- 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.
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- 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.
- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/145/66
- Title:
- Spitzer light curves of YSOs in IC 348
- Short Name:
- J/AJ/145/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on synoptic observations at 3.6 and 4.5{mu}m of young stellar objects in IC 348 with 38epochs covering 40days. We find that among the detected cluster members, 338 at [3.6] and 269 at both [3.6] and [4.5], many are variable on daily to weekly timescales with typical fluctuations of ~0.1mag. The fraction of variables ranges from 20% for the diskless pre-main sequence stars to 60% for the stars still surrounded by infalling envelopes. We also find that stars in the exposed cluster core are less variable than the stars in the dense, slightly younger, southwestern ridge. This trend persists even after accounting for the underlying correlation with infrared spectral energy distribution type, suggesting that the change in variable fraction is not simply a reflection of the change in relative fraction of class I versus class II sources across the cloud, but instead reflects a change in variability with age. We also see a strong correlation between infrared variability and X-ray luminosity among the class II sources. The observed variability most likely reflects large changes in the structure of the inner wall located at the dust sublimation radius. We explore the possibility that these structural perturbations could be caused by a hot spot on the star heating dust above the sublimation temperature, causing it to evaporate rapidly, and increasing the inner radius for a portion of the disk. Under a number of simplifying assumptions we show that this model can reproduce the size and timescale of the 3.6 and 4.5{mu}m fluctuations. Regardless of its source, the infrared variability indicates that the inner disk is not a slowly evolving entity, but instead is a bubbling, warped, dented mass of gas and dust whose global size and shape fluctuate in a matter of days.
- ID:
- ivo://CDS.VizieR/J/AJ/144/31
- Title:
- Spitzer+2MASS photometry of protostar candidates
- Short Name:
- J/AJ/144/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24{mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24{mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1L_{sun}_ and show a tail extending toward luminosities above 100L_{sun}_. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1L_{sun}_. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity functions to those predicted by models and find that our observed luminosity functions are best matched by models that invoke competitive accretion, although we do not find strong agreement between the high-mass SF clouds and any of the models.
- 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).
- 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.