TY - JOUR
T1 - Large-scale fluctuations in the X-ray background
AU - Treyer, Marie
AU - Scharf, Caleb
AU - Lahav, Ofer
AU - Jahoda, Keith
AU - Boldt, Elihu
AU - Piran, Tsvi
PY - 1998
Y1 - 1998
N2 - We present an attempt to measure the large angular scale fluctuations in the X-ray background (XRB) from the HEAO 1 A2 data, expressed in terms of spherical harmonics. We model the harmonic coefficients assuming a power spectrum and an epoch-dependent bias parameter, bx(z), and using a phenomenological scenario describing the evolution of the X-ray sources. From the few low-order multipoles detected above shot noise, we estimate the power-spectrum normalization on scales intermediate between those explored by local galaxy redshift surveys (∼100 h-1 Mpc) and those probed by the COBE cosmic microwave background (CMB) measurements (∼1000 h-1 Mpc). We find that the HEAO 1 harmonics are consistent with present-epoch rms fluctuations of the X-ray sources bx(0)σ8 ∼1-2 in 8 h-1 Mpc spheres. Therefore, the observed fluctuations in the XRB are roughly as expected from interpolation between the local galaxy surveys and the COBE CMB experiment. We predict that an X-ray all-sky surface brightness survey resolving sources a factor of 10 fainter than HEAO 1 could reveal fluctuations to significantly larger scales, and therefore more strongly constrain the large-scale structure of the universe on scales of hundreds of Mpc.
AB - We present an attempt to measure the large angular scale fluctuations in the X-ray background (XRB) from the HEAO 1 A2 data, expressed in terms of spherical harmonics. We model the harmonic coefficients assuming a power spectrum and an epoch-dependent bias parameter, bx(z), and using a phenomenological scenario describing the evolution of the X-ray sources. From the few low-order multipoles detected above shot noise, we estimate the power-spectrum normalization on scales intermediate between those explored by local galaxy redshift surveys (∼100 h-1 Mpc) and those probed by the COBE cosmic microwave background (CMB) measurements (∼1000 h-1 Mpc). We find that the HEAO 1 harmonics are consistent with present-epoch rms fluctuations of the X-ray sources bx(0)σ8 ∼1-2 in 8 h-1 Mpc spheres. Therefore, the observed fluctuations in the XRB are roughly as expected from interpolation between the local galaxy surveys and the COBE CMB experiment. We predict that an X-ray all-sky surface brightness survey resolving sources a factor of 10 fainter than HEAO 1 could reveal fluctuations to significantly larger scales, and therefore more strongly constrain the large-scale structure of the universe on scales of hundreds of Mpc.
KW - Cosmology: observations
KW - Diffuse radiation
KW - Large-scale structure of universe
UR - http://www.scopus.com/inward/record.url?scp=22444455824&partnerID=8YFLogxK
U2 - 10.1086/306515
DO - 10.1086/306515
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AN - SCOPUS:22444455824
SN - 0004-637X
VL - 509
SP - 531
EP - 536
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 PART I
ER -