Kuhn, Sherman M.

Pierce, Marc; Classen, Albrecht

doi:10.1515/9783110215588.2426

Cited by 12 publications

(20 citation statements)

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“…Studying the aperture colours of AGN host galaxies should help to resolve the question of the origin of the blue colour. Pierce et al (2010) find that X‐ray‐selected AGN hosted by UV–optical green valley galaxies typically exhibit extended optical colours that are similar to the extended colours of a control sample, which suggests that most green valley galaxies hosting AGN are intrinsically green and that it is rare for red sequence galaxies to host AGN contributing more than ∼10 per cent of the B ‐band light.…”

Section: Discussion and Summarymentioning

confidence: 58%

“…Based on an inspection of our simulated galaxies, it appears that the point sources in such systems should be visually identifiable for high AGN fractions. The results of Pierce et al (2010), in which the authors compare the observed nuclear, extended and integrated optical colours of galaxies hosting X‐ray‐selected AGN to a corresponding control sample, suggests a low incidence of systems with AGN fractions per cent AGN ≥20 per cent because the integrated colours of most of the AGN host galaxies correlate much more closely with the extended colours than with the nuclear colours.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…However, it is less obvious what to conclude about the AGN hosts located in the upper region of the blue cloud. Pierce et al (2010) address this further by considering the relationships between host galaxy aperture colours and the AGN X‐ray luminosities and hardness ratios.…”

Section: Experiments 2: Combining Agn and Non‐agn Galaxy Spectral Tementioning

confidence: 99%

“…At AGN fractions less than 20 per cent, there is reasonable concern that some AGN host galaxies are incorrectly classified as green valley galaxies and not easily identified as being problematic because of the low AGN fraction; thus extra caution should be taken when studying such systems. Using aperture photometry to separate the inner and outer colours of the AGN hosts can help with this, as discussed by Ammons et al (in preparation) and Pierce et al (2010).…”

Section: Colours Versus Sérsic Indices Of Simulated Agn Host Galaxiesmentioning

confidence: 99%

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The effects of an active galactic nucleus on host galaxy colour and morphology measurements

Pierce¹,

Lotz²,

Primack³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We assess the effects of simulated active galactic nuclei (AGN) on the colour and morphology measurements of their host galaxies. To test the morphology measurements, we select a sample of galaxies not known to host AGN and add a series of point sources scaled to represent specified fractions of the observed V‐band light detected from the resulting systems; we then compare morphology measurements of the simulated systems to measurements of the original galaxies. AGN contributions >rsim 20 per cent bias most of the morphology measurements tested, though the extent of the apparent bias depends on the morphological characteristics of the original galaxies. We test colour measurements by adding to non‐AGN galaxy spectra a quasar spectrum scaled to contribute specified fractions of the rest‐frame B‐band light detected from the resulting systems. A quasar fraction of 5 per cent can move the NUV −r colour of an elliptical galaxy from the ultraviolet–optical red sequence to the green valley, and 20 per cent can move it into the blue cloud. Combining the colour and morphology results, we find that a galaxy/AGN system with an AGN contribution >rsim 20 per cent may appear bluer and more bulge dominated than the underlying galaxy. We conclude that (1) bulge‐dominated, E/S0/Sa, and early‐type morphology classifications are accurate for red AGN host galaxies and may be accurate for blue host galaxies, unless the AGN manifests itself as a well‐defined point source and (2) although highly unobscured AGN, such as the quasar used for our experiments, can significantly bias the measured colours of AGN host galaxies, it is possible to identify such systems by examining optical images of the hosts for the presence of a point source and/or measuring the level of nuclear obscuration.

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Section: Discussion and Summarymentioning

confidence: 58%

Section: Discussion and Summarymentioning

confidence: 99%

Section: Experiments 2: Combining Agn and Non‐agn Galaxy Spectral Tementioning

confidence: 99%

Section: Colours Versus Sérsic Indices Of Simulated Agn Host Galaxiesmentioning

confidence: 99%

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The effects of an active galactic nucleus on host galaxy colour and morphology measurements

Pierce¹,

Lotz²,

Primack³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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“…The current work and a companion study (Pierce et al 2010) address this using complementary methods. Pierce et al (2010) added an AGN spectral template (the QSO template shown in Fig. 1) to three non-AGN templates (an elliptical galaxy, an Sb galaxy and a starburst galaxy).…”

mentioning

confidence: 99%

Host galaxy colour gradients and accretion disc obscuration in AEGIS z ∼ 1 X-ray-selected active galactic nuclei

