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Cold gas loss is thought to be important in star formation quenching and morphological transition during the evolution of S0 galaxies. In high-density environments, this gas loss can be achieved via many external mechanisms. However, in relatively isolated environments, where these external mechanisms cannot be efficient, the gas loss must then be dominated by some internal processes. We have performed Chandra analysis of hot gas in five nearby isolated S0 galaxies, based on the quantitative subtraction of various stellar contributions. We find that all the galaxies studied in the present work are X-ray faint, with the luminosity of the hot gas (LX) typically accounting for ≲5% of the expected Type la supernova (SN) energy injection rate. We have further compared our results with those from relevant recent papers, in order to investigate the energy budget, cold-hot gas relation, and gas removal from SO galaxies in isolated environments. We find that elliptical and S0 galaxies are not significantly different in Lx at the low-mass end (typically with K-band luminosity LK ≲ 1011 L⊙,K). However, at the high-mass end, S0 galaxies tend to have significantly lower LX than elliptical galaxies of the same stellar masses, as already shown in previous observational and theoretical works. We further discuss the potential relationship of the diffuse X-ray emission with the cold (atomíc and molecular) gas content in the SO and elliptical galaxies included in our study. We find that Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. tends to correlate positively with the total cold gas mass Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. for cold-gas-poor galaxies with Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., while they anti-correlate with each other for cold-gas-rich galaxies. This cold-hot gas relationship can be explained in a scenario of early-type galaxy evolution, with the leftover cold gas from the precursor star-forming galaxy mainly removed by the long-lasting Type la supernova (SN) feedback. The two different trends for cold-gas-rich and cold-gas-poor galaxies may be the results of the initial fast decreasing SN rate and the later fast decreasing mass loading to hot gas, respectively. [ABSTRACT FROM AUTHOR]

This is the third paper in a series aimed at finding reionization-era quasars with the combination of DESI Legacy imaging Surveys (DELS), the Pan-STARRS1 (PS1) Survey, and near-infrared imaging surveys, such as the UKIRT Hemisphere Survey (UHS), as well as the Wide-field Infrared Survey Explorer (WISE) mid-infrared survey. In this paper, we describe the updated quasar candidate selection procedure, report the discovery of 16 quasars at 6.4 ≲ z ≲ 6.9 from an area of ∼13,020 deg2, and present the quasar luminosity function (QLF) at z ∼ 6.7. The measured QLF follows in the magnitude range −27.6 < M1450 < −25.5. We determine the quasar comoving spatial density at = 6.7 and M1450 < −26.0 to be 0.39 ± 0.11 Gpc−3 and find the exponential density evolution parameter to be k = −0.78 ± 0.18 from z ∼ 6 to z ∼ 6.7, corresponding to a rapid decline by a factor of ∼6 per unit redshift toward earlier epochs. This indicates that the rapid decline of quasar spatial density at z > 5 that was found by previous works continues to z > 6, at a rate significantly faster than the average decline rate between z ∼ 3 and 5. We measured quasar comoving emissivity at z ∼ 6.7, which indicates that high-redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. The broad absorption line quasar fraction at z ≳ 6.5 is measured to be ≳22%. In addition, we also report the discovery of six additional quasars at z ∼ 6 in the Appendix. [ABSTRACT FROM AUTHOR]

We present new narrow-band Hα imaging for 24 nearby edge-on galaxies in the Continuum Halos in Nearby Galaxies—an EVLA Survey (CHANG-ES). We use the images in conjunction with the Wide-field Infrared Survey Explorer 22 μm imaging of the sample to estimate improved star formation rates (SFRs) using the updated recipe from Vargas et al. We explore correlations between the updated star formation properties and radio continuum scale heights, scale lengths, and diameters, measured in Krause et al. We find a newly discovered correlation between SFR and radio scale height that did not exist using mid-infrared (IR) only SFR calibrations. This implies that a mid-IR extinction correction should be applied to SFR calibrations when used in edge-on galaxies, due to attenuation by dust. The updated SFR values also show newly discovered correlations with radio scale length and radio diameter, implying that the previously measured relationship between radio scale height and radio diameter originates from star formation within the disk. We also identify a region of star formation located at extreme distance from the disk of NGC 4157, possibly ionized by a single O5.5 V star. This region is spatially coincident with an extended ultraviolet disk feature, as traced by the Galaxy Evolution Explorer near-ultraviolet imaging. We theorize that the star formation feature arose due to gravitational instability within gas from an accretion event. New Hα images from this work can be found at the CHANG-ES data release website, https://www.queensu.ca/changes. [ABSTRACT FROM AUTHOR]

