82 research outputs found
The 64 Mpixel wide field imager for the Wendelstein 2m Telescope: Design and Calibration
The Wendelstein Observatory of Ludwig Maximilians University of Munich has
recently been upgraded with a modern 2m robotic telescope. One Nasmyth port of
the telescope has been equipped with a wide-field corrector which preserves the
excellent image quality (< 0.8" median seeing) of the site (Hopp et al. 2008)
over a field of view of 0.7 degrees diameter. The available field is imaged by
an optical imager (WWFI, the Wendelstein Wide Field Imager) built around a
customized 2 2 mosaic of 4k 4k 15 \mu m e2v CCDs from
Spectral Instruments. This paper provides an overview of the design and the
WWFI's performance. We summarize the system mechanics (including a structural
analysis), the electronics (and its electromagnetic interference (EMI)
protection) and the control software. We discuss in detail detector system
parameters, i.e. gain and readout noise, quantum efficiency as well as charge
transfer efficiency (CTE) and persistent charges. First on sky tests yield
overall good predictability of system throughput based on lab measurements.Comment: 38 pages 19 Figures To be published in Springer Experimental
Astronom
The connection between star formation and stellar mass: Specific star formation rates to redshift one
We investigate the contribution of star formation to the growth of stellar
mass in galaxies over the redshift range 0.5 < z < 1.1 by studying the redshift
evolution of the specific star formation rate (SSFR), defined as the star
formation rate per unit stellar mass. We use an I-band selected sample of 6180
field galaxies from the Munich Near-Infrared Cluster Survey (MUNICS) with
spectroscopically calibrated photometric redshifts. The SSFR decreases with
stellar mass at all redshifts. The low SSFRs of massive galaxies indicates that
star formation does not significantly change their stellar mass over this
redshift range: The majority of massive galaxies have assembled the bulk of
their mass before redshift unity. Furthermore, these highest mass galaxies
contain the oldest stellar populations at all redshifts. The line of maximum
SSFR runs parallel to lines of constant star formation rate. With increasing
redshift, the maximum SFR is generally increasing for all stellar masses, from
SFR ~ 5 M_sun/yr at z = 0.5 to SFR ~ 10 M_sun/yr at z = 1.1. We also show that
the large SSFRs of low-mass galaxies cannot be sustained over extended periods
of time. Finally, our results do not require a substantial contribution of
merging to the growth of stellar mass in massive galaxies over the redshift
range probed. We note that highly obscured galaxies which remain undetected in
our sample do not affect these findings for the bulk of the field galaxy
population.Comment: 5 pages, 3 colour figures, accepted for publication in MNRAS Letter
Specific star formation rates to redshift 5 from the FORS Deep Field and the GOODS-S Field
We explore the build-up of stellar mass in galaxies over a wide redshift
range 0.4 < z < 5.0 by studying the evolution of the specific star formation
rate (SSFR), defined as the star formation rate per unit stellar mass, as a
function of stellar mass and age. Our work is based on a combined sample of ~
9000 galaxies from the FORS Deep Field and the GOODS-S field, providing high
statistical accuracy and relative insensitivity against cosmic variance. As at
lower redshifts, we find that lower-mass galaxies show higher SSFRs than higher
mass galaxies, although highly obscured galaxies remain undetected in our
sample. Furthermore, the highest mass galaxies contain the oldest stellar
populations at all redshifts, in principle agreement with the existence of
evolved, massive galaxies at 1 < z < 3. It is remarkable, however, that this
trend continues to very high redshifts of z ~ 4. We also show that with
increasing redshift the SSFR for massive galaxies increases by a factor of ~
10, reaching the era of their formation at z ~ 2 and beyond. These findings can
be interpreted as evidence for an early epoch of star formation in the most
massive galaxies, and ongoing star-formation activity in lower mass galaxies.Comment: Accepted for publication in ApJL; 4 pages, 2 color figures, uses
emulateapj.cl
The Munich Near-Infrared Cluster Survey (MUNICS) - IX. Galaxy Evolution to z ~ 2 From Optically Selected Catalogues
(Abridged) We present B, R, and I-band selected galaxy catalogues based on
the Munich Near-Infrared Cluster Survey (MUNICS) which, together with the
K-selected sample, serve as an important probe of galaxy evolution in the
redshift range 0 < z < 2. Furthermore, used in comparison they are ideally
suited to study selection effects. The construction of the B, R, and I-selected
photometric catalogues, containing ~9000, ~9000, and ~6000 galaxies,
respectively, is described in detail. The catalogues reach 50% completeness
limits for point sources of B ~ 24.5mag, R ~ 23.5mag, and I ~ 22.5mag and cover
an area of about 0.3 square degrees. Photometric redshifts are derived for all
galaxies with an accuracy of dz/(1+z) ~ 0.057. We investigate the influence of
selection band and environment on the specific star formation rate (SSFR). We
find that K-band selection indeed comes close to selection in stellar mass,
while B-band selection purely selects galaxies in star formation rate. We use a
galaxy group catalogue constructed on the K-band selected MUNICS sample to
study possible differences of the SSFR between the field and the group
environment, finding a marginally lower average SSFR in groups as compared to
the field, especially at lower redshifts. The field-galaxy luminosity function
in the B and R band as derived from the R-selected sample evolves out to z ~ 2
in the sense that the characteristic luminosity increases but the number
density decreases. This effect is smaller at longer rest-frame wavelengths and
