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2671. Spitzer/IRS debris disk catalog. I.
ID:
ivo://CDS.VizieR/J/ApJS/211/25
Title:
Spitzer/IRS debris disk catalog. I.
Short Name:
J/ApJS/211/25
Date:
21 Oct 2021
Publisher:
CDS
Description:
During the Spitzer Space Telescope cryogenic mission, Guaranteed Time Observers, Legacy Teams, and General Observers obtained Infrared Spectrograph (IRS) observations of hundreds of debris disk candidates. We calibrated the spectra of 571 candidates, including 64 new IRAS and Multiband Imaging Photometer for Spitzer (MIPS) debris disks candidates, modeled their stellar photospheres, and produced a catalog of excess spectra for unresolved debris disks. For 499 targets with IRS excess but without strong spectral features (and a subset of 420 targets with additional MIPS 70{mu}m observations), we modeled the IRS (and MIPS data) assuming that the dust thermal emission was well-described using either a one- or two-temperature blackbody model. We calculated the probability for each model and computed the average probability to select among models. We found that the spectral energy distributions for the majority of objects (~66%) were better described using a two-temperature model with warm (T_gr_~100-500K) and cold (T_gr_~50-150K) dust populations analogous to zodiacal and Kuiper Belt dust, suggesting that planetary systems are common in debris disks and zodiacal dust is common around host stars with ages up to ~1Gyr. We found that younger stars generally have disks with larger fractional infrared luminosities and higher grain temperatures and that higher-mass stars have disks with higher grain temperatures. We show that the increasing distance of dust around debris disks is inconsistent with self-stirred disk models, expected if these systems possess planets at 30-150AU. Finally, we illustrate how observations of debris disks may be used to constrain the radial dependence of material in the minimum mass solar nebula.
2672. Spitzer/IRS disk parameters in Serpens
ID:
ivo://CDS.VizieR/J/ApJ/762/128
Title:
Spitzer/IRS disk parameters in Serpens
Short Name:
J/ApJ/762/128
Date:
21 Oct 2021
Publisher:
CDS
Description:
Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud, based on photometry and Spitzer/IRS spectra. Most of the stars have spectroscopically determined spectral types. Taking a distance to the cloud of 415pc rather than 259pc, the distribution of ages is shifted to lower values, in the 1-3Myr range, with a tail up to 10Myr. The mass distribution spans 0.2-1.2M_{sun}_, with median mass of 0.7M_{sun}_. The distribution of fractional disk luminosities in Serpens resembles that of the young Taurus Molecular Cloud, with most disks consistent with optically thick, passively irradiated disks in a variety of disk geometries (L_disk_/L_star_~0.1). In contrast, the distributions for the older Upper Scorpius and {eta} Chamaeleontis clusters are dominated by optically thin lower luminosity disks (L_disk_/L_star_~0.02). This evolution in fractional disk luminosities is concurrent with that of disk fractions: with time disks become fainter and the disk fractions decrease. The actively accreting and non-accreting stars (based on H{alpha} data) in Serpens show very similar distributions in fractional disk luminosities, differing only in the brighter tail dominated by strongly accreting stars. In contrast with a sample of Herbig Ae/Be stars, the T Tauri stars in Serpens do not have a clear separation in fractional disk luminosities for different disk geometries: both flared and flat disks present wider, overlapping distributions. This result is consistent with previous suggestions of a faster evolution for disks around Herbig Ae/Be stars. Furthermore, the results for the mineralogy of the dust in the disk surface (grain sizes, temperatures and crystallinity fractions, as derived from Spitzer/IRS spectra) do not show any correlation to either stellar and disk characteristics or mean cluster age in the 1-10Myr range probed here. A possible explanation for the lack of correlation is that the processes affecting the dust within disks have short timescales, happening repeatedly, making it difficult to distinguish long-lasting evolutionary effects.
2673. Spitzer/IRS observations of the Galactic Center
ID:
ivo://CDS.VizieR/J/ApJ/857/59
Title:
Spitzer/IRS observations of the Galactic Center
Short Name:
J/ApJ/857/59
Date:
21 Oct 2021
Publisher:
CDS
Description:
It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of HII regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal HII regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, HII region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.
2674. 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.
2675. Spitzer/IRS spectral decompositon of AGN
ID:
ivo://CDS.VizieR/J/ApJ/803/109
Title:
Spitzer/IRS spectral decompositon of AGN
Short Name:
J/ApJ/803/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGNs) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method with no need to model extinction separately. We use full probability distribution functions to estimate expectation values and uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum with a 1{sigma} dispersion of 0.12dex in luminosity and typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGNs. This allows for unbiased studies of the AGN emission in intermediate- and high-redshift galaxies--currently inaccesible to ground-based observations--with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope.
