19 research outputs found
Exploring AGN Activity over Cosmic Time with the SKA
In this Chapter we present the motivation for undertaking both a wide and
deep survey with the SKA in the context of studying AGN activity across cosmic
time. With an rms down to 1 Jy/beam at 1 GHz over 1,000 - 5,000 deg in
1 year (wide tier band 1/2) and an rms down to 200 nJy/beam over 10 - 30
deg in 2000 hours (deep tier band 1/2), these surveys will directly detect
faint radio-loud and radio-quiet AGN (down to a 1 GHz radio luminosity of about
W/Hz at ). For the first time, this will enable us to
conduct detailed studies of the cosmic evolution of radio AGN activity to the
cosmic dawn (), covering all environmental densities.Comment: 17 pages, 7 figures, to appear as part of 'Continuum Science' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)
The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio luminosity functions of AGN with moderate-to-high radiative luminosities out to
We study a sample of 1,604 moderate-to-high radiative luminosity active
galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large
Project. These were classified by combining multiple AGN diagnostics: X-ray
data, mid-infrared data and broad-band spectral energy distribution fitting. We
decompose the total radio 1.4 GHz luminosity () into
the emission originating from star formation and AGN activity by measuring the
excess in relative to the infrared-radio
correlation of star-forming galaxies. To quantify the excess, for each source
we calculate the AGN fraction (), the fractional contribution
of AGN activity to . The majority of the HLAGN,
, are dominated by star-forming processes (),
while are dominated by AGN-related radio emission
(). We use the AGN-related 1.4 GHz emission to derive the 1.4
GHz AGN luminosity functions of HLAGN. By assuming pure density and pure
luminosity evolution models we constrain their cosmic evolution out to
, finding and . These evolutionary laws show that
the number and luminosity density of HLAGN increased from higher redshifts
() up to a maximum in the redshift range , followed by a
decline towards local values. By scaling the 1.4 GHz AGN luminosity to kinetic
luminosity using the standard conversion, we estimate the kinetic luminosity
density as a function of redshift. We compare our result to the semi-analytic
models of radio mode feedback finding that this feedback could have played an
important role in the context of AGN-host coevolution in HLAGN which show
evidence of AGN-related radio emission ().Comment: 20 pages, 14 figure
The XXL Survey XI: ATCA 2.1 GHz continuum observations
We present 2.1 GHz imaging with the Australia Telescope Compact Array (ATCA)
of a 6.5 deg^2 region within the XXM-Newton XXL South field using a band of
1.1-3.1 GHz. We achieve an angular resolution of 4.7" x 4.2" in the final radio
continuum map with a median rms noise level of 50 uJy/beam. We identify 1389
radio sources in the field with peak S/N >=5 and present the catalogue of
observed parameters. We find that 305 sources are resolved, of which 77 consist
of multiple radio components. These number counts are in agreement with those
found for the COSMOS-VLA 1.4 GHz survey. We derive spectral indices by a
comparison with the Sydney University Molongolo Sky Survey (SUMSS) 843MHz data.
We find an average spectral index of -0.78 and a scatter of 0.28, in line with
expectations. This pilot survey was conducted in preparation for a larger ATCA
program to observe the full 25 deg^2 southern XXL field. When complete, the
survey will provide a unique resource of sensitive, wide-field radio continuum
imaging with complementary X-ray data in the field. This will facilitate
studies of the physical mechanisms of radio-loud and radio-quiet AGNs and
galaxy clusters, and the role they play in galaxy evolution. The source
catalogue is publicly available online via the XXL Master Catalogue browser and
the Centre de Donn\'ees astronomiques de Strasbourg (CDS).Comment: 7 pages, 6 figures. Accepted by A&A 13th October 201
The XXL Survey: : XXIX. GMRT 610 MHz continuum observations
Accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30:4 square degrees, with rms <150 μJy beam -1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μJy beam -1, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μJy beam -1. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 × rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRTXXL- N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).Peer reviewedFinal Accepted Versio
The non-linear infrared-radio correlation of low-z galaxies: implications for redshift evolution, a new radio SFR recipe, and how to minimize selection bias
