We report a highly significant (>10σ) spatial correlation between galaxies with S
350 μm ≥ 30 mJy detected in the equatorial fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) ...with estimated redshifts ≳ 1.5, and Sloan Digital Sky Survey (SDSS) or Galaxy And Mass Assembly (GAMA) galaxies at 0.2 ≤ z ≤ 0.6. The significance of the cross-correlation is much higher than those reported so far for samples with non-overlapping redshift distributions selected in other wavebands. Extensive, realistic simulations of clustered sub-mm galaxies amplified by foreground structures confirm that the cross-correlation can be explained by weak gravitational lensing (μ < 2). The simulations also show that the measured amplitude and range of angular scales of the signal are larger than can be accounted for by galaxy–galaxy weak lensing. However, for scales ≲ 2 arcmin, the signal can be reproduced if SDSS/GAMA galaxies act as signposts of galaxy groups/clusters with halo masses in the range 1013.2–1014.5 M⊙. The signal detected on larger scales appears to reflect the clustering of such haloes.
This paper presents a compilation of clustering results taken from the literature for galaxies with highly enhanced (SFR 30-103 M yr−1) star formation activity observed in the redshift range z = 0-3. ...We show that, irrespective of the selection technique and only very mildly depending on the star-forming rate, the clustering lengths of these objects present a sharp increase of about a factor 3 between z ∼ 1 and z ∼ 2, going from values of ∼5 Mpc to about 15 Mpc and higher. This behaviour is reflected in the trend of the masses of the dark matter hosts of star-forming galaxies which increase from ∼1011.5 to ∼1013.5 M between z ∼ 1 and z ∼ 2. Our analysis shows that galaxies which actively form stars at high redshifts are not the same population of sources we observe in the more local universe. In fact, vigorous star formation in the early universe is hosted by very massive structures, while for z 1 a comparable activity is encountered in much smaller systems, consistent with the downsizing scenario. The available clustering data can hardly be reconciled with merging as the main trigger for intense star formation activity at high redshifts. We further argue that, after a characteristic time-scale of ∼1 Gyr, massive star-forming galaxies at z 2 evolve into z 1.5 passive galaxies with large (M
* 1011-1012 M) stellar masses.
We present a new approach to tackling the issue of radio loudness in quasars. We constrain a (simple) prescription for the intrinsic distribution of radio-to-optical ratios by comparing properties of ...Monte Carlo simulated samples with those of observed optically selected quasars. We find strong evidence for a dependence of the radio luminosity on the optical one, even though with a large scatter. The dependence of the fraction of radio-loud quasars on apparent and absolute optical magnitudes results in a selection effect related to the radio and optical limits of current surveys. The intrinsic distribution of the radio-to-optical ratios shows a peak at R*1.4∼ 0.3, with only ≲5 per cent of objects being included in a high-R*1.4 tail, which identifies the radio-loud regime. No lack or deficit of sources — but only a steep transition region — is present between the radio-loud and radio-quiet populations at any R*1.4. Briefly, we discuss possible origins for this behaviour (e.g. an absence of jets in radio-quiet sources, a large range of radiative radio efficiency, different lifetimes for the accretion and jet ejection phenomena, etc.).
Dark matter constitutes the great majority of the matter content in the Universe, but its microscopic nature remains an intriguing mystery, with profound implications for particle physics, ...astrophysics and cosmology. Here we shed light on the longstanding issue of whether the dark matter is warm or cold by combining the measurements of the galaxy luminosity functions out to high redshifts 0z∼ 1 from the Hubble Space Telescope with the recent cosmological data on the reionization history of the Universe from the Planck mission. We derive robust and tight bounds on the mass of warm dark matter particle, finding that the current data require it to be in the narrow range between 2 and 3 keV . In addition, we show that a mass not exceeding 3 keV is also concurrently indicated by astrophysical constraints related to the local number of satellites in Milky Way-sized galaxies, though it is in marginal tension with analysis of the Lyman-α forest. For warm dark matter masses above 3 keV as well as for cold dark matter, to satisfy the Planck constraints on the optical depth and not to run into the satellite problem would require invoking astrophysical processes that inhibit galaxy formation in halos with mass M{sub H} ∼< few × 10 {sup 8} M{sub ⊙}, corresponding to a limiting UV magnitude M{sub UV}≈ −11. Anyway, we predict a downturn of the galaxy luminosity function at z∼ 8 faintward of M{sub UV}≈ −12, and stress that its detailed shape is extremely informative both on particle physics and on the astrophysics of galaxy formation in small halos. These expectations will be tested via the Hubble Frontier Fields and with the advent of the James Webb Space Telescope, which will enable probing the very faint end of the galaxy luminosity function out to z ∼ 8–10.
