925 research outputs found
What drives the [CII]/FIR deficit in submillimeter galaxies?
Large scale structure and cosmolog
Red quasars blow out molecular gas from galaxies during the peak of cosmic star formation
Recent studies have suggested that red quasars are a phase in quasar
evolution when feedback from black hole accretion evacuates obscuring gas from
the nucleus of the host galaxy. Here, we report a direct link between
dust-reddening and molecular outflows in quasars at . By examining
the dynamics of warm molecular gas in the inner region of galaxies, we detect
outflows with velocities 500--1000 km s and infer timescales of
Myr that are due to ongoing quasar energy output. We observe
outflows only in systems where quasar radiation pressure on dust in the
vicinity of the black hole is sufficiently large to expel their obscuring gas
column densities. This result is in agreement with theoretical models that
predict radiative feedback regulates gas in the nuclear regions of galaxies and
is a major driving mechanism of galactic-scale outflows of cold gas. Our
findings suggest that radiative quasar feedback ejects star-forming gas from
within nascent stellar bulges at velocities comparable to those seen on larger
scales, and that molecules survive in outflows even from the most luminous
quasars.Comment: Submitted to MNRAS. 18 figures and 3 table
PRUSSIC II -- ALMA imaging of dense-gas tracers in SDP.81: Evidence for low mechanical heating and a sub-solar metallicity in a z=3.04 dusty galaxy
We present deep ALMA Band 3 observations of the HCN, HCO+, and HNC (4-3)
emission in SDP.81, a well-studied z = 3.042 strongly lensed galaxy. These
lines trace the high-density gas, which remains almost entirely unexplored in
z1 galaxies. Additionally, these dense-gas tracers are potentially
powerful diagnostics of the mechanical heating of the interstellar medium.
While the HCN(4-3) and HNC(4-3) lines are not detected, the HCO+(4-3) emission
is clearly detected and resolved. This is the third detection of this line in a
high-redshift star-forming galaxy. We find an unusually high HCO+/HCN intensity
ratio of 2.2. Based on the photodissociation region modelling, the most
likely explanation for the elevated HCO+/HCN ratio is that SDP.81 has low
mechanical heating - less than 10% of the total energy budget - and a sub-solar
metallicity, Z=0.5 Z. While such conditions might not be representative
of the general population of high-redshift dusty galaxies, lower-than-solar
metallicity might have a significant impact on gas masses inferred from CO
observations. In addition, we report the detection of CO(0-1) absorption from
the foreground lensing galaxy and CO(1-0) emission from a massive companion to
the lensing galaxy, approximately 50 kpc to the southeast.Comment: A&A accepted, in press. 10 pages, 10 figure
A novel Bayesian approach for decomposing the radio emission of quasars: I. Modelling the radio excess in red quasars
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Studies show that both radio jets from the active galactic nuclei (AGNs) and the star formation (SF) activity in quasar host galaxies contribute to the quasar radio emission; yet their relative contributions across the population remain unclear. Here, we present an improved parametric model that allows us to statistically separate the SF and AGN components in observed quasar radio flux density distributions, and investigate how their relative contributions evolve with AGN bolometric luminosity (\L\mathrm\bol\\) and redshift (z) using a fully Bayesian method. Based on the newest data from LOw-Frequency ARray Two-metre Sky Survey data release 2, our model gives robust fitting results out to \z\\, showing a quasar host galaxy SF rate (SFR) evolution that increases with bolometric luminosity and with redshift out to \z\\. This differs from the global cosmic SFR density, perhaps due to the importance of galaxy mergers. The prevalence of radio AGN emissions increases with quasar luminosity, but has little dependence on redshift. Furthermore, our new methodology and large sample size allow us to subdivide our data set to investigate the role of other parameters. Specifically, in this paper, we explore quasar colour and demonstrate that the radio excess in red quasars is due to an enhancement in AGN-related emission, since the host galaxy SF contribution to the total radio emission is independent of quasar colour. We also find evidence that this radio enhancement occurs mostly in quasars with weak or intermediate radio power.Peer reviewe
The LOFAR Two-metre Sky Survey Deep Fields: A new analysis of low-frequency radio luminosity as a star-formation tracer in the Lockman Hole region
