Warm, Dense Molecular Gas in the ISM of Starbursts, LIRGs, and ULIRGs

Narayanan, Desika; Groppi, Christopher; Kulesa, Craig; Walker, Christopher K.

doi:10.1086/431171

Cited by 63 publications

(95 citation statements)

References 57 publications

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“…These authors found a tight linear relationship between L IR and L HCN , suggesting that the star formation rate in galaxies is controlled by dense gas traced by HCN with effective density n > n eff ≈ 3 × 10 4 cm −3 . This result was supported by observations of CO (J=3-2) from nearby disks, LIRGs and ULIRGs that all found a roughly linear FIR-L COJ=3−2 relationship (Yao et al, 2003;Narayanan et al, 2005;Iono et al, 2009;Mao et al, 2010).…”

Section: Physics Learned From the Milky Way And Local Galaxiessupporting

confidence: 65%

Dusty star-forming galaxies at high redshift

2014

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Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10 13 L with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars. When summed up, all of the dusty, star-forming galaxies in the Universe produce an infrared radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at ultraviolet and optical wavelengths. The bulk of this infrared extragalactic background light emanates from galaxies as diverse as gas-rich disks to mergers of intense starbursting galaxies. Major advances in far-infrared instrumentation in recent years, both spacebased and ground-based, has led to the detection of nearly a million DSFGs, yet our understanding of the underlying astrophysics that govern the start and end of the dusty starburst phase is still in nascent stage. This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the bestunderstood subset (submillimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain et al. 2002), but also the selection and characterization of more recently discovered DSFG populations. We review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.

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Section: Physics Learned From the Milky Way And Local Galaxiessupporting

confidence: 65%

Dusty star-forming galaxies at high redshift

2014

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“…The results of Graciá-Carpio et al (2011) provide additional support for the existence of different properties of the interstellar medium in normal star-forming galaxies and extreme starburst systems. Krumholz & Thompson (2007; see also Narayanan et al 2008) studied how the power index of KS laws determined from observations should change depending on the critical density of the tracer used to probe the star-forming gas, a prediction confirmed by observations conducted in several dense gas tracers (Narayanan et al 2005;Bussmann et al 2008;Bayet et al 2009;Juneau et al 2009). In the particular case of HCN(1-0), only in galaxies where the average gas density exceeds a few 10 4 cm −3 (i.e., the effective critical density of the HCN J = 1-0 line), we would start to recover the expected superlinear behavior of the universal KS law derived by Krumholz & McKee (2005).…”

Section: Introductionmentioning

confidence: 90%

Star-formation laws in luminous infrared galaxies

García‐Burillo

Usero

Alonso‐Herrero

et al. 2012

A&A

167

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Context. The observational study of star-formation relations in galaxies is central for unraveling the related physical processes that are at work on local and global scales. It is still debated whether star formation can be described by a universal law that remains valid in different populations of galaxies. Aims. We aim to expand the sample of extreme starbursts, represented by local luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs), with high-quality observations in the 1-0 line of HCN, which is taken as a proxy for the dense molecular gas content. The new data presented in this work allow us to enlarge in particular the number of LIRGs studied in HCN by a factor 3 compared to previous works. The chosen LIRG sample has a range of HCN luminosities that partly overlaps with that of the normal galaxy population. We study if a universal law can account for the star-formation relations observed for the dense molecular gas in normal star-forming galaxies and extreme starbursts and explore the validity of different theoretical prescriptions of the star-formation law. Methods. We have used the IRAM 30 m telescope to observe a sample of 19 LIRGs in the 1-0 lines of CO, HCN and HCO + . The galaxies were extracted from a sample of local LIRGs with available high-quality and high-resolution images obtained at optical, near and mid IR wavelengths, which probe the star-formation activity. We therefore derived the star-formation rates using different tracers and determined the sizes of the star-forming regions of all targets. Results. The analysis of the new data proves that the efficiency of star formation in the dense molecular gas (SFE dense ) of extreme starbursts is a factor 3-4 higher compared to normal galaxies. Kennicutt-Schmidt (KS) power laws were also derived. We find a duality in KS laws that is further reinforced if we account for the likely different conversion factor for HCN (α HCN ) in extreme starbursts and for the unobscured star-formation rate in normal galaxies. This result extends the more extreme bimodal behavior of star-formation laws that was derived from CO molecular lines by two recent surveys to the higher molecular densities probed by HCN lines. Conclusions. We compared our observations with the predictions of theoretical models in which the efficiency of star formation is determined by the ratio of a constant star-formation rate per free-fall time (SFR ff ) to the local free-fall time (t ff ). We find that it is possible to fit the observed differences in the SFE dense between normal galaxies and LIRGs/ULIRGs using a common constant SFR ff and a set of physically acceptable HCN densities, but only if SFR ff ∼ 0.005-0.01 and/or if α HCN is a factor of ∼a few lower than our favored values. Star-formation recipes that explicitly depend on the galaxy global dynamical time scales do not significantly improve the fit to the new HCN data presented in this work.