gets more pronounced at shorter wavelengths. Parametrising the redshift
evolution of the Schechter parameters as M*(z) = M*(0) + a ln(1+z) and Phi*(z)
= Phi*(0) (1+z)^b we find evolutionary parameters a ~ -2.1 and b ~ -2.5 for the
B band, and a ~ -1.4 and b ~ -1.8 for the R band.Comment: 23 pages, 19 figures; accepted for publication in MNRAS; version with
high-resolution figures will be made available at
http://www.usm.uni-muenchen.de/people/feulner/munics9/preprint_munics9.pd
M31 PAndromeda Cepheid sample observed in four HST bands
Using the M31 PAndromeda Cepheid sample and the HST PHAT data we obtain the
largest Cepheid sample in M31 with HST data in four bands. For our analysis we
consider three samples: A very homogeneous sample of Cepheids based on the
PAndromeda data, the mean magnitude corrected PAndromeda sample and a sample
complementing the PAndromeda sample with Cepheids from literature. The latter
results in the largest catalog with 522 fundamental mode (FM) Cepheids and 102
first overtone (FO) Cepheids with F160W and F110W data and 559 FM Cepheids and
111 FO Cepheids with F814W and F475W data. The obtained dispersion of the
Period-Luminosity relations (PLRs) is very small (e.g. 0.138 mag in the F160W
sample I PLR). We find no broken slope in the PLRs when analyzing our entire
sample, but we do identify a subsample of Cepheids that causes the broken
slope. However, this effect only shows when the number of this Cepheid type
makes up a significant fraction of the total sample. We also analyze the sample
selection effect on the Hubble constant.Comment: 32 pages, 19 figures, 9 tables, accepted for publication in ApJ,
electronic data will be available on CD
Central rotations of Milky Way Globular Clusters
Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if
on a very low level. Both cluster rotation and tidal fields are thought to
cause this flattening. Nevertheless, rotation has only been confirmed in a
handful of GCs, based mostly on individual radial velocities at large radii. We
are conducting a survey of the central kinematics of Galactic GCs using the new
Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that
we have observed so far, rendering it likely that a large majority of the Milky
Way GCs rotate. We use published catalogs of the ACS survey of GCs to derive
central ellipticities and position angles. We show that in all cases where the
central ellipticity permits an accurate measurement of the position angle,
those angles are in excellent agreement with the kinematic position angles that
we derive from the VIRUS-W velocity fields. We find an unexpected tight
correlation between central rotation and outer ellipticity, indicating that
rotation drives flattening for the objects in our sample. We also find a tight
correlation between central rotation and published values for the central
velocity dispersion, most likely due to rotation impacting the old dispersion
measurements.Comment: 6 pages, 3 figures; accepted for publication in ApJ Letter
Exploring Cluster Ellipticals as Cosmological Standard Rods
We explore the possibility to calibrate massive cluster ellipticals as
cosmological standard rods using the Fundamental Plane relation combined with a
correction for luminosity evolution. Though cluster ellipticals certainly
formed in a complex way, their passive evolution out to redshifts of about 1
indicates that basically all major merging and accretion events took place at
higher redshifts. Therefore, a calibration of their luminosity evolution can be
attempted. We propose to use the Mg relation for that purpose because
it is independent of distance and cosmology. We discuss a variety of possible
caveats, ranging from dynamical evolution to uncertainties in stellar
population models and evolution corrections to the presence of age spread.
Sources of major random and systematic errors are analysed as well. We apply
the described procedure to nine elliptical galaxies in two clusters at
and derive constraints on the cosmological model. For the best
fitting -free cosmological model we obtain: , with
90% confidence limits being (the lower limit being due to the
presence of matter in the Universe). If the inflationary scenario applies (i.e.
the Universe has flat geometry), then, for the best fitting model, matter and
contribute about equally to the critical cosmic density (i.e.
). With 90% confidence
should be smaller than 0.9.Comment: 21 pages, including 5 eps-figures, Latex, uses aasms4.sty, accepted
by ApJ main journa
Properties of M31. II: A Cepheid disk sample derived from the first year of PS1 PAndromeda data
We present a sample of Cepheid variable stars towards M31 based on the first
year of regular M31 observations of the PS1 survey in the r_P1 and i_P1
filters. We describe the selection procedure for Cepheid variable stars from
the overall variable source sample and develop an automatic classification
scheme using Fourier decomposition and the location of the instability strip.
We find 1440 fundamental mode (classical \delta) Cep stars, 126 Cepheids in the
first overtone mode, and 147 belonging to the Population II types. 296 Cepheids
could not be assigned to one of these classes and 354 Cepheids were found in
other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31
known so far and the full catalog is presented in this paper. We briefly
describe the properties of our sample in its spatial distribution throughout
the M31 galaxy, in its age properties, and we derive an apparent
period-luminosity relation (PLR) in our two bands. The Population I Cepheids
nicely follow the dust pattern of the M31 disk, whereas the 147 Type II
Cepheids are distributed throughout the halo of M31. We outline the time
evolution of the star formation in the major ring found previously and find an
age gradient. A comparison of our PLR to previous results indicates a curvature
term in the PLR
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