CO (<i>J</i> = 7→6) Observations of NGC 253: Cosmic‐Ray–heated Warm Molecular Gas

Bradford, C. M.; Nikola, Thomas; Stacey, G. J.; Bolatto, Alberto D.; Jackson, James M.; Savage, Maureen L.; Davidson, J. A.; Higdon, Sarah J.U.

doi:10.1086/367854

Cited by 126 publications

(182 citation statements)

References 46 publications

Supporting

Mentioning

155

Contrasting

Order By: Relevance

“…Carral et al (1994) uses [CII] 158 μm to trace the atomic gas mass in the inner 40 of NGC 253 and finds an atomic mass of 2.4×10 6 M . This atomic mass is 30 times smaller than the molecular gas that we observe in our 32.5 beam, which is similar to the findings of Bradford et al (2003) and Hailey-Dunsheath et al (2008). Tielens & Hollenbach (1985) predict that in Galactic PDRs, the first ∼3A V s are irradiated and then cooled via atomic lines, whereas the next 3 A V are cooled through molecular lines.…”

Section: Pdr Analysissupporting

confidence: 89%

“…Thus, in addition to the mPDR models, we have run mCDR models. These models not only have photoelectric heating from the PDR but they also have mechanical heating and an increased cosmic ray ionization rate of 750 ζ gal or 3.75 × 10 −14 s −1 , as suggested by Bradford et al (2003). The enhanced cosmic ray ionization rate is paired with a varying mechanical heating rate from α = 0, or no mechanical heating, up to α = 1.0 which translates to a heating rate of Γ mech = 1.3 × 10 −15 erg s −1 cm −3 .…”

Section: Excitation Mechanismsmentioning

confidence: 87%

“…In order to study the excitation of the bulk of the molecular gas, we can use CO as a probe. Bradford et al (2003) have observed 12 CO up to J = 6−5 along with 13 CO up to J = 3−2 and derive a kinetic temperature of 120 K and an H 2 density of 4.5 × 10 4 cm −3 for the warm phase. However, they suggest that the CO is excited by cosmic rays, and not only by PDRs.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Radiative and mechanical feedback into the molecular gas of NGC 253

Rosenberg

Kazandjian

Werf

et al. 2014

A&A

View full text Add to dashboard Cite

Starburst galaxies are galaxies or regions of galaxies undergoing intense periods of star formation. Understanding the heating and cooling mechanisms in these galaxies can give us insight to the driving mechanisms that fuel the starburst. Molecular emission lines play a crucial role in the cooling of the excited gas. With Herschel Spectral and Photometric Imaging Receiver we have been able to observe the rich molecular spectrum towards the central region of NGC 253. Carbon monoxide (CO, J = 4−3 to 13−12) is the brightest molecule in the Herschel wavelength range and together with ground-based low-J observations, the line fluxes trace the excitation of CO. By studying the CO excitation ladder and comparing the intensities to models, we investigate whether the gas is excited by UV radiation, X-rays, cosmic rays, or turbulent heating. Comparing the 12 CO and 13 CO observations to large velocity gradient models and photon-dominated region (PDR) models we find three main interstellar medium (ISM) phases. We estimate the density, temperature, and masses of these ISM phases. By adding 13 CO, HCN, and HNC line intensities, we are able to constrain these degeneracies and determine the heating sources. The first ISM phase responsible for the low-J CO lines is excited by PDRs, but the second and third phases, responsible for the mid to high-J CO transitions, require an additional heating source. We find three possible combinations of models that can reproduce our observed molecular emission. Although we cannot determine which of these is preferable, we can conclude that mechanical heating is necessary to reproduce the observed molecular emission and cosmic ray heating is a negligible heating source. We then estimate the mass of each ISM phase; 6 × 10 7 M for phase 1 (low-J CO lines), 3 × 10 7 M for phase 2 (mid-J CO lines), and 9 × 10 6 M for phase 3 (high-J CO lines) for a total system mass of 1 × 10 8 M .

show abstract

Section: Pdr Analysissupporting

confidence: 89%

Section: Excitation Mechanismsmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Radiative and mechanical feedback into the molecular gas of NGC 253

