1910.06327
The fate of the interstellar medium in early-type galaxies. I. first direct measurement of the timescale of dust removal
Michalowski, et al
An important aspect of quenching star formation is the removal of the cold interstellar medium (ISM; non-ionised gas and dust) from a galaxy. In addition, dust grains can be destroyed in a hot or turbulent medium. The adopted timescale of dust removal usually relies on uncertain theoretical estimates. It is tricky to track the dust removal, because usually dust is constantly replenished by consecutive generations of stars. Our objective is to measure observationally the timescale of dust removal. We here explore an approach to select galaxies which do have detectable amounts of dust and cold ISM but exhibit a low current dust production rate. Any decrease of the dust and gas content as a function of the age of such galaxies therefore must be attributed to processes governing the ISM removal. We used a sample of galaxies detected by Herschel in the far-infrared with visually assigned early-type morphology or spirals with red colours. We also obtained JCMT/SCUBA-2 observations for five of them. We discovered an exponential decline of the dust-to-stellar mass ratio with age, which we interpret as an evolutionary trend of dust removal from these galaxies. For the first time we directly measure the dust removal timescale in such galaxies to be tau=(2.5+-0.4) Gyr (the corresponding half-life time is (1.75+-0.25) Gyr). This quantity may be used in models in which it must be assumed a priori and cannot be derived. Any process which removes dust in these galaxies, such as dust grain destruction, cannot happen on shorter timescales. The timescale is comparable to the quenching timescales found in simulations for galaxies with similar stellar masses. The dust is likely of internal, not external origin. It was either formed in the past directly by supernovae, or from seeds produced by SNe and with grain growth in the ISM contributing substantially to the dust mass accumulation.
The fate of the interstellar medium in early-type galaxies. I. first direct measurement of the timescale of dust removal
Michalowski, et al
An important aspect of quenching star formation is the removal of the cold interstellar medium (ISM; non-ionised gas and dust) from a galaxy. In addition, dust grains can be destroyed in a hot or turbulent medium. The adopted timescale of dust removal usually relies on uncertain theoretical estimates. It is tricky to track the dust removal, because usually dust is constantly replenished by consecutive generations of stars. Our objective is to measure observationally the timescale of dust removal. We here explore an approach to select galaxies which do have detectable amounts of dust and cold ISM but exhibit a low current dust production rate. Any decrease of the dust and gas content as a function of the age of such galaxies therefore must be attributed to processes governing the ISM removal. We used a sample of galaxies detected by Herschel in the far-infrared with visually assigned early-type morphology or spirals with red colours. We also obtained JCMT/SCUBA-2 observations for five of them. We discovered an exponential decline of the dust-to-stellar mass ratio with age, which we interpret as an evolutionary trend of dust removal from these galaxies. For the first time we directly measure the dust removal timescale in such galaxies to be tau=(2.5+-0.4) Gyr (the corresponding half-life time is (1.75+-0.25) Gyr). This quantity may be used in models in which it must be assumed a priori and cannot be derived. Any process which removes dust in these galaxies, such as dust grain destruction, cannot happen on shorter timescales. The timescale is comparable to the quenching timescales found in simulations for galaxies with similar stellar masses. The dust is likely of internal, not external origin. It was either formed in the past directly by supernovae, or from seeds produced by SNe and with grain growth in the ISM contributing substantially to the dust mass accumulation.
