Large-Scale Structure in the NIR-Selected MUNICS Survey

The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and Voronoi-approach.Comment: 4 pages, to appear in "The Evolution of Galaxies III. From Simple Approaches to Self-Consistent Models", proceedings of the 3rd EuroConference on the evolution of galaxies, held in Kiel, Germany, July 16-20, 200

The Munich Near-Infrared Cluster Survey - I. Field selection, object extraction, and photometry

The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. It covers an area of roughly one square degree in the K' and J near-IR pass-bands. The survey area consists of 16 6' x 6' fields targeted at QSOs with redshifts 0.5 < z < 2 and 7 28' x 13' stripes targeted at `random' high Galactic latitude fields. Ten of the QSO fields were additionally imaged in R and I, and 0.6 square degrees of the randomly selected fields were also imaged in the V, R, and I bands. The resulting object catalogues were strictly selected in K', having a limiting magnitude (50 per cent completeness) of K' ~ 19.5 mag and J ~ 21 mag, sufficiently deep to detect passively evolving systems up to a redshift of z ~ 1.5 and luminosity of 0.5 L*. The optical data reach a depth of roughly R ~ 23.5 mag. The project's main scientific aims are the identification of galaxy clusters at redshifts around unity and the selection of a large sample of field early-type galaxies at 0 < z < 1.5 for evolutionary studies. In this paper - the first in a series - we describe the survey's concept, the selection of the survey fields, the near-IR and optical imaging and data reduction, object extraction, and the construction of photometric catalogues. Finally, we show the J-K' vs. K' colour-magnitude diagramme and the R-J vs. J-K', V-I vs. J-K', and V-I vs. V-R colour-colour diagrammes for MUNICS objects, together with stellar population-synthesis models for different star-formation histories, and conclude that the data set presented is suitable for extracting a catalogue of massive field galaxies in the redshift range 0.5 < z < 1.5 for evolutionary studies and follow-up observations.Comment: Accepted for publication in MNRA

Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common

We detect a Neptune mass-ratio (q~8e-5) planetary companion to the lens star in the extremely high-magnification (A~800) microlensing event OGLE-2005-BLG-169. If the parent is a main-sequence star, it has mass M~0.5 M_sun implying a planet mass of ~13 M_earth and projected separation of ~2.7 AU. When intensely monitored over their peak, high-magnification events similar to OGLE-2005-BLG-169 have nearly complete sensitivity to Neptune mass-ratio planets with projected separations of 0.6 to 1.6 Einstein radii, corresponding to 1.6--4.3 AU in the present case. Only two other such events were monitored well enough to detect Neptunes, and so this detection by itself suggests that Neptune mass-ratio planets are common. Moreover, another Neptune was recently discovered at a similar distance from its parent star in a low-magnification event, which are more common but are individually much less sensitive to planets. Combining the two detections yields 90% upper and lower frequency limits f=0.37^{+0.30}_{-0.21} over just 0.4 decades of planet-star separation. In particular, f>16% at 90% confidence. The parent star hosts no Jupiter-mass companions with projected separations within a factor 5 of that of the detected planet. The lens-source relative proper motion is \mu~7--10 mas/yr, implying that if the lens is sufficiently bright, I<23.8, it will be detectable by HST by 3 years after peak. This would permit a more precise estimate of the lens mass and distance, and so the mass and projected separation of the planet. Analogs of OGLE-2005-BLG-169Lb orbiting nearby stars would be difficult to detect by other methods of planet detection, including radial velocities, transits, or astrometry.Comment: Submitted to ApJ Letters, 9 text pages + 4 figures + 1 tabl

A wide angle tail radio galaxy in the COSMOS field: evidence for cluster formation

