652 research outputs found
The Molecular Gas Content of z<0.1 Radio Galaxies: Linking the AGN Accretion Mode to Host Galaxy Properties
One of the main achievements in modern cosmology is the so-called `unified
model', which successfully describes most classes of active galactic nuclei
(AGN) within a single physical scheme. However, there is a particular class of
radio-luminous AGN that presently cannot be explained within this framework --
the `low-excitation' radio AGN (LERAGN). Recently, a scenario has been put
forward which predicts that LERAGN, and their regular `high-excitation' radio
AGN (HERAGN) counterparts represent different (red sequence vs. green valley)
phases of galaxy evolution. These different evolutionary states are also
expected to be reflected in their host galaxy properties, in particular their
cold gas content. To test this, here we present CO(1-0) observations toward a
sample of 11 of these systems conducted with CARMA. Combining our observations
with literature data, we derive molecular gas masses (or upper limits) for a
complete, representative, sample of 21 z<0.1 radio AGN. Our results yield that
HERAGN on average have a factor of ~7 higher gas masses than LERAGN. We also
infer younger stellar ages, lower stellar, halo, and central supermassive black
masses, as well as higher black hole accretion efficiencies in HERAGN relative
to LERAGN. These findings support the idea that high- and low-excitation radio
AGN form two physically distinct populations of galaxies that reflect different
stages of massive galaxy build-up.Comment: 8 pages, 4 figures, 4 tables; accepted for publication in Ap
On the occupation of X-ray selected galaxy groups by radio AGN since z=1.3
Previous clustering analysis of low-power radio AGN has indicated that they
preferentially live in massive groups. The X-ray surveys of the COSMOS field
have achieved a sensitivity at which these groups are directly detected out to
z=1.3. Making use of Chandra-, XMM- and VLA-COSMOS surveys we identify radio
AGN members (10**23.6 < L_1.4GHz/(W/Hz) < 10**25) of galaxy groups (10**13.2 <
M_200/M_sun < 10**14.4; 0.1<z<1.3) and study i) the radio AGN -- X-ray group
occupation statistics as a function of group mass, and ii) the distribution of
radio AGN within the groups. We find that radio AGN are preferentially
associated with galaxies close to the center (< 0.2r_200). Compared to our
control sample of group members matched in stellar mass and color to the radio
AGN host galaxies, we find a significant enhancement of radio AGN activity
associated with 10**13.6 < M_200/M_sun < 10**14 halos. We present the first
direct measurement of the halo occupation distribution (HOD) for radio AGN,
based on the total mass function of galaxy groups hosting radio AGN. Our
results suggest a possible deviation from the usually assumed power law HOD
model. We also find an overall increase of the fraction of radio AGN in galaxy
groups (<1r_200), relative to that in all environments.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
The radio AGN population dichotomy: Green valley Seyferts versus red sequence low-excitation AGN
Radio outflows of active galactic nuclei (AGN) are invoked in cosmological
models as a key feedback mechanism in the latest phases of massive galaxy
formation. Recently it has been suggested that the two major radio AGN
populations -- the powerful high-excitation, and the weak low-excitation radio
AGN (HERAGN and LERAGN, resp.) -- represent two earlier and later stages of
massive galaxy build-up. To test this, here we make use of a local (0.04<z<0.1)
sample of ~500 radio AGN with available optical spectroscopy, drawn from the
FIRST, NVSS, SDSS, and 3CRR surveys. A clear dichotomy is found between the
properties of low-excitation (absorption line AGN, and LINERs) and
high-excitation (Seyferts) radio AGN. The hosts of the first have the highest
stellar masses, reddest optical colors, and highest mass black holes but
accrete inefficiently (at low rates). On the other hand, the high-excitation
radio AGN have lower stellar masses, bluer optical colors (consistent with the
`green valley'), and lower mass black holes that accrete efficiently (at high
rates). Such properties can be explained if these two radio AGN populations
represent different stages in the formation of massive galaxies, and thus are
also linked to different phases of the `AGN feedback'.Comment: 5 pages, 4 figures, 1 table, to appear in ApJ
A Radio View of the Sky: the Cosmic History of Star-Forming and AGN Galaxies
We explore the cosmic evolution of radio detected star forming (SF) galaxies and active galactic nuclei (AGN), drawn from the VLA-COSMOS survey, out to z = 1.3. We present the 20 cm radio luminosity function for these populations, and find that SF galaxies evolve much more rapidly than low-power radio AGN. Our results imply that weak radio AGN (L_(1.4GHz) ā¤ 5Ć10^(25) WHz^(ā1)) occur in the most massive galaxies already at z ~ 1. They may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the āradio modeā AGN feedback in cosmological models
A closer view of the radio-FIR correlation: disentangling the contributions of star formation and AGN activity
We extend the Unified Radio Catalog, a catalog of sources detected by various
(NVSS, FIRST, WENSS, GB6) radio surveys, and SDSS, to IR wavelengths by
matching it to the IRAS Point and Faint Source catalogs. By fitting each
NVSS-selected galaxy's NUV-NIR spectral energy distribution (SED) with stellar
population synthesis models we add to the catalog star formation rates, stellar
masses, and attenuations.We further add information about optical emission line
properties for NVSS-selected galaxies with available SDSS spectroscopy. Using
an NVSS 20cm (F_{1.4GHz} ge 2.5mJy) selected sample, matched to the SDSS
spectroscopic ("main" galaxy and quasar) catalogs and IRAS data (0.04<z le 0.2)
we perform an in depth analysis of the radio-FIR correlation for various types
of galaxies, separated into i) quasars, ii) star forming, iii) composite, iv)
Seyfert, v) LINER and vi) absorption line galaxies using the standard optical
spectroscopic diagnostic tools. We utilize SED-based star formation rates to
independently quantify the source of radio and FIR emission in our galaxies.
