Exploring the infrared/radio correlation at high redshift

Ibar, E.; Cirasuolo, M.; Ivison, R. J.; Best, P. N.; Smail, Ian; Biggs, A. D.; Simpson, Chris; Dunlop, J. S.; Almaini, O.; McLure, R. J.; Foucaud, S.; Rawlings, Steve

doi:10.1111/j.1365-2966.2008.13077.x

Cited by 122 publications

(174 citation statements)

References 65 publications

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“…A possible way to overcome this resolution problem is by taking advantage of the observed correlation between the radio synchrotron and FIR emission in star-forming galaxies (van der Kruit 1971;Condon et al 1982;Helou et al 1985;Garrett 2002;Appleton et al 2004;Beelen et al 2006), which also seems to hold for SMGs out to z ∼ 3 (Kovács et al 2006;Vlahakis et al 2007;Ibar et al 2008;Michałowski et al 2009). Thanks to this FIR-radio correlation, radio interferometric observations can be used as a high-resolution proxy for the rest-frame FIR emission observed in the sub-mm.…”

Section: Fig 1 Summary Of the Results Presented Inmentioning

confidence: 99%

“…Given the low resolution and poor positional accuracy of the sub-mm map, it is very difficult to confirm the connection between SMM J04542-0301 and the optical/NIR lensed images. However, high resolution radio interferometric observations can help to establish this connection thanks to the FIR-radio correlation, which has being found to be valid for SMGs (Kovács et al 2006;Vlahakis et al 2007;Ibar et al 2008;Michałowski et al 2009). …”

Section: Discussionmentioning

confidence: 99%

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Radio counterpart of the lensed submm emission in the cluster MS0451.6-0305: new evidence for the merger scenario

Alba

Koopmans²,

Garrett³

et al. 2010

A&A

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Context. SMM J04542-0301 is an extended (∼1 ) submm source located near the core of the cluster MS0451.6-0305. It has been suggested that part of its emission arises from the interaction between a LBG and two EROs at z ∼ 2.9 that are multiply-imaged in the optical/NIR observations. However, the dramatic resolution difference between the sub-mm map and the optical/NIR images make it difficult to confirm this hypothesis. Aims. In a previous paper, we reported the detection of 1.4 GHz continuum radio emission coincident with this sub-mm source using VLA archival data. To fully understand the relation between this radio emission, the sub-mm emission, and the optical/IR multiplyimaged sources, we have re-observed the cluster with the VLA at higher resolution. Methods. The previous archival data has been re-reduced and combined with the new observations to produced a deep (∼10 μJy beam −1 ), high resolution (∼2 ) map centred on the cluster core. The strong lensing effect in the radio data has been quantified by constructing a new lens model of the cluster. Results. From the high resolution map we have robustly identified six radio sources located within SMM J 04542-0301. The brightest and most extended of these sources (RJ) is located in the middle of the sub-mm emission, and has no obvious counterpart in the optical/NIR. Three other detections (E1, E2 and E3) seem to be associated with the images of one of the EROs (B), although the NIR and radio emission appear to originate at slightly different positions in the source plane. The last two detections (CR1 and CR2), for which no optical/NIR counterpart have been found, seem to constitute two relatively compact emitting regions embedded in a ∼5 extended radio source located at the position of the sub-mm peak. The presence of this extended component (which contributes 38% of the total radio flux in this region) can only be explained if it is being produced by a lensed region of dust obscured star formation in the center of the merger. A comparison between the radio and sub-mm data at the same resolution suggests that E1, E2, E3, CR1 and CR2 are associated with the sub-mm emission. Conclusions. The radio observations presented in this paper provide strong observational evidence in favour of the merger hypothesis. However, the question if RJ is also contributing to the observed sub-mm emission remains open. These results illustrate the promising prospects for radio interferometry and strong gravitational lensing to study the internal structure of SMGs.

