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Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Large scale observations of nearby clouds

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K. Sun, M. Masur, B. Mookerjea, C. Kramer, J. Stutzki, V. Ossenkopf

Nearby low mass star forming molecular clouds: the Spitzer cores-to-disks sample


We conduct large-scale surveys of Perseus, Serpens, Ophiuchus, Chamaeleon, and Lupus in low- and mid-J CO transitions and atomic carbon using KOSMA and, in the future, NANTEN2. These surveys will provide an unbiased inventory of the physical properties of these large, nearby, low-mass star forming regions. A complete census of the stellar content of these four clouds is currently obtained by the Spitzer "Cores do Disks" (c2d) legacy project. The surveys of the northern sources are also coordinated with FCRAO surveys of the lowest CO and 13CO transition conducted by the COMPLETE team.

Data Sets

The 13CO 2-1 data and CO 3-2 data are observed by using the KOSMA 3-m telescope. The data cubes are in main beam temperature scales and the velocity range is from 0 to 15 km/s.



We have mapped the entire Perseus region with KOSMA in 12CO 3-2 and 13CO 2-1 covering a 7.1 deg2 region at scales of down to 0.1 pc. The Perseus molecular cloud at 350 pc distance is one of the best examples of nearby low- and intermediate-mass star forming regions. It contains an active star forming region (NGC1333), a young open cluster (IC348), and a dozen dense cloud cores with low levels of star forming activities (L1448, L1455, B1, B1 EAST, B3 and B5). The cloud exhibits a wealth of substructures seen in low-J CO transitions, such as cores, shells, filaments outflows, jets, and

Integrated CO 3-2 map of the Perseus clouds (Sun et al. 2006, A&A, 451, 539  ADS).

One way to analyze the large-scale structures of molecular clouds is to determine the power spectra from two dimensional maps of tracers of the clouds like CO. The slopes of the power spectra give the relative amount of structures at the different scales covered by the surveys. Power laws indicate invariant ranges of interstellar turbulence leading to self-similar structures while deviations from power laws indicate scales of energy input like outflows, supernovae, superbubbles, and Galactic rotation or scales of dissipation (Elmegreen & Scalo 2004). Studying the spectra thus helps to identify the importance of these different mechanisms. We measured the power spectra of the maps in terms of the delta-variance spectra which was introduced by Stutzki et al. (1998) and refined later on by Bensch et al. (2001) and Ossenkopf et al. (2005a).


The structure of the Perseus cloud: delta-variance results for the 12CO 3-2 and 13CO 2-1 KOSMA maps, the 2MASS map of optical extinctions, and the FCRAO 13CO and 12CO 1-0 data sets (Sun et al. 2006, A&A, 451, 539  ADS).

At scales between 0.1 and 2pc, we found that the power-law index of 12CO 3-2 and 13CO 2-1 integrated intensity maps of the whole region is almost constant at a value of 2.9 - similar to previous findings. However, it varies significantly in individual 50'x50' sub-regions, where, for both transitions, the index ranges between 2.8 and 3.6. Clearly, more active star forming regions like NGC1333 show the steepest slopes. This reflects the dominance of the main star-forming cloud for the overall structure in these regions. There is much less large scale structure in the quiescent regions. We also studied the velocity structure by looking at individual velocity channel maps and systematically studying the spectral index of the ?-variance as a function of the channel width. We found no uniform dependence as predicted by Lazarian & Pogosyan (2000) but steeper indices for line core channels and a gradually decreasing index for the channel maps as a function of velocity difference to the line center.

