arXiv subjects

Mladen Novak

Publications and source records attributed to Mladen Novak.

At least 19 recordsLinked to original sources

arXiv2022

The Decoupled Kinematics of high-z QSO Host Galaxies and their Lya halos

We present a comparison of the interstellar medium traced by [CII] (ALMA), and ionised halo gas traced by Lya (MUSE), in and around QSO host galaxies at z~6. To date, 18 QSOs at this redshift have been studied with both MUSE and high-resolution ALMA imaging; of these, 8 objects display a Lya halo. Using datacubes matched in velocity resolution, we compare and contrast the spatial and kinematic information of the Lya halos and the host galaxies' [CII] (and dust-continuum) emission. We find that the Lya halos extend typically 3-30 times beyond the interstellar medium of the host galaxies. The majority of the Lya halos do not show ordered motion in their velocity fields, whereas most of the [CII] velocity fields do. In those cases where a velocity gradient can be measured in Lya, the kinematics do not align with those derived from the [CII] emission. This implies that the Lya emission is not tracing the outskirts of a large rotating disk that is a simple extension of the central galaxy seen in [CII] emission. It rather suggests that the kinematics of the halo gas are decoupled from those of the central galaxy. Given the scattering nature of Lya, these results need to be confirmed with JWST IFU observations that can constrain the halo kinematics further using the non-resonant Ha line.

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arXiv2022

Physical constraints on the extended interstellar medium of the z=6.42 quasar J1148+5251: [CII] 158um, [NII] 205um and [OI] 146um observations

We report new Northern Extended Millimeter Array (NOEMA) observations of the [CII], [NII] and [OI] atomic fine structure lines and dust continuum emission of J1148+5251, a z=6.42 quasar, that probe the physical properties of its interstellar medium (ISM). The radially-averaged [CII] and dust continuum emission have similar extensions (up to $\theta = 2.51^{+0.46}_{-0.25}\ \rm{arcsec}$, corresponding to $r= 9.8^{+3.3}_{-2.1}\ \rm{kpc}$ accounting for beam-convolution), confirming that J1148+5251 is the quasar with the largest [CII]-emitting has reservoir known at these epochs.Moreover, if the [CII] emission is examined only along its NE-SW axis, a significant excess ($>5.8\sigma$) of [CII] emission (with respect to the dust) is detected. The new wide--bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad [CII] line wings that were reported in previous studies. We also report the first detection of the [OI] and (tentatively) [NII] emission lines in J1148+5251. Using Fine Structure Lines (FSL) ratios of the [CII], [NII], [OI] and previously measured [CI] emission lines, we show that J1148+5251 has similar ISM conditions compared to lower--redshift (ultra)-luminous infrared galaxies. CLOUDY modelling of the FSL ratios exclude X--ray dominated regions (XDR) and favours photodissociation regions (PDR) as the origin of the FSL emission. We find that a high radiation field ($10^{3.5-4.5}\,G_0$), high gas density ($n \simeq 10^{3.5-4.5}\, \rm{cm}^{-3}$) and HI column density of $10^{23} \,\rm{cm^{-2}}$ reproduce the observed FSL ratios well.

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arXiv2021

The Impact of Powerful Jets on the Far-infrared Emission of an Extreme Radio Quasar at z~6

The interactions between radio jets and the interstellar medium play a defining role for the co-evolution of central supermassive black holes and their host galaxies, but observational constraints on these feedback processes are still very limited at redshifts $z > 2$. We investigate the radio-loud quasar PSO J352.4034-15.3373 at $z \sim 6$ at the edge of the Epoch of Reionization. This quasar is among the most powerful radio emitters and the first one with direct evidence of extended radio jets ($\sim$1.6 kpc) at these high redshifts. We analyze NOEMA and ALMA millimeter data targeting the CO (6-5) and [CII] far-infrared emission lines, respectively, and the underlying continuum. The broad $440\pm 80$ km s$^{-1}$ and marginally resolved [CII] emission line yields a systemic redshift of $z\!=\!5.832 \pm 0.001$. Additionally, we report a strong 215 MHz radio continuum detection, $88\pm 7$ mJy, using the GMRT. This measurement significantly improves the constraints at the low-frequency end of the spectral energy distribution of this quasar. In contrast to what is typically observed in high-redshift radio-quiet quasars, we show that cold dust emission alone cannot reproduce the millimeter continuum measurements. This is evidence that the strong synchrotron emission from the quasar contributes substantially to the emission even at millimeter (far-infrared in the rest-frame) wavelengths. This quasar is an ideal system to probe the effects of radio jets during the formation of a massive galaxy within the first Gyr of the Universe.

