The presence of short-lived (∼Myr) radioactive isotopes in meteoritic inclusions at the time of their formation represents a unique opportunity to study the circumstances that led to the formation of ...the solar system. To interpret these observations, we need to calculate the evolution of radioactive-to-stable isotopic ratios in the Galaxy. We present an extension of the open-source galactic chemical evolution codes NuPyCEE and JINAPyCEE that enable the decay of radioactive isotopes in the interstellar medium to be tracked. We show how the evolution of the isotopic ratio depends on the star formation history and efficiency, star-to-gas mass ratio, and galactic outflows. Given the uncertainties in the observations used to calibrate our model, our predictions for isotopic ratios at the time of formation of the Sun are uncertain by a factor of 3.6. At that time, to recover the actual radioactive-to-stable isotopic ratios predicted by our model, one can multiply the steady-state solution (see Equation (1)) by . However, in the cases where the radioactive isotope has a half-life longer than ∼200 Myr, or the target radioactive or stable isotopes have mass- and/or metallicity-dependent production rates, or they originate from different sources with different delay-time distributions, or the reference isotope is radioactive, our codes should be used for more accurate solutions. Our preliminary calculations confirm the dichotomy between radioactive nuclei in the early solar system with r- and s-process origin, and that 55Mn and 60Fe can be explained by galactic chemical evolution, while 26Al cannot.
This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were ...identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R ∼ 31,500) with the 3.5 m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe i lines, taking into account non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have Fe/H < −1.5, 105 have Fe/H < −2.0, and 4 have Fe/H < −3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3 ≤ Eu/Fe ≤ +1.0 and Ba/Eu < 0) and 4 new r-II stars (with Eu/Fe > +1.0). Nineteen stars are found to exhibit a "limited-r" signature (Sr/Ba > +0.5, Ba/Eu < 0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, , and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia ...Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS ( 200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature Teff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.
We present a set of 144 Galactic chemical evolution models applied to a Milky Way analogue, computed using four sets of low+intermediate star nucleosynthetic yields, six massive star yield ...compilations, and six functional forms for the initial mass function. A comparison is made between a grid of multiphase chemical evolution models computed with these yield combinations and empirical data drawn from the Milky Way's disc, including the solar neighbourhood. By means of a χ2 methodology, applied to the results of these multiphase models, the best combination of stellar yields and initial mass function capable of reproducing these observations is identified.
Abstract
We use the Horizon Run 5 cosmological simulation to study the effect of galaxy intrinsic properties and the local environment on active galactic nuclei (AGNs) characterized by their ...threshold of the accretion rate. We select galaxies in the stellar mass range
10
9.5
≤
M
*
/
M
⊙
≤
10
10.5
in the snapshot at redshift
z
= 0.625. Among various intrinsic properties, we find that the star formation rate of the host galaxy is most correlated to the AGN activity. To quantify the environment, we use background galaxy number density (large-scale environment) and distance and morphological type of the nearest neighbors (small-scale environment), and study their relative effects on the AGN properties. We find that, compared to the background density, the nearest neighbor environment is the dominant quantity determining the bolometric luminosity, star formation rate, and kinematic properties of AGNs and better dictates the gas mass of the host galaxy. We show that the cold gas content in the host galaxies is crucial in triggering AGN activity. However, when the nearest neighbor environment effects start to act at the neighbor distance of less than about half the virial radius of the neighbor, the neighbor environmental effects are the most dominant factor for quasar activity.
ABSTRACT
The Milky Way underwent its last significant merger ten billion years ago, when the Gaia-Enceladus-Sausage (GES) was accreted. Accreted GES stars and progenitor stars born prior to the ...merger make up the bulk of the inner halo. Even though these two main populations of halo stars have similar durations of star formation prior to their merger, they differ in α/Fe-Fe/H space, with the GES population bending to lower α/Fe at a relatively low value of Fe/H. We use cosmological simulations of a ‘Milky Way’ to argue that the different tracks of the halo stars through the α/Fe-Fe/H plane are due to a difference in their star formation history and efficiency, with the lower mass GES having its low and constant star formation regulated by feedback whilst the higher mass main progenitor has a higher star formation rate prior to the merger. The lower star formation efficiency of GES leads to lower gas pollution levels, pushing α/Fe-Fe/H tracks to the left. In addition, the increasing star formation rate maintains a higher relative contribution of Type II SNe to Type Ia SNe for the main progenitor population that formed during the same time period, thus maintaining a relatively high α/Fe. Thus the different positions of the downturns in the α/Fe-Fe/H plane for the GES stars are not reflective of different star formation durations, but instead reflect different star formation efficiencies.