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“…We have used so far the Galactic solar neighborhood value, but there is ample evidence that X CO varies in other galaxies as a function of physical conditions (e.g. Maloney & Black 1988;Israel 1997;Barone et al 2000;Boselli et al 2002;Israel et al 2003;Israel 2005;Bolatto et al 2008;Narayanan et al 2005;Leroy et al 2011;Shetty et al 2011;Narayanan et al 2012;Bell et al 2007). Thus, we consider an alternative conversion factor, which depends on the metallicity, and varies radially following the metallicity gradient along the disk:…”

Section: Radial Profilesmentioning

confidence: 99%

TheHerschelVirgo Cluster Survey

Pappalardo

Bianchi

Corbelli

et al. 2012

A&A

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Aims. We investigate the dust-to-gas mass ratio and the environmental effects on the various components of the interstellar medium for a spatially resolved sample of Virgo spirals. Methods. We have used the IRAM-30 m telescope to map over their full extent NGC 4189, NGC 4298, NGC 4388, and NGC 4299 in the 12 CO(1-0) and the 12 CO(2-1) lines. We observed the same lines in selected regions of NGC 4351, NGC 4294, and NGC 4424. The CO observations are combined with Herschel maps in 5 bands between 100-500 μm from the HeViCS survey, and with HI data from the VIVA survey, to obtain spatially resolved dust and gas distributions. We studied the environmental dependencies by adding to our sample eight galaxies with 12 CO(1-0) maps from the literature. Results. We estimate the integrated mass of molecular hydrogen for the galaxies observed in the CO lines. We find molecular-to-total gas mass fractions between 0.04 ≤ f mol ≤ 0.65, with the lowest values for the dimmest galaxy in the B-band. The integrated dust-togas ratio ranges between 0.011 and 0.004. For the 12 mapped galaxies we derive the radial distributions of the atomic gas, molecular gas, and dust. We also study the effect of different CO-to-H 2 conversion factors. Both the molecular gas and the dust distributions show steeper radial profiles for HI-deficient galaxies and the average dust-to-gas ratio for these galaxies increases or stays radially constant. On scales of ∼3 kpc, we find a strong correlation between the molecular gas and the 250 μm surface brightness that is tighter than average for non-deficient galaxies. The correlation becomes linear if we consider the total gas surface mass density. However, the inclusion of atomic hydrogen does not improve the statistical significance of the correlation. Conclusions. The environment can modify the distributions of molecules and dust within a galaxy, although these components are more tightly bound than the atomic gas.

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Warm, Dense Molecular Gas in the ISM of Starbursts, LIRGs, and ULIRGs

Cited by 63 publications

References 57 publications

Dusty star-forming galaxies at high redshift

Dusty star-forming galaxies at high redshift

Star-formation laws in luminous infrared galaxies

TheHerschelVirgo Cluster Survey

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