First Detection of 12CO (1--0) Emission from Two Narrow-Line Seyfert 1 Galaxies
About
In order to investigate how the growth of galactic bulges progresses with the growth of central black holes (BHs), we observed molecular gas (fuel for the coming star formation) in possibly young active galaxies, narrow-line Seyfert 1 galaxies (NLS1s). We present the results of radio observations of 12CO(1--0) using the Nobeyama Millimeter Array (with 2--4 kpc spatial resolution) for two FIR-bright NLS1s, yielding the first detection of their CO emission. Corresponding molecular--gas masses M(H2) of (1-3) X 109 Msun are the 2nd and 4th largest ones among NLS1s. By estimating dynamical masses and bulge masses M(bulge) for these two NLS1s using CO channel map and CO line widths, we found M(H2) amount to 0.13--0.35 of these masses. Taking account the star formation efficiency (~ 0.1), the increase in M(bulge) in those NLS1s in the near future (~< 10^{7.5} yr) is expected not to be a huge fraction (1--5% of the preexisting stars). Bulge growth may have finished before BH growth, or bulge--BH coevolution may proceed with many, occasional discrete events, where one coevolution event produces only a small amount of mass growth of BHs and of bulges. We also discuss the ratios of star-formation rate--to--gas accretion rate onto BHs, finding that two NLS1s have very small ratios (~ 1) compared with the M(bulge)/M(BH) ratios found in active and inactive galaxies (~ 700). This huge difference suggests either the non-overlapped coevolution, long star formation duration or temporarily high accretion rate during NLS1 phase.
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