635 research outputs found
Bulgeless Giant Galaxies Challenge our Picture of Galaxy Formation by Hierarchical Clustering
We dissect giant Sc-Scd galaxies with Hubble Space Telescope photometry and
Hobby-Eberly Telescope spectroscopy. We use HET's High Resolution Spectrograph
(resolution = 15,000) to measure stellar velocity dispersions in the nuclear
star clusters and pseudobulges of the pure-disk galaxies M33, M101, NGC 3338,
NGC 3810, NGC 6503, and NGC 6946. We conclude: (1) Upper limits on the masses
of any supermassive black holes are MBH <= (2.6+-0.5) * 10**6 M_Sun in M101 and
MBH <= (2.0+-0.6) * 10**6 M_Sun in NGC 6503. (2) HST photometry shows that the
above galaxies contain tiny pseudobulges that make up <~ 3 % of the stellar
mass but no classical bulges. We inventory a sphere of radius 8 Mpc centered on
our Galaxy to see whether giant, pure-disk galaxies are common or rare. In this
volume, 11 of 19 galaxies with rotation velocity > 150 km/s show no evidence
for a classical bulge. Four may contain small classical bulges that contribute
5-12% of the galaxy light. Only 4 of the 19 giant galaxies are ellipticals or
have classical bulges that contribute 1/3 of the galaxy light. So pure-disk
galaxies are far from rare. It is hard to understand how they could form as the
quiescent tail of a distribution of merger histories. Recognition of
pseudobulges makes the biggest problem with cold dark matter galaxy formation
more acute: How can hierarchical clustering make so many giant, pure-disk
galaxies with no evidence for merger-built bulges? This problem depends
strongly on environment: the Virgo cluster is not a puzzle, because >2/3 of its
stellar mass is in merger remnants.Comment: 28 pages, 16 Postscript figures, 2 tables; requires emulateapj.sty
and apjfonts.sty; accepted for publication in ApJ; for a version with full
resolution figures, see http://chandra.as.utexas.edu/~kormendy/kdbc.pd
SDSS-IV MaNGA: Identification of active galactic nuclei in optical integral field unit surveys
In this paper, we investigate 2727 galaxies observed by MaNGA as of June 2016
to develop spatially resolved techniques for identifying signatures of active
galactic nuclei (AGN). We identify 303 AGN candidates. The additional spatial
dimension imposes challenges in identifying AGN due to contamination from
diffuse ionized gas, extra-planar gas and photoionization by hot stars. We show
that the combination of spatially-resolved line diagnostic diagrams and
additional cuts on H surface brighness and H equivalent width
can distinguish between AGN-like signatures and high-metallicity galaxies with
LINER-like spectra. Low mass galaxies with high specific star formation rates
are particularly difficult to diagnose and routinely show diagnostic line
ratios outside of the standard star-formation locus. We develop a new
diagnostic -- the distance from the standard diagnostic line in the line-ratios
space -- to evaluate the significance of the deviation from the star-formation
locus. We find 173 galaxies that would not have been selected as AGN candidates
based on single-fibre spectral measurements but exhibit photoionization
signatures suggestive of AGN activity in the MaNGA resolved observations,
underscoring the power of large integral field unit (IFU) surveys. A complete
census of these new AGN candidates is necessary to understand their nature and
probe the complex co-evolution of supermassive black holes and their hosts.Comment: 18 pages, 11 figures, accepted to MNRA
Starvation-Dependent Regulation of Golgi Quality Control Links the TOR Signaling and Vacuolar Protein Sorting Pathways
SummaryUpon amino acid (AA) starvation and TOR inactivation, plasma-membrane-localized permeases rapidly undergo ubiquitination and internalization via the vacuolar protein sorting/multivesicular body (VPS-MVB) pathway and are degraded in the yeast vacuole. We now show that specific Golgi proteins are also directed to the vacuole under these conditions as part of a Golgi quality-control (GQC) process. The degradation of GQC substrates is dependent upon ubiquitination by the defective-for-SREBP-cleavage (DSC) complex, which was identified via genetic screening and includes the Tul1 E3 ligase. Using a model GQC substrate, GFP-tagged Yif1, we show that vacuolar targeting necessitates upregulation of the VPS pathway via proteasome-mediated degradation of the initial endosomal sorting complex required for transport, ESCRT-0, but not downstream ESCRT components. Thus, early cellular responses to starvation include the targeting of specific Golgi proteins for degradation, a phenomenon reminiscent of the inactivation of BTN1, the yeast Batten disease gene ortholog
The effect of the Cox-maze procedure for atrial fibrillation concomitant to mitral and tricuspid valve surgery
