The origin of line emission in massive z ∼ 2.3 galaxies: Evidence for cosmic downsizing of AGN host galaxies

Markka Kriek, Pieter G. Van Dokkum, Marun Franx, Garth D. Illingworth, Paolo Coppi, Natascha M. Förster Schreiber, Eric Gawiser, Ivo Labbé, Paulina Lira, Danilo Marchesini, Ryan Quadri, Gregory Rudnick, Edward N. Taylor, C. Megan Urry, Paul P. Van Der Werf

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Abstract

Using the Gemini Near-Infrared Spectrograph (GNIRS), we have assembled a complete sample of 20 K-selected galaxies at 2.0 < z < 2.7 with high-quality near-infrared spectra. As described in a previous paper, 9 of these 20 galaxies have strongly suppressed star formation and no detected emission lines. The present paper concerns the 11 galaxies with detected Hα emission and studies the origin of the line emission using the GNIRS spectra and follow-up observations with SINFONI on the VLT. Based on their [N II]/Hα ratios, the spatial extent of the line emission, and several other diagnostics, we infer that 4 of the 11 emission-line galaxies host narrow-line active galactic nuclei (AGNs). The AGN host galaxies have stellar populations ranging from evolved to star-forming. Combining our sample with a UV-selected galaxy sample at the same redshift that spans a broader range in stellar mass, we find that black hole accretion is more effective at the high-mass end of the galaxy distribution (∼2.9 × 1011 M) at z ∼ 2.3. Furthermore, by comparing our results with SDSS data, we show that the AGN activity in massive galaxies has decreased significantly between z ∼ 2.3 and 0. AGNs with similar normalized accretion rates as those detected in our K-selected galaxies reside in less massive galaxies (∼4.0 × 10 10 M) at low redshift. This is direct evidence for downsizing of AGN host galaxies. Finally, we speculate that the typical stellar mass scale of the actively accreting AGN host galaxies, both at low and at high redshift, might be similar to the mass scale at which star-forming galaxies seem to transform into red, passive systems.

Original languageEnglish (US)
Pages (from-to)776-790
Number of pages15
JournalAstrophysical Journal
Volume669
Issue number2
DOIs
StatePublished - Nov 10 2007

Fingerprint

active galactic nuclei
galaxies
near infrared
accretion
transform
stellar mass
spectrographs
stars
star formation
infrared spectra

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high
  • Redshift

Cite this

Kriek, M., Van Dokkum, P. G., Franx, M., Illingworth, G. D., Coppi, P., Förster Schreiber, N. M., ... Van Der Werf, P. P. (2007). The origin of line emission in massive z ∼ 2.3 galaxies: Evidence for cosmic downsizing of AGN host galaxies. Astrophysical Journal, 669(2), 776-790. https://doi.org/10.1086/520789
Kriek, Markka ; Van Dokkum, Pieter G. ; Franx, Marun ; Illingworth, Garth D. ; Coppi, Paolo ; Förster Schreiber, Natascha M. ; Gawiser, Eric ; Labbé, Ivo ; Lira, Paulina ; Marchesini, Danilo ; Quadri, Ryan ; Rudnick, Gregory ; Taylor, Edward N. ; Urry, C. Megan ; Van Der Werf, Paul P. / The origin of line emission in massive z ∼ 2.3 galaxies : Evidence for cosmic downsizing of AGN host galaxies. In: Astrophysical Journal. 2007 ; Vol. 669, No. 2. pp. 776-790.
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abstract = "Using the Gemini Near-Infrared Spectrograph (GNIRS), we have assembled a complete sample of 20 K-selected galaxies at 2.0 < z < 2.7 with high-quality near-infrared spectra. As described in a previous paper, 9 of these 20 galaxies have strongly suppressed star formation and no detected emission lines. The present paper concerns the 11 galaxies with detected Hα emission and studies the origin of the line emission using the GNIRS spectra and follow-up observations with SINFONI on the VLT. Based on their [N II]/Hα ratios, the spatial extent of the line emission, and several other diagnostics, we infer that 4 of the 11 emission-line galaxies host narrow-line active galactic nuclei (AGNs). The AGN host galaxies have stellar populations ranging from evolved to star-forming. Combining our sample with a UV-selected galaxy sample at the same redshift that spans a broader range in stellar mass, we find that black hole accretion is more effective at the high-mass end of the galaxy distribution (∼2.9 × 1011 M⊙) at z ∼ 2.3. Furthermore, by comparing our results with SDSS data, we show that the AGN activity in massive galaxies has decreased significantly between z ∼ 2.3 and 0. AGNs with similar normalized accretion rates as those detected in our K-selected galaxies reside in less massive galaxies (∼4.0 × 10 10 M⊙) at low redshift. This is direct evidence for downsizing of AGN host galaxies. Finally, we speculate that the typical stellar mass scale of the actively accreting AGN host galaxies, both at low and at high redshift, might be similar to the mass scale at which star-forming galaxies seem to transform into red, passive systems.",
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Kriek, M, Van Dokkum, PG, Franx, M, Illingworth, GD, Coppi, P, Förster Schreiber, NM, Gawiser, E, Labbé, I, Lira, P, Marchesini, D, Quadri, R, Rudnick, G, Taylor, EN, Urry, CM & Van Der Werf, PP 2007, 'The origin of line emission in massive z ∼ 2.3 galaxies: Evidence for cosmic downsizing of AGN host galaxies', Astrophysical Journal, vol. 669, no. 2, pp. 776-790. https://doi.org/10.1086/520789

