HCN Survey of Normal Spiral, Infrared-luminous, and Ultraluminous Galaxies

By Yu Gao, P. Solomon. 2003

387 citations recorded by the source corpus.

We report systematic HCN J = 1-0 (and CO) observations of a sample of 53 infrared (IR) and/or CO-bright and/or luminous galaxies, including seven ultraluminous infrared galaxies, nearly 20 luminous infrared galaxies, and more than a dozen of the nearest normal spiral galaxies. This is the largest and most sensitive HCN survey of galaxies to date. All galaxies observed so far follow the tight correlation between the IR luminosity LIR and the HCN luminosity LHCN initially proposed by Solomon, Downes, & Radford, which is detailed in a companion paper. We also address here the issue of HCN excitation. There is no particularly strong correlation between LHCN and the 12 μm luminosity; in fact, of all the four IRAS bands, the 12 μm luminosity has the weakest correlation with the HCN luminosity. There is also no evidence of stronger HCN emission or a higher ratio of HCN and CO luminosities LHCN/LCO for galaxies with excess 12 μm emission. This result implies that mid-IR radiative pumping, or populating, of the J = 1 level of HCN by a mid-IR vibrational transition is not important compared with the collisional excitation by dense molecular hydrogen. Furthermore, large velocity gradient calculations justify the use of HCN J = 1-0 emission as a tracer of high-density molecular gas (≳3 × 104/τ cm-3) and give an estimate of the mass of dense molecular gas from HCN observations. Therefore, LHCN may be used as a measure of the total mass of dense molecular gas, and the luminosity ratio LHCN/LCO may indicate the fraction of molecular gas that is dense.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/adb16e12559b1adbc5b26411cfd086379993471e

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In Astronomy and Astrophysics