ObjectivesAtrial fibrillation (AF) is associated with less favorable outcomes in patients undergoing mitral valve and tricuspid valve surgery. Despite growing evidence on the potential benefits of surgical ablation for AF there is significant variability among surgeons in treatment of AF. The purpose of our study was to assess the effect of the Cox-maze procedure on operative and follow-up outcomes.MethodsIn our prospective study, patients who underwent isolated mitral valve or mitral valve+tricuspid valve surgery without history of AF (n = 506), with untreated AF (n = 75), or with Cox-maze procedure (n = 236) were included (N = 817). Sinus rhythm was captured according to Heart Rhythm Society guidelines. Patients who underwent the Cox-maze procedure were propensity score matched to patients without history of AF resulting in 208 pairs of patients.ResultsOperative outcomes were comparable after propensity score matching (Cox-maze procedure vs no AF) stroke/transient ischemic attack (0.5% vs 0.5%; P = 1.00), renal failure (2.9% vs 1.4%; P = .34), and operative mortality (1.4% vs 1.4%; P = 1.00). High return to sinus rhythm was documented at 6, 12, and 24 months (92%, 91%, and 86%, respectively) as well as sinus rhythm off antiarrhythmic drugs (79%, 84%, and 82%, respectively). Incidence of embolic stroke in patients who underwent Cox-maze procedure was 1.7% (4 out of 232 patients) and 5.1 cases per 1000 person-years. No difference in 4-year cumulative survival between propensity score-matched groups (91.9% vs 86.9%; log rank, 1.67; P = .20), but higher for patients who underwent Cox-maze procedure versus patients with untreated AF (hazard ratio, 2.47; P = .048). Higher additive European System for Cardiac Operative Risk Evaluation (odds ratio, 1.40; P < .001) and limited surgeon experience with Cox-maze procedure (odds ratio, 3.60; P < .001) were significant predictors for failure to perform Cox-maze procedure.ConclusionsIn our center, 76% of patients undergoing mitral valve or mitral valve+tricuspid valve surgery experiencing AF underwent concomitant Cox-maze procedure, which is considerably higher than the national average. No increased morbidity was associated with the Cox-maze procedure with the benefit of very low thromboembolic rate. These results suggest the need for performance-based education for AF surgical ablation to achieve optimal outcomes
Pulmonary Function Decline in Amyotrophic Lateral Sclerosis
Background: There has been no comprehensive longitudinal study of pulmonary functions (PFTS) in ALS determining which measure is most sensitive to declines in respiratory muscle strength. Objective: To determine the longitudinal decline of PFTS in ALS and which measure supports Medicare criteria for NIV initiation first. Methods: Serial PFTs (maximum voluntary ventilation (MVV), maximum inspiratory pressure measured by mouth (MIP) or nasal sniff pressure (SNIP), maximum expiratory pressure (MEP), and Forced Vital Capacity (FVC)) were performed over 12 months on 73 ALS subjects to determine which measure showed the sentinel decline in pulmonary function. The rate of decline for each measure was determined as the median slope of the decrease over time. Medicare-based NIV initiation criteria were met if %FVC was ≤ 50% predicted or MIP was ≤ 60 cMH2O. Results: 65 subjects with at least 3 visits were included for analyses. All median slopes were significantly different than zero. MEP and sitting FVC demonstrated the largest rate of decline. Seventy subjects were analyzed for NIV initiation criteria, 69 met MIP criteria first; 11 FVC and MIP criteria simultaneously and none FVC criteria first. Conclusions: MEP demonstrated a steeper decline compared to other measures suggesting expiratory muscle strength declines earliest and faster and the use of airway clearance interventions should be initiated early. When Medicare criteria for NIV initiation are considered, MIP criteria are met earliest. These results suggest that pressure-based measurements are important in assessing the timing of NIV and the use of pulmonary clearance interventions
The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design, Data Processing, and Spectral Analysis Methods
We present the survey design, data reduction, and spectral fitting pipeline
for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral
field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies.
Targets span a wide range in Hubble type, star formation activity, morphology,
and inclination. The VENGA data-cubes have 5.6'' FWHM spatial resolution, ~5A
FWHM spectral resolution, sample the 3600A-6800A range, and cover large areas
typically sampling galaxies out to ~0.7 R_25. These data-cubes can be used to
produce 2D maps of the star formation rate, dust extinction, electron density,
stellar population parameters, the kinematics and chemical abundances of both
stars and ionized gas, and other physical quantities derived from the fitting
of the stellar spectrum and the measurement of nebular emission lines. To
exemplify our methods and the quality of the data, we present the VENGA
data-cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA
observations of NGC 628 are described, as well as the construction of the
data-cube, our spectral fitting method, and the fitting of the stellar and
ionized gas velocity fields. We also propose a new method to measure the
inclination of nearly face-on systems based on the matching of the stellar and
gas rotation curves using asymmetric drift corrections. VENGA will measure
relevant physical parameters across different environments within these
galaxies, allowing a series of studies on star formation, structure assembly,
stellar populations, chemical evolution, galactic feedback, nuclear activity,
and the properties of the interstellar medium in massive disk galaxies.Comment: Accepted for publication in AJ, 25 pages, 18 figures, 6 table
- …