1910.06345
Stellar feedback sets the universal acceleration scale in galaxies
Grudic, et al
It has been established for decades that rotation curves deviate from the Newtonian gravity expectation given baryons alone below a characteristic acceleration scale $g_\dagger \sim 10^{-8}\,\rm{cm\,s^{-2}}$, a scale promoted to a new fundamental constant in MOND-type theories. In recent years, theoretical and observational studies have shown that the star formation efficiency (SFE) of dense gas scales with surface density, SFE $\sim \Sigma/\Sigma_{\rm crit}$ with $\Sigma_{\rm crit} \sim (\dot{p}/m_{\ast})/(\pi^{2}\,G)\sim 1000\,\rm{M_{\odot}\,pc^{-2}}$ (where $\dot{p}/m_{\ast}$ is the momentum flux output by stellar feedback per unit stellar mass formed). We show that the star formation efficiency, more correctly, scales with the gravitational acceleration, i.e. that SFE $\sim g_{\rm tot}/g_{\rm crit} \equiv (G\,M_{\rm enc}/R^{2}) / ([\dot{p}/m_{\ast}]/\pi)$, where $M_{\rm enc}(<r)$ is the total gravitating mass and $g_{\rm crit}=(\dot{p}/m_{\ast})/\pi = \pi\,G\,\Sigma_{\rm crit} \approx 10^{-8}\,\rm{cm\,s^{-2}} \approx g_\dagger$. It follows that the characteristic galactic acceleration $g_\dagger$ corresponds to the acceleration scale above which SF is `efficient' (and outflows `inefficient'), and so baryons inevitably dominate the mass. This also explains the ``deep MOND'' scaling $g_{\rm obs}\sim(g_{\rm baryon}\,g_\dagger)^{1/2}$ (where $g_{\rm baryon}$ is the acceleration due to baryons alone) apparent at low accelerations. We further show that $g_\dagger$ can be expressed in terms of fundamental constants (gravitational constant, proton mass, and Thomson cross-section): $g_\dagger\sim 0.1\,G\,m_{p}/\sigma_{\rm T}$.
1910.06400
The importance of magnification effects in galaxy-galaxy lensing
Unruh, et al
Magnification changes the observed number counts of galaxies on the sky. This biases the observed tangential shear profiles around galaxies, the so-called galaxy-galaxy lensing (GGL) signal, and the related excess mass profile. Correspondingly, inference of physical quantities, such as the mean mass profile of halos around galaxies, are affected by magnification effects. We use simulated shear and galaxy data of the Millennium Simulation to quantify the effect on shear and mass estimates from magnified lens and source number counts. The former are due to the large-scale matter distribution in the foreground of the lenses, the latter are caused by magnification of the source population by the matter associated with the lenses. The GGL signal is calculated from the simulations by an efficient fast-Fourier transform that can also be applied to real data. The numerical treatment is complemented by a leading-order analytical description of the magnification effects, which is shown to fit the numerical shear data well. We find the magnification effect is strongest for steep galaxy luminosity functions and high redshifts. For a lens redshift of $z_\mathrm{d}=0.83$, a limiting magnitude of $22\,\mathrm{mag}$ in the $r$-band and a source redshift of $z_\mathrm{s}=0.99$, we find that a magnification correction changes the shear profile up to $45\%$ and the mass is biased by up to $55 \%$. For medium-redshift galaxies the relative change in shear and mass is typically a few percent. As expected, the sign of the bias depends on the local slope of the lens luminosity function $\alpha_\mathrm{d}$, where the mass is biased low for $\alpha_\mathrm{d}<1$ and biased high for $\alpha_\mathrm{d}>1$. Whereas the magnification effect of sources is rarely than more $1\%$, the statistical power of future weak lensing surveys warrants correction for this effect.
1910.06722
Lensing corrections on galaxy-lensing cross correlations and galaxy-galaxy auto correlations
Boehm, et al
We study the impact of lensing corrections on modeling cross correlations between CMB lensing and galaxies, cosmic shear and galaxies, and galaxies in different redshift bins. Estimating the importance of these corrections becomes necessary in the light of anticipated high-accuracy measurements of these observables. While higher order lensing corrections (sometimes also referred to as post Born corrections) have been shown to be negligibly small for lensing auto correlations, they have not been studied for cross correlations. We evaluate the contributing four-point functions without making use of the Limber approximation and compute line-of-sight integrals with the numerically stable and fast FFTlog formalism. We find that the relative size of lensing corrections depends on the respective redshift distributions of the lensing sources and galaxies, but that they are generally small for high signal-to-noise correlations. We point out that a full assessment and judgement of the importance of these corrections requires the inclusion of lensing Jacobian terms on the galaxy side. We identify these additional correction terms, but do not evaluate them due to their large number. We argue that they could be potentially important and suggest that their size should be measured in the future with ray-traced simulations. We make our code publicly available.
