Small-Scale structure in the Galactic ISM: Implications for Galaxy Cluster Studies

Observations of extragalactic objects need to be corrected for Galactic absorption and this is often accomplished by using the measured 21 cm HI column. However, within the beam of the radio telescope there are variations in the HI column that can have important effects in interpreting absorption line studies and X-ray spectra at the softest energies. We examine the HI and DIRBE/IRAS data for lines of sight out of the Galaxy, which show evidence for HI variations in of up to a factor of three in 1 degree fields. Column density enhancements would preferentially absorb soft X-rays in spatially extended objects and we find evidence for this effect in the ROSAT PSPC observations of two bright clusters of galaxies, Abell 119 and Abell 2142. For clusters of galaxies, the failure to include column density fluctuations will lead to systematically incorrect fits to the X-ray data in the sense that there will appear to be a very soft X-ray excess. This may be one cause of the soft X-ray excess in clusters, since the magnitude of the effect is comparable to the observed values.Comment: 16 pages, 9 figures, to appear in the Astrophysical Journal, vol. 597 (1 Nov 2003

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

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

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

Spitzer/IRAC precision photometry: a machine learning approach

The largest source of noise in exoplanet and brown dwarf photometric time series made with Spitzer/IRAC is the coupling between intra-pixel gain variations and spacecraft pointing fluctuations. Observers typically correct for this systematic in science data by deriving an instrumental noise model simultaneously with the astrophysical light curve and removing the noise model. Such techniques for self-calibrating Spitzer photometric datasets have been extremely successful, and in many cases enabled near-photon-limited precision on exoplanet transit and eclipse depths. Self-calibration, however, can suffer from certain limitations: (1) temporal astrophysical signals can become aliased as part of the instrument model; (2) for some techniques adequate model estimation often requires a high degree of intra-pixel positional redundancy (multiple samples with nearby centroids) over long time spans; (3) many techniques do not account for sporadic high frequency telescope vibrations that smear out the point spread function. We have begun to build independent general-purpose intra-pixel systematics removal algorithms using three machine learning techniques: K-Nearest Neighbors (with kernel regression), Random Decision Forests, and Artificial Neural Networks. These methods remove many of the limitations of self-calibration: (1) they operate on a dedicated calibration database of approximately one million measurements per IRAC waveband (3.6 and 4.5 microns) of non-variable stars, and thus are independent of the time series science data to be corrected; (2) the database covers a large area of the "Sweet Spot, so the methods do not require positional redundancy in the science data; (3) machine learning techniques in general allow for flexibility in training with multiple, sometimes unorthodox, variables, including those that trace PSF smear. We focus in this report on the K-Nearest Neighbors with Kernel Regression technique. (Additional communications are in preparation describing Decision Forests and Neural Networks.

BAMBI Is Expressed in Endothelial Cells and Is Regulated by Lysosomal/Autolysosomal Degradation

BACKGROUND: BAMBI (BMP and Activin Membrane Bound Inhibitor) is considered to influence TGFβ and Wnt signaling, and thereby fibrosis. Surprisingly data on cell type-specific expression of BAMBI are not available. We therefore examined the localization, gene regulation, and protein turnover of BAMBI in kidneys. METHODOLOGY/PRINCIPAL FINDINGS: By immunofluorescence microscopy and by mRNA expression, BAMBI is restricted to endothelial cells of the glomerular and some peritubular capillaries and of arteries and veins in both murine and human kidneys. TGFβ upregulated mRNA of BAMBI in murine glomerular endothelial cells (mGEC). LPS did not downregulate mRNA for BAMBI in mGEC or in HUVECs. BAMBI mRNA had a half-life of only 60 minutes and was stabilized by cycloheximide, indicating post-transcriptional regulation due to AU-rich elements, which we identified in the 3' untranslated sequence of both the human and murine BAMBI gene. BAMBI protein turnover was studied in HUVECs with BAMBI overexpression using a lentiviral system. Serum starvation as an inducer of autophagy caused marked BAMBI degradation, which could be totally prevented by inhibition of lysosomal and autolysosomal degradation with bafilomycin, and partially by inhibition of autophagy with 3-methyladenine, but not by proteasomal inhibitors. Rapamycin activates autophagy by inhibiting TOR, and resulted in BAMBI protein degradation. Both serum starvation and rapamycin increased the conversion of the autophagy marker LC3 from LC3-I to LC3-II and also enhanced co-staining for BAMBI and LC3 in autolysosomal vesicles. CONCLUSIONS/SIGNIFICANCE: 1. BAMBI localizes to endothelial cells in the kidney and to HUVECs. 2. BAMBI mRNA is regulated by post-transcriptional mechanisms. 3. BAMBI protein is regulated by lysosomal and autolysosomal degradation. The endothelial localization and the quick turnover of BAMBI may indicate novel, yet to be defined functions of this modulator for TGFβ and Wnt protein actions in the renal vascular endothelium in health and disease

Absolute photometric calibration of IRAC: lessons learned using nine years of flight data

Significant improvements in our understanding of various photometric effects have occurred in the more than nine years of flight operations of the Infrared Array Camera aboard the Spitzer Space Telescope. With the accumulation of calibration data, photometric variations that are intrinsic to the instrument can now be mapped with high fidelity. Using all existing data on calibration stars, the array location-dependent photometric correction (the variation of flux with position on the array) and the correction for intra-pixel sensitivity variation (pixel-phase) have been modeled simultaneously. Examination of the warm mission data enabled the characterization of the underlying form of the pixelphase variation in cryogenic data. In addition to the accumulation of calibration data, significant improvements in the calibration of the truth spectra of the calibrators has taken place. Using the work of Engelke et al. (2006), the KIII calibrators have no offset as compared to the AV calibrators, providing a second pillar of the calibration scheme. The current cryogenic calibration is better than 3% in an absolute sense, with most of the uncertainty still in the knowledge of the true flux densities of the primary calibrators. We present the final state of the cryogenic IRAC calibration and a comparison of the IRAC calibration to an independent calibration methodology using the HST primary calibrators