학술논문
Disentangling the physical parameters of gaseous nebulae and galaxies
Document Type
Working Paper
Author
Source
Subject
Language
Abstract
We present an analysis to disentangle the connection between physical quantities that characterize the conditions of ionized HII regions -- metallicity ($Z$), ionization parameter ($U$), and electron density ($n_\mathrm{e}$) -- and the global stellar mass ($M_\ast$) and specific star formation rate ($\mathrm{sSFR}=\mathrm{SFR}/M_\ast$) of the host galaxies. We construct composite spectra of galaxies at $0.027 \le z \le 0.25$ from Sloan Digital Sky Survey, separating the sample into bins of $M_\ast$ and sSFR, and estimate the nebular conditions from the emission line flux ratios. Specially, metallicity is estimated from the direct method based on the faint auroral lines [OIII]$\lambda$4363 and [OII]$\lambda\lambda$7320,7330. The metallicity estimates cover a wide range from $12+\log\mathrm{O/H}\sim7.6\textrm{--}8.9$. It is found that these three nebular parameters all are tightly correlated with the location in the $M_\ast$--sSFR plane. With simple physically-motivated ans\"atze, we derive scaling relations between these physical quantities by performing multi regression analysis. In particular, we find that $U$ is primarily controlled by sSFR, as $U \propto \mathrm{sSFR}^{0.43}$, but also depends significantly on both $Z$ and $n_\mathrm{e}$. The derived partial dependence of $U \propto Z^{-0.36}$ is weaker than the apparent correlation ($U\propto Z^{-1.52}$). The remaining negative dependence of $U$ on $n_\mathrm{e}$ is found to be $U \propto n_\mathrm{e}^{-0.29}$. The scaling relations we derived are in agreement with predictions from theoretical models and observations of each aspect of the link between these quantities. Our results provide a useful set of equations to predict the nebular conditions and emission-line fluxes of galaxies in semi-analytic models.
Comment: 19 pages, 12 figures, submitted to MNRAS. Comments welcome
Comment: 19 pages, 12 figures, submitted to MNRAS. Comments welcome