Other
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011acasn..52...86a&link_type=abstract
Acta Astronomica Sinica, vol. 52, no. 1, p.86-88
Other
Galaxies: Formation, Galaxies: Ism, Ism: Molecules, Infrared: Galaxies
Scientific paper
To study the physical properties of the molecular gas in luminous infrared galaxies (LIRGs), this thesis presents the preliminary results of a small local sample, a case study on a distant LIRG IRAS F10214+4724 at z=2.286 and another case study on a local LIRG ARP 302. The molecular gas in Perseus A, the cD galaxy in the center of the Perseus Cluster, is presented in high angular resolution observation to study the gas distribution and its kinematics. A small sample of 5 LIRGs was observed and the CO (J=3→2) mapping results reveal the gas distribution concentrated in the galactic centers or the centers of mergers and their overlapping regions. For NGC 3256, the maps in the CO (J=3→2), CO (J=4→3) and CO (J=7→6) transitions are obtained. Together with the measurements in the lower transitions from literatures, the peak of the spectral energy distribution (SED) of CO line was found between CO (J=5→4) and CO (J=6→5). With the radiation transfer model and the CO ladder, the gas density is constrained to n(H2)=103.7~104.1 cm-3 for a kinematic temperature T kin=40~45 K adopted from the literature. Local LIRG NGC 3256 shows the similar excitation conditions as the submillimeter galaxies (SMGs) in the early universe, further supporting the view that the SMGs are the same type of the local LIRGs, but only at the early epoch. The CI (3P2→3P1), CO (J=3→2), CO (J=4→3), CO (J=6→5) and CO (J=7→6) transitions as well as the dust continuum at 3 mm and 1 mm were detected towards the distant LIRG IRAS F10214+4724 at z=2.286. IRAS F10214+4724 now belongs to a sample of only 3 extragalactic sources at any redshift where both of the carbon fine structure lines have been detected. The source is spatially resolved by our CI (3P2→3P1) observation and we detect a velocity gradient along the east-west direction. The CI line ratio allows us to derive a carbon excitation temperature of 42+12-9 K. The carbon excitation in conjunction with the CO ladder and the dust continuum constrains the gas density to n(H2)=103.6~104.0 cm-3 and the kinematic temperature to Tkin=45~80 K, similar to the excitation conditions found in nearby starburst galaxies. The rest-frame 360 μm dust continuum morphology is more compact than the line emitting region. This supports previous findings that the far infrared (FIR) luminosity arises from regions closer to the AGN. High angular resolution observation in CO (J=2→1) was carried out towards ARP 302N, the northern galaxy of the early merging system ARP 302, revealing the extended spatial distribution of the molecular gas in ARP 302N. The molecular gas was shown as a very asymmetric distribution with two strong concentrations on both sides of the center together with a weaker one offset by about 8 kpc to the north. The molecular gas distribution is also found to be consistent with that from the hot dust as traced by the 24 μm continuum emission observed by Spitzer. For an observed line ratio of CO (J=2→1/1→0), excitation analysis suggests that the gas density is low, less than 103 cm-3, over the entire galaxy. By fitting the SED of ARP 302N in the FIR band, we obtain a dust temperature of Td=26~36 K and a dust mass of M dust=2.0~3.6×10^8 M&sun;. The good spatial correspondence among the 3.6 cm radio continuum emission, the Spitzer 8 & 24μm data and the high resolution CO (J=2→1) observation from the SMA (submillimeter array) shows that there are asymmetrical star forming activities in ARP 302N. The molecular gas in Perseus A (Per A) has been imaged in CO (J=2→1) at a spatial resolution of ~1 kpc over a central region of radius ~10 kpc. Per A is known to contain ~1.3×10^10 M&sun; of molecular gas, which has been proposed to be captured from mergers or ram-pressure stripping of gas-rich galaxies, or accreted from an X-ray cooling flow. For the first time, the molecular gas detected in our images can be seen to be concentrated in three radial filaments with lengths ranging from 1.1 kpc to 2.4 kpc. These all lie in the east-west directions, spanning from the center of the galaxy to radii of ~8 kpc. The eastern and outer western filaments exhibit larger blueshifted velocities with decreasing radii, while the inner western filament spans the systemic velocity of the galaxy. The molecular gas shows no signature of orbital motion, and therefore is unlikely to have been captured from gas-rich galaxies. Instead, we are able to reproduce the observed kinematics of the two outer filaments as free-fall in the gravitational potential of Per A, suggesting that they originate from an X-ray cooling flow. Indeed, all three filaments lie between two prominent X-ray cavities carved out by radio jets from Per A, suggesting that they are located in a relatively undisturbed region where a cooling flow is able to operate. The inferred mass-deposition rate into the two outer filaments alone is roughly 76 M&sun;·yr-1. This cooling flow can provide a nearly continuous supply of molecular gas to fuel the active nucleus in Per A.
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