186,350 research outputs found
A census of radio-selected AGNs on the COSMOS field and of their FIR properties
No full textWe use the new catalogue by Laigle et al. to provide a full census of VLA-COSMOS radio sources.We identify 90 per cent of such sources and sub-divide them into active galactic nuclei (AGNs) and star-forming galaxies on the basis of their radio luminosity. The AGN sample is complete with respect to radio selection at all z ≲ 3.5. Out of 704 AGNs, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al.: the probability for a radio-selected AGN to be detected at far-infrared (FIR) wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z ≲ 1 universe. At higher redshifts, they are indistinguishable from each other, as there is no difference between FIR-emitting AGNs and star-forming galaxies. Lastly, we focus on radio AGNs which show AGN emission at other wavelengths. We find that midinfrared (MIR) emission is mainly associated with ongoing star formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray
Deep spectroscopic luminosity function of Abell 85 : no evidence for a steep upturn of the faint-end slope
No full textIA, AD and ALS acknowledge partial support from the INFN grant InDark and from the grant Progetti di Ateneo TO Call 2012 0011 ‘Marco Polo’ of the University of Torino.We present a new deep determination of the spectroscopic luminosity function (LF) within the virial radius of the nearby and massive Abell 85 (A85) cluster down to the dwarf regime (M* + 6) using Very Large Telescope/Visible Multi-Object Spectrograph (VLT/VIMOS) spectra for ∼2000 galaxies with mr ≤ 21 mag and 〈μe,r〉 ≤ 24 mag arcsec−2. The resulting LF from 438 cluster members is best modelled by a double Schechter function due to the presence of a statistically significant upturn at the faint end. The amplitude of this upturn (αf ~ -1.58+0.19-0.15), however, is much smaller than that of the Sloan Digital Sky Survey (SDSS) composite photometric cluster LF by Popesso et al., αf ∼ −2. The faint-end slope of the LF in A85 is consistent, within the uncertainties, with that of the field. The red galaxy population dominates the LF at low luminosities, and is the main factor responsible for the upturn. The fact that the slopes of the spectroscopic LFs in the field and in a cluster as massive as A85 are similar suggests that the cluster environment does not play a major role in determining the abundance of low-mass galaxies.Peer reviewe
The environmental properties of radio-emitting AGN
No full textWe study the environmental properties of z less than or similar to 1.2
radio-selected active galactic nuclei (AGNs) belonging to the similar to
2 deg(2) of the COSMOS field, finding that about 20 per cent of them
appear within overdense structures. AGNs with P-1.4 GHz > 10(23.5) W
Hz(-1) sr(-1) are twice more likely to be found in clusters with respect
to fainter sources (similar to 38 per cent vs similar to 15 per cent),
just as radio-selected AGNs with stellar masses M-* > 10(11) M-circle
dot are twice more likely to be found in overdense environments with
respect to objects of lower mass (similar to 24 per cent vs similar to
11 per cent). Comparisons with galaxy samples further suggest that
radio-selected AGN of large stellar mass tend to avoid underdense
environments more than normal galaxies with the same stellar content.
Stellar masses also seem to determine the location of radio-active AGN
within clusters: similar to 100 per cent of the sources found as
satellite galaxies have M* < 10(11.3) M-circle dot, while similar to
100 per cent of the AGNs coinciding with a cluster central galaxy have
M* > 10(11) M-circle dot. No different location within the cluster is
instead observed for AGN of various radio luminosities. Radio AGN, which
also emit in the Mid-Infrared show a marked preference to be found as
isolated galaxies (similar to 70 per cent) at variance with those also
active in the X-ray that all seem to reside within overdensities. What
emerges from our work is a scenario whereby physical processes on sub-pc
and kpc scales (e.g. emission, respectively, related to the AGN and to
star formation) are strongly interconnected with the large-scale
environment of the AGN itself
Two-face(s): ionized and neutral gas winds in the local Universe
No full textWe present a comprehensive study of the Na I λ5890, 5895 (Na I D) resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample to look for neutral gas outflows in the local galaxies. Individual galaxy spectra are stacked in bins of stellar mass (M⋆) and star formation rate (SFR) to investigate the dependence of galactic wind occurrence and velocity as a function of the galaxy position in the SFR-M⋆ plane. While in most cases the interstellar medium (ISM) absorption and emission lines are at the galaxy systemic velocity, in massive galaxies (M⋆ > 5 × M☉) at the high SFR tail (SFR > 10-12 M☉ yr-1) we find evidence of a significant blue-shifted Na I D absorption, which we interpret as evidence of neutral outflowing gas. The occurrence of the blue-shifted absorption in the stacked spectra does not depend on the contribution of the nuclear activity as it is observed at the same significance for purely star-forming (SF) galaxies, active galactic nuclei (AGN), and composite systems at fixed SFR. We confirm, instead, for all classes of objects a clear dependence on the galaxy disc inclination: the blueshift is the largest and the Na I D equivalent width the smallest for face-on galaxies, while the absorption feature is at the systemic velocity for edge-on systems. This indicates that the neutral outflow is mostly perpendicular or biconical with respect to the galactic disc. We also compare the kinematics of the neutral gas with the ionized gas phase as traced by the [OIII]λ5007, Hα, [NII]λ6548, and [NII]λ6584 emission lines in the same galaxy spectra. Differently for the neutral gas phase, all the emission lines show evidence of perturbed kinematics only in galaxies with a significant level of nuclear activity, and they are independent of the galactic disc inclination. This would suggest that, while neutral winds originate from the galactic disc and are powered by SF feedback, ionized outflows are instead due to AGN feedback originating from the black hole accretion disc. In both the neutral and ionized gas phases, the observed wind velocities (of the order of 100-200 kms-1) suggest that the outflowing gas remains bound to the galaxy with no definitive effect on the gas reservoir
The AGN fraction–velocity dispersion relation in clusters of galaxies
No full textContext.Some previous investigations have found that the fraction
(fAGN) of active galactic nuclei (AGNs) is lower in clusters than
in the field. This can result from the suppression of galaxy–galaxy
mergers in high-velocity dispersion () clusters, if the
formation and/or fueling of AGNs is directly related to the merging
process.
