1607.02507
How to quench a galaxy
Pontoon, Tremmel, Roth, Peiris, Saintonge, Volonteri, Quinn, Governato
Show how the interplay between AGN and merger history determines whether a galaxy quenches SF at high z. First simulate, in a full cosmo context, a galaxy of total dynamical mass 1e12 Msun at z=2. Then systematically alter the accretion history of the galaxy by minimally changing the linear overdensity in the initial conditions. This "genetic modification" approach allows the generation of 3 sets of LCDM initial conditions leading to maximum merger ratios of 1:10, 1:5, and 2:3 respectively. The changes leave the final halo mass, LSS and local environment unchanged, to a star-forming, temporarily-quenched and permanently-quenched galaxy. However the differences do not primarily lie in the BH accretion rates, but in the kinetic effects of the merger: the galaxy is resilient against AGN feedback unless its gaseous disk is first disrupted. Typical accretion rates are comparable in the 3 cases, falling below 0.1 Msun/yr, equivalent to around 2% of the Eddington rate or 1e-3 times the pre-quenching SFR, in agreement with observations. This low level of BH accretion can be sustained even when there is insufficient dense cold gas for SF. Conversely, SN feedback is too distributed to generate outflows in high-mass systems, and cannot maintain quenching over periods longer than the halo gas cooling time.
1607.02596
Large-scale fluctuations in the number density of galaxies in independent surveys of deep fields
Shirokov, et al
New arguments supporting the reality of LS fluctuations in the density of the visible matter in deep galaxy surveys are presented. A statistical analysis of the radial distributions of galaxies in the COSMOS and HDF-N deep fields is presented. Independent spectral and photometric surveys exist for each field, carried out in different wavelength ranges and using different observing methods. Catalogs of photo-z in the optical (COSMOS-Zphot) and IR (UltraVISTA) were used for the COSMOS field in 0.1<z<3.5, as well as the zCOSMOS (10kZ) spec-z survey and the XMM-COSMOS and ALHAMBRA-F4 photo-z surveys. The HDFN-Zphot and ALHAMBRA-F5 catalogs of photo-z were used for the HDF-N field. The Pearson correlation coefficient for the fluctuations in the numbers of galaxies obtained for independent surveys of the same deep field reaches R=0.70±0.16. The presence of this positive correlation supports the reality of fluctuations in the density of visible matter with sizes of up to 1k Mpc and amplitudes of up to 20% at z~2. The absence of correlations between the fluctuations in different fields (the correlation coefficient between COSMOS and HDF-N is r=-0.20±0.31 testifies to the independence of structures visible in different directions on the celestial sphere. This also indicates an absence of any influence from universal systematic errors (such as "spectral voids"), which could imitate the detection of correlated structures.
1607.02971
GAMA/H-ATLAS: common star-formation rate indicators and their dependence on galaxy physical parameters
Wang, et al
Compare common SFR indicators in the local Universe in the GAMA equatorial fields (around 160 sq. deg), using UV photometry from GALEX, FIR and sub-mm photometry from H-ATLAS, and Halpha spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift 0.08), consider 3 SFR tracers: UV luminosity corrected for dust attenuation using the UV spectral slope beta (SFRUV,corr), Halpha line luminosity corrected for dust using the Balmer decrement (BD) (SFRHalpha,corr), and the combination of UV and IR emission (SFRUV+IR). Demonstrate the SFRUV,corr can be reconciled with the other 2 tracers after applying attenuation corrections by calibrating IRX (i.e. the IR to UV luminosity ratio) and attenuation in the Halpha (derived from BD) against beta. However, beta on its own is very unlikely to be a reliable attenuation indicator. Find that attenuation correction factors depend on parameters such as stellar mass, z and dust temperature (Tdust), but not on Halpha equivalent width (EW) or Sersic index. Due to the large scatter in the IRX vs beta correlation, when compared to SFRUV+IR, the beta-corrected SFRUV,corr exhibits systematic deviations as a function of IRX,BD and Tdust.
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