Abstract
We present a recalibration of the photometric systems in the Pantheon+ sample of Type Ia supernovae (SNe Ia) including those in the SH0ES distance-ladder measurement of
H
0
. We utilize the ...large and uniform sky coverage of the public Pan-STARRS stellar photometry catalog to cross calibrate against tertiary standards released by individual SN Ia surveys. The most significant updates over the “SuperCal” cross calibration used for the previous Pantheon and SH0ES analyses are: (1) expansion of the number of photometric systems (now 25) and filters (now 105), (2) solving for all filter offsets in all systems simultaneously to produce a calibration uncertainty covariance matrix for cosmological-model constraints, and (3) accounting for the change in the fundamental flux calibration of the Hubble Space Telescope CALSPEC standards from previous versions on the order of 1.5% over a Δ
λ
of 4000 Å. We retrain the SALT2 model and find that our new model coupled with the new calibration of the light curves themselves causes a net distance modulus change (
d
μ
/
dz
) of 0.04 mag over the redshift range 0 <
z
< 1. We introduce a new formalism to determine the systematic impact on cosmological inference by propagating the covariance in the fitted calibration offsets through retraining simultaneously with light-curve fitting and find a total calibration uncertainty impact of
σ
w
= 0.013; roughly half the size of the sample statistical uncertainty. Similarly, we find the systematic SN calibration contribution to the SH0ES
H
0
uncertainty is less than 0.2 km s
−1
Mpc
−1
, suggesting that SN Ia calibration cannot resolve the current level of the “Hubble Tension.”
Abstract We present an all-southern sky survey for Mg ii λλ 2796, 2803 doublet absorbers in 951 z < 4 active galactic nucleus/quasar spectra from the Australian Dark Energy Survey. The spectral ...resolution ranges from R = 1400 to 1700 over the wavelengths 3700–8800 Å. The survey has a 5 σ detection completeness of 50% and above for rest-frame equivalent widths W r (2796) ≥ 0.3 Å. We studied 656 Mg ii absorption systems over the redshift range 0.33 ≤ z ≤ 2.19 with equivalent widths 0.3 ≤ W r (2796) ≤ 3.45 Å. The equivalent width distribution is well fit by an exponential function with W * = 0.76 ± 0.04 Å, and the redshift path density exhibits very little evolution. Overall, our findings are consistent with the large, predominantly northern sky, surveys of Mg ii absorbers. We developed and implemented a Monte Carlo model informed by a high-resolution Mg ii survey for determining the Mg ii mass density, Ω Mg II . We found Ω Mg II ∼ 5 × 10 −7 with no evidence of evolution over a ∼7 Gyr time span following Cosmic Noon. Incorporating measurements covering 2.0 ≤ z ≤ 6.4 from the literature, we extended our insights into Mg ii mass density evolution from the end of reionization well past the Cosmic Noon epoch. The presented Monte Carlo model has potential for advancing our knowledge of the evolution of mass densities of metal ions common to quasar absorption line studies, as it exploits the efficiency of large low-resolution surveys while requiring only small samples from expensive high-resolution surveys.
ABSTRACT
Periodically variable quasars have been suggested as close binary supermassive black holes. We present a systematic search for periodic light curves in 625 spectroscopically confirmed ...quasars with a median redshift of 1.8 in a 4.6 deg2 overlapping region of the Dark Energy Survey Supernova (DES-SN) fields and the Sloan Digital Sky Survey Stripe 82 (SDSS-S82). Our sample has a unique 20-yr long multicolour (griz) light curve enabled by combining DES-SN Y6 observations with archival SDSS-S82 data. The deep imaging allows us to search for periodic light curves in less luminous quasars (down to r ∼23.5 mag) powered by less massive black holes (with masses ≳ 108.5M⊙) at high redshift for the first time. We find five candidates with significant (at >99.74 per cent single-frequency significance in at least two bands with a global p-value of ∼7 × 10−4–3 × 10−3 accounting for the look-elsewhere effect) periodicity with observed periods of ∼3–5 yr (i.e. 1–2 yr in rest frame) having ∼4–6 cycles spanned by the observations. If all five candidates are periodically variable quasars, this translates into a detection rate of ${\sim }0.8^{+0.5}_{-0.3}$ per cent or ${\sim }1.1^{+0.7}_{-0.5}$ quasar per deg2. Our detection rate is 4–80 times larger than those found by previous searches using shallower surveys over larger areas. This discrepancy is likely caused by differences in the quasar populations probed and the survey data qualities. We discuss implications on the future direct detection of low-frequency gravitational waves. Continued photometric monitoring will further assess the robustness and characteristics of these candidate periodic quasars to determine their physical origins.
Weather conditions are a key factor in deciding where to build telescope facilities. It is also a critical factor when planning and designing large surveys. Siding Spring Observatory, located in ...Northern New South Wales, Australia, has been a national hub for optical astronomy for decades. Weather data have been gathered from multiple sources on site and analyzed to show long term trends in wind, humidity, temperatures, and observing conditions on site. A gradual decrease in humidity was observed due to the recent drought, a trend that is expected to continue into the future. Downtime due to high humidity occurs most in winter, with 17.5% of observing time sitting at >90%. Wind direction and speeds are highly variable across the mountain. Predominant winds are NNW in summer (December–February), and S in winter (June–August). Strong gusts in excess of 55 ms−1 can rarely be experienced near the apex of the mountain, however, the majority of the mountain does not experience this, and the median wind speed is 3.4 ms−1. Temperatures are consistent across the mountain, with a median of 14.1°C. Diurnal temperature variations are largest in summer, at 11°C. 46% of nights are cloudy, with a further 9%–29% having poor viewing conditions depending on wavelength range.
