730 research outputs found
Optical spectroscopy of radio galaxies in the 7C Redshift Survey
We present optical spectroscopy of all 49 radio galaxies in the 7C-I and
7C-II regions of the 7C Redshift Survey (7CRS). The low-frequency (151 MHz)
selected 7CRS sample contains all sources with flux-densities S_151 > 0.5 Jy in
three regions of the sky; 7C-I and 7C-II were chosen to overlap with the 5C6
and 5C7 surveys respectively, and cover a total sky area of 0.013 sr. The
sample has been completely identified and spectroscopy of the quasars and
broad-lined radio galaxies has been presented in Willott et al. (1998). Only
seven of the radio galaxies do not have redshift determinations from the
spectroscopy, giving a redshift completeness for the sample of >90%. The median
redshift of the 7CRS is 1.1. We present a composite 0.2<z<0.8 7CRS radio galaxy
spectrum and investigate the strengths of the 4000 Angstrom breaks in these
radio galaxies. We find an anti-correlation between the 4000 Angstrom break
strength and emission line luminosity, indicating that departures from old
elliptical galaxy continuum shapes are most likely due to non-stellar emission
associated with the active nucleus.Comment: 14 pages, 6 figures, MNRAS in pres
Dealing with the distress of people with intellectual disabilities reporting sexual assault and rape
When police officers interview people with intellectual disabilities who allege sexual assault and rape, they must establish rapport with the interviewee but deal with their distress in a way that does not compromise the interviewâs impartiality and its acceptability in court. Inspection of 19 videotaped interviews from an English police forceâs records reveals that the officers deal with expressed distress by choosing among three practices: minimal (e.g. okay) or no acknowledgement, acknowledging the expressed emotion as a matter of the complainantâs difficulty in proceeding (e.g. take your time) and rarely (and only if the complainants were apparently unable to resume their talk) explicit reference to their emotion (e.g. itâs obviously upsetting for you). We discuss these practices as ways of managing the conflicting demands of rapport and evidence-gathering
Extremely red radio galaxies
At least half the radio galaxies at z>1 in the 7C Redshift Survey have
extremely red colours (R-K>5), consistent with stellar populations which formed
at high redshift (z>5). We discuss the implications of this for the evolution
of massive galaxies in general and for the fraction of near-IR-selected EROs
which host AGN, a result which is now being tested by deep, hard X-ray surveys.
The conclusion is that many massive galaxies undergo at least two active
phases: one at z~5 when the black hole and stellar bulge formed and another at
z~1-2 when activity is triggered by an event such as an interaction or merger.Comment: 6 pages, 2 figures, to appear in the proceedings of the workshop on
"QSO hosts and their environments", IAA, Granada, 10-12 Jan 2001, Ed. I.
Marque
The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey
Context. Thanks to recent and ongoing large scale surveys, hundreds of brown
dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf
Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam
camera on the Canada-France-Hawaii Telescope telescope. Aims. Our objectives
are to find ultracool brown dwarfs and to constrain the field brown-dwarf
luminosity function and the mass function from a large and homogeneous sample
of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z'
images and follow them up with pointed near infrared (NIR) imaging on several
telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or
ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical
ultracool dwarfs i' - z' colours, found in 780 square degrees. Results. We have
currently completed the NIR follow-up on a large part of the survey for all
candidates from mid-L dwarfs down to the latest T dwarfs known with utracool
dwarfs' colours. This allows us to draw on a complete and well defined sample
of 102 ultracool dwarfs to investigate the luminosity function and space
density of field dwarfs. Conclusions. We found the density of late L5 to T0
dwarfs to be 2.0pm0.8 x 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs
to be 1.4pm0.3 x 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be
5.3pm3.1 x 10-3 objects pc-3 . We found that these results agree better with a
flat substellar mass function. Three latest dwarfs at the boundary between T
and Y dwarfs give the high density 8.3p9.0m5.1 x 10-3 objects pc-3. Although
the uncertainties are very large this suggests that many brown dwarfs should be
found in this late spectral type range, as expected from the cooling of brown
dwarfs, whatever their mass, down to very low temperature.Comment: Accepted for publication in A&
Extending the Canada-France brown Dwarfs Survey to the near-infrared: first ultracool brown dwarfs from CFBDSIR
We present the first results of the ongoing Canada-France Brown Dwarfs
