The upper bound on the lowest mass halo Jethwa, P; Erkal, D; Belokurov, V
Monthly Notices of the Royal Astronomical Society,
01/2018, Letnik:
473, Številka:
2
Journal Article
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Abstract
We explore the connection between galaxies and dark matter haloes in the Milky Way (MW) and quantify the implications on properties of the dark matter particle and the phenomenology of ...low-mass galaxy formation. This is done through a probabilistic comparison of the luminosity function of MW dwarf satellite galaxies to models based on two suites of zoom-in simulations. One suite is dark-matter-only, while the other includes a disc component, therefore we can quantify the effect of the MW's baryonic disc on our results. We apply numerous stellar-mass–halo-mass (SMHM) relations allowing for multiple complexities: scatter, a characteristic break scale, and subhaloes which host no galaxy. In contrast to previous works, we push the model/data comparison to the faintest dwarfs by modelling observational incompleteness, allowing us to draw three new conclusions. First, we constrain the SMHM relation for 102 < M*/ M⊙ < 108 galaxies, allowing us to bound the peak halo mass of the faintest MW satellite to Mvir > 2.4 × 108 M⊙ (1σ). Secondly, by translating to a warm dark matter (WDM) cosmology, we bound the thermal relic mass mWDM > 2.9 keV at 95 per cent confidence, on a par with recent constraints from the Lyman-α forest. Lastly, we find that the observed number of ultra-faint MW dwarfs is in tension with the theoretical prediction that reionization prevents galaxy formation in almost all 108 M⊙ haloes. This can be tested with the next generation of deep imaging surveys. To this end, we predict the likely number of detectable satellite galaxies in the Subaru/Hyper Suprime-Cam survey and the Large Synoptic Survey Telescope. Confronting these predictions with future observations will be amongst our strongest tests of WDM and the effect reionization on low-mass systems.
A Magellanic origin of the DES dwarfs Jethwa, P; Erkal, D; Belokurov, V
Monthly Notices of the Royal Astronomical Society,
09/2016, Letnik:
461, Številka:
2
Journal Article
Recenzirano
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We establish the connection between the Magellanic Clouds (MCs) and the dwarf galaxy candidates discovered in the Dark Energy Survey (DES) by building a dynamical model of the MC satellite ...populations, based on an extensive suite of tailor-made numerical simulations. Our model takes into account the response of the Galaxy to the MCs infall, the dynamical friction experienced by the MCs and the disruption of the MC satellites by their hosts. The simulation suite samples over the uncertainties in the MC's proper motions, the masses of the MW and the Clouds themselves, and allows for flexibility in the intrinsic volume density distribution of the MC satellites. As a result, we can accurately reproduce the DES satellites’ observed positions and kinematics. Assuming that Milky Way (MW) dwarfs follow the distribution of sub-haloes in Λ cold dark matter, we further demonstrate that, of 14 observed satellites, the MW halo contributes fewer than 4(8) of these with 68(95) per cent confidence and that 7(12) DES dwarfs have probabilities greater than 0.7(0.5) of belonging to the Large Magellanic Cloud (LMC). Marginalizing over the entire suite, we constrain the number of Magellanic satellites in the range −7 < MV
< −1 which exceed the DES surface brightness threshold at ∼70, and the mass of the LMC around 1011 M⊙. The data also strongly support a first-infall scenario for the LMC. Finally, we give predictions for the line-of-sight velocities and the proper motions of the satellites discovered in the vicinity of the LMC.
