A CANDELS WFC3 GRISM STUDY OF EMISSION-LINE GALAXIES AT<i>z</i>∼ 2: A MIX OF NUCLEAR ACTIVITY AND LOW-METALLICITY STAR FORMATION

Trump, Jonathan R.; Weiner, Benjamin J.; Scarlata, Claudia; Kocevski, Dale D.; Bell, Eric F.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Laird, E. S.; Mozena, Mark; Rangel, C.; Yan, Renbin; Yesuf, Hassen M.; Atek, Hakim; Dickinson, Mark; Donley, J. L.; Dunlop, James; Ferguson, Henry C.; Finkelstein, Steven L.; Grogin, Norman A.; Hathi, N. P.; Juneau, Stéphanie; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Nandra, K.; Newman, Jeffrey A.; Rodney, Steven A.; Straughn, Amber N.; Teplitz, Harry I.

doi:10.1088/0004-637x/743/2/144

Cited by 59 publications

(67 citation statements)

References 65 publications

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“…High redshift star-forming galaxies are systematically offset towards higher [O iii]/Hβ on the BPT diagram relative to the local star-forming galaxy locus (Shapley et al 2005;Erb et al 2006;Liu et al 2008;Brinchmann et al 2008;Hainline et al 2009;Wright et al 2010;Trump et al 2011Kewley et al 2013aSteidel et al 2014). The line ratio shifts of high-redshift star-forming galaxies are similar to DIG.…”

Section: Metallicity Gradients In the Local Universe And At High Redsmentioning

confidence: 88%

SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

Zhang

Yan

Bundy

et al. 2016

Mon. Not. R. Astron. Soc.

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204

157

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Diffuse Ionized Gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by MaNGA, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. The gradients in these line ratios are determined by metallicity gradients and Σ Hα . In line ratio diagnostic diagrams, contamination by DIG moves H ii regions towards composite or LI(N)ER-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H ii region models can only shift line ratios slightly relative to H ii region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favors ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission.DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R 23 , N2=[N ii]/Hα, and N2S2Hα (Dopita et al. 2016) to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself.The strong-line method of Blanc et al. (2015; IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H ii region models which fail to describe the DIG.

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Section: Metallicity Gradients In the Local Universe And At High Redsmentioning

confidence: 88%

SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

Zhang

Yan

Bundy

et al. 2016

Mon. Not. R. Astron. Soc.

Self Cite

204

157

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“…The misclassification of distant Seyferts will be exacerbated by the fact that at higher redshifts, most host galaxies will have much higher SFRs than they do currently, which will produce emission lines that can more easily outshine those of the active nucleus. It may be possible to overcome this problem, and identify the line emission produced by the AGN with spectroscopy at higher spatial resolution, as is possible, for example, with the Hubble Space Telescope (e.g., Atek et al 2010;Trump et al 2011). …”

Section: Discussionmentioning

confidence: 99%

Hα IMAGING OF NEARBY SEYFERT HOST GALAXIES

Theios

Malkan

Ross

2016

ApJ

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We used narrowband (Δλ=70 Å) interference filters with the CCD imaging camera on the Nickel 1.0 m telescope at Lick Observatory to observe 31 nearby (z<0.03) Seyfert galaxies in the 12 μm active galaxy sample. We obtained pure emission-line images of each galaxy, which reach down to a flux limit of 7.3×10 −15 erg cm −2 s −1 arcsec −2 , and corrected these images for [N II] emission and extinction. We separated the Hα emission line of the "nucleus" (central 100-1000 pc) from that of the host galaxy. The extended Hα emission is expected to be powered by newly formed hot stars, and indeed correlates well with other indicators of current star formation rates (SFRs) in these galaxies: extended 7.7 μm polycyclic aromatic hydrocarbon, total farinfrared, and radio luminosity. Relative to what would be expected from recent star formation, there is a 0.8 dex excess of radio emission in our Seyfert galaxies. The Hα luminosity we measured in the centers of our galaxies is dominated by the active galactic nucleus (AGN), and is linearly correlated with the hard X-ray luminosity. There is, however, an upward offset of 1 dex in this correlation for the Seyfert 1s, because their nuclear Hα emission includes a strong additional contribution from the broad-line region. We found a correlation between SFR and AGN luminosity. In spite of selection effects, we concluded that the absence of bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly significant. Finally, we used our measured spatial distributions of Hα emission to determine what these Seyfert galaxies would look like when observed through fixed apertures (e.g., a spectroscopic fiber) at high redshifts. We found that although all of these Seyfert galaxies would be detectable emission-line galaxies at any redshift, most of them would appear to be dominated by (>67%) their HII region emission. Only the most luminous AGNs (log(L Hα /erg s −1 )>41.5) would still be identified as such at z∼0.3.

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“…To verify the reliability of using the broadband flux excesses to derive emission-line strengths, we examine the SEDs of a moderate-redshift sample of nebular line emitters with spectroscopically measured [O iii] line fluxes from WFC3 grism observations of the Hubble Ultra Deep Field (UDF; Trump et al 2011). We choose this sample rather than larger ground-based samples because use of two-dimensional grism spectroscopy avoids uncertainties owing to slit losses.…”

Section: Nebular Line Strengthsmentioning

confidence: 99%

KECK SPECTROSCOPY OF 3 <z< 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY

Stark

Schenker

Ellis

et al. 2013

ApJ

463

110

619

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The physical properties inferred from the spectral energy distributions (SEDs) of z > 3 galaxies have been influential in shaping our understanding of early galaxy formation and the role galaxies may play in cosmic reionization. Of particular importance is the stellar mass density at early times, which represents the integral of earlier star formation. An important puzzle arising from the measurements so far reported is that the specific star formation rates (sSFRs) evolve far less rapidly than expected in most theoretical models. Yet the observations underpinning these results remain very uncertain, owing in part to the possible contamination of rest-optical broadband light from strong nebular emission lines. To quantify the contribution of nebular emission to broadband fluxes, we investigate the SEDs of 92 spectroscopically confirmed galaxies in the redshift range 3.8 < z < 5.0 chosen because the Hα line lies within the Spitzer/IRAC 3.6 μm filter. We demonstrate that the 3.6 μm flux is systematically in excess of that expected from stellar continuum alone, which we derive by fitting the SED with population synthesis models. No such excess is seen in a control sample of spectroscopically confirmed galaxies with 3.1 < z < 3.6 in which there is no nebular contamination in the IRAC filters. From the distribution of our 3.6 μm flux excesses, we derive an Hα equivalent width distribution and consider the implications for both the derived stellar masses and the sSFR evolution. The mean rest-frame Hα equivalent width we infer at 3.8 < z < 5.0 (270 Å) indicates that nebular emission contributes at least 30% of the 3.6 μm flux and, by implication, nebular emission is likely to have a much greater impact for galaxies with z 6-7 where both warm IRAC filters are contaminated. Via our empirically derived equivalent width distribution, we correct the available stellar mass densities and show that the sSFR evolves more rapidly at z > 4 than previously thought, supporting up to a 5× increase between z 2 and 7. Such a trend is much closer to theoretical expectations. Given our findings, we discuss the prospects for verifying quantitatively the nebular emission line strengths prior to the launch of the James Webb Space Telescope.

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A CANDELS WFC3 GRISM STUDY OF EMISSION-LINE GALAXIES ATz∼ 2: A MIX OF NUCLEAR ACTIVITY AND LOW-METALLICITY STAR FORMATION

Cited by 59 publications

References 65 publications

SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

Hα IMAGING OF NEARBY SEYFERT HOST GALAXIES

KECK SPECTROSCOPY OF 3 <z< 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY

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