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1631. Spitzer/IRAC variability survey of Bootes field
ID:
ivo://CDS.VizieR/J/ApJ/817/119
Title:
Spitzer/IRAC variability survey of Bootes field
Short Name:
J/ApJ/817/119
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Decadal IRAC Bootes Survey is a mid-IR variability survey of the ~9deg^2^ of the NDWFS Bootes Field and extends the time baseline of its predecessor, the Spitzer Deep, Wide-Field Survey (SDWFS), from 4 to 10 years. The Spitzer Space Telescope visited the field five times between 2004 and 2014 at 3.6 and 4.5{mu}m. We provide the difference image analysis photometry for a half a million mostly extragalactic sources. In mid-IR color-color plane, sources with quasar colors constitute the largest variability class (75%), 16% of the variable objects have stellar colors and the remaining 9% have the colors of galaxies. Adding the fifth epoch doubles the number of variable active galactic nuclei (AGNs) for the same false positive rates as in SDWFS, or increases the number of sources by 20% while decreasing the false positive rates by factors of 2-3 for the same variability amplitude. We quantify the ensemble mid-IR variability of ~1500 spectroscopically confirmed AGNs using single power-law structure functions (SFs), which we find to be steeper (index {gamma}~0.45) than in the optical ({gamma}~0.3), leading to much lower amplitudes at short time-lags. This provides evidence for large emission regions, smoothing out any fast UV/optical variations, as the origin of infrared quasar variability. The mid-IR AGN SF slope {gamma} seems to be uncorrelated with both the luminosity and rest-frame wavelength, while the amplitude shows an anti-correlation with the luminosity and a correlation with the rest-frame wavelength.
1632. Spitzer/IRS obs. of Magellanic carbon stars
ID:
ivo://CDS.VizieR/J/ApJ/826/44
Title:
Spitzer/IRS obs. of Magellanic carbon stars
Short Name:
J/ApJ/826/44
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C_2_H_2_ at 7.5{mu}m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.
1633. Spitzer-IRS spectra of Seyfert galaxies. II.
ID:
ivo://CDS.VizieR/J/ApJ/709/1257
Title:
Spitzer-IRS spectra of Seyfert galaxies. II.
Short Name:
J/ApJ/709/1257
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present our Spitzer-Infrared Spectrometer (IRS) spectroscopic survey from 10um to 37um of the Seyfert galaxies of the 12um Galaxy Sample (12MSG), collected in a high-resolution mode (R~600). The new spectra of 61 galaxies, together with the data we already published, give us a total of 91 12um Seyfert galaxies observed, out of 112. We discuss the mid-IR emission lines and features of the Seyfert galaxies, using an improved active galactic nucleus (AGN) classification scheme: instead of adopting the usual classes of Seyfert 1's and Seyfert 2's, we use the spectropolarimetric data from the literature to divide the objects into categories "AGN 1" and "AGN 2," where AGN 1's include all broad-line objects, including the Seyfert 2's showing hidden broad lines in polarized light. The remaining category, AGN 2's, contains only Seyferts with no detectable broad lines in either direct or polarized spectroscopy. We present various mid-IR observables, such as ionization-sensitive and density-sensitive line ratios, the polycyclic aromatic hydrocarbon (PAH) 11.25um feature and the H_2_S(1) rotational line equivalent widths (EWs), the (60-25um) spectral index, and the source extendedness at 19um, to characterize similarities and differences in the AGN populations, in terms of AGN dominance versus star formation dominance.
1634. Spitzer/IRS survey of Class II objects in Orion A. I.
ID:
ivo://CDS.VizieR/J/ApJS/226/8
Title:
Spitzer/IRS survey of Class II objects in Orion A. I.
