This paper presents the first measurement of the radio luminosity function of ‘jet-mode’ (radiatively inefficient) radio-AGN out to z = 1, in order to investigate the cosmic evolution of radio-AGN ...feedback. Eight radio source samples are combined to produce a catalogue of 211 radio-loud AGN with 0.5 < z < 1.0, which are spectroscopically classified into jet-mode and radiative-mode (radiatively efficient) AGN classes. Comparing with large samples of local radio-AGN from the Sloan Digital Sky Survey, the cosmic evolution of the radio luminosity function of each radio-AGN class is independently derived. Radiative-mode radio-AGN show an order of magnitude increase in space density out to z ≈ 1 at all luminosities, consistent with these AGN being fuelled by cold gas. In contrast, the space density of jet-mode radio-AGN decreases with increasing redshift at low radio luminosities (L
1.4 GHz ≲ 1024 W Hz−1) but increases at higher radio luminosities. Simple models are developed to explain the observed evolution. In the best-fitting models, the characteristic space density of jet-mode AGN declines with redshift in accordance with the declining space density of massive quiescent galaxies, which fuel them via cooling of gas in their hot haloes. A time delay of 1.5–2 Gyr may be present between the quenching of star formation and the onset of jet-mode radio-AGN activity. The behaviour at higher radio luminosities can be explained either by an increasing characteristic luminosity of jet-mode radio-AGN activity with redshift (roughly as (1 + z)3) or if the jet-mode radio-AGN population also includes some contribution of cold-gas-fuelled sources seen at a time when their accretion rate was low. Higher redshifts measurements would distinguish between these possibilities.
Abstract
We present the results of a new study of the relationship between infrared excess (IRX ≡ LIR/LUV), ultraviolet (UV) spectral slope (β) and stellar mass at redshifts 2 < z < 3, based on a ...deep Atacama Large Millimeter Array (ALMA) 1.3-mm continuum mosaic of the Hubble Ultra Deep Field. Excluding the most heavily obscured sources, we use a stacking analysis to show that z ≃ 2.5 star-forming galaxies in the mass range $9.25\le \log (M_{\ast }/\rm M_{{\odot }}) \le 10.75$ are fully consistent with the IRX–β relation expected for a relatively grey attenuation curve, similar to the commonly adopted Calzetti law. Based on a large, mass-complete sample of 2 ≤ z ≤ 3 star-forming galaxies drawn from multiple surveys, we proceed to derive a new empirical relationship between β and stellar mass, making it possible to predict UV attenuation (A1600) and IRX as a function of stellar mass, for any assumed attenuation law. Once again, we find that z ≃ 2.5 star-forming galaxies follow A1600–M* and IRX–M* relations consistent with a relatively grey attenuation law, and find no compelling evidence that star-forming galaxies at this epoch follow a reddening law as steep as the Small Magellanic Cloud (SMC) extinction curve. In fact, we use a simple simulation to demonstrate that previous determinations of the IRX–β relation may have been biased towards low values of IRX at red values of β, mimicking the signature expected for an SMC-like dust law. We show that this provides a plausible mechanism for reconciling apparently contradictory results in the literature and that, based on typical measurement uncertainties, stellar mass provides a cleaner prediction of UV attenuation than β. Although the situation at lower stellar masses remains uncertain, we conclude that for 2 < z < 3 star-forming galaxies with $\log (M_{\ast }/\rm M_{{\odot }}) \ge 9.75$, both the IRX–β and IRX–M* relations are well described by a Calzetti-like attenuation law.
The goal of this work is to determine the nature of the relation between morphology and accretion mode in radio galaxies, including environmental parameters. The CoNFIG extended catalogue (improved ...by new K
S-band identifications and estimated redshifts from UKIRT Infrared Deep Sky Survey (UKIDSS), and spectral index measurements from new GMRT observations) is used to select a sub-sample of 206 radio galaxies with z ≤ 0.3 over a wide range of radio luminosity, which are morphology-classified using the Fanaroff-Riley (FR) classification of extended radio sources. For each galaxy, spectroscopic data are retrieved to determine the high/low excitation status of the source, related to its accretion mode. Environmental factors, such as the host galaxy luminosity and a richness factor, are also computed, generally using the Sloan Digital Sky Survey data. We find the following results: (1) at a given radio luminosity, the FR morphological split of sources is consistent with being the same for both accretion modes. This remains true if analysis is restricted to only rich or only poor environments. If confirmed with a larger sample, this would imply that extended radio morphology is independent of the accretion mode of the black hole, depending only on the power of the resultant jet, and its interactions with the larger-scale environment. (2) Excitation modes seem to be linked to the source environment, with high-excitation galaxies found almost exclusively in low-density environments while low-excitation galaxies occupy a wider range of densities; this result is independent of FR morphology, and is consistent with the different fuelling mechanisms expected for these excitation modes. (3) Independent of excitation mode, FRI sources are found to lie in higher density environments, on average, than FRII sources, consistent with FRI sources having their jets disrupted by a denser surrounding medium. However, there is a significant overlap in environment between the two classes, and no clear driving factor between the FRI and FRII sources is found even when combining radio luminosity, accretion mode, large-scale environment and host galaxy luminosity.