Our results show that Seyfert galaxies have FIR/radio ratios lower than, but
still within the scatter of, the canonical value due to an additional (likely
AGN) contribution to their radio continuum emission. Furthermore, IR-detected
absorption and LINER galaxies are on average strongly dominated by AGN activity
in both their FIR and radio emission; however their average FIR/radio ratio is
consistent with that expected for star forming galaxies. In summary, we find
that most AGN-containing galaxies in our NVSS-IRAS-SDSS sample have FIR/radio
flux ratios indistinguishable from those of the star-forming galaxies that
define the radio-FIR correlation. Thus, attempts to separate AGNs from
star-forming galaxies by their FIR/radio flux ratios alone can separate only a
small fraction of the AGNs, such as the radio-loud quasars.Comment: 22 pages, 12 figures, 2 tables. Accepted for publication in Ap
Specific knowledge for managing ecotourism destinations
Management of ecotourism destinations is very demanding because of the specific and interdisciplinary knowledge that is necessary. Great knowledge, which consists of knowledge from human
and natural sciences at the same time, emphasizes the need for permanent education, formal and informal of ecotourism destination managers. In should be generally stated that countries which have a great areas and resources for ecotourism development should create a specific program for education about the relevant and
specific issues. Besides the availability of natural resources, knowledge is for sure the most important and basic element of ecotourism destination competitiveness improvement. In general these statements are applicable to all destinations which attractiveness arises from the quality and uniqueness of natural resources
Salami publication: definitions and examples
Salami publication or segmented publication is a distinct form of redundant publication which is usually characterized by similarity of hypothesis, methodology or results but not text similarity. These aspects of publications are not objectively detected by software applications and therefore present a serious threat to publication ethics. This article presents a practical approach for dealing with manuscripts suspected of salami publication during the submission process and after article publication in Biochemia Medica
Identifying dynamically young galaxy groups via wide-angle tail galaxies: A case study in the COSMOS field at z=0.53
We present an analysis of a wide-angle tail (WAT) radio galaxy located in a
galaxy group in the COSMOS field at a redshift of z=0.53 (hereafter CWAT-02).
We find that the host galaxy of CWAT-02 is the brightest galaxy in the group,
although it does not coincide with the center of mass of the system. Estimating
a) the velocity of CWAT-02, relative to the intra-cluster medium (ICM), and b)
the line-of-sight peculiar velocity of CWAT-02's host galaxy, relative to the
average velocity of the group, we find that both values are higher than those
expected for a dominant galaxy in a relaxed system. This suggests that
CWAT-02's host group is dynamically young and likely in the process of an
ongoing group merger. Our results are consistent with previous findings showing
that the presence of a wide-angle tail galaxy in a galaxy group or cluster can
be used as an indicator of dynamically young non-relaxed systems. Taking the
unrelaxed state of CWAT-02's host group into account, we discuss the impact of
radio-AGN heating from CWAT-02 onto its environment, in the context of the
missing baryon problem in galaxy groups. Our analysis strengthens recent
results suggesting that radio-AGN heating may be powerful enough to expel
baryons from galaxy groups.Comment: 8 pages, 6 figures, 1 table. Accepted for publication in Ap
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