489 research outputs found
Mass-Richness relations for X-ray and SZE-selected clusters at as seen by at 4.5m
We study the mass-richness relation of 116 spectroscopically-confirmed
massive clusters at by mining the archive. We
homogeneously measure the richness at 4.5m for our cluster sample within a
fixed aperture of radius and above a fixed brightness threshold,
making appropriate corrections for both background galaxies and foreground
stars. We have two subsamples, those which have a) literature X-ray
luminosities and b) literature Sunyaev-Zeldovich effect masses. For the X-ray
subsample we re-derive masses adopting the most recent calibrations. We then
calibrate an empirical mass-richness relation for the combined sample spanning
more than one decade in cluster mass and find the associated uncertainties in
mass at fixed richness to be dex. We study the dependance of the
scatter of this relation with galaxy concentration, defined as the ratio
between richness measured within an aperture radius of 1 and 2 arcminutes. We
find that at fixed aperture radius the scatter increases for clusters with
higher concentrations. We study the dependance of our richness estimates with
depth of the [4.5]m imaging data and find that reaching a depth of at
least [4.5]= 21 AB mag is sufficient to derive reasonable mass estimates. We
discuss the possible extension of our method to the mid-infrared all-sky
survey data, and the application of our results to the mission. This
technique makes richness-based cluster mass estimates available for large
samples of clusters at very low observational cost.Comment: Submitted to ApJ on Aug 31 2016, Revised version resubmitted on Apr
11th 201
Diffuse Optical Light in Galaxy Clusters. II. Correlations with Cluster Properties
We have measured the flux, profile, color, and substructure in the diffuse intracluster light (ICL) in a sample of 10 galaxy clusters with a range of mass, morphology, redshift, and density. Deep, wide-field observations for this project were made in two bands at the 1 m Swope and 2.5 m du Pont telescopes at Las Campanas Observatory. Careful attention in reduction and analysis was paid to the illumination correction, background subtraction, point-spread function determination, and galaxy subtraction. ICL flux is detected in both bands in all 10 clusters ranging from 7.6 Ć 10^(10) to 7.0 Ć 10^(11) h^(-1)_(70) L_ā in r and 1.4 Ć 10^(10) to 1.2 Ć 10^(11) h^(-1)_(70) L_ā in the B band. These fluxes account for 6%-22% of the total cluster light within one-quarter of the virial radius in r and 4%-21% in the B band. Average ICL B - r colors range from 1.5 to 2.8 mag when k- and evolution corrected to the present epoch. In several clusters we also detect ICL in group environments near the cluster center and up to 1 h^(-1)_(70) Mpc distant from the cluster center. Our sample, having been selected from the Abell sample, is incomplete in that it does not include high-redshift clusters with low density, low flux, or low mass, and it does not include low-redshift clusters with high flux, high mass, or high density. This bias makes it difficult to interpret correlations between ICL flux and cluster properties. Despite this selection bias, we do find that the presence of a cD galaxy corresponds to both centrally concentrated galaxy profiles and centrally concentrated ICL profiles. This is consistent with ICL either forming from galaxy interactions at the center or forming at earlier times in groups and later combining in the center
The Infrared Array Camera Dark Field: Far-Infrared to X-ray Data
We present 20 band photometry from the far-IR to X-ray in the Spitzer Infrared Array Camera (IRAC) dark field. The bias for the near-IR camera on Spitzer is calibrated by observing a ~20' diameter "dark" field near the north ecliptic pole roughly every two-to-three weeks throughout the mission duration of Spitzer. The field is unique for its extreme depth, low background, high quality imaging, time-series information, and accompanying photometry including data taken with Akari, Palomar, MMT, KPNO, Hubble, and Chandra. This serendipitous survey contains the deepest mid-IR data taken to date. This data set is well suited for studies of intermediate-redshift galaxy clusters, high-redshift galaxies, the first generation of stars, and the lowest mass brown dwarfs, among others. This paper provides a summary of the data characteristics and catalog generation from all bands collected to date as well as a discussion of photometric redshifts and initial and expected science results and goals. To illustrate the scientific potential of this unique data set, we also present here IRAC color-color diagrams
The IRAC Dark Field; Far- Infrared to X-ray Data
We present 20 band photometry from the far-IR to X-ray in the Spitzer IRAC
dark field. The bias for the near-IR camera on Spitzer is calibrated by
observing a ~20 arcminute diameter "dark" field near the north ecliptic pole
roughly every two-to-three weeks throughout the mission duration of Spitzer.
The field is unique for its extreme depth, low background, high quality
imaging, time-series information, and accompanying photometry including data
taken with Akari, Palomar, MMT, KPNO, Hubble, and Chandra. This serendipitous
survey contains the deepest mid-IR data taken to date. This dataset is well
suited for studies of intermediate redshift galaxy clusters, high redshift
galaxies, the first generation of stars, and the lowest mass brown dwarfs,
among others. This paper provides a summary of the data characteristics and
catalog generation from all bands collected to date as well as a discussion of
photometric redshifts and initial and expected science results and goals. To
illustrate the scientific potential of this unique dataset, we also present
here IRAC color color diagrams.Comment: 12 pages, ApJS accepte
Galaxy Clusters in the IRAC Dark Field II: Mid-IR Sources
We present infrared luminosities, star formation rates, colors, morphologies,
locations, and AGN properties of 24 micron-detected sources in photometrically
detected high-redshift clusters in order to understand the impact of
environment on star formation and AGN evolution in cluster galaxies. We use
three newly-identified z=1 clusters selected from the IRAC dark field; the
deepest ever mid-IR survey with accompanying, 14 band multiwavelength data
including deep HST imaging and deep wide-area Spitzer MIPS 24 micron imaging.
