arXiv subjects

Dinh-V-Trung

Publications and source records attributed to Dinh-V-Trung.

39 records · Page 3Linked to original sources

arXiv2001

Nature of widely separated ultraluminous infrared galaxies

In the complete sample of ultraluminous infrared galaxies (ULIRGs) compiled by Kim (1995) about 5% consists of widely separated galaxies which are presumably in the early phase of interaction. This fact is contrary to the conventional view that ULIRGs are in the final stages of the merger of two gas-rich disk galaxies. We have undertaken high resolution CO(J=1-0) observations for the ultraluminous infrared galaxies that have nuclear separations larger than 20 kpc. We have detected the CO emission in 5 out of 6 systems, but only in one component of the ULIRG pairs. 4 of them have LINER spectral type and 1 galaxy has Seyfert II spectral type. In K'-band images these components are also brighter than the other components which have either HII-region spectra or no detectable emission lines. Using the standard conversion factor, the molecular gas content is estimated to be a few times 10 $^{10}$ M$_\odot$, similar to that of the other ultraluminous galaxies. The result indicates that the galaxy containing the molecular gas is also the source of most, if not all, of the huge far-infrared luminosity of the system. The optical and K'-band imaging observations and optical spectra suggest multiple merger scenario for 1 system. If the remaining systems are in an early stage of a binary tidal interaction, the commonly accepted interpretation of the ULIRG phenomenon as the final merger stage of two disk galaxies may need to be re-examined.

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arXiv2000

Molecular Gas in the Powerful Radio Galaxies 3C~31 and 3C~264: Major or Minor Mergers?

We report the detection of $^{12}$CO~($1 \to 0$) and $^{12}$CO~($2 \to 1$) emission from the central regions ($\lesssim 5$--$10 {\rm kpc}$) of the two powerful radio galaxies 3C~31 and 3C~264. Their individual CO emission exhibits a double-horned line profile that is characteristic of an inclined rotating disk with a central depression at the rising part of its rotation curve. The inferred disk or ring distributions of the molecular gas is consistent with the observed presence of dust disks or rings detected optically in the cores of both galaxies. For a CO to H$_2$ conversion factor similar to that of our Galaxy, the corresponding total mass in molecular hydrogen gas is $(1.3 \pm 0.2) \times 10^9 {\rm M_{\odot}}$ in 3C~31 and $(0.31 \pm 0.06) \times 10^9 {\rm M_{\odot}}$ in 3C~264. Despite their relatively large molecular-gas masses and other peculiarities, both 3C~31 and 3C~264, as well as many other powerful radio galaxies in the (revised) 3C catalog, are known to lie within the fundamental plane of normal elliptical galaxies. We reason that if their gas originates from the mergers of two gas-rich disk galaxies, as has been invoked to explain the molecular gas in other radio galaxies, then both 3C~31 and 3C~264 must have merged a long time (a few billion years or more) ago but their remnant elliptical galaxies only recently (last tens of millions of years or less) become active in radio. Instead, we argue that the cannibalism of gas-rich galaxies provides a simpler explanation for the origin of molecular gas in the elliptical hosts of radio galaxies. Given the transient nature of their observed disturbances, these galaxies probably become active in radio soon after the accretion event when sufficient molecular gas agglomerates in their nuclei.

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arXiv1997

Search for 183 GHz water maser emission in starburst galaxies

We have searched for water vapor emission at 183 GHz, redshifted at 157 GHz and 161 GHz, in the two ultraluminous starburst galaxies Mrk1014 and VIIZw244. Due to the low energy level of the upper state of the 183 GHz transition (\approx 200K), it is expected that the emission regions are extended, as they are in the Orion or W49N molecular cloud cores. Since the warm and dense gas, typical of star-forming cores, is expected to have a large surface filling factor in ultraluminous starburst galaxies, the maser H_2O emission at 183 GHz could have been detected. In fact, no water line has been detected in Mrk1014 and VIIZw244 with an upper limit of σ= 1 mK. We compare the H_2O/CO emission ratio with that obtained towards the ultraluminous high-z object F10214+4724, which flux is amplified by a gravitationnal lens. We suggest that the amplification factor for the H_2O emitting cores in this galaxy should be higher than for the general CO emitting region. We conclude that the warm and dense H_2O cores are much less extended in the two observed starburst galaxies than in the Orion molecular cloud; this provides some information on the physical conditions and cooling processes of the interstellar medium in starburst galaxies.

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