Article

Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. III. Emission Line Diagnostics of Ensembles of Evolving H II Regions

The Astrophysical Journal Supplement Series (Impact Factor: 16.24). 12/2008; 167(2):177. DOI: 10.1086/508261
Source: arXiv

ABSTRACT We build, as far as theory will permit, self-consistent model H II regions around central clusters of aging stars. These produce strong emission line diagnostics applicable to either individual H II regions in galaxies or to the integrated emission line spectra of disk or starburst galaxies. The models assume that the expansion and internal pressure of individual H II regions is driven by the net input of mechanical energy from the central cluster, be it through winds or supernova events. This eliminates the ionization parameter as a free variable, replacing it with a parameter that depends on the ratio of the cluster mass to the pressure in the surrounding interstellar medium. These models explain why H II regions with low abundances have high excitation and demonstrate that at least part of the warm ionized medium is the result of overlapping faint, old, large, and low-pressure H II regions. We present line ratios (at both optical and IR wavelengths) that provide reliable abundance diagnostics for both single H II regions or for integrated galaxy spectra, and we find a number that can be used to estimate the mean age of the cluster stars exciting individual H II regions.

0 Bookmarks
 · 
108 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The abundance determinations in extragalactic HII regions are reviewed. The discussion is mainly focused on the different variants of the strong line method (calibrations). However, we do not list and consider in details a numerous relations suggested to convert metallicity-sensitive emission-line combinations into metallicity or temperature estimates. Instead we analyse the foundations of different types of calibrations and problems which those calibrations encounter. The empirical (defined by the HII regions with well-measured abundances) and theoretical or model (defined by the set of photoionization models of HII regions) metallicity scales are discussed.
    Advances in Astronomy and Space Physics. 08/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Blue compact dwarf galaxies (BCDGs) are dwarfs undergoing current burst of star formation (SF). In our work, we determine the ages of the underlying old stellar population to be ˜4 Gyr that is dominating the mass of the galaxy, underlying the current burst of SF. An intermediate population of ˜500 Myr which dominates the stellar light from the galaxy is also detected. The burst of SF at the present epoch spans ˜10 Myr as estimated from various age estimators like Hα, diagnostic diagrams and colour-colour diagrams. BCDGs undergo a burst of SF for a longer duration (of about a few 100 Myr to a Gyr) followed by a short/long quiescence. The amount of column density of localized neutral hydrogen required for the current burst to occur seems to be 10^{21} cm^{-2}. This could be the threshold required for SF. Radio continuum emission reveals that the emission is coincident with the star forming regions. The star formation rates (SFR) estimated from Hα match well with the SFR estimated using non-thermal radio emission for individual star forming regions, but are ˜6-7 times less as compared to the SFR calculated from far-IR (FIR) emission.
    01/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Based on high-resolution, spatially resolved data of 10 z ~ 2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGNs), shocks, and photoionization. We explore how these spatially resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the "composite" region of the z ~ 0 [N II]/Hα versus [O III]/Hβ diagnostic (BPT) diagram, between star-forming galaxies and those with AGNs. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from an enhanced ionization parameter as compared with H II regions in normal, local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [O III]/Hβ versus stellar mass plane, does not properly separate z ~ 2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z ~ 2 mass-metallicity relation (i.e., to the mass they would have at z ~ 0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [N II]/Hα are more biased by shocks and AGNs at high-z than the [O III]/Hβ/[N II]/Hα calibration. Based on observations at the Very Large Telescope (VLT) of the European Southern Observatory (ESO), Paranal, Chile (ESO program IDs 073.B-9018, 076.A-0527, 079.A-0341, 080.A-0330, 080.A-0339, 080.A-0635, 083.A-0781,084.A-0853, 087.A-0081, 091.A.-0126) and at the Large Binocular Telescope (LBT) on Mt. Graham in Arizona.
    The Astrophysical Journal 01/2014; 781(1):21-. · 6.73 Impact Factor

Full-text (2 Sources)

Download
31 Downloads
Available from
Jun 5, 2014

Similar Publications