Browsing by Author "Kallivayalil, N."

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    A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21
    (IOP PUBLISHING LTD, 2017) Privon, G. C.; Stierwalt, S.; Patton, D. R.; Besla, G.; Pearson, S.; Putman, M.; Johnson, K. E.; Kallivayalil, N.; Liss, S.
    Interactions between pairs of isolated dwarf galaxies provide a critical window into low-mass hierarchical, gas-dominated galaxy assembly and the build-up of stellar mass in low-metallicity systems. We present the first Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) optical integral field unit (IFU) observations of the interacting dwarf pair dm1647+21 selected from the TiNy Titans survey. The Ha emission is widespread and corresponds to a total unobscured star formation rate (SFR) of 0.44 M-circle dot yr(-1), which is 2.7 times higher than the SFR inferred from Sloan Digital Sky Survey (SDSS) data. The implied specific SFR (sSFR) for the system is elevated by more than an order of magnitude above non-interacting dwarfs in the same mass range. This increase is dominated by the lower-mass galaxy, which has a sSFR enhancement of > 50. Examining the spatially resolved maps of classic optical line diagnostics, we find that the interstellar medium (ISM) excitation can be fully explained by star formation. The velocity field of the ionized gas is not consistent with simple rotation. Dynamical simulations indicate that the irregular velocity field and the stellar structure is consistent with the identification of this system as an ongoing interaction between two dwarf galaxies. The widespread, clumpy enhancements in the star formation in this system point to important differences in the effect of mergers on dwarf galaxies, compared to massive galaxies; rather than the funneling of gas to the nucleus and giving rise to a nuclear starburst, starbursts in low-mass galaxy mergers may be triggered by large-scale ISM compression, and thus may be more distributed.
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    Direct evidence of hierarchical assembly at low masses from isolated dwarf galaxy groups
    (2017) Stierwalt, S.; Liss, S. E.; Johnson, K. E.; Patton, D. R.; Privon, G. C.; Besla, G.; Kallivayalil, N.; Putman, M.
    The demographics of dwarf galaxy populations have long been in tension with predictions from the Cold Dark Matter (CDM) paradigm. If primordial density fluctuations were scale-free as predicted, dwarf galaxies should themselves host dark matter subhaloes, the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as satellites of more massive galaxies, and there is observational and theoretical evidence to suggest that these satellites at z=0 were captured by the massive host halo as a group. However, the evolution of dwarf galaxies is highly susceptible to environment making these satellite groups imperfect probes of CDM in the low mass regime. We have identified one of the clearest examples to date of hierarchical structure formation at low masses: seven isolated, spectroscopically confirmed groups with only dwarf galaxies as members. Each group hosts 3-5 known members, has a baryonic mass of similar to 4.4 x 10 degrees to 2 x 10(10) (M-circle dot and requires a mass-to-light ratio of <100 to be gravitationally bound. Such groups are predicted to be rare theoretically and found to be rare observationally at the current epoch and thus provide a unique window into the possible formation mechanism of more massive, isolated galaxies.
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    Mapping Milky Way And Local Volume Structure With LSST
    (2011) Geha, Marla C.; Willman, B.; Bochanski, J.; Bullock, J.; Catelan, Márcio; Debattista, V.; Grillmair, C.; Jordan, A.; Juric, M.; Kalirai, J.; Kallivayalil, N.; McGehee, P.; Minniti, D.; Munoz, R.; Roskar, R.; Sarajedini, A.; Simon, J.; Strader, J.
    The LSST will yield revolutionary, multi-dimensional maps of the Milky Way (MW) galaxy and its neighbors. With its planned 1000 epochs over 6 bands and a final limiting magnitude of r=27.5 (AB mag; 5-sigma), it will provide an excellent resource for mapping the structure and accretion history of the MW and beyond in a way that the present generation of surveys can only hint at. LSST is expected to catalog 10 billion stars, including photometric metallicities for the 200 million F/G stars within 100 kpc and map the tangential velocity field of stars bright than r=24 mag to at least 10 kpc (at 10 km/s precision) and as far as 25 kpc (at 60 km/s precision). Specific related science to be enabled by LSST includes: mapping the 3D distribution of dust in the MW's disk, including variations in RV; understanding the smooth distribution of stars in the MW and other nearby galaxies; understanding large-scale chemical gradients in the MW; discovering lumps and streams in metallicity and phase-space; inferring the mass distribution in the MW; discovering ultra-faint galaxies throughout the Local Volume....