A strongly star-forming group : three massive galaxies associated with a quasi-stellar object
Carrera, F. J.
Page, M. J.
Stevens, J. A.
Ivison, R. J.
We present here photometric redshift confirmation of the presence of large-scale structure around the z = 1.82 quasi-stellar object (QSO) RX J0941, which shows an overdensity of submillimetre (submm) sources. Radio imaging confirms the presence of the submm sources and pinpoints their likely optical near-infrared (NIR) counterparts. Four of the five submm sources present in this field (including the QSO) have counterparts with redshifts compatible with z = 1.82. We show that our photometric redshifts are robust against the use of different spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M-*/M-circle dot) similar to 11.5 +/- 0.2, slightly larger than the Schechter mass of present-day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the five Submillimetre Common-User Bolometer Array (SCUBA) sources. The emission of RX J0941 is dominated by reprocessed active galactic nucleus (AGN) emission in the observed mid-IR (MIR) range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above similar to 24 mu m, with star formation rates similar to 2000 M-circle dot yr-1, central dust masses log(M-dust/M-circle dot) similar to 9 +/- 0.5 and hence central gas masses log(M-gas/M-circle dot) similar to 10.7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24 mu m flux, we derive a maximum 2-10 keV X-ray luminosity of 1044 erg s-1 for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(M-center dot/M-circle dot) less than or similar to 8 and hence stellar-to-black hole mass ratios about 1 order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole mass ratios can be reached if similar to 1.3 per cent of the available nuclear gas mass is accreted.
Published inMonthly Notices of the Royal Astronomical Society
MetadataShow full item record
Showing items related by title, author, creator and subject.
The H alpha galaxy survey. I. The galaxy sample, H alpha narrow-band observations and star formation parameters for 334 galaxies James, P.A.; Shane, N.S.; Beckman, J.E.; Cardwell, A.; Collins, C.A.; Etherton, J.; de Jong, R.S.; Fathi, K.; Knapen, J.; Peletier, R.F.; Percival, S.M.; Pollacco, D.L.; Seigar, M.S.; Stedman, S. (2004)We discuss the selection and observations of a large sample of nearby galaxies, which we are using to quantify the star formation activity in the local Universe. The sample consists of 334 galaxies across all Hubble types ...
On the Key Processes that Drive Galaxy Evolution: the Role of Galaxy Mergers, Accretion, Local Environment and Feedback in Shaping the Present-Day Universe Martin, Garreth (2019-07-17)The study of galaxy evolution is a fundamental discipline in modern astrophysics, dealing with how and why galaxies of all types evolve over time. The diversity of present-day galaxies is a reflection of the processes ...
X-ray constraints on galaxy-gas-jet interactions in the Dumbbell Galaxies NGC4782 and NGC4783 in the LGG316 group Machacek, M.E.; Kraft, R.P.; Jones, C.; Forman, W.R.; Hardcastle, M.J. (2007)