- ID:
- ivo://CDS.VizieR/J/ApJ/845/96
- Title:
- [CII] emission in the ISM of 20 nearby galaxies
- Short Name:
- J/ApJ/845/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The [CII]158{mu}m fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [CII] balances the heating, including that due to far- ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [CII] emission remains unclear because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [CII] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [NII]205{mu}m fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [CII]/[NII]122{mu}m. Using the FIR [CII] and [NII] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%-80% of [CII] emission originates from neutral gas. We find that the fraction of [CII] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [CII] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/898/85
- Title:
- CII emission-line stars in LMC with MagE spectra
- Short Name:
- J/ApJ/898/85
- Date:
- 21 Mar 2022 08:48:14
- Publisher:
- CDS
- Description:
- We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the CII{lambda}{lambda}7231,7236 emission lines in objects as faint as m_{lambda}7400_~18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by CII emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged ~50deg^2^ using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known CII emitters were easily recovered, validating the survey design. We find 38 new CII emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding CII emission in each. One is a new [WC11]. Another shows both the narrow CII emission lines characteristic of a [WC11], but also broad emission of CIV, OV, and HeII characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak CII emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous OII transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected CII emitters are largely of an old population.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/68
- Title:
- [CII]157.7um feature in LIRGs
- Short Name:
- J/ApJ/774/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a survey of the [CII]157.7{mu}m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained with the PACS instrument on board the Herschel Space Observatory. The [CII] luminosities, L_[CII]_, of the LIRGs in GOALS range from ~10^7^ to 2x10^9^L_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/171
- Title:
- [CII]158um line fluxes of AGN from Herschel
- Short Name:
- J/ApJ/755/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results are presented for [CII] 158{mu}m line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and active galactic nucleus (AGN) classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L_ir_ from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2{mu}m polycyclic aromatic hydrocarbon (PAH) feature. It is found that the [CII] line flux correlates closely with the flux of the 11.3{mu}m PAH feature independent of AGN/starburst classification, log[f([CII]158{mu}m)/f(11.3{mu}mPAH)]=-0.22+/-0.25. It is concluded that the [CII] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate (SFR) for the starburst component in any source having [CII] is derived comparing [CII] luminosity L([CII]) to L_ir_ with the result that logSFR=logL([CII)])-7.08+/-0.3, for SFR in M_{sun}_/yr and L([CII]) in L_{sun}_. The decreasing ratio of L([CII]) to L_ir_ in more luminous sources (the "[CII] deficit") is shown to be a consequence of the dominant contribution to L_ir_arising from a luminous AGN component because the sources with the largest L_ir_ and smallest L([CII])/L_ir_ are AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A86
- Title:
- Circumstellar disks in Lupus complex
- Short Name:
- J/A+A/642/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous star formation studies have, out of necessity, often defined a population of young stars confined to the proximity of a molecular cloud. Gaia allows us to examine a wider, three-dimensional structure of nearby star forming regions, leading to a new understanding of their history. We present a wide-area survey covering 494 deg^2^ of the Lupus complex, a prototypical low-mass star forming region. Our survey includes all known molecular clouds in this region as well as parts of the Upper Scorpius and Upper Centaurus Lupus (UCL) groups of the Sco-Cen complex. We combine Gaia DR2 proper motions and parallaxes as well as ALLWISE mid-infrared photometry to select young stellar objects (YSOs) with disks. The YSO ages are inferred from Gaia color-magnitude diagrams, and their evolutionary stages from the slope of the spectral energy distributions. We find 98 new disk-bearing sources. Our new sample includes objects with ages ranging from 1 to 15Myr and masses ranging from 0.05 to 0.5M_{sun}_, and consists of 56 sources with thick disks and 42 sources with anemic disks. While the youngest members are concentrated in the clouds and at distances of 160 pc, there is a distributed population of slightly older stars that overlap in proper motion, spatial distribution, distance, and age with the Lupus and UCL groups. The spatial and kinematic properties of the new disk-bearing YSOs indicate that Lupus and UCL are not distinct groups. Our new sample comprises some of the nearest disks to Earth at these ages, and thus provides an important target for follow-up studies of disks and accretion in very low mass stars, for example with ALMA and ESO-VLT X-shooter.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/67
- Title:
- Circumstellar emission measures with Keck
- Short Name:
- J/ApJ/734/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4AU from the star. We find one significant detection ({eta} Crv), two marginal detections ({gamma} Oph and {alpha} Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are {eta} Crv (1250+/-260), {gamma} Oph (200+/-80), and {alpha} Aql (600+/-200), where the uncertainties are 1{sigma}. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1{sigma}). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding {eta} Crv and {gamma} Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3{sigma} upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.
- ID:
- ivo://CDS.VizieR/J/A+A/293/833
- Title:
- Circumstellar silicate grains
- Short Name:
- J/A+A/293/833
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the radiative transfer modelling studies relative to a large sample of circumstellar envelopes (~300 sources) undertaken by David & Papoular (1990A&A...237..425D) the complex dielectric function for circumstellar silicate grains is derived in the wavelength region from 0.35 to ~1355m.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/29
- Title:
- Classical and type II Cepheids IR excesses
- Short Name:
- J/ApJ/813/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral energy distributions for 132 classical and type II Cepheids were searched for evidence of excess flux above the photospheric level in the mid-infrared. Eight of them were found to have unambiguously strong excess emission while a further 13 showed evidence of weak emission. The presence of emission appears to be unrelated to either the pulsational amplitude or the effective temperature while strong emission is limited to stars with periods longer than 11 days, with a single exception. For the stars with strong emission we attempted to fit the energy distribution with a stellar wind model. No acceptable fit could be found for silicate grains. With graphite or iron grains we could only obtain an acceptable fit if the maximum dust temperature was significantly lower than the condensation temperature. We conclude that the excess emission is not evidence of mass loss.
- ID:
- ivo://CDS.VizieR/J/ApJS/152/201
- Title:
- Classification of 2000 bright IRAS sources
- Short Name:
- J/ApJS/152/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An artificial neural network (ANN) scheme has been employed that uses a supervised back-propagation algorithm to classify 2000 bright sources from the Calgary database of Infrared Astronomical Satellite (IRAS) spectra in the region 8-23{mu}m. The database has been classified into 17 predefined classes based on the spectral morphology. We have been able to classify over 80% of the sources correctly in the first instance. The speed and robustness of the scheme will allow us to classify the whole of the Low Resolution Spectrometer database, containing more than 50,000 sources, in the near future.
- ID:
- ivo://CDS.VizieR/J/A+A/453/535
- Title:
- Classification of bright mid-IR sources
- Short Name:
- J/A+A/453/535
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context: The stellar populations in the central region of the Galaxy are poorly known because of the high visual extinction and very great source density in this direction. Aims: To use recent infrared surveys for studying the dusty stellar objects in this region. Methods: We analyse the content of a ~20x20arcmin^2 field centred at (l,b)=(-0.27,-0.06) observed at 7 and 15 microns as part of the ISOGAL survey. These ISO observations are more than an order of magnitude better in sensitivity and spatial resolution than the IRAS observations. The sources are cross-associated with other catalogues to identify various types of objects. We then derive criteria to distinguish young objects from post-main sequence stars. Results: We find that a sample of about 50 young stellar objects and ultra-compact HII regions emerges, out of a population of evolved AGB stars. We demonstrate that the sources colours and spatial extents, as they appear in the ISOGAL catalogue, possibly complemented with MSX photometry at 21 microns, can be used to determine whether the ISOGAL sources brighter than 300mJy at 15 microns (or [15]<4.5mag) are young objects or late-type evolved stars.
