A<i>Herschel</i>[C ii] Galactic plane survey

Langer, W. D.; Velusamy, T.; Pineda, J. L.; Willacy, Karen; Goldsmith, Paul F.

doi:10.1051/0004-6361/201322406

Cited by 156 publications

(202 citation statements)

References 55 publications

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“…This zone is well outside the cold and FUV-shielded core where most of the hydrogen is in H 2 and most of the carbon in CO (e.g., Roellig et al 2007). Recently, Herschel/HIFI observations demonstrated that a significant fraction, between 20% and 75%, of the ISM gas that is undetected in H Iand CO is bright in the [C II] FIR line at 158 μm (Langer et al 2014). Orr et al (2014) To summarize, the available data suggest that the Na I and K I absorption lines trace the warm (∼100 K) atomic envelope of the cold molecular CO gas in Taurus.…”

Section: Origin Of the Narrow Absorption In The Na I And K I Profilesmentioning

confidence: 99%

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Pascucci

Edwards

Rigliaco

et al. 2015

ApJ

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We present a detailed analysis of narrow Na I and K I absorption resonance lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying their origin. The Na I λ5889.95 line is detected toward all but one source, while the weaker K I λ7698.96 line is detected in about two-thirds of the sample. The similarity in their peak centroids and the significant positive correlation between their equivalent widths demonstrate that these transitions trace the same atomic gas. The absorption lines are present toward both disk and diskless young stellar objects, which excludes cold gas within the circumstellar disk as the absorbing material. A comparison of Na I and CO detections and peak centroids demonstrates that the atomic gasand molecular gas are not co-located, the atomic gas being more extended than the molecular gas. The width of the atomic lines corroborates this finding and points to atomic gas about an order of magnitude warmer than the molecular gas. The distribution of Na I radial velocities shows a clear spatial gradient along the length of the Taurus molecular cloud filaments. This suggests that absorption is associated with the Taurus molecular cloud. Assuming that the gradient is due to cloud rotation, the rotation of the atomic gas is consistent with differential galactic rotation, whereas the rotation of the molecular gas, although with the same rotation axis, is retrograde. Our analysis shows that narrow Na I and K I absorption resonance lines are useful tracers of the atomic envelope of molecular clouds. In line with recent findings from giant molecular clouds, our results demonstrate that the velocity fields of the atomic and molecular gas are misaligned. The angular momentum of a molecular cloud is not simply inherited from the rotating Galactic disk from which it formed but may be redistributed by cloud-cloud interactions.

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Section: Origin Of the Narrow Absorption In The Na I And K I Profilesmentioning

confidence: 99%

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Pascucci

Edwards

Rigliaco

et al. 2015

ApJ

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“…In their derivation of the CO-dark H 2 gas fraction Langer et al (2014) used an exponential Galactic carbon abundance gradient N(C + )/N(H) ∝ exp(−R/6.2 kpc) following Wolfire et al (2003) and based on the [O/H] metallicity gradient at that epoch. This would imply a factor of two difference between the value at R = 8.5 kpc and that at the inner edge of the Galactic molecular ring at R = 4 kpc.…”

Section: Galactic Metallicity Gradientmentioning

confidence: 99%

Molecular gas in absorption and emission along the line of sight to W31C G10.62-0.38