1. Mark R. Krumholz
2. D. Narayanan
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In Spectroscopy

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Citations in the corpus

• THE PROPERTIES OF MASSIVE, DENSE CLUMPS: MAPPING SURVEYS OF HCN AND CS (2010, methodology): “Recent work (Gao & Solomon 2004a,b) shows that the luminosity of HCN 1-0 has a tight and linear correlation with infrared luminosity, for both nearby normal galaxies and distant starburst galaxies, suggesting that star formation efficiency may be constant in these different systems when measured…”
• THE EVOLVING INTERSTELLAR MEDIUM OF STAR-FORMING GALAXIES SINCE z = 2 AS PROBED BY THEIR INFRARED SPECTRAL ENERGY DISTRIBUTIONS (2012, background): “However, LIR, and subsequently SFR, is known to strongly correlate with the HCN luminosity, which is a measure of dense gas (H2 volume densities >104 cm−3), for spirals, local (U)LIRGs and QSOs, with an almost linear relation (Gao & Solomon 2004; Juneau et al. 2009).”
• Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines (2011, background): “The ratio ofL′HCN/L ′ CO in the Gao & Solomon (2004) sample, however, is in the range 0.03 - 0.18, which is very similar to what we find in the CMZ (0.095).”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…star formation using HCN, HCO+, higher rotational transitions CO, and other molecules that have critical densities ranging from nH2 ∼ 104 − 108 cm−3 (Gao & Solomon 2004a,b; Narayanan et al. 2005; Graciá-Carpio et al. 2006; Gao et al. 2007; Bussmann et al. 2008; Baan et al. 2008; Juneau et al.…”
• Tracing the molecular gas in distant submillimetre galaxies via CO(1-0) imaging with the EVLA (2010, methodology): “…the natal sites of the OB stars (where the Eddington limit is set), which explains why the HCN-bright gas phase yields higher values of SFE in ULIRGs, closer to the maximum value than those associated with the CO-bright gas phase (e.g. Gao & Solomon 2004). mCQ/SF and Mbest are listed in Table 3.”
• THE INTERSTELLAR MEDIUM IN DISTANT STAR-FORMING GALAXIES: TURBULENT PRESSURE, FRAGMENTATION, AND CLOUD SCALING RELATIONS IN A DENSE GAS DISK AT z = 2.3 (2011, background): “…be noted that the molecular gas in compact starbursts (e.g. ULIRGs – perhaps the closest analogues to SMMJ2135) may be very different from that found in the disk of the Milky Way, with a much larger – perhaps dominant – gas-mass fraction at densities of n(H2) & 10 5 cm−3 (e.g. Gao & Solomon 2004).”
• STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS (2011, background): “Among the more interesting investigations of the extragalactic scaling laws for star formation was that of Gao and Solomon (2004) who used molecular-line emission from HCN, rather than CO, to trace the molecular gas.”
• A Multi-Transition HCN and HCO+ Study of 12 Nearby Active Galaxies: Active Galactic Nucleus versus Starburst Environments (2007, background): “This conversion factor is ∼2 times smaller than that derived for ULIRGs by Solomon, Downes & Radford (1992) and Greve et al. (2007) of X(HCN)=20+30 −10 M⊙ (K km s −1 pc2)−1 but agrees with that favored by Gao & Solomon (2004a) for their sample of nearby active galaxies and ULIRGs.”
• IMAGING THE MOLECULAR GAS IN A SUBMILLIMETER GALAXY AT z = 4.05: COLD MODE ACCRETION OR A MAJOR MERGER? (2010, background): “Gao & Solomon 2004; Solomon & Vanden Bout 2005; Carilli et al. 2002; Wang et al. 2009; Daddi et al. 2010b).”
• Cool Gas in High-Redshift Galaxies (2013, background): “We note that a linear relation between L′HCN(1−0) and LFIR has been found for local galaxies , including spirals and ULIRGs (Gao & Solomon 2004a, 2004b), unlike the non-linear relationship between L′CO(1−0) and LFIR.”
• OBSERVATIONS OF Arp 220 USING HERSCHEL-SPIRE: AN UNPRECEDENTED VIEW OF THE MOLECULAR GAS IN AN EXTREME STAR FORMATION ENVIRONMENT (2011, background): “HCN can be a very good tracer of dense molecular gas (Gao & Solomon 2004): its rotational transitions have critical densities 100 – 1000 times higher than CO.”
• Ionized gas outflows and global kinematics of low-z luminous star-forming galaxies (2014, background): “…from about 50% in z∼ 1-2 star-forming galaxies (Tacconi et al. 2010), to 24% and 15% for ULIRGs in the 0.6-1.0 and 0.2-0.4 redshift ranges, respectively (Combes et al. 2013), and 5% to 7% (low-z U/LIRGs; Gao & Solomon 2004; Chung et al. 2009), a lower threshold would be expected 23 at low-z.”
• Luminous Infrared Galaxies with the Submillimeter Array. I. Survey Overview and the Central Gas to Dust Ratio (2008, methodology): “Does the central gas surface density correlate with LFIR/MH2?”
• THE MOLECULAR GAS IN LUMINOUS INFRARED GALAXIES. II. EXTREME PHYSICAL CONDITIONS AND THEIR EFFECTS ON THE Xco FACTOR (2012, methodology): “For such high XHCN values and L ′ HCN,1−0/L ′ co,1−0=1/4-1/6 observed in ULIRGs (e.g. Solomon et al. 1992; Gao & Solomon 2004; Gracia-Burillo et al. 2012) it is easy to show that X (2−ph) co (Equation 10) will yield near-Galactic or higher values in such systems.”
• CO excitation of normal star forming galaxies out to $z=1.5$ as regulated by the properties of their interstellar medium (2014, background): “If this is the case, then CO[5-4] could be used as a more efficient/accessible tracer of the dense gas than standard molecules like HCN or HCO which also scale basically linearly with LIR but are intrinsically 10–20 times fainter and harder to observe (Gao & Solomon 2004ab; Gao et al 2007)5.”
• GeV OBSERVATIONS OF STAR-FORMING GALAXIES WITH THE FERMI LARGE AREA TELESCOPE (2012, methodology): “In order to select a sample of galaxies with unambiguous ongoing star formation, we base our sample of galaxies on the HCN survey of Gao & Solomon (2004a).”
• Star-formation laws in luminous infrared galaxies. New observational constraints on models (2011, methodology): “4, does not apply to mergers either (Gao & Solomon 2004a; Graciá-Carpio et al. 2008).”
• DIFFERENT STAR FORMATION LAWS FOR DISKS VERSUS STARBURSTS AT LOW AND HIGH REDSHIFTS (2010, background): “This is consistent with the existence of a unique and approximately linear correlation betweenLIR and HCN luminosity for spirals and local (U)LIRGs (Gao & Solomon 2004; Juneau et al. 2009) and QSOs (with the exception of the highest redshift objects; Riechers et al. 2007; Gao et al. 2007).”