X-Ray Nondetection of the Lyα Emitters at
                    <i>z</i>
                     ~ 4.5

Wang, J. X.; Rhoads, James E.; Malhotra, Sangeeta; Dawson, Steve; Stern, Daniel; Dey, Arjun; Heckman, Timothy M.; Norman, C.; Spinrad, Hyron

doi:10.1086/422311

Cited by 102 publications

(138 citation statements)

References 33 publications

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“…Previous studies of LAEs at higher redshifts exhibited very small AGN contributions, from less than one percent in the z ∼ 4.5 LAEs studied by Wang et al (2004) to ∼1% at z ∼ 3 as inferred by Gawiser et al (2007). Lehmer et al (2008) calculated the "AGN fraction function" of Lyα emitters at z ∼ 3 both in the field and the overdense region of SSA22 (Fig.…”

Section: Agn Contributionmentioning

confidence: 81%

Evolution in the properties of Lyman-αemitters from redshiftsz~ 3 toz ~ 2

Nilsson¹,

Tapken²,

Møller

et al. 2009

A&A

155

237

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Context. Narrow-band surveys to detect Lyα emitters are powerful tools for identifying high, and very high, redshift galaxies. Although samples are increasing at redshifts z = 3−6, the nature of these galaxies is still poorly known. The number of galaxies detected at redshifts below z ∼ 3 are also small. Aims. We study the properties of z = 2.25 Lyα emitters and compare them with those of z > 3 Lyα emitters.Methods. We present narrow-band imaging made with the MPG/ESO 2.2m telescope and the WFI (Wide Field Imager) detector. Using this data, we have searched for emission-line objects. We find 170 candidate typical Lyα emitters and 17 candidates that we regard as high UV-transmission Lyα emitters. We have derived the magnitudes of these objects in 8 photometric bands from u * to K s , and studied whether they have X-ray and/or radio counterparts. Results. We demonstrate that there has been significant evolution in the properties of Lyα emitters between redshift z ∼ 3 and z = 2.25. The spread in spectral energy distributions (SEDs) at the lower redshift is larger and we detect a significant AGN contribution in the sample. The distribution of the equivalent widths is narrower than at z ∼ 3, with only a few candidates with rest-frame equivalent width above the predicted limit of 240 Å. The star formation rates derived from the Lyα emission compared to those derived from the UV emission are lower by on average a factor of ∼1.8, indicative of a significant absorption by dust. Conclusions. Lyα emitters at redshift z = 2.25 may be more evolved than Lyα emitters at higher redshift. The red SEDs imply more massive, older and/or dustier galaxies at lower redshift than observed at higher redshifts. The decrease in equivalent widths and star formation rates indicate more quiescent galaxies, with in general less star formation than in higher redshift galaxies. At z = 2.25, AGN appear to be more abundant and also to contribute more to the Lyα emitting population.

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Section: Agn Contributionmentioning

confidence: 81%

Evolution in the properties of Lyman-αemitters from redshiftsz~ 3 toz ~ 2

Nilsson¹,

Tapken²,

Møller

et al. 2009

A&A

155

237

View full text Add to dashboard Cite

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“…It has already been shown in that the AGN fraction among these lower redshift galaxies is greater than (Atek et al 2009;Cowie et al 2010;Finkelstein et al 2009;Scarlata et al 2009), z = 2.1 (Guaita et al 2010), z = 3 (Gronwall et al 2007;Ouchi et al 2008) and at z ∼ 4−5 (Wang et al 2004;Ouchi et al 2008). Lines indicate best-fit models (see text for details).…”

Section: The Agn Fraction Of Laesmentioning

confidence: 83%

Lyman-αemitters as tracers of the transitioning Universe

Nilsson

Møller²

2011

A&A

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Of all the many ways of detecting high-redshift galaxies, the selection of objects by their redshifted Lyα emission has become one of the most successful. But what types of galaxies are selected in this way? Until recently, Lyα emitters were understood to be small star-forming galaxies, the possible building-blocks of larger galaxies. But with increased number of observations of Lyα emitters at lower redshifts, a new picture emerges. Lyα emitters display strong evolution in their properties from higher to lower redshift. It has previously been shown that the fraction of ultra-luminous infrared galaxies (ULIRGs) among the Lyα emitters increases dramatically between redshifts three and two. Here, the fraction of AGN among the LAEs is shown to follow a similar evolutionary path. We argue that Lyα emitters are not a homogeneous class of objects and that the objects selected with this method reflect the general star forming and active galaxy populations at that redshift. Lyα emitters should thus be excellent tracers of galaxy evolution in future simulations and modelling.

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“…The new AGN detections are LAE_COSMOS# 14,20,52,67,76,120,130,134,151 and 175. Thus the confirmed AGN contamination in the non-GALEXdetected sample increases from 9% (before Chandra detections but after spectroscopic rejections) to at least 11%, i.e. 18/159 (see also Table 1), a much larger percentage than in high redshift samples (Wang et al 2004;Gawiser et al 2007). Lower redshift samples of Lyα emitters at z = 0.3 and z = 2.2 have also been shown to contain large AGN fractions, of e.g.…”

Section: Updated Photometrymentioning

confidence: 90%

The nature ofz ~ 2.3 Lyman-αemitters

Nilsson

Östlin

Møller

et al. 2011

A&A

116

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We study the multi-wavelength properties of a set of 171 Lyα emitting candidates at redshift z = 2.25 found in the COSMOS field, with the aim of understanding the underlying stellar populations in the galaxies. We especially seek to understand what the dust contents, ages and stellar masses of the galaxies are, and how they relate to similar properties of Lyα emitters at other redshifts. The candidates here are shown to have different properties from those of Lyα emitters found at higher redshift, by fitting the spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique and including nebular emission in the spectra. The stellar masses, and possibly the dust contents, are higher, with stellar masses in the range log M * = 8.5−11.0 M and A V = 0.0−2.5 mag. Young population ages are well constrained, but the ages of older populations are typically unconstrained. In 15% of the galaxies only a single, young population of stars is observed. We show that the Lyα fluxes of the best fit galaxies are correlated with their dust properties, with higher dust extinction in Lyα faint galaxies. Testing for whether results derived from a light-weighted stack of objects correlate to those found when fitting individual objects we see that stellar masses are robust to stacking, but ages and especially dust extinctions are derived incorrectly from stacks. We conclude that the stellar properties of Lyα emitters at z = 2.25 are different from those at higher redshift and that they are diverse. Lyα selection appears to be tracing systematically different galaxies at different redshifts.

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X-Ray Nondetection of the Lyα Emitters at z ~ 4.5

Cited by 102 publications

References 33 publications

Evolution in the properties of Lyman-αemitters from redshiftsz~ 3 toz ~ 2

Evolution in the properties of Lyman-αemitters from redshiftsz~ 3 toz ~ 2

Lyman-αemitters as tracers of the transitioning Universe

The nature ofz ~ 2.3 Lyman-αemitters

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