Science Validation of the Spitzer Source List

The Spitzer Science Center will produce a source list (SL) of photometry for a large subset of imaging data in the Spitzer Heritage Archive (SHA). The list will enable a large range of science projects. The primary requirement on the SL is very high reliability — with areal coverage, completeness and limiting depth being secondary considerations. The SHA at the NASA Infrared Science Archive (IRSA) will serve the SL as an enhanced data product. The SL will include data from the four channels of IRAC (3–8 microns) and the 24 micron channel of MIPS. The Source List will include image products (mosaics) and photometric data for Spitzer observations of about 1500 square degrees and include around 30 million sources. We describe ongoing science validation of the Spitzer Source List, and discuss the range of use cases which will be supported

Charges on Strange Quark Nuggets in Space

Since Witten's seminal 1984 paper on the subject, searches for evidence of strange quark nuggets (SQNs) have proven unsuccessful. In the absence of experimental evidence ruling out SQNs, the validity of theories introducing mechanisms that increase their stability should continue to be tested. To stimulate electromagnetic SQN searches, particularly space searches, we estimate the net charge that would develop on an SQN in space exposed to various radiation baths (and showers) capable of liberating their less strongly bound electrons, taking into account recombination with ambient electrons. We consider, in particular, the cosmic background radiation, radiation from the sun, and diffuse galactic and extragalactic $\gamma$-ray backgrounds. A possible dramatic signal of SQNs in explosive astrophysical events is noted.Comment: CitationS added, new subsection added, more discussion, same numerical result

The Spitzer Archival Far-InfraRed Extragalactic Survey

We present the Spitzer Archival Far-InfraRed Extragalactic Survey (SAFIRES). This program produces refined mosaics and source lists for all far-infrared extragalactic data taken during the more than six years of the cryogenic operation of the Spitzer Space Telescope. The SAFIRES products consist of far-infrared data in two wavelength bands (70 um and 160 um) across approximately 180 square degrees of sky, with source lists containing far-infrared fluxes for almost 40,000 extragalactic point sources. Thus, SAFIRES provides a large, robust archival far-infrared data set suitable for many scientific goals.Comment: 7 pages, 6 figures, published in ApJ

Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features

Spectra have been obtained with the low-resolution modules of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources having f$_{\nu}$(24 micron) > 0.75 mJy. Sources were chosen from a survey of 8.2 deg$^{2}$ within the NOAO Deep Wide-Field Survey region in Bootes (NDWFS) using the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope. Most sources are optically very faint (I > 24mag). Redshifts have previously been determined for 34 sources, based primarily on the presence of a deep 9.7 micron silicate absorption feature, with a median z of 2.2. Spectra are presented for the remaining 24 sources for which we were previously unable to determine a confident redshift because the IRS spectra show no strong features. Optical photometry from the NDWFS and infrared photometry with MIPS and the Infrared Array Camera on the Spitzer Space Telescope (IRAC) are given, with K photometry from the Keck I telescope for some objects. The sources without strong spectral features have overall spectral energy distributions (SEDs) and distributions among optical and infrared fluxes which are similar to those for the sources with strong absorption features. Nine of the 24 sources are found to have feasible redshift determinations based on fits of a weak silicate absorption feature. Results confirm that the "1 mJy" population of 24 micron Spitzer sources which are optically faint is dominated by dusty sources with spectroscopic indicators of an obscured AGN rather than a starburst. There remain 14 of the 58 sources observed in Bootes for which no redshift could be estimated, and 5 of these sources are invisible at all optical wavelengths.Comment: Accepted by Ap

PAH Emission from Ultraluminous Infrared Galaxies

We explore the relationships between the Polycyclic Aromatic Hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths within a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 micron PAH equivalent widths (EQWs) in the sample span more than two orders of magnitude (0.006-0.8 micron), and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes (S_{25} / S_{60} < 0.2) typically have 6.2 micron PAH EQWs that are half that of lower-luminosity starbursts. A significant fraction (~40-60%) of HII-like, LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also have large (tau_{9.7} > 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EQW, but not with silicate optical depth. In addition, the PAH EQW decreases with increasing rest-frame 24 micron luminosity. We argue that this trend results primarily from dilution of the PAH EQW by continuum emission from dust heated by a compact central source, probably an AGN. High luminosity, high-redshift sources studied with Spitzer appear to have a much larger range in PAH EQW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs.Comment: 15 pages, 9 Figures; Accepted for publication in Ap

Mirror Matter as Self Interacting Dark Matter

It has been argued that the observed core density profile of galaxies is inconsistent with having a dark matter particle that is collisionless and alternative dark matter candidates which are self interacting may explain observations better. One new class of self interacting dark matter that has been proposed in the context mirror universe models of particle physics is the mirror hydrogen atom whose stability is guaranteed by the conservation of mirror baryon number. We show that the effective transport cross section for mirror hydrogen atoms, has the right order of magnitude for solving the ``cuspy'' halo problem. Furthermore, the suppression of dissipation effects for mirror atoms due to higher mirror mass scale prevents the mirror halo matter from collapsing into a disk strengthening the argument for mirror matter as galactic dark matter.Comment: 6 pages; some references adde

The Infrared Spectrograph on the Spitzer Space Telescope

The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38micron with spectral resolutions, R \~90 and 600, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 6 pages, 4 figure

Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope: Early Results on Mrk 1014, Mrk 463, and UGC 5101

We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38micron region of three Ultraluminous Infrared Galaxies (ULIRGs): Mrk 1014 (z=0.163), and Mrk 463 (z=0.051), and UGC 5101 (z=0.039). The continua of UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant optical depths to the nuclei at 10microns. UGC 5101 also shows the clear presence of water ice in absorption. PAH emission features are seen in both Mrk 1014 and UGC 5101, including the 16.4micron line in UGC 5101. The fine structure lines are consistent with dominant AGN power sources in both Mrk 1014 and Mrk 463. In UGC 5101 we detect the [NeV] 14.3micron emission line providing the first direct evidence for a buried AGN in the mid-infrared. The detection of the 9.66micron and 17.03micron H$_{2}$ emission lines in both UGC 5101 and Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the total molecular gas masses in these galaxies.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 3 figure

PAH Emission from Ultraluminous Infrared Galaxies

We explore the relationships between the Polycyclic Aromatic Hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths within a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 µm PAH equivalent widths (EQWs) in the sample span more than two orders of magnitude (∼0.006–0.8 µm), and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes (S25/S60 \u3c 0.2) typically have 6.2 µm PAH EQWs that are half that of lower-luminosity starbursts. A significant fraction (∼40–60%) of HII-like, LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also have large (τ9.7 \u3e 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EQW, but not with silicate optical depth. In addition, the PAH EQW decreases with increasing rest-frame 24 µm luminosity. We argue that this trend results primarily from dilution of the PAH EQW by continuum emission from dust heated by a compact central source, probably an AGN. High luminosity, highredshift sources studied with Spitzer appear to have a much larger range in PAH EQW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs