2,102 research outputs found
The ATESP 5 GHz radio survey IV. 19, 38, and 94 GHz observations and radio spectral energy distributions
It is now established that the faint radio population is a mixture of
star-forming galaxies and faint active galactic nuclei (AGNs), with the former
dominating below S(1.4GHz) \sim 100 muJy and the latter at larger flux
densities. The faint radio AGN component can itself be separated into two main
classes, mainly based on the host-galaxy properties: sources associated with
red/early-type galaxies (like radio galaxies) are the dominant class down to
\sim 100 muJy; quasar/Seyfert--like sources contribute an additional 10-20\%.
One of the major open questions regarding faint radio AGNs is the physical
process responsible for their radio emission. This work aims at investigating
this issue, with particular respect to the AGN component associated with
red/early-type galaxies. Such AGNs show, on average, flatter radio spectra than
radio galaxies and are mostly compact (<= 30 kpc in size). Various scenarios
have been proposed to explain their radio emission. For instance they could be
core/core-jet dominated radio galaxies, low-power BL LACs, or
advection-dominated accretion flow (ADAF) systems. We used the Australia
Telescope Compact Array (ATCA) to extend a previous follow-up multi-frequency
campaign to 38 and 94 GHz. (abridged)Comment: 16 pages, 7 figures, 6 tables. Accepted for publication in A&
The core fundamental plane of B2 radio galaxies
The photometric, structural and kinematical properties of the centers of
elliptical galaxies, harbor important information of the formation history of
the galaxies. In the case of non active elliptical galaxies these properties
are linked in a way that surface brightness, break radius and velocity
dispersion of the core lie on a fundamental plane similar to that found for
their global properties. We construct the Core Fundamental Plane (CFP) for a
sizeable sample of low redshift radio galaxies and compare it with that of non
radio ellipticals. To pursue this aim we combine data obtained from high
resolution HST images with medium resolution optical spectroscopy to derive the
photometric and kinematic properties of ~40 low redshift radio galaxies. We
find that the CFPs of radio galaxies is indistinguishable from that defined by
non radio elliptical galaxies of similar luminosity. The characteristics of the
CFP of radio galaxies are also consistent (same slope) with those of the
Fundamental Plane (FP) derived from the global properties of radio (and non
radio) elliptical galaxies. The similarity of CFP and FP for radio and non
radio ellipticals suggests that the active phase of these galaxies has minimal
effects for the structure of the galaxies.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Cognitive and social delays in the initiation of conversational repair
The exact timing of a conversational turn conveys important information to a listener. Most turns are initiated within 250ms after the previous turn. However, interlocutors take longer to initiate certain types of turns: those that either require more cognitive processing or are socially dispreferred. Many dispreferred turns are also cognitively demanding, so it is difficult to attribute specific conversational delays to social or cognitive mechanisms. In this paper, we evaluate the relative contribution of cognitive and social variables to the timing of utterances in conversation.
We focus on a type of turn that is socially dispreferred, cognitively demanding, and generally delayed: other-initiations of repair (OIRs). OIRs occur when a listener notices and decides to signal a comprehension problem (e.g., "What?"). We analyzed the Floor Transfer Offsets of 456 OIRs, and found that interlocutors initiated OIRs later when trouble sources had weaker discourse context or were shorter, and when the OIR was more face-threatening. Our results suggest that both cognitive and social variables contribute to the timing of delayed utterances in conversation. We discuss how attention, prediction, planning, and social preference manifest in the timing of turns
The lives of FR I radio galaxies
After a brief introduction to the morphological properties of FRI radio
sources, we discuss the possibility that FRI jets are relativistic at their
bases and decelerate quickly to non-relativistic velocities. From two-frequency
data we determine spectral index distributions and consequently the ages of FRI
sources. We show that in the large majority of cases synchrotron theory
provides unambiguous and plausible answers; in a few objects re-acceleration of
electrons may be needed. The derived ages are of the order 10^7-10^8 years, 2-4
times larger than the ages inferred from dynamical arguments and a factor 5-10
larger than the ages of FRII sources. The linear sizes of FRI and FRII sources
make it unlikely that many FRII's evolve into FRI's. A brief discussion is
given of the possibility that radio sources go through different cycles of
activity.Comment: 19 pages, including 13 figures, to appear in `Life Cycles of Radio
Galaxies', ed. J. Biretta et al., New Astronomy Review
The ATESP 5 GHz radio survey. II. Physical properties of the faint radio population
One of the most debated issues about sub-mJy radio sources, which are
responsible for the steepening of the 1.4 GHz source counts, is the origin of
their radio emission. Particularly interesting is the possibility of combining
radio spectral index information with other observational properties to assess
whether the sources are triggered by star formation or nuclear activity. The
aim of this work is to study the optical and near infrared properties of a
complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5
GHz as part of the ATESP radio survey. We use deep multi-colour (UBVRIJK)
images, mostly taken in the framework of the ESO Deep Public Survey, to
optically identify and derive photometric redshifts for the ATESP radio
sources. Deep optical coverage and extensive colour information are available
for 3/4 of the region covered by the radio sample. Typical depths of the images
are U~25, B~26, V~25.4, R~25.5, I~24.3, 19.5<K_s<20.2, J<22.2. Optical/near
infrared counterparts are found for ~78% (66/85) of the radio sources in the
region covered by the deep multi-colour imaging, and for 56 of these reliable
estimates of the redshift and type are derived. We find that many of the
sources with flat radio spectra are characterised by high radio-to-optical
ratios (R>1000), typical of classical powerful radio galaxies and quasars.
Flat-spectrum sources with low R values are preferentially identified with
early type galaxies, where the radio emission is most probably triggered by
low-luminosity active galactic nuclei. Considering both early type galaxies and
quasars as sources with an active nucleus, such sources largely dominate our
sample (78%). Flat-spectrum sources associated with early type galaxies are
quite compact (d<10-30 kpc), suggesting core-dominated radio emission.Comment: 15 pages, 13 figures, accepted for pubblication in A&
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