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arXiv2021

The XXL Survey: XLIII. The quasar radio loudness dichotomy exposed via radio luminosity functions obtained by combining results from COSMOS and XXL-S X-ray selected quasars

We studied a sample of 274 radio and X-ray selected quasars (XQSOs) detected in the COSMOS and XXL-S radio surveys at 3 GHz and 2.1 GHz, respectively. This sample was identified by adopting a conservative threshold in X-ray luminosity, Lx [2-10\ keV] >= 10^44 erg/s, selecting only the most powerful quasars. Using available multiwavelength data, we examined various criteria for the selection of radio-loud (RL) and radio-quiet (RQ) XQSOs, finding that the number of RL/RQ XQSOs changes significantly depending on the chosen criterion. This discrepancy arises due to the different criteria tracing different physical processes and due to our sample being selected from flux-limited radio and X-ray surveys. Another approach to study the origin of radio emission in XQSOs is via their radio luminosity function (RLF). We constructed the XQSO 1.4 GHz radio luminosity functions (RLFs) in six redshift bins at 0.5 <= z <= 3.7. The lower-1.4 GHz luminosity end shows a higher normalization than expected only from AGN contribution in all studied redshift bins. The found "bump" is mostly dominated by emission due to star-forming (SF) processes within the XQSO host galaxies. As expected, AGN-related radio emission dominates at the higher-luminosity end of RLF. The evolution of XQSO RLF was studied via combination of analytic forms from the literature to constrain the lower-luminosity "bump" and the higher-luminosity AGN part of the RLF. We defined two 1.4 GHz luminosity thresholds, L_th,SF and L_th,AGN, below and above which more than 80% of sources contributing to the RLF are dominated by SF and AGN-related activity, respectively. These thresholds evolve with redshift, most likely due to the strong evolution of SFRs of the XQSO host galaxies.

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arXiv2021

The Kinematics of z ~ 6 Quasar Host Galaxies

We explore the kinematics of 27 z~6 quasar host galaxies observed in [CII]-158 micron ([CII]) emission with the Atacama Large Millimeter/sub-millimeter Array at a resolution of ~0.25''. We find that nine of the galaxies show disturbed [CII] emission, either due to a close companion galaxy or recent merger. Ten galaxies have smooth velocity gradients consistent with the emission arising from a gaseous disk. The remaining eight quasar host galaxies show no velocity gradient, suggesting that the gas in these systems is dispersion-dominated. All galaxies show high velocity dispersions with a mean of 129+-10 km/s. To provide an estimate of the dynamical mass within twice the half-light radius of the quasar host galaxy, we model the kinematics of the [CII] emission line using our publicly available kinematic fitting code, qubefit. This results in a mean dynamical mass of 5.0+-0.8(+-3.5) x 10^10 Msun. Comparison between the dynamical mass and the mass of the supermassive black hole reveals that the sample falls above the locally derived bulge mass--black hole mass relation at 2.4sigma significance. This result is robust even if we account for the large systematic uncertainties. Using several different estimators for the molecular mass, we estimate a gas mass fraction of >10%, indicating gas makes up a large fraction of the baryonic mass of z~6 quasar host galaxies. Finally, we speculate that the large variety in [CII] kinematics is an indication that gas accretion onto z~6 super massive black holes is not caused by a single precipitating factor.

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arXiv2020

No evidence for [CII] halos or high-velocity outflows in z>6 quasar host galaxies

We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z>6, using the [CII] 158um emission line and the underlying dust continuum observed at ~1kpc resolution with ALMA. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas, and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [CII] and the dust continuum emission can be described by a steep component within a radius of 2kpc, and a shallower component with a scale length of 2kpc, detected up to ~10kpc. The surface brightness of the extended emission drops below ~1% of the peak at radius of ~5kpc, beyond which it constitutes 10-20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [CII] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [CII] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [CII] broad-line emission (velocities in excess of >500km/s), that would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10kpc, whereas we find no evidence for halos or outflows.

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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.

