Abstract
The Large High Altitude Air Shower Observatory (LHAASO) is a major ground-based array of cosmic-ray (CR) detectors in the Sichuan Province in China. The Water Cherenkov Detector Array (WCDA) ...is an essential component of LHAASO, which is designed to measure ~1-50 TeV CRs and gamma rays. As observed on Earth, the Moon blocks some CRs to create a shadow. Although CRs are mostly protons, WCDA can probabilistically identify some constituents (mostly electrons and photons) of CRs which produce electromagnetic (EM) showers in the atmosphere, using the “compactness” (
C
) of the showers as the criterion for which the higher
C
indicates the higher probability of an event being EM. The observed CR Moon shadow positions must be shifted from that of the actual Moon due to the deflection of charged particles by the Earth’s magnetic field. We analyze the LHAASO WCDA data from March 2021 to December 2022 to study the properties of the CR Moon shadows for events with
C
< 10 and
C
> 10, such as the shifted position and the size of the shadow at different energies. We found that i) CR shadows’ shifts decrease when energy increases, and ii) the higher the energy, the size of the CR shadows are more compact. This analysis is useful for detector calibration, event selection study, and understanding CR trajectories in the geomagnetic field.
We propose a tool to distinguish between Galactic globular clusters (GCs) and dwarf galaxies based on physical properties of RR Lyrae (RRL) variables in the systems. Normally, these two systems show ...various distinctive properties; for instance, mass, size, and luminosity. Nevertheless, these properties overlap each other in recently discovered systems. The subsequent classification between GCs and dwarf spheroidal (dSph) galaxy is ambiguous. An RRL variable is a pulsating variable star with a short period of 0.2-1 days. It is relatively easy to observe the complete period of its light curve. The age of RRL stars is typically more than 10 Gyr; therefore, they can provide information of the host system at its early stage. In this study, we provide an extensive data collection of RRLs in 96 GCs, 23 dSphs, and 10 dwarf irregular (dIrr) galaxies. Based on public catalogs, we analyze various RRL properties such as Oosterhoff dichotomy, fraction of high amplitude short period (HASP) variables, metallicity, and specific frequency of RRLs (SRR). We examine correlations among all properties in an attempt to distinguish between GCs and dSphs.
The quasar SDSS 0956+5128 exhibits three distinct velocity components with large offsets in emission: the systemic velocity of O II, O III and Ne III narrow lines have redshift \(z=0.7142\); broad Mg ...II line is shifted by \(-1200\) km s\(^{-1}\) with respect to the narrow lines; broad H\(\alpha\), H\(\beta\) lines are at \(-4100\) km s\(^{-1}\). We present new Hubble Space Telescope spectra of Ly\(\alpha\) and C IV emission lines and high-resolution images of the quasar. The offsets of these lines are consistent with the velocity component of the Balmer emission, and the photometry in optical and near-infrared wavelengths does not show any signs of recent mergers in the host galaxy or irregularities in the location of the quasar. The data do not confirm predictions of the previous most-likely hypotheses involving a special orientation and morphology of the quasar disk, such as in the recoiling black hole scenario, neither it is consistent with accretion disk winds. Instead, based on the cumulative evidence, we propose a new scenario, in which the broad line region is in the state of outflow caused by a strong shock wave, with a supernova as a possible event for producing the shock ejecta.
ABSTRACT 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 data set of the Sloan Digital Sky Survey (SDSS) Data Release 9. In total, we found more than 6000 objects with redshifts between z ∼ 0.05 and z ∼ 1.3, 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 ∼ −23.5 at z ∼ 0.8 to M ∼ −20.3 at z ∼ 0.1. 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 (∼1%) 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 the star formation rate of the universe is happening.
We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II quasars selected from the Sloan Digital Sky Survey (SDSS), using Triplespec on the Apache Point Observatory 3.5 m telescope, ...the Folded-port InfraRed Echellette at the Magellan/Baade 6.5 m telescope, and the Gemini Near-Infrared Spectrograph on Gemini. At redshifts of 2 < z < 3.4, our NIR spectra probe the rest-frame optical region of these targets, which were initially selected to have strong lines of CIV and Ly alpha, with FWHM < 2000 km s super(-1) from the SDSS pipeline. We use the OIII lambda5007 line shape as a model for the narrow-line region emission and find that Halphaconsistently requires a broad component with FWHMs ranging from 1000 to 7500 km s super(-1). Interestingly, the CIV lines also require broad bases, but with considerably narrower widths of 1000-4500 km s super(-1). Estimating the extinction using the Balmer decrement and also the relationship in lower-z quasars between rest equivalent width and luminosity in the Oiii line, we find typical A sub(V) values of 0-2 mag, which naturally explains the attenuated CIV lines relative to Halpha. We propose that our targets are moderately obscured quasars. We also describe one unusual object with three distinct velocity peaks in its OIII spectrum.
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.
We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II quasars selected from the Sloan Digital Sky Survey, using Triplespec on the Apache Point Observatory 3.5m telescope, FIRE at ...the Magellan/Baade 6.5m telescope, and GNIRS on Gemini. At redshifts of 2 < z < 3.4, our NIR spectra probe the rest-frame optical region of these targets, which were initially selected to have strong lines of CIV and Ly alpha, with FWHM<2000 km/s from the SDSS pipeline. We use the OIII5007 line shape as a model for the narrow line region emission, and find that \halpha\ consistently requires a broad component with FWHMs ranging from 1000 to 7500 km/s. Interestingly, the CIV lines also require broad bases, but with considerably narrower widths of 1000 to 4500 km/s. Estimating the extinction using the Balmer decrement and also the relationship in lower-z quasars between rest equivalent width and luminosity in the OIII line, we find typical A_V values of 0-2 mag, which naturally explain the attenuated CIV lines relative to Halpha. We propose that our targets are moderately obscured quasars. We also describe one unusual object with three distinct velocity peaks in its OIII spectrum.
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.
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