A deep ALMA image of the Hubble Ultra Deep Field Dunlop, J. S; McLure, R. J; Biggs, A. D ...
Monthly notices of the Royal Astronomical Society,
04/2017, Letnik:
466, Številka:
1
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Abstract
We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ≃4.5 arcmin2 of the Hubble Ultra Deep Field (HUDF) imaged with Wide Field Camera ...3/IR on HST. Using a 45-pointing mosaic, we have obtained a homogeneous 1.3-mm image reaching σ1.3 ≃ 35 μJy, at a resolution of ≃0.7 arcsec. From an initial list of ≃50 > 3.5σ peaks, a rigorous analysis confirms 16 sources with S
1.3 > 120 μJy. All of these have secure galaxy counterparts with robust redshifts (〈z〉 = 2.15). Due to the unparalleled supporting data, the physical properties of the ALMA sources are well constrained, including their stellar masses (M
*) and UV+FIR star formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-redshift Universe; indeed at z ≥ 2 our ALMA sample contains seven of the nine galaxies in the HUDF with M
* ≥ 2 × 1010 M⊙, and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S
1.3 ≃ 10 μJy. We find strong evidence for a steep star-forming ‘main sequence’ at z ≃ 2, with SFR ∝M
* and a mean specific SFR ≃ 2.2 Gyr−1. Moreover, we find that ≃85 per cent of total star formation at z ≃ 2 is enshrouded in dust, with ≃65 per cent of all star formation at this epoch occurring in high-mass galaxies (M
* > 2 × 1010 M⊙), for which the average obscured:unobscured SF ratio is ≃200. Finally, we revisit the cosmic evolution of SFR density; we find this peaks at z ≃ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured at z ≃ 4.
Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solar masses. The growth of these black holes releases vast amounts of energy ...that powers quasars and other weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejecting ambient gas. A central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies.
We present a study of the prevalence and luminosity of active galactic nuclei (AGN; traced by optical spectra) as a function of both environment and galaxy interactions. For this study, we used a ...sample of more than 250 000 galaxies drawn from the Sloan Digital Sky Survey and, crucially, we controlled for the effect of both stellar mass and central star formation activity. Once these two factors are taken into account, the effect of the local density of galaxies and of one-on-one interactions is minimal in both the prevalence of AGN activity and AGN luminosity. This suggests that the level of nuclear activity depends primarily on the availability of cold gas in the nuclear regions of galaxies and that secular processes can drive the AGN activity in the majority of cases. Large-scale environment and galaxy interactions only affect AGN activity in an indirect manner, by influencing the central gas supply.
We present adaptive optics assisted integral field spectroscopy of nine Halpha-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrowband survey. Our observations map the kinematics of these ...star-forming galaxies on ~kpc scales. We demonstrate that within the interstellar medium of these galaxies, the velocity dispersion of the star-forming gas (sigma) follows a scaling relation sigma is proportional to Sigma super(1/)n sub(SF R) + constant (where Sigma sub(SFR) is the star formation surface density and the constant includes the stellar surface density). Assuming the disks are marginally stable (Toomre Q = 1), this follows from the Kennicutt-Schmidt relation (Sigma sub(SFR) = ASigman sub(gas)), and we derive best-fit parameters of n = 1.34 + or - 0.15 and A = 3.4 super(+2.5) sub(-1.6) x 10 super(-4) M sub(middot in circle) yr super(-1) kpc super(-2), consistent with the local relation, and implying cold molecular gas masses of M sub(gas) = 10 super(9-10) M sub(middot in circle) and molecular gas fractions of M sub(gas)/(M sub(gas) + M sub(sstarf)) = 0.3 + or - 0.1, with a range of 10%-75%. We also identify 11 ~kpc-scale star-forming regions (clumps) within our sample and show that their sizes are comparable to the wavelength of the fastest growing mode. The luminosities and velocity dispersions of these clumps follow the same scaling relations as local H II regions, although their star formation densities are a factor ~15 + or - 5 x higher than typically found locally. We discuss how the clump properties are related to the disk, and show that their high masses and luminosities are a consequence of the high disk surface density.
