Volume 544, August 2012
|Number of page(s)||9|
|Published online||25 July 2012|
Spectrally resolved C II emission in M 33 (HerM33es)
Physical conditions and kinematics around BCLMP 691⋆
Univ. Bordeaux, Laboratoire d’Astrophysique de Bordeaux,
2 CNRS, LAB, UMR 5804, 33270 Floirac, France
3 IRAM, 300 rue de la Piscine, 38406 St Martin d’Hères, France
4 Instituto Radioastronomia Milimetrica (IRAM), Av. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain
5 Leiden Observatory, Leiden University, PO Box 9513, NL 2300 RA Leiden, The Netherlands
6 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
7 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
8 Laboratoire d’Astrophysique de Marseille – LAM, Université d’Aix-Marseille & CNRS UMR 7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
9 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
10 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
11 Astron. Dept., King Abdulaziz University, PO Box 80203, Jeddah, Saudi Arabia
Received: 5 April 2012
Accepted: 15 June 2012
This work presents high spectral resolution observations of the [C ii] line at 158 μm, one of the major cooling lines of the interstellar medium, taken with the HIFI heterodyne spectrometer on the Herschel satellite. In BCLMP 691, an H ii region far north (3.3 kpc) in the disk of M 33, the [C ii] and CO line profiles show similar velocities within 0.5 km s-1, while the H i line velocities are systematically shifted towards lower rotation velocities by ~5 km s-1. Observed at the same 12′′angular resolution, the [C ii] lines are broader than those of CO by about 50% but narrower than the H i lines. The [C ii] line intensities also follow those of CO much better than those of H i. A weak shoulder on the [C ii] line suggests a marginal detection of the [13C ii] line, insufficient to constrain the [C ii] optical depth. The velocity coincidence of the CO and [C ii] lines and the morphology at optical/UV wavelengths indicate that the emission is coming from a molecular cloud behind the H ii region. The relative strength of [C ii] with respect to the FIR continuum emission is comparable to that observed in the Magellanic Clouds on similar linear scales but the CO emission relative to [C ii] is stronger in M 33. The [C ii] line to far-infrared continuum ratio suggests a photoelectric heating efficiency of 1.1%. The data, together with published models indicate a UV field G0 ~ 100 in units of the solar neighborhood value, a gas density nH~1000 cm-3, and a gas temperature T ~ 200 K. Adopting these values, we estimate the C+ column density to be NC + ≈ 1.3×1017cm-2. The [C ii] emission comes predominantly from the warm neutral region between the H ii region and the cool molecular cloud behind it. From published abundances, the inferred C+ column corresponds to a hydrogen column density of NH~2×1021cm-2. The CO observations suggest thatNH=2NH2~3.2×1021cm-2 and 21 cm measurements, also at 12′′resolution, yield NH i≈1.2×1021cm-2 within the [C ii] velocity range. Thus, some H2 not detected in CO must be present, in agreement with earlier findings based on the SPIRE 250−500 μm emission.
Key words: galaxies: individual: M 33 / Local Group / galaxies: evolution / galaxies: ISM / ISM: clouds / stars: formation
© ESO, 2012
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.