Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........19g&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF HAWAII, 1995.Source: Dissertation Abstracts International, Volume: 56-10, Section: B, page: 5548.
Other
2
Scientific paper
Luminous infrared galaxies are a significant population of objects in the local universe. To better understand these galaxies, I have analyzed spectra at resolving powers of 340-680 of the 2 μm region for 56 systems with infrared luminosities L_ {IR} > 1.5 times 1011L_odot. The galaxies are divided into two groups: those with 11.2 _sp{~}< log(LIR/L_ &sun;) _sp{ ~}< 12, the "luminous infrared bright galaxies" (LIBGs), and those with log(L IR/L_&sun;) _sp{~} > 12, the "ultraluminous infrared bright galaxies" (ULIBGs). The spectra of most of the LIBGs and ULIBGs show descending continua with strong emission lines from atomic and molecular hydrogen, and absorption from CO in the atmospheres of red supergiants. In the LIBGs, L_{Brgamma } ~ 10^{-5} times LIR,~ilar to levels found in star forming regions. Simple starburst models provide a reasonable match to the properties of the LIBGs. On energetics grounds alone, there seems no reason to require that luminous, obscured active galactic nuclei (AGN) be present in the majority of the LIBGs. The ULIBGs tend to be weaker in Brgamma and 2 μm continuum than can be accounted for by these starburst models. One possibility is that the actual extinctions at 2 μm are higher in these systems than conventional measures indicate. Or, hidden AGN may provide a significant fraction of the bolometric luminosities of the ULIBGs. Although the extinction at 2 mu m is 1/10 that at optical wavelengths, no previously unrecognized Seyfert 1 nuclei were found. If they are present, they are weak or deeply buried. The galaxies with known AGN tend to have more luminous 2 mu m continua, relative to L_{IR }, than the galaxies with no evidence for an AGN, but both samples obey the same correlations between line luminosity and LIR.. The strength of the H_2 v = 1-0 S(1) line is correlated with L_ {IR} in both the LIBGs and ULIBGs. The H_2 seems to be excited by shocks in many cases, although other mechanisms operating at high densities cannot be excluded. What actually powers the H_2 emission remains unknown. Heating of the H_2 gas by shock waves from supernova remnants requires a supernova rate consistent with the starburst models and radio emission, but the simplest versions of this model may fail observational tests.
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