The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity-star formation rate (SFR) calibrations. In preparation for the new generation of radio surveys we revisit the IRRC of low-z galaxies by (a) drawing on the best currently available IR and 1.4 GHz radio photometry, plus ancillary data over the widest possible area, and (b) carefully assessing potential systematics. We compile a catalogue of ∼9,500 z < 0.2 galaxies and derive their 1.4 GHz radio (L1.4), total IR, and monochromatic IR luminosities in up to seven bands, allowing us to parameterize the wavelength-dependence of monochromatic IRRCs from 22-500 μm. For the first time for low-z samples, we quantify how poorly matched IR and radio survey depths bias measured median IR/radio ratios, q¯¯TIR , and discuss the level of biasing expected for low-z IRRC studies in ASKAP/MeerKAT fields. For our subset of ∼2,000 high-confidence star-forming galaxies we find a median q¯¯TIR of 2.54 (scatter: 0.17 dex). We show that q¯¯TIR correlates with L1.4, implying a non-linear IRRC with slope 1.11±0.01. Our new L1.4-SFR calibration, which incorporates this non-linearity, reproduces SFRs from panchromatic SED fits substantially better than previous IRRC-based recipes. Finally, we match the evolutionary slope of recently measured q¯¯TIR -redshift trends without having to invoke redshift evolution of the IRRC. In this framework, the redshift evolution of q¯¯TIR reported at GHz frequencies in the literature is the consequence of a partial, redshift-dependent sampling of a non-linear IRRC obeyed by low-z and distant galaxies
"Super-deblended" dust emission in galaxies: II. Far-IR to (sub)millimeter photometry and high redshift galaxy candidates in the full COSMOS field
We present a "super-deblended" far-infrared to (sub)millimeter photometric catalog in the Cosmic Evolution Survey (COSMOS), prepared with the method recently developed by Liu et al. 2018, with key adaptations. We obtain point spread function (PSF) fitting photometry at fixed prior positions including 88,008 galaxies detected in either VLA 1.4~GHz, 3~GHz and/or MIPS 24~μm images. By adding a specifically carved mass-selected sample (with an evolving stellar mass limit), a highly complete prior sample of 194,428 galaxies is achieved for deblending FIR/(sub)mm images. We performed ``active' removal of non relevant priors at FIR/(sub)mm bands using spectral energy distribution (SED) fitting and redshift information. In order to cope with the shallower COSMOS data we subtract from the maps the flux of faint non-fitted priors and explicitly account for the uncertainty of this step. The resulting photometry (including data from Spitzer, Herschel, SCUBA2, AzTEC, MAMBO and NSF's Karl G. Jansky Very Large Array at 3~GHz and 1.4~GHz) displays well behaved quasi-Gaussian uncertainties, calibrated from Monte Carlo simulations and tailored to observables (crowding, residual maps). Comparison to ALMA photometry for hundreds of sources provide a remarkable validation of the technique. We detect 11,220 galaxies over the 100--1200~μm range, extending to zphot∼7. We conservatively selected a sample of 85 z>4 high redshift candidates, significantly detected in the FIR/(sub)mm, often with secure radio and/or Spitzer/IRAC counterparts. This provides a chance to investigate the first generation of vigorous starburst galaxies (SFRs∼1000M⊙~yr−1). The photometric and value added catalogs are publicly released
Measuring cosmic density of neutral hydrogen via stacking the DINGO-VLA data
We use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H I of the Universe at redshifts z \u3c 0.1. Results are obtained using a stacking analysis, combining the H I signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H I mass measurement from the stacked spectrum, indicating an average H I mass of MHI=(1.67±0.18)×109 M⊙ role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eMHI=(1.67±0.18)×109 M⊙MHI=(1.67±0.18)×109 M⊙. The corresponding cosmic density of neutral atomic hydrogen is ΩHI=(0.38±0.04)×10−3 role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eΩHI=(0.38±0.04)×10−3ΩHI=(0.38±0.04)×10−3 at redshift of z = 0.051. These values are in good agreement with earlier results, implying there is no significant evolution of ΩHI role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eΩHIΩHI at lower redshifts
MIGHTEE-\HI: Possible interactions with the galaxy NGC~895
The transformation and evolution of a galaxy is strongly influenced by
interactions with its environment. Neutral hydrogen (\HI) is an excellent way
to trace these interactions. Here, we present \HI\ observations of the spiral
galaxy NGC~895, which was previously thought to be isolated. High-sensitivity
\HI\ observations from the MeerKAT large survey project MIGHTEE reveal possible
interaction features, such as extended spiral arms, and the two newly
discovered \HI\ companions, that drive us to change the narrative that it is an
isolated galaxy. We combine these observations with deep optical images from
the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and
its companions. We do find an excess of light in the outer parts of the
companion galaxy MGTHJ022138.1-052631 which could be an indication of
external perturbation and thus possible sign of interactions. Our analysis
shows that NGC~895 is an actively star-forming galaxy with a SFR of
, a value typical for high stellar mass
galaxies on the star forming main sequence. It is reasonable to state that
different mechanisms may have contributed to the observed features in NGC~895
and this emphasizes the need to revisit the target with more detailed
observations. Our work shows the high potential and synergy of using
state-of-the-art data in both \HI\ and optical to reveal a more complete
picture of galaxy environments.Comment: 14 pages, 10 figures. Accepted for publication in MNRA