Pierce

Lotz

Salim

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We describe the effect of active galactic nucleus (AGN) light on host galaxy optical and UV‐optical colours, as determined from X‐ray‐selected AGN host galaxies at z∼ 1, and compare the AGN host galaxy colours to those of a control sample matched to the AGN sample in both redshift and stellar mass. We identify as X‐ray‐selected AGNs 8.7+4−3 per cent of the red‐sequence control galaxies, 9.8 ± 3 per cent of the blue‐cloud control galaxies and 14.7+4−3 per cent of the green‐valley control galaxies. The nuclear colours of AGN hosts are generally bluer than their outer colours, while the control galaxies exhibit redder nuclei. AGNs in blue‐cloud host galaxies experience less X‐ray obscuration, while AGNs in red‐sequence hosts have more, which is the reverse of what is expected from general considerations of the interstellar medium. Outer and integrated colours of AGN hosts generally agree with the control galaxies, regardless of X‐ray obscuration, but the nuclear colours of unobscured AGNs are typically much bluer, especially for X‐ray luminous objects. Visible point sources are seen in many of these, indicating that the nuclear colours have been contaminated by AGN light and that obscuration of the X‐ray radiation and visible light are therefore highly correlated. Red AGN hosts are typically slightly bluer than red‐sequence control galaxies, which suggests that their stellar populations are slightly younger. We compare these colour data to current models of AGN formation. The unexpected trend of less X‐ray obscuration in blue‐cloud galaxies and more in red‐sequence galaxies is problematic for all AGN feedback models, in which gas and dust is thought to be removed as star formation shuts down. A second class of models involving radiative instabilities in hot gas is more promising for red‐sequence AGNs but predicts a larger number of point sources in red‐sequence AGNs than is observed. Regardless, it appears that multiple AGN models are necessary to explain the varied AGN host properties discussed in the current work. Finally, we find that integrated optical and UV − optical colours are not strongly affected by X‐ray‐selected AGNs except in rare cases (<10 per cent), where the AGN is very luminous, unobscured and/or visible as a point source.

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AGN-host galaxy connection: morphology and colours of X-ray selected AGN atz ≤ 2

Pović

Sánchez‐Portal

García

et al. 2012

A&A

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Context. The connection between active galactic nuclei (AGN) and their host galaxies has been widely studied and found to be of great importance for providing answers to some fundamental questions related to AGN fuelling mechanisms, and both their formation and evolution. Aims. Using X-ray data and one of the deepest broad-band optical data sets available, we study how morphology and colours are related to X-ray properties for sources at redshifts z ≤ 2.0, using a sample of 262 AGN in the Subaru/XMM-Newton Deep Survey (SXDS). Methods. We performed our morphological classification using the galSVM code, which is a new method that is particularly suited to dealing with high-redshift sources. Colour-magnitude diagrams were studied in relationship to redshift, morphology, X-ray obscuration, and X-ray-to-optical flux ratio. We analysed the different regions in the colour-magnitude diagrams, and searched for correlations with the observed properties of AGN populations using models of their formation and evolution. Results. We confirm that a robust and reliable morphological classification of a general galaxy population at high redshift should be based on a multi-parametric approach. At least 50% of X-ray detected AGN at z ≤ 2.0 analysed in this work reside in spheroidal and bulge-dominated galaxies, while at least 18% have disk-dominated hosts. This suggests that different mechanisms may be responsible for triggering the nuclear activity. When analysing populations of X-ray detected AGN in both colour-magnitude and colour-stellar mass diagrams, the highest number of sources is found to reside in the green valley at redshifts ≈0.5-1.5. However, a larger number of low-luminosity AGN have been detected than in previous works owing to the substantial depth of the SXDS optical data. Whether AGN are hosted by early-or late-type galaxies, no clear relationship has been found with the optical colours (independently of redshift), as is typical of normal galaxies. Both early-and late-type AGN cover similar ranges of X-ray obscuration, for both unobscured and obscured sources. Conclusions. Our findings appear to confirm some previous suggestions that X-ray selected AGN residing in the green valley represent a transitional population, quenching star formation by means of different AGN feedback mechanisms and evolving to red-sequence galaxies. They might be hosted by similar sources (the majority of sources being late-type elliptical and lenticular galaxies, and early-type spirals) with similar stellar populations, which are triggered mainly by major and/or minor mergers, and in some cases by means of secular mechanism, as shown in previous numerical simulations. In the aforementioned transition we observe different phases of AGN activity, with some AGN being in the "QSO-mode" detected as compact, blue, and unobscured in X-rays, and with others passing through different phases before and after the "QSO-mode", being obscured and unobscured in X-rays, respectively.

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Kuhn, Sherman M.

Cited by 12 publications

References 0 publications

The effects of an active galactic nucleus on host galaxy colour and morphology measurements

The effects of an active galactic nucleus on host galaxy colour and morphology measurements

Host galaxy colour gradients and accretion disc obscuration in AEGIS z ∼ 1 X-ray-selected active galactic nuclei

AGN-host galaxy connection: morphology and colours of X-ray selected AGN atz ≤ 2

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