Klaus Meisenheimer

Nearly 5000 Distant Early-Type Galaxies in COMBO-17: A Red Sequence and Its Evolution since z ~ 1

We present the rest-frame colors and luminosities of ~25,000 mR 24 galaxies in the redshift range 0.2 < z ≤ 1.1 drawn from 0.78 deg2 of the COMBO-17 survey (Classifying Objects by Medium-Band Observations in 17 Filters). We find that the rest-frame color distribution of these galaxies is bimodal at all redshifts out to z ~ 1. This bimodality permits a model-independent definition of red early-type galaxies and blue late-type galaxies at any given redshift. The colors of the blue peak become redder toward the present day, and the number density of blue luminous galaxies has dropped strongly since z ~ 1. Focusing on the red galaxies, we find that they populate a color-magnitude relation. Such red sequences have been identified in galaxy cluster environments, but our data show that such a sequence exists over this redshift range even when averaging over all environments. The mean color of the red galaxy sequence evolves with redshift in a way that is consistent with the aging of an ancient stellar population. The rest-frame B-band luminosity density in red galaxies evolves only mildly with redshift in a Λ-dominated cold dark matter universe. When we account for the change in stellar mass-to-light ratio implied by the redshift evolution in red galaxy colors, the COMBO-17 data indicate an increase in stellar mass on the red sequence by a factor of 2 since z ~ 1. The largest source of uncertainty is large-scale structure, implying that considerably larger surveys are necessary to further refine this result. We explore mechanisms that may drive this evolution in the red galaxy population, finding that both galaxy merging and truncation of star formation in some fraction of the blue star-forming population are required to fully explain the properties of these galaxies.

The central dusty torus in the active nucleus of NGC 1068.

Active galactic nuclei (AGNs) display many energetic phenomena—broad emission lines, X-rays, relativistic jets, radio lobes—originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the observational appearance of AGNs. Seen from certain directions, circum-nuclear dust clouds would block our view of the central powerhouse. Indirect evidence suggests that the dust clouds form a parsec-sized torus-shaped distribution. This explanation, however, remains unproved, as even the largest telescopes have not been able to resolve the dust structures. Here we report interferometric mid-infrared observations that spatially resolve these structures in the galaxy NGC 1068. The observations reveal warm (320 K) dust in a structure 2.1 parsec thick and 3.4 parsec in diameter, surrounding a smaller hot structure. As such a configuration of dust clouds would collapse in a time much shorter than the active phase of the AGN, this observation requires a continual input of kinetic energy to the cloud system from a source coexistent with the AGN.

The stellar masses of 25 000 galaxies at 0.2 ≤ z ≤ 1.0 estimated by the COMBO-17 survey

We present an analysis of stellar mass estimates for a sample of 25000 galaxies from the COMBO-17 survey over the interval

The merger rate of massive galaxies

0.2

GEMS: The Surface Brightness and Surface Mass Density Evolution of Disk Galaxies

60\%

Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy

) of massive galaxies with

GEMS: Galaxy Fitting Catalogs and Testing Parametric Galaxy Fitting Codes: GALFIT and GIM2D

M_* > 10^{11} M_{\odot}

The STAGES view of red spirals and dusty red galaxies: mass-dependent quenching of star formation in cluster infall

at all

Stellar rotation and variability in the Orion Nebula Cluster

z < 1

Three-dimensional radiative transfer models of clumpy tori in Seyfert galaxies

are non-star-forming; blue star-forming galaxies dominate at lower masses. We have used these mass estimates to explore the evolution of the stellar mass function since