The absolute flux calibration of the James Webb Space Telescope will be based on a set of stars observed by the Hubble and Spitzer Space Telescopes. In order to cross-calibrate the two facilities, ...several A, G, and white dwarf (WD) stars are observed with both Spitzer and Hubble and are the prototypes for a set of JWST calibration standards. The flux calibration constants for the four Spitzer IRAC bands 1-4 are derived from these stars and are 2.3, 1.9, 2.0, and 0.5% lower than the official cold-mission IRAC calibration of Reach et al. (2005), i.e. in agreement within their estimated errors of ~2%. The causes of these differences lie primarily in the IRAC data reduction and secondarily in the SEDs of our standard stars. The independent IRAC 8 micron band-4 fluxes of Rieke et al. (2008) are about 1.5 +/- 2% higher than those of Reach et al. and are also in agreement with our 8 micron result.
We present a three-year series of observations at 24 microns with the Spitzer Space Telescope of the interstellar material in a 200 x 200 arcmin square area centered on Cassiopeia A. Interstellar ...dust heated by the outward light pulse from the supernova explosion emits in the form of compact, moving features. Their sequential outward movements allow us to study the complicated three-dimensional structure of the interstellar medium (ISM) behind and near Cassiopeia A. The ISM consists of sheets and filaments, with many structures on a scale of a parsec or less. The spatial power spectrum of the ISM appears to be similar to that of fractals with a spectral index of 3.5. The filling factor for the small structures above the spatial wavenumber k ~ 0.5 cycles/pc is only ~ 0.4%.
The infrared spectral energy distributions (SEDs) of \(z\gtrsim 5\) quasars can be reproduced by combining a low-metallicity galaxy template with a standard AGN template. The host galaxy is ...represented by Haro 11, a compact, moderately low metallicity, star-bursting galaxy that shares typical features of high-\(z\) galaxies. For the vast majority of \(z\gtrsim 5\) quasars, the AGN contribution is well modeled by a standard empirical template with the contamination of star formation in the infrared subtracted. Together, these two templates can separate the contributions from the host galaxy and the AGN even in the case of limited data points, given that this model has only two free parameters. Using this method, we re-analyze 69 \(z\gtrsim 5\) quasars with extensive Herschel observations, and derive their AGN luminosities \(L_{\rm AGN}\) in a range \(\sim (0.78-27.4) \times10^{13}\, L_{\odot}\), the infrared luminosities from star formation \(L_{\rm SF,IR} \sim (<1.5-25.7)\times10^{12}\, L_{\odot}\), and the corresponding star formation rates \({\rm SFR}\sim (<290-2650)\, M_\odot/{\rm yr}\). The average infrared luminosity from star formation and the average total AGN luminosity of the \(z\gtrsim5\) quasar sample follows the correlation defined by quasars at \(z < 2.6\). We assume these quasar host galaxies maintain a constant average SFR (\(\sim620\, M_\odot/{\rm yr}\)) during their mass assembly and estimate the stellar mass that could form till \(z\sim5-6\) to be \(\langle M_* \rangle \sim(3-5)\times10^{11} M_\odot\). Combining with the black hole (BH) mass measurements, this stellar mass is adequate to establish a BH-galaxy mass ratio \(M_{\rm BH}/M_{*}\) at 0.1-1%, consistent with the local relation.
The feasibility of MRI-guided interstitial ultrasound thermal therapy of the prostate was evaluated in an in vivo canine prostate model. MRI compatible, multielement interstitial ultrasound ...applicators were developed using
1.5
mm
diameter cylindrical piezoceramic transducers (7 to
8
MHz
) sectored to provide
180
°
of angular directional heating. Two in vivo experiments were performed in canine prostate. The first using two interstitial ultrasound applicators, the second using three ultrasound applicators in conjunction with rectal and urethral cooling. In both experiments, the applicators were inserted transperineally into the prostate with the energy directed ventrally, away from the rectum. Electrical power levels of
5
–
17
W
per element (
∼
1.6
–
5.4
W
acoustic output power) were applied for heating periods of 18 and
48
min
. Phase-sensitive gradient-echo MR imaging was used to monitor the thermal treatment in real-time on a
0.5
T
interventional MRI system. Contrast-enhanced T1-weighted images and vital-stained serial tissue sections were obtained to assess thermal damage and correlate to real-time thermal contour plots and calculated thermal doses. Results from these studies indicated a large volume of ablated (nonstained) tissue within the prostate, extending 1.2 to
2.0
cm
from the applicators to the periphery of the gland, with the dorsal margin of coagulation well-defined by the applicator placement and directionality. The shape of the lesions correlated well to the hypointense regions visible in the contrast-enhanced T1-weighted images, and were also in good agreement with the contours of the
52
°
C
threshold temperature and
t
43
>
240
min
. This study demonstrates the feasibility of using directional interstitial ultrasound in conjunction with MRI thermal imaging to monitor and possibly control thermal coagulation within a targeted tissue volume while potentially protecting surrounding tissue, such as rectum, from thermal damage.