We have exploited LOFAR deep observations of the Lockman Hole field at 150 MHz to investigate the relation between the radio luminosity of star-forming galaxies (SFGs) and their star-formation rates (SFRs), as well as its dependence on stellar mass and redshift. The adopted source classification, SFRs, and stellar masses are consensus estimates based on a combination of four different spectral energy distribution fitting methods. We note a flattening of the radio spectra of a substantial minority of sources below âŒ1.4 GHz. Such sources have thus a lower `radio-loudness' level at 150 MHz than expected from extrapolations from 1.4 GHz using the average spectral index. We found a weak trend towards a lower SFR/L150 MHz ratio for higher stellar mass, Mâ. We argue that such a trend may account for most of the apparent redshift evolution of the L150 MHz/SFR ratio, in line with previous work. Our data indicate a weaker evolution than found by some previous analyses. We also find a weaker evolution with redshift of the specific SFR than found by several (but not all) previous studies. Our radio selection provides a view of the distribution of galaxies in the SFR-Mâ plane complementary to that of optical and near-IR selection. It suggests a higher uniformity of the star-formation history of galaxies than implied by some analyses of optical and near-IR data. We have derived luminosity functions at 150 MHz of both SFGs and radio-quiet (RQ) AGN at various redshifts. Our results are in very good agreement with the T-RECS simulations and with literature estimates. We also present explicit estimates of SFR functions of SFGs and RQ AGN at several redshifts derived from our radio survey data
Low frequency radio properties of the z > 5 quasar population
Optically luminous quasars at are important probes of super-massive
black hole (SMBH) formation. With new and future radio facilities, the
discovery of the brightest low-frequency radio sources in this epoch would be
an important new probe of cosmic reionization through 21-cm absorption
experiments. In this work, we systematically study the low-frequency radio
properties of a sample of 115 known spectroscopically confirmed quasars
using the second data release of the Low Frequency Array (LOFAR) Two Metre Sky
survey (LoTSS-DR2), reaching noise levels of 80 Jy beam (at
144 MHz) over an area of deg. We find that 41 sources (36%) are
detected in LoTSS-DR2 at significance and we explore the evolution
of their radio properties (power, spectral index, and radio loudness) as a
function of redshift and rest-frame ultra-violet properties. We obtain a median
spectral index of by stacking 93 quasars using
LoTSS-DR2 and Faint Images of the Radio Sky at Twenty Centimetres (FIRST) data
at 1.4 GHz, in line with observations of quasars at . We compare the radio
loudness of the high- quasar sample to a lower- quasar sample at
and find that the two radio loudness distributions are consistent with no
evolution, although the low number of high-z quasars means that we cannot rule
out weak evolution. Furthermore, we make a first order empirical estimate of
the quasar radio luminosity function, which is used to derive the
expected number of high- sources that will be detected in the completed
LoTSS survey. This work highlights the fact that new deep radio observations
can be a valuable tool in selecting high- quasar candidates for follow-up
spectroscopic observations by decreasing contamination of stellar dwarfs and
reducing possible selection biases introduced by strict colour cuts.Comment: 11 pages, 10 figures, accepted for publication in A&
LOFAR/H-ATLAS: The low-frequency radio luminosity - star-formation rate relation
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Radio emission is a key indicator of star-formation activity in galaxies, but the radio luminosity-star formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above. At lower radio frequencies the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz. We select a sample from the MPA-JHU catalogue of SDSS galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star-formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity--star-formation relation in the nearby Universe. For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz radio luminosity () and SFR. Interestingly, we find that a single power-law relationship between and SFR is not a good description of all SFGs: a broken power law model provides a better fit. This may indicate an additional mechanism for the generation of radio-emitting cosmic rays. Also, at given SFR, the radio luminosity depends on the stellar mass of the galaxy. Objects which were not classified as SFGs have higher 150-MHz radio luminosity than would be expected given their SFR, implying an important role for low-level active galactic nucleus activity.Peer reviewedFinal Published versio
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