PROBING THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT
                    <i>z</i>
                    ∼ 4 IN THE COSMOS FIELD

Ikeda, Hiroyuki; Nagao, Tohru; Matsuoka, Kenta; Taniguchi, Yoshiaki; Shioya, Yasuhiro; Trump, Jonathan R.; Capak, P.; Comastri, A.; Enoki, Motohiro; Ideue, Y.; Kakazu, Y.; Koekemoer, Anton M.; Morokuma, Tomoki; Murayama, Takashi; Saito, Tomoki; Salvato, M.; Schinnerer, E.; Scoville, N. Z.; Silverman, John D.

doi:10.1088/2041-8205/728/2/l25

Cited by 53 publications

(130 citation statements)

References 48 publications

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“…To compare these data at z=4 with our results, we computed the Chandra COSMOS-Legacy space density in two redshift bins at z= [3.5-4.5] where L-COSMOS3 is not complete (see Figure 9); therefore, these two data points should be treated as lower limits. We found that our data are in good agreement with the result obtained by Glikman et al (2011), while the estimates by Ikeda et al (2011) lie below our estimates by a factor of ∼2-3. However, it is worth noting that both of these optical surveys are sampling unobscured Type 1 AGNs, while in L-COSMOS3 a significant fraction of obscured objects is also taken into account.We will discuss the agreement between the optical surveys and our Type 1 AGN population space density in the next section.…”

Section: 55supporting

confidence: 91%

“…The limitation of optical surveys is that at low optical luminosities (−24.5  M AB  −22), the standard color-color quasar identification procedures become less reliable because stars can be misinterpreted as quasars. As a result, low-luminosity AGN luminosity functions from optical surveys are so far in disagreement (e.g., Glikman et al 2011;Ikeda et al 2011;Masters et al 2012). Moreover, optical surveys are biased against obscured sources, whose contribution also becomes more significant at low luminosities (e.g., Ueda et al 2014).…”

Section: Introductionmentioning

confidence: 99%

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THE CHANDRA COSMOS-LEGACY SURVEY: THE z > 3 SAMPLE

Marchesi

Civano

Salvato

et al. 2016

ApJ

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We present the largest high-redshift (3 < z < 6.85) sample of X-ray-selected active galactic nuclei (AGNs) on a contiguous field, using sources detected in the Chandra COSMOS-Legacy survey. The sample contains 174 sources, 87 with spectroscopic redshift and the other 87 with photometric redshift (z phot ). In this work, we treat z phot as a probability-weighted sum of contributions, adding to our sample the contribution of sources with z phot <3 but z phot probability distribution >0 at z>3. We compute the number counts in the observed 0.5-2 keV band, finding a decline in the number of sources at z>3 and constraining phenomenological models of the X-ray background. We compute the AGN space density at z>3 in two different luminosity bins. At higher luminosities (logL(2-10 keV) > 44.1 erg s −1 ), the space density declines exponentially, dropping by a factor of ∼20 from z∼3 to z∼6. The observed decline is ∼80% steeper at lower luminosities (43.55 erg s −1 < logL(2-10 keV)<44.1 erg s) from z∼3 to z∼4.5. We study the space density evolution dividing our sample into optically classified Type 1 and Type 2 AGNs. At logL (2-10 keV)>44.1 erg s −1, unobscured and obscured objects may have different evolution with redshift, with the obscured component being three times higher at z∼5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGNs. These models significantly overpredict the number of expected AGNs at logL (2-10 keV)>44.1 erg s −1 with respect to our data.

