107 research outputs found
Accretion indicators for the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field
We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field
(SXDF). Using mid-IR (Spitzer MIPS 24 micron) data we expect to trace nuclear
accretion activity, even if it is obscured at optical wavelengths, unless the
obscuring column is extreme. Our results suggest that above the `FRI/FRII'
radio luminosity break most of the radio sources are associated with objects
that have excess mid-IR emission, only some of which are broad-line objects,
although there is one clear low-accretion-rate FRI. The fraction of objects
with mid-IR excess drops dramatically below the FRI/FRII break, although there
exists at least one high-accretion-rate QSO. Investigation of mid-IR and blue
excesses shows that they are correlated as predicted by a model in which a
torus of dust absorbs ~30% of the light, and the dust above and below the torus
scatters >~1% of the light.Comment: 4 pages, 2 figures, to appear in conference proceedings of 'A Century
of Cosmology; Past, Present and Future', Venice 200
Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio
Luminous infrared galaxies are systems enshrouded in dust, which absorbs most
of their optical/UV emission and re-radiates it in the mid- and far-infrared.
Radio observations are largely unaffected by dust obscuration, enabling us to
study the central regions of LIRGs in an unbiased manner. The main goal of this
project is to examine how the radio properties of local LIRGs relate to their
infrared spectral characteristics. Here we present an analysis of the radio
continuum properties of a subset of the Great Observatories All-sky LIRG Survey
(GOALS), which consists of 202 nearby systems (z<0.088). Our radio sample
consists of 35 systems, or 46 individual galaxies, that were observed at both
1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The
aim of the project is to use the radio imagery to probe the central kpc of
these LIRGs in search of active galactic nuclei. We used the archival data at
1.49 and 8.44 GHz to create radio-spectral-index maps using the standard
relation between flux density Sv and frequency v, S~v^-a, where a is the radio
spectral index. By studying the spatial variations in a, we classified the
objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the
presence of an active nucleus using the radio morphology, deviations from the
radio/infrared correlation, and spatially resolved spectral index maps, and
then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII]
line ratios and EQW of the 6.2 um PAH feature) and optical (BPT diagram) AGN
diagnostics. We find that 21 out of the 46 objects in our sample are radio-AGN,
9 are classified as starbursts (SB), and 16 are AGN/SB. After comparing to
other AGN diagnostics we find 3 objects out of the 46 that are identified as
AGN based on the radio analysis, but are not classified as such based on the
mid-infrared and optical AGN diagnostics presented in this study.Comment: 33 pages, 7 figures, 5 tables, to appear in A&
The evolution of the radio luminosity function of group galaxies in COSMOS
To understand the role of the galaxy group environment on galaxy evolution,
we present a study of radio luminosity functions (RLFs) of group galaxies based
on the Karl G. Jansky Very Large Array-COSMOS 3 GHz Large Project. The
radio-selected sample of 7826 COSMOS galaxies with robust optical/near-infrared
counterparts, excellent photometric coverage, and the COSMOS X-ray galaxy
groups (M_200c > 10^13.3 M_0) enables us to construct the RLF of group galaxies
(GGs) and their contribution to the total RLF since z ~ 2.3. Using the Markov
chain Monte Carlo algorithm, we fit a redshift-dependent pure luminosity
evolution model and a linear and power-law model to the luminosity functions.
