1510.06738
Cold-gas outflows in typical low-redshift galaxies are driven by stars formation, not AGN
Sarzi, Kaviraj, Nedelchev, Tiffany, Shabala, Deller, Niddleberg
Energetic feedback from AGN is an important ingredient for regulating the SFH of galaxies in models of galaxy formation, which makes it important to study how AGN feedback actually occurs in practice. In order to catch AGNs in the act of quenching SF, use the interstellar NaD absorption lines to look for cold-gas outflows in a sample of 456 nearby galaxies for which the presence of radio AGN activity can be unambiguously ascertained, thanks to radio imaging at milli-arcsecond scales. While compact radio emission indicating a radio AGN was found in 103 galaxies (23% of the sample), and 23 objects (5%) exhibited NaD absorption-line kinematics suggested of cold-gas outflows, not one object showed evidence of a radio AGN and of a cold-gas outflow simultaneously. Radio AGN activity was found predominantly in early-type galaxies, while cold-gas outflows were mainly seen in spiral galaxies with central SF or composite SF/AGN activity. Optical AGNs also do not seem capable of driving galactic winds in the sample. The work adds to a picture of the low-z Universe where cold-gas outflows in massive galaxies are generally driven by SF and where radio-AGN activity occurs most often in systems in which the gas reservoir has already been significantly depleted.
1510.06744
First results from COPSS: the CO power spectrum survey
Keating, Bower, et al
Present constraints on the abundance of CO in the early Universe from COPSS. Utilize a dataset collected between 2005 and 2008 using SZA, which were previously used to measured arcminute-scale fluctuations of the CMB. This data set features observations of 44 fields, covering an effective area of 1.7 sq.deg., over a frequency range of 27 to 35 GHz. Using the technique of intensity mapping, it is possible to probe the CO(1-0) transition, with sensitivity to spatial modes between k=0.5-2 h/Mpc over a range in redshift of z-2.3-3.3, spanning a comoving volume of 3.6e6 h^-3 Mpc^3. Demonstrate the ability to mitigate foregrounds, and present estimates of the impact of continuum sources on the measurement. Constrain the CO PS to P_CO<2.6e4 muK^2(Mpc/h)^3 at 95% CL. This limit resides near optimistic predictions for the CO PS. Under the assumption that CO emission is proportional to halo mass during bursts of active SF, this corresponds to a limit on the ratio of CO(1-0) luminosity to host halo mass of A_CO<1.2e-5 Lsun/Msun. Further assuming a MW-like conversion factor between CO luminosity and molecular gas mass (a_CO-4.3Msun(K km/s /pc^2)^-1), constrain the global density of molecular gas to rho_{z~3}(M_H2)<2.8e8Msun/Mpc^3.
1510.06752
Intrinsic alignments of BOSS LOWZ galaxies II: impact of shape measurement methods
Singh, Mandelbaum
Measurements of IA of galaxy shapes with the LS density field, and the inferred IA model parameters, are sensitive to the shape measurement methods used. In this paper, measure the IA of SDSS-III BOSS LOWZ galaxies using 3 different shape measurement methods (re-Gaussianization, isophotal, and deVaucouleurs), identifying a variation in the inferred IA amplitude at the 40% level between these methods, independent of the galaxy luminosity or other properties. Also carry out a suite of systematics tests on the shapes and their 2PCFs, identifying a pronounced contribution from additive PSF systematics in the deV shapes. Since different methods measure galaxy shapes at different effective radii, the trends identified in the IA amplitude are consistent with the interpretation that the outer regions of galaxy shapes are more responsive to tidal fields, resulting in isophote twisting and stronger alignments for isophotal shapes. Observe environmental dependence of ellipticity, with brightest galaxies in groups being rounder on average compared to satellite and field galaxies. Also study the anisotropy in IA measurements introduced by projected shapes, finding effects consistent with predictions of the nonlinear alignment model and hydrodynamic simulations. The large variations seen using the different shape measurement methods have important implications for IA forecasting and mitigation with future surveys.
1510.07024
Intrinsic alignments of disk and elliptical galaxies in the Massive Black-II and Illustris simulations
Tenneti, Mandelbaum, Di Matteo
Study the shapes and IA of disks and elliptical galaxies in MBII and Illustris cosmo hydro sims, with volumes of (100Mpc/h)^3 and (75Mpc/h)^3, respectively. Find that simulated disk galaxies are more oblate in shape and more misaligned with the shape of their host DM sub halo when compared with ellipticals. The disk major axis is found to be oriented towards the location of nearby elliptical galaxies. Also find that the disks are thinner in MBII and misalignments with DM halo orientations are smaller in both disks and ellipticals when compared with Illustris. As a result, the IA correlation functions at fixed mass have a higher amplitude in MBII than in Illustris. Despite significant differences in the treatments of hydrodynamics and baryonic physics in the simulations, find that the correlation function scale similarly with transverse separation (yet both have a different scale dependence to the correlation functions of the shapes of DM sub haloes within the same simulation). This is true for both disks and ellipticals. This results makes it likely that we should be able to use information from hydro sims to understand IA 2pt stats. Finally in scales above ~0.1 Mpc/h, the intrinsic alignment 2PCF for disk galaxies in both simulations are consistent with a null detection, unlike those for ellipticals.
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