16 research outputs found
American Astronomical Society logo iop-2016.png Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields. I. Spectral Index and Radio–FIR Correlation
We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North (σ = 3.5 μJy beam−1, synthesized beam size θ = 147 × 142, and 52 sources over 109 arcmin2) and GOODS-South (σ = 3.0 μJy beam−1, θ = 098 × 045, and 88 sources over 190 arcmin2) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around α = 0.8, but only within S 5 GHz \u3c 150 μJy. We demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radio–FIR correlation, and adopting a single value of α = 0.8 leads to a significant scatter and a strong bias in the analysis of the radio–FIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio–FIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe
Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields – I. Spectral Index and Radio-FIR Correlation
We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North (σ = 3.5 μJy beam−1, synthesized beam size θ = 147 × 142, and 52 sources over 109 arcmin2) and GOODS-South (σ = 3.0 μJy beam−1, θ = 098 × 045, and 88 sources over 190 arcmin2) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around α = 0.8, but only within S 5 GHz \u3c 150 μJy. We demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radio–FIR correlation, and adopting a single value of α = 0.8 leads to a significant scatter and a strong bias in the analysis of the radio–FIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio–FIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe
CHILES: HI morphology and galaxy environment at z=0.12 and z=0.17
We present a study of 16 HI-detected galaxies found in 178 hours of
observations from Epoch 1 of the COSMOS HI Large Extragalactic Survey (CHILES).
We focus on two redshift ranges between 0.108 <= z <= 0.127 and 0.162 <= z <=
0.183 which are among the worst affected by radio frequency interference (RFI).
While this represents only 10% of the total frequency coverage and 18% of the
total expected time on source compared to what will be the full CHILES survey,
we demonstrate that our data reduction pipeline recovers high quality data even
in regions severely impacted by RFI. We report on our in-depth testing of an
automated spectral line source finder to produce HI total intensity maps which
we present side-by-side with significance maps to evaluate the reliability of
the morphology recovered by the source finder. We recommend that this become a
common place manner of presenting data from upcoming HI surveys of resolved
objects. We use the COSMOS 20k group catalogue, and we extract filamentary
structure using the topological DisPerSE algorithm to evaluate the \hi\
morphology in the context of both local and large-scale environments and we
discuss the shortcomings of both methods. Many of the detections show disturbed
HI morphologies suggesting they have undergone a recent interaction which is
not evident from deep optical imaging alone. Overall, the sample showcases the
broad range of ways in which galaxies interact with their environment. This is
a first look at the population of galaxies and their local and large-scale
environments observed in HI by CHILES at redshifts beyond the z=0.1 Universe.Comment: 23 pages, 12 figures, 1 interactive 3D figure, accepted to MNRA
JWST's PEARLS: TN J1338-1942 -- I. Extreme jet triggered star-formation in a z=4.11 luminous radio galaxy
We present the first JWST observations of the z = 4.11 luminous radio galaxy TN J1338–1942, obtained as part of the ‘Prime Extragalactic Areas for Reionization and Lensing Science’ (‘PEARLS’) project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of log10(M/M) ∼ 10.9, TN J1338–1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is best fit by radiative shocks surrounded by extensive recent star formation. We estimate the total star-formation rate (SFR) could be as high as ∼ 1600 M yr−1 , with the SFR that we attribute to the jet induced burst conservatively 500 M yr−1. The mass-weighted age of the star-formation, tmass < 4 Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.KJD acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement number 892117 (HIZRAD) and support from the STFC through an Ernest Rutherford Fellowship (grant number ST/W003120/1). RAW, SHC, and RAJ acknowledge support from NASA JWST Interdisciplinary Scientist grants NAG5-12460, NNX14AN10G, and 80NSSC18K0200 from GSFC. Work by CJC acknowledges support from the European Research Council (ERC) Advanced Investigator Grant EPOCHS (788113). BLF thanks the Berkeley Center for Theoretical Physics for their hospitality during the writing of this paper. MAM acknowledges the support of a National Research Council of Canada Plaskett Fellowship, and the Australian Research Council center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE17010001. CNAW acknowledges funding from the JWST/NIRCam contract NASS-0215 to the University of Arizona. TAH is supported by an appointment to the NASA Postdoctoral Program (NPP) at NASA Goddard Space Flight Center, administered by Oak Ridge Associated Universities under contract with NASA.Peer reviewe
A search for high-redshift direct collapse black hole candidates in the PEARLS north ecliptic pole field
Direct-collapse black holes (DCBHs) of mass - that
form in HI-cooling halos in the early Universe are promising progenitors of the
supermassive black holes that fuel the observed quasars. Efficient accretion of the surrounding gas onto such DCBH
seeds may render them sufficiently bright for detection with the James Webb
Space Telescope (JWST) up to . Additionally, the very steep and
red spectral slope predicted across the -5 m wavelength range
of the JWST/NIRSpec instrument during their initial growth phase should make
them photometrically identifiable up to very high redshifts. Here, we present a
search for such DCBH candidates across the 34 arcmin in the first two
spokes of the JWST cycle-1 "Prime Extragalactic Areas for Reionization and
Lensing Science" (PEARLS) survey of the North Ecliptic Pole Time Domain Field
(NEP), covering 8 NIRCam filters down to a maximum depth of 29 AB mag.
We identify three objects with spectral energy distributions consistent with
the Pacucci et al. (2016) DCBH models. However, we also note that even with
data in 8 NIRCam filters, objects of this type remain degenerate with dusty
galaxies and obscured active galactic nuclei over a wide range of redshifts.
Follow-up spectroscopy would be required to pin down the nature of these
objects, and two of our DCBH candidates are sufficiently bright to make this
practical. Based on our sample of DCBH candidates and assumptions on the
typical duration of the DCBH steep-slope state, we set a conservative upper
limit of comoving Mpc (cMpc) on the
comoving density of host halos capable of hosting DCBHs with spectral energy
distributions similar to the Pacucci et al. (2016) models at -13.Comment: 10 pages, 6 figures, 1 table, submitted to A&