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Intermediate Redshifts (intermediate + redshift)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The sizes of disc galaxies in intermediate-redshift clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007
S. P. Bamford
ABSTRACT We examine how the location of star formation within disc galaxies depends on environment at intermediate redshift. This is achieved by comparing emission-line (rem) and rest-frame B -band (rB) scalelengths for matched samples of 50 field and 19 cluster, star-forming, disc galaxies, with 0.25 ,z, 1.0 and MB,,19.5 mag. We find that at a given rB the majority of our cluster galaxies have rem smaller than those in the field, by 25 per cent on average. These results are compared with studies of local galaxies, which find a very similar behaviour. From the relations of rem and rB versus B -band absolute magnitude (MB) we infer that the difference between the intermediate- z cluster and field samples is mostly attributable to variation in rem at a given MB, while the rB versus MB relation is similar for the two samples. [source]

Supermassive black hole mass functions at intermediate redshifts from spheroid and AGN luminosity functions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006
Naoyuki Tamura
ABSTRACT Redshift evolution of supermassive black hole mass functions (BHMFs) is investigated up to z, 1. BHMFs at intermediate redshifts are calculated in two ways. One way is from early-type galaxy luminosity functions (LFs); we assume an MBH,Lsph correlation at a redshift by considering a passive evolution of Lsph in the local relationship. The resultant BHMFs (spheroid-BHMFs) from LFs of red-sequence galaxies indicate a slight decrease of number density with increasing redshift at MBH, 107.5,8 M,. Since a redshift evolution in slope and zeropoint of the MBH,Lsph relation is unlikely to be capable of making such an evolution in BHMF, the evolution of the spheroid-BHMFs is perhaps due mainly to the decreasing normalization in the galaxy LFs. We also derive BHMFs from LFs of morphologically selected early-type galaxies. The resultant BHMFs are similar to those from the red-sequence galaxies, but show a small discrepancy at z, 1 corresponding to an increase of supermassive black hole (SMBH) number density by ,0.3 dex. We also investigate how spheroid-BHMFs are affected by uncertainties existing in the derivation in detail. The other way of deriving a BHMF is based on the continuity equation for number density of SMBHs and LFs of active galactic nucleus (AGN). The resultant BHMFs (AGN-BHMFs) show no clear evolution out to z= 1 at MBH, 108 M,, but exhibit a significant decrease with redshift in the lower mass range. Interestingly, these AGN-BHMFs are quite different in the range of MBH, 108 M, from those derived by Merloni (2004), where the fundamental plane of black hole activity is exploited. Comparison of the spheroid-BHMFs with the AGN-BHMFs suggests that at MBH, 108 M,, the spheroid-BHMFs are broadly consistent with the AGN-BHMFs out to z, 1. Although the decrease of SMBH number density with redshift suggested by the spheroid-BHMFs is slightly faster than that suggested by the AGN-BHMFs, we presume this to be due at least partly to a selection effect on the LFs of red-sequence galaxies; the colour selection could miss spheroids with blue colours. The agreement between the spheroid-BHMFs and the AGN-BHMFs appears to support that most of the SMBHs are already hosted by massive spheroids at z, 1 and they evolve without significant mass growth since then. [source]

The redshift distribution of FIRST radio sources at 1 mJy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000
M. Magliocchetti
We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels. We targeted 365 sources and obtained 46 redshifts (13 per cent of the sample). We find that our sample is complete in redshift measurement to R,18.6, corresponding to z,0.2. Galaxies were assigned spectral types based on emission-line strengths. Early-type galaxies represent the largest subset (45 per cent) of the sample and have redshifts 0.15,z,0.5; late-type galaxies make up 15 per cent of the sample and have redshifts 0.05,z,0.2; starbursting galaxies are a small fraction (,6 per cent), and are very nearby (z,0.05). Some 9 per cent of the population have Seyfert 1/quasar-type spectra, all at z,0.8, and 4 per cent are Seyfert 2 type galaxies at intermediate redshifts (z,0.2). Using our measurements and data from the Phoenix survey (Hopkins et al.), we obtain an estimate for N(z) at S1.4 GHz,1 mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up ,5 per cent of the radio population at S,1 mJy. [source]

Dust-enshrouded star formation in XMM-LSS galaxy clusters

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
S. Temporin
Abstract In recent years, infrared studies of individual galaxy clusters at intermediate redshifts led to the identification of several luminous infrared galaxies (LIR > 1011 L,). These findings were interpreted as an evidence ofvigorous, dust-enshrouded star formation activity, hinting at the presence of an infrared Butcher-Oemler effect. In order to explore this effect, we have undertaken a statistical investigation based on a cluster sample drawn from the XMM-Newton Large Scale Structure survey (XMM-LSS) and exploiting the contiguous coverage of the XMM-LSS field by the Spitzer SWIRE legacy survey. We adopted a stacking technique to investigate the distribution of 24- , m sources out to the cluster periphery and compare it with the distribution of sources in a sample of control fields. Among putative cluster members, selected by means of photometric redshifts, we identified surprisingly high numbers of bright 24- , m sources toward intermediate redshift clusters (z > 0.3). Our analysis indicates the presence of an excess of bright mid-IR sources at redshift z > 0.3 at clustercentric radii ,200,500 kpc (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]