Context. The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only ...2.35 kpc distance. Aims. We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas. Methods. The NANTEN2-4 m submillimeter telescope was used to map the C I super(3) P sub(1)- super(3) P sub(0), super(3) P sub(2)- super(3) P sub(1) and CO 4-3, 7-6 lines in two 4'\times4' regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr 14, and the second region is in the molecular cloud south of eta Car and Tr 16. These data were combined with super(13) CO SEST spectra, HIRES/IRAS 60 mum and 100 mum maps of the FIR continuum, and maps of 8 mum IRAC/Spitzer and MSX emission. Results. We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 10 super(3) in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8\,\mum emission lights up at the edges of the molecular clouds, CO and also C I appear to trace the H sub(2) gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38'' beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2\times10 super(5) cm super(-3) is needed to reproduce the observed line emission at two selected interface positions. Conclusions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.
Clumpy photon-dominated regions in Carina Kramer, C.; Cubick, M.; Röllig, M. ...
Astronomy and astrophysics (Berlin),
01/2008, Letnik:
477, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Context.The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only ...2.35 kpc distance. Aims.We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas. Methods.The NANTEN2-4 m submillimeter telescope was used to map the C I 3P1-3P0, 3P2-3P1 and CO 4–3, 7–6 lines in two 4'$\times$4' regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr 14, and the second region is in the molecular cloud south of η Car and Tr 16. These data were combined with 13CO SEST spectra, HIRES/IRAS 60 μm and 100 μm maps of the FIR continuum, and maps of 8 μm IRAC/Spitzer and MSX emission. Results.We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 103 in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8$\,\mu$m emission lights up at the edges of the molecular clouds, CO and also C I appear to trace the H2 gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the $38''$ beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2$\times$105 cm-3 is needed to reproduce the observed line emission at two selected interface positions. Conclusions.Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.
Clumpy photon-dominated regions in Carina Kramer, C.; Cubick, M.; Röllig, M. ...
Astronomy and astrophysics (Berlin),
01/2008, Letnik:
477, Številka:
2
Journal Article
To date the onset of large-scale star formation in galaxies and its link to gravitational stability of the galactic disk have not been fully understood. The nearby face-on spiral galaxy M51 is an ...ideal target for studying this subject. This paper combines CO, dust, HI, and stellar maps of M51 and its companion galaxy to study the H2/HI transition, the gas-to-dust ratios, and the stability of the disk against gravitational collapse. We combine maps of the molecular gas using 12CO 2--1 map HERA/IRAM-30m data and HI VLA data to study the total gas surface density and the phase transition of atomic to molecular gas. The total gas surface density is compared to the dust surface density from 850 micron SCUBA data. Taking into account the velocity dispersions of the molecular and atomic gas, and the stellar surface densities derived from the 2MASS K-band survey, we derive the total Toomre Q parameter of the disk. The gas surface density in the spiral arms is approximately 2-3 higher compared to that of the interarm regions. The ratio of molecular to atomic surface density shows a nearly power-law dependence on the hydrostatic pressure P_hydro. The gas surface density distribution in M51 shows an underlying exponential distribution with a scale length of h_gas=7.6 kpc representing 55% of the total gas mass, comparable to the properties of the exponential dust disk. In contrast to the velocity widths observed in HI, the CO velocity dispersion shows enhanced line widths in the spiral arms compared to the interarm regions. The contribution of the stellar component in the Toomre Q-parameter analysis is significant and lowers the combined Q-parameter Q_tot by up to 70% towards the threshold for gravitational instability. The value of Q_tot varies from 1.5-3 in radial averages. A map of Q_tot shows values around 1 on the spiral arms.
Star formation laws, like i.e. the Schmidt law relating star formation rate and total gas density, have been studied in several spiral galaxies but the underlying physics are not yet well understood. ...M51, as a nearby face-on, grand design spiral galaxy studied in many line transitions, is an ideal target to study the connection between physical conditions of the gas and star formation activity. In this contribution we combine molecular, atomic, total gas and stellar surface densities and study the gravitational stability of the gas (Schuster et al.2007, Hitschfeld et al. in prep.). From our IRAM-30m 12 CO2-1 map and complementary HI-, Radio Continuum- and ACS-HST B-band-data we derive maps of the total gas density and the stellar surface density to study the gravitational stability of the gas via the Toomre Q parameter.
The nearby, almost face-on, and interacting galaxy M51 offers an excellent
opportunity to study the distribution of molecular gas and the mechanisms
governing the star formation rate. We have created ...a complete map of M51 in
12CO 2-1 at a resolution of 11 arcsec corresponding to 450 kpc using HERA at
the IRAM-30m telescope. In Schuster et al. (2006) we have combined these data
with maps of HI and the radio-continuum to study the star formation efficiency,
the local Schmidt law, and Toomre stability of the disk in radial averages out
to radii of 12 kpc. Here, we also discuss the distribution of giant molecular
associations and its mass spectrum, in comparison with similar studies in the
literature.
The mechanisms governing the star formation rate in spiral galaxies are not
yet clear. The nearby, almost face-on, and interacting galaxy M51 offers an
excellent opportunity to study at high spatial ...resolutions the local star
formation laws. In this first paper, we investigate the correlation of H2, HI,
and total gas surface densities with the star forming activity, derived from
the radio continuum (RC), along radial averages out to radii of 12kpc.
We have created a complete map of M51 in 12CO 2-1 at a resolution of 450kpc
using HERA at the IRAM-30m telescope. These data are combined with maps of HI
and the radio-continuum at 20cm wavelength. The latter is used to estimate the
star formation rate (SFR), thus allowing to study the star formation efficiency
and the local Schmidt law. The velocity dispersion from CO is used to study the
critical surface density and the gravitational stability of the disk.
The critical gas velocity dispersions needed to stabilize the gas against
gravitational collapse in the differentially rotating disk of M51 using the
Toomre criterion, vary with radius between 1.7 and 6.8 km/s. Observed radially
averaged dispersions derived from the CO data vary between 28 km/s in the
center and 8 km/s at radii of 7 to 9 kpc. They exceed the critical dispersions
by factors Q_gas of 1 to 5. We speculate that the gravitational potential of
stars leads to a critically stable disk.
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