The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, ...COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg super(2) to a depth of 26 AB mag (3sigma) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5 mum. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 + or - 1.0 and 4.4 + or - 0.8 nW m super(-2) sr super(-1) at 3.6 and 4.5 mum to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component.
Using three newly identified galaxy clusters at image (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 image and image M sub(image). For all three clusters we create a composite color-magnitude diagram in rest-frame image 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 image taken from COSMOS, 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 image 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.
We present mid-IR and radio observations of the Galactic luminous blue variables (LBVs) candidate HD 168625 and its associated nebula. We obtained mid-IR spectroscopic observations using the Infrared ...Spectrograph on board the Spitzer Space Telescope, and performed mid-IR and radio imaging observations using VISIR on the Very Large Telescope and the Very Large Array with comparable angular resolution. Our spectroscopic observations detected spectral features attributable to polycyclic aromatic hydrocarbons (PAHs) and therefore indicate the presence of a photodissociation region (PDR) around the ionized nebula. This result increases the number of LBVs and LBV candidates where a PDR has been found, confirming the importance of such a component in the total mass-loss budget of the central object during this elusive phase of massive star evolution. We have analyzed and compared the mid-IR and radio maps, and derive several results concerning the associated nebula. There is evidence for grain distribution variations across the nebula, with a predominant contribution from bigger grains in the northern part of the nebula while PAH and smaller grains are more concentrated in the southern part. A compact radio component located where there is a lack of thermal dust grains corroborates the presence of a shock in the southern nebula, which could arise as a consequence of the interaction of a fast outflow with the slower, expanding dusty nebula. Such a shock would be a viable means for PAH production as well as for changes in the grain size distribution. Finally, from the detection of a central radio component probably associated with the wind from the central massive supergiant, we derive a current mass-loss rate of M-dot =(1.46{+-}0.15)x10{sup -6} M{sub sun} yr{sup -1}.
Context. The source MWC 930 is a star just ~2° above the Galactic plane whose nature is not clear and has not been studied in detail so far. While a post-asymptotic giant branch classification was ...proposed in the past, studies of its optical spectrum and photometry pointed toward strong variability, therefore, the object was reclassified as a luminous blue variable (LBV) candidate. Aims. The LBVs typically undergo phases of strong mass loss in the form of eruptions that can create shells of ejecta around the star. Our goal is to search for the presence of such a circumstellar nebula in MWC 930 and investigate its properties. Methods. To do so, we make use of space-based infrared data from our Spitzer campaign performed with the InfraRed Array Camera (IRAC) and the InfraRed Spectrograph (IRS), as well as data from optical and infrared (IR) surveys. Results. In our Spitzer images, we clearly detect an extended shell around MWC 930 at wavelengths longer than 5 μm. The mid-infrared spectrum is dominated by the central star and mostly shows forbidden lines of FeII with an underlying continuum that decreases with wavelengths up to ~15 μm and then inverts its slope, displaying a second peak around 60 μm, which is evidence of cold dust grains formed in a past eruption. By modeling the spectral energy distribution, we identify two central components, beside the star and the outer shell. These extra sources of radiation are interpreted as material close to the central star, which may be due to a recent ejection. Features of C-bearing molecules or grains are not detected.
We present mid-IR observations of the Galactic Luminous Blue Variable (LBV) HR Car and its associated nebula carried out with the Spitzer Space Telescope using both Infrared Array Camera and Infrared ...Spectrograph, as part of a GTO program aimed to study stellar ejecta from evolved stars. Our observations reveal a rich mid-IR spectrum of the inner nebula showing both solid state and atomic gas signatures. Strong low-excitation atomic fine structure lines such as 26.0 mm Fe II and 34.8 mm Si II, indicate, for the first time, the presence of a PDR in this object class. While the physics and chemistry of the low-excitation gas appears to be dominated by photodissociation, a possible contribution due to shocks can be inferred from the evidence of gas phase Fe abundance enhancement. The presence of amorphous silicates, inferred from the observed characteristic broad feature at 10 mm located in the inner nebula, suggests that dust has formed during the LBV outburst. This is in contrast with the detection of crystalline dust in other probably more evolved Galactic LBVs, which is similar to the crystalline dust observed in red supergiants. This has been considered to be evidence of dust production during evolutionary phases prior to the outburst.
We have selected a small sample of post-AGB (Asymptotic Giant Branch) stars in transition towards the planetary nebula and present new Very Large Array multi-frequency high-angular resolution radio ...observations of them. The multi-frequency data are used to create and model the targets' radio continuum spectra, proving that these stars started their evolution as very young planetary nebulae. In the optically thin range, the slopes are compatible with the expected spectral index (−0.1). Two targets (IRAS 18062+2410 and 17423−1755) seem to be optically thick even at high frequency, as observed in a handful of other post-AGB stars in the literature, while a third one (IRAS 20462+3416) shows a possible contribution from cold dust. In IRAS 18062+2410, where we have three observations spanning a period of four years, we detect an increase in its flux density, similar to that observed in CRL 618. High-angular resolution imaging shows bipolar structures that may be due to circumstellar tori, although a different hypothesis (i.e. jets) could also explain the observations. Further observations and monitoring of these sources will enable us to test the current evolutionary models of planetary nebulae.
We report on results of observations of near-Earth objects (NEOs) performed with the NASA Spitzer Space Telescope as part of our ongoing (2009-2011) Warm Spitzer NEO survey ('ExploreNEOs'), the ...primary aim of which is to provide sizes and albedos of some 700 NEOs. The emphasis of the work described here is an assessment of the overall accuracy of our survey results, which are based on a semi-empirical generalized model of asteroid thermal emission. The NASA Spitzer Space Telescope has been operated in the so-called Warm Spitzer mission phase since the cryogen was depleted in 2009 May, with the two shortest-wavelength channels, centered at 3.6 Delta *mm and 4.5 Delta *mm, of the Infrared Array Camera continuing to provide valuable data. The set of some 170 NEOs in our current Warm Spitzer results catalog contains 28 for which published taxonomic classifications are available, and 14 for which relatively reliable published diameters and albedos are available. A comparison of the Warm Spitzer results with previously published results ('ground truth'), complemented by a Monte Carlo error analysis, indicates that the rms Warm Spitzer diameter and albedo errors are ?20% and ?50%, respectively. Cases in which agreement with results from the literature is worse than expected are highlighted and discussed; these include the potential spacecraft target 138911 2001 AE2. We confirm that 1.4 appears to be an appropriate overall default value for the relative reflectance between the V band and the Warm Spitzer wavelengths, for use in correction of the Warm Spitzer fluxes for reflected solar radiation.
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