We present a study of the origin of infrared (IR) emission in the opticallynormal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features andcontinua in the range of 3600-8000 A from the Slo...We present a study of the origin of infrared (IR) emission in the opticallynormal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features andcontinua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellarpopulations, we derive the stellar properties for the nuclear region of NGC 4418. We compare theobserved infrared luminosity with the one derived from the starburst model, and find thatstar-forming activity contributes only 7% to the total IR emission, that as the IR emission regionis spatially very compact, the most possible source for the greater part of the IR emission is adeeply embedded AGN, though an AGN component is found to be unnecessary for fitting the opticalspectrum.展开更多
We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273. Thepresence of high-order Balmer absorption lines (H8, H9, H10) and weak equivalent widths of CaII Kλ3933, CN λ4200, G-band λ4300 and MgIb λ5...We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273. Thepresence of high-order Balmer absorption lines (H8, H9, H10) and weak equivalent widths of CaII Kλ3933, CN λ4200, G-band λ4300 and MgIb λ5173 clearly indicate recent star-forming activity inthe nuclear region. Using a simple stellar population synthesis model, we find that for the bestfit, the contributions of a power-law featureless continuum, an intermediate-age (～ 10~8 yr) and anold (> 10~9 yr) stellar population to the total light at the reference normalization wavelength are10.0%, 33.4% and 56.6%, respectively. The existence of recent starburst activity is also consistentwith its high far-infrared luminosity (log L_(FIR.)/L☉ = 9.9), its infrared color indexes[α(25,60) = ― 1.81 and α(60,100) = ― 0.79, typical values for Seyfert galaxies withcircumnuclear starburst], and its q-value (2.23, ratio of infrared to radio flux, very similar tothat of normal spirals and starburst galaxies). Byrd et al. have suggested that NGC 2273 might haveinteracted with NGC 2273B in less than 10~9 yr ago, so the starburst activity in this galaxy couldhave been triggered by tidal interaction, as indicated in recent numerical simulations.展开更多
基金the National Natural Science Foundation of China.
文摘We present a study of the origin of infrared (IR) emission in the opticallynormal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features andcontinua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellarpopulations, we derive the stellar properties for the nuclear region of NGC 4418. We compare theobserved infrared luminosity with the one derived from the starburst model, and find thatstar-forming activity contributes only 7% to the total IR emission, that as the IR emission regionis spatially very compact, the most possible source for the greater part of the IR emission is adeeply embedded AGN, though an AGN component is found to be unnecessary for fitting the opticalspectrum.
文摘We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273. Thepresence of high-order Balmer absorption lines (H8, H9, H10) and weak equivalent widths of CaII Kλ3933, CN λ4200, G-band λ4300 and MgIb λ5173 clearly indicate recent star-forming activity inthe nuclear region. Using a simple stellar population synthesis model, we find that for the bestfit, the contributions of a power-law featureless continuum, an intermediate-age (～ 10~8 yr) and anold (> 10~9 yr) stellar population to the total light at the reference normalization wavelength are10.0%, 33.4% and 56.6%, respectively. The existence of recent starburst activity is also consistentwith its high far-infrared luminosity (log L_(FIR.)/L☉ = 9.9), its infrared color indexes[α(25,60) = ― 1.81 and α(60,100) = ― 0.79, typical values for Seyfert galaxies withcircumnuclear starburst], and its q-value (2.23, ratio of infrared to radio flux, very similar tothat of normal spirals and starburst galaxies). Byrd et al. have suggested that NGC 2273 might haveinteracted with NGC 2273B in less than 10~9 yr ago, so the starburst activity in this galaxy couldhave been triggered by tidal interaction, as indicated in recent numerical simulations.
