A Photodissociation Region study of NGC 4038

Abstract

We present a model of the photodissociation regions of NGC 4038, which is part of the Antennae galaxies. We have considered one-dimensional slabs of uniform density all having a maximum $A_V=10\mathrm{mag}$, interacting with plane-parallel radiation. The density range in our simulations spans four orders of magnitude ($100\le n\le 10^6{\mathrm{cm}}^{-3}$) and the UV field strength spans more than three orders of magnitude ($10\le \chi \le 10^{4.5}$ multiples of the $\mathrm{Draine}$ field), from which we generated a grid of about 1400 simulations. We compare our results with Herschel SPIRE-FTS, CSO and ISO-LWS observations of eight CO transition lines ($J=1-0$ to $8-7$) and the [CI] 609μm and [OI] 146μm fine structure lines. We find that the molecular and atomic emission lines trace different gas components of NGC 4038, thus single emission models are insufficient to reproduce the observed values. In general, low-$J$ CO transition lines correspond to either low density regions interacting with low UV field strengths, or high density regions interacting with high UV field strengths. Higher $J$ CO transition lines are less dependent on the UV field strength and are fitted by gas with density $n\sim 10^{4.5}-10^{5.2}{\mathrm{cm}}^{-3}$. We find that the observed fine structure line ratio of [CI] 609μm/[OI] 146μm is reproduced by clouds subject to weaker UV fields compared to the CO lines. We make estimates of the $X_{\mathrm{CO}}$ factor which relates the CO emission with the column density of molecular hydrogen, and find that it is less than the canonical Milky Way value.

arXiv comment12 pages, 6 figures, 3 tables, to appear in MNRAS

References in corpus (45)

• The chemical composition of the Sun
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• The Global Schmidt Law in Star Forming Galaxies
• Starburst99: Synthesis Models for Galaxies with Active Star Formation
• The CO-to-H2 Conversion Factor
• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• The UMIST database for astrochemistry 2012
• Far Infrared and Submillimeter Emission from Galactic and Extragalactic Photo-Dissociation Regions
• The Luminosity Function of Young Star Clusters In "The Antennae" Galaxies (NGC 4038/4039)
• Optimization of Starburst99 for Intermediate-Age and Old Stellar Populations
• A PDR-Code Comparison Study
• Mocassin: A fully three-dimensional Monte Carlo photoionization code
• Molecular hydrogen formation in the interstellar medium
• The CI lines as tracers of molecular gas, and their prospects at high redshifts
• The dusty MOCASSIN: fully self-consistent 3D photoionisation and dust radiative transfer models
• The Chemistry of Interstellar OH+, H2O+, and H3O+: Inferring the Cosmic Ray Ionization Rates from Observations of Molecular Ions
• High-Resolution Imaging of Molecular Gas and Dust in the Antennae (NGC 4038/39): Super Giant Molecular Complexes
• Molecular line intensities as measures of cloud masses - I. Sensitivity of CO emissions to physical parameter variations
• 3D-PDR: A new three-dimensional astrochemistry code for treating Photodissociation Regions
• A New Distance to The Antennae Galaxies (NGC 4038/39) Based on the Type Ia Supernova 2007sr
• The Mass Function of Super Giant Molecular Complexes and Implications for Forming Young Massive Star Clusters in the Antennae (NGC 4038/39)
• Atomic Carbon in Galaxies
• Chemistry in Cosmic-Ray Dominated Regions (CRDRs)
• Molecular Gas and the Modest Star Formation Efficiency in the ``Antennae'' Galaxies: Arp~244=NGC 4038/39
• Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field
• An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\mathrm{CI}}$-Factor"
• CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469
• One moment in time - modeling star formation in the Antennae
• A survey of submillimeter C and CO lines in nearby galaxies
• Infrared Spectroscopy of a Massive Obscured Star Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC
• CI and CO in nearby galaxy centers. The star-burst galaxies NGC 278, NGC 660, NGC 3628, NGC 4631, and NGC 4666
• Molecular tracers of PDR-dominated galaxies
• Spitzer-IRS Study of the Antennae Galaxies NGC 4038/39
• Molecular line intensities as measures of cloud masses - II. Conversion factors for specific galaxy types
• A new red giant-based distance modulus of 13.3 Mpc to the Antennae galaxies and its consequences
• Tracing the sites of obscured star formation in the Antennae galaxies with Herschel-PACS
• Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds
• [CI] and CO in the center of M 51
• Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas
• CII Emission From NGC 4038/39 (The Antennae)
• ALMA CO and VLT/SINFONI H2 observations of the Antennae overlap region: mass and energy dissipation
• The interstellar medium of the Antennae Galaxies
• Chemical enrichment of the complex hot ISM of the Antennae Galaxies: II. Physical properties of the hot gas and supernova feedback
• Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations

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