Claudia Cicone — Page 4

arXiv2017

ALMA Observations Show Major Mergers Among the Host Galaxies of Fast-growing, High-redshift Supermassive Black Holes

We present new ALMA band-7 data for a sample of six luminous quasars at z~4.8, powered by fast-growing supermassive black holes (SMBHs) with rather uniform properties: the typical accretion rates and black hole masses are L/L_Edd~0.7 and M_BH~10^9 M_sol. Our sample consists of three "FIR-bright" sources, which were individually detected in previous Herschel/SPIRE observations, with star formation rates of SFR>1000 M_sol/yr, and three "FIR-faint" sources for which Herschel stacking analysis implies a typical SFR of ~400 M_sol/yr. The dusty interstellar medium in the hosts of all six quasars is clearly detected in the ALMA data and resolved on scales of ~2 kpc, in both continuum (λ_rest ~150 um) and [C II]157.74 um line emission. The continuum emission is in good agreement with the expectations from the Herschel data, confirming the intense SF activity in the quasar hosts. Importantly, we detect companion sub-millimeter galaxies (SMGs) for three sources -- one FIR-bright and two FIR-faint, separated by ~14-45 kpc and <450 km/s from the quasar hosts. The [C II]-based dynamical mass estimates for the interacting SMGs are within a factor of ~3 of the quasar hosts' masses, while the continuum emission implies SFR(quasar)~(2-11)xSFR(SMG). Our ALMA data therefore clearly support the idea that major mergers are important drivers for rapid early SMBH growth. However, the fact that not all high-SFR quasar hosts are accompanied by interacting SMGs and the gas kinematics as observed by ALMA suggest that other processes may be fueling these systems. Our analysis thus demonstrates the diversity of host galaxy properties and gas accretion mechanisms associated with early and rapid SMBH growth.

astro-ph.GA↗

arXiv2016

Outflows and complex stellar kinematics in SDSS star forming galaxies

We investigate the properties of star formation-driven outflows by using a large spectroscopic sample of ~160,000 local "normal" star forming galaxies, drawn from the SDSS, spanning a wide range of star formation rates and stellar masses. The galaxy sample is divided into a fine grid of bins in the M_*-SFR parameter space, for each of which we produce a composite spectrum by stacking together the SDSS spectra of the galaxies contained in that bin. We exploit the high signal-to-noise of the stacked spectra to study the emergence of faint features of optical emission lines that may trace galactic outflows and would otherwise be too faint to detect in individual galaxy spectra. We adopt a novel approach that relies on the comparison between the line-of-sight velocity distribution (LoSVD) of the ionised gas (as traced by the [OIII]5007 and Halpha+[NII]6548,6583 emission lines) and the LoSVD of the stars, which are used as a reference tracing virial motions. Significant deviations of the gas kinematics from the stellar kinematics in the high velocity tail of the LoSVDs are interpreted as a signature of outflows. Our results suggest that the incidence of ionised outflows increases with SFR and sSFR. The outflow velocity (v_out) correlates tightly with the SFR for SFR>1 M_Sun/yr, whereas at lower SFRs the dependence of v_out on SFR is nearly flat. The outflow velocity, although with a much larger scatter, increases also with the stellar velocity dispersion, and we infer velocities as high as v_out~(6-8)*sigma_stars. Strikingly, we detect the signature of ionised outflows only in galaxies located above the main sequence (MS) of star forming galaxies in the M_*-SFR diagram, and the incidence of such outflows increases sharply with the offset from the MS. Our complementary analysis of the stellar kinematics reveals the presence of blue asymmetries of a few 10 km/s in the stellar LoSVDs. [abridged]

astro-ph.GA↗