518 research outputs found
Molecular Gas in Intermediate Redshift ULIRGs
We report on the results of observations in the CO(1-0) transition of a
complete sample of Southern, intermediate redshift (z = 0.2 - 0.5)
Ultra-Luminous Infra-Red Galaxies using the Mopra 22m telescope. The eleven
ULIRGs with L_FIR > 10^12.5 L_Sun south of Dec = -12 deg were observed with
integration times that varied between 5 and 24 hours. Four marginal detections
were obtained for individual targets in the sample. The "stacked" spectrum of
the entire sample yields a high significance, 10{\sigma} detection of the
CO(1-0) transition at an average redshift of z = 0.38. The tightest correlation
of L_FIR and L_CO for published low redshift ULIRG samples (z < 0.2) is
obtained after normalisation of both these measures to a fixed dust
temperature. With this normalisation the relationship is linear. The
distribution of dust-to-molecular hydrogen gas mass displays a systematic
increase in dust-to-gas mass with galaxy luminosity for low redshift samples
but this ratio declines dramatically for intermediate redshift ULIRGs down to
values comparable to that of the Small Magellanic Cloud. The upper envelope to
the distribution of ULIRG molecular mass as function of look-back time
demonstrates a dramatic rise by almost an order of magnitude from the current
epoch out to 5 Gyr. This increase in maximum ULIRG gas mass with look-back time
is even more rapid than that of the star formation rate density.Comment: 7 pages, 5 figures, accepted for publication by MNRA
Virtue and austerity
Virtue ethics is often proposed as a third way in health-care ethics, that while consequentialism and deontology focus on action guidelines, virtue focuses on character; all three aim to help agents discern morally right action although virtue seems to have least to contribute to political issues, such as austerity. I claim: (1) This is a bad way to characterize virtue ethics. The 20th century renaissance of virtue ethics was first proposed as a response to the difficulty of making sense of ‘moral rightness’ outside a religious context. For Aristotle the right action is that which is practically best; that means best for the agent in order to live a flourishing life.There are no moral considerations besides this. (2) Properly characterized, virtue ethics can contribute to discussion of austerity.
A criticism of virtue ethics is that fixed characteristics seem a bad idea in ever-changing environments; perhaps we should be generous in prosperity, selfish in austerity. Furthermore, empirical evidence suggests that people indeed do change with their environment. However, I argue that
virtues concern fixed values not fixed behaviour; the values underlying virtue allow for different behaviour in different circumstances: in austerity, virtues still give the agent the best chance of flourishing. Two questions
arise. (a) In austere environments might not injustice help an individual flourish by, say, obtaining material goods? No, because unjust acts undermine the type of society the agent needs for flourishing. (b) What good is virtue to those lacking the other means to flourish? The notion of degrees of flourishing shows that most people would benefit
somewhat from virtue. However, in extreme circumstances virtue might harm rather than benefit the agent: such circumstances are to be avoided; virtue ethics thus has a political agenda to enable flourishing.
This requires justice, a fortiori when in austerity
ORCA: The Overdense Red-sequence Cluster Algorithm
We present a new cluster detection algorithm designed for the Panoramic
Survey Telescope and Rapid Response System (Pan-STARRS) survey but with generic
application to any multiband data. The method makes no prior assumptions about
the properties of clusters other than (a) the similarity in colour of cluster
galaxies (the "red sequence") and (b) an enhanced projected surface density.
