arXiv subjects

Emanuele Farina

Publications and source records attributed to Emanuele Farina.

5 recordsLinked to original sources

arXiv2020

Kiloparsec-scale ALMA Imaging of [CII] and Dust Continuum Emission of 27 Quasar Host Galaxies at z~6

We present a study of the [CII] 158micron line and underlying far-infrared (FIR) continuum emission of 27 quasar host galaxies at z~6, traced by the Atacama Large Millimeter/submillimeter Array at a spatial resolution of ~1 physical kpc. The [CII] emission in the bright, central regions of the quasars have sizes of 1.0-4.8kpc. The dust continuum emission is typically more compact than [CII]. We find that 13/27 quasars (approximately one-half) have companion galaxies in the field, at projected separations of 3-90kpc. The position of dust emission and the Gaia-corrected positions of the central accreting black holes are cospatial (typical offsets <0.1"). This suggests that the central black holes are located at the bottom of the gravitational wells of the dark matter halos in which the z>6 quasar hosts reside. Some outliers with offsets of ~500pc can be linked to disturbed morphologies, most likely due to ongoing or recent mergers. We find no correlation between the central brightness of the FIR emission and the bolometric luminosity of the accreting black hole. The FIR-derived star-formation rate densities (SFRDs) in the host galaxies peak at the galaxies' centers, at typical values between 100 and 1000 M_sun/yr/kpc^2. These values are below the Eddington limit for star formation, but similar to those found in local ultraluminous infrared galaxies. The SFRDs drop toward larger radii by an order of magnitude. Likewise, the [CII]/FIR luminosity ratios of the quasar hosts are lowest in their centers (few x10^-4) and increase by a factor of a few toward the galaxies' outskirts, consistent with resolved studies of lower-redshift sources.

astro-ph.GA↗

arXiv2019

A Quasar Discovered at redshift 6.6 from Pan-STARRS1

Luminous high-redshift quasars can be used to probe of the intergalactic medium (IGM) in the early universe because their UV light is absorbed by the neutral hydrogen along the line of sight. They help us to measure the neutral hydrogen fraction of the high-z universe, shedding light on the end of reionization epoch. In this paper, we present a discovery of a new quasar (PSO J006.1240+39.2219) at redshift $z=6.61\pm0.02$ from Panoramic Survey Telescope & Rapid Response System 1. Including this quasar, there are nine quasars above $z>6.5$ up to date. The estimated continuum brightness is $M_\text{1450}$=$-25.96\pm0.08$. PSO J006.1240+39.2219 has a strong Ly~$α$ emission compared with typical low-redshift quasars, but the measured near-zone region size is $R_\text{NZ}=3.2\pm1.1$ proper megaparsecs, which is consistent with other quasars at z$\sim$6.

astro-ph.GA↗

arXiv2018

No evidence for enhanced [OIII] 88um emission in a z~6 quasar compared to its companion starbursting galaxy

We present ALMA band 8 observations of the [OIII] 88um line and the underlying thermal infrared continuum emission in the z=6.08 quasar CFHQS J2100-1715 and its dust-obscured starburst companion galaxy (projected distance: ~60 kpc). Each galaxy hosts dust-obscured star formation at rates > 100 M_sun/yr, but only the quasar shows evidence for an accreting 10^9 M_sun black hole. Therefore we can compare the properties of the interstellar medium in distinct galactic environments in two physically associated objects, ~1 Gyr after the Big Bang. Bright [OIII] 88um emission from ionized gas is detected in both systems; the positions and line-widths are consistent with earlier [CII] measurements, indicating that both lines trace the same gravitational potential on galactic scales. The [OIII] 88um/FIR luminosity ratios in both sources fall in the upper range observed in local luminous infrared galaxies of similar dust temperature, although the ratio of the quasar is smaller than in the companion. This suggests that gas ionization by the quasar (expected to lead to strong optical [OIII] 5008A emission) does not dominantly determine the quasar's FIR [OIII] 88um luminosity. Both the inferred number of photons needed for the creation of O++ and the typical line ratios can be accounted for without invoking extreme (top-heavy) stellar initial mass functions in the starbursts of both sources.

astro-ph.GA↗

arXiv2018

Dust emission in an accretion-rate-limited sample of z>6 quasars

We present Atacama Large Millimeter Array 1mm observations of the rest-frame far-infrared (FIR) dust continuum in 27 quasars at redshifts 6.0 < z < 6.7. We detect FIR emission at >3sigma in all quasar host galaxies with flux densities at ~1900GHz in the rest-frame of 0.12 < S_rest,1900GHz < 5.9mJy, with a median (mean) flux density of 0.88mJy (1.59mJy). The implied FIR luminosities range from L_FIR = (0.27-13)x10^12 L_sun, with 74% of our quasar hosts having L_FIR > 10^12 L_sun. The estimated dust masses are M_dust = 10^7-10^9 M_sun. If the dust is heated only by star formation, then the star formation rates in the quasar host galaxies are between 50 and 2700 M_sun/yr. In the framework of the host galaxy-black hole coevolution model a correlation between ongoing black hole growth and star formation in the quasar host galaxy would be expected. However, combined with results from the literature to create a luminosity-limited quasar sample, we do not find a strong correlation between quasar UV luminosity (a proxy for ongoing black hole growth) and FIR luminosity (star formation in the host galaxy). The absence of such a correlation in our data does not necessarily rule out the coevolution model, and could be due to a variety of effects (including different timescales for black hole accretion and FIR emission).

astro-ph.GA↗

arXiv2017

Copious Amounts of Dust and Gas in a z=7.5 Quasar Host Galaxy

We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at z=7.54 and report detections of copious amounts of dust and [CII] emission in the interstellar medium (ISM) of its host galaxy. At this redshift, the age of the universe is 690 Myr, about 10% younger than the redshift of the previous quasar record holder. Yet, the ISM of this new quasar host galaxy is significantly enriched by metals, as evidenced by the detection of the [CII] 158micron cooling line and the underlying far-infrared (FIR) dust continuum emission. To the first order, the FIR properties of this quasar host are similar to those found at a slightly lower redshift (z~6), making this source by far the FIR-brightest galaxy known at z>7.5. The [CII] emission is spatially unresolved, with an upper limit on the diameter of 7 kpc. Together with the measured FWHM of the [CII] line, this yields a dynamical mass of the host of <1.5x10^11 M_sun. Using standard assumptions about the dust temperature and emissivity, the NOEMA measurements give a dust mass of (0.6-4.3)x10^8 M_sun. The brightness of the [CII] luminosity, together with the high dust mass, imply active ongoing star formation in the quasar host. Using [CII]-SFR scaling relations, we derive star formation rates of 85-545 M_sun/yr in the host, consistent with the values derived from the dust continuum. Indeed, an episode of such past high star formation is needed to explain the presence of ~10^8 M_sun of dust implied by the observations.

astro-ph.GA↗