Wednesday 25th July 2012


Title: Type 1 AGN at low z. II. The relative strength of narrow lines and the nature of intermediate type AGN

Authors: Jonathan Stern, Ari Laor

We explore the relative strength of the narrow emission lines in an SDSS based sample of broad H-alpha selected AGN, defined in paper I. We find a decrease in the narrow to broad H-alpha luminosity (L_bHa) ratio with increasing L_bHa, such that both L([OIII] lambda5007) and L(narrow H-alpha) scale as L_bHa^0.7 for 10^40 < L_bHa < 10^45 ergs s^-1. Following our earlier result that L_bHa \propto L_bol, this trend indicates that the relative narrow line luminosity decreases with increasing L_bol. We derive L_bol / 10^43 ergs s^-1 = 4000 (L([OIII]) / 10^43 ergs s^-1)^1.39. This implies that the bolometric correction factor, L_bol / L([OIII]), decreases from 3,000 at L_bol = 10^46.1 ergs s^-1 to 300 at L_bol = 10^42.5 ergs s^-1. At low luminosity, the narrow component dominates the observed H-alpha profile, and most type 1 AGN appear as intermediate type AGN. Partial obscuration or extinction cannot explain the dominance of intermediate type AGN at low luminosity, and the most likely mechanism is a decrease in the narrow line region covering factor with increasing L_bol. Deviations from the above trend occur in objects with L / L_Edd <~ 10^-2.6, probably due to the transition to LINERs with suppressed [OIII] emission, and in objects with M_BH > 10^8.5 M_Sun, probably due to the dominance of radio loud AGN, and associated enhanced [OIII] emission.

Title: FMOS near-IR spectroscopy of Herschel selected galaxies: star formation rates, metallicity and dust attenuation at z~1

Authors: I. G. Roseboom (Edinburgh), A. Bunker, M. Sumiyoshi, L. Wang, G. Dalton, M. Akiyama, J. Bock, D. Bonfield, V. Buat, C. Casey, E. Chapin, D. L. Clements, A. Conley, E. Curtis-Lake, A. Cooray, J. S. Dunlop, D. Farrah, S. J. Ham, E. Ibar, F. Iwamuro, M. Kimura, I. Lewis, E. Macaulay, G. Magdis, T.Maihara, G. Marsden, T. Mauch, Y. Moritani, K. Ohta, S. J. Oliver, M. J. Page, B. Schulz, Douglas Scott, M. Symeonidis, N. Takato, N. Tamura, T. Totani, K. Yabe, M. Zemcov

We investigate the properties (e.g. star formation rate, dust attentuation, stellar mass and metallicity) of a sample of infrared luminous galaxies at z \sim 1 via near-IR spectroscopy with Subaru-FMOS. Our sample consists of Herschel SPIRE and Spitzer MIPS selected sources in the COSMOS field with photometric redshifts in the range 0.7 < z-phot < 1.8, which have been targeted in 2 pointings (0.5 sq. deg.) with FMOS. We find a modest success rate for emission line detections, with candidate H{\alpha} emission lines detected for 57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we directly measure the mean Balmer decrement for the H{\alpha} and H{\beta} lines, finding a value of <E(B-V)> = 0.51\pm0.27 for <LIR> = 10^12 Lsol sources at <z> = 1.36. By comparing star formation rates estimated from the IR and from the dust uncorrected H{\alpha} line we find a strong relationship between dust attenuation and star formation rate. This relation is broadly consistent with that previously seen in star-forming galaxies at z ~ 0.1. Finally, we investigate the metallicity via the N2 ratio, finding that z ~ 1 IR-selected sources are indistinguishable from the local mass-metallicity relation. We also find a strong correlation between dust attentuation and metallicity, with the most metal-rich IR-sources experiencing the largest levels of dust attenuation.

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