2008ApJ...676..137K

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)x10⁹ M_☉ are the second and fourth largest among NLS1s. By estimating dynamical masses and bulge masses M_bulge for these two NLS1s using CO channel maps and CO line widths, we found that M(H₂) amounted to 13%-35% of these masses. Taking into account the star formation efficiency (∼0.1), the increase in M_bulge in those NLS1s in the near future (≲10^7.5 yr) is not expected 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 occasionally discrete events, where one coevolution event produces only a small amount of mass growth of BHs and 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_BHratios found in active and inactive galaxies (~700). This huge difference suggests either nonoverlapped coevolution, a long star formation duration, or a temporarily high accretion rate during the NLS1 phase.