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 0.08 &lt; z &lt; 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 $z\sim0$ and $z\sim0.7$ 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 $\sim$13$\mu$m) 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 $z\sim0$ and $z\sim0.7$. 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 $z\sim$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 $z\sim$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 $\sigma$ 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 $\alpha_1=0.28\pm0.03$ below the break frequency $\nu_b=(4.1\pm0.2)$ GHz and $\alpha_2=1.16\pm0.04$ above, while a simple power-law model yields a single spectral index of $\alpha=0.64\pm0.07$. 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

The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies

We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z ~ 4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared-radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies' (SFGs) SED. To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published Very Large Array observations of the COSMOS field at 1:4 GHz and 3 GHz with unpublished Giant Meterwave Radio Telescope (GMRT) observations at 325MHz and 610MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (z ? [0:3; 4]; SFR = 100 M yr-1) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from a1 = 0:42-0:06 below a rest-frame frequency of 4:3 GHz to a2 = 0:94 ± 0:06 above 4:3 GHz. Our results are in line with previous low-redshift studies of HSFGs ( SFR &gt; 10 M yr-1) that show the SED of HSFGs to differ from the SED found for normal SFGs ( SFR &lt; 10 M yr-1). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free-free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q-z trend in SFGs

The first Swift X-ray Flash: The faint afterglow of XRF 050215B

We present the discovery of XRF 050215B and its afterglow. The burst was detected by the Swift BAT during the check-out phase and observations with the X-ray telescope began approximately 30 minutes after the burst. These observations found a faint, slowly fading X-ray afterglow near the centre of the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10 hours also revealed a very faint K-band afterglow. The afterglow appear unusual since it is very faint, especially in the infrared with K>20 only 9 hours post burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with alpha=0.8 and no evidence for steepening associated with the jet break to 10 days post burst. We discuss possible explanations for the faintness and slow decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap

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 z ~ 0 and z ~ 0.7 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 ~ 13 µm) and FUV luminosities gives the most inclination-independent SFRs and reduces the intrinsic SFR scatter of the methods we tested. However, applying the radiative transfer based method also gives corrections to the FUV SFR that are inclination independent and in agreement with the expected SFRs at both z ~ 0 and z ~ 0.7. SFR corrections based on the UV-slope perform worse than the other two methods we tested. For our local sample, the UV-slope method works on average, but does not remove inclination biases. At z ~ 0.7, we find that the UV-slope correction we used locally flattens the inclination dependence compared to the raw FUV measurements, but was not sufficient to correct for the large attenuation observed at z ~ 0.7.SL acknowledges funding from Deutsche Forschungsgemeinschaft (DFG) Grant BE 1837/13-1 r. ES and PL acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 694343). MTS acknowledges support from a Royal Society Leverhulme Trust Senior Research Fellowship (LT150041). BG acknowledges the support of the Australian Research Council as the recipient of a Future Fellowship (FT140101202)

Black hole masses, accretion rates and hot- and cold-mode accretion in radio galaxies at z ~ 1

Date of Acceptance: 25/11/2014Understanding the evolution of accretion activity is fundamental to our understanding of how galaxies form and evolve over the history of the Universe. We analyse a complete sample of 27 radio galaxies which includes both high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs), spanning a narrow redshift range of 0.9 < z < 1.1 and covering a factor of ~1000 in radio luminosity. Using data from the Spitzer Space Telescope combined with ground-based optical and near-infrared imaging, we show that the host galaxies have masses in the range of 10.7<log10(M/M⊙)<12.0with HEGs and LEGs exhibiting no difference in their mass distributions. We also find that HEGs accrete at significantly higher rates than LEGs, with the HEG/LEG division lying at an Eddington ratio of λ~0.04, which is in excellent agreement with theoretical predictions of where the accretion rate becomes radiatively inefficient, thus supporting the idea of HEGs and LEGs being powered by different modes of accretion. Our study also shows that at least up to L151MHz ~ 3 × 1027WHz-1 sr-1, HEGs and LEGs are indistinguishable in terms of their radio properties. From this result we infer that, at least for the lower radio luminosity range, another factor besides accretion rate must play an important role in the process of triggering jet activity.Peer reviewe

Automated mining of the ALMA archive in the COSMOS field (A3COSMOS): I. Robust ALMA continuum photometry catalogs and stellar mass and star formation properties for ∼700 galaxies at z = 0.5–6

The rich information on (sub)millimeter dust continuum emission from distant galaxies in the public Atacama Large Millimeter/submillimeter Array (ALMA) archive is contained in thousands of inhomogeneous observations from individual PI-led programs. To increase the usability of these data for studies deepening our understanding of galaxy evolution, we have developed automated mining pipelines for the ALMA archive in the COSMOS field (A3COSMOS) which efficiently exploit the available information for large numbers of galaxies across cosmic time, and keep the data products in sync with the increasing public ALMA archive: (a) a dedicated ALMA continuum imaging pipeline; (b) two complementary photometry pipelines for both blind source extraction and prior source fitting; (c) a counterpart association pipeline utilizing the multi-wavelength data available (including quality assessment based on machine-learning techniques); (d) an assessment of potential (sub-)mm line contribution to the measured ALMA continuum; and (e) extensive simulations to provide statistical corrections to biases and uncertainties in the ALMA continuum measurements. Application of these tools yields photometry catalogs with ∼ 1000 (sub-)mm detections (spurious fraction ∼ 8 − 12%) from over 1500 individual ALMA continuum images. Combined with ancillary photometric and redshift catalogs and the above quality assessments, we provide robust information on redshift, stellar mass and star formation rate for ∼700 galaxies at redshifts 0.5-6 in the COSMOS field (with undetermined selection function). The ALMA photometric measurements and galaxy properties are released publicly within our blind-extraction, prior-fitting and galaxy property catalogs, plus the images. These products will be updated on a regular basis in the future