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Abstract:

In a recent paper we presented the first semi-analytic model of galaxy formation in which the Thermally-Pulsing Asymptotic Giant Branch phase of stellar evolution has been fully implemented. Here we address the comparison with observations, and show how the TP-AGB recipe affects the performance of the model in reproducing the colours and near-IR luminosities of high-redshift galaxies. We find that the semi-analytic model with the TP-AGB better matches the colour-magnitude and colour-colour relations at z ~ 2, both for nearly-passive and for star-forming galaxies. The model with TP-AGB produces star-forming galaxies with red V-K colours, thus revising the unique interpretation of high-redshift red objects as 'red & dead'. We also show that without the TP-AGB the semi-analytic model fails at reproducing the observed colours, a situation that cannot be corrected by dust reddening. We also explore the effect of nebular emission on the predicted colour-magnitude relation of star-forming galaxies, to conclude that it does not play a significant role in reddening their colours, at least in the range of star-formation rates covered by the model. Finally, the rest-frame K-band luminosity function at z ~ 2.5 is more luminous by almost 1 magnitude. This indicates that the AGN feedback recipe that is adopted to regulate the high-mass end of the luminosity function should be sophisticated to take the effect of the stellar populations into account at high redshifts.

Abstract:

ATLAS^3D is a multi-wavelength, volume-limited survey of 263 morphologicallyselected early-type galaxies within a distance of 42 Mpc and complete to MK ≤ -21.5. Here we present the ATLAS^3D project and our first results on the stellar populations of galaxies in the ATLAS^3Dsample based on SAURON integral-field spectroscopy. We show relations between integrated line-strength indices and stellar velocity dispersion o in the range 55 ≤ Σ(km/s) ≤ 350. We derive simple-stellar-population-equivalent age, metallicity and α/Fe abundance ratio and discuss their relation to stellar velocity dispersion, environment and galaxy internal kinematics. These preliminary results indicate that slow rotators tend to be older and have less variation in age than fast rotators. We also find that galaxies in lower density environments are on average younger than those in denser environments, as found by other authors. © 2009 American Institute of Physics.

Abstract:

PDS 456 is a nearby (z=0.184), luminous (L_bol ~10^47 erg/s) type I quasar. A deep 190 ks Suzaku observation in February 2007 revealed the complex, broad band X-ray spectrum of PDS 456. The Suzaku spectrum exhibits highly statistically significant absorption features near 9 keV in the quasar rest--frame. We show that the most plausible origin of the absorption is from blue-shifted resonance (1s-2p) transitions of hydrogen-like iron (at 6.97 keV in the rest frame). This indicates that a highly ionized outflow may be present moving at near relativistic velocities (~0.25c). A possible hard X-ray excess is detected above 15 keV with HXD (at 99.8% confidence), which may arise from high column density gas (Nh>10^24cm^-2) partially covering the X-ray emission, or through strong Compton reflection. Here we propose that the iron K-shell absorption in PDS 456 is associated with a thick, possibly clumpy outflow, covering about 20% of $4Ï€$ steradian solid angle. The outflow is likely launched from the inner accretion disk, within 15-100 gravitational radii of the black hole. The kinetic power of the outflow may be similar to the bolometric luminosity of PDS 456. Such a powerful wind could have a significant effect on the co-evolution of the host galaxy and its supermassive black hole, through feedback.

Abstract:

The spectro-photometric properties of galaxies in galaxy formation models are obtained by combining the predicted history of star formation and mass accretion with the physics of stellar evolution through stellar population models. In the recent literature, significant differences have emerged regarding the implementation of the Thermally-Pulsing Asymptotic Giant Branch phase of stellar evolution. The emission in the TP-AGB phase dominates the bolometric and near-IR spectrum of intermediate-age (~1 Gyr) stellar populations, hence it is crucial for the correct modeling of the galaxy luminosities and colours. In this paper for the first time, we incorporate a full prescription of the TP-AGB phase in a semi-analytic model of galaxy formation. We find that the inclusion of the TP-AGB in the model spectra dramatically alters the predicted colour-magnitude relation and its evolution with redshift. When the TP-AGB phase is active, the rest-frame V-K galaxy colours are redder by almost 2 magnitudes in the redshift range z~2-3 and by 1 magnitude at z~1. Very red colours are produced in disk galaxies, so that the V-K colour distributions of disk and spheroids are virtually undistinguishable at low redshifts. We also find that the galaxy K-band emission is more than 1 magnitude higher in the range z~1-3. This may alleviate the difficulties met by the hierarchical clustering scenario in predicting the red galaxy population at high redshifts. The comparison between simulations and observations have to be revisited in the light of our results.