Wednesday.
1806.09822
Morphological properties of galaxies in different Local Volume environments
Karachentsev, Kaisina, Makarov
Consider an all-sky sample of 1029 Local Volume (LV) galaxies situated within a distance of 11 Mpc. Their majority have precise distances, estimates of H mass fraction and SFR drives from far-UV or H_alpha fluxes. To describe an environment, attribute two dimensionless values: the density contrast created by the most significant neighbor and the local density contrast produced by all neighbors within a separation of 1Mpc. The H mass fraction exhibits a weak effect of HI deficiency being the most pronounced for dwarf irregular galaxies. The sSFR is more sensitive to the environment than the H mass fraction. Almost all (99%) LV galaxies have their sSFR below -9.4 dex (1/yr). Notice that irregular dwarfs as well as late-type bulgeless galaxies are capable to reproduce their stellar mass with the observed sSFR over the cosmic time. Thus, the transformation of gas into stars in dIrs and spiral disks is rather sluggish unlike that in E, S0, dSph galaxies, whose SFH has been stormy and short. Scatter of SFR(H_alpha)-to-SFR(FUV) ratio increases from Sc, Sd, Sm galaxies towards BCD, Im, Ir types that favors the idea of bursty SFs in low-mass galaxies. However, the bursty activity is caused rather by internal processes than by an external tidal action. A fraction of quenched E, S0, dSph galaxies increases from ~5% in the field up to ~50% in the densest regions.
1806.10003
An almanac of predicted micorlneing events for the 21st century
Bramich, Nielsen
Using Gaia DR2, present an almanac of 2,509 predicted microlensing events, caused by 2,130 unique lens stars, that will peak between 25 July 2026 and the end of the century. This work extends and completes a thorough search for future microlensing events initiated by Bramich (2018) and Nielsen&Bramich (2018) using GDR2. The almanac includes 161 lenses that will cause at least two microlensing events. A few highlights are presented and discussed, including (i) an astrometric microlensing event with a peak amplitude of ~9.7 mas, (ii) an event that will probe the planetary system of a lens with 3 known planets, and (iii) an event (resolvable from space) where the lens will brighten by a detectable amount (~2 mmag) due to the appearance of the minor source image.
1806.10122
Testing general relativity in cosmology
Ishak
Review recent developments and results in testing GR at cosmological scales. The subject has witnessed rapid growth during the last 2 decades with the aim of addressing the question of cosmic acceleration and the DE associated with it. However, with the advent of precision cosmology, it has also become a well-motivated endeavor by itself to test gravitational physics at cosmic scales. Overview cosmological probes of gravity, formalisms and parameterizations for testing deviations from GR at cosmological scales, selected MG theories, gravitational screening mechanisms, and computer codes developed for these tests. Then provide summaries of recent cosmo constraints on MG parameters and selected MG models. Supplement these cosmological constraints with a summary of implications from the recent binary neutron star merger event. Next, summarize some results on MG parameter forecasts with and without astrophysical systematics that will dominate the uncertainties. The review aims at providing an overall picture of at the subject and an entry point to students and researchers interested in joining the field. It can also serve as a quick reference to recent results and constraints on testing gravity at cosmological scales.
1806.09822
Morphological properties of galaxies in different Local Volume environments
Karachentsev, Kaisina, Makarov
Consider an all-sky sample of 1029 Local Volume (LV) galaxies situated within a distance of 11 Mpc. Their majority have precise distances, estimates of H mass fraction and SFR drives from far-UV or H_alpha fluxes. To describe an environment, attribute two dimensionless values: the density contrast created by the most significant neighbor and the local density contrast produced by all neighbors within a separation of 1Mpc. The H mass fraction exhibits a weak effect of HI deficiency being the most pronounced for dwarf irregular galaxies. The sSFR is more sensitive to the environment than the H mass fraction. Almost all (99%) LV galaxies have their sSFR below -9.4 dex (1/yr). Notice that irregular dwarfs as well as late-type bulgeless galaxies are capable to reproduce their stellar mass with the observed sSFR over the cosmic time. Thus, the transformation of gas into stars in dIrs and spiral disks is rather sluggish unlike that in E, S0, dSph galaxies, whose SFH has been stormy and short. Scatter of SFR(H_alpha)-to-SFR(FUV) ratio increases from Sc, Sd, Sm galaxies towards BCD, Im, Ir types that favors the idea of bursty SFs in low-mass galaxies. However, the bursty activity is caused rather by internal processes than by an external tidal action. A fraction of quenched E, S0, dSph galaxies increases from ~5% in the field up to ~50% in the densest regions.
1806.10003
An almanac of predicted micorlneing events for the 21st century
Bramich, Nielsen
Using Gaia DR2, present an almanac of 2,509 predicted microlensing events, caused by 2,130 unique lens stars, that will peak between 25 July 2026 and the end of the century. This work extends and completes a thorough search for future microlensing events initiated by Bramich (2018) and Nielsen&Bramich (2018) using GDR2. The almanac includes 161 lenses that will cause at least two microlensing events. A few highlights are presented and discussed, including (i) an astrometric microlensing event with a peak amplitude of ~9.7 mas, (ii) an event that will probe the planetary system of a lens with 3 known planets, and (iii) an event (resolvable from space) where the lens will brighten by a detectable amount (~2 mmag) due to the appearance of the minor source image.
1806.10122
Testing general relativity in cosmology
Ishak
Review recent developments and results in testing GR at cosmological scales. The subject has witnessed rapid growth during the last 2 decades with the aim of addressing the question of cosmic acceleration and the DE associated with it. However, with the advent of precision cosmology, it has also become a well-motivated endeavor by itself to test gravitational physics at cosmic scales. Overview cosmological probes of gravity, formalisms and parameterizations for testing deviations from GR at cosmological scales, selected MG theories, gravitational screening mechanisms, and computer codes developed for these tests. Then provide summaries of recent cosmo constraints on MG parameters and selected MG models. Supplement these cosmological constraints with a summary of implications from the recent binary neutron star merger event. Next, summarize some results on MG parameter forecasts with and without astrophysical systematics that will dominate the uncertainties. The review aims at providing an overall picture of at the subject and an entry point to students and researchers interested in joining the field. It can also serve as a quick reference to recent results and constraints on testing gravity at cosmological scales.
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