A far-infrared survey at the North Galactic Pole - I. Nearby star-forming galaxies and effect of confused sources on source counts

Abstract

We present follow‐up observations of the far‐infrared (FIR) sources at 90, 150 and 180 μm detected as part of the ISOPHOT EBL project, which has recently measured the absolute surface brightness of the cosmic infrared background (CIRB) radiation for the first time independently from COBE data. We have observed the fields at the North Galactic Pole region in the optical and near‐IR, and complement these data with Sloan Digital Sky Survey photometry, and spectroscopy where available, and present identifications of the 25 FIR sources which reach down to ∼150 mJy in all three ISOPHOT bands. Identifications are done by means of full spectral energy density fitting to all sources in the FIR error circle areas. Approximately 80 per cent are identified as star‐forming or star‐bursting galaxies at z < 0.3. We also find that more than half of the counterparts have disturbed morphologies, with signs of past or present interactions. However, only 20 per cent of all the sources are uniquely matched with a single galaxy –40 per cent are blends of two or more of these nearby star‐forming galaxies, while another 20 per cent are likely blends of nearby and fainter galaxies. The final 20 per cent are likely to be more luminous IR galaxies at higher redshifts. The blended sources have an effect on the FIR source counts. In particular, taking into account realistic confusion or blending of sources, the differential FIR counts move down by a factor of ∼1.5 and steepen in the 100 to 400 mJy range.

A joint analysis of BLAST 250-500 μm and LABOCA 870 μm observations in the Extended Chandra Deep Field-South

“…This is plausible, since it is known that about 10 per cent of SCUBA sources are associated with double radio sources (e.g. Ivison et al 2002; Chapman et al 2005; Pope et al 2006; Ivison et al 2007), and Väisänen et al (2010) show that many of their 180 μm selected sources are blends of multiple galaxies at z < 0.3. We also note that a significant clustering signal on angular scales <1 arcmin has been measured for the LESS catalogue in excess of the Poisson expectation (Weiss et al 2009).…”

De-Confusing blended field images using graphs and bayesian priors

“…Apart from radio astronomy (Blain et al 1998;Condon 1974;Condon et al 2012), confusion noise is important for many other types of observations as well, such as FIR observations (Nguyen et al 2010;Magnelli et al 2013;Jeong et al 2005;Väisänen et al 2010;Gáspár & Rieke 2014;Kennedy & Wyatt 2012), X-ray deep observations (Barcons & Fabian 1990;Barcons 1992), gravitational waves (Crowder & Cornish 2004), weak lensing (Melchior & Viola 2012), Sunyaev-Zel'dovich (SZ) cluster surveys (Bartlett & Melin 2006), high precision astrometry (Hogg 2001) and studies of the galactic center (Eckart et al 2012;Stone et al 2012). A typical rule of thumb has been that one reaches diminishing returns when there are more than 1/30 sources per beam.…”