TheHerschelM 33 extended survey (HerM33es): PACS spectroscopy of the star-forming region BCLMP 302

Abstract

ContextResults. The [C ii] line observed with HIFI is significantly broader than that of CO, and slightly blue-shifted. In addition, there is little spatial correlation between [C ii] observed with PACS and CO over the mapped region. There is even less spatial correlation between [C ii] and the atomic gas traced by H i. Detailed comparison of the observed intensities towards the H ii region with models of photo-ionization and photon-dominated regions, confirms that a significant fraction, 20-30%, of the observed [C ii] emission stems from the ionized gas and not from the molecular cloud. The gas heating efficiency, using the ratio of [C ii] to the TIR as a proxy, varies between 0.07 and 1.5%, with the largest variations found outside the H ii region.

Origin andz-distribution of Galactic diffuse [C II] emission

“…We estimate a similar amount, ∼12% of [C ii] in H i gas associated with the denser molecular H 2 clouds (assuming a H i gas pressure P = 5000 K cm −3 and metallicity ∼2.2 × 10 −4 appropriate to the median spaxel radius R G ∼ 5.5 kpc). Thus our estimate of a total ∼27% for [C ii] in H i gas is close to those derived by Pineda et al (2013) for the Milky Way and Mookerjea et al (2011) for M 33. Therefore, we conclude that the total observed [C ii] intensity originating from the H i gas (see Fig.…”

Spectrally resolved C II emission in M 33 (HerM33es)

“…and excitation parameters of u = R Stromgren n 2/3 e = 180 and 200 pc cm −2 , corresponding to excitation by the equivalent of 3 and 4 O5 exciting stars (Israel & van der Kruit 1974). More significant differences between BCLMP 691, the H ii region studied in this paper, and BCLMP 302 (Mookerjea et al 2011) are tied to their location. BCLMP 691 is a major H ii region 3.3 kpc from the center, and relatively isolated, whereas BCLMP 302 is a major star-forming region embedded in the northern spiral arm at 2.1 kpc from the center of M 33.…”

“…2 and the small triangles forming an "X" in and around the rectangle indicate the individual positions of the [C ii] HIFI observations. The large lower rectangle shows the region around BCLMP302 observed with PACS by Mookerjea et al (2011). The center of M 33 is at the position of the triangle to the lower right of the image of M 33.…”

“…1, the HerM33es project observes [C ii] in a long strip along the major axis. In this work, we investigate the relationship between [C ii] FIR, CO, and H i emission at the scale of individual clouds (∼50 pc) in an area centered on the H ii region BCLMP 691 (Boulesteix et al 1974) and compare it with the results from Mookerjea et al (2011) on BCLMP 302, both part of the strip. In particular, we estimate the amount of gas traced by the [C ii] emission and and relate that to the CO and HI emission.…”

“…A series of [C ii] observations in the Local Group galaxy M 33 with the HIFI (Heterodyne Instrument for Far Infrared astronomy) instrument on the Herschel Space Observatory (Pilbratt 2010;de Graauw et al 2010;Roelfsema et al 2012) is the essential component of the open time key project HerM33ES . A first article (Mookerjea et al 2011 Despite its importance, only a few velocity-resolved observations have been made of the [C ii] line (e.g. Boreiko & Betz 1991).…”