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arXiv2020

A Closer Look at Two of the Most Luminous Quasars in the Universe

Ultra-luminous quasars ($M_{1450} \leq -29$) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341${+}$1720 ($M_{1450}=-29.56$, $z=3.71$) and J2125${-}$1719 ($M_{1450}=-29.39$, $z=3.90$), in the Extremely Luminous Quasar Survey (ELQS) and its extension to the Pan-STARRS\,1 footprint (PS-ELQS), we herein present an analysis of their rest-frame UV to optical spectroscopy. Both quasars harbor very massive SMBHs with $M_{\rm{BH}}=6.73_{-0.83}^{+0.75}\times10^{9}\,M_{\odot}$ and $M_{\rm{BH}}=5.45_{-0.55}^{+0.60}\times10^{9}\,M_{\odot}$, respectively, showing evidence of accretion above the Eddington limit ($L_{\rm{bol}}/L_{\rm{Edd}}=2.74_{-0.27}^{+0.39}$ and $L_{\rm{bol}}/L_{\rm{Edd}}=3.01_{-0.30}^{+0.34}$). NOEMA 3 millimeter observations of J0341${+}$1720 reveal a highly star-forming ($\rm{SFR}\approx1500\,M_{\odot}\,\rm{yr}^{-1}$), ultra-luminous infrared galaxy ($L_{\rm{TIR}}\approx1.0\times10^{13}\,L_{\odot}$) host, which, based on an estimate of its dynamical mass, is only ${\sim}30$ times more massive than the SMBH it harbors at its center. As examples of luminous super-Eddington accretion, these two quasars provide support for theories, which explain the existence of billion solar mass SMBHs ${\sim}700$ million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.

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arXiv2020

The ALMA Spectroscopic Survey in the HUDF: Multi-band constraints on line luminosity functions and the cosmic density of molecular gas

We present a CO and atomic fine-structure line luminosity function analysis using the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). ASPECS consists of two spatially-overlapping mosaics that cover the entire ALMA 3mm and 1.2mm bands. We combine the results of a line candidate search of the 1.2mm data cube with those previously obtained from the 3mm cube. Our analysis shows that $\sim$80% of the line flux observed at 3mm arises from CO(2-1) or CO(3-2) emitters at $z$=1-3 (`cosmic noon'). At 1.2mm, more than half of the line flux arises from intermediate-J CO transitions ($J_{\rm up}$=3-6); $\sim12$% from neutral carbon lines; and $< 1$% from singly-ionized carbon, [CII]. This implies that future [CII] intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2mm show a decrease in the number density at a given line luminosity (in units of $L'$) at increasing $J_{\rm up}$ and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal sub-thermal conditions on average in galaxies up to $z\sim 4$. In addition, the comparison of the CO luminosity functions for the same transition at different redshifts reveals that the evolution is not driven by excitation. The cosmic density of molecular gas in galaxies, $\rho_{\rm H2}$, shows a redshift evolution with an increase from high redshift up to $z\sim1.5$ followed by a factor $\sim 6$ drop down to the present day. This is in qualitative agreement with the evolution of the cosmic star-formation rate density, suggesting that the molecular gas depletion time is approximately constant with redshift, after averaging over the star-forming galaxy population.

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arXiv2020

The ALMA Spectroscopic Survey Large Program: The Infrared Excess of z=1.5-10 UV-selected Galaxies and the Implied High-Redshift Star Formation History

We make use of sensitive (9.3 microJy/beam RMS) 1.2mm-continuum observations from the ASPECS ALMA large program of the Hubble Ultra Deep Field (HUDF) to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range z=1.5-10 (to ~7-28 Msolar/yr at 4 sigma over the entire range). We find that the fraction of ALMA-detected galaxies in our z=1.5-10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 10^9 Msolar to 85(-18)(+9)% at >10^{10} Msolar. Moreover, stacking all 1253 low-mass (<10^{9.25} Msolar) galaxies over the ASPECS footprint, we find a mean continuum flux of -0.1+/-0.4 microJy/beam, implying a hard upper limit on the obscured SFR of <0.6 Msolar/yr (4 sigma) in a typical low-mass galaxy. The correlation between the infrared excess IRX of UV-selected galaxies (L(IR)/L(UV)) and the UV-continuum slope is also seen in our ASPECS data and shows consistency with a Calzetti-like relation at >10^{9.5} M_{solar} and a SMC-like relation at lower masses. Using stellar-mass and beta measurements for z~2 galaxies over CANDELS, we derive a new empirical relation between beta and stellar mass and then use this correlation to show that our IRX-beta and IRX-stellar mass relations are consistent with each other. We then use these constraints to express the infrared excess as a bivariate function of beta and stellar mass. Finally, we present updated estimates of star-formation rate density determinations at z>3, leveraging current improvements in the measured infrared excess and recent probes of ultra-luminous far-IR galaxies at z>2.