The origin of line emission in massive z ∼ 2.3 galaxies : Evidence for cosmic downsizing of AGN host galaxies. / Kriek, Markka; Van Dokkum, Pieter G.; Franx, Marun; Illingworth, Garth D.; Coppi, Paolo; Förster Schreiber, Natascha M.; Gawiser, Eric; Labbé, Ivo; Lira, Paulina; Marchesini, Danilo; Quadri, Ryan; Rudnick, Gregory; Taylor, Edward N.; Urry, C. Megan; Van Der Werf, Paul P.

In: Astrophysical Journal, Vol. 669, No. 2, 10.11.2007, p. 776-790.

Research output: Contribution to journalArticle

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T1 - The origin of line emission in massive z ∼ 2.3 galaxies

T2 - Evidence for cosmic downsizing of AGN host galaxies

AU - Kriek, Markka

AU - Van Dokkum, Pieter G.

AU - Franx, Marun

AU - Illingworth, Garth D.

AU - Coppi, Paolo

AU - Förster Schreiber, Natascha M.

AU - Gawiser, Eric

AU - Labbé, Ivo

AU - Lira, Paulina

AU - Marchesini, Danilo

AU - Quadri, Ryan

AU - Rudnick, Gregory

AU - Taylor, Edward N.

AU - Urry, C. Megan

AU - Van Der Werf, Paul P.

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N2 - Using the Gemini Near-Infrared Spectrograph (GNIRS), we have assembled a complete sample of 20 K-selected galaxies at 2.0 < z < 2.7 with high-quality near-infrared spectra. As described in a previous paper, 9 of these 20 galaxies have strongly suppressed star formation and no detected emission lines. The present paper concerns the 11 galaxies with detected Hα emission and studies the origin of the line emission using the GNIRS spectra and follow-up observations with SINFONI on the VLT. Based on their [N II]/Hα ratios, the spatial extent of the line emission, and several other diagnostics, we infer that 4 of the 11 emission-line galaxies host narrow-line active galactic nuclei (AGNs). The AGN host galaxies have stellar populations ranging from evolved to star-forming. Combining our sample with a UV-selected galaxy sample at the same redshift that spans a broader range in stellar mass, we find that black hole accretion is more effective at the high-mass end of the galaxy distribution (∼2.9 × 1011 M⊙) at z ∼ 2.3. Furthermore, by comparing our results with SDSS data, we show that the AGN activity in massive galaxies has decreased significantly between z ∼ 2.3 and 0. AGNs with similar normalized accretion rates as those detected in our K-selected galaxies reside in less massive galaxies (∼4.0 × 10 10 M⊙) at low redshift. This is direct evidence for downsizing of AGN host galaxies. Finally, we speculate that the typical stellar mass scale of the actively accreting AGN host galaxies, both at low and at high redshift, might be similar to the mass scale at which star-forming galaxies seem to transform into red, passive systems.

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KW - Galaxies: evolution

KW - Galaxies: formation

KW - Galaxies: high

KW - Redshift

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Kriek M, Van Dokkum PG, Franx M, Illingworth GD, Coppi P, Förster Schreiber NM et al. The origin of line emission in massive z ∼ 2.3 galaxies: Evidence for cosmic downsizing of AGN host galaxies. Astrophysical Journal. 2007 Nov 10;669(2):776-790. https://doi.org/10.1086/520789