333 research outputs found
First CO J=6-5, 4-3 detections in local ULIRGs: the dense gas in Mrk231, and its colling budget
We report on detections of the high-excitation CO J=6-5, J=4-3 lines in
Mrk231, a prototypical Ultra Luminous Infrared Galaxy (ULIRG) and Seyfert 1
QSO. These observations are combined with CO J=3-2, HCN J=4-3 (this work), and
CO J=2-1, J=1-0, 13CO J=2-1, HCN J=1-0 measurements taken from the literature
to provide better constraints on the properties of the molecular gas in an
extreme starburst/QSO in the local Universe. We find that the CO J=4-3 and
J=6-5 transitions trace a different gas phase from that dominating the lower
three CO transitions, with n(H_2) ~ (1-3)x10^4 cm-3 and Tk ~ (40-70) K. This
phase is responsible for the luminous HCN emission, and contains most of the H2
gas mass of this galaxy. The total CO line cooling emanating from this dense
phase is found similar to that of the [CII] line at 158 micron, suggesting a
very different thermal balance to that seen in lower IR-luminosity galaxies,
and one likely dominated by dense photon-dominated regions. Our dense
"sampling" of the CO rotational ladder and the HCN lines enables us to produce
well-constrained Spectral Line Energy Distributions (SLEDs) for the dense
molecular gas in Mrk231 and compare them to those of high redshift starbursts,
many of which have SLEDs that may be affected by strong lensing. Finally, we
use our local molecular line excitation template to assess the capabilities of
future cm and mm/sub-mm arrays in detecting CO and HCN transitions in similar
systems throughout the local and distant universe.Comment: accepted for publication in The Astrophysical Journal; 37 pages,
preprint format; 5 figures (2 in color
The spatial distribution of excited H_2 in T Tau: a molecular outflow in a young binary system
Strong extended emission from molecular hydrogen
in the v = 1 → 0 S(l) transition is mapped around T Tau. In
addition, the v = 2 → 1 S(l) line is detected close to the star. The ratio of the two transitions is consistent with an excitation process in which both fluorescence by stellar ultraviolet radiation and collisions in a warm, dense medium play a role. The morphology is interpreted as emission from a molecular outflow which appears to wiggle as a result of the fact that T Tau is a binary system seen almost pole-on. It is shown that an outflow with a small opening angle can reproduce the observed extended emission. From comparison with previous studies it is argued that the molecular outflow originates from T Tau S, the infrared component. The presented model constrains the orientation and geometry of the system
Warm molecular gas temperature distribution in six local infrared bright Seyfert galaxies
We simultaneously analyze the spectral line energy distributions (SLEDs) of
CO and H2 of six local luminous infrared (IR) Seyfert galaxies. For the CO
SLEDs, we used new Herschel/SPIRE FTS data (from J=4-3 to J=13-12) and
ground-based observations for the lower-J CO transitions. The H2 SLEDs were
constructed using archival mid-IR Spitzer/IRS and near-IR VLT/SINFONI data for
the rotational and ro-vibrational H2 transitions, respectively. In total, the
SLEDs contain 26 transitions with upper level energies between 5 and 15000 K. A
single, constant density, model (n ~ 10 cm) with a
broken power-law temperature distribution reproduces well both the CO and H2
SLEDs. The power-law indices are ~ 1-3 for warm molecular gas (20 K <
T 100 K). We show that
the steeper temperature distribution (higher ) for hot molecular gas can
be explained by shocks and photodissociation region (PDR) models, however, the
exact values are not reproduced by PDR or shock models alone and a
combination of both is needed. We find that the three major mergers among our
targets have shallower temperature distributions for warm molecular gas than
the other three spiral galaxies. This can be explained by a higher relative
contribution of shock excitation, with respect to PDR excitation, for the warm
molecular gas in these mergers. For only one of the mergers, IRASF 05189-2524,
the shallower H2 temperature distribution differs from that of the spiral
galaxies. The presence of a bright active galactic nucleus in this source might
explain the warmer molecular gas observed.Comment: A&A in press; 15 pages, 7 figures. Fixed several typo
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