The detector has three main steps: (i) it identifies cluster members by
photometrically filtering the input catalogue to isolate galaxies in
colour-magnitude space, (ii) a Voronoi diagram identifies regions of high
surface density, (iii) galaxies are grouped into clusters with a
Friends-of-Friends technique. Where multiple colours are available, we require
systems to exhibit sequences in two colours. In this paper we present the
algorithm and demonstrate it on two datasets. The first is a 7 square degree
sample of the deep Sloan Digital Sky Survey equatorial stripe (Stripe 82), from
which we detect 97 clusters with z<=0.6. Benefiting from deeper data, we are
100% complete in the maxBCG optically-selected cluster catalogue (based on
shallower single epoch SDSS data) and find an additional 78 previously
unidentified clusters. The second dataset is a mock Medium Deep Survey (MDS)
Pan-STARRS catalogue, based on the Lambda-CDM model and a semi-analytic galaxy
formation recipe. Knowledge of galaxy-halo memberships in the mock allows a
quantification of algorithm performance. We detect 305 mock clusters in haloes
with mass >10^13 solar masses at z<=0.6 and determine a spurious detection rate
of <1%, consistent with tests on the Stripe 82 catalogue. The detector performs
well in the recovery of model Lambda-CDM clusters. (abridged)Comment: 22 pages, 17 figures. Accepted for publication in MNRAS. ORCA cluster
catalogues available at http://orca.dur.ac.uk
The Clustering of Ha Emitters at z=2.23 from HiZELS
We present a clustering analysis of 370 high-confidence Hα emitters (HAEs) at z = 2.23. The HAEs are detected in the Hi-Z Emission Line Survey (HiZELS), a large-area blank field 2.121 μm narrow-band survey using the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). Averaging the two-point correlation function of HAEs in two ∼1° scale fields [United Kingdom Infrared Deep Sky Survey/Ultra Deep Survey (UDS) and Cosmological Evolution Survey (COSMOS) fields] we find a clustering amplitude equivalent to a correlation length of r0 = 3.7 ± 0.3 h−1 Mpc for galaxies with star formation rates of ≳7 M⊙ yr−1. The data are also well-fitted by the expected correlation function of cold dark matter (CDM), scaled by a bias factor: ωHAE = b2ωDM where . The corresponding ‘characteristic’ mass for the haloes hosting HAEs is log (Mh/[h−1 M⊙]) = 11.7 ± 0.1. Comparing to the latest semi-analytic galform predictions for the evolution of HAEs in a ΛCDM cosmology, we find broad agreement with the observations, with galform predicting an HAE correlation length of ∼4 h−1 Mpc. Motivated by this agreement, we exploit the simulations to construct a parametric model of the halo occupation distribution (HOD) of HAEs, and use this to fit the observed clustering. Our best-fitting HOD can adequately reproduce the observed angular clustering of HAEs, yielding an effective halo mass and bias in agreement with that derived from the scaled ωDM fit, but with the relatively small sample size the current data provide a poor constraint on the HOD. However, we argue that this approach provides interesting hints into the nature of the relationship between star-forming galaxies and the matter field, including insights into the efficiency of star formation in massive haloes. Our results support the broad picture that ‘typical’ (≲L⋆) star-forming galaxies have been hosted by dark matter haloes with Mh ≲ 1012 h−1 M⊙ since z ≈ 2, but with a broad occupation distribution and clustering that is likely to be a strong function of luminosity
[NII] fine-structure emission at 122 and 205um in a galaxy at z=2.6: a globally dense star-forming interstellar medium
© 2020. The American Astronomical Society. All rights reserved.We present new observations with the Atacama Large Millimeter/sub-millimeter Array of the 122um and 205um fine-structure line emission of singly-ionised nitrogen in a strongly lensed starburst galaxy at z=2.6. The 122/205um [NII] line ratio is sensitive to electron density, n_e, in the ionised interstellar medium, and we use this to measure n_e~300cm^-3 averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, but comparable to localised Galactic star-forming regions. Combined with observations of the atomic carbon (CI(1-0)) and carbon monoxide (CO(4-3)) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionised phase, presumably co-located with myriad HII regions that litter the gas-rich disk.Peer reviewedFinal Accepted Versio
A Redline Starburst: Co(2-1) Observations of an Eddington-Limited Galaxy Reveal Star Formation at its Most Extreme
We report observations of the CO(2-1) emission of SDSSJ1506+54, a compact (r_e~135pc) starburst galaxy at z=0.6. SDSSJ1506+54 appears to be forming stars close to the limit allowed by stellar radiation pressure feedback models: the measured L_IR/L\u27_CO 1500 is one of the highest measured for any galaxy. With its compact optical morphology but extended low surface brightness envelope, post-starburst spectral features, high infrared luminosity (L_IR\u3e10^12.5 L_Sun), low gas fraction (M_H2/M_stars~15%), and short gas depletion time (tens of Myr), we speculate that this is a feedback- limited central starburst episode at the conclusion of a major merger. Taken as such, SDSSJ1504+54 epitomizes the brief closing stage of a classic model of galaxy growth: we are witnessing a key component of spheroid formation during what we term a \u27redline\u27 starburst
The Environments of Low and High Luminosity Radio Galaxies at Moderate Redshifts
In the local Universe, high-power radio galaxies live in lower density
environments than low-luminosity radio galaxies. If this trend continues to
higher redshifts, powerful radio galaxies would serve as efficient probes of
moderate redshift groups and poor clusters. Photometric studies of radio
galaxies at 0.3 < z < 0.5 suggest that the radio luminosity-environment
correlation disappears at moderate redshifts, though this could be the result
of foreground/background contamination affecting the photometric measures of
environment. We have obtained multi-object spectroscopy of in the fields of 14
lower luminosity (L_1.4GHz
1.2x10^25 W/Hz) radio galaxies at z ~ 0.3 to spectroscopically investigate the
link between the environment and the radio luminosity of radio galaxies at
moderate redshifts. Our results support the photometric analyses; there does
not appear to be a correlation between the luminosity of a radio galaxy and its
environment at moderate redshifts. Hence, radio galaxies are not efficient
signposts for group environments at moderate redshifts.Comment: 7 pages, 9 figures, Accepted for publication in A
An orientation bias in observations of submillimetre galaxies
Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies.