Context . Knowledge of the spectrograph’s instrumental profile (IP) provides important information needed for wavelength calibration and for the use in scientific analyses. Aims . This work develops ...new methods for IP reconstruction in high-resolution spectrographs equipped with astronomical laser frequency comb (astrocomb) calibration systems and assesses the impact that assumptions on the IP shape have on achieving accurate spectroscopic measurements. Methods . Astrocombs produce ≈ 10 000 bright, unresolved emission lines with known wavelengths, making them excellent probes of the IP. New methods based on Gaussian process regression were developed to extract detailed information on the IP shape from these data. Applying them to HARPS, an extremely stable spectrograph installed on the ESO 3.6m telescope, we reconstructed its IP at 512 locations of the detector, covering 60% of the total detector area. Results . We found that the HARPS IP is asymmetric and that it varies smoothly across the detector. Empirical IP models provide a wavelength accuracy better than 10m s −1 (5m s −1 ) with a 92% (64%) probability. In comparison, reaching the same accuracy has a probability of only 29% (8%) when a Gaussian IP shape is assumed. Furthermore, the Gaussian assumption is associated with intra-order and inter-order distortions in the HARPS wavelength scale as large as 60 m s −1 . The spatial distribution of these distortions suggests they may be related to spectrograph optics and therefore may generally appear in cross-dispersed echelle spectrographs when Gaussian IPs are used. Empirical IP models are provided as supplementary material in machine readable format. We also provide a method to correct the distortions in astrocomb calibrations made under the Gaussian IP assumption. Conclusions . Methods presented here can be applied to other instruments equipped with astrocombs, such as ESPRESSO, but also ANDES and G-CLEF in the future. The empirical IPs are crucial for obtaining objective and unbiased measurements of fundamental constants from high-resolution spectra, as well as measurements of the redshift drift, isotopic abundances, and other science cases.
We announce the discovery of the Aquarius 2 dwarf galaxy, a new distant satellite of the Milky Way, detected on the fringes of the VLT Survey Telescope (VST) ATLAS and the Sloan Digital Sky Survey ...(SDSS) surveys. The object was originally identified as an overdensity of red giant branch stars, but chosen for subsequent follow-up based on the presence of a strong blue horizontal branch, which was also used to measure its distance of ∼110 kpc. Using deeper imaging from the Inamori-Magellan Areal Camera and Spectrograph camera on the 6.5m Baade and spectroscopy with DEep Imaging Multi-Object Spectrograph on Keck, we measured the satellite's half-light radius 5.1 ± 0.8 arcmin, or ∼160 pc at this distance, and its stellar velocity dispersion of
$5.4^{+3.4}_{-0.9}$
km s−1. With μ = 30.2 mag arcsec−2 and M
V = −4.36, the new satellite lies close to two important detection limits: one in surface brightness; and one in luminosity at a given distance, thereby making Aquarius 2 one of the hardest dwarfs to find.
ABSTRACT
We use a sample of powerful $z\, \approx \, 0.1$ type 2 quasars (‘obscured’; log LAGN/erg s$^{-1}\, \gtrsim \, 45$), which host kpc-scale ionized outflows and jets, to identify possible ...signatures of AGN feedback on the total molecular gas reservoirs of their host galaxies. Specifically, we present Atacama Pathfinder EXperiment (APEX) observations of the CO(2–1) transition for nine sources and the CO(6–5) for a subset of three. We find that the majority of our sample reside in starburst galaxies (average specific star formation rates – sSFR – of 1.7 Gyr−1), with the seven CO-detected quasars also having large molecular gas reservoirs (average Mgas = 1.3 × 1010 M⊙), even though we had no pre-selection on the star formation or molecular gas properties. Despite the presence of quasars and outflows, we find that the molecular gas fractions (Mgas/M⋆ = 0.1–1.2) and depletion times (Mgas/SFR = 0.16–0.95 Gyr) are consistent with those expected for the overall galaxy population with matched stellar masses and sSFRs. Furthermore, for at least two of the three targets with the required measurements, the CO(6–5)/CO(2–1) emission-line ratios are consistent with star formation dominating the CO excitation over this range of transitions. The targets in our study represent a gas-rich phase of galaxy evolution with simultaneously high levels of star formation and nuclear activity; furthermore, the jets and outflows do not have an immediate appreciable impact on the global molecular gas reservoirs.