Abstract
We propose a new method for finding galaxy protoclusters that is motivated by structure formation theory and also directly applicable to observations. We adopt the conventional definition ...that a protocluster is a galaxy group whose virial mass
M
vir
<
M
cl
at its epoch, where
M
cl
= 10
14
M
⊙
, but would exceed that limit when it evolves to
z
= 0. We use the critical overdensity for complete collapse at
z
= 0 predicted by the spherical top-hat collapse model to find the radius and total mass of the regions that would collapse at
z
= 0. If the mass of a region centered at a massive galaxy exceeds
M
cl
, the galaxy is at the center of a protocluster. We define the outer boundary of a protocluster as the zero-velocity surface at the turnaround radius so that the member galaxies are those sharing the same protocluster environment and showing some conformity in physical properties. We use the cosmological hydrodynamical simulation Horizon Run 5 (
HR5
) to calibrate this prescription and demonstrate its performance. We find that the protocluster identification method suggested in this study is quite successful. Its application to the high-redshift
HR5
galaxies shows a tight correlation between the mass within the protocluster regions identified according to the spherical collapse model and the final mass to be found within the clusters at
z
= 0, meaning that the regions can be regarded as the bona fide protoclusters with high reliability. We also confirm that the redshift-space distortion does not significantly affect the performance of the protocluster identification scheme.
Abstract One intriguing approach for studying the dynamical evolution of galaxy clusters is to compare the spatial distributions among various components such as dark matter, member galaxies, gas, ...and intracluster light (ICL). Utilizing the recently introduced weighted overlap coefficient (WOC), we analyze the spatial distributions of components within 174 galaxy clusters ( M tot > 5 × 10 13 M ⊙ , z = 0.625) at varying dynamical states in the cosmological hydrodynamical simulation Horizon Run 5. We observe that the distributions of gas and the combination of ICL with the brightest cluster galaxy (BCG) closely resembles the dark matter distribution, particularly in more relaxed clusters, characterized by the half-mass epoch. The similarity in spatial distribution between dark matter and BCG+ICL mimics the changes in the dynamical state of clusters during a major merger. Notably, at redshifts >1, BCG+ICL traced dark matter more accurately than the gas. Additionally, we examined the one-dimensional radial profiles of each component, which show that the BCG+ICL is a sensitive component revealing the dynamical state of clusters. We propose a new method that can approximately recover the dark matter profile by scaling the BCG+ICL radial profile. Furthermore, we find a recipe for tracing dark matter in unrelaxed clusters by including the most massive satellite galaxies together with the BCG+ICL distribution. Combining the BCG+ICL and the gas distribution enhances the dark matter tracing ability. Our results imply that the BCG+ICL distribution is an effective tracer for the dark matter distribution, and the similarity of the spatial distribution may be a useful probe of the dynamical state of a cluster.
We describe our new ‘mlapm halo finder’ (mhf), which is based on the adaptive grid structure of the N-body code mlapm. We then extend the mhf code in order to track the orbital evolution of ...gravitationally bound objects through any given cosmological N-body simulation – our so-called ‘mlapm halo tracker’ (mht). The mode of operation of mht is demonstrated using a series of eight high-resolution N-body simulations of galaxy clusters. Each of these haloes hosts more than one million particles within their virial radii rvir. We use mht as well as mhf to follow the temporal evolution of hundreds of individual satellites, and show that the radial distribution of these substructure satellites follows a ‘universal’ radial distribution irrespective of the environment and formation history of the host halo. This in fact might pose another problem for simulations of cold dark matter structure formation, as there are recent findings by Taylor, Silk & Babul that the Milky Way satellites are found preferentially closer to the Galactic Centre and simulations underestimate the amount of central substructure. Further, this universal substructure profile is anti-biased with respect to the underlying dark matter profile. The halo finder mhf will become part of the open source mlapm distribution.
Abstract
We investigate the impact of the surface-brightness (SB) limit on the galaxy stellar mass functions (GSMFs) using galaxy catalogs generated from the
Horizon Run 5
(
HR5
) simulation. We ...compare the stellar-to-halo-mass relation, GSMF, and size–stellar mass relation of the
HR5
galaxies with observational data and other cosmological simulations. The mean SB of simulated galaxies are computed using their effective radii, luminosities, and colors. To examine the cosmic SB dimming effect, we compute
k
-corrections from the spectral energy distributions of individual simulated galaxy at each redshift, apply the
k
-corrections to the galaxies, and conduct mock surveys based on the various SB limits. We find that the GSMFs are significantly affected by the SB limits at the low-mass end. This approach can ease the discrepancy between the GSMFs obtained from simulations and observations at 0.6 ≲
z
≤ 2. We also find that a redshift survey with an SB selection limit of
μ
r
e
=
25 mag arcsec
−2
will miss 20% of galaxies with
M
⋆
g
=
10
9
M
⊙
at
z
= 0.625. The missing fraction of low-surface-brightness galaxies increases to 35%, 55%, and 80% at
z
= 0.9, 1.1, and 1.9, respectively, at the same SB limit.
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