Witnessing the transformation of a quasar host galaxy at z = 1.6

Humphrey, A.; Roche, N.; Gomes, J. M.; Papaderos, P.; Villar-Martín, M.; Filho, M.; Emonts, Bjorn; Aretxaga, I.; Binette, L.; Flaquer, B. Ocaña; Lagos, P.; Torrealba, J.

doi:10.1093/mnras/stu2510

Cited by 3 publications

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“…For 5C 7.245, we also show the g-band photometry of the extended blob of emission located ∼1 SW of the near-infrared position of the radio galaxy (blue). Humphrey et al (2015) argued that we here witness a rare (or rarely observed) phase in the evolution of quasar hosts, when stellar mass assembly, accretion onto the back hole, and/or powerful feedback activity have eradicated cold gas from the central ∼20 kpc, but is still in the process of cleansing cold gas from its extended halo.…”

Section: Resultsmentioning

confidence: 72%

“…2). Long-slit spectroscopy presented by Humphrey et al (2015) detected no lines from the K-band position at a 3σ limit of ∼3 × 10 −17 erg s −1 cm −2 . However, these authors detected HeII λ1640, CII] λ2326, [NeIV] λ2423 and MgII λ2800 at the position of the g-band blob to the south-east at a redshift of z = 1.609, consistent with the tentative detection of Hα at z = 1.61 reported by W01.…”

Section: Resultsmentioning

confidence: 90%

“…5C 7.245: This radio galaxy has been discussed in detail in Humphrey et al (2015), but is included here for completeness. Our g-band image shows no significant emission at the position of the peak of the W01 K-band emission, but we detected a blob of extended emission located ∼2 ′′ SE of the K-band position, along a similar position angle to that of the radio source, with a fainter blob diametrically opposed to the NW (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…By fitting simple stellar populations to their R through K broad-band spectral energy distributions (SEDs), W01 obtained tentative photometric redshifts for five of the LDRRGs (5C 6.17, 5C 6.83, 5C 6.242, 5C 7.47, and 5C 7.208) and obtained tentative spectroscopic redshifts based on single line detections for two further LDRRGs in our sample (5C 6.62 and 5C 7.245). Humphrey et al (2015) have recently obtained a firm spectroscopic redshift for 5C 7.245 after detecting four rest-frame ultraviolet emission lines.…”

Section: Sample and Observationsmentioning

confidence: 99%

“…Redshifts shown in parentheses are tentative values from W01, based on fitting twelve simple stellar populations to their R through K broad-band SEDs, or in the case of 5C 6.62, on their tentative detection of a single emission line thought to be Hα. The firm redshift determination for 5C 7.245 comes from Humphrey et al (2015)…”

Section: Sample and Observationsmentioning

confidence: 99%

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GTC optical imaging of extremely red 5C radio galaxies at high redshift

Humphrey

Villar-Martín

Lagos

2015

A&A

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Aims. We investigate the nature of seven unusual radio galaxies from the 5C catalogue that were previously known to have extremely red R − K colours, and for which emission lines were previously found to be weak or absent in their optical spectra. Methods. We present and discuss u, g, or r images of these radio galaxies, obtained using the Optical System for Imaging and lowIntermediate-Resolution Integrated Spectroscopy (OSIRIS) at the Gran Telescopio Canarias (GTC). Results. We have detected all seven targets in our g-band imaging. Their optical emission is extended, and we tentatively detect a radio-optical alignment effect in this sample. A subset of our sample (three sources) shows broad-band spectral energy distributions that flatten out near the wavelength range of the g-band, implying a dominant contribution there due to young stars and/or scattered or reprocessed radiation from the active nucleus.