Rosenberg

Kazandjian

Werf

et al. 2014

A&A

View full text Add to dashboard Cite

show abstract

“…Such a large H abundance will cause noticeable 21 cm signals, which have indeed been seen in H absorption surveys toward some GC clouds (e.g., Schwarz et al 1977;Lang et al 2010). For comparison, Bradford et al (2003) estimate that a high supernova rate in the nucleus of NGC 253 results in a cosmic-ray ionization rate of 1.5−5.3 × 10 −14 s −1 . This mechanism may also play an important role in regulating the gas in ultraluminous infrared galaxies (ULIRGs) where the cosmic ray energy density may be as high as 1000 times that of the local Galactic value or even higher (Papadopoulos 2010;Papadopoulos et al 2011).…”

Section: Cosmic-ray Heatingmentioning

confidence: 99%

The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating

Henkel

Menten

et al. 2013

A&A

146

226

View full text Add to dashboard Cite

We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J K A Kc = 3 03 → 2 02 , 3 22 → 2 21 , and 3 21 → 2 20 transitions of para-H 2 CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40 × 8 (∼100 × 20 pc 2 ) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H 2 CO (3 03 → 2 02 ) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H 2 CO is 0.5−1.2 × 10 −9 , which is consistent with results from lower frequency H 2 CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50 K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65 ± 10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and/or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).

show abstract

“…This is appropriate for a zero order simulation of the physical conditions of the complex. The input parameters are taken as follows: the column density obtained from the mass and size of the complex, N(H 2 ) = (0.5-1.0)×10 22 cm −2 ; the CO abundance from Bradford et al (2003), [CO/H 2 ] = 8 × 10 −5 ; the abundance ratio [ 12 CO/ 13 CO] = 40-100 (Wilson & Rood 1994); and the line ratios from the data, 12 CO(2-1)/(1-0) = 0.6-0.7, 12 CO/ 13 CO = 7-13, 12 CO(3-2)/(1-0) = 0.11-0.26. Then, the LVG model gives temperatures in the range of 10-30 K, densities in the range of 200-700 cm −3 , area filling factors of the order of f a ∼ 0.02 and a velocity gradient of ∼10 km s −1 pc −1 .…”

Section: Physical Conditionsmentioning

confidence: 99%

Properties and environment of the molecular complex near Holmberg IX

Boone¹,

Brouillet

Huettemeister³

et al. 2004

A&A

View full text Add to dashboard Cite

Abstract. This paper is aimed at providing new insight into the nature and origin of the molecular complex situated near the line of sight toward Holmberg IX in the M 81 group of galaxies. The first high resolution CO maps of the complex as well as single dish 13 CO(1-0), 12 CO(3-2) and millimeter continuum observations and the results of a survey of 12 CO in the region are presented. These data together with the available HI, optical and X-ray observations are analyzed to study the properties and environment of the complex. We confirm there is no unobscured massive star formation inside the complex, and from the millimeter constraint on the extinction it must have a low star formation rate or be forming only low mass stars. According to the CO line ratios the abundances and physical conditions could be similar to that of cold gas in spirals. We find from its dynamics (no rotation) and its mass (2-6 million solar masses) that it resembles a massive GMC. Also, re-inspecting N-body simulations of the M 81 group and the H  data we find that it might be located inside the extreme outer disk of M 81 and be cospatial with the H  feature known as Concentration . The negative result of the CO survey suggests that the complex is unique in this region and calls for a peculiar local formation process. We find that the distribution of the CO emission in the data cube is asymmetrical in a way similar to a cometary object. The optical observations of the nearby supershell MH9/10 suggest the existence of an outflow toward the complex. We consider the possibility that the molecular complex is related to this hypothetical outflow.

show abstract

CO (J = 7→6) Observations of NGC 253: Cosmic‐Ray–heated Warm Molecular Gas

Cited by 126 publications

References 46 publications

Radiative and mechanical feedback into the molecular gas of NGC 253

Radiative and mechanical feedback into the molecular gas of NGC 253

The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating

Properties and environment of the molecular complex near Holmberg IX

Contact Info

Product

Resources

About