2676. Spitzer/IRS spectra of GOALS luminous IR galaxies
ID:
ivo://CDS.VizieR/J/ApJ/777/156
Title:
Spitzer/IRS spectra of GOALS luminous IR galaxies
Short Name:
J/ApJ/777/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the data and our analysis of mid-infrared atomic fine-structure emission lines detected in Spitzer/Infrared Spectrograph high-resolution spectra of 202 local Luminous Infrared Galaxies (LIRGs) observed as part of the Great Observatories All-sky LIRG Survey (GOALS). We readily detect emission lines of [SIV], [NeII], [NeV], [NeIII], [SIII]_18.7{mu}m_, [OIV], [FeII], [SIII]_33.5{mu}m_, and [SiII]. More than 75% of these galaxies are classified as starburst-dominated sources in the mid-infrared, based on the [NeV]/[NeII] line flux ratios and equivalent width of the 6.2{mu}m polycyclic aromatic hydrocarbon feature. We compare ratios of the emission-line fluxes to those predicted from stellar photo-ionization and shock-ionization models to constrain the physical and chemical properties of the gas in the starburst LIRG nuclei. Comparing the [SIV]/[NeII] and [NeIII]/[NeII] line ratios to the Starburst99-Mappings III models with an instantaneous burst history, the emission-line ratios suggest that the nuclear starbursts in our LIRGs have ages of 1-4.5 Myr, metallicities of 1-2Z_{sun}_, and ionization parameters of 2-8x10^7^cm/s. Based on the [SIII]_33.5{mu}m_/[SIII]_18.7{mu}m_ ratios, the electron density in LIRG nuclei is typically one to a few hundred/cm3, with a median electron density of ~300/cm3, for those sources above the low density limit for these lines.
2677. 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.
2678. Spitzer-IRS study of massive YSOs in galactic center
ID:
ivo://CDS.VizieR/J/ApJ/736/133
Title:
Spitzer-IRS study of massive YSOs in galactic center
Short Name:
J/ApJ/736/133
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic center (GC). Our sample of 107 YSO candidates was selected based on Infrared Array Camera (IRAC) colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone, which spans the central ~300pc region of the Milky Way. We obtained IRS spectra over 5-35um using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4um shoulder on the absorption profile of 15um CO_2_ ice, suggestive of CO_2_ ice mixed with CH_3_OH ice on grains. This 15.4um shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that nine massive YSOs also reveal molecular gas-phase absorption from CO_2_, C_2_H_2_, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8-23M_{sun}_, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of ~0.07M_{sun}/yr at the GC.
2679. Spitzer mid-IR spectra of 3 molecular clouds
ID:
ivo://CDS.VizieR/J/A+A/469/575
Title:
Spitzer mid-IR spectra of 3 molecular clouds
Short Name:
J/A+A/469/575
Date:
21 Oct 2021
Publisher:
CDS
Description:
This work was conducted as part of the SPECPDR program, dedicated to the study of very small particles and astrochemistry, in Photo-Dissociation Regions (PDRs). We present the analysis of the mid-IR spectro-imagery observations of Ced 201, NCG 7023 East and North-West and rho Ophiuchi West filament. Using the data from all four modules of the InfraRed Spectrograph onboard the Spitzer Space Telescope, we produced a spectral cube ranging from 5 to 35{mu}m, for each one of the observed PDRs. The resulting cubes were analysed using Blind Signal Separation methods (NMF and FastICA).
2680. Spitzer mid-IR spectroscopy of LIRGs
ID:
ivo://CDS.VizieR/J/MNRAS/395/1695
Title:
Spitzer mid-IR spectroscopy of LIRGs
Short Name:
J/MNRAS/395/1695
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results on low-resolution mid-infrared (MIR) spectra of 70 IR-luminous galaxies obtained with the infrared spectrograph (IRS) onboard Spitzer. We selected sources from the European Large Area Infrared Survey with S_15_>0.8mJy and photometric or spectroscopic z>1. About half of the samples are quasi-stellar objects (QSOs) in the optical, while the remaining sources are galaxies, comprising both obscured active galactic nuclei (AGN) and starbursts. Redshifts were obtained from optical spectroscopy, photometric redshifts and the IRS spectra. The later turn out to be reliable for obscured and/or star-forming sources, thus becoming an ideal complement to optical spectroscopy for redshift estimation.

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