We find 90 cluster members with MIPS detections within two virial radii of the
cluster centers, of which 17 appear to have spectral energy distributions
dominated by AGN and the rest dominated by star formation. We find that 43 of
the star forming are luminous infrared galaxies (LIRGs). The majority of
sources (81%) are spirals or irregulars. A large fraction (at least 25%) show
obvious signs of interactions. The MIPS -detected member galaxies have varied
spatial distributions as compared to the MIPS-undetected members with one of
the three clusters showing SF galaxies being preferentially located on the
cluster outskirts, while the other 2 clusters show no such trend. Both the AGN
fraction and the summed SFR of cluster galaxies increases from z=0 to 1, at a
rate that is a few times faster in clusters than over the same redshift range
in the field. Cluster environment does have an effect on the evolution of both
AGN fraction and SFR from redshift one to the present, but does not effect the
infrared luminosities or morphologies of the MIPS sample. Star formation
happens in the same way regardless of environment making MIPS sources look the
same in the cluster and field, however the cluster environment does encourage a
more rapid evolution with time as compared to the field.Comment: 18 pages, 9 figures, ApJ accepte
Calibration and data quality of warm IRAC
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month- long calibration and characterization campaign was conducted. The array temperature and bias setpoints were revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500 mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the same as the cryogenic mission with the 3.6 Ī¼m array being slightly less sensitive (10%) and the 4.5 Ī¼m array within 5% of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 Ī¼m, and better than milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the early universe, and in our understanding of the properties of exoplanets
Spitzer Infrared Array Camera (IRAC) Pipeline: final modifications and lessons learned
In more than ten years of operations, the Spitzer Space Telescope has conducted a wide range of investigations from observing nearby asteroids to probing atmospheric properties of exoplanets to measuring masses of the most distance galaxies. Observations using the Infrared Array Camera (IRAC) at 3.6 and 4.5um will continue through mid-2019 when the James Webb Space Telescope will succeed Spitzer. In anticipation of the eventual end of the mission, the basic calibrated data reduction pipeline designed to produce flux-calibrated images has been finalized and used to reprocess all the data taken during the Spitzer warm mission. We discuss all final modifications made to the pipeline
Intra-pixel gain variations and high-precision photometry with the Infrared Array Camera (IRAC)
The Infrared Array Camera (IRAC) on the Spitzer Space Telescope has been used to measure < 10^(-4) temporal variations in point sources (such as transiting extrasolar planets) at 3.6 and 4.5 Ī¼m. Due to the under-sampled nature of the PSF, the warm IRAC arrays show variations of as much as 8% in sensitivity as the center of the PSF moves across a pixel due to normal spacecraft pointing wobble and drift. These intra-pixel gain variations are the largest source of correlated noise in IRAC photometry. Usually this effect is removed by fitting a model to the science data themselves (self-calibration), which could result in the removal of astrophysically interesting signals. We describe a new technique for significantly reducing the gain variations and improving photometric precision in a given observation, without using the data to be corrected. This comprises: (1) an adaptive centroiding and repositioning method ("Peak-Up") that uses the Spitzer Pointing Control Reference Sensor (PCRS) to repeatedly position a target to within 0.1 IRAC pixels of an area of minimal gain variation; and (2) the high-precision, high-resolution measurement of the pixel gain structure using non-variable stars. We show that the technique currently allows the reduction of correlated noise by almost an order of magnitude over raw data, which is comparable to the improvement due to self-calibration. We discuss other possible sources of correlated noise, and proposals for reducing their impact on photometric precision
A Spitzer IRAC Measure of the Zodiacal Light
The dominant non-instrumental background source for spaceābased infrared observatories is the zodiacal light
(ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4.5, 5.8, and 8.0 Ī¼m,
taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately
weekly IRAC observations near the north ecliptic pole over the period of roughly 8.5 years. This long time
baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk
with respect to the ecliptic, which is the true signal of the ZL. This is compared to both Cosmic Background
Explorer Diffuse Infrared Background Experiment data and a ZL model based thereon. Our data show a few
percent discrepancy from the Kelsall et al.(1998) model including a potential warping of the interplanetary dust
disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate
knowledge of the ZL is important for both extragalactic and Galactic astronomy including measurements of the
cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary
dust models. IRAC data can be used to further inform and test future ZL models
Galaxy Clusters in the IRAC Dark Field I: Growth of the red sequence
Using three newly identified galaxy clusters at z~1 (photometric redshift) we
measure the evolution of the galaxies within clusters from high redshift to the
present day by studying the growth of the red cluster sequence. The clusters
are located in the Spitzer Infrared Array Camera (IRAC) Dark Field, an
extremely deep mid-infrared survey near the north ecliptic pole with photometry
in 18 total bands from X-ray through far-IR. Two of the candidate clusters are
additionally detected as extended emission in matching Chandra data in the
survey area allowing us to measure their masses to be M_{500}= 6.2 \pm 1.0
\times 10^{13} and 3.6 \pm 1.1 \times 10^{13} solar masses. For all three
clusters we create a composite color magnitude diagram in rest-frame B-K using
our deep HST and Spitzer imaging. By comparing the fraction of low luminosity
member galaxies on the composite red sequence with the corresponding population
in local clusters at z=0.1 taken from the COSMOS survey, we examine the effect
of a galaxy's mass on its evolution. We find a deficit of faint galaxies on the
red sequence in our z~1 clusters which implies that more massive galaxies have
evolved in clusters faster than less massive galaxies, and that the less
massive galaxies are still forming stars in clusters such that they have not
yet settled onto the red sequence.Comment: 10 pages including 6 figures and 1 table, ApJ accepte
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