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Section: Resultsmentioning

confidence: 72%

Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Sample and Observationsmentioning

confidence: 99%

Section: Sample and Observationsmentioning

confidence: 99%

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GTC optical imaging of extremely red 5C radio galaxies at high redshift

Humphrey

Villar-Martín

Lagos

2015

A&A

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Identifying type II quasars at intermediate redshift with few-shot learning photometric classification

Cunha,

Humphrey,

Brinchmann

et al. 2024

A&A

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A sub-population of AGNs where the central engine is obscured are known as type II quasars (QSO2s). These luminous AGNs have a thick and dusty torus that obscures the accretion disc from our line of sight. Thus, their special orientation allows for detailed studies of the AGN-host co-evolution. Increasing the sample size of QSO2 sources in critical redshift ranges is crucial for understanding the interplay of AGN feedback, the AGN-host relationship, and the evolution of active galaxies. We aim to identify QSO2 candidates in the `redshift desert' using optical and infrared photometry. At this intermediate redshift range (i.e. $1 z 2$), most of the prominent optical emission lines in QSO2 sources (e.g. CIV$ OIII 4959, 5008$) fall either outside the wavelength range of the SDSS optical spectra or in particularly noisy wavelength ranges, making QSO2 identification challenging. Therefore, we adopted a semi-supervised machine learning approach to select candidates in the SDSS galaxy sample. Recent applications of machine learning in astronomy focus on problems involving large data sets, with small data sets often being overlooked. We developed a `few-shot' learning approach for the identification and classification of rare-object classes using limited training data (200 sources). The new AMELIA pipeline uses a transfer-learning based approach with decision trees, distance-based, and deep learning methods to build a classifier capable of identifying rare objects on the basis of an observational training data set. We validated the performance of AMELIA by addressing the problem of identifying QSO2s at $1 z 2$ using SDSS and WISE photometry, obtaining an F1-score above 0.8 in a supervised approach. We then used AMELIA to select new QSO2 candidates in the `redshift desert' and examined the nature of the candidates using SDSS spectra, when available. In particular, we identified a sub-population of NeV emitters at $z which are highly likely to contain obscured AGNs. We used X-ray and radio cross-matching to validate our classification and investigated the performance of photometric criteria from the literature showing that our candidates have an inherent dusty nature. Finally, we derived physical properties for our QSO2 sample using photoionisation models and verified the AGN classification using an SED fitting. Our results demonstrate the potential of few-shot learning applied to small data sets of rare objects, in particular QSO2s, and confirms that optical-IR information can be further explored to search for obscured AGNs. We present a new sample of candidates to be further studied and validated using multi-wavelength observations.

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An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole

Loon

Sansom

2015

Mon. Not. R. Astron. Soc.

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SAGE1C J053634.78−722658.5 is a galaxy at redshift z = 0.14, discovered behind the Large Magellanic Cloud in the Spitzer Space Telescope "Surveying the Agents of Galaxy Evolution" Spectroscopy survey (SAGE-Spec). It has very strong silicate emission at 10 µm but negligible far-IR and UV emission. This makes it a candidate for a bare AGN source in the IR, perhaps seen pole-on, without significant IR emission from the host galaxy. In this paper we present optical spectra taken with the Southern African Large Telescope (SALT) to investigate the nature of the underlying host galaxy and its AGN. We find broad Hα emission characteristic of an AGN, plus absorption lines associated with a mature stellar population (> 9 Gyr), and refine its redshift determination to z = 0.1428 ± 0.0001. There is no evidence for any emission lines associated with star formation. This remarkable object exemplifies the need for separating the emission from any AGN from that of the host galaxy when employing infrared diagnostic diagrams. We estimate the black hole mass, M BH = 3.5 ± 0.8 × 10 8 M ⊙ , host galaxy mass, M stars = 2.5 2.5 1.2 × 10 10 M ⊙ , and accretion luminosity, L bol (AGN) = 5.3 ± 0.4 × 10 45 erg s −1 (≈ 12 per cent of the Eddington luminosity) and find the AGN to be more prominent than expected for a host galaxy of this modest size. The old age is in tension with the downsizing paradigm in which this galaxy would recently have transformed from a star-forming disc galaxy into an early-type, passively evolving galaxy.

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Witnessing the transformation of a quasar host galaxy at z = 1.6

Cited by 3 publications

References 50 publications

GTC optical imaging of extremely red 5C radio galaxies at high redshift

GTC optical imaging of extremely red 5C radio galaxies at high redshift

Identifying type II quasars at intermediate redshift with few-shot learning photometric classification

An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole

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