Galaxies are surrounded by halos of hot gas whose mass and origin remain unknown. One of the most challenging properties to measure is the metallicity, which constrains both of these. We present a measurement of the metallicity around NGC 891, a nearby, edge-on, Milky Way analog. We find that the hot gas is dominated by low-metallicity gas near the virial temperature at and and that this gas coexists with hotter () gas that is concentrated near the star-forming regions in the disk. Model choices lead to differences of , and higher signal-to-noise ratio observations would be limited by systematic error and plasma emission model or abundance ratio choices. The low-metallicity gas is consistent with the inner part of an extended halo accreted from the intergalactic medium, which has been modulated by star formation. However, there is much more cold gas than hot gas around NGC 891, which is difficult to explain in either the accretion or supernova-driven outflow scenarios. We also find a diffuse nonthermal excess centered on the galactic center and extending to 5 kpc above the disk with a 0.3–10 keV . This emission is inconsistent with inverse Compton scattering or single-population synchrotron emission, and its origin remains unclear. [ABSTRACT FROM AUTHOR]

We mapped 12CO J = 1–0, 12CO J = 2–1, 13CO J = 1–0, and 13CO J = 2–1 lines toward supernova remnant (SNR) Cassiopeia A with the IRAM 30 m telescope. The molecular clouds (MCs) along the line of sight of Cas A do not show optically thin, shock-broadened 12CO lines ( toward Cas A), or high-temperature features from shock heating ( toward Cas A). Therefore, we suggest that there is no physical evidence to support that the SNR is impacting the molecular gas. All the detected MCs are likely in front of Cas A, as implied by the HCO+ absorption line detected in the same velocity ranges. These MCs contribute H2 column densities of , , and in the west, south, and center of the SNR, respectively. The 20 K warm gas at is distributed along a large-scale molecular ridge in the south of Cas A. Part of the gas is projected onto Cas A, providing a foreground H2 mass of , consistent with the mass of cold dust (15–20 K; 2–4 ) found in front of the SNR. We suggest that the 20 K warm gas is heated by background cosmic rays with an ionization rate of . The cosmic rays and X-ray emission from Cas A are excluded as the heating sources of the clouds. [ABSTRACT FROM AUTHOR]

We present ∼400 ks NuSTAR observations of the northeast (NE) and southwest (SW) nonthermal limbs of the Galactic SNR SN1006. We discovered three sources with X-ray emission detected at ≳50 keV. Two of them are identified as background active galactic nuclei. We extract the NuSTAR spectra from a few regions along the nonthermal limbs and jointly analyze them with the XMM-Newton spectra and the radio data. The broadband radio/X-ray spectra can be well described with a synchrotron emission model from a single population of CR electrons with a power-law energy distribution and an exponential cutoff. The power-law index of the electron particle distribution function (PDF) is ≈1.88–1.95 for both the NE and SW limbs, and we do not find significant evidence for a variation of this index at different energy (curvature). There are significant spatial variations of the synchrotron emission parameters. The highest energy electrons are accelerated in regions with the lowest expansion velocity, which is opposite to what has been found in Tycho’s supernova remnant. In addition to a gradual steepening of synchrotron emission from the center of the nonthermal limbs to larger azimuthal angles, we also find that both the emission spectrum and the PDF are significantly flatter in three regions in the SW limb where the shock encounters a higher density ambient medium. The NE limb also shows significantly higher cutoff energy in the PDF than the SW limb. By comparing with the roughly symmetric TeV emission and largely asymmetric GeV emission from the two nonthermal limbs, we conclude that the asymmetry in the ambient medium and magnetic fields may have largely modified the acceleration and emission of CR leptons. [ABSTRACT FROM AUTHOR]