Context. Remnant radio galaxies represent the final dying phase of radio galaxy evolution in which the jets are no longer active. Remnants are rare in flux-limited samples, comprising at most a few ...percent. As a result of their rarity and because they are difficult to identify, this dying phase remains poorly understood and the luminosity evolution is largely unconstrained. Aims. Here we present the discovery and detailed analysis of a large (700 kpc) remnant radio galaxy with a low surface brightness that has been identified in LOFAR images at 150 MHz. Methods. By combining LOFAR data with new follow-up Westerbork observations and archival data at higher frequencies, we investigated the source morphology and spectral properties from 116 to 4850 MHz. By modelling the radio spectrum, we probed characteristic timescales of the radio activity. Results. The source has a relatively smooth, diffuse, amorphous appearance together with a very weak central compact core that is associated with the host galaxy located at z = 0.051. From our ageing and morphological analysis it is clear that the nuclear engine is currently switched off or, at most, active at a very low power state. We find that the source has remained visible in the remnant phase for about 60 Myr, significantly longer than its active phase of 15 Myr, despite being located outside a cluster. The host galaxy is currently interacting with another galaxy located at a projected separation of 15 kpc and a radial velocity offset of ~ 300 km s-1. This interaction may have played a role in the triggering and/or shut-down of the radio jets. Conclusions. The spectral shape of this remnant radio galaxy differs from most of the previously identified remnant sources, which show steep or curved spectra at low to intermediate frequencies. Our results demonstrate that remnant radio galaxies can show a wide range of evolutionary paths and spectral properties. In light of this finding and in preparation for new-generation deep low-frequency surveys, we discuss the selection criteria to be used to select representative samples of these sources.
Evolution of the radio-loud galaxy population Donoso, E.; Best, P. N.; Kauffmann, G.
Monthly notices of the Royal Astronomical Society,
01/2009, Letnik:
392, Številka:
2
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A catalogue of 14 453 radio-loud active galactic nuclei (AGN) with 1.4 GHz fluxes above 3.5 mJy in the redshift range 0.4 < z < 0.8, has been constructed from the cross-correlation of the National ...Radio Astronomy Observatory Very Large Array Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty centimetres (FIRST) radio surveys with the MegaZ-luminous red galaxy (MegaZ-LRG) catalogue of LRGs derived from Sloan Digital Sky Survey imaging data. The NVSS provides accurate flux measurements for extended sources, while the angular resolution of FIRST allows the host galaxy to be identified accurately. New techniques were developed for extending the cross-correlation algorithm to FIRST detections that are below the nominal 1 mJy signal-to-noise ratio limit of the catalogued sources. The matching criteria were tested and refined using Monte Carlo simulations, leading to an estimated reliability of ∼98.3 per cent and completeness level (for LRGs) of about 95 per cent for our new catalogue. We present a new determination of the luminosity function of radio AGN at z∼ 0.55 and compare this to the luminosity function of nearby (z∼ 0.1) radio sources from the Sloan Digital Sky Survey main survey. The comoving number density of radio AGN with luminosities less than 1025 W Hz−1 increases by a factor of ∼1.5 between z= 0.1 and 0.55. At higher luminosities, this factor increases sharply, reaching values of more than 10 at radio luminosities larger than 1026 W Hz−1. We then study how the relation between radio AGN and their host galaxies evolves with redshift. Our main conclusion is that the fraction of radio-loud AGN increases towards higher redshift in all massive galaxies, but the evolution is particularly strong for the lower mass galaxies in our sample. These trends may be understood if there are two classes of radio galaxies (likely associated with the ‘radio’ and ‘quasar mode’ dichotomy) that have different fuelling/triggering mechanisms and hence evolve in different ways.
Abstract
We present adaptive optics (AO) assisted SINFONI integral field unit (IFU) spectroscopy of 11 Hα emitting galaxies selected from the High-Z Emission Line Survey (HiZELS). We obtain spatially ...resolved dynamics on ∼kpc-scales of star-forming galaxies stellar mass M
⋆ = 109.5 − 10.5 M⊙ and star formation rate (SFR) = 2–30 M⊙ yr−1 near the peak of the cosmic star formation rate history. Combining these observations with our previous SINFONI-HiZELS campaign, we construct a sample of 20 homogeneously selected galaxies with IFU AO-aided observations – the ‘SHiZELS’ survey, with roughly equal number of galaxies per redshift slice, at z = 0.8, 1.47 and 2.23. We measure the dynamics and identify the major kinematic axis by modelling their velocity fields to extract rotational curves and infer their inclination-corrected rotational velocities. We explore the stellar mass Tully–Fisher relationship, finding that galaxies with higher velocity dispersions tend to deviate from this relation. Using kinemetry analyses, we find that galaxy interactions might be the dominant mechanism controlling the star formation activity at z = 2.23 but they become gradually less important down to z = 0.8. Metallicity gradients derived from the N ii/Hα emission line ratio show a median negative gradient for the SHiZELS survey of Δlog(O/H)/ΔR = −0.026 ± 0.008 dex kpc−1. We find that metal-rich galaxies tend to show negative gradients, whereas metal-poor galaxies tend to exhibit positive metallicity gradients. This result suggests that the accretion of pristine gas in the periphery of galaxies plays an important role in replenishing the gas in ‘typical’ star-forming galaxies.
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