Liszt

Gérin

2015

A&A

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Context. The sightline to W31C G10.62-0.38 was extensively observed in absorption under the PRISMAS program on Herschel. Aims. We relate absorbing material to the older view of Galactic molecules gained from CO emission. Methods. We used the Arizona Radio Observatory Kitt Peak 12m antenna to observe emission from the J = 1−0 lines of carbon monoxide, HCO + , and HNC, and the J = 2−1 line of CS toward and around the continuum peak used for absorption studies and we compare them with CH, HNC, C + , and other absorption spectra from PRISMAS. We develop a kinematic analysis that allows a continuous description of the spectral properties and relates them to viewing geometry in the Galaxy. Results. As it is for CH, HF, C + , HCO + , and other species observed in absorption, mm-wave emission in CO, HCO + , HNC, and CS is continuous over the full velocity range expected for material between the Sun and W31 4.95 kpc away. CO emission is much stronger than average in the Galactic molecular ring and the mean H 2 density derived from CH, 4 cm −3 < ∼ 2 n(H 2 ) < ∼ 10 cm −3 at 4 < ∼ R < ∼ 6.4 kpc, is similarly elevated. The CO-H 2 conversion factor falls in a narrow range X CO = 1−2 × 10 20 H 2 cm −2 (K − km s −1 ) −1 if the emitting gas is mostly on the near side of the subcentral point, as we suggest. The brightnesses of HCO + , HNC, and CS are comparable (0.83%, 0.51%, and 1.1%, respectively, relative to CO) and have no variation in galactocentric radius with respect to CO. Comparison of the profile-averaged HCO + emission brightness and optical depth implies local densities n(H) ≈ 135 ± 25 cm −3 with most of the excitation of HCO + from electrons. At this level of density, a consistent picture of the H 2 -bearing gas, which also accounts for the CO emission, has a volume filling factor of 3% and a 5 pc clump or cloud size.

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“…Furthermore, the filling factor of the ionized gas appears larger relatively to the neutral gas. As a consequence of the low metallicity and low extinction in dwarf galaxies, it is possible that a significant fraction of the molecular gas is not traced by CO, but may be residing in the C + or C 0 -emitting region; for example (referred to as the "dark gas" in Wolfire et al 2010), this is quantified in low metallicity environments using C + by Poglitsch et al (1995) and Madden et al (1997) and, more recently, in our Galaxy by Langer et al (2014) and Pineda et al (2014).…”

Section: Introductionmentioning

confidence: 99%

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

Chevance

Madden

Lebouteiller

et al. 2016

A&A

103

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Context. More complete knowledge of galaxy evolution requires understanding the process of star formation and the interaction between the interstellar radiation field and interstellar medium (ISM) in galactic environments traversing a wide range of physical parameter space. We focus on the impact of massive star formation on the surrounding low metallicity ISM in 30 Doradus in the Large Magellanic Cloud (LMC). A low metal abundance, which can characterizes some galaxies of the early Universe, results in less ultraviolet (UV) shielding for the formation of the molecular gas necessary for star formation to proceed. The half-solar metallicity gas in this region is strongly irradiated by the super star cluster R136, making it an ideal laboratory to study the structure of the ISM in an extreme environment. Aims. Our goal is to construct a comprehensive, self-consistent picture of the density, radiation field, and ISM structure in the most active star-forming region in the LMC, 30 Doradus. Our spatially resolved study investigates the gas heating and cooling mechanisms, particularly in the photodissociation regions (PDR) where the chemistry and thermal balance are regulated by far-UV photons (6 eV < hν < 13.6 eV). Methods. We present Herschel observations of far-infrared (FIR) fine-structure lines obtained with PACS and SPIRE/FTS. We combined atomic fine-structure lines from Herschel and Spitzer observations with ground-based CO data to provide diagnostics on the properties and structure of the gas by modeling it with the Meudon PDR code. For each tracer we estimate the possible contamination from the ionized gas to isolate the PDR component. We derive the spatial distribution of the radiation field, the pressure, the size, and the filling factor of the photodissociated gas and molecular clouds. Results. We find a range of pressure of ∼10 5 −1.7×10 6 cm −3 K and a range of incident radiation field G UV ∼ 10 2 −2.5×10 4 through PDR modeling. Assuming a plane-parallel geometry and a uniform medium, we find a total extinction A max V of 1-3 mag, which corresponds to a PDR cloud size of 0.2 to 3pc with small CO depth scale of 0.06 to 0.5 pc. At least 90% of the [C ii] originates in PDRs in this region, while a significant fraction of the L FIR (up to 70% in some places) can be associated with an ionized gas component. Theratio (2 to 60) throughout the observed map, correlated with the filling factor, reveals the porosity of the ISM in this region, which is traversed by hard UV photons surrounding small PDR clumps. We also determine the three-dimensional structure of the gas, showing that the clouds are distributed 20 to 80 pc away from the main ionizing cluster, R136.

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AHerschel[C ii] Galactic plane survey

Cited by 156 publications

References 55 publications

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Molecular gas in absorption and emission along the line of sight to W31C G10.62-0.38

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

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