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arXiv2020

Probing the Nature of High Redshift Weak Emission Line Quasars: A Young Quasar with a Starburst Host Galaxy

We present the discovery of PSO J083.8371+11.8482, a weak emission line quasar with extreme star formation rate at $z=6.3401$. This quasar was selected from Pan-STARRS1, UHS, and unWISE photometric data. Gemini/GNIRS spectroscopy follow-up indicates a MgII-based black hole mass of $M_\mathrm{BH}=\left(2.0^{+0.7}_{-0.4}\right)\times10^9~M_\odot$ and an Eddington ratio of $L_\mathrm{bol}/L_\mathrm{Edd}=0.5^{+0.1}_{-0.2}$, in line with actively accreting supermassive black hole (SMBH) at $z\gtrsim6$. HST imaging sets strong constraint on lens-boosting, showing no relevant effect on the apparent emission. The quasar is also observed as a pure point-source with no additional emission component. The broad line region (BLR) emission is intrinsically weak and not likely caused by an intervening absorber. We found rest-frame equivalent widths of EW(Ly$\alpha$+NV) $=5.7\pm0.7$ Angstrom, EW(CIV) $\leq5.8$ Angstrom (3-sigma upper limit), and EW(MgII) $=8.7\pm0.7$ Angstrom. A small proximity zone size ($R_\mathrm{p}=1.2\pm0.4$ pMpc) indicates a lifetime of only $t_\mathrm{Q}=10^{3.4\pm0.7}$ years from the last quasar phase ignition. ALMA shows extended [CII] emission with a mild velocity gradient. The inferred far-infrared luminosity ($L_\mathrm{FIR}=(1.2\pm0.1)\times10^{13}\,L_\odot$) is one of the highest among all known quasar hosts at $z\gtrsim6$. Dust and [CII] emissions put a constraint on the star formation rate of SFR $=900-4900~M_\odot\,\mathrm{yr^{-1}}$, similar to that of hyper-luminous infrared galaxy. Considering the observed quasar lifetime and BLR formation timescale, the weak-line profile in the quasar spectrum is most likely caused by a BLR which is not yet fully formed rather than continuum boosting by gravitational lensing or a soft continuum due to super-Eddington accretion.

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arXiv2020

A Comparison of the Stellar, CO and Dust-Continuum Emission from Three, Star-Forming HUDF Galaxies at $z\sim 2$

We compare the extent of the dust, molecular gas and stars in three star-forming galaxies, at $z= 1.4, 1.6$ and $2.7$, selected from the Hubble Ultra Deep Field based on their bright CO and dust-continuum emission as well as their large rest-frame optical sizes. The galaxies have high stellar masses, $\mathrm{M}_*>10^{11}\mathrm{M}_\odot$, and reside on, or slightly below, the main sequence of star-forming galaxies at their respective redshifts. We probe the dust and molecular gas using subarcsecond Atacama Large Millimeter/submillimeter Array observations of the 1.3 mm continuum and CO line emission, respectively, and probe the stellar distribution using \emph{Hubble Space Telescope} observations at 1.6 \textmu m. We find that for all three galaxies the CO emission appears $\gtrsim 30\%$ more compact than the stellar emission. For the $z= 1.4$ and $2.7$ galaxies, the dust emission is also more compact, by $\gtrsim 50\%$, than the stellar emission, whereas for the $z=1.6$ galaxy, the dust and stellar emission have similar spatial extents. This similar spatial extent is consistent with observations of local disk galaxies. However, most high redshift observations show more compact dust emission, likely due to the ubiquity of central starbursts at high redshift and the limited sensitivity of many of these observations. Using the CO emission line, we also investigate the kinematics of the cold interstellar medium in the galaxies, and find that all three have kinematics consistent with a rotation-dominated disk.

