[Paper Review] FIRBACK: I. A deep survey at 175 $μ$m with ISO, preliminary results

J.‐L. Puget, G. Lagache+11 more|arXiv (Cornell University)|Dec 2, 1998

Astronomy and Astrophysical Research3 citations

TL;DR

This paper presents preliminary results from FIRBACK, a deep far-infrared survey at 175 μm using the ISOPHOT instrument on the Infrared Space Observatory. It detects a source density about ten times higher than expected from IRAS deep surveys, indicating strong cosmological evolution in high-redshift infrared-luminous galaxies, which account for only 10% of the cosmic infrared background at this wavelength and require extrapolation to fainter fluxes to explain the full background.

ABSTRACT

FIRBACK is a deep survey conducted with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) at an effective wavelength of 175 $μ$m. We present here results we have obtained on the first field, the so-called Marano1 which covers around 0.25 square degree. We find that the source density for objects with a flux above 200 mJy exceeds the counts expected for sources found in the IRAS deep surveys with a similar flux by about an order of magnitude. Such an excess was expected on the basis of the high far infrared background detected with the FIRAS and DIRBE instruments aboard the Cosmic Background Explorer (COBE). These sources are likely to be redshifted infrared galaxies. The steep number counts indicate strong cosmological evolution in this population. The detected sources account for only 10 % of the cosmic IR background. An extrapolation of the counts down to about 10 mJy would be needeed to account for the whole background at this wavelength.

Motivation & Objective

• To measure the number counts of far-infrared sources at 175 μm using deep observations from the ISO satellite.
• To investigate the origin of the cosmic infrared background (CIB) detected by COBE's FIRAS and DIRBE instruments.
• To determine whether the excess source density observed in deep surveys can be attributed to high-redshift, evolved infrared galaxies.
• To assess the contribution of detected sources to the total cosmic infrared background at 175 μm.
• To evaluate the need for extrapolation of source counts to fainter fluxes to account for the full CIB.

Proposed method

• Conducted a deep survey using the ISOPHOT instrument on the Infrared Space Observatory (ISO) at an effective wavelength of 175 μm.
• Focused on the Marano1 field, covering approximately 0.25 square degrees.
• Measured source counts for objects with fluxes above 200 mJy.
• Compared the observed source counts with predictions from IRAS deep surveys and COBE background measurements.
• Used extrapolation of the observed counts to estimate the contribution to the cosmic infrared background.
• Evaluated the role of cosmological evolution in explaining the discrepancy between observed counts and expectations.

Experimental results

Research questions

• RQ1 What is the number count of far-infrared sources at 175 μm in a deep survey, and how does it compare to IRAS predictions?
• RQ2 Why is the source density in this survey significantly higher than expected from IRAS deep surveys?
• RQ3 To what extent do the detected sources account for the cosmic infrared background measured by COBE?
• RQ4 What is the role of cosmological evolution in the population of high-redshift infrared galaxies?
• RQ5 Is an extrapolation of the source counts to fainter fluxes necessary to account for the full cosmic infrared background at 175 μm?

Key findings

• The source density for objects with fluxes above 200 mJy exceeds the counts expected from IRAS deep surveys by approximately an order of magnitude.
• The observed excess is consistent with the high far-infrared background measured by COBE's FIRAS and DIRBE instruments.
• The detected sources are likely to be high-redshift, evolved infrared galaxies undergoing strong cosmological evolution.
• These sources account for only about 10% of the cosmic infrared background at 175 μm.
• Extrapolation of the source counts down to around 10 mJy is required to account for the full cosmic infrared background at this wavelength.
• The steep number counts suggest significant evolution in the luminosity function of the infrared galaxy population over cosmic time.