1910.06723
A method of real-time analysis for stray light uniformity of optical telescope
Li
The stray light uniformity is one of the important factors affecting the signal-to-noise ratio of the optical astronomical telescope. It will cause regional differences in the background intensity of the detector image, resulting in a decrease of the differential photometry accuracy. The source that affects stray light uniformity is the inconsistency of the brightness of the sky background, which comes from moonlight, bright star, and city lighting pollution. During CCD reduction, the effect of background uniformity cannot be eliminated by dividing the flat field. Star deletion method is used in real-time stray light analysis. It's very convenient to achieve a 'clear' background image without stars in MATLAB. A contour map of stray light distribution for each object image will be given to demonstrate the background uniformity directly. The stray light uniformity analysis method is implemented by the following steps: 1) CCD reduction, including preprocessing of an object image with bias and flat field; 2) Histogram generation, performing star subtraction automatically based on ADU value and frequency; 3) Background stray light contour map generation, stray light uniformity and other parameters calculations. This method will calculate the uniformity of image surface in real time, provide background intensity distribution, statistical data of the CCD image and suggestion on compare star selection during CCD data processing and improve the photometry accuracy.
1910.06919
Anisotropy of cosmic ray fluxes measured with the Alpha Magnetic Spectrometer on the ISS
Molero, et al
A measurement of the dipole anisotropy in galactic coordinates for different charged cosmic rays has been performed with the Alpha Magnetic Spectrometer (AMS) onboard the International Space Station (ISS). Results are presented for the first 7.5 years of data taking for protons, Helium, Carbon and Oxygen, and 6.5 years for positrons and electrons. All the species are found to be consistent with isotropy and upper limits to the dipole amplitude have been computed. In particular, for energies above 16 GeV a limit of delta < 1.9% and delta < 0.5% at the 95% C.I. is found for positrons and electrons respectively. For rigidities above 200 GV a limit of delta < 0.38%, delta < 0.36%, delta < 1.9% and delta < 1.7% is obtained for protons, Helium, Carbon and Oxygen.
1910.07127
Redshift inference from the combination of galaxy colors and clustering in a hierarchical Bayesian model $-$ Application to realistic $N$-body simulations
Alarcon, et al
Photometric galaxy surveys constitute a powerful cosmological probe but rely on the accurate characterization of their redshift distributions using only broadband imaging, and can be very sensitive to incomplete or biased priors used for redshift calibration. S\'anchez & Bernstein (2019) presented a hierarchical Bayesian model which estimates those from the robust combination of prior information, photometry of single galaxies and the information contained in the galaxy clustering against a well-characterized tracer population. In this work, we extend the method so that it can be applied to real data, developing some necessary new extensions to it, especially in the treatment of galaxy clustering information, and we test it on realistic simulations. After marginalizing over the mapping between the clustering estimator and the actual density distribution of the sample galaxies, and using prior information from a small patch of the survey, we find the incorporation of clustering information with photo-$z$'s to tighten the redshift posteriors, and to overcome biases in the prior that mimic those happening in spectroscopic samples. The method presented here uses all the information at hand to reduce prior biases and incompleteness. Even in cases where we artificially bias the spectroscopic sample to induce a shift in mean redshift of $\Delta \bar z \approx 0.05,$ the final biases in the posterior are $\Delta \bar z \lesssim0.003.$ This robustness to flaws in the redshift prior or training samples would constitute a milestone for the control of redshift systematic uncertainties in future weak lensing analyses.
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