Gralla M.B.,Johns Hopkins University |
Crichton D.,Johns Hopkins University |
Marriage T.A.,Johns Hopkins University |
Mo W.,Johns Hopkins University |
And 43 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014
We present a statistical analysis of the millimetre-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich (SZ) effect associated with the haloes that host them. We stack data at 148, 218 and 277GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4GHz. The thermal SZ effect associated with the haloes that host the AGN is detected at the 5σ level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowestmass haloes (average M200 ≈ 1013 M h -170) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous haloes. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyse the contribution of radio sources to the angular power spectrum of the cosmic microwave background. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Jose C.,University of Pune |
Subramanian K.,University of Pune |
Srianand R.,University of Pune |
Samui S.,Astrophysics and Cosmology Research Unit
Monthly Notices of the Royal Astronomical Society | Year: 2013
We present a physically motivated semi-analytic model to understand the clustering of highredshift Lyman-break galaxies (LBGs). We show that the model parameters constrained by the observed luminosity function can be used to predict large-scale (i.e. θ ≥ 80 arcsec) bias and angular correlation function of galaxies. These predictions are shown to reproduce the observations remarkably well. We then adopt these model parameters to calculate the halo occupation distribution (HOD) using the conditional mass function. The halo model using this HOD is shown to provide a reasonably good fit to the observed clustering of LBGs at both large and small (θ ≤ 10 arcsec) angular scales for the whole range of z = 3-5 and limiting magnitudes. However, our models underpredict the clustering amplitude at intermediate angular scales, where quasi-linear effects are important. The average mass of haloes contributing to the observed clustering is found to be 6.2 × 1011M⊙ and the characteristic mass of a parent halo hosting satellite galaxies is 1.2 × 1012M⊙ for a limiting absolute magnitude of -20.5 at z = 4. For a given threshold luminosity, these masses decrease with increasing z and at any given z these are found to increase with increasing value of threshold luminosity. Our physical model for the HOD suggests that approximately 40 per cent of the haloes above a minimum mass Mmin can host detectable central galaxies and about 5-10 per cent of these haloes are likely to also host a detectable satellite. These satellites form typically a dynamical time-scale prior to the formation of the parent halo. The small angular scale clustering is mainly due to central-satellite pairs rather than a few large clusters. It is quite sensitive to changes in the duration of star formation in a halo and hence could provide a probe of this quantity. The present data favour star formation in a halo lasting typically for a few dynamical time-scales, with 50 per cent of stars formed in a time of T ~ 300-500 Myr for dark matter haloes that collapse in the redshift range of 5.5-3.5. Our models also reproduce different known trends between parameters related to star formation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.