The Evolution of Post-Starburst Galaxies from z∼1z\sim1 to the Present

Post-starburst galaxies are in the transitional stage between blue, star-forming galaxies and red, quiescent galaxies, and therefore hold important clues for our understanding of galaxy evolution. In this paper, we systematically searched for and identified a large sample of post-starburst galaxies from the spectroscopic dataset of the Sloan Digital Sky Survey (SDSS) Data Release 9. In total, we found more than 6000 objects with redshifts between $z\sim0.05$ and $z\sim1.3$, making this the largest sample of post-starburst galaxies in the literature. We calculated the luminosity function of the post-starburst galaxies using two uniformly selected subsamples: the SDSS Main Galaxy Sample and the Baryon Oscillation Spectroscopic Survey CMASS Sample. The luminosity functions are reasonably fit by half-Gaussian functions. The peak magnitudes shift as a function of redshift from $M\sim-23.5$ at $z\sim0.8$ to $M\sim-20.3$ at $z\sim0.1$. This is consistent with the downsizing trend, whereby more massive galaxies form earlier than low-mass galaxies. We compared the mass of the post-starburst stellar population found in our sample to the decline of the global star-formation rate and found that only a small amount ($\sim1\%$) of all star-formation quenching in the redshift range $z=0.2-0.7$ results in post-starburst galaxies in the luminosity range our sample is sensitive to. Therefore, luminous post-starburst galaxies are not the place where most of the decline in star-formation rate of the universe is happening.Comment: 26 pages, 24 figures, 8 tables. Accepted for publication in The Astrophysical Journa

Identification of a WNT5A-Responsive Degradation Domain in the Kinesin Superfamily Protein KIF26B.

Noncanonical WNT pathways function independently of the β-catenin transcriptional co-activator to regulate diverse morphogenetic and pathogenic processes. Recent studies showed that noncanonical WNTs, such as WNT5A, can signal the degradation of several downstream effectors, thereby modulating these effectors' cellular activities. The protein domain(s) that mediates the WNT5A-dependent degradation response, however, has not been identified. By coupling protein mutagenesis experiments with a flow cytometry-based degradation reporter assay, we have defined a protein domain in the kinesin superfamily protein KIF26B that is essential for WNT5A-dependent degradation. We found that a human disease-causing KIF26B mutation located at a conserved amino acid within this domain compromises the ability of WNT5A to induce KIF26B degradation. Using pharmacological perturbation, we further uncovered a role of glycogen synthase kinase 3 (GSK3) in WNT5A regulation of KIF26B degradation. Lastly, based on the identification of the WNT5A-responsive domain, we developed a new reporter system that allows for efficient profiling of WNT5A-KIF26B signaling activity in both somatic and stem cells. In conclusion, our study identifies a new protein domain that mediates WNT5A-dependent degradation of KIF26B and provides a new tool for functional characterization of noncanonical WNT5A signaling in cells

The Sloan Digital Sky Survey Reverberation Mapping Project: Post-Starburst Signatures in Quasar Host Galaxies at z < 1

Quasar host galaxies are key for understanding the relation between galaxies and the supermassive black holes (SMBHs) at their centers. We present a study of 191 broad-line quasars and their host galaxies at z < 1, using high signal-to-noise ratio (SNR) spectra produced by the Sloan Digital Sky Survey Reverberation Mapping project. Clear detection of stellar absorption lines allows a reliable decomposition of the observed spectra into nuclear and host components, using spectral models of quasar and stellar radiations as well as emission lines from the interstellar medium. We estimate age, mass (M*), and velocity dispersion (sigma*) of the host stars, the star formation rate (SFR), quasar luminosity, and SMBH mass (Mbh), for each object. The quasars are preferentially hosted by massive galaxies with M* ~ 10^{11} Msun characterized by stellar ages around a billion years, which coincides with the transition phase of normal galaxies from the blue cloud to the red sequence. The host galaxies have relatively low SFRs and fall below the main sequence of star-forming galaxies at similar redshifts. These facts suggest that the hosts have experienced an episode of major star formation sometime in the past billion years, which was subsequently quenched or suppressed. The derived Mbh - sigma* and Mbh - M* relations agree with our past measurements and are consistent with no evolution from the local Universe. The present analysis demonstrates that reliable measurements of stellar properties of quasar host galaxies are possible with high-SNR fiber spectra, which will be acquired in large numbers with future powerful instruments such as the Subaru Prime Focus Spectrograph.Comment: ApJ in pres

Deep Photometry in a Remote M31 Major Axis Field Near G1

We present photometry from Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 parallel imagery of a remote M31 field at a projected distance of about 34 kpc from the nucleus near the SW major axis. This field is near the globular cluster G1, and near one of the candidate tidal plumes identified by Ferguson et al. (2002). The F606W (V) and F814W (I) images were obtained in parallel with Space Telescope Imaging Spectrograph spectroscopy of G1 (GO-9099) and total 7.11 hours of integration time -- the deepest HST field in the outer disk of M31 to date, reaching to V ~ 28. The color-magnitude diagram of the field shows a clearly-defined red clump at V = 25.25 and a red giant branch consistent with [Fe/H] ~ -0.7. The lack of a blue horizontal branch contrasts with other M31 halo fields, the Andromeda dwarf spheroidals, and with the nearby globular cluster G1. Comparing the observed luminosity function to the Padova models, we find that at least some of the stellar population must be younger than 6 - 8 Gyr. The outermost detected neutral hydrogen gas disk of M31 lies only 2 kpc in projection from our field. The finding that some giants in the field have radial velocities close to that of the neutral hydrogen gas (Reitzel, Guhathakurta, & Rich 2003) leads us to conclude that our field samples the old, low-surface-brightness disk rather than the true Population II spheroid.Comment: 15 pages, 3 figures. accepted for publication in the A

Impaired heart rate recovery is associated with new-onset atrial fibrillation: a prospective cohort study

<p>Abstract</p> <p>Background</p> <p>Autonomic dysfunction appears to play a significant role in the development of atrial fibrillation (AF), and impaired heart rate recovery (HRR) during exercise treadmill testing (ETT) is a known marker for autonomic dysfunction. However, whether impaired HRR is associated with incident AF is unknown. We studied the association of impaired HRR with the development of incident AF, after controlling for demographic and clinical confounders.</p> <p>Methods</p> <p>We studied 8236 patients referred for ETT between 2001 and 2004, and without a prior history of AF. Patients were categorized by normal or impaired HRR on ETT. The primary outcome was the development of AF. Cox proportional hazards modeling was used to control for demographic and clinical characteristics. Secondary analyses exploring a continuous relationship between impaired HRR and AF, and exploring interactions between cardiac medication use, HRR, and AF were also conducted.</p> <p>Results</p> <p>After adjustment, patients with impaired HRR were more likely to develop AF than patients with normal HRR (HR 1.43, 95% confidence interval (CI) 1.06, 1.93). In addition, there was a linear trend between impaired HRR and AF (HR 1.05 for each decreasing BPM in HRR, 95% CI 0.99, 1.11). No interactions between cardiac medications, HRR, and AF were noted.</p> <p>Conclusion</p> <p>Patients with impaired HRR on ETT were more likely to develop new-onset AF, as compared to patients with normal HRR. These findings support the hypothesis that autonomic dysfunction mediates the development of AF, and suggest that interventions known to improve HRR, such as exercise training, may delay or prevent AF.</p