Aims.We investigate the existence of a relation between fAGN
and in galaxy clusters in order to shed light on the
formation and evolution processes of AGNs and cluster galaxies.
Methods.Using data from the Sloan Digital Sky Survey we determine
fAGN and for the clusters in two samples, extracted
from the catalogs of Popesso et al. (2006a, A&A, in press) and Miller et al. (2005, AJ, 130, 968),
and excluding clusters with significant evidence for substructures.
Results.We find a significant anti-correlation. Clusters with lower and, respectively, higher than 500 km s-1 have AGN fractions of and , on
average. The relation can be described by a model
that assumes fAGN is proportional to the galaxies merging rate,
plus a constant.
Conclusions.Since fAGN increases with decreasing
, AGNs are likely to have played a significant rôle in
heating the intra-cluster medium and driving galaxy evolution in
cluster precursors and groups
Weak lensing observations of potentially X-ray underluminous galaxy clusters
No full textOptically selected clusters of galaxies display a relation between their optical mass estimates and their X-ray luminosities LX that has a large scatter. A substantial fraction of optically selected clusters have LX estimates or upper limits significantly below the values expected from the L_X-mass relation established for X-ray selected clusters, i.e., these clusters are X-ray underluminous for their mass. We attempt to confirm or falsify the X-ray underluminous nature of two clusters, Abell 315 and Abell 1456, by using weak gravitational lensing as a third and independent measure of the clusters' masses. We obtained optical wide-field imaging data and selected background galaxies using their colors and measured the shear exerted by the tidal field of the foreground galaxy clusters. We then fitted parametrized models to our shear catalogs. After accounting for projections of large-scale structure and halo triaxiality, we find that A 315 is significantly X-ray underluminous for its mass, while no significant lensing signal was detected for A 1456. We re-evaluate earlier kinematic and X-ray analyses of these two clusters and discuss the nature of the X-ray underluminous cluster A 315 and why A 1456 was probably erroneously identified as being X-ray underluminous
Light breeze in the local Universe
No full textWe analyze a complete spectroscopic sample of galaxies (~600 000) drawn from Sloan Digital Sky Survey (SDSS, DR7) to look for evidence of galactic winds in the local Universe. We focus on the shape of the [OIII]λ5007 emission line as a tracer of ionizing gas outflows. We stack our spectra in a fine grid of star formation rate (SFR) and stellar mass to analyze the dependence of winds on the position of galaxies in the SFR versus mass diagram. We do not find any significant evidence of broad and shifted [OIII]λ5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. We have also classified these galaxies as star-forming or AGN-dominated according to their position in the standard BPT diagram. We show how the average [OIII]λ5007 profile changes as a function of the nature of the dominant ionizing source. We find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. The AGN or composite AGNstar-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad Gaussian component that is blue-shifted from a narrow symmetric core. In particular, we find that the blue wings of the average [OIII]λ5007 profiles are increasingly prominent in the LINERs and Seyfert galaxies. We conclude that, through the identification of strong bulk motion as traced by the warm ionized gas, in the low-redshift Universe, "pure" star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected AGN seems to play a primary role. We discuss the implications of these results for the role of the quenching mechanism in the present-day Universe
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The dust and cold gas content of local star-forming galaxies
No full textWe use dust masses (Mdust) derived from far-infrared data and molecular gas masses (Mmol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, disc inclination, and gas metallicity. We use such proxies to estimate Mdust and Mmol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of Mdust and Mmol along and across the main sequence (MS) of SFGs. We find that Mdust and Mmol increase rapidly along the MS with increasing stellar mass (M∗), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M∗ is sub-linear for both Mdust and Mmol. Thus, the fraction of dust (fdust) and molecular gas mass (fmol) decreases monotonically towards large M∗. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of fdust and fgas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars
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