Summary
Peroral endoscopic myotomy (POEM) is a novel approach to performing esophageal myotomy for the treatment of achalasia. This review aims to assess subjective and objective metrics of achalasia ...treatment efficacy, perioperative adverse events and the incidence of postoperative gastroesophageal reflux disease in patients treated with POEM. Secondary aims include a pooled analysis comparison of the clinical outcomes and procedural safety of POEM versus laparoscopic Heller's myotomy (LHM). A systematic review of the literature, up to and including January 15, 2015, was conducted for studies reporting POEM outcomes. Studies comparing POEM to LHM were also included for the purpose of pooled analysis. Outcomes from 1122 POEM patients, from 22 studies, are reported in this systematic review. Minor operative adverse events included capno/pneumo‐peritoneum (30.6%), capno/pneumo‐thorax (11.0%) and subcutaneous emphysema (31.6%). Major operative adverse events included mediastinal leak (0.3%), postoperative bleeding (1.1%) and a single mortality (0.09%). There was an improvement in lower esophageal sphincter pressure and timed barium esophagram column height of 66% and 80% post‐POEM, respectively. Symptom improvement was demonstrated with a pre‐ and post‐POEM Eckardt score ± standard deviation of 6.8 ± 1.0 and 1.2 ± 0.6, respectively. Pre‐ and post‐POEM endoscopy showed esophagitis in 0% and 19% of patients, respectively. The median (interquartile range) points scored for study quality was 15 (14–16) out of total of 32. Pooled analysis of three comparative studies between LHM and POEM showed similar results for adverse events, perforation rate, operative time and a nonsignificant trend toward a reduced length of hospital stay in the POEM group. In conclusion, POEM is a safe and effective treatment for achalasia, showing significant improvements in objective metrics and achalasia‐related symptoms. Randomized comparative studies of LHM and POEM are required to determine the most effective treatment modality for achalasia.
Abstract
We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS ). Situated 18 deg (∼20 kpc) ...from the LMC and separated from each other by only 18 arcmin, Carina II and III form an intriguing pair. By simultaneously modelling the spatial and the colour–magnitude stellar distributions, we find that both Carina II and Carina III are likely dwarf galaxies, although this is less clear for Carina III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina II is located at ∼36 kpc from the Sun, with MV ∼ −4.5 and rh ∼ 90 pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina III is much more elongated, measured to be fainter (MV ∼ −2.4), significantly more compact (rh ∼ 30 pc), and closer to the Sun, at ∼28 kpc, placing it only 8 kpc away from Car II. Together with several other systems detected by the Dark Energy Camera, Carina II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.
Abstract
We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the Carina II (Car II) and Carina III (Car III) dwarf galaxy ...candidates, recently discovered in the Magellanic Satellites Survey (MagLiteS). We identify 18 member stars in Car II, including two binaries with variable radial velocities and two RR Lyrae stars. The other 14 members have a mean heliocentric velocity
and a velocity dispersion of
. Assuming Car II is in dynamical equilibrium, we derive a total mass within the half-light radius of
, indicating a mass-to-light ratio of
/
. From equivalent width measurements of the calcium triplet lines of nine red giant branch (RGB) stars, we derive a mean metallicity of
with dispersion
. Considering both the kinematic and chemical properties, we conclude that Car II is a dark-matter-dominated dwarf galaxy. For Car III, we identify four member stars, from which we calculate a systemic velocity of
. The brightest RGB member of Car III has a metallicity of
. Due to the small size of the Car III spectroscopic sample, we cannot conclusively determine its nature. Although these two systems have the smallest known physical separation (
) among Local Group satellites, the large difference in their systemic velocities,
, indicates that they are unlikely to be a bound pair. One or both systems are likely associated with the Large Magellanic Cloud (LMC), and may remain LMC satellites today. No statistically significant excess of
γ
-ray emission is found at the locations of Car II and Car III in eight years of
Fermi
-LAT data.
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified ...as a resolved overdensity of old and metal-poor stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.
We present the discovery of a faint, resolved stellar system, BLISS J0321+0438 (BLISS 1), found in Dark Energy Camera data from the first observing run of the Blanco Imaging of the Southern Sky ...(BLISS) survey. BLISS J0321+0438 (BLISS 1) is located at with a heliocentric distance of . It is a faint, , and compact, , system consistent with previously discovered faint halo star clusters. Using data from the second data release of the Gaia satellite, we measure a proper motion of mas yr−1. Combining the available positional and velocity information with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC), we find that it is unlikely that BLISS J0321+0438 (BLISS 1) originated with the LMC.
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