dominant central object while star-galaxies merge less frequently. Thus, simulations in which galaxies remain gaseous appear to suffer an ``overmerging'' problem, but this problem is much less severe if the gas is allowed to turn into stars. We compare the kinematics of the galaxy population in these two representations to that of dark halos and of the underlying dark matter distribution. Galaxies in the stellar representation are positively biased (\ie over-represented in the cluster) both by number and by mass fraction. Both representations predict the galaxies to be more centrally concentrated than the dark matter, whereas the dark halo population is more extended. A modest velocity bias also exists in both representations, with the largest effect, $\sigma_{gal}/\sigma_{DM} \simeq 0.7$, found for the more massive star-galaxies. Phase diagrams show that the galaxy population has a substantial net inflow in the gas representation, while in the stellar case it is roughly in hydrostatic equilibrium. Virial mass estimators can underestimate the true cluster mass by up to a factor of 5. The discrepancy is largest if only the most massive galaxies are used, reflecting significant mass segregation.Comment: 30 pages, self-unpacking (via uufiles) postscript file without figures. Eighteen figures (and slick color version of figure 3) and entire paper available at ftp://oahu.physics.lsa.umich.edu/groups/astro/fews Total size of paper with figures is ~9.0 Mb uncompressed. Submitted to Ap.J