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arXiv2020

The VLA-COSMOS 3 GHz Large Project: Evolution of specific star formation rates out to $z\sim5$

We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate (SFR) - stellar mass ($M_*$) relation, called the main sequence of star-forming galaxies (MS), for galaxies out to $z\sim5$. We measure the MS using mean stacks of 3 GHz radio continuum images to derive average SFRs for $\sim$200,000 mass-selected galaxies at $z>0.3$ in the COSMOS field. We describe the MS relation adopting a new model that incorporates a linear relation at low stellar mass (log($M_*$/M$_\odot$)$<$10) and a flattening at high stellar mass that becomes more prominent at low redshift ($z<1.5$). We find that the SFR density peaks at $1.5<z<2$ and at each epoch there is a characteristic stellar mass ($M_* = 1 - 4 \times 10^{10}\mathrm{M}_\odot$) that contributes the most to the overall SFR density. This characteristic mass increases with redshift, at least to $z\sim2.5$. We find no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy number density at $0.3<z<3$, nor for galaxies in X-ray groups at $z\sim0.75$. We confirm that massive bulge-dominated galaxies have lower SFRs than disk-dominated galaxies at a fixed stellar mass at $z<1.2$. As a consequence, the increase in bulge-dominated galaxies in the local star-forming population leads to a flattening of the MS at high stellar masses. This indicates that "mass-quenching" is linked with changes in the morphological composition of galaxies at a fixed stellar mass.

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arXiv2020

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The nature of the faintest dusty star-forming galaxies

We present a characterization of the physical properties of a sample of 35 securely-detected, dusty galaxies in the deep ALMA 1.2-mm image obtained as part of the ALMA Spectroscopic Survey in the {\it Hubble} Ultra Deep Field (ASPECS) Large Program. This sample is complemented by 26 additional sources identified via an optical/infrared source positional prior. Using their well-characterized spectral energy distributions, we derive median stellar masses and star formation rates (SFR) of $4.8\times10^{10}~M_\odot$ and 30 $M_\odot$ yr$^{-1}$, and interquartile ranges of $(2.4-11.7)\times10^{10}~M_\odot$ and $20-50~M_\odot$ yr$^{-1}$, respectively. We derive a median spectroscopic redshift of 1.8 with an interquartile range $1.1-2.6$, significantly lower than submillimeter galaxies detected in shallower, wide-field surveys. We find that 59\%$\pm$13\%, 6\%$\pm$4\%, and 34\%$\pm$9\% of our sources are within, above and below $\pm0.4$ dex from the SFR-stellar mass relation or main-sequence (MS), respectively. The ASPECS galaxies closely follow the SFR-molecular gas mass relation and other previously established scaling relations, confirming a factor of five increase of the gas-to-stellar mass ratio from $z=0.5$ to $z=2.5$ and a mild evolution of the gas depletion timescales with a typical value of 0.7 Gyr at $z=1-3$. ASPECS galaxies located significantly below the MS, a poorly exploited parameter space, have low gas-to-stellar-mass ratios of $\sim0.1-0.2$ and long depletion timescales $>1$ Gyr. Galaxies along the MS dominate the cosmic density of molecular gas at all redshifts. Systems above the main sequence have an increasing contribution to the total gas reservoirs from $z<1$ to $z=2.5$, while the opposite is found for galaxies below the MS.

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arXiv2020

The ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $z\sim3$

Using the deepest 1.2 mm continuum map to date in the Hubble Ultra Deep Field obtained as part of the ALMA Spectroscopic Survey (ASPECS) large program, we measure the cosmic density of dust and implied gas (H$_{2}+$H I) mass in galaxies as a function of look-back time. We do so by stacking the contribution from all $H$-band selected galaxies above a given stellar mass in distinct redshift bins, $\rho_{\rm dust}(M_\ast>M,z)$ and $\rho_{\rm gas}(M_\ast>M,z)$. At all redshifts, $\rho_{\rm dust}(M_\ast>M,z)$ and $\rho_{\rm gas}(M_\ast>M,z)$ grow rapidly as $M$ decreases down to $10^{10}\,M_\odot$, but this growth slows down towards lower stellar masses. This flattening implies that at our stellar mass-completeness limits ($10^8\,M_\odot$ and $10^{8.9}\,M_\odot$ at $z\sim0.4$ and $z\sim3$), both quantities converge towards the total cosmic dust and gas mass densities in galaxies. The cosmic dust and gas mass densities increase at early cosmic time, peak around $z\sim2$, and decrease by a factor $\sim4$ and 7, compared to the density of dust and molecular gas in the local universe, respectively. The contribution of quiescent galaxies -- i.e., with little on-going star-formation -- to the cosmic dust and gas mass densities is minor ($\lesssim10\%$). The redshift evolution of the cosmic gas mass density resembles that of the star-formation rate density, as previously found by CO-based measurements. This confirms that galaxies have relatively constant star-formation efficiencies (within a factor $\sim2$) across cosmic time. Our results also imply that by $z\sim0$, a large fraction ($\sim90\%$) of dust formed in galaxies across cosmic time has been destroyed or ejected to the intergalactic medium.

