arXiv subjects

Jacinta Delhaize

Publications and source records attributed to Jacinta Delhaize.

23 records · Page 2Linked to original sources

arXiv2017

The infrared-radio correlation of spheroid- and disc-dominated star-forming galaxies to z $\sim$ 1.5 in the COSMOS field

Using infrared data from the Herschel Space Observatory and Karl G. Jansky Very Large Array (VLA) 3 GHz observations in the COSMOS field, we investigate the redshift evolution of the infrared-radio correlation (IRRC) for star-forming galaxies (SFGs) we classify as either spheroid- or disc-dominated based on their morphology. The sample predominantly consists of disc galaxies with stellar mass ${\gtrsim}10^{10}\,M_{\odot}$, and residing on the star-forming main sequence (MS). After the removal of AGN using standard approaches, we observe a significant difference between the redshift-evolution of the median IR/radio ratio $\overline{q}_{\mathrm{TIR}}$ of (i) a sample of ellipticals, plus discs with a substantial bulge component (`spheroid-dominated' SFGs) and, (ii) virtually pure discs and irregular systems (`disc-dominated' SFGs). The spheroid-dominated population follows a declining $\overline{q}_{\mathrm{TIR}}$ vs. $z$ trend similar to that measured in recent evolutionary studies of the IRRC. However, for disc-dominated galaxies, where radio and IR emission should be linked to star formation in the most straightforward way, we measure very little change in $\overline{q}_{\mathrm{TIR}}$. This suggests that low-redshift calibrations of radio emission as an SFR-tracer may remain valid out to at least $z\,{\simeq}\,1\,{-}\,1.5$ for pure star-forming systems. We find that the different redshift-evolution of $q_{\rm TIR}$ for the spheroid- and disc-dominated sample is mainly due to an increasing radio excess for spheroid-dominated galaxies at $z\,{\gtrsim}\,$0.8, hinting at some residual AGN activity in these systems. This finding demonstrates that in the absence of AGN the IRRC is independent of redshift, and that radio observations can therefore be used to estimate SFRs at all redshifts for genuinely star-forming galaxies.

astro-ph.GA↗

arXiv2017

The XXL Survey XVIII. ATCA 2.1 GHz radio source catalogue and source counts for the XXL-South field

The 2.1 GHz radio source catalogue of the 25 deg$^2$ ultimate XMM extragalactic survey south (XXL-S) field, observed with the Australia Telescope Compact Array (ATCA), is presented. The final radio mosaic achieved a resolution of $\sim$$4.8"$ and a median rms noise of $σ\approx41$ $μ$Jy/beam. To date, this is the largest area radio survey to reach this flux density level. A total of 6350 radio components above 5$σ$ are included in the component catalogue, 26.4% of which are resolved. Of these components, 111 were merged together to create 48 multiple-component radio sources, resulting in a total of 6287 radio sources in the source catalogue, 25.9% of which were resolved. A survival analysis revealed that the median spectral index of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz sources in the field is $α$ = $-$0.75, consistent with the values of $-0.7$ to $-0.8$ commonly used to characterise radio spectral energy distributions of active galactic nuclei (AGN). The 2.1 GHz and 1.4 GHz differential radio source counts are presented and compared to other 1.4 GHz radio surveys. The XXL-S source counts show good agreement with the other surveys.

astro-ph.GA↗

arXiv2015

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 Données astronomiques de Strasbourg (CDS).

astro-ph.GA↗

arXiv2015

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 $μ$Jy/beam at 1 GHz over 1,000 - 5,000 deg$^2$ in 1 year (wide tier band 1/2) and an rms down to 200 nJy/beam over 10 - 30 deg$^2$ 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 $2\times10^{23}$ W/Hz at $z=6$). For the first time, this will enable us to conduct detailed studies of the cosmic evolution of radio AGN activity to the cosmic dawn ($z\gtrsim6$), covering all environmental densities.

astro-ph.GA↗

arXiv2013

Detection of HI in distant galaxies using spectral stacking

Using the Parkes radio telescope, we study the 21cm neutral hydrogen (HI) properties of a sample of galaxies with redshifts z<0.13 extracted from the optical 2dF Galaxy Redshift Survey (2dFGRS). Galaxies at 0.04<z<0.13 are studied using new Parkes observations of a 42deg^2 field near the South Galactic Pole (SGP). A spectral stacking analysis of the 3,277 2dFGRS objects within this field results in a convincing 12sigma detection. For the low-redshift sample at 0<z<0.04, we use the 15,093 2dFGRS galaxies observed by the HI Parkes All-Sky Survey (HIPASS) and find a 31sigma stacked detection. We measure average HI masses of (6.93 +/- 0.17)*10^9 h^{-2} Msun and (1.48 +/- 0.03)*10^9 h^{-2} Msun for the SGP and HIPASS samples, respectively. Accounting for source confusion and sample bias, we find a cosmic HI mass density of Omega_HI=(3.19_{-0.59} ^{+0.43})*10^{-4} h^{-1} for the SGP sample and (2.82_{-0.59}^{+0.30})*10^{-4} h^{-1} for the HIPASS sample. This suggests no (12 +/- 23%) evolution in the cosmic HI density over the last ~1h^{-1} Gyr. Due to the very large effective volumes, cosmic variance in our determination of Omega_HI is considerably lower than previous estimates. Our stacking analysis reproduces and quantifies the expected trends in the HI mass and mass-to-light ratio of galaxies with redshift, luminosity and colour.

astro-ph.CO↗