DENSE MOLECULAR GAS EXCITATION AT HIGH REDSHIFT: DETECTION OF HCO{sup +}(J = 4 {yields} 3) EMISSION IN THE CLOVERLEAF QUASAR

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/726/1/50· OSTI ID:21567701

Riechers, Dominik A ^[1]; Walter, Fabian ^[2]; Carilli, Christopher L ^[3]; Cox, Pierre ^[4]; Weiss, Axel; Menten, Karl M ^[5]; Bertoldi, Frank ^[6]

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1. Astronomy Department, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
2. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
3. National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
4. Institut de RadioAstronomie Millimetrique, 300 Rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Heres (France)
5. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, Bonn (Germany)
6. Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, Bonn (Germany)

We report the detection of HCO{sup +}(J = 4 {yields} 3) emission in the Cloverleaf Quasar at z = 2.56, using the IRAM Plateau de Bure Interferometer. HCO{sup +} emission is a star formation indicator similar to HCN, tracing dense molecular hydrogen gas (n(H{sub 2}) {approx_equal} 10{sup 5} cm{sup -3}) within star-forming molecular clouds. We derive a lensing-corrected HCO{sup +}(J = 4 {yields} 3) line luminosity of L'{sub HCO}{sup +}{sub (4-3)} = (1.6 {+-} 0.3) x 10{sup 9}, ({mu}{sub L}/11){sup -1} K km s{sup -1} pc{sup 2}, which corresponds to only 48% of the HCO{sup +}(J = 1 {yields} 0) luminosity, and {approx}<4% of the CO(J = 3 {yields} 2) luminosity. The HCO{sup +} excitation thus is clearly subthermal in the J = 4 {yields} 3 transition. Modeling of the HCO{sup +} line radiative transfer suggests that the HCO{sup +} emission emerges from a region with physical properties comparable to that exhibiting the CO line emission, but 2x higher gas density. This suggests that both HCO{sup +} and CO lines trace the warm, dense molecular gas where star formation actively takes place. The HCO{sup +} lines have only {approx}2/3 the width of the CO lines, which may suggest that the densest gas is more spatially concentrated. In contrast to the z = 3.91 quasar APM 08279+5255, the dense gas excitation in the Cloverleaf is consistent with being purely collisional, rather than being enhanced by radiative processes. Thus, the physical properties of the dense gas component in the Cloverleaf are consistent with those in the nuclei of nearby starburst galaxies. This suggests that the conditions in the dense, star-forming gas in active galactic nucleus-starburst systems at early cosmic times like the Cloverleaf are primarily affected by the starburst itself, rather than the central active black hole.

• OSTI ID: 21567701
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 726; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CLOUDS
COSMIC RADIO SOURCES
DENSITY
DETECTION
ELEMENTS
EMISSION
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EVOLUTION
EXCITATION
GALAXIES
HEAT TRANSFER
HYDROGEN
LUMINOSITY
NONMETALS
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
QUASARS
RADIANT HEAT TRANSFER
RED SHIFT
STAR EVOLUTION