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arXiv2020

The ALMA Spectroscopic Survey in the HUDF: Deep 1.2 mm continuum number counts

We present the results from the 1.2 mm continuum image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). The 1.2 mm continuum image has a size of 2.9 (4.2) arcmin$^2$ within a primary beam response of 50% (10%) and a rms value of $9.3\thinspace{\rm\mu Jy\thinspace beam^{-1}}$. We detect 35 sources at high significance (Fidelity $\geq0.5$), 32 of these have well characterized near-infrared HST counterparts. We estimate the 1.2 mm number counts to flux levels of $<30\thinspace{\rm\mu Jy}$ in two different ways: we first use the detected sources to constrain the number counts and find a significant flattening of the counts below $S_\nu \sim 0.1$ mJy. In a second approach, we constrain the number counts by using a probability of deflection statistics (P(D)) analysis. For this latter approach, we describe new methods to accurately measure the noise in interferometric imaging (employing jack-knifing in the cube and in the visibility plane). This independent measurement confirms the flattening of the number counts. Our analysis of the differential number counts shows that we are detecting $\sim$93% ($\sim$100% if we include the lower fidelity detections) of the total continuum dust emission associated to galaxies in the HUDF. The ancillary data allows us to study the dependence of the 1.2 mm number counts on redshift ($z=0-4$), galaxy dust mass (${\rm M}_{\rm dust}=10^{7}-10^{9}{\rm M}_{\odot}$), stellar mass (${\rm M}_{*}=10^{9}-10^{12}{\rm M}_{\odot}$), and star-formation rate (${\rm SFR}=1-1000\thinspace{\rm M}_{\odot}\thinspace{\rm yr^{-1}}$). In an accompanying paper we show that the number counts are crucial to constrain galaxy evolution models and the understanding of star-forming galaxies at high redshift.

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arXiv2020

Detecting and Characterizing Young Quasars I: Systemic Redshifts and Proximity Zones Measurements

In a multi-wavelength survey of $13$ quasars at $5.8\lesssim z\lesssim6.5$, that were pre-selected to be potentially young, we find five objects with extremely small proximity zone sizes that may imply UV-luminous quasar lifetimes of $\lesssim 100,000$ years. Proximity zones are regions of enhanced transmitted flux in the vicinity of the quasars that are sensitive to the quasars' lifetimes because the intergalactic gas has a finite response time to their radiation. We combine sub-mm observations from the Atacama Large Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA), as well as deep optical and near-infrared spectra from medium-resolution spectrograph on the Very Large Telescope (VLT) and on the Keck telescopes, in order to identify and characterize these new young quasars, which provide valuable clues about the accretion behavior of supermassive black holes (SMBHs) in the early universe, and pose challenges on current black hole formation models to explain the rapid formation of billion solar mass black holes. We measure the quasars' systemic redshifts, black hole masses, Eddington ratios, emission line luminosities, and star formation rates of their host galaxies. Combined with previous results we estimate the fraction of young objects within the high-redshift quasar population at large to be $5\%\lesssim f_{\rm young}\lesssim 10\%$. One of the young objects, PSO J158-14, shows a very bright dust continuum flux ($F_{\rm cont}=3.46\pm 0.02\,\rm mJy$), indicating a highly star-bursting host galaxy with a star formation rate of approximately $1420\,M_{\odot}\,\rm yr^{-1}$.

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arXiv2019

The z=7.54 Quasar ULAS J1342+0928 Is Hosted by a Galaxy Merger

We present ALMA 0.28"x0.20" (1.4kpc x 1.0kpc) resolution observations of the [CII] 158um line and underlying dust continuum in the host galaxy of the most distant quasar currently known, ULAS J1342+0928 at z=7.5413. Both the [CII] and continuum are detected and spatially resolved. The [CII] line is ~1.5 times more extended than the continuum emission, showing an elongated and complex structure of approximately 3.2kpc x 6.4kpc. Two separate peaks are clearly seen (>6sigma each) in three 100 km/s width [CII] channel maps. The velocity field of the [CII] gas does not show evidence of a coherent rotation field but rather chaotic motion, reminiscent of an on-going merger.

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