We compare it with past RLF studies from VLA-COSMOS on individual populations
of radio-selected star-forming galaxies (SFGs) and galaxies hosting active
galactic nuclei (AGN). These populations are classified based on the presence
or absence of a radio excess concerning the star-formation rates derived from
the infrared emission. We find that the fraction of radio group galaxies
evolves by a factor of ~ 3 from z ~ 2 to the present day. The increase in the
galaxy group contribution is due to the radio activity in groups being nearly
constant at z < 1, while it is declining in the field. We show that massive
galaxies inside galaxy groups remain radio active below redshift 1, contrary to
the ones in the field. This evolution in the GG RLF is driven mainly by
satellite galaxies in groups. Group galaxies associated with SFGs dominate the
GG RLF at z_med = 0.3, while at z_med = 0.8, the peak in the RLF, coinciding
with a known overdensity in COSMOS, is mainly driven by AGN. The study provides
an observational probe for the accuracy of the numerical predictions of the
radio emission in galaxies in a group environment.Comment: submitted to A&A; 15 pages, 6 figures, 8 table
Bent It Like FRs: Extended Radio AGN in the COSMOS Field and Their Large-Scale Environment
A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.0
Bent It Like FRs: Extended Radio AGN in the COSMOS Field and Their Large-Scale Environment
A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.0
Bent it like frs: Extended radio agn in the cosmos field and their large-scale environment
A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.08 < z < 3, which we cross-correlate to a wide range of large-scale environments (X-ray galaxy groups, density fields, and cosmic web probes) in the COSMOS field. The median BA of FRs in COSMOS at zmed∼0.9 is 167.5 +11.5/−37.5 degrees. We do not find significant correlations between BA and large-scale environments within COSMOS covering scales from a few kpc to several hundred Mpc, nor between BA and host properties. Finally, we compare our observational data to magnetohydrodynamical (MHD) adaptive-mesh simulations ENZO-MHD of two FR sources at z = 0.5 and at z = 1. Although the scatter in BA of the observed data is large, we see an agreement between observations and simulations in the bent angles of FRs, following a mild redshift evolution with BA. We conclude that, for a given object, the dominant mechanism affecting the radio structures of FRs could be the evolution of the ambient medium, where higher densities of the intergalactic medium at lower redshifts as probed by our study allow more space for jet interactions
Probing star formation and ISM properties using galaxy disk inclination II: testing typical FUV attenuation corrections out to z~0.7
We evaluate dust-corrected far ultraviolet (FUV) star formation rates (SFRs) for samples of star-forming galaxies at and and find significant differences between values obtained through corrections based on UV colour, from a hybrid mid-infrared (MIR) plus FUV relation, and from a radiative transfer based attenuation correction method. The performances of the attenuation correction methods are assessed by their ability to remove the dependency of the corrected SFR on inclination, as well as returning, on average, the expected population mean SFR. We find that combining MIR (rest-frame 13m) and FUV luminosities gives the most inclination independent SFRs and reduces the intrinsic SFR scatter out of the methods tested. However, applying the radiative transfer based method of Tuffs et al. gives corrections to the FUV SFR that are inclination independent and in agreement with the expected SFRs at both and . SFR corrections based on the UV-slope perform worse than the other two methods tested. For our local sample, the UV-slope method works on average but does not remove inclination biases. At 0.7 we find that the UV-slope correction used locally flattens the inclination dependence compared to the raw FUV measurements but was not sufficient to correct for the large attenuation observed at 0.7
The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of active galactic nuclei
As the SKA is expected to be operational in the next decade, investigations
of the radio sky in the range of 100 MHz to 10 GHz have become important for
simulations of the SKA observations. In determining physical properties of
galaxies from radio data, the radio SED is often assumed to be described by a
simple power law, usually with a spectral index of 0.7 for all sources. Even
though radio SEDs have been shown to exhibit deviations from this assumption,
both in differing spectral indices and complex spectral shapes, it is often
presumed that their individual differences cancel out in large samples. We
constructed the average radio SED of radio-excess active galactic nuclei
(RxAGN), defined as those that exhibit a 3 radio luminosity excess
with respect to the value expected only from contribution from star formation,
out to z~4. We combined VLA observations of the COSMOS field at 1.4 GHz and 3
GHz with GMRT observations at 325 MHz and 610 MHz. To account for nondetections
in the GMRT maps, we employed the survival analysis technique. We selected a
sample of RxAGN out to z~4. We find that a sample of RxAGN can be described by
a spectral index of below the break frequency
GHz and above, while a simple
power-law model yields a single spectral index of . By
binning in 1.4 GHz radio luminosity and redshift, we find that the power-law
spectral index, as well as broken power-law spectral indices, may increase for
larger source sizes, while the power-law spectral index and lower-frequency (<4
GHz) broken power-law spectral index are additionally positively correlated
with redshift.Comment: 12 pages, 11 figure
- …