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A FORMATION SCENARIO FOR THE DISK OF SATELLITES: ACCRETION OF SATELLITES DURING MERGERS
Smith, Rory,Duc, Pierre Alain,Bournaud, Frederic,Yi, Sukyoung K. American Astronomical Society 2016 The Astrophysical journal Vol.818 No.1
<P>The Disk of Satellites (DoS) observed in the Andromeda galaxy is a thin and extended group of satellites, nearly perpendicular to the disk plane, that share a common direction of rotation about the center of Andromeda. Although a DoS is also observed in the Milky Way galaxy, the prevalance of such structures in more distant galaxies remains controversial. Explanations for the formation of such DoSs vary widely from filamentary infall, or flattening due to the potential field from the large-scale structure, to galaxy interactions in a Mondian paradigm. Here we present an alternative scenario-during a merger, a galaxy may bring its own satellite population when merging with another galaxy. We demonstrate how, under the correct circumstances, during the coalescence of the two galaxies, the satellite population can be spread into an extended, flattened structure, with a common direction of rotation about the merger remnant. We investigate the key parameters of the interaction and the satellite population that are required to form a DoS in this scenario.</P>
Sargent, M. T.,Daddi, E.,Bournaud, F.,Onodera, M.,Feruglio, C.,Martig, M.,Gobat, R.,Dannerbauer, H.,Schinnerer, E. IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.806 No.1
<P>Gas and dust in star-forming galaxies at the peak epoch of galaxy assembly are presently the topic of intense study, but little is known about the interstellar medium (ISM) of distant, passively evolving galaxies. We report on a deep 3 mm band search with the IRAM/Plateau de Bure Interferometer for molecular (H-2) gas in a massive (M-star similar to 6 x 10(11) M-circle dot) elliptical galaxy at z= 1.4277, the first observation of this kind ever attempted. We place a 3 sigma upper limit of 0.32 Jy kms(-1) on the flux of the CO-(J = 2 -> 1) line or L-CO' < 8.8 x 10(9) Kkms(-1) pc(2), assuming a disk-like CO-morphology and a circular velocity scaling with the stellar velocity dispersion as in local early-type galaxies (ETGs). This translates to an H-2 mass of < 3.9 x 10(10) (alpha(CO)/4.4) M-circle dot or a gas fraction of less than or similar to 6% assuming a Salpeter initial mass function and an ISM dominated by H-2, as observed in many local, high-mass ellipticals. This low value approaches that of local ETGs, suggesting that the low star formation activity in massive, high-z passive galaxies reflects a true dearth of gas and a lesser role for inhibitive mechanisms like morphological quenching.</P>
An extremely young massive clump forming by gravitational collapse in a primordial galaxy
Zanella, A.,Daddi, E.,Le Floc’h, E.,Bournaud, F.,Gobat, R.,Valentino, F.,Strazzullo, V.,Cibinel, A.,Onodera, M.,Perret, V.,Renaud, F.,Vignali, C. Nature Publishing Group, a division of Macmillan P 2015 Nature Vol.521 No.7550
When cosmic star formation history reaches a peak (at about redshift z ≈ 2), galaxies vigorously fed by cosmic reservoirs are dominated by gas and contain massive star-forming clumps, which are thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not yet been observed, and it is debated whether clumps can survive energetic feedback from young stars, and afterwards migrate inwards to form galaxy bulges. Here we report the spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates star formation in the galaxy disk, its stellar continuum remains undetected in deep imaging, revealing an extremely young (less than ten million years old) massive clump, forming through the gravitational collapse of more than one billion solar masses of gas. Gas consumption in this young clump is more than tenfold faster than in the host galaxy, displaying high star-formation efficiency during this phase, in agreement with our hydrodynamic simulations. The frequency of older clumps with similar masses, coupled with our initial estimate of their formation rate (about 2.5 per billion years), supports long lifetimes (about 500 million years), favouring models in which clumps survive feedback and grow the bulges of present-day galaxies.
METAL DEFICIENCY IN CLUSTER STAR-FORMING GALAXIES AT<i>Z</i>= 2
Valentino, F.,Daddi, E.,Strazzullo, V.,Gobat, R.,Onodera, M.,Bournaud, F.,Juneau, S.,Renzini, A.,Arimoto, N.,Carollo, M.,Zanella, A. IOP Publishing 2015 The Astrophysical journal Vol.801 No.2
<P>We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = 1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 <= log(M/M-circle dot) <= 11, we find a similar to 4 sigma. lower [N II]/H alpha ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with H beta and [O III] in the observed range, we measure an [O III]/H beta ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher H alpha luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on. the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.</P>
Valentino, Francesco,Daddi, Emanuele,Finoguenov, Alexis,Strazzullo, Veronica,Brun, Amandine Le,Vignali, Cristian,Bournaud, Fré,dé,ric,Dickinson, Mark,Renzini, Alvio,Bé,thermin, Matth American Astronomical Society 2016 The Astrophysical journal Vol.829 No.1
<P>We present the discovery of a giant >= 100 kpc Ly alpha nebula detected in the core of the X-ray emitting cluster CL J1449 +0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Lya nebulae and overdense regions of the universe to the dense core of a 5-7 x 10(13) M-circle dot cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly alpha to X-ray luminosity ratio (L-Ly alpha/L-X approximate to 0.3, greater than or similar to 10-1000 times. higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly alpha-emitting gas and the possible interplay with the X-ray phase, we argue that the Ly alpha nebula would be short-lived (less than or similar to 10 Myr) if not continuously replenished with cold gas at a rate of greater than or similar to 1000 M-circle dot yr(-1). We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of approximate to 2 keV per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds. of the mass, while the rest is supplied by supernovae-driven winds.</P>