Browsing by Subject "haloes"
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Item Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream Around NGC 4449 and Hierarchical Galaxy Formation on Small Scales(2012-04) Martinez-Delgado, David; Romanowsky, Aaron J.; Gabany, R. Jay; Annibali, Francesca; Arnold, Jacob A.; Fliri, Jurgen; Zibetti, Stefano; van der Marel, Roeland P.; Rix, Hans-Walter; Chonis, Taylor S.; Carballo-Bello, Julio A.; Aloisi, Alessandra; Maccio, Andrea V.; Gallego-Laborda, J.; Brodie, Jean P.; Merrifield, Michael R.; Chonis, Taylor S.A candidate diffuse stellar substructure was previously reported in the halo of the nearby dwarf starburst galaxy NGC 4449 by Karachentsev et al. We map and analyze this feature using a unique combination of deep integrated-light images from the BlackBird 0.5 m telescope, and high-resolution wide-field images from the 8 m Subaru Telescope, which resolve the nebulosity into a stream of red giant branch stars, and confirm its physical association with NGC 4449. The properties of the stream imply a massive dwarf spheroidal progenitor, which after complete disruption will deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The stellar mass ratio between the two galaxies is similar to 1:50, while the indirectly measured dynamical mass ratio, when including dark matter, may be similar to 1:10-1:5. This system may thus represent a "stealth" merger, where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial dynamical influence on its host galaxy. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.Item PHIBSS: Molecular Gas Content And Scaling Relations In Z Similar To 1-3 Massive, Main-Sequence Star-Forming Galaxies(2013-05) Tacconi, L. J.; Neri, R.; Genzel, R.; Combes, Francoise; Bolatto, A.; Cooper, Michael C.; Wuyts, S.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Omont, A.; Saintonge, A.; Griffin, K. S.; Shapley, A.; Sternberg, Assaf; Weiner, B.; Comerford, J.We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z similar to 1.2 and 2.2, with log(M-*(M-circle dot)) >= 10.4 and log(SFR(M-circle dot/yr)) >= 1.5. Including a correction for the incomplete coverage of the M-*-SFR plane, and adopting a "Galactic" value for the CO-H-2 conversion factor, we infer average gas fractions of similar to 0.33 at z similar to 1.2 and similar to 0.47 at z similar to 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z similar to 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a similar to 0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z similar to 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M-*, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z similar to 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.Item Variations in A Universal Dark Matter Profile for Dwarf Spheroidals(2013-09) Jardel, John R.; Gebhardt, Karl; Jardel, John R.; Gebhardt, KarlUsing a newly developed modeling technique, we present orbit-based dynamical models of the Carina, Draco, Fornax, Sculptor, and Sextans dwarf spheroidal (dSph) galaxies. These models calculate the dark matter profiles non-parametrically without requiring any assumptions to be made about their profile shapes. By lifting this restriction, we discover a host of dark matter profiles in the dSphs that are different from the typical profiles suggested by both theorists and observers. However, when we scale these profiles appropriately and plot them on a common axis, they appear to follow an approximate r (1) power law with considerable scatter.