The DEEP2 and COMBO-17 surveys are compared to study luminosity functions of red and blue galaxies to z ~ 1. The two surveys have different methods and sensitivities, but nevertheless results agree. After z ~ 1, M has dimmed by 1.2-1.3 mag for all colors of galaxies, * for blue galaxies has hardly changed, and * for red galaxies has at least doubled (our formal value is ~0.5 dex). Luminosity density jB has fallen by 0.6 dex for blue galaxies but has remained nearly constant for red galaxies. These results imply that the number and total stellar mass of blue galaxies have been substantially constant since z ~ 1, whereas those of red galaxies (near L*) have been significantly rising. To explain the new red galaxies, a ``mixed'' scenario is proposed in which star formation in blue cloud galaxies is quenched, causing them to migrate to the red sequence, where they merge further in a small number of stellar mergers. This mixed scenario matches the local boxy-disky transition for nearby ellipticals, as well as red sequence stellar population scaling laws such as the color-magnitude and Mg-? relations (which are explained as fossil relics from blue progenitors). Blue galaxies enter the red sequence via different quenching modes, each of which peaks at a different characteristic mass and time. The red sequence therefore likely builds up in different ways at different times and masses, and the concept of a single process that is ``downsizing'' (or upsizing) probably does not apply. Our claim in this paper of a rise in the number of red galaxies applies to galaxies near L*. Accurate counts of brighter galaxies on the steep part of the Schechter function require more accurate photometry than is currently available.

https://iopscience.iop.org/article/10.1086/519294/pdf

Galaxy luminosity functions to z∼ 1 from DEEP2 and COMBO-17: Implications for red galaxy formation

The strong deviation in the properties of X-ray clusters from simple scaling laws highlights the importance of non-gravitational heating and cooling processes in the evolution of proto-cluster gas. We investigate this from two directions: by finding the amount of `excess energy' required in intra-cluster gas in order to reproduce the observed X-ray cluster properties, and by studying the excess energies obtained from supernovae in a semi-analytic model of galaxy formation. Using the insights obtained from the model, we then critically discuss possible ways of achieving the high excess specific energies required in clusters. These include heating by supernovae and active galactic nuclei, the role of entropy, and the effect of removing gas through radiative cooling. 
Our model self-consistently follows the production of excess energy as well as its effect on star formation in galaxies. Excess energy is retained in gas as gravitational, kinetic and/or thermal energy. The gas distribution of virialized halos are modelled with a 2-parameter family of gas density profiles; gas profiles are then chosen according to the total energy of the gas. We investigate four contrasting ways of modifying gas density profiles in the presence of excess energy, in order to study the sensitivity of results to the model. In addition, we estimate the minimum excess specific energy required when all available gas profiles are considered, using a fiducial cluster with a temperature of around 2 keV. We find that the excess specific energies required in clusters lie roughly in the range 1--3 keV/particle. (abridged)

Non-Gravitational Heating in the Hierarchical Formation of X-ray Clusters

We present clear spectroscopic detections of molecular hydrogen in the outer filaments of the Ha nebula surrounding the central galaxy of the Perseus cluster, NGC 1275. This implies the presence of warm molecular gas clouds at projected distances up to 24 kpc from the nucleus of the host galaxy, embedded in the hot intracluster medium. The emission-line intensity ratios reveal that the H 2 is predominately thermally excited with excitation temperatures of 1600-2200 K, suggesting a lack of pressure balance between the molecular component and its surrounding medium. Excitation by stellar ultraviolet or by the central active galactic nucleus is shown to be unlikely, while thermal excitation by X-rays or conduction from the ICM or shocks are all possibilities. Evidence for a non-thermal component is found in the spectra of some regions based on a low ortho-to-para ratio.

/pdf/detections-of-molecular-hydrogen-in-the-outer-filaments-of-1qm8qi9ta5.pdf

Detections of molecular hydrogen in the outer filaments of NGC 1275

Chandra and XMM-Newton observations have confirmed the presence of large temperature gradients within the cores of many relaxed clusters of galaxies. Here we investigate whether thermal conduction operating over those gradients can supply sufficient heat to offset radiative cooling. Narayan & Medvedev (2001) and Gruzinov (2002) have noted, using published results on cluster temperatures, that conduction within a factor of a few of the Spitzer rate is sufficient to balance bremsstrahlung cooling. From a detailed study of the temperature and emission measure profiles of Abell 2199 and Abell 1835, we find that the heat flux required by conduction is consistent with or below the rate predicted by Spitzer in the outer regions of the core. Conduction may therefore explain the lack of observational evidence for large mass cooling rates inferred from arguments based simply on radiative cooling, provided that conductivity is suppressed by no more than a factor of three below the full Spitzer rate. To stem cooling in the cluster centre, however, would necessitate conductivity values at least a factor of two larger than the Spitzer values, which we consider implausible. This may provide an explanation for the observed star formation and optical nebulosities in cluster cores. The solution is likely to be time dependent. We briefly discuss the possible origin of the cooler gas and the implications for massive galaxies.

Conduction and cooling flows

Current, accumulating evidence for (mildly) relativistic blue- and red-shifted absorption lines in AGNs is reviewed XMM-Newton and Chandra sensitive X-ray observations are starting to probe not only the kinematics (velocity) but also the dynamics (accelerations) of highly ionized gas flowing in-and-out from, likely, a few gravitational radii from the black hole It is thus emphasized that X-ray absorption-line spectroscopy provides new potential to map the accretion flows near black holes, to probe the launching regions of relativistic jets/outflows, and to quantify the cosmological feedback of AGNs Prospects to tackle these issues with future high energy missions are briefly addressed (© 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Relativistic blue- and red-shifted absorption lines in AGNs

Two lines of evidence indicate that active galaxies, principally radio galaxies, have heated the diffuse hot gas in clusters. The first is the general need for additional heating to explain the steepness of the X-ray luminosity-temperature relation in clusters, the second is to solve the cooling-flow problem in cluster cores. The inner core of many clusters is radiating energy as X-rays on a time-scale much shorter than its likely age. Although the temperature in this region drops by a factor of about three from that of the surrounding gas, little evidence is found for gas much cooler than that. Some form of heating appears to be taking place, probably by energy transported outward from the central accreting black hole or radio source. How that energy heats the gas depends on poorly understood transport properties (conductivity and viscosity) of the intracluster medium. Viscous heating is discussed as a possibility. Such heating processes have consequences for the truncation of the luminosity function of massive galaxies.

Active galaxies and cluster gas

The X-ray spectra of many Seyfert 1 galaxies show an iron-K emission line. Some of these lines are broad and skew, reflecting the rapid motion of the accreting gas together with the deep gravitational potential of the central black hole. The observational evidence for broad iron lines is reviewed, from ASCA to recent Chandra and XMM-Newton spectra. Examples are shown from MCG-6-30-15, for which line variability is discussed. Current results indicate that we are studying accretion flows well within 6GM/c 2 .

A. C. Fabian

Papers

Active galaxies and cluster gas

X-rays from active galactic nuclei: relativistically broadened emission lines

X-rays from active galactic nuclei: relativistically broadened emission lines