Short Name:
J/ApJS/226/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present our investigation of 319 Class II objects in Orion A observed by Spitzer/IRS. We also present the follow-up observations of 120 of these Class II objects in Orion A from the Infrared Telescope Facility/SpeX. We measure continuum spectral indices, equivalent widths, and integrated fluxes that pertain to disk structure and dust composition from IRS spectra of Class II objects in Orion A. We estimate mass accretion rates using hydrogen recombination lines in the SpeX spectra of our targets. Utilizing these properties, we compare the distributions of the disk and dust properties of Orion A disks with those of Taurus disks with respect to position within Orion A (Orion Nebular Cluster [ONC] and L1641) and with the subgroups by the inferred radial structures, such as transitional disks (TDs) versus radially continuous full disks (FDs). Our main findings are as follows. (1) Inner disks evolve faster than the outer disks. (2) The mass accretion rates of TDs and those of radially continuous FDs are statistically significantly displaced from each other. The median mass accretion rate of radially continuous disks in the ONC and L1641 is not very different from that in Taurus. (3) Less grain processing has occurred in the disks in the ONC compared to those in Taurus, based on analysis of the shape index of the 10{mu}m silicate feature (F_11.3_/F_9.8_). (4) The 20-31{mu}m continuum spectral index tracks the projected distance from the most luminous Trapezium star, {theta}^1^ Ori C. A possible explanation is UV ablation of the outer parts of disks.
1635. Spitzer/MIPS observations of the COSMOS field
ID:
ivo://CDS.VizieR/J/AJ/138/1261
Title:
Spitzer/MIPS observations of the COSMOS field
Short Name:
J/AJ/138/1261
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Spitzer 70 and 160um observations of the COSMOS Spitzer survey (S-COSMOS). The data processing techniques are discussed for the publicly released products consisting of images and source catalogs. We present accurate 70 and 160um source counts of the COSMOS field and find reasonable agreement with measurements in other fields and with model predictions. The previously reported counts for GOODS-North and the extragalactic First Look Survey are updated with the latest calibration, and counts are measured based on the large area SWIRE survey to constrain the bright source counts. We measure an extragalactic confusion noise level of {sigma}_c_=9.4+/-3.3mJy (q=5) for the MIPS 160um band based on the deep S-COSMOS data and report an updated confusion noise level of {sigma}_c_=0.35+/-0.15mJy (q=5) for the MIPS 70um band.
1636. Spitzer MIR AGN survey. I.
ID:
ivo://CDS.VizieR/J/ApJS/208/24
Title:
Spitzer MIR AGN survey. I.
Short Name:
J/ApJS/208/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate active galactic nuclei (AGNs) selected in the mid-infrared. This survey selects both normal and obscured AGNs closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L _bol_~10^10^L_{sun}_ to highly luminous quasars (L_bol_~10^14^L_{sun}_), all with redshifts ranging from 0 to 4.3. Samples of candidate AGNs were selected with mid-infrared color cuts at several different 24{mu}m flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGNs and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type 1 AGNs with blue continua, 294 (44%) are type 2 objects with extinctions A_V_>~5 toward their AGNs, 96 (14%) are AGNs with lower extinctions (A_V_~1), and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. Of the survey objects 50% have L_bol_>10^12^L_{sun}_, in the quasar regime. We present composite spectra for type 2 quasars and objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared - emission-line luminosity correlation and present the results of cross correlations with serendipitous X-ray and radio sources.
1637. Spitzer observations of stars in M33
ID:
ivo://CDS.VizieR/J/ApJ/664/850
Title:
Spitzer observations of stars in M33
Short Name:
J/ApJ/664/850
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze five epochs of Spitzer Space Telescope Infrared Array Camera (IRAC) observations of the nearby spiral galaxy M33. Each epoch covered nearly a square degree at 3.6, 4.5, and 8.0um. The point-source catalog from the full data set contains 37650 stars. The stars have luminosities characteristic of the asymptotic giant branch and can be separated into oxygen-rich and carbon-rich populations by their [3.6]-[4.5] colors. The [3.6]-[8.0] colors indicate that over 80% of the stars detected at 8.0um have dust shells. Photometric comparison of epochs using conservative criteria yields a catalog of 2923 variable stars. These variables are most likely long-period variables amid an evolved stellar population. At least one-third of the identified carbon stars are variable.