We summarize and reanalyze observations bearing on missing galactic baryons, where we propose a consistent picture for halo gas in L ≳ L* galaxies. The hot X-ray-emitting halos are detected to 50–70 kpc, where typically Mhot(<50 kpc) ∼ 5 × 109M⊙, and with density n ∝ r−3/2. When extrapolated to R200, the gas mass is comparable to the stellar mass, but about half of the baryons are still missing from the hot phase. If extrapolated to 1.7R200–3R200, the ratio of baryon to dark matter approaches the cosmic value. Significantly flatter density profiles are unlikely for R < 50 kpc, and they are disfavored but not ruled out for R > 50 kpc. For the Milky Way, the hot halo metallicity lies in the range 0.3–1 solar for R < 50 kpc. Planck measurements of the thermal Sunyaev–Zel’dovich (SZ) effect toward stacked luminous galaxies (primarily early type) indicate that most of their baryons are hot, are near the virial temperature, and extend beyond R200. This stacked SZ signal is nearly an order of magnitude larger than that inferred from the X-ray observations of individual (mostly spiral) galaxies with M* > 1011.3M⊙. This difference suggests that the hot halo properties are distinct for early- and late-type galaxies, possibly due to different evolutionary histories. For the cooler gas detected in UV absorption line studies, we argue that there are two absorption populations: extended halos, and disks extending to ∼50 kpc, containing most of this gas, and with masses a few times lower than the stellar masses. Such extended disks are also seen in 21 cm H i observations and in simulations. [ABSTRACT FROM AUTHOR]

We present the first discoveries from a survey of z ≳ 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg2 of sky down to zAB ∼ 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < +60°, reaching JVEGA ∼ 19.6 (5-σ). The combination of these data sets allows us to discover quasars at redshift z ≳ 7 and to conduct a complete census of the faint quasar population at z ≳ 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z ≳ 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z ∼ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 Å being M1450 = −25.83 and M1450 = −25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z ≳ 6. The new z = 6.63 quasar has an absolute magnitude of M1450 = −25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z ≳ 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield ∼200 z ∼ 6 quasars to zAB < 21.5, ∼1000 z ∼ 6 quasars to zAB < 23, and ∼30 quasars at z > 6.5 to JVEGA < 19.5. [ABSTRACT FROM AUTHOR]

The Circum-Galactic Medium of MASsive Spirals is a project studying the overall content, physical and chemical properties, and spatial distributions of the multi-phase circumgalactic medium around a small sample of the most massive (, ) isolated spiral galaxies in the local universe. We introduce the sample and present a detailed case study of the XMM-Newton observation of the hot gas halo of NGC 5908. After data calibration, point source removal, and background analysis, we find that the diffuse soft X-ray emission of NGC 5908 is significantly more extended than the stellar light in the vertical direction. The 0.5–1.25 keV radial intensity profile tracing hot gas emission can be detected above the background out to about , or from the nucleus. The unresolved soft X-ray emission can be characterized using a β-model with a slope of . The unresolved 0.5–2 keV luminosity within is , but young stellar sources may contribute significantly to it. Assuming a metallicity of 0.2 solar, an upper limit (without subtracting the very uncertain young stellar contribution) to the mass of hot gas within this radius is . The cooling radius is or , within which the hot gas could cool radiatively in less than 10 Gyr, and the cooling of hot gas could significantly contribute to replenishing the gas consumed in star formation. The hot gas accounts for of the baryons detected within the cooling radius. By comparing NGC 5908 to other galaxies, we find that its X-ray luminosity per stellar mass is consistent with lower-mass non-starburst field spiral galaxies. However, a large scatter in hot gas soft X-ray emissivity is indicated for spiral galaxies with . [ABSTRACT FROM AUTHOR]