This survey is coordinated with D. Johnstone from the COMPLETE team (Goodman 2004) which has mapped the Perseus clouds with the FCRAO in the 1-0 12CO and 13CO transitions. The aim of both molecular line surveys is to allow for a detailed excitation analysis of the emitting gas. A second aim is to obtain complementary data to the ongoing cores-to-disks (c2d) Spitzer Legacy project (Evans et al. 2003). The c2d team is currently surveying the five nearest large molecular clouds: Perseus, Serpens, Ophiuchus, Chamaeleon, and Lupus with IRAC (3.6-8µm) and MIPS (24-160µm). The aim is to obtain an unbiased overview of the embedded star formation and to discover a large number of new candidate protostars and substellar objects as faint as 0.001 solar luminosities (Evans et al. 2003).

The IC348 star forming region in Perseus observed with SMART/KOSMA in the winter 04/05 period by Kefeng Sun using the kosma_control software and the on-the-fly mode which have been developed within A1. Contours show integrated intensities of [CI] 1-0, color show the integrated intensities of CO 4-3 (Sun et al. 2007, in prep.).

With KOSMA, we have recently started to map the Serpens core region also covered by Spitzer. One square-degree has so far been mapped in 13CO 2-1 and 12CO 3-2.

We have also started to extend the low-J CO observations to the submillimeter by mapping the extended emission of atomic carbon at 492 GHz using the SMART array receiver with 2x4 pixels at KOSMA and the newly installed on-the-fly observing mode (see below). The preliminary map of IC348 has an extent of 15'x30' and is, next to a recently obtained map of Cepheus B, the largest CI map ever mapped with KOSMA. Competing large-scale mapping projects of CI are being successfully pursued at the Mt. Fuji telescope using the frequency switching mode (e.g. NGC1333 in Perseus by Oka et al. 2004).
At the NANTEN2 4m telescope, we plan to map in [CI] and CO 4-3 the southern clouds Ophiuchus, Chamaeleon and Lupus, i.e. the southern sources of the c2d Spitzer legacy project with the relocated SMART receiver upgraded to 2x8 pixels.

Collaboration: This Ph.D. project of K.Sun is conducted together with C.Kramer, V.Ossenkopf, F. Bensch (RAIUB), and D. Johnstone (Viktoria, Canada).

Large scale mapping of the Cepheus OB3 molecular cloud using KOSMA

We are studying the large-scale properties of the giant molecular cloud complexes associated with the Cepheus OB3 association. At 730 pc from the Sun (Crawford & Barnes 1970), Cep OB3 is one of the nearest examples of an OB association (Sargent 1977, Evans et al. 1981, Lefloch et al. 1996, Heyer et al. 1996).

CO 3-2 map of integrated intensities of the Cepheus OB3 molecular cloud. Observations were carried in winter 04/05 as part of the diploma thesis of M.Masur using the newly installed kosma_control software and the on-the-fly observing mode.

Detailed multiline analysis using the KOSMA-tau PDR model (Störzer et al. 2000) of a small 15'x15' region in Cep B was done previously using KOSMA data (Beuther et al. 2000). The newly observed data will be used in combination with the FCRAO dataset to derive the kinetic temperature, column density and volume density using an escape probability based radiation transfer model (Stutzki & Winnewisser 1985). Since 12CO(3-2) has a higher critical density, it not only traces regions of higher temperature but also density enhancements and a comparison with MSX maps will be done to correlate star formation activity with such density enhancements. Dust temperatures derived from IRAS maps will be compared with gas temperatures derived from excitation analysis (using escape probability based methods) of the CO emission. Following this the data will be used to analyse the statistical properties of the substructures contributing to the CO emission.

Additionally, the Cepheus B region has been mapped in CI 1-0 and CO 4-3 with SMART/KOSMA for detailed studies of the PDR emission characteristics of the region using the KOSMA-tau PDR models. Rich complementary data are available: CO 7-6 was mapped by C.Kramer and D.Muders at the HHT. CI 1-0 and CO 4-3 was mapped with the CHAMP array receiver at the CSO by Muders et al.. H. Beuther observed the 1.2mm dust continuum with MAMBO/30m and H.Ungerechts mapped the 13CO 1-0 and 2-1 lines with the IRAM-30m telescope.