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Section: Fig 1 Summary Of the Results Presented Inmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Radio counterpart of the lensed submm emission in the cluster MS0451.6-0305: new evidence for the merger scenario

Alba

Koopmans²,

Garrett³

et al. 2010

A&A

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“…This correlation, observed primarily in local star-forming galaxies and starbursts, is found to hold out to high redshifts (z ≈ 2; e.g. Ibar et al 2008;Sargent et al 2010b;Ivison et al 2010;Mao et al 2011;Bourne et al 2011).…”

Section: Introductionmentioning

confidence: 99%

GOODS-Herschel: radio-excess signature of hidden AGN activity in distant star-forming galaxies

Moro

Alexander

Mullaney

et al. 2012

A&A

130

112

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Context. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z ≈ 2). Any excess of radio emission over that expected from star formation processes is most likely produced by an active galactic nucleus (AGN), often hidden by large amounts of dust and gas. Identifying these radio-excess sources will allow us to study a population of AGN unbiased by obscuration and thus find some of the most obscured, Compton-thick AGN, which are in large part unidentified even in the deepest X-ray and infrared (IR) surveys. Aims. We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Methods. Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 µm detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (∼1300 deg −2 ) out to redshift z ≈ 3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q < 1.68, 3σ) than the typical relation observed for star-forming galaxies (q ≈ 2.2). Results. We find that ≈45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The presence of an AGN is also confirmed by the detection of a compact radio core in deep VLBI 1.4 GHz observations for eight of our radio-excess sources (≈16%; ≈66% of the VLBI detected sources in this field), with the excess radio flux measured from our SED analysis agreeing, to within a factor of two, with the radio core emission measured by VLBI. We find that the fraction of radio-excess AGN increases with X-ray luminosity reaching ∼60% at L X ≈ 10 44 −10 45 erg s −1 , making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. Amongst the radio-excess AGN we can distinguish three groups of objects: i) AGN clearly identified in infrared (and often in X-rays), a fraction of which are likely to be distant Compton-thick AGN; ii) moderate luminosity AGN (L X 10 43 erg s −1 ) hosted in strong star-forming galaxies; and iii) a small fraction of low accretion-rate AGN hosted in passive (i.e. weak or no star-forming) galaxies. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching.

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“…For these reasons, and because of recent observational advances at both far-IR and radio wavelengths, there has been a deluge of FIRRC-related work recently, exploring why the correlation exists and whether it continues to hold at progressively larger look-back times (Garrett 2002;Appleton et al 2004;Ibar et al 2008;Seymour et al 2009;Ivison et al 2010;Sargent et al 2010a). Prevailing theory (e.g.…”

Section: Introductionmentioning

confidence: 99%

The far-infrared/radio correlation as probed byHerschel

Ivison

Magnelli

Ibar³

et al. 2010

A&A

223

153

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We set out to determine the ratio, q IR , of rest-frame 8-1000-μm flux, S IR , to monochromatic radio flux, S 1.4 GHz , for galaxies selected at far-infrared (IR) and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, T d , and to identify any far-IR-bright outliers -useful laboratories for exploring why the far-IR/radio correlation (FIRRC) is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-μm and 1.4-GHz samples, obtained using Herschel and the Very Large Array (VLA) in GOODS-North (-N). We determine bolometric IR output using ten bands spanning λ obs = 24−1250 μm, exploiting data from PACS and SPIRE (PEP; HerMES), as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L IR -matched sample, designed to reveal evolution of q IR with redshift, spanning log L IR = 11-12 L and z = 0−2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies in GOODS-N, we see tentative evidence of a break in the flux ratio, q IR , at L 1.4 GHz ∼ 10 22.7 W Hz −1 , where active galactic nuclei (AGN) are starting to dominate the radio power density, and of weaker correlations with redshift and T d . From our 250-μm-selected sample we identify a small number of far-IR-bright outliers, and see trends of q IR with L 1.4 GHz , L IR , T d and redshift, noting that some of these are inter-related. For our L IR -matched sample, there is no evidence that q IR changes significantly as we move back into the epoch of galaxy formation: we find q IR ∝ (1 + z) γ , where γ = −0.04 ± 0.03 at z = 0 − 2; however, discounting the least reliable data at z < 0.5 we find γ = −0.26 ± 0.07, modest evolution which may be related to the radio background seen by ARCADE 2, perhaps driven by <10-μJy radio activity amongst ordinary star-forming galaxies at z > 1.

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Exploring the infrared/radio correlation at high redshift

Cited by 122 publications

References 65 publications

Radio counterpart of the lensed submm emission in the cluster MS0451.6-0305: new evidence for the merger scenario

Radio counterpart of the lensed submm emission in the cluster MS0451.6-0305: new evidence for the merger scenario

GOODS-Herschel: radio-excess signature of hidden AGN activity in distant star-forming galaxies

The far-infrared/radio correlation as probed byHerschel

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