We have identified a complex galaxy cluster system in the COSMOS field via a wide angle tail (WAT) radio galaxy consistent with the idea that WAT galaxies can be used as tracers of clusters. The WAT galaxy, CWAT-01, is coincident with an elliptical galaxy resolved in the HST-ACS image. Using the COSMOS multiwavelength data set, we derive the radio properties of CWAT-01 and use the optical and X-ray data to investigate its host environment. The cluster hosting CWAT-01 is part of a larger assembly consisting of a minimum of four X-ray luminous clusters within ~2 Mpc distance. We apply hydrodynamical models that combine ram pressure and buoyancy forces on CWAT-01. These models explain the shape of the radio jets only if the galaxy's velocity relative to the intra-cluster medium (ICM) is in the range of about 300-550 km/s which is higher than expected for brightest cluster galaxies (BCGs) in relaxed systems. This indicates that the CWAT-01 host cluster is not relaxed, but is possibly dynamically young. We argue that such a velocity could have been induced through subcluster merger within the CWAT-01 parent cluster and/or cluster-cluster interactions. Our results strongly indicate that we are witnessing the formation of a large cluster from an assembly of multiple clusters, consistent with the hierarchical scenario of structure formation. We estimate the total mass of the final cluster to be approximately 20% of the mass of the Coma cluster.Comment: 18 pages, 13 figures; accepted for publication in ApJS, COSMOS special issue; added color figure (Fig. 13) which was previously unavailabl

Integrated specific star formation rates of galaxies, groups, and clusters: A continuous upper limit with stellar mass?

Aims: We investigate the build-up of stellar mass through star formation in field galaxies, galaxy groups, and clusters in order to better understand the physical processes regulating star formation in different haloes. Methods: In order to do so we relate ongoing star formation activity to the stellar mass by studying the integrated specific star formation rate (SSFR), defined as the star-formation rate per unit stellar mass, as a function of integrated stellar mass for samples of field galaxies, groups of galaxies, and galaxy clusters at 0.18 < z < 0.85. The star formation rate (SFR) is derived from the ultraviolet continuum for the galaxies and group members, and from emission line fluxes for the cluster galaxies. The stellar masses are computed from multi-band photometry including the near-infrared bands for the galaxies and groups, and from the dynamical mass for the cluster sample. Results: For the first time, integrated SSFRs for clusters and groups are presented and related to the SSFRs of field galaxies. Tentatively, we find a continuous upper limit for galaxies, groups, and clusters in the SSFR-stellar mass plane over seven orders of magnitude in stellar mass. This might indicate that the physical processes which control star formation in dark matter haloes of different mass have the same scaling with mass over a wide range of masses from dwarf galaxies to massive clusters of galaxies.Comment: Accepted for publication in A&A Letters; 4 pages, 1 figur

Determining the Physical Lens Parameters of the Binary Gravitational Microlensing Event MOA-2009-BLG-016

We report the result of the analysis of the light curve of the microlensing event MOA-2009-BLG-016. The light curve is characterized by a short-duration anomaly near the peak and an overall asymmetry. We find that the peak anomaly is due to a binary companion to the primary lens and the asymmetry of the light curve is explained by the parallax effect caused by the acceleration of the observer over the course of the event due to the orbital motion of the Earth around the Sun. In addition, we detect evidence for the effect of the finite size of the source near the peak of the event, which allows us to measure the angular Einstein radius of the lens system. The Einstein radius combined with the microlens parallax allows us to determine the total mass of the lens and the distance to the lens. We identify three distinct classes of degenerate solutions for the binary lens parameters, where two are manifestations of the previously identified degeneracies of close/wide binaries and positive/negative impact parameters, while the third class is caused by the symmetric cycloid shape of the caustic. We find that, for the best-fit solution, the estimated mass of the lower-mass component of the binary is (0.04 +- 0.01) M_sun, implying a brown-dwarf companion. However, there exists a solution that is worse only by \Delta\chi^2 ~ 3 for which the mass of the secondary is above the hydrogen-burning limit. Unfortunately, resolving these two degenerate solutions will be difficult as the relative lens-source proper motions for both are similar and small (~ 1 mas/yr) and thus the lens will remain blended with the source for the next several decades.Comment: 7 pages, 2 tables, and 5 figure