(abridged) Infrared selection is a potentially powerful way to identify heavily obscured AGN missed in even the deepest X-ray surveys. Using a 24 micron-selected sample in GOODS-S, we test the ...reliability and completeness of three infrared AGN selection methods: (1) IRAC color-color selection, (2) IRAC power-law selection, and (3) IR-excess selection; we also evaluate a number of infrared excess approaches. We find that the vast majority of non-power-law IRAC color-selected AGN candidates in GOODS-S have colors consistent with those of star-forming galaxies. Contamination by star-forming galaxies is most prevalent at low 24 micron flux densities (~100 uJy) and high redshifts (z~2), but the fraction of potential contaminants is still high (~50%) at 500 uJy, the highest flux density probed reliably by our survey. AGN candidates selected via a simple, physically-motivated power-law criterion (PLGs), however, appear to be reliable. We confirm that the infrared excess methods successfully identify a number of AGN, but we also find that such samples may be significantly contaminated by star-forming galaxies. Adding only the secure Spitzer-selected PLG, color-selected, IR-excess, and radio/IR-selected AGN candidates to the deepest X-ray-selected AGN samples directly increases the number of known X-ray AGN (84) by 54-77%, and implies an increase to the number of 24 micron-detected AGN of 71-94%. Finally, we show that the fraction of MIR sources dominated by an AGN decreases with decreasing MIR flux density, but only down to f_24 = 300 uJy. Below this limit, the AGN fraction levels out, indicating that a non-negligible fraction (~10%) of faint 24 micron sources (the majority of which are missed in the X-ray) are powered not by star formation, but by the central engine.
We report on the development of a new type of astronomical polarimeter for the spectral region 1-2.6 µm. This instrument incorporates a fused silica stress-birefringent modulator Capable of producing ...square-wave polarimetrie modulation of over 95% efficiency from dc to 2 Hz and quarter-wave retardation at wavelengths as long as the photometric band (2.2 µm). Thus, the modulator readily accommodates the new class of integrating infrared detectors. In its current configuration, using an HR polarization analyzer and a single germanium photodiode detector, the polarimeter achieves an uncertainty in circular polarization of σv = 1% for aJ= 14.5 object in a total integration time of one-half hour with the Multiple Mirror Telescope. When fully upgraded with a 12 × 30 pixel HgCdTe array and four-channel pupil format (described herein), we expect an increase of more than a factor of four in efficiency as well as the proper elimination of the systematic effects. The nature of polarization in faint active galactic nuclei, a search for comparatively weak magnetic fields in white-dwarf accretion binaries, and a near-infrared survey of isolated magnetic white dwarfs are but a few of the many astronomical problems which may be addressed with this new breed of near-infrared polarimeter.
The star formation rate (SFR) and black hole accretion rate (BHAR) functions are measured to be proportional to each other at z < ~3. This close correspondence between SF and BHA would naturally ...yield a BH mass-galaxy mass correlation, whereas a BH mass-bulge mass correlation is observed. To explore this apparent contradiction we study the SF in spheroid-dominated galaxies between z=1 and the present day. We use 903 galaxies from the COMBO-17 survey with M* >2x10^10M_sun, ultraviolet and infrared-derived SFRs from Spitzer and GALEX, and morphologies from GEMS HST/ACS imaging. Using stacking techniques, we find that <25% of all SF occurs in spheroid-dominated galaxies (Sersic index n>2.5), while the BHAR that we would expect if the global scalings held is three times higher. This rules out the simplest picture of co-evolution, in which SF and BHA trace each other at all times. These results could be explained if SF and BHA occur in the same events, but offset in time, for example at different stages of a merger event. However, one would then expect to see the corresponding star formation activity in early-stage mergers, in conflict with observations. We conclude that the major episodes of SF and BHA occur in different events, with the bulk of SF happening in isolated disks and most BHA occurring in major mergers. The apparent global co-evolution results from the regulation of the BH growth by the potential well of the galactic spheroid, which includes a major contribution from disrupted disk stars.
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