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Section: 55supporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

THE CHANDRA COSMOS-LEGACY SURVEY: THE z > 3 SAMPLE

Marchesi

Civano

Salvato

et al. 2016

ApJ

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“…Specifically, Glikman et al (2011) claimed roughly a factor four more sources at z 3 than did Ikeda et al (2011). More recently, Masters et al (2012) found a decrease by a factor of four in the number density of faint QSOs in COSMOS between z ∼ 3.2 and z ∼ 4, supporting the results of Ikeda et al (2011). Overall, the results from Masters et al (2012) suggest a similar evolution of the UV and X-ray LFs at z 3.…”

Section: Observational Parametersmentioning

confidence: 55%

“…While different groups agreed on the faint-end slope of the LF, 1.7, they derived quite different absolute space densities. Specifically, Glikman et al (2011) claimed roughly a factor four more sources at z 3 than did Ikeda et al (2011). More recently, Masters et al (2012) found a decrease by a factor of four in the number density of faint QSOs in COSMOS between z ∼ 3.2 and z ∼ 4, supporting the results of Ikeda et al (2011).…”

Section: Observational Parametersmentioning

confidence: 65%

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

Haardt

Salvaterra

2015

A&A

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The rapidly declining population of bright quasars at z 3 appears to make an increasingly smaller contribution to the ionising background at the H I Lyman limit. It is thererfore generally thought that massive stars in (pre-)Galactic systems may provide the additional ionising flux needed to complete H I reionisation by z 6. A galaxy-dominated background, however, may require that the escape fraction of Lyman continuum radiation from high-redshift galaxies is as high as 10%, which is somewhat at odds with (admittedly scarce) observational constraints. High escape fractions from dwarf galaxies have been advocated, or, alternatively, a so-far undetected (or barely detected) population of unobscured, high-redshift faint AGNs. Here we examine the latter hypothesis and show that such sources, to be consistent with the measured level of the unresolved X-ray background at z = 0, can provide a fraction of the H II filling factor no larger than 13% by z 6. The fraction rises to 27% in the somewhat extreme case of a constant comoving redshift evolution of the AGN emissivity. This still calls for a mean escape fraction of ionising photons from high-z galaxies of 10%.

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“…One high-redshift source (α = 150.35980δ = 2.0737081) is detected in the X-ray by Chandra in the C-COSMOS survey (Elvis et al 2009), though unlike the XMM survey of COSMOS the Chandra survey is not uniform over the entire field. Two of the LBG sources are point sources in ACS (α = 149.87082δ = 1.8827920, and α = 150.13036δ = 2.4660110 taken from Ikeda et al 2011), but show no signs of AGNs in their spectra, nor have X-ray detections.…”

Section: Redshift Agns and Lyα Identificationmentioning

confidence: 99%

Lyα EMISSION FROM HIGH-REDSHIFT SOURCES IN COSMOS

Mallery

Mobasher

Capak

et al. 2012

ApJ

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We investigate spectroscopically measured Lyα equivalent widths (EWs) and escape fractions of 244 sources of which 95 are Lyman break galaxies (LBGs) and 106 Lyman alpha emitters (LAEs) at z ∼ 4.2, z ∼ 4.8, and z ∼ 5.6 selected from intermediate and narrowband observations. The sources were selected from the Cosmic Evolution Survey and observed with the DEIMOS spectrograph. We find that the distribution of EWs shows no evolution with redshift for both the LBG selected sources and the intermediate/narrowband LAEs. We also find that the Lyα escape fraction of intermediate/narrowband LAEs is on average higher and has a larger variation than the escape fraction of LBG selected sources. The escape fraction does not show a dependence with redshift. Similar to what has been found for LAEs at low redshifts, the sources with the highest extinctions show the lowest escape fractions. The range of escape fractions increases with decreasing extinction. This is evidence that the dust extinction is the most important factor affecting the escape of Lyα photons, but at low extinctions other factors, such as the H i covering fraction and gas kinematics, can be just as effective at inhibiting the escape of Lyα photons.

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PROBING THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT z ∼ 4 IN THE COSMOS FIELD

Abstract: We searched for quasars that are ∼ 3 mag fainter than the SDSS quasars in the redshift range 3.7 z 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function. Using optical photometric data, we selected

Cited by 53 publications

References 48 publications

THE CHANDRA COSMOS-LEGACY SURVEY: THE z > 3 SAMPLE

THE CHANDRA COSMOS-LEGACY SURVEY: THE z > 3 SAMPLE

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

Lyα EMISSION FROM HIGH-REDSHIFT SOURCES IN COSMOS

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