The University of Southampton
University of Southampton Institutional Repository

The star formation history of the Universe as revealed by deep radio observations

The star formation history of the Universe as revealed by deep radio observations
The star formation history of the Universe as revealed by deep radio observations
Discerning the exact nature of the sub-mJy radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep ground based optical follow-up and observations from the Spitzer Space Telescope we are able to disentangle the radio-selected active galactic nuclei (AGN) and star-forming galaxy (SFG) populations for the first time in a deep multifrequency VLA/MERLIN Survey of the 13HXMM–Newton/Chandra Deep Field. The discrimination diagnostics include radio morphology, radio spectral index, radio/near-infrared (near-IR) and mid-IR/radio flux density ratios. We are now able to calculate the extragalactic Euclidean normalized source counts separately for AGN and SFGs. We find that while SFGs dominate at the faintest flux densities and account for the majority of the upturn in the counts, AGN still make up around one quarter of the counts at ?50 ?Jy (1.4 GHz). Using radio luminosity as an unobscured star formation rate (SFR) measure we are then able to examine the comoving SFR density of the Universe up to z= 3 which agrees well with measures at other wavelengths. We find a rough correlation of SFR with stellar mass for both the sample presented here and a sample of local radio-selected SFGs from the 6df-NVSS survey. This work also confirms the existence of, and provides alternative evidence for, the evolution of distribution of star formation by galaxy mass: 'downsizing'. As both these samples are SFR-selected, this result suggests that there is a maximum SFR for a given galaxy that depends linearly on its stellar mass. The low 'characteristic times' (inverse specific SFR) of the SFGs in our sample are similar to those of the 6dF-NVSS sample, implying that most of these sources are in a current phase of enhanced star formation.

galaxies: evolution, galaxies: starburst, radio continuum: galaxies
1365-2966
1695-1708
Seymour, N.
9642614b-0e44-4bb4-8e6d-28e9875c088b
Dwelly, T.
c4368952-92c1-45c1-b3c5-5a2a4f18fa60
Moss, D.
52b4b19f-a36d-44c6-b165-d6025587b209
McHardy, I.
4f215137-9cc4-4a08-982e-772a0b24c17e
Zoghbi, A.
06e09477-a459-4c81-b7fb-cafeb08b69f4
Rieke, G.
e5caa2c8-911e-4be3-b03a-2fccffc3b048
Page, M.
eff24007-74aa-4b22-8a94-beb6631955b8
Hopkins, A.
d5fbfd4c-dc5d-4368-b0be-431710a31ebe
Loaring, N.
bcd99b67-6dc0-45b7-abc0-f66db506be1e
Seymour, N.
9642614b-0e44-4bb4-8e6d-28e9875c088b
Dwelly, T.
c4368952-92c1-45c1-b3c5-5a2a4f18fa60
Moss, D.
52b4b19f-a36d-44c6-b165-d6025587b209
McHardy, I.
4f215137-9cc4-4a08-982e-772a0b24c17e
Zoghbi, A.
06e09477-a459-4c81-b7fb-cafeb08b69f4
Rieke, G.
e5caa2c8-911e-4be3-b03a-2fccffc3b048
Page, M.
eff24007-74aa-4b22-8a94-beb6631955b8
Hopkins, A.
d5fbfd4c-dc5d-4368-b0be-431710a31ebe
Loaring, N.
bcd99b67-6dc0-45b7-abc0-f66db506be1e

Seymour, N., Dwelly, T., Moss, D., McHardy, I., Zoghbi, A., Rieke, G., Page, M., Hopkins, A. and Loaring, N. (2008) The star formation history of the Universe as revealed by deep radio observations. Monthly Notices of the Royal Astronomical Society, 386 (3), 1695-1708. (doi:10.1111/j.1365-2966.2008.13166.x).

Record type: Article

Abstract

Discerning the exact nature of the sub-mJy radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep ground based optical follow-up and observations from the Spitzer Space Telescope we are able to disentangle the radio-selected active galactic nuclei (AGN) and star-forming galaxy (SFG) populations for the first time in a deep multifrequency VLA/MERLIN Survey of the 13HXMM–Newton/Chandra Deep Field. The discrimination diagnostics include radio morphology, radio spectral index, radio/near-infrared (near-IR) and mid-IR/radio flux density ratios. We are now able to calculate the extragalactic Euclidean normalized source counts separately for AGN and SFGs. We find that while SFGs dominate at the faintest flux densities and account for the majority of the upturn in the counts, AGN still make up around one quarter of the counts at ?50 ?Jy (1.4 GHz). Using radio luminosity as an unobscured star formation rate (SFR) measure we are then able to examine the comoving SFR density of the Universe up to z= 3 which agrees well with measures at other wavelengths. We find a rough correlation of SFR with stellar mass for both the sample presented here and a sample of local radio-selected SFGs from the 6df-NVSS survey. This work also confirms the existence of, and provides alternative evidence for, the evolution of distribution of star formation by galaxy mass: 'downsizing'. As both these samples are SFR-selected, this result suggests that there is a maximum SFR for a given galaxy that depends linearly on its stellar mass. The low 'characteristic times' (inverse specific SFR) of the SFGs in our sample are similar to those of the 6dF-NVSS sample, implying that most of these sources are in a current phase of enhanced star formation.

This record has no associated files available for download.

More information

Published date: 21 May 2008
Keywords: galaxies: evolution, galaxies: starburst, radio continuum: galaxies
Organisations: Astronomy and Space Science

Identifiers

Local EPrints ID: 144651
URI: http://eprints.soton.ac.uk/id/eprint/144651
ISSN: 1365-2966
PURE UUID: 77cd8eb6-eff7-47e1-946e-6e98a7969eda

Catalogue record

Date deposited: 26 May 2010 15:54
Last modified: 14 Mar 2024 00:47

Export record

Altmetrics

Contributors

Author: N. Seymour
Author: T. Dwelly
Author: D. Moss
Author: I. McHardy
Author: A. Zoghbi
Author: G. Rieke
Author: M. Page
Author: A. Hopkins
Author: N. Loaring

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×