arXiv subjects

N. Flagey

Publications and source records attributed to N. Flagey.

21 records · Page 2Linked to original sources

arXiv2009

The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in 7 mid- and far-infrared bands with the Spitzer Space Telescope. There are 215 previously-identified members of the Taurus star-forming region in our ~44 square degree map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ~20% of the bonafide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 candidate new members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, 3 probable new members, and 10 possible new members, an increase of 15-20% in Taurus members. Of the objects for which we have spectroscopy, 7 are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously-identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and AGN.

astro-ph.SR↗

arXiv2009

Evidence for dust evolution within the Taurus Complex from Spitzer images

We present Spitzer images of the Taurus Complex (TC) and take advantage of the sensitivity and spatial resolution of the observations to characterize the diffuse IR emission across the cloud. This work highlights evidence of dust evolution within the translucent sections of the archetype reference for studies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100 um observations to produce a dust temperature map and a far-IR dust opacity map at 5' resolution. The average dust temperature is about 14.5K with a dispersion of +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger than the average value for the diffuse ISM. This opacity increase and the attenuation of the radiation field (RF) both contribute to account for the lower emission temperature of the large grains. The structure of the TC significantly changes in the mid-IR images that trace emission from PAHs and VSGs. We focus our analysis of the mid-IR emission to a range of ecliptic latitudes where the zodiacal light residuals are small. Within this cloud area, there are no 8 and 24 um counterparts to the brightest 160 um emission features. Conversely, the 8 and 24 um images reveal filamentary structure that is strikingly inconspicuous in the 160 um and extinction maps. The IR colors vary over sub-parsec distances across this filamentary structure. We compare the observed colors with model calculations quantifying the impact of the RF intensity and the abundance of stochastically heated particles on the dust SED. To match the range of observed colors, we have to invoke variations by a factor of a few of both the interstellar RF and the abundance of PAHs and VSGs. We conclude that within this filamentary structure a significant fraction of the dust mass cycles in and out the small size end of the dust size distribution.

astro-ph.GA↗

arXiv2006

Spitzer/IRAC and ISOCAM/CVF insights on the origin of the Near to Mid-IR Galactic diffuse emission

We measure IRAC colors of extended emission in several fields covering a range of Galactic latitudes and longitudes outside of star forming regions. We determine the nature of the Galactic diffuse emission in Spitzer/IRAC images by combining them with spectroscopic data. We show that PAH features make the emission in the IRAC 5.8 and 8.0 $μ$m channels, whereas the 3.3 $μ$m feature represents only 20 to 50% of the IRAC 3.6 $μ$m channel. A NIR continuum is necessary to account for IRAC 4.5 $μ$m emission and the remaining fraction of the IRAC 3.6 $μ$m emission. This continuum cannot be accounted by scattered light. It represents 9% of the total power absorbed by PAHs and 120% of the interstellar UV photon flux. The 3.3 $μ$m feature is observed to vary from field-to-field with respect to the IRAC 8.0 $μ$m channel. The continuum and 3.3 $μ$m feature intensities are not correlated. We present model calculations which relate our measurements of the PAHs spectral energy distribution to the particles size and ionization state. Cation and neutral PAHs emission properties are inferred empirically from \object{NGC7023} observations. PAHs caracteristics are best constrained in a line of sight towards the inner Galaxy, dominated by the Cold Neutral Medium phase : we find that the PAH cation fraction is about 50% and that their mean size is about 60 carbon atoms. A significant field-to-field dispersion in the PAH mean size, from 40 to 80 carbon atoms, is necessary to account for the observed variations in the 3.3 $μ$m feature intensity relative to the IRAC 8.0 $μ$m flux. However, one cannot be secure about the feature interpretation as long as the continuum origin remains unclear.

astro-ph↗