Follow-up spectroscopy of wide-area XMM fields: studying the conditions of black hole growth to z = 1


Photo of Antonis Georgakakis
Antonis Georgakakis
National Observatory of Athens


A spectroscopic survey of AGN, selected from X-ray data, conducted to better characterize AGN population properties

Finding Targets

An object whose ANCILLARY_TARGET2 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description Number of Fibers
XMM_PRIME 32 Candidate AGN identified from the XMM-XXL survey observed at higher priority 2,417
XMM_SECOND 33 Candidate AGN identified from the XMM-XXL survey observed at lower priority 645


Characterization of the population properties of AGN can reveal information on the conditions under which super-massive black holes grow their mass, and can shed light on the physical processes responsible for the accretion history of the Universe.

X-ray selection provides an advantage in AGN population studies because it provides the least-biased samples of active black holes with a selection function that can be quantified accurately.

In this ancillary science program, four special plates were dedicated to spectroscopically classify X-ray selected AGN. Like the SPIDERS pilot survey ancillary target program, this program targeted X-ray-selected AGN from the XMM-XXL field, now using the full range of sensitivity from 0.5 to 10 keV.

Target Selection

Candidates were identified in the northern field of the wide-area XMM-XXL survey (PI: Marguerite Pierre), which is centered at α = 35 deg, δ = -5 deg. This X-ray field covers a total area of 25 deg2 to the shallow X-ray flux limit of fX(0.5-10 keV) ≈ 10-14 erg per s per cm2. As of January 2015, XMM-XXL is the largest contiguous X-ray survey at this depth. The key feature of the sample is that it includes a large number of the luminous X-ray AGN that dominate the accretion history of the Universe at almost any redshift.

The X-ray source catalogue in the XMM-XXL field was constructed following the methodology described in Georgakakis & Nandra (2011). Optical counterparts were identified via the maximum-likelihood method (Georgakakis & Nandra 2011) using the SDSS DR8 photometric catalog.

The main spectroscopic target sample was selected to have fX(0.5 – 10 keV) > 10-14 erg s-1 cm-2 and 15 < r < 22.5, where r is either the PSF magnitude (in the case of optical unresolved sources) or the model magnitude (in the case of resolved sources). Targets in this sample are denoted XMM_PRIME.

Secondary targets are sources with fX(0.5 – 10 keV) < 10-14 erg s-1 cm-2 and 15 < r < 22.5, OR are radio sources selected in eitehr 325 or 610 MHz from targets in the catalog of Tasse et al. (2008). These targets are denoted XMM_SECOND.


Georgakakis, A., & Nandra, K. 2011, MNRAS, 414, 992

Tasse, C., Le Borgne, D., Röttgering, H., Best, P. N., Pierre, M., & Rocca-Volmerange, B. 2008, A&A, 490, 879