We show that the small scatter around the fundamental plane (FP) of massive elliptical galaxies can be used to derive important properties about their dark and luminous matter. The central velocity ...dispersion σ0 (appearing in the fundamental plane) is linked to photometric, dynamical and geometrical properties of (luminous and dark) matter. We find that, inside the effective radius Re, the matter traced by the light must largely dominate over the dark matter (DM) in order to keep the ellipticals close enough to the FP. This recalls analogous findings for spiral galaxies. In particular we also find that cuspy DM distributions, as predicted by numerical simulations in ΛCDM cosmology, are unable to explain the very existence of the FP; in fact, according to this theory, the structural properties of dark and luminous matter are so interwoven that a curved surface is predicted in the log-space (σ0, Re, L), rather than a plane. To agree with the FP implies that CDM haloes have values in the range of 5–9 for the concentration parameter c (i.e. values significantly lower than the current predictions). Assuming a more heuristic approach and allowing for cored DM haloes, we find that the small intrinsic scatter of the FP yields: (i) an average value of about 0.3 for the dark-to-light-traced mass ratio, (ii) a mass-to-light of the matter traced by the light increasing with spheroidal luminosity: Msph/Lr∝L0.2r (Gunn-r band), with a value of 5.3 at L*r≡ 2.7 × 1010 Lr⊙.
Under the assumption that accretion on to massive black holes (BHs) powers active galactic nuclei (AGNs), the mass function (MF) of the BHs responsible for their past activity is estimated. For this, ...we take into account not only the activity related to the optically selected AGNs, but also that required to produce the hard X-ray background (HXRB). The MF of the massive dark objects (MDOs) in nearby quiescent galaxies is computed by means of the most recent results on their demography. The two mass functions match well under the assumption that the activity is concentrated in a single significant burst with λLLEdd being a weakly increasing function of luminosity. This behaviour may be indicative of some level of recurrence and/or of accretion rates insufficient to maintain the Eddington rates in low-luminosity/low-redshift objects. Our results support the scenario in which the early phase of intense nuclear activity occurred mainly in early-type galaxies (E/S0) during the relatively short period in which they still had an abundant interstellar medium. Only recently, with the decline of the quasi-stellar object (QSO) luminosities, did the activity in late-type galaxies (Sa/Sab) become statistically significant.
We present high signal-to-noise ratio Spitzer Infrared Spectrograph observations of 17 Virgo early-type galaxies. The galaxies were selected from those that define the color-magnitude relation of the ...cluster, with the aim of detecting the silicate emission of their dusty, mass-losing evolved stars. To flux calibrate these extended sources, we have devised a new procedure that allows us to obtain the intrinsic spectral energy distribution and to disentangle resolved and unresolved emission within the same object. We have found that 13 objects of the sample (76%) are passively evolving galaxies with a pronounced broad silicate feature that is spatially extended and likely of stellar origin, in agreement with model predictions. The other four objects (24%) are characterized by different levels of activity. In NGC 4486 (M87), the line emission and the broad silicate emission are evidently unresolved, and, given also the typical shape of the continuum, they likely originate in the nuclear torus. NGC 4636 shows emission lines superposed on extended (i.e., stellar) silicate emission, thus pushing the percentage of galaxies with silicate emission to 82%. Finally, NGC 4550 and NGC 4435 are characterized by polycyclic aromatic hydrocarbon (PAH) and line emission, arising from a central unresolved region. A more detailed analysis of our sample, with updated models, will be presented in a forthcoming paper.
We present a detailed analysis of a sample of radio-detected quasars, obtained by matching together objects from the FIRST survey and the 2dF Quasar Redshift Survey (2dF). The data set consists of ...113 sources, spanning a redshift range 0.35 ≲z≲ 2.2, with optical magnitudes 18.25 ≤bJ≤ 20.85 and radio fluxes S1.4 GHz≥ 1 mJy. These objects exhibit properties such as redshift and colour distribution in full agreement with those derived for the whole quasar population, suggesting that the mechanism(s) controlling the birth and lifetime of quasars are independent of their level of radio emission. The long-debated question of the radio-loud/radio quiet (RL/RQ) dichotomy is then iestigated for the combined FIRST–2dF and FIRST–LBQS (Large Bright Quasar Survey) samples, as they present similar selection criteria. We find the fraction of radio detections to increase with magnitude from ≲3 per cent at the faintest levels up to ∼20 per cent for the brightest sources. The classical RL/RQ dichotomy, in which the distribution of radio-to-optical ratios and/or radio luminosities shows a lack of sources, is ruled out by our analysis. We also find no tight relationship between optical and radio luminosities for sources in the sample considered, a result that tends to exclude the mass of the quasar black hole as the physical quantity determining the level of radio emission.
We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their angular power spectrum in each channel foreseen for the Planck Surveyor (formerly ...COBRAS/SAMBA) mission. The contribution to fluctuations owing to clustering of both radio and far-IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be ‘clean’: at high galactic latitude (|b| > 20°), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, the ‘flat’ angular power spectrum of fluctuations resulting from extragalactic sources substantially differs from that of primordial fluctuations; therefore, the removal of contaminating signals is eased even at frequencies where point sources give a sizeable contribution to the foreground noise.
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