The peculiar QSO J0927+2943 shows multiple sets of emission lines in its optical spectrum. This signature has been interpreted as the relative motion between a black hole, either recoiling or bound in a binary system, and its host galaxy, or as a sup
erposition of two galaxies along the line of sight. In order to test these scenarios, we have collected 2mm CO(2-1) observations using the IRAM Plateau de Bure Interferometer, and optical images and spectroscopy at the Calar Alto observatory. Together with archival HST images, these data provide unique insights on the nature of this system. The recoiling/binary black hole scenarios are ruled out by the clear detection of a galactic-scale molecular gas reservoir at the same redshift of the QSO broad lines. The observations presented here also disfavour the superposition model, although with less constraints. Thus, the origin of the second, bright set of narrow emission lines in J0927+2943 is still unknown.
We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, $rho_{rm H2}$(z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM
Plateau de Bure Interferometer. Our line scan of the entire 3mm window (79-115 GHz) covers a cosmic volume of ~7000 Mpc$^3$, and redshift ranges z<0.45, 1.01<z<1.89 and z>2. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from HST) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density $rho_{rm H2}$(z) out to redshifts z~3. A comparison to empirical predictions of $rho_{rm H2}$(z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted $rho_{rm H2}$(z) in the redshift bins <z>~1.5 and <z>~2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities $rho_{rm H2}$(z) that are higher than current predictions. We note however that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory.
We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z<0.45, 1<z<1.9 and all z>2. We reach a CO detection
limit that is deep enough to detect essentially all z>1 CO lines reported in the literature so far. We have developed and applied different line searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ~2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available SEDs. Two secure CO detections in our scan are identified with star-forming galaxies at z=1.784 and at z=2.047. These galaxies have colors consistent with the `BzK color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF850.1 at z=5.183. We consider an additional 9 line candidates as high quality. Our observations also provide a deep 3mm continuum map (1-sigma noise level = 8.6 $mu$Jy/beam). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the SFR density at 1<z<3, unless high dust temperatures are invoked. The present study represents a first, fundamental step towards an unbiased census of molecular gas in `normal galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era.
We study the sub-mm properties of color-selected galaxies via a stacking analysis applied for the first time to interferometric data at sub-mm wavelengths. We base our study on 344 GHz ALMA continuum observations of ~20-wide fields centered on 86 sub
-mm sources detected in the LABOCA Extended Chandra Deep Field South Sub-mm Survey (LESS). We select various classes of galaxies (K-selected, star-forming sBzK galaxies, extremely red objects and distant red galaxies) according to their optical/NIR fluxes. We find clear, >10-sigma detections in the stacked images of all these galaxy classes. We include in our stacking analysis Herschel/SPIRE data to constrain the dust SED of these galaxies. We find that their dust emission is well described by a modified black body with Tdust~30 K and beta=1.6 and IR luminosities of (5-11)x10^{11} Lsun, or implied star formation rates of 75-140 Msun/yr. We compare our results with those of previous studies based on single-dish observations at 870 micron and find that our flux densities are a factor 2-3 higher than previous estimates. The discrepancy is observed also after removing sources individually detected in ALESS maps. We report a similar discrepancy by repeating our analysis on 1.4,GHz observations of the whole ECDFS. Hence we find tentative evidence that galaxies that are associated in projected and redshift space with sub-mm bright sources are brighter than the average population. Finally, we put our findings in the context of the cosmic star formation rate density as a function of redshift.
Theoretically, bound binaries of massive black holes are expected as the natural outcome of mergers of massive galaxies. From the observational side, however, massive black hole binaries remain elusive. Velocity shifts between narrow and broad emissi
on lines in quasar spectra are considered a promising observational tool to search for spatially unresolved, dynamically bound binaries. In this series of papers we investigate the nature of such candidates through analyses of their spectra, images and multi-wavelength spectral energy distributions. Here we investigate the properties of the optical spectra, including the evolution of the broad line profiles, of all the sources identified in our previous study. We find a diverse phenomenology of broad and narrow line luminosities, widths, shapes, ionization conditions and time variability, which we can broadly ascribe to 4 classes based on the shape of the broad line profiles: 1) Objects with bell-shaped broad lines with big velocity shifts (>1000 km/s) compared to their narrow lines show a variety of broad line widths and luminosities, modest flux variations over a few years, and no significant change in the broad line peak wavelength. 2) Objects with double-peaked broad emission lines tend to show very luminous and broadened lines, and little time variability. 3) Objects with asymmetric broad emission lines show a broad range of broad line luminosities and significant variability of the line profiles. 4) The remaining sources tend to show moderate to low broad line luminosities, and can be ascribed to diverse phenomena. We discuss the implications of our findings in the context of massive black hole binary searches.
The first spectroscopic census of AGNs associated to late-type galaxies in the Virgo cluster is carried on by observing 213 out of a complete set of 237 galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are classified as AGNs (in
cluding 21 transition objects, 47 LINERs and 9 Seyferts), and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic incompleteness at most 21 AGNs are missed in the survey, so that the fraction would increase up to 41%. Using corollary Near-IR observations, that enable us to estimate galaxies dynamical masses, it is found that AGNs are hosted exclusively in massive galaxies, i.e. M_dyngsim 10^{10} solar masses. Their frequency increases steeply with the dynamical mass from zero at M_dynapprox10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar masses. These frequencies are consistent with the ones of low luminosity AGNs found in the general field by the SDSS. Massive galaxies that harbor AGNs commonly show conspicuous r-band star-like nuclear enhancements. Conversely they often, but not necessarily contain massive bulges. Few well known AGNs (e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no bulge. The AGN fraction seems to be only marginally sensitive to galaxy environment. We infer the black hole masses using the known scaling relations of quiescent black holes. No black holes lighter than $sim 10^6$ msol are found active in our sample.