This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and
does this result in an ‘orientation bias’ in the selection and analysis of such galaxies in flux-limited cosmological surveys? We
investigate these questions using the Simba cosmological simulation paired with the dust radiative transfer code Powderday.
We select eight simulated SMGs (850 & 2 mJy) at = 2, and measure the variance of their ‘observed’ emission over 50 random
orientations. Each galaxy exhibits significant scatter in its emission close to the peak of the thermal dust emission, with variation
in flux density of up to ∼50 mJy at the peak. This results in an appreciable dispersion in the inferred dust temperatures and
infrared luminosities (16th − 84th percentile ranges of 5 K and 0.1 dex, respectively) and therefore a fundamental uncertainty in
derived parameters such as dust mass and star formation rate (∼30% for the latter using simple calibrations). Using a Monte
Carlo simulation we also assess the impact of orientation on flux-limited surveys, finding a bias in the selection of SMGs towards
those with face–on orientations, as well as those at lower redshifts. We predict that the orientation bias will affect flux-limited
single-dish surveys, most significantly at THz frequencies, and this bias should be taken into account when placing the results
of targeted follow–up studies in a statistical context
Morphological Composition of z~0.4 groups: The site of S0 formation
The low redshift Universe (z<~0.5) is not a dull place. Processes leading to
the suppression of star formation and morphological transformation are
prevalent: this is particularly evident in the dramatic upturn in the fraction
of S0-type galaxies in clusters. However, until now, the process and
environment of formation has remained unidentified. We present a HST-based
morphological analysis of galaxies in the redshift-space selected group and
field environments at z~0.4. Groups contain a much higher fraction of S0s at
fixed luminosity than the lower density field, with >99.999% confidence. Indeed
the S0 fraction in groups is at least as high as in z~0.4 clusters and X-ray
selected groups, which have more luminous Intra Group Medium (IGM). An 97%
confident excess of S0s at >=0.3Mpc from the group centre at fixed luminosity,
tells us that formation is not restricted to, and possibly even avoids, the
group cores. Interactions with a bright X-ray emitting IGM cannot be important
for the formation of the majority of S0s in the Universe. In contrast to S0s,
the fraction of elliptical galaxies in groups at fixed luminosity is similar to
the field, whilst the brightest ellipticals are strongly enhanced towards the
group centres (>99.999% confidence within 0.3Mpc). We conclude that the group
and sub-group environments must be dominant for the formation of S0 galaxies,
and that minor mergers, galaxy harassment and tidal interactions are the most
likely responsible mechanisms. This has implications not only for the inferred
pre-processing of cluster galaxies, but also for the global morphological and
star formation budget of galaxies: as hierarchical clustering progresses, more
galaxies will be subject to these transformations as they enter the group
environment.Comment: 13 pages, 6 figures. Accepted for publication in Ap
The impact of the dusty torus on obscured quasar halo mass measurements
Recent studies have found that obscured quasars cluster more strongly and are thus hosted by dark matter haloes of larger mass than their unobscured counterparts. These results pose a challenge for the simplest unification models, in which obscured objects are intrinsically the same as unobscured sources but seen through a dusty line of sight. There is general consensus that a structure like a ‘dusty torus’ exists, meaning that this intrinsic similarity is likely the case for at least some subset of obscured quasars. However, the larger host halo masses of obscured quasars imply that there is a second obscured population that has an even higher clustering amplitude and typical halo mass. Here, we use simple assumptions about the host halo mass distributions of quasars, along with analytical methods and cosmological N-body simulations to isolate the signal from this population. We provide values for the bias and halo mass as a function of the fraction of the ‘non-torus-obscured’ population. Adopting a reasonable value for this fraction of ∼25 per cent implies a non-torus-obscured-quasar bias that is much higher than the observed obscured quasar bias, because a large fraction of the obscured population shares the same clustering strength as the unobscured objects. For this non-torus-obscured population, we derive a bias of ∼3, and typical halo masses of ∼3 × 1013 M⊙ h−1 at z = 1. These massive haloes are likely the descendants of high-mass unobscured quasars at high redshift, and will evolve into members of galaxy groups at z = 0.Peer reviewe
- …