Weather conditions are a key factor in deciding where to build telescope facilities. It is also a critical factor when planning and designing large surveys. Siding Spring Observatory, located in ...Northern New South Wales, Australia, has been a national hub for optical astronomy for decades. Weather data have been gathered from multiple sources on site and analyzed to show long term trends in wind, humidity, temperatures, and observing conditions on site. A gradual decrease in humidity was observed due to the recent drought, a trend that is expected to continue into the future. Downtime due to high humidity occurs most in winter, with 17.5% of observing time sitting at >90%. Wind direction and speeds are highly variable across the mountain. Predominant winds are NNW in summer (December–February), and S in winter (June–August). Strong gusts in excess of 55 ms−1 can rarely be experienced near the apex of the mountain, however, the majority of the mountain does not experience this, and the median wind speed is 3.4 ms−1. Temperatures are consistent across the mountain, with a median of 14.1°C. Diurnal temperature variations are largest in summer, at 11°C. 46% of nights are cloudy, with a further 9%–29% having poor viewing conditions depending on wavelength range.
We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift z sub( s) = 2.74 and image separation of 2.9 arcsec lensed by a foreground z sub( ...l) = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and gi multicolour photometric observations from the Dark Energy Survey (DES), near-IR JK photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with i sub( AB) = 18.61 and i sub( AB) = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of z = 2.739 plus or minus 0.003 and a foreground early-type galaxy with z = 0.400 plus or minus 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius thetas sub( E) ~ 1.47 arcsec, enclosed mass M sub( enc) ~ 4 x 10 super( 11) M... and a time delay of ~52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present deep, multiwavelength radio observations of SpARCS104922.6 + 564032.5, a z = 1.71 galaxy cluster with a starbursting core. Observations were made with the Karl G. Jansky Very ...Large Array (JVLA) in three bands: 1–2 GHz, 4–8 GHz, and 8–12 GHz. We detect a radio source coincident with the brightest cluster galaxy (BCG) that has a spectral index of α = 0.44 ± 0.29 and is indicative of emission from an active galactic nucleus. The radio luminosity is consistent with the average luminosity of the lower redshift BCG sample, but the flux densities are 6σ below the predicted values of the star-forming spectral energy distribution based on far infrared data. Our new fit fails to simultaneously describe the far infrared and radio fluxes. This, coupled with the fact that no other bright source is detected in the vicinity of the BCG implies that the star formation region, traced by the infrared emission, is extended or clumpy and not located directly within the BCG. Thus, we suggest that the star-forming core might not be driven by a single major wet merger, but rather by several smaller galaxies stripped of their gas or by a displaced cooling flow, although more data are needed to confirm any of those scenarios.
Abstract
We present ALMA CO (2-1) detections of 24 star-forming brightest cluster galaxies (BCGs) over 0.2 <
z
< 1.2, constituting the largest and most distant sample of molecular gas measurements in ...BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate and stellar mass, calculated from existing MIPS 24
μ
m and IRAC 3.6
μ
m fluxes, respectively. We find these galaxies have molecular gas masses of 0.7–11.0 × 10
10
M
⊙
, comparable to other BCGs in this redshift range, and specific star formation rates that trace the main sequence of Elbaz et al. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge and find that at
z
≲ 0.6 the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the ∼10% of BCGs that are star-forming process accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass.
ABSTRACT
We present a sample of 706, z < 1.5 active galactic nuclei (AGNs) selected from optical photometric variability in three of the Dark Energy Survey (DES) deep fields (E2, C3, and X3) over an ...area of 4.64 deg2. We construct light curves using difference imaging aperture photometry for resolved sources and non-difference imaging PSF photometry for unresolved sources, respectively, and characterize the variability significance. Our DES light curves have a mean cadence of 7 d, a 6-yr baseline, and a single-epoch imaging depth of up to g ∼ 24.5. Using spectral energy distribution (SED) fitting, we find 26 out of total 706 variable galaxies are consistent with dwarf galaxies with a reliable stellar mass estimate ($M_{\ast }\lt 10^{9.5}\, {\rm M}_\odot$; median photometric redshift of 0.9). We were able to constrain rapid characteristic variability time-scales (∼ weeks) using the DES light curves in 15 dwarf AGN candidates (a subset of our variable AGN candidates) at a median photometric redshift of 0.4. This rapid variability is consistent with their low black hole (BH) masses. We confirm the low-mass AGN nature of one source with a high S/N optical spectrum. We publish our catalogue, optical light curves, and supplementary data, such as X-ray properties and optical spectra, when available. We measure a variable AGN fraction versus stellar mass and compare to results from a forward model. This work demonstrates the feasibility of optical variability to identify AGNs with lower BH masses in deep fields, which may be more ‘pristine’ analogues of supermassive BH seeds.
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