Survey-InfraRed, hereafter CFBDSIR, a Near InfraRed extension to the optical
wide-field survey CFBDS. Our final objectives are to constrain ultracool
atmosphere physics by finding a statistically significant sample of objects
cooler than 650K and to explore the ultracool brown dwarf mass function
building on a well defined sample of such objects. Candidates are identified in
CFHT/WIRCam J and CFHT/MegaCam z' images using optimised psf-fitting, and we
follow them up with pointed near infrared imaging with SOFI at NTT. We finally
obtain low resolution spectroscopy of the coolest candidates to characterise
their atmospheric physics. We have so far analysed and followed up all
candidates on the first 66 square degrees of the 335 square degrees survey. We
identified 55 T-dwarfs candidates with z'-J > 3:5 and have confirmed six of
them as T-dwarfs, including 3 that are strong later-than-T8 candidates, based
on their far-red and NIR colours. We also present here the NIR spectra of one
of these ultracool dwarfs, CFBDSIR1458+1013 which confirms it as one of the
coolest brown dwarf known, possibly in the 550-600K temperature range. From the
completed survey we expect to discover 10 to 15 dwarfs later than T8, more than
doubling the known number of such objects. This will enable detailed studies of
their extreme atmospheric properties and provide a stronger statistical base
for studies of their luminosity function.Comment: A&A, Accepte
Radio galaxy evolution: what you can learn from a Brief Encounter
We describe the pitfalls encountered in deducing from classical double radio
source observables (luminosity, spectral index, redshift and linear size) the
essential nature of how these objects evolve. We discuss the key role played by
hotspots in governing the energy distribution of the lobes they feed, and
subsequent spectral evolution. We present images obtained using the new 74 MHz
receivers on the VLA and discuss constraints which these enforce on models of
the backflow and ages in classical doubles.Comment: invited talk at `Lifecycles of Radio Galaxies' workshop; eds John
Biretta et a
Mid-infrared sources in the ELAIS Deep X-ray Survey
We present a crossâcorrelation of the European Large Area Infrared Space Observatory (ISO) survey (ELAIS) with the ELAIS Deep Xâray Survey of the N1 and N2 fields. There are seven Chandra point sources with matches in the ELAIS Final Analysis 15âÎŒm catalogue, out of a total of 28 extragalactic ISO sources present in the Chandra fields. Five of these are consistent with active galactic nuclei (AGN) giving an AGN fraction of âŒ19 per cent in the 15âÎŒm flux range 0.8â6âmJy. We have coâadded the hard Xâray fluxes of the individually undetected ISO sources and find a low significance detection consistent with star formation in the remaining population. We combine our point source crossâcorrelation fraction with the XMMâNewton observations of the Lockman Hole and Chandra observations of the Hubble Deep Field North to constrain source count models of the midâinfrared galaxy population. The low dustâenshrouded AGN fraction in ELAIS implied by the number of crossâidentifications between the ELAIS midâinfrared sample and the Chandra point sources is encouraging for the use of midâinfrared surveys to constrain the cosmic star formation history, provided there are not further large undetected populations of Comptonâthick AGN
Constraints on the faint end of the quasar luminosity function at z~5 in the COSMOS field
We present the result of our low-luminosity quasar survey in the redshift
range of 4.5 < z < 5.5 in the COSMOS field. Using the COSMOS photometric
catalog, we selected 15 quasar candidates with 22 < i' < 24 at z~5, that are ~
3 mag fainter than the SDSS quasars in the same redshift range. We obtained
optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope
and did not identify any low-luminosity type-1 quasars at z~5 while a
low-luminosity type-2 quasar at z~5.07 was discovered. In order to constrain
the faint end of the quasar luminosity function at z~5, we calculated the
1sigma confidence upper limits of the space density of type-1 quasars. As a
result, the 1sigma confidence upper limits on the quasar space density are Phi<
1.33*10^{-7} Mpc^{-3} mag^{-1} for -24.52 < M_{1450} < -23.52 and Phi<
2.88*10^{-7} Mpc^{-3} mag^{-1} for -23.52 < M_{1450} < -22.52. The inferred
1sigma confidence upper limits of the space density are then used to provide
constrains on the faint-end slope and the break absolute magnitude of the
quasar luminosity function at z~5. We find that the quasar space density
decreases gradually as a function of redshift at low luminosity (M_{1450} ~
-23), being similar to the trend found for quasars with high luminosity
(M_{1450}<-26). This result is consistent with the so-called downsizing
evolution of quasars seen at lower redshifts.Comment: 8 pages, 9 figures, 1 table, accepted for publication in Ap
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