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 language | English (US) |
|---|---|
| Pages (from-to) | 776-790 |
| Number of pages | 15 |
| Journal | Astrophysical Journal |
| Volume | 669 |
| Issue number | 2 |
| DOIs | |
| State | Published - Nov 10 2007 |
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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
}
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 journal › Article
TY - JOUR
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.
PY - 2007/11/10
Y1 - 2007/11/10
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.
AB - 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.
KW - Galaxies: active
KW - Galaxies: evolution
KW - Galaxies: formation
KW - Galaxies: high
KW - Redshift
UR - http://www.scopus.com/inward/record.url?scp=39049115978&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=39049115978&partnerID=8YFLogxK
U2 - https://doi.org/10.1086/520789
DO - https://doi.org/10.1086/520789
M3 - Article
VL - 669
SP - 776
EP - 790
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
ER -