1638. Spitzer sources in SWIRE/XMM/ELAIS-S1 field
ID:
ivo://CDS.VizieR/J/ApJ/703/1778
Title:
Spitzer sources in SWIRE/XMM/ELAIS-S1 field
Short Name:
J/ApJ/703/1778
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of optical spectroscopic identifications of sources detected by Spitzer at 3.6 or 24um down to ~10 and ~280uJy, respectively, in the SWIRE/XMM-Newton/ELAIS-S1 field and classified via line width analysis and diagnostic diagrams. A total of 1376 sources down to R~24.2mag have been identified (1362 detected at 3.6um, 419 at 24um, and 405 at both) by low-resolution optical spectroscopy carried out with FORS2, VIMOS, and EFOSC2 at the Very Large Telescope and 3.6m ESO telescope. The spectroscopic campaigns have been carried out over the central 0.6deg^2^ area of ELAIS-S1 which, in particular, has also been observed by XMM-Newton and Chandra. We find the first direct optical spectroscopic evidence that the fraction of active galactic nuclei (AGNs; mostly AGN2) increases with increasing F(24um)/F(R) ratio, reaching values of 70(+/-20)% in the range 316<F(24um)/F(R)<1000. We present an Infrared Array Camera-Multiband Imaging Photometer color-color diagram able to separate AGN1 from obscured AGN2 candidates. After having corrected for the spectroscopic incompleteness of our sample, the result is that the AGN fraction at F(24um)~0.8mJy is ~22(+/-7)% and decreases slowly to ~19(+/-5)% down to F(24um)~0.3mJy.
1639. Spitzer survey of Serpens YSO population
ID:
ivo://CDS.VizieR/J/ApJ/663/1149
Title:
Spitzer survey of Serpens YSO population
Short Name:
J/ApJ/663/1149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss the combined IRAC/MIPS c2d Spitzer Legacy observations of the Serpens star-forming region. We describe criteria for isolating bona fide YSOs from the extensive background of extragalactic objects. We then discuss the properties of the resulting high-confidence set of 235 YSOs. An additional 51 lower confidence YSOs outside this area are identified from the MIPS data and 2MASS photometry. We present color-color diagrams to compare our observed source properties with those of theoretical models for star/disk/envelope systems and our own modeling of the objects that are well represented by a stellar photosphere plus circumstellar disk.
1640. Spitzer Survey of Stellar Structure in Galaxies
ID:
ivo://CDS.VizieR/J/PASP/122/1397
Title:
Spitzer Survey of Stellar Structure in Galaxies
Short Name:
J/PASP/122/1397
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Spitzer Survey of Stellar Structure in Galaxies (S^4^G) is an Exploration Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a volume-, magnitude-, and size-limited (d<40Mpc, |b|>30{deg}, m_Bcorr_<15.5, and D_25_>1') survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5um. Each galaxy is observed for 240s and mapped to >=1.5D_25_. The final mosaicked images have a typical 1sigma rms noise level of 0.0072 and 0.0093MJy/sr at 3.6 and 4.5um, respectively. Our azimuthally averaged surface brightness profile typically traces isophotes at {mu}_3.6um_(AB)(1sigma)~27mag/arcsec^2^, equivalent to a stellar mass surface density of ~1M_{sun}_/pc^2^. thus provides an unprecedented data set for the study of the distribution of mass and stellar structures in the local universe. This large, unbiased, and extremely deep sample of all Hubble types from dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also as a function of the local environment. This article introduces the survey and describes the sample selection, the significance of the 3.6 and 4.5um bands for this study, and the data collection and survey strategies.