30 research outputs found
: Modeling a Universe of Molecular Line Luminosities in Hydrodynamical Simulations
We present {\sc slick} (the Scalable Line Intensity Computation Kit), a
software package that calculates realistic CO, [\ion{C}{1}], and [\ion{C}{2}]
luminosities for clouds and galaxies formed in hydrodynamic simulations. Built
on the radiative transfer code {\sc despotic}, {\sc slick} computes the
thermal, radiative, and statistical equilibrium in concentric zones of model
clouds, based on their physical properties and individual environments. We
validate our results applying {\sc slick} to the high-resolution run of the
{\sc Simba} simulations, testing the derived luminosities against empirical and
theoretical/analytic relations. To simulate the line emission from a universe
of emitting clouds, we have incorporated random forest machine learning (ML)
methods into our approach, allowing us to predict cosmologically evolving
properties of CO, [\ion{C}{1}] and [\ion{C}{2}] emission from galaxies such as
luminosity functions. We tested this model in 100,000 gas particles, and 2,500
galaxies, reaching an average accuracy of 99.8\% for all lines. Finally,
we present the first model light cones created with realistic and ML-predicted
CO, [\ion{C}{1}], and [\ion{C}{2}] luminosities in cosmological hydrodynamical
simulations, from to .Comment: 17 pages, 11 figures, comments are welcom
The Molecular Gas Reservoirs of Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses
We test the use of long-wavelength dust continuum emission as a molecular gas
tracer at high redshift, via a unique sample of 12, z~2 galaxies with
observations of both the dust continuum and CO(1-0) line emission (obtained
with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array,
respectively). Our work is motivated by recent, high redshift studies that
measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration
of the rest-frame m luminosity () against the
CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We
hereby test whether this method is valid for the types of high-redshift,
star-forming galaxies to which it has been applied. We recover a clear
correlation between the rest-frame m luminosity, inferred from the
single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent
with the samples used to perform the m calibration. The molecular gas
masses, derived from , agree to within a factor of
two with those derived from CO(1-0). We show that this factor of two
uncertainty can arise from the values of the dust emissivity index and
temperature that need to be assumed in order to extrapolate from the observed
frequency to the rest-frame at 850. The extrapolation to
850 therefore has a smaller effect on the accuracy of \Mmol\
derived via single-band dust-continuum observations than the assumed
CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore
conclude that single-band observations of long-wavelength dust emission can be
used to reliably constrain the molecular gas masses of massive, star-forming
galaxies at
The COSMOS-[O II] survey: Evolution of electron density with star formation rate
Star-forming galaxies at z > 1 exhibit significantly different properties to local galaxies of equivalent stellar mass. Not only are high-redshift star-forming galaxies characterized by higher star formation rates and gas fractions than their local counterparts, they also appear to host star-forming regions with significantly different physical conditions, including greater electron densities. To understand what physical mechanisms are responsible for the observed evolution of the star-forming conditions, we have assembled the largest sample of star-forming galaxies at z ~ 1.5 with emission-line measurements of the [O II]λλ3726, 3729 doublet. By comparing our z ~ 1.5 sample to local galaxy samples with equivalent distributions of stellar mass, star formation rate and specific star formation rate we investigate the proposed evolution in electron density and its dependence on global properties. We measure an average electron density of 114-27+28 cm-3 for our z ~ 1.5 sample, a factor of 5 greater than the typical electron density of local star-forming galaxies. However, we find no offset between the typical electron densities of local and high-redshift galaxies with equivalent star formation rates. Our work indicates that the average electron density of a sample is highly sensitive to the star formation rates, implying that the previously observed evolution is mainly the result of selection effectsBG gratefully acknowledges the support of the Australian Research Council as the recipient of a Future Fellowship
(FT140101202). LK gratefully acknowledges support from an ARC Laureate Fellowship (FL150100113)
To See or Not to See a Galaxy? That is the Question
``When did the first galaxies form?'' is still one of the greatest unanswered
questions in astronomy. Theory and current stellar population models imply that
the first galaxies formed at least at z=14-15. Yet, the highest redshift galaxy
to have been securely confirmed remains GN-z11, at z11. The galaxy
``HD1'' was recently proposed to be a z=13.27 galaxy based on its potential
Lyman break and tentative [O III] 88 {\mu}m detection with ALMA. We hereby aim
to test this scenario with new ALMA Band 4, DDT observations of what would be
the [C II] 158 {\mu}m emission, if HD1 is at z13.27. We carefully analyse
the new ALMA Band 4 observations as well as re-analysing the existing ALMA Band
6 data on the source to determine the proposed redshift. We find a tentative
feature in the Band 4 data that is spatially offset by 1.7" and
spectrally offset by 190 km s-1 from the previously-reported ``[O
III] 88 {\mu}m'' feature. Through various statistical tests, we demonstrate
that these tentative features are fully consistent with being random noise
features. The chances of finding a noise peak of the same significance as the
tentative [C II] and [O III] features are 50\% and 100\%, respectively. Given
the noise properties of the ALMA data, we recover at least a 50\% chance of
finding two, matched noise peaks that are spatially and
spectrally offset by 10 kpc and 1000 km s-1. We conclude that we are more
likely to be recovering noise features than both [O III] and [C II] emission
from a source at . Although we find no evidence of a
galaxy, we cannot entirely rule out this scenario. Non-detections are also
possible for a source with a low interstellar gas-phase metallicity
and density. Determining where and exactly what type of galaxy HD1 is, will now
likely require JWST/NIRSpec spectroscopy.Comment: Submitted to A&A, 9 pages, 6 figures
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.Comment: 24 pages, 11 figures. Published in Ap
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.Comment: 32 pages, 20 figures, 1 table, accepted for publication in Ap
Obscuration beyond the nucleus: infrared quasars can be buried in extreme compact starbursts
In the standard quasar model, the accretion disk obscuration is due to the
canonical dusty torus. Here, we argue that a substantial part of the quasar
obscuration can come from the interstellar medium (ISM) when the quasars are
embedded in compact starbursts. We use an obscuration-unbiased sample of 578
infrared (IR) quasars at and archival ALMA submillimeter host
galaxy sizes to investigate the ISM contribution to the quasar obscuration. We
calculate SFR and ISM column densities for the IR quasars and a control sample
of submillimeter galaxies (SMGs) not hosting quasar activity and show that: (1)
the quasar obscured fraction is constant up to , and then increases towards higher SFR, suggesting that the ISM
obscuration plays a significant role in starburst host galaxies, and (2) at
, the SMGs and IR quasars have
similarly compact submillimeter sizes () and,
consequently, the ISM can heavily obscure the quasar, even reaching
Compton-thick () levels in extreme cases.
Based on our results, we infer that of the IR quasars with
are obscured solely by the ISM.Comment: Accepted for publication in MNRAS Letter